usbr engineering geology field manual volume 1 chapter 1
TRANSCRIPT
Chapter 1
INTRODUCTION
This manual provides guidelines and instructions forperforming and documenting field work. The manual isa ready reference for anyone engaged in field-orientedengineering geology or geotechnical engineering. Themanual is written for general engineering geology use aswell as to meet Reclamation needs. The application ofgeology to solving engineering problems is emphasized,rather than academic or other aspects of geology. Themanual provides guidance for:
• Geologic classification and description of rock androck discontinuities
• Engineering classification and description of soiland surficial deposits
• Application of standard indexes, descriptors, andterminology
• Geologic mapping, sampling, testing, andperforming discontinuity surveys
• Exploratory drilling
• Soil and rock logging
• Acquisition of groundwater data
• Core logging
• Soil logging
• Investigation of hazardous waste sites
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Although the methods described in this manual areappropriate for most situations, complex sites, conditions,or design needs may require modification or expansion ofthe suggestions, criteria, and indices to fit specificrequirements.
Many of the chapters in this manual will always needrevision because they cover material that changes astechnology changes. Critical comments, especially sug-gestions for improvement, are welcome from all users,not just the Bureau of Reclamation.
The appendix contains abbreviations and acronymscommonly used in engineering geology.
1 Brackets refer to bibliography entries at end of each chapter.
Chapter 2
GEOLOGIC TERMINOLOGY AND CLASSIFICATIONS FOR
GEOLOGIC MATERIALS
Established References for GeologicalTerminology
Adaptations or refinements of the Bureau of Reclamation(Reclamation) standards presented in this and subse-quent chapters may be established to meet specific designrequirements or site-specific geologic complexity whenjustified.
The Glossary of Geology, Fourth Edition [1]1, published bythe American Geological Institute (AGI), 1997, is acceptedby Reclamation as the standard for definitions of geologicwords and terms except for the nomenclature, definitions,or usage established in this chapter and chapters 3, 4,and 5.
The North American Stratigraphic Code (NASC) [2] is theaccepted system for classifying and naming stratigraphicunits. However, Reclamation's engineering geology pro-grams are focused primarily on the engineering prop-erties of geologic units, not on the details of formalstratigraphic classification. Stratigraphic names are notalways consistent within the literature, often change fromone locality to another, and do not necessarily conveyengineering properties or rock types. Use of stratigraphicnames in Reclamation documents normally will beinformal (lower case) (see NASC for discussion of formalversus informal usage). Exceptions to informal usage arefor names previously used formally in the area in discus-sions of geologic setting or regional geology. Normally,
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the first use of formal names in a report should include areference to a geologic map or publication in which theterm is defined.
Geologic Classification of Materials
The following definitions of geologic materials more fullysatisfy general usage and supersede those in the Glossaryof Geology. These definitions are for geologic classifica-tion of materials. They should not be confused with engi-neering classifications of materials such as rock and soilor rock and common excavation.
• Bedrock is a general term that includes any of the gen-erally indurated or crystalline materials that make up theEarth's crust. Individual stratigraphic units or units sig-nificant to engineering geology within bedrock may in-clude poorly or nonindurated materials such as beds,lenses, or intercalations. These may be weak rock unitsor interbeds consisting of clay, silt, and sand (such as thegenerally soft and friable St. Peter Sandstone), or claybeds and bentonite partings in siliceous shales of theMorrison Formation.
•Surficial Deposits are the relatively younger materialsoccurring at or near the Earth's surface overlying bed-rock. They occur as two major classes: (1) transporteddeposits generally derived from bedrock materials bywater, wind, ice, gravity, and man's intervention and(2) residual deposits formed in place as a result ofweathering processes. Surficial deposits may be stratifiedor unstratified such as soil profiles, basin fill, alluvial orfluvial deposits, landslides, or talus. The material may bepartially indurated or cemented by silicates, oxides,carbonates, or other chemicals (caliche or hardpan). Thisterm is often used interchangeably with the imprecisely
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defined word “overburden.” “Overburden” is a miningterm meaning, among other things, material overlying auseful material that has to be removed. “Surficialdeposit” is the preferred term.
In some localities, where the distinction between bedrockand surficial deposits is not clear, even if assigned astratigraphic name, a uniform practice should be estab-lished and documented and that definition followed forthe site or study.
Guidelines for the collection of data pertaining to bedrockand surficial deposits are presented in chapter 6.
Engineering Classification of GeologicMaterials
General
Geologic classification of materials as surficial deposits orbedrock is insufficient for engineering purposes. Usually,surficial deposits are described as soil for engineeringpurposes, and most bedrock is described as rock; however,there are exceptions. Contract documents often classifystructure excavations as to their ease of excavation. Also,classification systems for tunneling in geologic materialshave been established.
Classification as Soil or Rock
In engineering applications, soil may be defined as gener-ally unindurated accumulations of solid particlesproduced by the physical and/or chemical disintegrationof bedrock and which may or may not contain organicmatter. Surficial deposits, such as colluvium, alluvium,or residual soil, normally are described using Recla-
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mation Procedure 5005, Determining Unified SoilClassification (Visual Method) [3]. American Society forTesting and Materials (ASTM) Standards D2487-85,Standard Test Method for Classification of Soils forEngineering Purposes or D2488-84, Standard Practice forDescription and Identification of Soils (Visual-ManualProcedure), which are based on Reclamation 5000 and5005 [3] also may be used. Instructions for thedescription and classification of soils are provided inchapter 3. Chapter 11 provides instructions for thelogging of soils in geologic explorations. In some cases,partially indurated soils may have rock-likecharacteristics and may be described as rock.
The United States Department of Agriculture (USDA)Agricultural Soils Classification System is used for drain-age and land classification and some detailed Quaternarygeology studies, such as for seismotectonic investigations.
Rock as an engineering material is defined as lithified orindurated crystalline or noncrystalline materials. Rockis encountered in masses and as large fragments whichhave consequences to design and construction differingfrom those of soil. Field classification of igneous,metamorphic, sedimentary, and pyroclastic rocks areprovided in chapter 4. Chapter 4 also presents asuggested description format, standard descriptors, anddescriptive criteria for the lithologic and engineeringphysical properties of rock. Nonindurated materials with-in bedrock should be described using the Reclamation soilclassification standards and soil descriptors presented inchapter 3. Engineering and geological classification anddescription of discontinuities which may be present ineither soil or rock are discussed in chapter 5.
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Classification of Excavations
The engineering classification of excavation as either rockexcavation or common excavation or the definition of rockin specifications must be evaluated and determined foreach contract document and should be based on thephysical properties of the materials (induration and othercharacteristics), quantity and method of excavation, andequipment constraints and size.
Classification of Materials for Tunneling
Classification systems are used for data reports, speci-fications, and construction monitoring for tunnel designsand construction. When appropriate for design, otherload prediction and classification systems may be usedsuch as the Q system developed by the Norwegian Geo-technical Institute (NGI), Rock Mass Rating SystemGeomechanics Classification (RMR), and Rock StructureRating (RSR).
The following terms for the classification of rock [4] fortunneling are suggested:
• Intact rock contains neither joints nor hairline cracks.If it breaks, it breaks across sound rock. On account ofdamage to the rock due to blasting, spalls may drop offthe roof several hours or days after blasting. This isknown as spalling condition. Hard, intact rock may alsobe encountered in the popping condition (rock burst)involving the spontaneous and violent detachment of rockslabs from sides or roof.
• Stratified rock consists of individual strata with littleor no resistance against separation along the boundaries
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between strata. The strata may or may not be weakenedby transverse joints. In such rock, the spalling conditionis quite common.
• Moderately jointed rock contains joints and hairlinecracks, but the blocks between joints are locally growntogether or so intimately interlocked that vertical wallsdo not require lateral support. In rocks of this type, boththe spalling and the popping condition may beencountered.
• Blocky and seamy rock consists of chemically intactor almost intact rock fragments which are entirelyseparated from each other and imperfectly interlocked.In such rock, vertical walls may require support.
• Crushed but chemically intact rock has the char-acter of a crusher run. If most or all of the fragments areas small as fine sand and no recementation has takenplace, crushed rock below the water table exhibits theproperties of a water-bearing sand.
• Squeezing rock slowly advances into the tunnelwithout perceptible volume increase. Movement is theresult of overstressing and plastic failure of the rock massand not due to swelling.
• Swelling rock advances into the tunnel chiefly on ac-count of expansion. The capacity to swell is generallylimited to those rocks which contain smectite, amontmorillonite group of clay minerals, with a highswelling capacity.
Although the terms are defined, no distinct boundariesexist between rock categories. Wide variations in thephysical properties of rocks classified by these terms androck loading are often the case.
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Table 2-1, Ground behavior for earth tunneling with steelsupports, provides ground classifications for differentreactions of ground to tunneling operations.
Application and Use of Standard Indexes,Terminology, and Descriptors
This section and subsequent chapters 3, 4, and 5 providedefinitions and standard descriptors for physicalproperties of geologic materials which are of engineeringsignificance. The ability of a foundation to support loadsimposed by various structures depends primarily on thedeformability and stability of the foundation materialsand the groundwater conditions. Description of geologicand some manmade materials (embankments) is one ofthe geologist's direct contributions to the design process.Judgment and intuition alone are not adequate for thesafe and economical design of large complex engineeringprojects. Preparation of geologic logs, maps and sections,and detailed descriptions of observed material is the leastexpensive aspect and most continuous record of a sub-surface exploration program. It is imperative to developdesign data properly because recent advances in soil androck mechanics have enabled engineers and geologists toanalyze more conditions than previously possible. Theseanalyses rely on physical models that are developedthrough geologic observation and which must bedescribed without ambiguity.
The need for standard geologic terminology, indexes, anddescriptors has long been recognized because it isimportant that design engineers and contractors, aswell as geologists, be able to have all the facts and quali-tative information as a common basis to arrive atconclusions from any log of exploration, report, or draw-ing, regardless of the preparer. Geologic terminology,
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Table 2-1.— Ground behavior for earth tunneling with steel supports (after Terzaghi, 1977) [4]
Ground classification Reaction of ground to tunneling operation
HARD Tunnel heading may be advanced without roof support.
FIRM Ground in which a roof section of a tunnel can be leftunsupported for several days without inducing aperceptible movement of the ground.
RAVELING Chunks or flakes of soil begin to drop out of roof at somepoint during the ground-movement period.
SLOW RAVELING The time required to excavate 5 feet of tunnel andinstall a rib set and lagging in a small tunnel is about6 hours. Therefore, if the stand-up time of ravelingground is more than 6 hours, by using ribs and lagging,the steel rib sets may be spaced on 5-foot centers. Sucha soil would be classed as slow raveling.
FAST RAVELING If the stand-up time is less than 6 hours, set spacingmust be reduced to 4 feet, 3 feet, or even 2 feet. If thestand-up time is too short for these smaller spacings,liner plates should be used, either with or without ribsets, depending on the tunnel size.
SQUEEZING Ground slowly advances into tunnel without any signsof fracturing. The loss of ground caused by squeeze andthe resulting settlement of the ground surface can besubstantial.
SWELLING Ground slowly advances into the tunnel partly or chieflybecause of an increase in the volume of the ground. Thevolume increase is in response to an increase of watercontent. In every other respect, swelling ground in atunnel behaves like a stiff non-squeezing, or slowlysqueezing, non-swelling clay.
RUNNING The removal of lateral support on any surface rising atan angle of more than 34E (to the horizontal) isimmediately followed by a running movement of the soilparticles. This movement does not stop until the slopeof the moving soil becomes roughly equal to 34E• ifrunning ground has a trace of cohesion, then the run ispreceded by a brief period of progressive raveling.
VERY SOFT SQUEEZING Ground advances rapidly into tunnel in a plastic flow.
FLOWING Ground supporting a tunnel cannot be classified asflowing ground unless water flows or seeps through ittoward the tunnel. For this reason, a flowing conditionis encountered only in free air tunnels below thewatertable or under compressed air when the pressureis not high enough in the tunnel to dry the bottom. Asecond prerequisite for flowing is low cohesion of soil.Therefore, conditions for flowing ground occur only ininorganic silt, fine silty sand, clean sand or gravel, orsand-and-gravel with some clay binder. Organic siltmay behave either as a flowing or as a very soft,squeezing ground.
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standard descriptors, and descriptive criteria for physicalproperties have been established so that geologic data arerecorded uniformly, objectively, consistently, and accu-rately. The application of these indexes, terminology,descriptors, and various manual and visual tests must beapplied consistently by all geologists for each particularproject. The need to calibrate themselves with others per-forming similar tests and descriptions is imperative toensure that data are recorded and interpreted uniformly.The use of these standard descriptors and terminology isnot intended to replace the geologist's or engineer's indi-vidual judgment. The established standard qualitativeand quantitative descriptors will assist newly employedgeologists and engineers in understanding Reclamationterminology and procedures, permit better analysis ofdata, and permit better understanding by other geologistsand engineers, and by contractors. Most of the physicaldimensions established for the descriptive criteria per-taining to rock and discontinuity characteristics havebeen established using a 1-3-10-30-100 progression forconsistency, ease of memory, conversion from English tometric (30 millimeters [mm] = 0.1 foot [ft]) units, and toconform to many established standards used throughoutthe world. Their use will improve analysis, design andconstruction considerations, and specifications prepara-tion. Contractor claims also should be reduced due toconsistent and well defined terminology and descriptors.
Alphanumeric values for many physical properties havebeen established to enable the geotechnical engineer andengineering geologist to readily analyze the geologic data.These alphanumeric descriptors also will assist in compi-lation of data bases and computer searches when usingcomputer generated logs. For consistency, the lower thealphanumeric value, the more favorable the conditionbeing described. However, alphanumeric codes do notreplace a complete description of what is observed. A
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complete description provides physical dimensionsincluding a range and/or average in size, width, length orother physical property, and/or descriptive information.
It is important to start physical testing of the geologicmaterials as early as possible in an exploration program;descriptors alone are not sufficient. As data are inter-preted, index properties tests can be performed in thefield to obtain preliminary strength estimates for repre-sentative materials or materials requiring special con-sideration. The scope of such a program must be tailoredto each feature. Tests which are to be considered includepoint load, Schmidt hammer, sliding tilt, and pocketTorvane or penetrometer tests. These tests are describedbriefly in chapters 4 and 5. Indexes to be consideredinclude rock hardness, durability (slaking), and RockQuality Designation (RQD). The type of detailed labora-tory studies can be formulated better and the amount ofsampling and testing may be reduced if results from fieldtests are available.
Units of Measurements for Geologic Logs ofExploration, Drawings, and Reports
Metric Units
For metric specifications and studies, metric (Interna-tional System of Units) should be used from the start ofwork if possible. Logs of exploration providing depthmeasurements should be given to tenths or hundredths ofmeters. All linear measurements such as particle orcrystal sizes, ranges or averages in thickness, openness,and spacing, provided in descriptor definitions inchapters 3, 4, and 5, should be expressed in millimetersor meters as appropriate. Pressures should be given inpascals (Pa). Permeability (hydraulic conductivity)
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should be in centimeters per second (cm/s). In somecases, local usage of other units such as kilogram persquare centimeter (kg/cm2) for pressure or centimeters(cm) may be used.
English Units (U.S. Customary)
For specifications and studies using United States cus-tomary or English units (inch-pound), depth measure-ments should be given in feet and tenths of feet. Rangesin thickness, openness, and spacing, are preferred intenths or hundredths of a foot, or feet as shown in thedescriptor definitions in chapters 4 and 5. Pressureshould be in pound-force per square inch (lbf/in2 orPSI). Permeability should be in feet per year (ft/yr). Theexceptions to the use of English units (inch-pound) are fordescribing particle and grain sizes and age dating.Particle sizes for soils classified using American Societyfor Testing and Materials/Unified Soil ClassificationSystems (ASTM/USCS) should be in metric units on alllogs of exploration. For description of bedrock, particleand grain sizes are to be in millimeters.
Age Dates
If age dates are abbreviated, the North American Strati-graphic Commission (NASC) recommends ka for thousandyears and Ma for million years, but my or m.y. (millionyears) for time intervals (for example, ". . . during aperiod of 40 my . . .").
Conversion of Metric and English (U.S. Customary)Units
Table 2-2 provides many of the most frequently usedmetric and English (U.S. Customary) units forgeotechnical work.
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Table 2-2.— Useful conversion factors— metric and English units (inch-pound)
To convert units in column 1 to units in column 4, multiply column 1 by the factor in column 2.To convert units in column 4 to units in column 1, multiply column 4 by the factor in column 3.
Column 1 Column 2 Column 3 Column 4
Lengthinch (in) 2.540 X 10 1 3.937 X 10-2 millimeter (mm)hundredths of feet 3.048 X 102 3.281 X 10 -3 millimeter (mm)foot (ft) 3.048 X 10 -1 3.281 meter (m)mile (mi) 1.6093 6.2137 X 10-1 kilometer (km)
Areasquare inch (in2) 6.4516 X 10-4 1.550 X 10-3 square meter (m2)square foot (ft2) 9.2903 X 10 -2 1.0764 X 101 square meter (m2)acre 4.0469 X 10 -1 2.4711 hectaresquare mile (mi2) 0.386 X 10 -2 259.0 hectares
Volumecubic inch (in3) 1.6387 X 10-2 6.102 X 10-2 cubic centimeter (cm2)cubic feet (ft3) 2.8317 X 10-2 3.5315 x 101 cubic meter (m3)
cubic yard (yd3) 7.6455 X 101 1.3079 cubic meter (ms)cubic feet (ft3) 7.4805 1.3368 x 10-1 gallon (gal)gallon (gal) 3.7854 2.6417 X 10-1 liter (L)acre-feet (acre-ft) 1.2335 X 103 8.1071 X 10 -4 cubic meter (m3)
Flowgallon per minute (gal/min) 6.309 X 10-2 1.5850 X 101 liter per second (L/s)cubic foot per second (ft3/s) 4.4883 X 102 2.228 X 10-3 gallons per minute (gal/min)
1.9835 5.0417 X 10-1 acre-feet per day (acre-ft/d)cubic foot per second (ft3/s) 7.2398 X 102 1.3813 X 10-3 acre-feet per year (acre-ft/yr)
2.8317 X 10-2 3.531 X 101 cubic meters per second (m3/s)8.93 X 105 1.119 X 10-6 cubic meters per year (m3/yr)
Permeabilityk, feet/year 9.651 X 10-7 1.035 X 106 k, centimeter per second
(cm/sec)Density
pound-mass per cubic foot 1.6018 X 101 6.2429 X 10-2 kilogram per cubic meter (lb/ft3) (kg/m3)
Unit Weightpound force per cubic foot 0.157 6.366 kilonewton per cubic meter (lb/ft3) (kN/m3)
Pressurepounds per square inch (psi) 7.03 X 10-2 1.4223 X 101 kilogram per square
centimeter (kg/cm3)6.8948 0.145 kiloPascal (kPa)
Forceton 8.89644 1.12405 X 10-1 kilonewton (kN)pound-force 4.4482 X 10-3 224.8096 kilonewton (kN)
Temperature EC = 5/9 (EF - 32 E) EF = (9/5 EC) + 32 E
GroutingMetric bag cement per meter 3.0 0.33 U.S. bag cement per footWater:cement ratio 0.7 1.4 water:cement ratio by weight by volumepounds per square inch 0.2296 4.3554 kilogram per square centi- per foot meter per meter (kg/cm2/m)k, feet/year 0.1 10 Lugeon
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BIBLIOGRAPHY
[1] The Glossary of Geology, 4th edition, AmericanGeologic Institute, Alexandria, VA, 1997.
[2] The American Association of Petroleum GeologistsBulletin, v. 67, No. 5, pp. 841-875, May 1983.
[3] Bureau of Reclamation, Earth Manual, 3rd edition,part 2, Denver, CO, 1990.
[4 ] Proctor, Robert V., and Thomas L. White, "EarthTunneling with Steel Supports," CommercialShearing, Inc., 1775 Logan Avenue, Youngstown, OH44501, 1977.
Chapter 3
ENGINEERING CLASSIFICATIONAND DESCRIPTION OF SOIL
General
Application
Soil investigations conducted for engineering purposesthat use test pits, trenches, auger and drill holes, or otherexploratory methods and surface sampling and mappingare logged and described according to the Unified SoilClassification System (USCS) as presented in Bureau ofReclamation (Reclamation) standards USBR 5000 [1] and5005 [2]. Also, bedrock materials with the engineeringproperties of soils are described using these standards(chapter 2). The Reclamation standards are consistentwith the American Society for Testing Materials (ASTM)Designation D2487 and 2488 on the USCS system [3,4].Descriptive criteria and terminology presented areprimarily for the visual classification and manual tests.The identification portion of these methods in assigninggroup symbols is limited to soil particles smaller than3 inches (in) (75 millimeters [mm]) and to naturallyoccurring soils. Provisions are also made to estimate thepercentages of cobbles and boulders by volume. Thisdescriptive system may also be applied to shale, shells,crushed rock, and other materials if done according tocriteria established in this section. Chapter 11 addressesthe logging format and criteria for describing soil in testpits, trenches, auger holes, and drill hole logs.
All investigations associated with land classification forirrigation suitability, data collection, analyses of soiland substratum materials related to drainage inves-tigations, and Quaternary stratigraphy (e.g., fault andpaleoflood studies) are logged and described using the
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U.S. Department of Agriculture terminology outlined inappendix I to Agriculture Handbook No. 436 (SoilTaxonomy), dated December 1975 [5].
All soil classification descriptions for particle sizes lessthan No. 4 sieve size are to be in metric units.
Performing Tests and Obtaining DescriptiveInformation
The USCS groups soils according to potential engineeringbehavior. The descriptive information assists with esti-mating engineering properties such as shear strength,compressibility, and permeability. These guidelines canbe used not only for identification of soils in the field butalso in the office, laboratory, or wherever soil samples areinspected and described.
Laboratory classification of soils [1] is not alwaysrequired but should be performed as necessary and can beused as a check of visual-manual methods. The descrip-tors obtained from visual-manual inspection providevaluable information not obtainable from laboratorytesting. Visual-manual inspection is always required. The visual-manual method has particular value inidentifying and grouping similar soil samples so that onlya minimum number of laboratory tests are required forpositive soil classification. The ability to identify anddescribe soils correctly is learned more readily under theguidance of experienced personnel, but can be acquired bycomparing laboratory test results for typical soils of eachtype with their visual and manual characteristics. Whenidentifying and describing soil samples from an area orproject, all the procedures need not be followed. Similarsoils may be grouped together; for example, one sampleshould be identified and described completely, with theothers identified as similar based on performing only afew of the identification and descriptive procedures.
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Descriptive information should be evaluated and reportedon every sample.
The sample used for classification must be representativeof the stratum and be obtained by an appropriate ac-cepted or standard procedure. The origin of the materialmust be correctly identified. The origin description maybe a boring number and depth and/or sample number, ageologic stratum, a pedologic horizon, or a locationdescription with respect to a permanent monument, agrid system, or a station number and offset.
Terminology for Soils
Definitions for soil classification and description are inaccordance with USBR 3900 Standard Definitions ofTerms and Symbols Relating to Soil Mechanics [6]:
Cobbles and boulders—particles retained on a 3-inch(75-mm) U.S. Standard sieve. The following terminologydistinguishes between cobbles and boulders:
• Cobbles—particles of rock that will pass a 12-in(300-mm) square opening and be retained on a 3-in(75-mm) sieve.
• Boulders—particles of rock that will not pass a12-in (300-mm) square opening.
Gravel—particles of rock that will pass a 3-in (75-mm)sieve and is retained on a No. 4 (4.75-mm) sieve. Gravelis further subdivided as follows:
• Coarse gravel—passes a 3-in (75-mm) sieve and isretained on 3/4-in (19-mm) sieve.
• Fine gravel—passes a ¾-in (19-mm) sieve and isretained on No. 4 (4.75-mm) sieve.
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Sand—particles of rock that will pass a No. 4 (4.75-mm)sieve and is retained on a No. 200 (0.075-mm or 75-micro-meter [µm]) sieve. Sand is further subdivided as follows:
• Coarse sand—passes No. 4 (4.75-mm) sieve and isretained on No. 10 (2.00-mm) sieve.
• Medium sand—passes No. 10 (2.00-mm) sieve andis retained on No. 40 (425-µm) sieve.
• Fine sand—passes No. 40 (425-µm) sieve and isretained on No. 200 (0.075-mm or 75-µm) sieve.
Clay—passes a No. 200 (0.075-mm or 75-µm) sieve. Soilhas plasticity within a range of water contents and hasconsiderable strength when air-dry. For classification,clay is a fine-grained soil, or the fine-grained portion of asoil, with a plasticity index greater than 4 and the plot ofplasticity index versus liquid limit falls on or above the"A"-line (figure 3-5, later in this chapter).
Silt—passes a No. 200 (0.075-mm or 75-µm) sieve. Soilis nonplastic or very slightly plastic and that exhibitslittle or no strength when air-dry is a silt. Forclassification, a silt is a fine-grained soil, or the fine-grained portion of a soil, with a plasticity index less than4 or the plot of plasticity index versus liquid limit fallsbelow the "A"-line (figure 3-5).
Organic clay—clay with sufficient organic content to in-fluence the soil properties is an organic clay. For classifi-cation, an organic clay is a soil that would be classified asa clay except that its liquid limit value after oven-dryingis less than 75 percent of its liquid limit value beforeoven-drying.
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Organic silt—silt with sufficient organic content to in-flu-ence the soil properties. For classification, an organicsilt is a soil that would be classified as a silt except thatits liquid limit value after oven-drying is less than75 percent of its liquid limit value before oven-drying.
Peat—material composed primarily of vegetable tissuesin various stages of decomposition, usually with an or-ganic odor, a dark brown to black color, a spongy con-sistency, and a texture ranging from fibrous to amor-phous. Classification procedures are not applied to peat.
Classifications of Soils
Group Names and Group Symbols
The identification and naming of a soil based on resultsof visual and manual tests is presented in a subsequentsection. Soil is given an identification by assigning agroup symbol(s) and group name. Important informationabout the soil is added to the group name by the term"with" when appropriate (figures 3-1, 3-2, 3-3, 3-4). Thegroup name is modified using “with” to stress othersignificant components in the soil.
Figure 3-2 is a flow chart for assigning typical names andgroup symbols for inorganic fine-grained soils; figure 3-3is a flow chart for organic fine-grained soils; figure 3-4 isa flow chart for coarse-grained soils. Refer to tables 3-1and 3-2 for the basic group names without modifiers. Ifthe soil has properties which do not distinctly place it in
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FINE-GRAINED SOILS
Sandy BASIC
GROUP NAME
with sand
Gravelly with gravel
COARSE-GRAINED SOILS
with silt BASIC
GROUP NAME
with sand
with clay with gravel
Figure 3-1.—Modifiers to basic soil group names(for visual classification).
a specific group, borderline symbols may be used. Thereis a distinction between dual symbols and borderlinesymbols.
Dual Symbols.—Dual symbols separated by a hyphenare used in laboratory classification of soils and in visualclassification when soils are estimated to contain10 percent fines. A dual symbol (two symbols separatedby a hyphen, e.g., GP-GM, SW-SC, CL-ML) should beused to indicate that the soil has the properties of aclassification where two symbols are required. Dual sym-bols are required when the soil has between 5 and12 percent fines from laboratory tests (table 3-2), or finesare estimated as 10 percent by visual classification. Dualsymbols are also required when the liquid limit andplasticity index values plot in the CL-ML area of theplasticity chart (figure 3-5, later in this chapter).
SO
IL
23 Figure 3-2.—Flow chart for inorganic fine-grained soils, visual method.
FIE
LD
MA
NU
AL
24
Figure 3-3.—Flow chart for organic soils, visual method.
SO
IL
25 Figure 3-4.—Flow chart for coarse-grained soils, visual method.
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Table 3-1.—Basic group names, primary groups
Coarse-grained soils Fine-grained soils
GW - Well graded gravelGP - Poorly graded gravelGM - Silty gravelGC - Clayey gravel sandSW - Well graded sandSP - Poorly graded sandSM - Silty sandSC - Clayey sand
CL - Lean clayML - SiltOL - Organic clay (on or
above A-line- Organic silt (below A-line)
CH - Fat clayMH - Elastic siltOH - Organic clay (on or above
A-line)- Organic silt (below A-line)
Basic group name—hatched area on Plasticity Chart(Laboratory Classification)
CL-ML - Silty clayGC-GM - Silty, clayey gravelSC-SM - Silty, clayey sand
Table 3-2.—Basic group names, 5 to 12 percent fines(Laboratory Classification)
GW-GM - Well graded gravel with siltGW-GC - Well graded gravel with clay (if fines =
CL-ML) Well graded gravel with silty clayGP-GM - Poorly graded gravel with siltGP-GC - Poorly graded gravel with clay (if fines =
CL-ML) Poorly graded gravel with silty claySW-SM - Well graded sand with siltSW-SC - Well graded sand with clay (if fines = CL-ML)
Well graded sand with silty claySP-SM - Poorly graded sand with siltSP-SC - Poorly graded sand with clay (if fines =
CL-ML) Poorly graded sand with silty clay
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Borderline Symbols.—Borderline symbols are usedwhen soil properties indicate the soil is close to anotherclassification group. Two symbols separated by a slash,such as CL/CH, SC/CL, GM/SM, CL/ML, should be usedto indicate that the soil has properties that do notdistinctly place the soil into a specific group. Because thevisual classification of soil is based on estimates ofparticle-size distribution and plasticity characteristics, itmay be difficult to clearly identify the soil as belonging toone category. To indicate that the soil may fall into oneof two possible basic groups, a borderline symbol may beused with the two symbols separated by a slash. Aborderline classification symbol should not be usedindiscriminately. Every effort should be made first toplace the soil into a single group. Borderline symbols canalso be used in laboratory classification, but lessfrequently.
A borderline symbol may be used when the percentage offines is visually estimated to be between 45 and 55 per-cent. One symbol should be for a coarse-grained soil withfines and the other for a fine-grained soil. For example:GM/ML, CL/SC.
A borderline symbol may be used when the percentage ofsand and the percentage of gravel is estimated to beabout the same, for example, GP/SP, SC/GC, GM/SM. Itis practically impossible to have a soil that would have aborderline symbol of GW/SW. However, a borderlinesymbol may be used when the soil could be either wellgraded or poorly graded. For example: GW/GP, SW/SP.
A borderline symbol may be used when the soil could beeither a silt or a clay. For example: CL/ML, CH/MH,SC/SM.
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A borderline symbol may be used when a fine-grained soilhas properties at the boundary between a soil of low com-pressibility and a soil of high compressibility. Forexample: CL/CH, MH/ML.
The order of the borderline symbol should reflect simi-larity to surrounding or adjacent soils. For example, soilsin a borrow area have been predominantly identified asCH. One sample has the borderline symbol of CL andCH. To show similarity to the adjacent CH soils, theborderline symbol should be CH/CL.
The group name for a soil with a borderline symbolshould be the group name for the first symbol, except for:
CL/CH - lean to fat clayML/CL - clayey siltCL/ML - silty clay
Preparation for Identification and VisualClassification
A usually dark-brown to black material composedprimarily of vegetable tissue in various stages of decom-position with a fibrous to amorphous texture and organicodor is a highly organic soil and classified as peat, PT.Plant forms may or may not be readily recognized. Ingeneral, the greater the organic content, the greater thewater content, void ratio, and compressibility of peat. Organic soils are often identified by their odor. To checkfor organic content, the soil can be subjected to thelaboratory classification liquid limit test criteria. Organicsoils can also be identified through laboratory loss-on-ignition tests. Materials identified as peat are not sub-jected to the following identification procedures.
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Soil identification procedures are based on the minus 3-in(75-mm) particle sizes. All plus 3-in (75-mm) particlesmust be manually removed from a loose sample, ormentally for an intact sample, before classifying the soil. Estimate and note the percent by volume of the plus 3-in(75-mm) particles, both the percentage of cobbles and thepercentage of boulders.
Note: Because the percentages of the particle-size distribution in laboratory classification(ASTM: D 2487) are by dry weight and theestimates of percentages for gravel, sand, andfines are by dry weight, the description shouldstate that the percentages of cobbles andboulders are by volume, not weight, for visualclassification. Estimation of the volume of cob-bles and boulders is not an easy task. Accurateestimating requires experience. While exper-ienced loggers may be able to successfullyestimate the minus 3-in fraction to within5 percent, the margin of error could be larger foroversize particles. Estimates can be confirmedor calibrated with large scale field gradationtests on critical projects. Given the large pos-sible errors in these estimates, the estimatesshould not be used as the sole basis for design ofprocessing equipment. Large scale gradationsshould be obtained as part of the process plantdesigns.
In most cases, the volume of oversize is estimated inthree size ranges, 3 to 5, 5 to 12, and 12 inches andlarger. Cobbles are often divided into two size ranges,because in roller compacted fill of 6-in compacted liftthickness, the maximum size cobble is 5 inches. If thepurpose of the investigation is not for roller compactedfill, a single size range for cobbles can be estimated.
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Estimate and note the percentage by dry weight of thegravel, sand, and fines of the fraction of the soil smallerthan 3 in (75-mm). The percentages are estimated to theclosest 5 percent. The percentages of gravel, sand, andfines must add up to 100 percent, excluding traceamounts. The presence of a component not in sufficientquantity to be considered 5 percent in the minus 3-in(75-mm) portion, is indicated by the term "trace." For ex-ample: trace of fines. A trace is not considered in thetotal of 100 percent for the components.
The first step in the identification procedure is todetermine the percentages of fine-grained and coarse-grained materials in the sample. The soil is fine-grainedif it contains 50 percent or more fines. The soil is coarse-grained if it contains less than 50 percent fines.Procedures for the description and classification of thesetwo preliminary identification groups follow.
Procedures and Criteria for Visual Classificationof Fine-Grained Soils
Select a representative sample of the material forexamination and remove particles larger than theNo. 40 sieve (medium sand and larger) until a specimenequivalent to about a handful of representative materialis available. Use this specimen for performing theidentification tests.
Identification Criteria for Fine-Grained Soils.—Thetests for identifying properties of fines are dry strength,dilatency, toughness, and plasticity.
1. Dry strength.—Select from the specimen enoughmaterial to mold into a ball about 1 in (25 mm) indiameter. Mold or work the material until it has theconsistency of putty, adding water if necessary.
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From the molded material, make at least three testspecimens. Each test specimen should be a ball ofmaterial about ½ in (12 mm) in diameter. Allow thetest specimens to dry in air or sun, or dry by artificialmeans, as long as the temperature does not exceed60 degrees Centigrade (EC). In most cases, it will benecessary to prepare specimens and allow them todry over night. If the test specimen contains naturaldry lumps, those that are about ½ in (12 mm) indiameter may be used in place of molded balls. (Theprocess of molding and drying usually produceshigher strengths than are found in natural dry lumpsof soil). Test the strength of the dry balls or lumps bycrushing them between the fingers and note thestrength as none, low, medium, high, or very highaccording to the criteria in table 3-3. If natural drylumps are used, do not use the results of any of thelumps that are found to contain particles of coarsesand.
Table 3-3.—Criteria for describing dry strength
None The dry specimen crumbles with merepressure of handling.
Low The dry specimen crumbles with somefinger pressure.
Medium The dry specimen breaks into pieces orcrumbles with considerable fingerpressure.
High The dry specimen cannot be broken withfinger pressure. Specimen will break intopieces between thumb and a hard surface.
Very High The dry specimen cannot be brokenbetween thumb and a hard surface.
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The presence of high-strength, water-soluble cement-ing materials, such as calcium carbonate, may causeexceptionally high dry strengths. The presence ofcalcium carbonate can usually be detected from theintensity of the reaction with dilute hydrocloric acid(HCl). Criteria for reaction with HCl are presentedin a subsequent paragraph.
2. Dilatancy.—Select enough material from thespecimen to mold into a ball about ½ in (12 mm) indiameter. Mold the material, adding water if neces-sary, until it has a soft, but not sticky, consistency.Smooth the soil ball in the palm of one hand with theblade of a knife or spatula. Shake horizontally (thesoil ball), striking the side of the hand vigorouslyagainst the other hand several times. Note thereaction of the water appearing on the surface of thesoil. Squeeze the sample by closing the hand orpinching the soil between the fingers and notereaction as none, slow, or rapid according to thecriteria in table 3-4. The reaction criteria are thespeeds with which water appears while shaking anddisappears while squeezing.
Table 3-4.—Criteria for describing dilatancy
None No visible change in the specimen.
Slow Water slowly appears on the surface of thespecimen during shaking and does not disap-pear or disappears slowly upon squeezing.
Rapid Water quickly appears on the surface of thespecimen during shaking and disappearsupon squeezing.
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3. Toughness.—Following completion of thedilatancy test, the specimen is shaped into anelongated pat and rolled by hand on a smooth surfaceor between the palms into a thread about c in(3 mm) diameter. (If the sample is too wet to rolleasily, spread the sample out into a thin layer andallow some water loss by evaporation). Fold thesample threads and reroll repeatedly until the threadcrumbles at a diameter of about c in (3 mm) whenthe soil is near the plastic limit. Note the timerequired to reroll the thread to reach the plasticlimit. Note the pressure required to roll the threadnear the plastic limit. Also, note the strength of thethread. After the thread crumbles, the pieces shouldbe lumped together and kneaded until the lumpcrumbles. Note the toughness of the material duringkneading.
Describe the toughness of the thread and lump aslow, medium, or high according to the criteria intable 3-5.
Table 3-5.—Criteria for describing toughness
Low Only slight pressure is required to roll thethread near the plastic limit. The threadand the lump are weak and soft.
Medium Medium pressure is required to roll thethread to near the plastic limit. The threadand the lump have medium stiffness.
High Considerable pressure is required to roll thethread to near the plastic limit. The threadand the lump have very high stiffness.
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4. Plasticity.—On the basis of observations madeduring the toughness test, describe the plasticity ofthe material according to the criteria given intable 3-6 (figure 3-5).
Table 3-6.—Criteria for describing plasticity
Nonplastic A 3-mm thread cannot be rolled at anywater content.
Low The thread can barely be rolled, and thelump cannot be formed when drier thanthe plastic limit.
Medium The thread is easy to roll, and not muchtime is required to reach the plastic limit.The thread cannot be rerolled afterreaching the plastic limit. The lumpcrumbles when drier than the plasticlimit.
High It takes considerable time rolling andkneading to reach the plastic limit. Thethread can be rolled several times afterreaching the plastic limit. The lump canbe formed without crumbling when drierthan the plastic limit.
After the dry strength, dilatency, toughness, andplasticity tests have been performed, decide onwhether the soil is an organic or an inorganic fine-grained soil.
SO
IL
35 Figure 3-5.—Plasticity chart.
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Identification of Inorganic Fine-Grained Soils.—Classify the soils using the results of the manual testsand the identifying criteria shown in table 3-7. Possibleinorganic soils include lean clay (CL), fat clay (CH), silt(ML), and elastic silt (MH). The properties of an elasticsilt are similar to those for a lean clay. However, the siltwill dry quickly on the hand and have a smooth, silky feelwhen dry. Some soils which classify as MH according tothe field classification criteria are difficult to distinguishfrom lean clays, CL. It may be necessary to performlaboratory testing to ensure proper classification.
Table 3-7.—Identification of inorganic fine-grained soils from manual tests
Group symbol
Dry strength Dilatancy Toughness
ML None to low Slow to rapid
Low or thread cannot be formed
CL Medium to high None to slow Medium
MH Low to medium None to slow Low to medium
CH High to very high
None High
Some soils undergo irreversible changes upon air drying.These irreversible processes may cause changes inatterberg limits and other index tests. Even unsuspectedsoils such as low plasticity silts may have differingatterberg limits due to processes like disaggregation. When tested at natural moisture, clay particles cling tosilt particles resulting in less plasticity. When dried, theclay disaggregates, making a finer and more well gradedmix of particles with increased plasticity.
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For foundation studies of existing or new structures,natural moisture atterberg limits are preferred becausethe in-place material will remain moist. Natural mois-ture atterberg limits are especially important in criticalstudies, such as earthquake liquefaction evaluation ofsilts. On some foundation studies, such as for pumpingplant design, consolidation tests will govern, and naturalmoisture atterbergs are not required. For borrow studies,soils will likely undergo moisture changes, and naturalmoisture atterberg limits are not required unless unusualmineralogy is encountered.
Identification of Organic Fine-Grained Soils.—If thesoil contains enough organic particles to influence the soilproperties, classify the soil as an organic soil, OL or OH.Organic soils usually are dark brown to black and usuallyhave an organic odor. Often organic soils will changecolor, (black to brown) when exposed to air. Organic soilsnormally do not have high toughness or plasticity. Thethread for the toughness test is spongy. In some cases,further identification of organic soils as organic silts ororganic clays, OL or OH is possible. Correlations betweenthe dilatancy, dry strength, and toughness tests withlaboratory tests can be made to classify organic soils insimilar materials.
Modifiers for Fine-Grained Soil Classifications.—Ifbased on visual observation, the soil is estimated to have15 to 25 percent sand and/or gravel, the words "with sandand/or gravel" are added to the group name, for example,LEAN CLAY WITH SAND, (CL); SILT WITH SAND ANDGRAVEL (ML). Refer to figures 3-2 and 3-3. If the soil isvisually estimated to be 30 percent or more sand and/orgravel, the words "sandy" or "gravelly" are added to thegroup name. Add the word "sandy" if there appears to bemore sand than gravel. Add the word "gravelly" if thereappears to be more gravel than sand, for example,SANDY LEAN CLAY (CL); GRAVELLY FAT CLAY (CH);
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SANDY SILT (ML). Refer to figures 3-2 and 3-3. Notethat the Laboratory Classification follows differentcriteria.
Procedures and Criteria for Visual Classificationof Coarse-Grained Soils
A representative sample containing less than 50 percentfines is identified as a coarse-grained soil.
The soil is a gravel if the percentage by weight of gravelis estimated to be more than the percentage of sand.
The soil is a sand if the percentage by weight of sand isestimated to be more than the percentage of gravel.
The soil is a clean gravel or clean sand if the percentagesof fines are visually estimated to be 5 percent or less. Aclean gravel or sand is further classified by grain sizedistribution.
The soil is classified as a WELL GRADED GRAVEL(GW), or as a WELL GRADED SAND (SW), if a widerange of particle sizes and substantial amounts of theintermediate particle sizes are present. The soil isclassified as a POORLY GRADED GRAVEL (GP) or as aPOORLY GRADED SAND (SP) if the material ispredominantly one size (uniformly graded) or the soil hasa wide range of sizes with some intermediate sizesobviously missing (gap or skip graded).
The soil is identified as either gravel with fines or sandwith fines if the percentage of fines is visually estimatedto be 15 percent or more.
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Classify the soil as a CLAYEY GRAVEL (GC) or aCLAYEY SAND (SC) if the fines are clayey as determinedby the procedures for fine-grained soil identification.
Identify the soil as a SILTY GRAVEL (GM) or a SILTYSAND (SM) if the fines are silty as determined by the pro-cedures for fine-grained soil identification.
If the soil is visually estimated to contain 10 percentfines, give the soil a dual classification using two groupsymbols. The first group symbol should correspond to aclean gravel or sand (GW, GP, SW, SP), and the secondsymbol should correspond to a gravel or sand with fines(GC, GM, SC, SM). The typical name is the first groupsymbol plus "with clay" or "with silt" to indicate theplasticity characteristics of the fines. For example,WELL GRADED GRAVEL WITH CLAY (GW-GC);POORLY GRADED SAND WITH SILT (SP-SM). Refer tofigure 3-4.
If the specimen is predominantly sand or gravel but con-tains an estimated 15 percent or more of the othercoarse-grained constituent, the words "with gravel" or"with sand" are added to the group name. For example:POORLY GRADED GRAVEL WITH SAND (GP); CLAY-EY SAND WITH GRAVEL (SC). Refer to figure 3-4.
If the field sample contained any cobbles and/or boulders,the words "with cobbles" or "with cobbles and boulders"are added to the group name, for example, SILTY GRA-VEL WITH COBBLES (GM).
Abbreviated Soil Classification Symbols
If space is limited, an abbreviated system may be used toindicate the soil classification symbol and name such asin logs, data bases, tables, etc. The abbreviated system
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is not a substitute for the full name and descriptive infor-mation but can be used in supplementary presentations.The abbreviated system consists of the soil classificationsystem based on this chapter, with prefixes and suffixesas listed below.
Prefix: s = sandy g = gravellySuffix: s = with sand g = with gravel
c = with cobbles b = with boulders
The soil classification symbol is enclosed in parentheses.Examples are:
CL, sandy lean clay s(CL)SP-SM, poorly graded sand (SP-GM)g with silt and gravelGP, poorly graded gravel with sand, (GP)scb cobbles, and bouldersML, gravelly silt with sand g(ML)sc and cobbles
Description of the Physical Properties of Soil
Descriptive information for classification and reportingsoil properties such as angularity, shape, color, moistureconditions, and consistency are presented in the followingparagraphs.
Angularity
Angularity is a descriptor for coarse-grained materialsonly. The angularity of the sand (coarse sizes only),gravel, cobbles, and boulders, are described as angular,
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subangular, subrounded, or rounded as indicated by thecriteria in table 3-8. A range of angularity may be stated,such as: sub-rounded to rounded.
Table 3-8.—Criteria for describing angularity of coarse-grained particles
Angular Particles have sharp edges and relativelyplanar sides with unpolished surfaces.
Subangular Particles are similar to angular descriptionbut have rounded edges.
Subrounded Particles have nearly planar sides but well-rounded corners and edges.
Rounded Particles have smoothly curved sides and noedges.
Shape
Describe the shape of the gravel, cobbles, and boulders as“flat, elongated” or “flat and elongated” if they meet thecriteria in table 3-9. Indicate the fraction of the particlesthat have the shape, such as: one-third of gravel particlesare flat. If the material is to be processed or used asaggregate for concrete, note any unusually shapedparticles.
Color
Color is an especially important property in identifyingorganic soils and is often important in identifying othertypes of soils. Within a given locality, color may also beuseful in identifying materials of similar geologic units.Color should be described for moist samples. Note if color
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Table 3-9.—Criteria for describing particle shape
The particle shape is described as follows, where length,width, and thickness refer to the greatest, intermediate, andleast dimensions of a particle, respectively.
Flat Particles with width/thickness >3.
Elongated Particles with length/width >3.
Flat and Particles meet criteria for both flat and elongated elongated.
represents a dry condition. If the sample contains layersor patches of varying colors, this should be noted, andrepresentative colors should be described. The MunselColor System may be used for consistent colordescriptions.
Odor
Describe the odor if organic or unusual. Soils containinga significant amount of organic material usually havea distinctive odor of decaying vegetation. This is espe-cially apparent in fresh samples, but if the samples aredried, the odor often may be revived by heating a moist-ened sample. If the odor is unusual, such as that of apetroleum product or other chemical, the material shouldbe described and identified if known. The material maybe hazardous, and combustion or exposure should beconsidered.
Moisture Conditions
Describe the moisture condition as dry, moist, or wet, asindicated by the criteria in table 3-10.
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Table 3-10.—Criteria for describing moisturecondition
Dry Absence of moisture, dusty, dry to the touch.
Moist Damp but no visible water.
Wet Visible free water, usually soil is below watertable.
Reaction with HCl
Describe the reaction with HCl as none, weak, or strong,as indicated by the criteria in table 3-11. Calciumcarbonate is a common cementing agent. The reactionwith dilute hydrochloric acid is important in determiningthe presence and abundance of calcium carbonate.
Table 3-11.—Criteria for describing reaction with HCl
None No visible reaction.
Weak Some reaction, with bubbles forming slowly.
Strong Violent reaction, with bubbles forming immediately.
Consistency
Describe consistency (degree of firmness) for intact fine-grained soils as very soft, soft, firm, hard, or very hard, asindicated by the criteria in table 3-12. This observationis inappropriate for soils with significant amounts ofgravel. Pocket penetrometer or torvane testing may sup-plement this data.
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Table 3-12.—Criteria for describing consistency of in-place orundisturbed fine-grained soils
Very soft Thumb will penetrate soil more than 1 in (25 mm).
Soft Thumb will penetrate soil about 1 in (25 mm).
Firm Thumb will indent soil about 1/4 in (5 mm).
Hard Thumb will not indent soil but readily indented with thumbnail.
Very hard Thumbnail will not indent soil.
Cementation
Describe the cementation of intact soils as weak,moderate, or strong, as indicated by the criteria intable 3-13.
Table 3-13.—Criteria for describing cementation
Weak Crumbles or breaks with handling or littlefinger pressure.
Moderate Crumbles or breaks with considerable fingerpressure.
Strong Will not crumble or break with finger pressure.
Structure (Fabric)
Describe the structure of the soil according to criteriadescribed in table 3-14. The descriptors presented are forsoils only; they are not synonymous with descriptors forrock.
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Table 3-14.—Criteria for describing structure
Stratified Alternating layers of varying material orcolor; note thicknesses.
Laminated1 Alternating layers of varying material orcolor with layers less than 6 mm thick; notethicknesses.
Fissured1 Breaks along definite planes with littleresistance to fracturing.
Slickensided1 Fracture planes appear polished or glossy,sometimes striated.
Blocky1 Cohesive soil that can be broken down intosmall angular lumps which resist furtherbreakdown.
Lenses Inclusion of small pockets of different soils,such as small lenses of sand scatteredthrough a mass of clay; note thicknesses.
Homogeneous Same color and textural or structuralappearance throughout.
1 Do not use for coarse-grained soils with the exception of finesands which can be laminated.
Particle Sizes
For gravel and sand-size components, describe the rangeof particle sizes within each component as defined in theprevious terminology paragraph. Descriptive terms,sizes, and examples of particle sizes are shown intable 3-15.
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Table 3-15.—Particle sizes
Descriptiveterm Size
Familiar example withinthe size range
Boulder 300 mm or more Larger than a volleyball
Cobble 300 mm to 75 mm Volleyball - grapefruit -orange
Coarse gravel 75 mm to 20 mm Orange - grape
Fine gravel 20 mm to No. 4sieve (5 mm)
Grape - pea
Coarse sand No. 4 sieve toNo. 10 sieve
Sidewalk salt
Medium sand No. 10 sieve toNo. 40 sieve
Openings in windowscreen
Fine sand No. 40 sieve toNo. 200 sieve
Sugar - table salt, grainsbarely visible
Describe the maximum particle size found in the sample.For reporting maximum particle size, use the followingdescriptors and size increments:
Fine sandMedium sand Coarse sand5-mm increments from 5 mm to 75 mm25-mm increments from 75 mm to 300 mm100-mm increments over 300 mm
For example: "maximum particle size 35 mm""maximum particle size 400 mm"
If the maximum particle size is sand size, describe asfine, medium, or coarse sand; for example, maximum par-ticle size, medium sand.
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If the maximum particle size is gravel size, describe themaximum particle size as the smallest sieve opening thatthe particle would pass.
If the maximum particle size is cobble or boulder size,describe the maximum dimension of the largest particle.
Particle Hardness
Describe the hardness of coarse sand and larger particlesas hard, or state what happens when the particles are hitby a hammer; e.g., gravel-size particles fracture withconsiderable hammer blow, some gravel-size particlescrumble with hammer blow. Hard means particles do notfracture or crumble when struck with a hammer.Remember that the larger the particle, the harder theblow required to fracture it. A good practice is to describethe particle size and the method that was used todetermine the hardness.
Additional Descriptive Information
Additional descriptive information may include unusualconditions, geological interpretation or other classifi-cation methods, such as:
Presence of roots or root holes or other organicmaterial or debris;
Degree of difficulty in drilling or augering hole or ex-cavating a pit; or
Raveling or caving of the trench, hole, pit, or exposure;
or
Presence of mica or other predominant minerals.
A local or commercial name and/or a geologic interpreta-tion should be provided for the soil.
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A classification or identification of the soil according toother classification systems may be added.
Narrative Descriptions and Examples
The description should include the information shown intables 3-16 and 3-17, a checklist for the description ofsoils. Example descriptions follow.
Table 3-16.—Checklist for the description of soilclassification and identification
1.2.3.4.
5.
6.
7.8.9.
10.
11.
12.
13.14.15.
16.
Group name and symbolPercent gravel, sand, and/or finesPercent by volume of cobbles and bouldersParticle size
Gravel - fine, coarseSand - fine, medium, coarse
Particle angularity angular subangular subrounded roundedParticle shape flat elongated flat and elongatedMaximum particle size or dimensionHardness of coarse sand and larger particlesPlasticity of fines nonplastic low medium highDry strength none low medium high very highDilatancy none slow rapidToughness low medium highColor (when moist)Odor (if organic or unusual)Moisture dry moist wetReaction with HCL none weak strong
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Table 3-17.—Checklist for the description of in-place conditions
In-place conditions:
1.
2.
3.
4.5.
Consistency (fine-grained soils only) very soft soft firm hard very hardCementation weak moderate strongStructure stratified laminated fissured slickened lensed homogeneousGeologic interpretation and/or local name, if anyAdditional comments and description
Presence of roots or root holesPresence of mica, gypsum, etc.Surface coatingsCaving or sloughing of excavationExcavation difficulty
Example 1: CLAYEY GRAVEL WITH SAND AND COB-BLES (GC)—Approximately 50 percent fine to coarse,sub-rounded to subangular gravel; approximately30 percent fine to coarse, subrounded sand;approximately 20 per-cent fines with medium plasticity,high dry strength, no dilatancy, medium toughness; weakreaction with HCl; original field sample had about5 percent (by volume) subrounded cobbles, maximum size150 mm.
IN-PLACE CONDITIONS: firm, homogeneous, dry,brown.
GEOLOGIC INTERPRETATION: alluvial fan.
Abbreviated symbol is (GC)sc.
Example 2: WELL GRADED GRAVEL WITH SAND(GW)—Approximately 75 percent fine to coarse, hard,sub-angular gravel; approximately 25 percent fine to
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coarse, hard, subangular sand; trace of fines; maximumsize 75 mm, brown, dry; no reaction with HCl.
Abbreviated symbol is (GW)s
Example 3: SILTY SAND WITH GRAVEL (SM)—Ap-proximately 60 percent predominantly fine sand; approxi-mately 25 percent silty fines with low plasticity, low drystrength, rapid dilatancy, and low toughness; approxi-mately 15 percent fine, hard, subrounded gravel, a fewgravel-size particles fractured with hammer blow;maximum size 25 mm; no reaction with HCl.
IN-PLACE CONDITIONS: firm, stratified, and containslenses of silt 1- to 2-in thick, moist, brown to gray;in-place density was 106 pounds per cubic foot (lb/ft3), andin-place moisture was 9 percent.
GEOLOGIC INTERPRETATION: ALLUVIUM
Abbreviated symbol is (SM)g.
Example 4: ORGANIC SOIL (OL/OH)—Approximately100 percent fines with low plasticity, slow dilatancy, lowdry strength, and low toughness; wet, dark brown,organic odor, weak reaction with HCl.
Abbreviated symbol is (OL/OH).
Example 5: SILTY SAND WITH ORGANIC FINES(SM)—Approximately 75 percent fine to coarse, hard, sub-angular reddish sand, approximately 25 percent organicand silty dark-brown nonplastic fines with no drystrength and slow dilatancy; wet; maximum size, coarsesand; weak reaction with HCl.
Abbreviated symbol is (SM)
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Example 6: POORLY GRADED GRAVEL WITH SILT,SAND, COBBLES, AND BOULDERS (GP-GM)—Approx-imately 75 percent fine to coarse, hard, subrounded tosubangular gravel; approximately 15 percent fine, hard,subrounded to subangular sand; approximately 10 per-cent silty nonplastic fines; moist, brown; no reaction withHCl; original field sample had approximately 5 percent(by volume) hard, subrounded cobbles and a trace of hard,subrounded boulders with a maximum dimension of500 mm.
Abbreviated symbol is (GP-GM)scb.
Use of Soil Classification as Secondary Identification Method for Materials Other
Than Natural Soils
General
Materials other than natural soils may be classified andtheir properties identified and described using the sameprocedures presented in the preceding subsections. Thefollowing materials are not considered soils and shouldnot be given a primary USCS soil classification:
Partially lithified or poorly cemented materials
Shale ClaystoneSandstone SiltstoneDecomposed granite
Processed, manmade, or other materials
Crushed rock SlagCrushed sandstone ShellsCinders Ashes
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Identification criteria may be used for describing thesematerials, especially for describing particle sizes andshapes and identifying those materials which convert tosoils after field or laboratory processing. Description for-mat and classification for these materials are discussedindividually in the following paragraphs.
Partially Lithified or Cemented Materials
Partially lithified or poorly cemented materials may needto be classified because the material will be excavated,processed, or manipulated for use as a constructionmaterial. When the physical properties are to be deter-mined for these materials for classification, the materialmust be processed into a soil by grinding or slaking inwater (shale, siltstone, poorly indurated ash deposits).
The physical properties and resulting classificationdescribe the soil type as created by reworking the originalmaterial. Soil classifications can then be used as asecondary identification. However, the classificationsymbol and group name must be reported in quotationmarks in any 1ogs, tables, figures, and reports. Iflaboratory tests are performed on these materials, theresults must be reported as shown in figure 3-6.
An example of a written narrative for either a test pit orauger hole log based on visual classification is as follows:Symbol Description
Shale Fragments 3.4- to 7.8-foot (ft) Shale Fragments—Retrieved as 2- to 4-in pieces of shalefrom power auger hole, dry, brown,no reaction with HCl. After slakingin water for 24 hours, materialclassified as "SANDY CLAY (CH)"—
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Figure 3-6.—Sample of test results summary.
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Approximately 60 percent fines withhigh plasticity, high dry strength, nodilatancy and high toughness;approximately 35 percent fine tomedium, hard sand; approximately5 percent gravel-size pieces of shale.
Processed or Manmade Materials
Processed, manmade, or other materials are also used asconstruction materials, and classification can be used asa secondary identification. However, for these processedmaterials, the group name and classification symbol areto be within quotation marks. If laboratory tests areperformed on these materials, the results must bereported as shown in table 3-6.
An example of a written narrative for logs for visual clas-sification is as follows:
Symbol Description
CRUSHED ROCK Stockpile No. 3 CRUSHEDROCK— processed gravel and cob-bles from P.T. NO. 7; "POORLY GRADEDGRAVEL (GP)"—approximately90 percent fine, hard, angular,gravel-size particles; approximately10 percent coarse, angular, sand-size particles; dry, tan, no reactionwith HCl.
Special Cases for Classification
Some materials that require a classification and descrip-tion according to USBR 5000 [1] or USBR 5005 [2] shouldnot have a heading that is a classification group name.
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When these materials will be used in, or influence, designand construction, they should be described according tothe criteria for logs of test pits and auger holes and theclassification symbol and typical name placed in quota-tion marks similar to the previous discussion on second-ary identification method for materials other thannatural soils. The heading should be as follows:
TopsoilLandfillRoad surfacing Uncompacted or CompactedFill
For example:
Classification
Symbol Description
TOPSOIL 0.0-0.8 meter (m) TOPSOIL—would beclassified as "ORGANIC SILT (OL)."Approximately 80 percent fines with lowplasticity, slow dilatancy, low drystrength, and low toughness; approxi-mately 20 percent fine to medium sand;wet, dark brown, organic odor, weak reac-tion with HCl; roots present throughout.
Some material should be described but not given a classi-fication symbol or group name, such as landfill (trash,garbage, etc.) or asphalt road. All of the above listedterms are only examples; this is not a complete list. If theabove materials are not to be used and will not influencedesign or construction, only the basic term listed aboveneed be shown on the logs without a complete descriptionor classification.
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BIBLIOGRAPHY
[1] Bureau of Reclamation, U.S. Department of theInterior, USBR-5000, “Procedure for DeterminingUnified Soil Classification (Laboratory Method),”Earth Manual, Part II, 3rd edition, 1990.
[2] Bureau of Reclamation, U.S. Department of theInterior, USBR-5005, “Procedure for DeterminingUnified Soil Classification (Visual Method),” EarthManual, Part II, 3rd edition, 1990.
[3] American Society for Testing and Materials, ASTMD-2487, “Standard Classification of Soils forEngineering Purposes,” ASTM Annual Book ofStandards, Volume 04.08 on Soil and Rock,Section 4 - Construction, West Conshohocken, PA,1996.
[4] American Society for Testing and Materials, ASTMD-2488, “Standard Practice for Description andIdentification of soils (Visual-Manual Procedure),”ASTM Annual Book of Standards, Volume 04.08 onSoil and Rock, Section 4 - Construction, West Con-shohocken, PA, 1996.
[5] U.S. Department of Agriculture, Agriculture Hand-book No. 436, Appendix I (Soil Taxonomy), December1975.
[6] Bureau of Reclamation, U.S. Department of theInterior, USBR 3900, “Standard Definitions ofTerms and Symbols Relating to Soil Mechanics,”Earth Manual, Part II, 3rd edition, 1990.
Chapter 4
CLASSIFICATION OF ROCKS AND DESCRIPTION OF PHYSICAL
PROPERTIES OF ROCK
Introduction
Uniformity of definitions, descriptors, and identificationof rock units is important to maintain continuity ingeologic logs, drawings, and reports from a project withmultiple drilling sessions, different loggers and mappers.Also important is the recording of all significant observ-able parameters when logging or mapping. This chapterpresents a system for the identification and classificationof rocks and includes standard terminology anddescriptive criteria for physical properties of engineeringsignificance. The standards presented in this chaptermay be expanded or modified to fit project requirements.
Rock Classification
Numerous systems are in use for field and petrographicclassification of rocks. Many classifications requiredetailed petrographic laboratory tests and thin sections,while others require limited petrographic examinationand field tests. The Bureau of Reclamation (Reclamation)has adopted a classification system which is modifiedfrom R.B. Travis [1]. While not based entirely on fieldtests or field identification of minerals, many of theclassification categories are sufficiently broad that fieldidentification is possible. Even where differences in themineral constituents cannot be determined precisely inthe field, differences usually are not significant enough toaffect the engineering properties of the rock if classifiedsomewhat incorrectly by lithologic name. Detailedmineralogical identification and petrographicclassification can be performed on hand samples or coresamples submitted to a petrographic laboratory.
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If samples are submitted to a petrographic laboratory, thepetrographic classification generally will coincide with theclassification according to Travis. The petrographicigneous rock classifications are somewhat more preciseand include specialty rock types based upon mineral com-position, texture, and occurrence. For example, alamprophyric dike composed of green hornblendephenocrysts or clinopyroxene in the groundmass could beclassified as spessartite, whereas a lamprophyrecontaining biotite with or without clinopyroxene could beclassified as a kersantite. Sedimentary rockclassifications generally include grain size, type of cementor matrix, mineral composition in order of increasingamounts greater than 15 percent, and the rock type, suchas medium-grained, calcite-cemented, feldspathic-quartzose sandstone, and coarse- to fine-grained, lithic-feldspathic-quartzose gray-wacke with an argillaceous-ferruginous-calcareous matrix. Metamorphic rockclassifications include specific rock types based uponcrystal size, diagnostic accessory minerals, mineralogicalcomposition in increasing amounts greater than15 percent, and structure. Two examples of metamorphicrock descriptions are medium-grained, hornblende-biotiteschist, or fine- to medium-grained, garnetiferous,muscovite-chlorite-feldspar-quartz gneiss. The aboveclassification can be abbreviated by the deletion ofmineral names from the left to right as desired. Themineral type immediately preceding the rock name is themost diagnostic.
The term "quartzite” is restricted to a metamorphic rockonly. The sedimentary sandstone equivalent is termed a"quartz cemented quartzose sandstone."
Samples submitted to a petrographic laboratory should berepresentative of the in-place rock unit. For example, ifa granitic gneiss is sampled but only the granite portionsubmitted, the rock will be petrographically classified as
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a granite since the gneissic portion cannot be observed orsubstantiated by the thin section and hand specimen.Petrographic classifications can be related to theengineering properties of rock units and are important.
Geologic rock unit names should be simple, and generalrock names should be based on either field identification,existing literature, or detailed petrographic examination,as well as engineering properties. Overclassification isdistracting and unnecessary. For example, use "horn-blende schist" or "amphibolite" instead of "sericite-chlorite-calcite-hornblende schist." The term "granite"may be used as the rock name and conveys more to thedesigner than the petrographically correct term"nepheline-syenite porphyry." Detailed mineralogicaldescriptions may be provided in reports when describingthe various rock units and may be required to correlatebetween observations, but mineralogical classificationsare not desirable as a rock unit name unless the mineralconstituents or fabric are significant to engineeringproperties.
The classification for igneous, sedimentary, metamorphic,and pyroclastic rocks is shown on figures 4-1, 4-2, 4-3, and4-4, respectively. These figures are condensed andmodified slightly from Travis' classifications, but themore detailed original classifications of Travis areacceptable. Figure 4-5 or appropriate AmericanGeological Institute (AGI) data sheets are suggested foruse when estimating composition percentages inclassification.
Description of Rock
Adequate descriptors, a uniform format, and standardterminology must be used for all geologic investigationsto properly describe rock foundation conditions. These
FIE
LD
MA
NU
AL
60
Figure 4-1.—Field classification of igneous rocks (modified after R.B. Travis [1955]).
RO
CK
S
61 Figure 4-2.—Field classification of sedimentary rocks (modified after R.B. Travis [1955]).
FIE
LD
MA
NU
AL
62
Figure 4-3.—Field classification of metamorphic rocks (modified after R.B. Travis [1955]).
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Figure 4-4.—Field classification of pyroclastic rocks.Blocks are angular to subangular clasts > 64 millimeters(mm); bombs are rounded to subrounded clasts > 64 mm.Determine percent of each size present (ash, lapilli,blocks, and bombs) and list in decreasing order after rockname. Preceed rock name with the term "welded" forpyroclastic rocks which retained enough heat to fuseafter deposition. Rock names for such deposits areusually selected from the lower right portion of theclassification diagram above. (Modified from Fisher, 1966[2] and Williams and McBirney, 1979 [3]).
paragraphs provide descriptors for those physical charac-teristics of rock that are used in logs of exploration, innarratives of reports, and on preconstruction geologicmaps and cross sections, as well as construction or "as-built" drawings. The alphanumeric descriptors providedmay be used in data-field entries of computer generated
FIE
LD
MA
NU
AL
64
Figure 4-5.—Charts for estimating percentage of composition of rocks and sediments.[4]
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logs. Chapter 5 establishes descriptors for the physicalcharacteristics of discontinuities in rock required forengineering geologic studies.
All descriptors should be defined and included in alegend when submitting data for design and/or records ofconstruction. An example of a legend and explanation isfigure 4-6, Reclamation standard drawing 40-D-6493,may be used for geologic reports and specifications wherethe standard descriptors and terminology established forrock are used during data collection.
Format for Descriptions of Rock
Engineering geology rock descriptions should include gen-eralized lithologic and physical characteristics usingqualitative and quantitative descriptors. A generalformat for describing rock in exploration logs and legendson general note drawings is:
• Rock unit (member or formation) name• Lithology with lithologic descriptors
composition (mineralogy) grain/particle size
texture color
• Bedding/foliation/flow texture• Weathering• Hardness/strength• Contacts• Discontinuities (includes fracture indexes)• Permeability data (as available from testing)• Moisture conditions
Example descriptions are presented in a later section.
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Rock Unit Names and Identification
Rock unit names not only are required for identificationpurposes but may also provide indicators of depositionalenvironment and geologic history, geotechnical char-acteristics, and correlations with other areas. A simpledescriptive name and map symbol should be assigned toprovide other users with possible engineeringcharacteristics of the rock type. The rock unit names maybe stratigraphic, lithologic, genetic, or a combination ofthese, such as Navajo Sandstone (Jn), Tertiary shale(Tsh), Jurassic chlorite schist (Jcs), Precambrian granite(Pcgr), or metasediments (ms). Bedrock units of similarphysical properties should be delineated and identified asto their engineering significance as early as possibleduring each geologic study. Planning study maps andother large-scale drawings may require geologicformations or groups of engineering geologic units withdescriptions of their engineering significance inaccompanying discussions.
Units should be differentiated by engineering propertiesand not necessarily formal stratigraphic units wheredifferences are significant. Although stratigraphicnames are not required, units should be correlated tostratigraphic names in the data report or by anillustration, such as a stratigraphic column.Stratigraphic names and ages (formation, member) maybe used as the rock unit name.
For engineering studies, each particular stratigraphicunit may require further subdivisions to identifyengineering parameters. Examples of importantengineering properties are:
• Susceptibility to weathering or presence ofalteration
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Figure 4-6.—Descriptor legend and explanation example.
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• Dominant discontinuity characteristics
• Hardness and/or strength
• Deformability
• Deletereous minerals or beds (such as swellingsusceptibility, sulfates, or clays)
For example, a Tertiary shale unit, Tsh, may bedifferentiated as Tsh1 or Tsh2 if unit 2 contains bentoniteinterbeds and unit 1 does not, and Tshc could be used asa unit name for the bentonite beds. A chlorite schist unit,Cs, may be differentiated as CsA or CsB where unit Acontains higher percentages of chlorite or talc and issignificantly softer (different deformation properties) thanunit B. A metasediment unit, ms, may be furtherdifferentiated on more detailed maps and logs as mssh
(shale) or msls (limestone). All differentiated units shouldbe assigned distinctive map symbols and should bedescribed on the General Geologic Legend, Explanation,and Notes drawings.
Descriptors and Descriptive Criteria for PhysicalCharacteristics of Rock
Lithologic Descriptors (Composition, Grain Size,and Texture).—Provide a brief lithologic description ofthe rock unit. This includes a general description ofmineralogy, induration, cementation, crystal and grainsizes and shapes, textural adjectives, and color.Lithologic descriptors are especially important for thedescription of engineering geology subunits when rockunit names are not specific. Examples of rock unit namesthat are not specific are metasediments, Tertiaryintrusives, or Quaternary volcanics.
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1. Composition.—Use standard adjectives such assandy, silty, calcareous, etc. Detailed mineral composition generally is not necessary or desirable unlessuseful in correlating units or indicating pertinentengineering physical properties. Note uniquefeatures such as fossils, large crystals, inclusions,concretions, and nodules which may be used asmarkers for correlations and interpretations.
2. Crystal or particle sizes and shapes.—Describe the typical crystal or grain shapes andprovide a description of sizes present in the rock unitbased on the following standards:
• Igneous and metamorphic rocks.—Table 4-1 isrecommended for descriptions of crystal sizes inigneous and metamorphic rocks. Crystal sizesgiven in millimeters (mm) are preferred ratherthan fractional inch (in) equivalents.
Table 4-1.—Igneous and metamorphic rock grain size descriptors
DescriptorAverage crystal
diameter
Very coarse-grained or pegmatiticCoarse-grainedMedium-grainedFine-grainedAphanitic (cannot be seen with the unaided eye
> 10 mm (3/8 in)5-10 mm (3/16 - 3/8 in)1-5 mm (1/32 - 3/16 in)0.1-1 mm (0.04 - 1/32 in)<0.1 mm (<0.04 in)
• S e d i m e n t a r y a n d p y r o c l a s t i crocks.—Terminology for particle sizes and theirlithified products which form sedimentary andpyroclastic rocks is provided in table 4-2. The size
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Table 4-2.—Sedimentary and pyroclastic rock particle-size descriptors (AGI Glossary)
USGS(soils only)
Particle size
Sizein
mm (inches)
Sedimentary (epiclastic)Rounded, subrounded,
subangular Volcanic (pyroclastic)
Particle orfragment
Lithifiedproduct
Frag-ment
Lithifiedproduct*
Boulder
Cobble
Coarse gravel
Fine gravel
Coarse sand
Medium sand
Fine sand
Fines Non- plastic Silt
Plastic Clay
300 (12)
256 (10)
75 (3) 64 (2.5)
32 (1.3)
20 (0.8)
4.75 (0.19) 4 (0.16)
2 (0.08)
1 (0.04) 0.5 (0.02)
0.42 0.25 0.125 0.074 0.0625
0.00391
Boulder
Cobble
Pebble
Granule
Very coarse sand Coarse sand
Medium sand Fine sand Very fine sand
Silt
Clay
Boulder conglomerate
Cobble conglomerate
Pebble conglomerate
Granule conglomerate
Sandstone (Very coarse, coarse, medium fine, or very fine)
Siltstone Shale
Claystone Shale
Block+
Bomb
Lapilli
Coarse ash
Fine ash
Volcanic breccia+
Agglo- merate
Lapilli tuff
Coarse tuff
Fine tuff
+ Broken from previous igneous rock block shaped (angular to subangular). Solidified from plastic material while in flight, rounded clasts. * Refer to figure 4-4.
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limits do not correspond to the Unified SoilClassification System for soil particle size but areused for the field description and petrographicclassification of rocks. These limits are theaccepted sizes in geologic literature and are usedby petrographic laboratories.
3. Textural adjectives.—Texture describes the ar-rangements of minerals, grains, or voids. Thesemicrostructural features can affect the engineeringproperties of the rock mass. Use simple, standard,textural adjectives or phrases such as porphyritic,vesicular, scoriaceous, pegmatitic, granular, welldeveloped grains, dense, fissile, slaty, or amorphous.Use of terms such as holohyaline, hypidiomorphicgranular, and crystaloblastic is inappropriate.
Textural terms which identify solutioning, leaching,or voids in bedrock are useful for describing primarytexture, weathering, alteration, permeability, anddensity.
The terminology which follows defines sizes of voids, orholes in bedrock. However, when describing pits, vugs,cavities, or vesicles, a complete description which includesthe typical diameter, or the "mostly" range, and the max-imum size observed is required. For example:
". . . randomly oriented, elliptically shaped vugs rangemostly from 0.03 to 0.06 foot (ft) in diameter,maximum size 0.2 foot; decreases in size away fromquartz-calcite vein; about 15 percent contain calcitecrystals. . .”
or". . . cavity, 3.3 ft wide by 16.4 ft long by 2.3 ft high,striking N 45EW, dipping 85ESW was. . ..”
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• Pit (pitted).—Pinhole to 0.03 ft [d in] (<1 to10 mm) openings.
• Vug (vuggy).—Small opening (usually lined withcrystals) ranging in diameter from 0.03 ft [d in] to0.33 ft [4 in] (10 to 100 mm).
• Cavity.—An opening larger than 0.33 ft [4 in](100 mm), size descriptions are required, and adjec-tives such as small, or large, may be used, if defined.
• Honeycombed.—Individual pits or vugs are sonumerous that they are separated only by thin walls;this term is used to describe a cell-like form.
• Vesicle (vesicular).—Small openings in volcanicrocks of variable shape formed by entrapped gasbubbles during solidification.
4. Color.—As a minimum, provide the color of wetaltered and unaltered or fresh rock. Reporting colorfor both wet and dry material is recommended sincethe colors may differ significantly and causeconfusion. The Munsell Color System, as used in theGeologic Society of America Rock Color Chart [5], isused to provide standard color names and assist incorrelation. The chart also provides uniform andidentifiable colors to others. Color designators areoptional unless necessary for clarity, e.g., light brown(5YR 5/6). Terms such as banded, streaked, mottled,speckled, and stained may be used to further describecolor. Also describe colors of bands, etc.
Bedding, Foliation, and Flow Texture.—Thesefeatures give the rock anisotropic properties or representpotential failure surfaces. Continuity and thickness ofthese features influence rock mass properties and cannot
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always be tested in the laboratory. Descriptors intable 4-3 are used to identify these thicknesses.
Table 4-3.—Bedding, foliation, or flow texture descriptors
Descriptors Thickness/spacing
Massive Greater than 10 ft (3 meters [m])
Very thickly, bedded, foliated, or banded
3 to 10 ft (1 to 3 m)
Thickly 1 to 3 ft (300 mm to 1 m)
Moderately 0.3 to 1 ft (100 to 300 mm)
Thinly 0.1 to 0.3 ft (30 to 100 mm)
Very thinly 0.03 [3/8 in] to 0.1 ft (10 to 30 mm)
Laminated (intensely foliated or banded)
Less than 0.03 ft [3/8 in] (<10 mm)
Weathering and Alteration.—
1. Weathering.—Weathering, the process ofchemical or mechanical degradation of rock, cansignificantly affect the engineering properties of therock and rock mass. For engineering geologydescriptions, the term "weathering" includes bothchemical disintegration (decomposition) andmechanical disaggregation as agents of alteration.
Weathering effects generally decrease with depth, al-though zones of differential weathering can occur andmay modify a simple layered sequence of weathering.
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Examples are: (1) differential weathering within asingle rock unit, apparently due to relatively higherpermeability along fractures; (2) differentialweathering due to compositional or texturaldifferences; (3) differential weathering of contactzones associated with thermal effects such asinterflow zones within volcanics; (4) directionalweathering along permeable joints, faults, shears, orcontacts which act as conduits along whichweathering agents penetrate more deeply into therock mass; and (5) topographic effects.
Weathering does not correlate directly with specificgeotechnical properties used for many rock massclassifications. However, weathering is importantbecause it may be the primary criterion fordetermining depth of excavation, cut slope design,method and ease of excavation, and use of excavatedmaterials. Porosity, absorption, compressibility,shear and compressive strengths, density, andresistance to erosion are the major engineeringparameters influenced by weathering. Weatheringgenerally is indicated by changes in the color andtexture of the body of the rock, color, and condition offracture fillings and surfaces, grain boundaryconditions, and physical properties such as hardness.
Weathering is reported using descriptors presentedin table 4-4, which divides weathering into categoriesthat reflect definable physical changes due tochemical and mechanical processes. This tablesummarizes general descriptions which are intendedto cover ranges in bedrock conditions. Weatheringtables are generally applicable to all rock types;however, they are easier to apply to crystalline rocksand rocks that contain ferromagnesian minerals.Weathering in many sedimentary rocks will notalways conform to the criteria established in
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table 4-4, and weathering categories may have to bemodified for particular site conditions. However, thebasic horizontal categories and descriptors presentedcan be used. Site-specific conditions, such as fractureopenness, filling, and degree and depth ofpenetration of oxidation from fracture surfaces,should be identified and described.
2. Alteration.—Chemical alteration effects aredistinct from chemical and mechanical degradation(weathering), such as hydrothermal alteration, maynot fit into the horizontal suite of weatheringcategories portrayed in table 4-4. Oxides may or maynot be present. Alteration is site-specific, may beeither deleterious or beneficial, and may affect somerock units and not others at a particular site. Forthose situations where the alteration does not relatewell to the weathering categories, adjusting thedescription within the framework of table 4-4 may benecessary. Many of the general characteristics maynot change, but the degree of discoloration andoxidation in the body of the rock and on fracturesurfaces could be very different. Appropriatedescriptors, such as moderately altered or intenselyaltered, may be assigned for each alteration category.Alteration products, depths of alteration, andminerals should be described.
3. Slaking.—Slaking is another type ofdisintegration which affects engineering properties ofrock. Terminology and descriptive criteria to identifythis deleterious property are difficult to standardizebecause some materials air slake, many water slake,and some only slake after one or more wet-dry cycles.The Durability Index (DI) is a simplified method fordescribing slaking. Criteria for the index are based
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Table 4-4.—Weathering descriptors
Descriptors
Diagnostic features
General characteristics(strength, excavation, etc.)§
Chemical weathering—Discoloration and/or oxidation
Mechanical weathering- Grain boundaryconditions(disaggregation)primarily for graniticsand some coarse-grained sediments
Texture and solutioning
Alpha-numeric
descriptor Descriptive term Body of rockFracture surfaces† Texture Solutioning
W1 Fresh. No discoloration, not oxidized. No discoloration oroxidation.
No separation, intact(tight).
No change. No solutioning. Hammer rings when crystalline rocksare struck. Almost always rock exca-vation except for naturally weak orweakly cemented rocks such assiltstones or shales.
W2 Slightly weathered tofresh.*
W3 Sllightly weathered. Discoloration or oxidation is limitedto surface of, or short distancefrom, fractures; some feldsparcrystals are dull.
Minor to completediscoloration oroxidation of mostsurfaces.
No visible separation,intact (tight).
Preserved. Minor leaching ofsome solubleminerals may benoted.
Hammer rings when crystalline rocksare struck. Body of rock notweakened. With few exceptions, suchas siltstones or shales, classified asrock excavation.
W4 Moderately to slightlyweathered.*
W5 Moderatelyweathered.
Discoloration or oxidation extendsfrom fractures, usually throughout;Fe-Mg minerals are “rusty,”feldspar crystals are “cloudy.”
All fracture surfacesare discolored oroxidized.
Partial separation ofboundaries visible.
Generallypreserved.
Soluble mineralsmay be mostlyleached.
Hammer does not ring when rock isstruck. Body of rock is slightly weak-ened. Depending on fracturing,usually is rock excavation except innaturally weak rocks such assiltstone or shales.
W6 Intensely tomoderatelyweathered.*
W7 Intensely weathered. Discoloration or oxidationthroughout; all feldspars and Fe-Mg minerals are altered to clay tosome extent; or chemical alterationproduces in situ disaggregation, seegrain boundary conditions.
All fracture surfacesare discolored oroxidized, surfacesfriable.
Partial separation, rockis friable; in semiaridconditions granitics aredisaggregated.
Texture al-tered bychemicaldisintegration(hydration,argillation).
Leaching of solubleminerals may becomplete.
Dull sound when struck withhammer; usually can be broken withmoderate to heavy manual pressureor by light hammer blow withoutreference to planes of weakness suchas incipient or hairline fractures, orveinlets. Rock is significantlyweakened. Usually commonexcavation.
W8 Very intenselyweathered.
W9 Decomposed. Discolored or oxidized throughout,but resistant minerals such asquartz may be unaltered; allfeldspars and Fe-Mg minerals arecompletely altered to clay.
Complete separation ofgrain boundaries(disaggregated).
Resembles a soil, partial or completeremnant rock structure may bepreserved; leaching of solubleminerals usually complete.
Can be granulated by hand. Alwayscommon excavation. Resistantminerals such as quartz may bepresent as “stringers” or “dikes.”
Note: This chart and its horizontal categories are more readily applied to rocks with feldspars and mafic minerals. Weathering in various sedimentary rocks, particularly limestones and poorly induratedsediments, will not always fit the categories established. This chart and weathering categories may have to be modified for particular site conditions or alteration such as hydrothermal effects; however, thebasic framework and similar descriptors are to be used. * Combination descriptors are permissible where equal distribution of both weathering characteristics are present over significant intervals or where characteristics present are “in between” thediagnostic feature. However, dual descriptors should not be used where significant, identifiable zones can be delineated. When given as a range, only two adjacent terms may be combined (i.e., decomposedto lightly weathered or moderately weathered to fresh) are not acceptable. † Does not include directional weathering along shears or faults and their associated features. For example, a shear zone that carried weathering to great depths into a fresh rock mass would not requirethe rock mass to be classified as weathered. § These are generalizations and should not be used as diagnostic features for weathering or excavation classification. These characteristics vary to a large extent based on naturally weak materials orcementation and type of excavation.
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on time exposed and effects noted in the field(see table 4-5). These simplified criteria do notspecify whether the specimen or exposure iswetted, dried, or subjected to cyclic wetting anddrying, and/or freeze-thaw. When reportingslaking or durability, a complete descriptionincludes the test exposure conditions. Forexample, the material could be classified ashaving "characteristics of DI 3 upon drying."Slaking is not the same as the effects of beddingseparation or disaggregation produced by stressrelief.
Table 4-5.—Durability index descriptors
Alpha-numeric
descriptor Criteria
DI0 Rock specimen or exposure remains intact withno deleterious cracking after exposure longerthan 1 year.
DI1 Rock specimen or exposure develops hairlinecracking on surfaces within 1 month, but nodisaggregation within 1 year of exposure.
DI2 Rock specimen or exposure develops hairlinecracking on surfaces within 1 week and/ordisaggregation within 1 month of exposure.
DI3 Specimen or exposure may develop hairlinecracks in 1 day and displays pronouncedseparation of bedding and/or disaggregationwithin 1 week of exposure.
DI4 Specimen or exposure displays pronouncedcracking and disaggregation within 1 day(24 hours) of exposure. Generally ravels anddegrades to small fragments.
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A field test suitable for evaluating the degreeand rate of slaking for materials, primarilyclayey materials and altered volcanics, isdescribed below. The slaking test evaluates thedisaggregation of an intact specimen in waterand reflects the fabric of the material, internalstresses, and character of the interparticlebonds.
To evaluate slaking behavior, immerse twointact specimens (pieces of core or rockfragments consisting of a few cubic inches orcentimeters) in water. One piece should be atnatural water content (wrapped jar sample) andone piece from an air-dried sample. Test resultsshould be photographed with labels to identifyspecimens and exposure times.
Results of the evaluation should be reported foreach specimen. Describe the behavior of thespecimens as follows:
a. Volume changes.—The volume of the materialreduced to individual particles should be estimatedand compared to the initial volume of material.The degree of disaggregation is described using thefollowing descriptive criteria:
None No discernable disaggregationSlight Less than 5 percent of the volume
disaggregatedModerate Between 5 and 25 percent of the
volume disaggregatedIntense More than 25 percent but less
than the total volume disaggregated
Complete No intact piece of the material remains
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b. Rate of slaking.—The following descriptors areused to identify the time to slake:
Slow slaking Action continues for several hours
Moderate Action completed within 1 hour slaking
Rapid Action completed within slaking 2 minutesSudden Complete reaction, action com- slaking pleted instantaneously
[Generally, slaking applies to rock; disaggregation appliesto soils.]
4. Character of material.—The character of theremaining pieces of material after the test iscompleted is described as follows:
No change Material remains intactPlates remain Remaining material present as
platy fragments of generally uniform thickness
Flakes remain Remaining material present as flaky or wedge-shaped fragments
Blocks remain Blocky fragments remainGrains remain Remaining material chiefly present
as sand-size grains
No fragments Remaining material entirely disag- gregated to clay-size particles
Hardness—Strength.—Hardness can be related tointact rock strength as a qualitative indication of densityand/or resistance to breaking or crushing. Strength is anecessary engineering parameter for design that
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frequently is not assessed, but plays a role in engineeringdesign and construction, such as tunnel supportrequirements, bit wear for drilling or tunnel boringmachine (TBM) operations, allowable bearing pressures,excavation methods, and support.
The hardness and strength of intact rock is a function ofthe individual rock type but may be modified byweathering or alteration. Hardness and strength aredescribed for each geologic unit when they are functionsof the rock type and also for zones of alteration orweathering when there are various degrees of hardnessand/or strength due to different degrees of weathering orchemical alteration. When evaluating strengths, it isimportant to note whether the core or rock fragmentsbreak around, along, or through grains; or along or acrossincipient fractures, bedding, or foliation.
Hardness and especially strength are difficultcharacteristics to assess with field tests. Two field testscan be used; one is a measure of the ability to scratch thesurface of a specimen with a knife, and the other is theresistance to fracturing by a hammer blow. Results fromboth tests should be reported. The diameter and lengthof core or the fragment size will influence the estimationof strength and should be kept in mind when correlatingstrengths. A 5- to 8-inch (130- to 200-mm) length ofN-size core or rock fragment, if available, should be usedfor hardness determinations to preclude erroneouslyreporting point, rather than average hardness, and toevaluate the tendency to break along incipient fracturesand textural or structural features when struck with arock pick. Standards (heavy, moderate, and lighthammer blow) should be calibrated with other geologistsmapping or logging core for a particular project.Descriptors used for rock hardness/strength are shown ontable 4-6.
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Table 4-6.—Rock hardness/strength descriptors
Alpha-numeric
descriptor Descriptor Criteria
H1 Extremely hard
Core, fragment, or exposure cannot bescratched with knife or sharp pick; can onlybe chipped with repeated heavy hammerblows.
H2 Very hard Cannot be scratched with knife or sharppick. Core or fragment breaks withrepeated heavy hammer blows.
H3 Hard Can be scratched with knife or sharp pickwith difficulty (heavy pressure). Heavyhammer blow required to break specimen.
H4 Moderately hard
Can be scratched with knife or sharp pickwith light or moderate pressure. Core orfragment breaks with moderate hammerblow
H5 Moderately soft
Can be grooved 1/16 inch (2 mm) deep byknife or sharp pick with moderate or heavypressure. Core or fragment breaks with lighthammer blow or heavy manual pressure.
H6 Soft Can be grooved or gouged easily by knife orsharp pick with light pressure, can bescratched with fingernail. Breaks with lightto moderate manual pressure.
H7 Very soft Can be readily indented, grooved or gougedwith fingernail, or carved with a knife.Breaks with light manual pressure.
Any bedrock unit softer than H7, very soft, is to be described usingUSBR 5000 consistency descriptors.
Note: Although "sharp pick" is included in these definitions, descrip-tions of ability to be scratched, grooved, or gouged by a knife is thepreferred criteria
A few empirical and quantitative field techniques whichare quick, easy, and inexpensive are available to providestrength estimates. Quantitative strength estimates can
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be obtained from the point load test. A lightweight andportable testing device is used to break a piece of core(with a minimum length at least 1.5 times the diameter)between two loading points. If a new fracture does notrun from one loading point to the other upon completionof the test, or if the points sink into the rock surfacecausing excessive deformation or crushing, the testshould not be recorded. Raw data are given with thereduced data (equations to empirically convert load datato compressive strengths are usually supplied with theequipment). The Schmidt (L) hammer may also be usedfor estimating rock strengths; refer to Field Index Testsin chapter 5. Each of these tests can be used to calibratethe manual index (empirical) properties described intable 4-6, and a range of compressive strengths can beassigned. Depending on the scope of the study andstructure being considered, laboratory testing may berequired and used to confirm the field test data.
Discontinuities.—Describe all discontinuities such asjoints, fractures, shear/faults, and shear/fault zones, andsignificant contacts. These descriptions should include allobservable characteristics such as orientation, spacing,continuity, openness, surface conditions, and fillings.Appropriate terminology, descriptive criteria anddescriptors, and examples pertaining to discontinuitiesare presented in chapter 5.
Contacts.—Contacts between various rock units or rock/soil units must be described. In addition to providing ageologic classification, describe the engineeringcharacteristics such as the planarity or irregularity andother descriptors used for discontinuities.
Descriptors applicable to the geologic classification of con-tacts are:
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• Conformable• Unconformable• Welded—contact between two lithologic units, one
of which is igneous, that has not been disruptedtectonically
• Concordant (intrusive rocks)• Discordant (intrusive rocks)
Descriptors pertinent to engineering classification of con-tacts are:
• Jointed—contact not welded, cemented, orhealed—a fracture
• Intact• Healed (by secondary process)• Sharp• Gradational• Sheared• Altered (baked or mineralized)• Solutioned
If jointed or sheared, additional discontinuity descriptorssuch as thickness of fillings, openness, moisture, androughness, should be provided also (see discontinuitydescriptors in chapter 5).
Permeability Data.—Permeability (hydraulicconductivity) is an important physical characteristic thatmust be described. Suggested methods for testing,terminology, and descriptors are available in the EarthManual and Ground Water Manual. Numerical valuesfor hydraulic conductivity (K) can be determined usingany of several methods. These values may be shown ondrill hole logs. For narrative discussions or summarydescriptions, the numerical value and descriptors may beused. Descriptors to be used—such as low,
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moderate—are those shown on figure 4-7. Whetherpermeability is primary (through intact rock) orsecondary (through fractures) should be indicated.
Example Descriptions
The examples which follow are in representative formatsfor describing bedrock in the physical conditions columnof drill hole logs and on a legend, explanation, and notesdrawing.
Core Log Narrative
Several examples of descriptions for core logs arepresented. These examples illustrate format and the useof the lithologic descriptors but do not include adescription of discontinuities.
Log with Alphanumeric Descriptors and EnglishUnits.—
. . . 12.6 to 103.6: Amphibolite Schist (JKam). Fine-grained (0.5 to 1 mm); subschistose to massive; greenish-black (5G 2/1) with numerous blebs andstringers of white calcite to 0.02 ft thick withsolution pits and vugs to 0.03 ft, mostly 0.01 ft,aligned subparallel to foliation; very thinly foliated,foliation dips 65E to 85E, steepening with depth.Moderately to slightly weathered (W4), iron oxidestaining on all discontinuities. Hard (H3), can bescratched with knife with heavy pressure, corebreaks parallel to foliation with heavy hammerblow. Slightly fractured (FD3),. . ..
RO
CK
S
87 Figure 4-7.—Permeability conversion chart.
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Log with Alphanumeric Descriptors Using MetricUnits.—
103.60 to 183.22: Sandstone (TUsa). Ferruginousquartzose sandstone. Medium-grained (0.25 to0.5 mm), well sorted, subrounded to rounded quartzgrains are well cemented by silica; hematite occursas minor cement agent and as thin coating ongrains. Moderate reddish-brown (10R 6/6).Moderately bedded, beds 250 to 310 mm thick,bedding dips 15E to 29E, averages 18E. Slightlyweathered. Hard, cannot be scratched with knife,core breaks with heavy hammer blow across beddingand through grains. Moderately fractured. Corerecovered. . ..
172.41-176.30: Claystone (TUc2). Calcareousmontmorillonitic clay with 20 percent subangular,fine sand-size quartz fragments. Strong reactionwith hydrochloric acid (HCl), grayish pink (5R 8/2).Moderately to rapidly slaking when dropped inwater. Very thinly bedded to laminated with bedthickness from 8 to 20 mm. Very intenselyweathered. Very soft, can be gouged with fingernail,friable, core breaks with manual pressure, smallerfragments can be crushed with fingers. . . Uppercontact is parallel to bedding, conformable,gradational, and intact; lower contact isunconformable, sharp and jointed but tight; dips 35E. . ..
Legend
The example which follows could be typical of a rock unitdescription on a general legend, explanation, and notedrawing. The object is to describe as many physicalproperties as possible which apply to the entire rock unitat the site. If individual subunits can be differentiated,they could be assigned corresponding symbols and
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described below the undifferentiated description. Thosecharacteristics in the subunits which are similar or areincluded in the undifferentiated unit do not need to berepeated for each subunit.
Amphibolite Schist - Undifferentiated.—Mineralogyvariable but generally consists of greater than 30 percentamphibole. Contains varying percentages of feldspar,quartz, and epidote in numerous, thin, white and lightgreen (5G 7/4), discontinuous stringers and blebs.Texture ranges from fine grained and schistose tomedium grained and subschistose. Overall, color rangesfrom greenish black (5G 2/1) to olive black (5Y 2/1).Thinly foliated; foliation dips steeply 75E to 85E NE.Weathering is variable but generally moderately wea-thered to depths of 75 ft, slightly weathered to 120 ft, andfresh below. Where oxidized, moderate reddish-brown(10R 4/6), frequently with dendritic patterns of oxides ondiscontinuities. Hard, fresh rock can be scratched slightlywith heavy knife pressure; fresh N-size core breaks alongfoliation with moderate to heavy hammer blow. Foliationjoints are variably spaced and discontinuous, spaced moreclosely where weathered. Joint sets are prominent butdiscontinuous. (Joint sets are identified in thespecifications paragraphs). Commonly altered 0.1 to 6 ftalong contacts of dikes and larger shears with epidote andquartz ("altered amphibolite" on logs of exploration).When altered, harder than amphibolite. Based on drillhole permeability testing, hydraulic conductivity is verylow to low, with values ranging from 0.09 to 130 feet peryear (ft/yr) averages 1.5 ft/yr in slightly weathered andfresh rock.
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BIBLIOGRAPHY
[1] Travis, Russell B., "Classification of Rocks," v. 50,No. 1, Quarterly of the Colorado School of Mines,Golden, CO, January 1955.
[2] Fisher, R.V., "Rocks Composed of Volcanic Frag-ments: Earth Science Review, v. I, pp. 287-298, 1966.
[3] Williams, H., and McBirney, A., Volcanology,published by Freeman, Cooper and Company,San Francisco, CA. 391 pp., 1979.
[4] Compton, Robert R., Geology in the Field, publishedby John Wiley & Sons, Inc., New York, NY, 1985.
[5] Geological Society of America Rock Color Chart,8th printing, 1995.
Chapter 5
TERMINOLOGY AND DESCRIPTIONSFOR DISCONTINUITIES
General
Structural breaks or discontinuities generally control themechanical behavior of rock masses. In most rock massesthe discontinuities form planes of weakness or surfaces ofseparation, including foliation and bedding joints, joints,fractures, and zones of crushing or shearing. Thesediscontinuities usually control the strength, deformation,and permeability of rock masses. Most engineeringproblems relate to discontinuities rather than to rock typeor intact rock strength. Discontinuities must be carefullyand adequately described. This chapter describesterminology, indexes, qualitative and quantitativedescriptive criteria, and format for describingdiscontinuities. Many of the criteria contained in thischapter are similar to criteria used in other establishedsources which are accepted as international standards(for example, International Journal of Rock Mechanics,1978 [1]).
Discontinuity Terminology
The use of quantitative and qualitative descriptorsrequires that what is being described be clearly identified.Nomenclature associated with structural breaks ingeologic materials is frequently misunderstood. Forexample, bedding, bedding planes, bedding planepartings, bedding separations, and bedding joints mayhave been used to identify similar or distinctly differentgeological features. The terminology for discontinuitieswhich is presented in this chapter should be useduniformly for all geology programs. Additional definitionsfor various types of discontinuities are presented in theGlossary of Geology [2]; these may be used to furtherdescribe structural breaks. The following basic defi-nitions should not be modified unless clearly justified,and defined.
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Discontinuity.—A collective term used for all structuralbreaks in geologic materials which usually have zero tolow tensile strength. Discontinuities also may be healed.Discontinuities comprise fractures (including joints),planes of weakness, shears/faults, and shear/fault zones.Depositional or erosional contacts between variousgeologic units may be considered discontinuities. Fordiscussion of contacts, refer to chapter 4.
Fracture.—A term used to describe any natural break ingeologic material, excluding shears and shear zones.Examples of the most common fractures are defined asfollows:
1. Joint.—A fracture which is relatively planaralong which there has been little or no obviousdisplacement parallel to the plane. In many cases, aslight amount of separation normal to the jointsurface has occurred. A series of joints with similarorientation form a joint set. Joints may be open,healed, or filled; and surfaces may be striated due tominor movement. Fractures which are parallel tobedding are termed bedding joints or bedding planejoints. Those fractures parallel to metamorphicfoliation are called foliation joints.
2. Bedding plane separation.—A separation alongbedding planes after exposure due to stress relief orslaking.
3. Random fracture.—A fracture which does notbelong to a joint set, often with rough, highlyirregular, and nonplanar surfaces along which therehas been no obvious displacement.
4. Shear.—A structural break where differentialmovement has occurred along a surface or zone of
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failure; characterized by polished surfaces, striations,slickensides, gouge, breccia, mylonite, or anycombination of these. Often direction of movement,amount of displacement, and continuity may not beknown because of limited exposures or observations.
5. Fault.—A shear with significant continuity whichcan be correlated between observation locations;foundation areas, or regions; or is a segment of afault or fault zone reported in the literature. Thedesignation of a fault or fault zone is a site-specificdetermination.
6. Shear/fault zone.—A band of parallel or subpar-allel fault or shear planes. The zone may consist ofgouge, breccia, or many fault or shear planes withfractured and crushed rock between the shears orfaults, or any combination. In the literature, manyfault zones are simply referred to as faults.
7. Shear/fault gouge.—Pulverized (silty, clayey, orclay-size) material derived from crushing or grindingof rock by shearing, or the subsequent decompositionor alteration. Gouge may be soft, uncemented,indurated (hard), cemented, or mineralized.
8. Shear/fault breccia.—Cemented or uncemented,predominantly angular (may be platy, rounded, orcontorted) and commonly slickensided rockfragments resulting from the crushing or shatteringof geologic materials during shear displacement.Breccia may range from sand-size to large boulder-size fragments, usually within a matrix of faultgouge. Breccia may consist solely of mineral grains.
9. Shear/fault-disturbed zone.—An associatedzone of fractures and/or folds adjacent to a shear or
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shear zone where the country rock has beensubjected to only minor cataclastic action and may bemineralized. If adjacent to a fault or fault zone, theterm is fault-disturbed zone. Occurrence,orientation, and areal extent of these zones dependupon depth of burial (pressure and temperature)during shearing, brittleness of materials, and the in-place stresses.
Terminology for joint (JT), foliation joint (FJ), beddingjoint (BJ), incipient joint (IJ) or incipient fracture (IF),random fracture (RF), mechanical break (MB), and frac-ture zone (FZ) is given on figure 5-9 (drawing No. 40-D-6499 following later in this chapter). Suggestedabbreviations are in parentheses.
Indexes for Describing Fracturing
Fracture Density
Fracture density is based on the spacing between allnatural fractures in an exposure or core recovery lengthsfrom drill holes, excluding mechanical breaks, shears, andshear zones; however, shear-disturbed zones (fracturingoutside the shear) are included. In this context, fractureis a general term and includes all natural breaks such asjoints, bedding joints, foliation joints, and randomfractures. Fracture density should always be described inphysical measurements, but summary descriptive termsrelating to these measurements are a convenient aid incommunicating characteristics of the rock mass.Standard descriptors apply to all rock exposures, such astunnel walls, dozer trenches, outcrops, or foundation cutslopes and inverts, as well as boreholes. Fracture
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descriptors presented in table 5-1 and figure 5-9 arebased on drill hole cores where lengths are measuredalong the core axis.
When describing fracture density, a percentage of thetypes of fractures should be provided. A completedescription for fracture density might read: SlightlyFractured (FD3), recovered core in 0.8- to 4.7-feet (0.2- to1.4-meter [m]) lengths, mostly 1.7 feet (520 millimeters[mm]), 25 percent bedding joints/75 percent joints.
Fracture Frequency
Fracture frequency is the number of fractures occurringwithin a unit length. The number of natural fractures isdivided by the length and is reported as fractures per footor fractures per meter.
Rock Quality Designation
Rock Quality Designation (RQD) [2] is a fracture indexused in many rock classification systems. To determinethe RQD value, add the total length of solid core that is4 inches (100 mm) or more long regardless of corediameter. If the core is broken by handling or the drillingprocess (mechanical breaks), the broken pieces are fittedtogether and counted as one piece, provided that theyform the requisite length of 4 inches (100 mm). Thelength of these pieces is measured along the centerline ofthe core. This sum is divided by the length of the run(drill interval) and recorded on the log as a percentage ofeach run. Figure 5-1 illustrates RQD measurements andprocedures.
RQD estimates can be determined from outcrops. RQD =115 - 3.3 where Jv equals the total number of joints in acubic meter. RQD may also be estimated from an
FIE
LD
MA
NU
AL
96
Figure 5-1.—Rock Quality Designation (RQD) computation.
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Table 5-1.—Fracture density descriptors
Alpha-numeric
descriptor DescriptorCriteria
(excludes mechanical breaks)
FD0 Unfractured No observed fractures.
FD1 Very slightlyfractured
Core recovered mostly in lengthsgreater than 3 feet (1 m).
FD2 Slightly to veryslightly fractured
FD3 Slightly fractured Core recovered mostly in lengthsfrom 1 to 3 feet (300 to 1,000 mm)with few scattered lengths less than1 foot (300 mm) or greater than 3 feet(1,000 mm).
FD4 Moderately toslightly fractured1
FD5 Moderatelyfractured
Core recovered mostly in lengthsfrom 0.33 to 1.0 foot (100 to 300 mm)with most lengths about 0.67 foot(200 mm).
FD6 Intensely tomoderatelyfractured1
FD7 Intensely fractured Lengths average from 0.1 to 0.33 foot(30 to 100 mm) with fragmentedintervals. Core recovered mostly inlengths less than 0.33 foot (100 mm).
FD8 Very intensely tointenselyfractured1
FD9 Very intenselyfractured
Core recovered mostly as chips andfragments with a few scattered shortcore lengths.
1 Combinations of fracture densities are permissible where equaldistribution of both fracture density characteristics are present over asignificant core interval or exposure, or where characteristics are "inbetween" the descriptor definitions.
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outcrop by determining the sum of solid rock (fracturefree) in lengths 4 inches long or greater along a line thatsimulates either a 5- or 10-foot "core run." Detail linesurveys provide the data needed to calculate RQD.Orienting the lines in different directions reducesdirectional bias. Either of these methods offers anadvantage over RQDs determined from drill core, becauseall fracture orientations are included. Also, these RQDvalues more realistically represent rock conditions.
Description of Fractures
An accurate description of fractures is as important as thephysical characteristics of the rock mass. Fractures affectand usually control the strength, deformation, andpermeability characteristics of a rock mass. Fractures aregrouped into sets based on similar orientations, and eachset is labeled and described. Along with the physicalmeasurements, such as attitude, spacing, and continuity,include information such as composition, thickness, andhardness of fillings or coatings; characteristics of surfacessuch as hardness, roughness, waviness, and alteration;healing; fracture openness; and presence of water orwater flow. Joint and fracture properties also may beuseful for correlating purposes. Cleavage (CL) inmetamorphic rocks includes slaty cleavage, crenulationcleavage, phyllitic structure, and schistosity (after Davis[4]) and often can be used to evaluate the tectonic setting.
Figure 5-9 may be used for geologic reports orspecifications where the standard descriptors andterminology established for discontinuities are usedduring data collection.
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Format for the Description of Fractures
Identifying and recording the physical characteristics offractures during mapping and logging is the leastexpensive part of most geologic investigations. Anaccurate and concise description of these characteristicspermits interpretation in geologic terms directlyapplicable to design and construction. As many of thecharacteristics should be described as possible, limitedonly by the type of observation. For example, continuityand waviness cannot be provided for joints observed incore. Examples of fracture descriptions recorded for adrill hole log and for an outcrop or exposure are in afollowing section. A general format for recording fracturedescriptions follows:
• Orientation• Spacing• Continuity • Openness • Fillings
ThicknessCompositionWeathering/alterationHardness
• Healing • Surfaces
RoughnessWavinessWeathering/alterationHardness
• Field index test results• Moisture
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Descriptors for Fracture Characteristics
The following paragraphs present terminology, descriptorcriteria, and descriptors for recording fracture data.Alphanumeric descriptors are amenable to computersorting. Alphanumeric descriptors are not a substitutefor a complete description of the fracture characteristics.
Orientation.—The orientation of all fractures withrespect to applied loads can be critical to deformation orstability. Seepage or grouting also may be affected orcontrolled by orientation. Orientation is usuallymeasured in the field, and the raw data tabulated andinterpreted. The analysis typically includes stereonets,contour diagrams, fracture sets, and their arealdistribution. A detailed statistical analysis of the fracturedata may be necessary. Azimuths or quadrants may beused, but azimuths are becoming the standard, in partbecause they are easier to computerize. The Americanright-hand rule for dip direction notation is preferred.The method of measuring the dip of planar dis-continuities, foliation, and bedding in cores is shown infigure 5-9. Figures 5-1 and 5-2 illustrate how inclinationof a joint in core from an angle hole can be interpreted asa horizontal joint (A) or vertical joint (B) by rotating thecore 180 degrees (E). If the core is oriented and the top ofthe core is known, the inclination can be recorded aspositive (+) or negative (-) to avoid ambiguity and to assistin determining sets.
Fracture orientation is recorded as strike and dip, or asazimuth and dip, preferably using the right-hand rule.Orientation of planar features with undetermined strikecan be measured directly and reported as dip in verticalholes. In angle holes, where true dip is not known, theangle of the plane should be measured from the core axis
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Figure 5-2.—Comparison of true and apparent spacing.
and reported as inclination, i.e., "bedding plane jointsinclined 65 degrees from the core axis."
Spacing.—Spacing affects block size and geometry in therock mass. Spacing is a required input to several rockmass classification systems. When a set can be distin-guished (parallel or subparallel joints), true spacing canbe measured and is described for each joint set, as shownon figure 5-2 and in table 5-2. If apparent spacing isgiven, label as such.
Continuity.—A continuous joint or fracture is weakerand more deformable than a short discontinuous fracturebridged by intact bedrock. Recording trace lengths todescribe continuity is useful in large exposures.Identification of the more continuous fractures is animportant aspect of formulating rock stability input data,especially for high cut slopes and in large undergroundopenings. Record the longest observable trace regardlessof end type and note whether it is a strike (S), dip (D), orapparent (A) trace. Descriptors for continuity areprovided in table 5-3.
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Table 5-2.—Fracture spacing descriptors
Alpha-numeric
descriptorJoint or fracture
spacing descriptor True spacing
SP1 Extremely widely spaced
Greater than 10 feet (ft)(<3 m)
SP2 Very widely spaced 3 to 10 ft (1 to 3 m)
SP3 Widely spaced 1 to 3 ft (300 mm to 1 m)
SP4 Moderately spaced 0.3 to 1 ft (100 to 300 mm)
SP5 Closely spaced 0.1 to 0.3 ft (30 to 100 mm)
SP6 Very closely spaced Less than 0.1 ft (<30 mm)
Table 5-3.—Fracture continuity descriptors
Alpha-numeric
descriptor Descriptor Lengths
C1 Discontinuous Less than 3 ft (>1 m)
C2 Slightly continuous 3 to 10 ft (1 to 3 m)
C3 Moderately continuous 10 to 30 ft (3 to 10 m)
C4 Highly continuous 30 to 100 ft (10 to 30 m)
C5 Very continuous Greater than 100 ft (>30 m)
This information alone is not sufficient to completelyassess joint or fracture continuity because trace lengthsmay be partially obscured. When performing jointstudies or surveys, record the number of ends (fractureterminations) that can be seen in the exposure using thealphanumeric descriptors shown in table 5-4. The size ofthe exposure should be noted because this is adetermining factor when surveying for visible ends.
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Table 5-4.—Descriptors for recording fracture ends in joint surveys
Alpha-numeric
descriptor Criteria
E0 Zero ends leave the exposure (both ends of thefracture can be seen in the exposure).
E1 One end can be seen (one end of the fractureterminates in the exposure).
E2 Both ends cannot be observed (two fracture endsdo not terminate in the exposure).
Openness.—The width or aperture is measured normalto the fracture surface. This aperture or openness affectsthe strength, deformability, and seepage characteristics.Describe fracture openness by the categories shown intable 5-5. For drill logs, if actual openness cannot bemeasured or estimated, use only open or tight and do notassign an alphanumeric descriptor.
Characteristics of Fracture Fillings.—Describing thepresence or absence of coatings or fillings anddistinguishing between types, alteration, weathering, andstrength and hardness of the filling material may be assignificant as fracture spatial relationships or planarity.Strength and permeability of fractures may be affectedby fillings. Descriptions of fracture coatings and fillingsare site specific but must address the followingconsiderations:
1. Thickness of fillings.—Table 5-6 providesdescriptors for recording the thickness of fracturefillings or coatings.
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Table 5-5.—Fracture openness descriptors
Alpha-numeric
descriptor Descriptor Openness
O0 Tight No visible separation
O1 Slightly open Less than 0.003 ft [1/32 inch (in)] (<1 mm)
O2 Moderately open 0.003 to 0.01 ft [1/32 in to 1/8 in] (1 to 3 mm)
O3 Open 0.01 to 0.03 ft [1/8 to 3/8 in] (3 to 10 mm)
O4 Moderately wide 0.03 ft [3/8 in] to 0.1 ft (10 to 30 mm)
O5 Wide Greater than 0.1 ft (>30 mm) (record actual openness)
Table 5-6.—Fracture filling thickness descriptors
Alpha-numeric
descriptor Descriptor Thickness
T0 Clean No film coating
T1 Very thin Less than 0.003 ft [1/32 in] (<1 mm)
T2 Moderately thin 0.003 to 0.01 ft [1/32 to 1/8 in] (1 to 3 mm)
T3 Thin 0.01 to 0.03 ft [1/8 to 3/8 in] (3 to 10 mm)
T4 Moderately thick 0.03 ft [3/8 in] to 0.1 ft (10 to 30 mm)
T5 Thick Greater than 0.1 ft (>30 mm) (record actual thickness)
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2. Composition of fillings.—The mineralogicalclassification of fillings, such as quartz, gypsum, andcarbonates, must be identified to convey physicalproperties of fractures that may be significantcriteria for design. Soil materials in open fracturesshould be described and classified according to theUnified Soil Classification System (USCS) (seeUSBR 5000 and USBR 5005 [5]).
Fractures may be filled or "healed" entirely or over asignificant portion of their areal extent by quartz,calcite, or other minerals. Veins may be presentwithout healing the fracture or may have beenbroken again forming new surfaces. Soluble fillings,such as gypsum, may cause foundation or structuraldegradation during the facility's expected lifetime.Fracture fillings must be considered during design,construction investigations, and monitoring orpotential long-term stability, deformability, andseepage problems may require expensiverehabilitation efforts.
Coatings or fillings of chlorite, talc, graphite, or otherlow-strength materials need to be identified becauseof their deleterious effects on strength, especiallywhen wet. Some fillings, such as dispersive, erosive,or micaceous materials, can squeeze, pipe under fluidflow, and contribute to a loss of strength andstability. Montmorillonitic clays may swell or causeswelling pressures. Cohesionless materials, such assands and silts, or materials which have beencrushed or altered may run or flow into undergroundexcavations or serve as seepage conduits.
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3. Weathering or alteration.—Descriptors forweathering or alteration of fracture fillings(excluding soil materials) are the same as those usedfor rock weathering.
4. Hardness/strength.—Descriptors for hardness/strength of fillings should be the same as thosepresented for bedrock hardness or soil consistency(chapters 3 and 4). Various field index tests may alsobe performed to determine strengths of fillings.Refer to the Field Index Tests in chapter 4.
5. Healing.—Fractures may be healed orrecemented by one or more episodes ofmineralization or precipitation of soluble materials.A description of fracture healing or rehealing shouldinclude not only the type of healing or cementingagent, but an estimate of the degree to which thefracture has been healed. The subjective criteria anddescriptors shown in table 5-7 should be used todescribe healing.
Characteristics of Fracture Surfaces.—The physicalcharacteristics of fracture surfaces are very important fordeformability and stability analyses. Dimensionalcharacteristics such as roughness and waviness (seefigure 5-3) and characteristics, such as weathering andhardness of the surfaces, are important in evaluating theshear strength of fractures. Fracture roughnessdescriptors are given in table 5-8. Surface characteristicsare less important only when low-strength materialscomprise fracture fillings.
The description of fracture asperities is divided into twocategories: small-scale asperities, or roughness, andlarge-scale undulations, or waviness. Figure 5-3 shows.
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Table 5-7.—Fracture healing descriptors
Alpha-numeric
descriptor Descriptor Criteria
HL0 Totally healed Fracture is completely healed orrecemented to a degree at least ashard as surrounding rock.
HL2 Moderately Greater than 50 percent of fracturematerial, fracture surfaces, orhealed filling is healed orrecemented; and/or strength of thehealing agent is less hard thansurrounding rock.
HL3 Partly healed Less than 50 percent of fracturedmaterial, filling, or fracture surfaceis healed or recemented.
HL5 Not healed Fracture surface, fracture zone, orfilling is not healed or recemented;rock fragments or filling (ifpresent) is held in place by iits ownangularity and/or cohesiveness.
examples of these asperities. Descriptors for roughnessand waviness and additional items related to fracturesurfaces follow.
1. Roughness.—The roughness (small-scale asper-ities) of fracture surfaces is critical for evaluatingshear strengths. Roughness descriptors such asstriated or slickensided should be used wheneverobserved. For oriented core or outcrops, theorientation of striations or slickensides should berecorded. The rake of striations or slickensidesshould be recorded when observed in core fromvertical drill holes which have not been oriented. In
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Figure 5-3.—Examples of roughness and waviness offracture surfaces, typical roughness profiles, andterminology. The length of each profile is in the range of3 to 15 feet (1 to 5 m); the vertical and horizontal scalesare equal.
Coulomb's equation for shear strength (S = C + N tann), the large scale undulations (i) are entered into theequation as N tan (n + i).
2. Waviness.—Waviness (large-scale undulations)also should be recorded for fracture surveys along
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Table 5-8.—Fracture roughness descriptors
Alpha-numeric
descriptor Descriptor Criteria
R1 Stepped Near-normal steps and ridges occuron the fracture surface.
R2 Rough Large, angular asperities can beseen.
R3 Moderately rough
Asperities are clearly visible andfracture surface feels abrasive.
R4 Slightly rough Small asperities on the fracturesurface are visible and can be felt.
R5 Smooth No asperities, smooth to the touch.
R6 Polished Extremely smooth and shiny.
exposures. This is done by recording amplitude andwavelength, or as a minimum, describing as eitherplanar or undulating.
3. Weathering/alteration.—Weathering or altera-tion of fracture surfaces is one of the criteria used forclassifying rock mass weathering. Even though it isinherent in the weathering categories, the actualdescription of surface alteration and the associatedloss of strength of the rock needs to be reported.Qualitative information can be presented whendescribing a particular joint set, joint, or fracture.The condition of the surface(s), such as depth ofpenetration and degree of staining or oxidation,should be recorded.
Moisture Conditions.—The presence of moisture or thepotential for water flow along fractures may be an
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indicator of potential grout takes or seepage paths.Criteria and descriptors shown in table 5-9 describemoisture conditions for fractures. The presence orabsence of moisture cannot be determined in core, butevidence of previous long-term water flow is found inleaching, color changes, oxidation, and dissolutioning.
Table 5-9.—Fracture moisture conditions descriptors
Alpha-numeric
descriptor Criteria
M1 The fracture is dry, tight, or filling (wherepresent) is of sufficient density or composition toimpede water flow. Water flow along the fracturedoes not appear possible.
M2 The fracture is dry with no evidence of previouswater flow. Water flow appears possible.
M3 The fracture is dry but shows evidence of waterflow such as staining, leaching, and vegetation.
M4 The fracture filling (where present) is damp, butno free water is present.
M5 The fracture shows seepage and is wet withoccasional drops of water.
M6 The fracture emits a continuous flow (estimateflow rate) under low pressure. Filling materials(where present) may show signs of leaching orpiping.
M7 The fracture emits a continuous flow (estimateflow rate) under moderate to high pressure. Water is squirting, and/or filling material (wherepresent) may be substantially washed out.
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Field Index Tests
Schmidt Hammer tests can be used to estimate the hard-ness/strength of the rock surfaces along a discontinuity(which may be weaker than the body of the rock). Therebound of a spring-actuated projectile is measured fromthe surface being tested. The sample should be largeenough, preferably intact or securely fastened to a stablebase (i.e., concrete), so that it does not move during tests.Unclamped specimens should measure at least 0.7 foot(200 mm) in each direction. Direct testing on rockoutcrops is usually the best method. Results should beobtained from both wet and dry surfaces. Ten readingsare taken at various locations on each surface. The fivelowest readings are discounted, and the five highestreadings are averaged to obtain a realistic reboundnumber (Schmidt hardness). The hammer is alwaysoriented perpendicular to the surface being tested. A unitdry weight must also be determined for the materialbeing tested. Using the Schmidt hardness and the unitdry weight, the uniaxial compressive strength of thesample can be estimated.
Tilt-type sliding-friction tests are also useful inestimating the shear strength of fractures. Samples canbe obtained from outcrops or rock core. A representativesample is tilted, and the angle at which the top of thesample slides relative to the bottom is measured. Thisangle is an approximation of the friction angle. Both wetand dry surfaces should be tested. The weight, thickness,and approximate dimensions of the sample parts also arerecorded. A friction angle can be estimated in a similarmanner using three pieces of core. Two representativepieces of core are used as a base, and the third piece isplaced on top. The base is then tilted until the top pieceof core slides, and this angle is measured.
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Pocket penetrometers may be used to estimate thestrength of soil-like fillings or surfaces. The surface or afilling is penetrated by the penetrometer to the line onthe penetrometer (about a quarter of an inch), and theapproximate compressive strength is read directly from acalibrated scale on the penetrometer.Example Descriptions of Fractures
The examples which follow show a representative formatfor recording data. Actual descriptions vary and dependon whether the observations were recorded fromexposures, drill core, or detailed joint surveys. Datareport descriptions of discontinuities should be expandedto provide ranges and typical characteristics or additionalsignificant data for each set or individual fractures fromall observations.
Drill Core.—The following metric example is taken froma log of a rock core interval from a vertical drillhole; in anangle hole, orientation would be recorded as inclinationfrom the core axis:
“. . . Moderately to slightly fractured (35%bedding joints, 65% joints). Core recovered in210 to 730 mm lengths, mostly as 300 mmlengths. Bedding joints dip 30 to 35E, widelyspaced (SP3) at 370 to 790 mm, avg 580 mm; 29are tight, 6 are open; all are clean; 20 aremoderately rough (R3), 15 are slightly rough(R4); oxidation penetrates 30 mm from surfaces(W4); all surfaces can be scratched by moderateknife pressure (H4). Joint set A dips 50 to 75E,mostly 60 to 65E, normal bedding; very widelyspaced (SP2) at 0.9 to 1.2 m, avg 1 m; 3 are open,1 is tight, and 9 are tight and healed by 3 to30 mm thick, fresh (W1), very hard (H2), quartz-calcite fillings; the 3 open joints are clean,slightly rough (R4), oxidation stains penetrate
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60 mm from surfaces (W4) which can bescratched by light to moderate knife pressure, all3 show evidence of water flow (W6) . . .. ”
Exposure Mapping.—An example of fracturedescriptions for an exposure, using English units, follows:
“Joint set A-1 strikes N. 20-38E W., mostly N. 20-25E W.; dips 50-65E NE, averages 54E NE. Verywidely spaced (SP2), 3.8 to 7.3 ft apart, mostly5 ft apart; most have moderately to highlycontinuous (C3 to C4) 25 to 55 ft trace lengths.Approx. 60% are open to moderately wide (O3 toO4), ranging in openness from 0.1 to 0.3 ft,remainder are tight to slightly open (O0 to O1).Approx. 10% of the joints contain thin, hardquartz fillings, 25% are clean, and 65% containfirm fat clay (CH) fillings which can be indentedwith thumbnail. All rock surfaces aremoderately weathered with dendritic iron oxidestaining which can be scratched with light tomoderate knife pressure. Most surfaces areslightly rough (R4) and undulatory, approx. 20%are rough (R2) and planar. Undulations havewavelengths of 10 to 20 ft, average 15 ft, andamplitudes range from 0.2 to 0.5 ft. Clean jointsare dry but show evidence of moisture flow (M3),most clay filled joints are damp but show noevidence of flow (M4).”
Fracture Survey.—Statistical evaluations are valuable,so it is important to collect joint properties for analysis.This can be readily accomplished using fracture surveytechniques. Data sheets are prepared with appropriatecolumns for recording the data, a traverse distance and
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direction are established, and all pertinent data aremeasured and recorded. Data are analyzed usingstatistical methods. Refer to chapter 7 for detaileddescriptions of discontinuity surveys.
Descriptions of Shears and Shear Zones
Shear, fault, and associated terminology are defined atthe beginning of this chapter. The following describes amethod to classify shears, shear zones, and theirassociated features. A format to describe and quantifyshear and fault physical characteristics and exampledescriptions is provided. For each discussion, the word"fault" can be substituted for "shear."
Identification or Naming of Shears
Significant shears should be named for ease of identifi-cation in logs of exploration, mapping of exposures, inter-pretations on geologic drawings, discussion in reports,sample identification, and design treatment. Identifica-tion of a shear or shear zone by letter/number desig-nation, such as S-9 (shear zone No. 9) or F-1 (fault zoneNo. 1), is recommended. Major splays may be identifiedby an appropriate combination of letters and numberssuch as S-la or F-2c. Shears also may be named by theirlocation such as "powerplant shear," "Salt Creek Shearzone," or "left abutment fault" if only a few shears arepresent in the study area.
Uniform and Structured Shear Zones
The identification and correlation of shears and shearzones from multiple but separate observations inboreholes, trenches, and limited outcrops are oftendifficult. The identification and description of shear and
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Figure 5-4.—Uniform shear zone.
shear zone components and their physical characteristicsare necessary to both assist in correlating observationsand for design analyses. Together with physical meas-urements of attitude and thickness, the description of thecomponent parts and internal structure of a shear may beused for correlation in much the same way thatgeophysical signatures or lithology are used to identifycertain stratigraphic units. The composition of a shear orshear zone at each exposure can be described as eitheruniform or structured. Illustrated in figure 5-4 is a0.5-foot (150-mm) thick uniform shear composed of40 percent breccia distributed relatively uniformlythroughout 60 percent clay gouge. Although the shearcontains two components, clay gouge and brecciatedfragments, the components are distributed uniformlythroughout the 0.5-foot shear zone.
In contrast, a structured shear zone is composed of two ormore zones which differ significantly in composition orphysical properties. A structured shear zone could consistof components similar to the uniform shear describedabove with an additional 0.2-foot (60-mm) thick quartzvein along one contact, as shown on figure 5-5.
A more complex structured shear zone might have a0.1-foot (30-mm) thick chloritic gouge layer adjacent tothe vein as shown on figure 5-6.
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Figure 5-5.—Structured shear zone (two zones or layers).
Figure 5-6.—Structured shear zone (three layers).
Figure 5-7.—Uniform shear zone with veinlets.
Numerous small quartz-calcite or other mineral veinletscommonly occur irregularly distributed throughoutshears. The veinlets do not form distinct layers; there-fore, they should be considered a percentage componentof a uniform shear as illustrated on figure 5-7.
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Figure 5-8.—Uniform shear zone (composite).
Shear zones may have minor or major lateral variationsin the percentages of components within short distancesat an exposure. The shear zone illustrated in figure 5-4consists of 60 percent clay gouge and 40 percent rockfragments. Because the various components are notarranged in layers, the shear is of the uniform type. Inan adjacent tunnel, the same shear zone may consist of40 percent clay gouge and 60 percent rock fragments. Ifthe exposure is limited, as in most tunnels or exploratorytrenches, the percentages of the various componentsshould be averaged, as illustrated on figure 5-8, and theaverage composition should be described.
Descriptors and Description Format for Shears andShear Zones
For shears to be uniformly and adequately described, abrief discussion of each applicable item in the followinglist should be included. The recommended format fordescribing a shear or shear zone, either uniform orstructured as follows:
• Attitude
• Thickness
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• Composition
GougePercent by volumeColorMoisture contentConsistency (hardness/strength)CompositionOccurrence — layers or matrix
BrecciaPercent by volumeFragment size(s)Fragment shape(s)Fragment surface characteristicsLithologyHardness/strength
Other components (vein or dike materials)PercentageThicknessComposition (mineralogy, texture, fracturing, etc.)
• Healing
• Zone strength
• Direction of movement (if determinable)
Attitude.—Measure strike and dip in exposures andfrom oriented core, report dip in vertical core, andmeasure angle from core axis for inclined drill core.Report an average figure if only moderate variations areobserved. Provide both a range and average if largevariations in orientation are apparent.
Thickness.—Report the true thickness of the shear orshear zone. True thickness can be measured directly orcomputed. Indicate an average figure for minorvariations, as well as a range and average for significant
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variations. Do not include associated features beyondthe shear contacts (the shear-disturbed zone), or intactblocks of rock around which the shear has bifurcated ascomponents of the thickness.
Composition.—Report an average percentage for eachdescription-format component. The various layers orzones of structured shears may be indicated by use ofbracketed numbers [i.e., shear 1(1), 1(2)]. Describe eachindividual layer or zone in the order it occurs as if eachwere a uniform shear.
1. Gouge.—
• Percentage.—Report an average percent byvolume for each exposure or layer.
• Color.—Report color to help distinguish betweenseveral types of gouge or to indicate alteration.The Munsel Color System can be used to recordboth the wet and dry color.
• Moisture content.—Describe the apparentmoisture content upon initial exposure, using thefollowing terms: wet (visible free water); moist(damp but without visible water); and dry (absenceof moisture, dusty, dry to the touch).
• Consistency (strength/hardness).—Reportthe ease with which gouge can be worked by hand:Very soft [thumb penetrates gouge more than 1 in(25 mm) if the gouge occurs in a sufficientquantity]; soft [easily molded, penetration ofthumb about 1 in (25 mm)]; firm [easily crumbled,can be penetrated by thumb up to 1/4 in : (5 mm)];hard (can be broken with finger pressure, noindentation with thumb, readily indented with
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thumbnail); and very hard (cannot be indentedwith thumbnail). Use a pocket penetrometer toestimate gouge strength.
• Composition.—Report identifiable mineraltypes; talc, chlorite, mica. Otherwise, report thesoil classification group name and/or symbol, suchas CH, ML, lean clay, etc.
• Occurrence.—Describe how the gouge occurs,such as thin coatings on fragments, a matrix, or alayer.
2. Breccia.—
• Percentage.—Report an average percent byvolume for each exposure or layer.
• Fragment size.—Estimate or measure thedimension of the most common fragment sizes andreport as a range. Use fractions of an inch andtenths of a foot or metric equivalents.
• Fragment shape.—Unless the distribution ofseveral shapes is nearly equal, report the mostcommon shapes and degree of angularity as shownin figure 5-9.
• Fragment characteristics.—These should beincluded because they affect or provide anindication of the strength of the zone or help toidentify a particular zone in several exposures orobservations. Descriptions should include striated,slickensided, polished, rough, chloritic coatings,and weathering.
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Figure 5-9.—Standard descriptors and descriptivecriteria for discontinuities.
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• Lithology.—The identification of rockfragments (rock type) is essential, particularly ifdifferent from the surrounding rock mass or ifseveral rock types are present in the zone.Indicate if fragments within the zone are altered.
• Fragment hardness/strength.—Describe howthe average-size fragment can be broken across itsleast dimension using the following format: canbe broken with (light, moderate, heavy) manualpressure or hammer blow.
3. Other components (vein or dike material).—Describe any large veins or dikes which occur withinthe shear, either as a component of a uniform shearzone, usually occurring in the form of branching,discontinuous veinlets less than 1/2-inch (13-mm)thick, or as a layer (zone) within a structured shear.Dikes or large veins should be included as a singlelayer of a shear zone if they are bounded by shears.Also, they should be described as a rock unit. If ashear occurs only along one border of a dike or vein,the dike or vein should be described only as a rockunit.
• Percentage.—Report as an average percent byvolume for the exposure or layer.
• Thickness.—Report as an average or range ofthickness.
• Composition.—Provide a brief description ofmineralogy and texture (e.g., leached, vuggy).Fracture density may be reported here ifsignificant.
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Healing.—Small veinlets which are components of auniform shear zone and which actually form a bondbetween fragments tend to increase the strength of theshear zone (see following section). Healing should bedetermined by attempting to separate fragmentsmanually or using a rock or pick. If fragments arebonded by some healing or cementing agent, the shearzone is described as partly healed (less than 50 percentof fragments bonded), mostly healed (more than 50percent of fragments bonded), and totally healed (allfragments bonded by vein material).
Zone Strength.—When possible, the strength of theentire shear zone exposed in outcrops, tunnels, andexploratory trenches should be reported by the ease ofwhich the sheared material can be dug from theexposure. The following guide is to be used: can be dugfrom wall, floor, or outcrop with light, moderate, orheavy finger pressure or hammer blow. Strength shouldbe reported for each significant layer of a shear zone.
Direction of Movement.—If determinable, the amount,direction, and type of displacement are reported. Typeand direction of displacement (dip-slip, strike-slip,oblique-slip, normal, reverse, right-lateral) may bedirectly observable as shown by drag, tension fractures,striations, offset "marker units" (such as beds, dikes,veins, or other structural units). The amount of bothhorizontal and vertical separation and, if possible, a net-slip solution should be included. Regional stress fieldsmay be used to postulate displacement in the absence ofsite observations.
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Example Descriptions for Shears and Shear Zones
The following are example descriptions for both auniform and a structured shear zone; actual descriptionsmay depend on the type of observation.
A description, using metric units, of a uniform shear inan angle hole could be:
“21.30 to 22.31: Shear. 210 mm thick, uppercontact inclined 40E, lower contact inclined 61Efrom core axis, averages 51E, parallel tobedding. Composed of approx. 15%, blackish-green, moist, soft, chloritic clay and 85% 2 to 10mm thick platy and lens-shaped, subrounded,polished, intensely weathered (W7)metasandstone fragments. Fragments breakwith light hand pressure. Fragments partlyhealed by 1 mm thick quartz-calcite veinlets.”
A structured shear zone in a vertical drill hole core couldbe reported in English units as:
“118.6 to 121.9': Shear zone. 2.3 ft thick, upperand lower contacts dip 40 to 45E, subparallel tofoliation. Zone 1, upper 0.3 ft; consists of 45%green, moist, soft, chloritic clay gouge and 55%0.05 to 0.1 ft subrounded, blocky, polished, freshdike fragments; fragments break with moderatehammer blow. Zone 2 is 1.1 ft thick; consists ofvery intensely fractured, fresh dike which ispartly healed by 0.01 to 0.3 ft-thick calciteveinlets and a 0.l ft-thick, vuggy quartz-calcitevein at base of dike. Zone 3 is 0.5 ft of NoRecovery. Zone 4, the lower 0.3 ft; consists of70% gray, moist, firm, silty gouge, and 15% 0.01to 0.03 ft-thick, wedge-shaped, fresh, striated
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horn-blende schist fragments, and 15% 0.02 ft-thick,angular, blocky, fresh quartz fragments. Fragmentsbreak with light hammer blow.”
Description of Shear-Disturbed Zones
Fractures, fracture zones, drag zones, mineralizedbedrock, and dikes or large veins along which one contactis sheared but are not themselves sheared or enclosedwithin a zone, are not included in the thickness of ashear or shear zone. The associated zone should beidentified to adequately describe geologic conditions ofengineering significance. For example, the shear-disturbed zone and an adjacent dike might be describedas:
“. . . The shear is bounded by a 1.5- to 4-ft wideshear-disturbed zone of very intensely tointensely fractured chloritized dike (FD8). Thiszone averages 3 ft wide along the upper contactand 2 ft wide in the associated chloritized dikeadjacent to the lower contact. Hydrothermalalteration consisting of epidote, chlorite, pyrite,and quartz extends irregularly outward 2 to 7 ftnormal to the shear boundaries.”
BIBLIOGRAPHY
[1] International Journal of Rock Mechanics MiningScience and Geomechanics Abstracts, v. 15, pp. 319-368, 1978.
[2] The Glossary of Geology, 4th edition, AmericanGeologic Institute, Alexandria, Virginia, 1997.
[3] Deere, D.U., and D.W. Deere, “RQD After TwentyYears,” U.S. Army Corps of Engineers, 1989.
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[4] Davis, George H., Structural Geology of Rocks andRegions, John Wiley & Sons, 1984.
[5] Earth Manual, Part II, Third Edition, Bureau ofReclamation, U.S. Department of the Interior, 1990.
Chapter 6
GEOLOGIC MAPPING ANDDOCUMENTATION
Geologic mapping is defined as the examination ofnatural and manmade exposures of rock or uncon-solidated materials, the systematic recording of geologicdata from these exposures, and the analysis and inter-pretation of these data in two- or three-dimensionalformat (maps, cross sections, and perspective [block]diagrams). The maps and cross sections generated fromthese data: (1) serve as a record of the location of factualdata; (2) present a graphic picture of the conceptualmodel of the study area based on the available factualdata; and (3) serve as tools for solving three-dimensionalproblems related to the design, construction, and/ormaintenance of engineered structures or site characteri-zation. This chapter presents guidelines for thecollection and documentation of surface and subsurfacegeologic field data for use in the design, specifications,construc-tion, or maintenance of engineered structuresand site characterization studies.
Responsibilities of the Engineering Geologist
An engineering geologist defines, evaluates, and docu-ments site-specific geologic conditions relating to thedesign, construction, maintenance, and remediation ofengineered structures or other sites. This responsibilityalso may include more regionally based geologic studies,such as materials investigations or regional reconnais-sance mapping. An engineering geologist engaged ingeologic mapping is responsible for:
• Recognizing the key geologic conditions in a studyarea that will or could significantly affect hazardousand toxic waste sites or a proposed or existingstructure;
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• Integrating all the available, pertinent geologicdata into a rational, interpretive, three-dimensionalconceptual model of the study area and presentingthis conceptual model to design and constructionengineers, other geologists, hydrologists, sitemanagers, and contractors in a form that can beunderstood.
The process and responsibilities of engineering geologymapping are illustrated in figure 6-1.
The engineering geologist needs to realize that geologicmapping for site characterization is a dynamic process ofgathering, evaluating, and revising geologic data andthat the significance of these data, both to the structureand to further exploration, must be continually assessed.The initial exploration program for a structure is alwaysbased on incomplete data and must be modifiedcontinuously as the site geology becomes betterunderstood. The key to understanding the site geologyis through interpretive geologic drawings such asgeologic maps, cross sections, isopachs, and contourmaps of surfaces. These working drawings, periodicallyrevised and re-interpreted as new data become available,are continuously used to assess the effects of the sitegeology and to delineate areas where additional explora-tion is needed. These drawings are used in designs,specifica-tions, and modeling and maintained in thetechnical record of the project.
Development of a Study Plan
Prior to mapping any project, a study plan must bedeveloped. Depending on the complexity of the sitegeology, the nature of the engineered structure, and thelevel of
MA
PP
ING
131 Figure 6-1.—Process of engineering geology mapping.
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previous studies, the study plan may be preliminary orcomprehensive. Although elements of the plan may bemodified, expanded, or deleted as geologic data becomeavailable, the primary purpose of the study plan—coordination among all geologists and engineers workingon the project—should be retained. Early study plandevelopment and agreement to this plan by thoseinvolved in the project are necessary to prevent thecollection of unneeded, possibly costly data and ensureneeded data are available at the correct time in theanalysis, design, and construction process.
Scope of Study
The purpose and scope of the mapping project arestrongly influenced by the primary engineering andgeologic considerations, the level of previous studies, andoverall job schedules. The purpose and scope areformulated jointly by the geologists and engineers on theproject. Time of year and critical dates for neededinformation also will have a great impact on the pace ofdata collection and the personnel needed to handle amapping project. Discussion of these factors prior toinitiating the mapping program is essential so that onlynecessary data are obtained and the work can becompleted on schedule. Items to consider when definingthe scope of a mapping program are:
1. Study limits.—Set general regional and site studylimits based on engineering and geologic needs.
2. Critical features and properties.—Determine thecritical geologic features and physical properties of sitematerials that will need to be defined and discuss thedifficulties in collecting data on these features.
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3. Schedules.—Determine schedules under which thework will be performed and define key data due dates.Prioritize work to be done. The time of year the mappingis to be performed, the type of mapping required,available personnel and their skills, the availability ofsupport personnel such as drill crews and surveyors, andbudget constraints will influence the work schedule andmust be carefully evaluated.
4. Extent of previous studies.—Collect and study allavailable geologic literature for the study area. The ex-tent and adequacy of previous studies helps to define thetypes of mapping required and how data will becollected, i.e., based on analyses, design, or constructionneeds.
5. Photography.—Aerial and terrestrial photo-graphy should be considered for any project. As a mini-mum, aerial photographs of the site should be reviewed.Aerial photographs reveal features that are difficult torecognize from the ground or at small scales. Extensiveuse of terrestrial or aerial photography will require adifferent approach to the mapping program. Defineareas where terrestrial photogrammetry could aidmapping progress. Terrestrial photography of varioustypes is an integral part of the final study record.
Specific Mapping Requirements
This section provides the basic considerations anengineering geologist should evaluate prior to startingany mapping project or portion of a mapping project.
Map Type
Define the types of mapping required and how data areto be collected, including special equipment needed for
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data collection. The types of mapping required dependon the study purpose or the type of structure or site thatis to be built or rehabilitated, structure size, the phase ofstudy (planning through operation and maintenance),and the specific design needs.
Scales and Controls
Define the required scales for design or constructionneeds. Although finished maps can be enlarged orreduced photographically or by Computer-Aided DraftingDesign (CADD)-generated drawings to any desired scale,in most cases map text and symbols will have to beredone for legibility. Selection of an adequate map scaleat the beginning of a mapping project will save time andenergy as well as help ensure that the types of dataneeded can be portrayed adequately on the finaldrawings. Suggested map scales for various types ofinvestigations are listed under specific mappingtechniques.
The horizontal and vertical accuracy and precision oflocations on a map depend on the spatial control of thebase map. General base map controls are listed indecreasing significance: (1) Survey Control or ControlledTerrestrial Photogrammetry—geology mapped fromsurvey controlled observation points or by plane table orstadia; (2) Existing Topographic Maps—control for thesemaps vary with scale. The most accurate are large-scalephotogrammetric topographic maps generated fromaerial photographs for specific site studies; (3)U n c o n t r o l l e d A e r i a l / T e r r e s t r i a lPhotogrammetry—Camera lens distor-tion is the chiefsource of error; (4) Brunton Compass/ Tape Surveys—canbe reasonably accurate if measure-ments are taken withcare; and (5) Sketch Mapping— Practice is needed tomake reasonably accurate sketch
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maps. The Global Positioning System can provide ade-quate position locations depending on the requiredaccuracy or precision.
Global Positioning System
The Global Positioning System (GPS) is a system ofsatellites that provides positioning data to receivers onearth. The receiver uses the positioning data to calculatethe location of the receiver on earth. Accuracy and typeof data output depends on many factors that must beevaluated before using the system. The factors thatmust be evaluated are: (1) the needs of the project, (2)the capabilities of the GPS equipment, and (3) theparameters necessary for collecting the data in anappropriate form.
Project Requirements
The location accuracy or precision needed by the projectis a controlling factor whether GPS is appropriate for theproject. The actual needs of the project should be deter-mined, being careful to differentiate with “what would benice.” Costs should be compared between traditionalsurveying and GPS.
GPS Equipment
Different GPS receiver/systems have differentaccuracies. Accuracies can range from 300 ft to inches(100 m to cm) depending on the GPS system. Costsincrease exponen-tially with the increase in accuracy. Arealistic evalua-tion of the typical accuracy of theequipment to be used is necessary, and a realisticevaluation of the needed, not “what would be nice,”accuracy is important. Possible accuracy and typicalaccuracy are often not the same.
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Datums
The datum or theoretical reference surface to be used forthe project must be determined at the start. U.S.Geologi-cal Survey (USGS) topographic maps commonlyuse North American Datum (NAD) 27, but most newsurveys use NAD 83. Changing from one datum toanother can result in apparent location differences ofseveral hundred feet or meters if not done properly.
Map Projections
The map projection is the projection used to depict theround shape of the earth on a flat plane or map. Themost common projections used in the United States arethe Transverse Mercator and the Lambert ConformalConic. State plane coordinate systems almostexclusively use one or the other. To use these stateplane projections, location and definition parameters arenecessary. Table 6-1 has the types of projections and theprojection parameters for each state in the UnitedStates. A discussion of map projections and coordinatesystems is in Map Projections - A Working Manual,USGS Profes-sional Paper 1395[1].
Transverse Mercator.—The Transverse Mercatorprojection requires a central meridian, scale reduction,and origin for each state or state zone.
Lambert Conformal Conic.—The Lambert ConformalConic projection requires two standard parallels and anorigin for each state or state zone.
Coordinate System.—The coordinate system is the gridsystem that is to be used on the project. The state plane
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum
(T indicates Transverse Mercator: L. Lambert Conformal Conic: H. Hotine Oblique Mercator. Modified slightly and updated from
Mitchell and Simmons, 1945, p. 45-47)
AreaProjec-
tion Zones AreaProjec-
tion Zones
Alabama _______Alaska ________
Arizona _______Arkansas ______California _____Colorado ______Connecticut ____Deleware ______Florida ________
Georgia _______Hawaii ________Idaho _________Illinois ________Indiana _______Iowa __________Kansas ________Kentucky ______Louisiana _____Maine _________Maryland _____Massachusetts _Michigan1
obsolete _____current _____
Minnesota _____Mississippi ____Missouri ______Montana ______Nebraska _____
TTLHTLLLLTTLTTTTTLLLLTLL
TLLTTLL
281132731121253222223212
3332332
Nevada _______New Hampshire __New Jersey ___New Mexico ___New York _____
North Carolina North Dakota _Ohio __________Oklahoma _____Oregon _______Pennsylvania __Puerto Rico & Virgin Islands _____Rhode Island __Samoa ________South Carolina ____South Dakota _Tennessee ____Texas ________Utah _________Vermont ______Virginia ______Washington ___West Virginia _Wisconsin ____Wyoming _____
T
TTTTL
LLLLLL
LTL
LLLLLTLLLLT
3
11331
122222
211
22153122234
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum(continued)
Transverse Mercator Projection
ZoneCentral
meridianScale
reduction2Origin3
(latitude)
AlabamaEast ______________West _____________
85E87
50' W.30
1:25,0001:15,000
30E30
30' N.00
Alaska4
2 _________________ 142 00 1:10,000 54 003 _________________ 146 00 1:10,000 54 004 _________________ 150 00 1:10,000 54 005 _________________ 154 00 1:10,000 54 006 _________________ 158 00 1:10,000 54 007 _________________ 162 00 1:10,000 54 008 _________________ 166 00 1:10,000 54 009 _________________ 170 00 1:10,000 54 00
ArizonaEast _____________ 110 10 1:10,000 31 00Central ___________ 111 55 1:10,000 31 00West _____________ 113 45 1:15,000 31 00
Delaware ___________ 75 25 1:200,000 38 00Florida4
East _____________ 81 00 1:17,000 24 20West _____________ 82 00 1:17,000 24 20
GeorgiaEast _____________ 82 10 1:10,000 30 00 West ____________ 84 10 1:10,000 30 00
Hawaii1 ________________ 155 30 1:30,000 18 502 ________________ 156 40 1:30,000 20 203 ________________ 158 00 1:100,000 21 104 ________________ 159 30 1:100,000 21 505 ________________ 160 10 0 21 40
IdahoEast ______________ 112 10 1:19,000 41 40Central ___________ 114 00 1:19,000 41 40West _____________ 115 45 1:15,000 41 40
IllinoisEast ______________ 88 20 1:40,000 36 40West _____________ 90 10 1:17,000 36 40
Indiana East _____________ 85 40 1:30,000 37 30West _____________ 87 05 1:30,000 37 30
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum(continued)
Transverse Mercator Projection
ZoneCentral
meridianScale
reduction2Origin3
(latitude)
MaineEast _____________ 68E30' W. 1:10,000 43E 50' N.West _____________ 70 10 1:30,000 42 50
Michigan (old)4
East _____________ 83 40 1:17,500 41 30Central ___________ 85 45 1:11,000 41 30West _____________ 88 45 1:11,000 41 30
MississippiEast ______________ 88 50 1:25,000 29 40West _____________ 90 20 1:17,000 30 30
MissouriEast ______________ 90 30 1:15,000 35 50Central ___________ 92 30 1:15,000 35 50West _____________ 94 30 1:17,000 36 10
NevadaEast ______________ 115 35 1:10,000 34 45Central ___________ 116 40 1:10,000 34 45West _____________ 118 35 1:10,000 34 45
New Hampshire ______ 71 40 1:30,000 42 30New Jersey __________ 74 40 1:40,000 38 50New Mexico
East ______________ 104 20 1:11,000 31 00Central ___________ 106 15 1:10,000 31 00West _____________ 107 50 1:12,000 31 00
New York4
East ______________ 74 20 1:30,000 40 00Central ___________ 76 35 1:16,000 40 00West _____________ 78 35 1:16,000 40 00
Rhode Island ________ 71 30 1:160,000 41 05Vermont _____________ 72 30 1:28,000 42 30Wyoming
East _____________ 105 10 1:17,000 40 40East Central 107 20 1:17,000 40 40West Central 108 45 1:17,000 40 40West _____________ 110 05 1:17,000 40 40
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum(continued)
Lambert Conformal Conic projection
ZoneStandardparallels
Origin5
Longitude Latitude
Alaska4
10 ___________ 51E50' N. 53E 50' N. 176E00' W.5a 51E 00' N.Arkansas
North ________ 34 56 36 14 92 00 34 20South ________ 33 18 34 46 92 00 32 40
California I ____________ 40 00 41 40 122 00 39 20II ___________ 38 20 39 50 122 00 37 40III ___________ 37 04 38 26 120 30 36 30IV ___________ 36 00 37 15 119 00 35 20V ____________ 34 02 35 28 118 00 33 30VI ___________ 32 47 33 53 116 15 32 10VII __________ 33 52 34 25 118 20 34 085b
ColoradoNorth _______ 39 43 40 47 105 30 39 20Central ______ 38 27 39 45 105 30 37 50South _______ 37 14 38 26 105 30 36 40
Connecticut ____ 41 12 41 52 72 45 40 505d
Florida4 North _______ 29 35 30 45 84 30 29 00
Iowa North _______ 42 04 43 16 93 30 41 30South _______ 40 37 41 47 93 30 40 00
Kansas North _______ 38 43 39 47 98 00 38 20South _______ 37 16 38 34 98 30 36 40
Kentucky North _______ 37 58 38 58 84 15 37 30South _______ 36 44 37 56 85 45 36 20
Louisiana North _______ 31 10 32 40 92 30 30 40South _______ 29 18 30 42 91 20 28 40Offshore _____ 26 10 27 50 91 20 25 40
Maryland ______ 38 18 39 27 77 00 37 505c
Massachusetts Mainland ____ 41 43 42 41 71 30 41 005d
Island _______ 41 17 41 29 70 30 41 005c
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum(continued)
Lambert Conformal Conic projection (continued)
ZoneStandardparallels
Origin5
Longitude LatitudeMichigan
(current)4
North _______ 45E29' N. 47E 05' N. 87E00' W. 44E 47' N.Central ______ 44 11 45 42 84 20 43 19South _______ 42 06 43 40 84 20 41 30
MinnesotaNorth _______ 47 02 48 38 93 06 46 30Central ______ 45 37 47 03 94 15 45 00South _______ 43 47 45 13 94 00 43 00
MontanaNorth _______ 47 51 48 43 109 30 47 00Central ______ 46 27 47 53 109 30 45 50South _______ 44 52 46 24 109 30 44 00
NebraskaNorth _______ 41 51 42 49 100 00 41 20South _______ 40 17 41 43 99 30 39 40
New York4
Long Island __ 40 40 41 02 74 00 40 305f
North Carolina ______
34 20 36 10
79 00 33 45
North Dakota North _______ 47 26 48 44 100 30 47 00South _______ 46 11 47 29 100 30 45 40
OhioNorth _______ 40 26 41 42 82 30 39 40South _______ 38 44 40 02 82 30 38 00
Oklahoma North _______ 35 34 36 46 98 00 35 00South _______ 33 56 35 14 98 00 33 20
OregonNorth _______ 44 20 46 00 120 30 43 40South _______ 42 20 44 00 120 30 41 40
PennsylvaniaNorth _______ 40 53 41 57 77 45 40 10South _______ 39 56 40 58 77 45 39 20
Puerto Rico and Virgin Islands
1 ___________ 18E 02' N. 18E 26' N. 66E 26' W. 17E 50' N.5g
2 (St. Croix) __ 18 02 18 26 66 26 17 505f, g
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Table 6-1.—U.S. State plane coordinate systems – 1927 datum(continued)
Lambert Conformal Conic projection (continued)
ZoneStandardparallels
Origin5
Longitude Latitude
Samoa _________ 14E16' S. (single) 170 005h — —South Carolina
North _______ 33E46' N. 34 58 81 00 33 00South _______ 32 20 33 40 81 00 31 50
South DakotaNorth ________ 44 25 45 41 100 00 43 50South _______ 42 50 44 24 100 20 42 20
Tennessee ______ 35 15 36 25 86 00 34 405f
Note: All these systems are based on the Clarke 1866 ellipsoid and arebased on the 1927 datum. Origin refers to rectangular coordinates. 1 The major and minor axes of the ellipsoid are taken at exactly1.0000382 times those of the Clarke 1866, for Michigan only. Thisincorporates an average elevation throughout the State of about 800 ft,with limited variation. 2 Along the central meridian. 3 At origin, x = 500,000 ft, y = 0 ft, except for Alaska zone 7, x =700,000 ft; Alaska zone 9, x = 600,000 ft; and New Jersey, x =2,000,000 ft. 4 Additional zones listed in this table under other projection(s). 5 At origin, x = 2,000,000 ft, 7 = 0 ft, except (a) x = 3,000,000 ft, (b) x =4,186,692.58, y = 4,160,926.74 ft, (c) x = 800,000 ft, (d) x = 600,000 ft,(e) x = 200,000 ft, (f) y = 100,000 ft, (g) x = 500,000 ft, (h) x = 500,000 ft,y = 0, but radius to latitude of origin = -82,000,000 ft.
system is used by most projects, but latitude/longitude,universal transverse mercator, or a local coordinatesystem may be used.
State Plane Coordinate Systems-changes for 1983datum.—This listing indicates changes for the NAD1983 datum from projections, parameters, and origins ofzones for the NAD 1927 datum. State plane coordinatesbased on the 1927 datum cannot be correctly convertedto coordinates on the 1983 datum merely by usinginverse formulas to convert from 1927 rectangularcoordinates to latitude and longitude, and then using
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forward formulas with this latitude and longitude toconvert to 1983 rectangular coordinates. Due toreadjustment of the survey control networks and to thechange of ellipsoid, the latitude and longitude alsochange slightly from one datum to the other.
These changes are given in the same order as the entriesin the 1927 table, except that only the changes areshown. All parameters not listed remain as before,except for the different ellipsoid and datum. Because allcoordinates at the origin have been changed, and becausethey vary considerably, the coordinates are presented inthe body of the table rather than as footnotes. Somoa isnot being changed to the new datum.
Table 6-2.—U.S. State plane coordinate systems – 1983 datum
[L indicates Lambert Conformal Conic]
Area Projection Zones
California L 6
Montana L 1
Nebraska L 1
Puerto Rico and Virgin Islands L 1
South Carolina L 1
Wyoming UnresolvedTransverse Mercator projection
Coordinates of origin (meters)
Zone x y Other Changes
AlabamaEastWest
200,000600,000
00
Alaska, 2-9 500,000 0
Arizona, all 213,360 0 Origin in Intl. feet1
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Table 6-2.—U.S. State plane coordinate systems – 1983 datum(continued)
Transverse Mercator projection (continued)
Coordinates of origin (meters)
Zone x y Other Changes
Delaware 200,000 0
FloridaEast, West 200,000 0
GeorgiaEastWest
200,000700,000
00
Hawaii, all 500,000 0
IdahoEastCentralWest
200,000500,000800,000
000
IllinoisEastWest
300,000700,000
00
IndianaEastWest
100,000900,000
250,000250,000
MaineEastWest
300,000900,000
00
Lat. of origin 43E40' N.
MississippiEast
West
300,000
700,000
0
0
Scale reduction 1:20,000,Lat. of origin 29E30' N.Scale reduction 1:20,000,Lat. of origin 29E30' N.
MissouriEastCentralWest
250,000500,000850,000
000
NevadaEastCentralWest
200,000500,000800,000
8,000,0006,000,0004,000,000
New Hampshire 300,000 0
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Table 6-2.—U.S. State plane coordinate systems – 1983 datum(continued)
Transverse Mercator projection (continued)
Coordinates of origin (meters)
Zone x y Other Changes
New Jersey 150,000 0 Central meridian 74E30'W.Scale reduction 1:10,000.
New MexicoEastCentralWest
165,000500,000830,000
000
New YorkEast All parameters identical with above New Jersey zone.CentralWest
250,000350,000
00
Rhode Island 100,000 0
Vermont 500,000 0
Wyoming Unresolved
Lambert Conformal Conic projection
Coordinates of origin (meters)
Zone x y Other Changes
Alaska, 10 1,000,000 0
ArkansasNorth 400,000 0South 400,000 400,000
California1-6 2,000,000 500,000
Zone 7 deleted.
Colorado, all 914,401.8289 304,800.6096
Connecticut 304,800.6096 152,400.3048
Florida, North 600,000 0Iowa
North 1,500,000 1,000,000South 500,000 0
KansasNorth 400,000 0South 400,000 400,000
KentuckyNorth 500,000 0South 500,000 500,000
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Table 6-2.—U.S. State plane coordinate systems – 1983 datum(continued)
Lambert Conformal Conic projection (continued)
Coordinates of origin (meters)
Zone x y Other Changes
KansasNorth 400,000 0South 400,000 400,000
KentuckyNorth 500,000 0South 500,000 500,000
LouisianaNorthSouthOffshore
1,000,0001,000,0001,000,000
000
Lat. of origin 30E30' N.Lat. of origin 28E30' N.Lat of origin 25E30' N.
Maryland 400,000 0 Lat. of origin 37E40' N.
MassachusettsMainland 200,000 750,000Island 500,000 0
MichiganGRS 80 ellipsoid usedwithout alteration.
NorthCentralSouth
8,000,0006,000,0004,000,000
000
Long. of origin 84E22'W.Long. of origin 84E22'W.
Minnesota, all 800,000 100,000
Montana(single zone)
600,000 0 Standard parallels, 45E00'and 49E00' N.Long. of origin 109E30' W.Lat. of origin 44E15' N.
Nebraska(single zone)
500,000 0 Standard parallels, 40E00'and 43E00' N.Long. of origin 100E00' W.Lat. of origin 39E50' N.
New YorkLong Island 300,000 0 Lat. of origin 40E10' N.
North Carolina 609,621.22 0
North Dakota, all 600,000 0
Ohio, all 600,000 0
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Table 6-2.—U.S. State plane coordinate systems – 1983 datum(continued)
Lambert Conformal Conic projection (continued)
Coordinates of origin (meters)
Zone x y Other Changes
Oklahoma, all 600,000 0
OregonNorthSouth
2,500,0001,500,000
00
Pennsylvania, all 600,000 0
Puerto Rico andVirgin Islands
200,000 200,000 (Two previous zonesidentical except for x and yor origin.)
South Carolina(single zone)
609,600 0 Standard parallels, 32E30'and 34E50' N.Long. of origin 81E00' W.Lat. of origin 31E50' N.
South Dakota, all 600,000 0
Tennessee 600,000 0 Lat. of origin 34E20' N.
TexasNorthNorth CentralCentralSouth CentralSouth
200,000600,000700,000600,000300,000
1,000,0002,000,0003,000,0004,000,0005,000,000
Central meridian 98E30' W.
UtahNorthCentralSouth
500,000500,000500,000
1,000,0002,000,0003,000,000
VirginiaNorthSouth
3,500,0003,500,000
2,000,0001,000,000
Washington, all 500,000 0
West Virginia, all 600,000 0
Wisconsin, all 600,000 0
NOTE: All these systems are based on the GRS 80 ellipsoid. 1 For the International foot, 1 in = 2.54 cm, or 1 ft = 30.48 cm.
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Units
English or metric units should be selected as early in theproject as possible. Conversions are possible, butconvert-ing a large 1-foot contour map to meters is notrivial matter.
Remember that when using several sources of locationdata, the reference datum must be known. Systematicdifferences in location data are generally due to mixingdatums.
Specific Nomenclature and Definitions
Establish a uniform nomenclature system with writtendefinitions for rock types, map units, and map symbolsused. The American Geologic Institute Glossary ofGeology [2] is the standard for geologic terms exceptwhere Reclamation has established definitions for itsown needs. These definitions and nomenclature arediscussed in chapters 2 through 5.
Field Equipment and Techniques
General geologic mapping equipment and techniques arediscussed in field geology manuals such as Lahee (1961)[3] and Compton (1985) [4]. Refer to these texts for dis-cussions of suggested field equipment and generalgeologic mapping techniques.
Use of Computers
Computers are used during a mapping program in fourbasic ways: (1) to process and analyze voluminousnumerical data (e.g., joint data), (2) as a tool in theanalysis of basic geologic data (e.g., construction of pre-liminary or final plan and section views which
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incorporate previously entered geologic data),(3) Computer Aided Drafting and Design (CADD) ofsection and plan views, and (4) in modeling geologicconditions. How computers will be used in the reduction,analysis, and drafting of the geologic data generatedduring a mapping program needs to be decided earlybecause records of field data will depend on whetherdata are to be stored in digital format and restructuringthese data at a later date is costly, time consuming, andintroduces transcription errors.
Right-of-Way
Right-of-way is needed for any mapping of non-Reclamation land and should be obtained early toprevent work delays. Although "walk on" permissionusually is obtained easily, permission for trenching anddrilling may take several months, especially ifarcheological or environmental assessment is necessary.
Records
Systematic methods of recording field observations,traverse data, outcrop data, and trench logs areimportant. Suggested sample field book formats areshown under each section below dealing with specificmapping procedures, but any format should allow clearrepresentation of the field data.
Geologic Considerations
The following are some key items that should beevaluated during a mapping project. The degree ofimportance varies with the project but the factors arecommon to most.
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Lithology.—Differentiation between the various geo-logic deposits and lithologies in a study area is basic togeologic mapping. However, an engineering geologist ismore concerned with the engineering characteristics ofthe unit than with its geologic definition, and these char-acteristics should be the controlling factor in how geo-logic units are subdivided. For some engineeringgeologic purposes, it may be reasonable to consolidategeologic units with similar engineering properties into asingle engineering geologic map unit. Depending on theneeds of the project, lithologic subunits may be definedjointly between the engineers and the geologists workingon the job.
After the basic geologic subdivisions for a mapping jobhave been agreed upon, detailed descriptions of eachsubunit should be compiled and mapping symbolsselected. Map unit definitions usually will applyspecifically to the job or project area and normally will bemodified as additional data are collected. Map symbolsfall into several categories. American GeologicalInstitute data sheets have a comprehensive tabulation ofsymbols.
Geologic contacts.—Two different line types normallyare used on geologic maps to denote the precision andaccuracy of geologic contacts. These are solid and broken(dashed or dotted) lines. Solid lines usually are usedwhere exposures are excellent, such as a cleanedfoundation or an area with nearly continuous outcrops.Solid lines indicate that the contacts are located with aprescribed degree of accuracy. Broken contacts are usedwhen unsure of the accurate location of the contact, i.e.,when the contact is covered by thin slopewash deposits(dashed line) or where the contact is buried by deepsurficial deposits (dotted line). Confidence levels,expressed in feet or meters, for both types of contactsshould be stated clearly in the definition of the contact
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line. The mapper should keep in mind the type of geo-logic data being compiled and use the appropriate line.
Discontinuities.—Discontinuities separate geologicalmaterials into discrete blocks that can control thestability and bearing capacity of a foundation or slope.Intersecting discontinuities in cut slopes can formunstable wedges. Because of the destabilizing orweakening effects, mapping and adequately describingdiscontinuities is critical in engineering geology studies.The various types of discontinuities and the terminologyfor describing their engineering properties are discussedin chapter 5.
Weathering and alteration.—The mechanical andchemical alteration of geological materials can signifi-cantly affect stability and bearing strengths. Adequatelydetermining weathering depths, extent of alteredmaterials and the engineering properties of theseweathered and altered materials is critical inengineering geologic mapping. Refer to chapter 4 fordefinitions of weathering and alteration descriptors.
Water.—The location and amount of groundwater to beexpected in an excavation and how it can be controlled iscritical to the overall success of a project.
Geomorphology.—Study of landforms is often the keyto interpreting the geologic history, structure, lithology,and materials at a site. Exploration programs can bebetter designed and implemented using landforms as abasis. The geomorphic history is important indetermining the relative age of faults.
Vegetation indicators.—Differences in vegetationtypes and patterns can provide indirect data onlithologies, dis-continuities, weathering, groundwater,
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and mineralization. The water holding capacity of soildeveloped on one rock (e.g., shale) may differ con-siderably from the water holding capacity of soildeveloped on another type of rock (e.g., sandstone);consequently, the types of vegetation that grow in thesesoils can vary considerably. Minerals present in theparent rock may affect soil chemistry and may limitvegetation to types tolerant of highly acidic or alkalinesoils or high concentrations of trace elements.Vegetation seeking groundwater moving up major jointsand faults will form vegetation lineations that are highlyvisible on aerial photographs, particularly color infraredphoto-graphs. In most locations, local conditions have tobe assessed to use vegetative indicators effectively.
Cultural features (manmade).—Cultural features,such as water, gas or oil wells, road cuts or foundationexcavations, can provide surface and subsurface dataand should be reviewed early in the mapping project.When data collection through trenching and core drillingprograms is considered, buried utility lines (water, gas,electrical, sewage, or specialized lines) can be hazardousor embarrassing when broken. Usually the utility orowners will locate their lines.
Field checking.—Field checking by both mapper andindependent reviewer is a critical part of the mappingprocess. Field checking after a map is complete allowsthe mapper to check the interpretations at a givenlocation with the geologic concepts developed on the mapas a whole. Field checking by the independent reviewerensures that the basic field data are correct and conformto project standards. Periodic field checking of pre-viously mapped areas can be useful as the mapper'sconcept of the site geology changes with the addition ofnew surface and subsurface data.
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Site Mapping
Engineering geologic mapping has two phases—mappingprior to construction and mapping during construction.In general, the following guidelines are for: (1) generalmapping requirements, (2) suggested equipment, (3) spe-cific preparations needed for the job, (4) type of documen-tation needed, and (5) special considerations that themapping may require. General
Detailed site geologic mapping studies generally are donefor most structures or sites. Site mapping requirementsare controlled by numerous factors, the most importantof which are the type and size of structure to be built orrehabilitated or site to be remediated, the phase of study(planning through operation and maintenance), and thespecific design needs.
Site mapping studies for major engineering featuresshould be performed within an approximate 5-mile (8-km) radius of the feature, with smaller areas mapped forless critical structures. These studies consist of detailedmapping and a study of the immediate site, with moregeneralized studies of the surrounding area. Thisapproach allows an integration of the detailed sitegeology with the regional geology. The overall process ofsite mapping is a progression from preliminary, highlyinterpretive concepts based on limited data to finalconcepts based on detailed, reasonably well-defined dataand interpretation. This progression builds on each pre-vious step using more detailed methods of data collectionto acquire better defined geologic information. Typically,site mapping is performed in two phases:(1) preliminary surface geologic mapping and (2) detailedsurface geologic mapping. All site mapping studies begin
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with preparation of a preliminary surface geologic mapwhich delineates surficial deposits and existing bedrockexposures. The preliminary surface geologic map is thenused to select sites for dozer trenches, backhoe trenches,and drill holes. Surface geologic maps are then re-interpreted based on the detailed surface and subsurfacedata. If required, detailed subsurface geologic data arealso obtained from exploratory shafts and adits.
Suggested Equipment
The following list of basic equipment should meet mostneeds. Not all listed equipment is necessary for everyproject, but a Brunton Compass, geologist’s pick, (2-pound hammer may be necessary for rock sampling),maps, map board, aerial photographs, notebook, scale,tape measure, protractor, knife, hand lens, various pensand pencils, and a GPS should meet most needs.
Preparation
Whether a site mapping program is completed in onefield season or over several years, the overall projectschedule and budget are critical. A critical assessmentshould be made of the time available for the mappingprogram, the skills and availability of personnel toaccomplish the work, weather conditions, and budgetconstraints.
Documentation
Site data are documented on drawings (and associatednotes) generated during the study. The drawings fallinto two general categories—working drawings and finaldrawings. Working drawings serve as tools to evaluateand analyze data as it is collected and to define areaswhere additional data are needed. Analysis of data in athree-dimensional format is the only way the geologist
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can understand the site geology. Drawings should begenerated early in the study and continuously updatedas the work progresses. These drawings are used forpre-liminary data transmittals. Scales used for workingdrawings may permit more detailed descriptions andcollection of data that are not as significant to the finaldrawings. Final drawings are generated late in themapping program, after the basic geology is wellunderstood. Many times new maps and cross sectionsare generated to illustrate specific data that were notavailable or well understood when the working drawingswere made. Final drawings serve as a record of theinvestigations for special studies, specifications, ortechnical record reports.
Preliminary Surface Geologic Mapping.—Thepurpose of preliminary surface geologic mapping is todefine the major geologic units and structures in the sitearea and the general engineering properties of the units.Suggested basic geologic maps are a regional recon-naissance map at scales between 1 inch = 2,000 feet and1 inch = 5,280 feet (1:24,000 to 1:62,500), and a sitegeology map at scales between 1 inch = 20 feet and 1inch = 1,000 feet (1:250 to 1:12,000). Scale selectiondepends on the size of the engineered structure and thecomplexity of the geology. Maps of smaller areas may begenerated at scales larger than the base map toillustrate critical conditions. Cross sections should bemade at a natural scale (equal horizontal and vertical) asthe base maps unless specific data are better illustratedat an exaggerated scale. Exaggerated scale crosssections are generally not suited for geologic analysisbecause the distortion makes projection andinterpretation of geologic data difficult.
Initial studies generally are a reconnaissance-level effort,and the time available to do the work usually is limited.
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Initially, previous geologic studies in the general sitearea are used. These studies should be reviewed andfield checked for adequacy and new data added. Initialbase maps usually are generated from existingtopographic maps, but because most readily availabletopography is unsuitable for detailed studies, sitetopography at a suitable scale should be obtained ifpossible. Existing aerial photographs can be used astemporary base maps if topographic maps are notavailable. Sketch maps and Brunton/tape surveys orGPS location of surface geologic data can be done ifsurvey accuracy or control is not available or necessary.Good notes and records of outcrop locations and data areimportant to minimize re-examination of previouslymapped areas. Aerial photo-graphy is useful at thisstage in the investigation, as photos can be studied inthe office for additional data. Only after reasonablyaccurate surface geology maps have been compiled canother investigative techniques, such as trenching andcore drilling, be used to full advantage. For some levelsof study, this phase may be all that is required.
Detailed Surface Geologic Mapping.— The purposeof detailed surface geologic mapping is to define theregional geology and site geology in sufficient detail sogeologic questions critical to the structure can beanswered and addressed. Specific geologic featurescritical to this assessment are identified and studied,and detailed descriptions of the engineering properties ofthe site geologic units are compiled. Projectnomenclature should be systematized and standarddefinitions used. Suggested basic geologic maps aresimilar to those for preliminary studies, althoughdrawing scales may be changed based on the results ofthe initial mapping program. Maps of smaller areas maybe generated to illustrate critical data at scales largerthan the base map.
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The preliminary surface geology maps are used to selectsites for dozer trenches, backhoe trenches, and drill coreholes. As the surface geology is better defined, drill holelocations can be selected to help clarify multiple geologicproblems. Detailed topography of the study site shouldbe obtained, if not obtained during the initialinvestigations. Data collected during the preliminaryinvestigations should be transferred to the new basemaps, if possible, to save drafting time. Field mappingcontrol is provided primarily by the detailed topographicmaps and/or GPS, supplemented by survey control ifavailable or Brunton/ tape survey. If not, large scaleaerial photographs of a site area flown to obtain detailedtopography are useful in geologic mapping.
Dozer Trench Mapping
General
Dozer trenches are cut to expose rock or unconsolidatedmaterials below the surface and major surface creep.Walls normally should be excavated vertically, free ofnarrow benches and loose debris. Upon completion ofexcavation, floors must be cleaned below any depth ofripping, loose rubble should be removed, and a newsurface exposed. Structures such as contacts and shearzones must be traceable from wall into floor for optimumdetermination of their nature and attitude. Thegeologist is responsible to ensure the dozer operatorproduces a safe finished trench that meets Reclamationand Occupational Safety and Health Administration(OSHA) safety standards. If livestock are present,fencing of the trench with four strands of barbed wiremay be required. After trench logging is completed,decide whether to leave the trench open or to backfill. Atsites with complex geology, it is desirable to leave the
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trench open for reinterpretation of the trench in light ofnewly acquired data. Backfilling of the dozer trench maybe necessary where an open trench would be a safetyhazard. Generally, all trenches should be backfilled andcom-pacted prior to abandonment.
Suggested Equipment
Additional equipment needed may include hard hat,scraper or putty knife, square-nosed shovel, plasticflagging, nails, wooden stakes, surveyors chain or tapemeasure (feet or meters) and log book. Use putty knife,shovel, and whisk broom for cleaning trench exposuresand a Brunton tripod for more accurate trench bearings.
Preparation
Prior to working in a dozer trench, the geologist shouldinspect the excavation trench walls for failure planes(obvious or incipient) or loose materials. These should beremoved before mapping starts. An examination of thewhole trench should be made at the start of each workperiod. A baseline should be laid out along the toe of thetrench wall or at the top of the excavation. Becausedozer trenches often are not straight, the trench shouldbe divided into a series of straight segments withstations established at each point where the trenchchanges direction. Each station should be marked by astake, tied with flagging, and marked with the trenchnumber and station letter (e.g., DT-12A). Flaggingstrips should be nailed to the wall approximately 6 feet(2 meters [m]) vertically above or below the station foranother reference point in case minor sloughing buries ordislodges the stake.
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Documentation
The scale and format selected for logging a backhoetrench depends on the type of data needed and theamount of detail to be illustrated. Typical dozer trenchlog scales are between 1 inch (in) = 5 feet (ft) (1:100) and1 in = 10 ft (1 : 200), but scales of 1 in = 1 ft (1: 50) maybe required in critical areas to adequately showstructural and stratigraphic details. If trench geology isnot complex, record trench logs, along with names of thefield party and date in a field book. Determine andrecord the bearing, slope distance, and slope anglebetween each station. Survey the coordinates andelevations of each station. Orient the log book so thesketch and description may be viewed together (seefigure 6-2). Sketch the walls and floors across the toppage of the open log book. Mark the baseline at 5-foot(1.5-m) intervals and draw a single "hinge line”; wallabove, floor below. Determine the vertical heights of thetrench walls at each station and between stations, if theprofile or thickness of surficial materials changesbetween stations.
Sketches should be accurate and illustrate the fieldrelationship of soil and geologic units and structures.Use nails and flagging strips to mark obscure contacts orother features for ready reference during logging.Designate geologic units by name and symbol. Accuratelyplot the attitude of contacts, bedding, foliation orcleavage, faults, shear zones, and joints where they aredetermined using standard symbols, and write adescription. If attitudes are determined from the wall,they may be projected along strike into the floor, if nochange is apparent in the floor. Note and show thebedding or foliation wherever relationships are complexand differ from the recorded attitude (i.e., where surfacecreep, drag folds, or disturbed zones are exposed in thewall). Record unit attitudes that may have beenaffected
FIE
LD
MA
NU
AL
160
Figure 6-2.—Sample trench log.
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by surface creep or slumping. Written descriptions ofsoil and rock units and structural zones should berestricted to the page below the sketch and should notbe written over the sketch. Main heading for writtendescriptions are restricted to mappable geologic units.Intervals are noted where the contacts intersect thebaseline. Indent subheadings within text to describelithologic or structural variations within the mappableunit. An example of heading order is as follows:
DT-58, Sta. B-C, Distance - 27.5', Bearing - S. 45EW., Slope + 2 22.5-50.0': Metasediments (description) 39.9-41.0': Chlorite Schist B (description) 47.5-49.0': Talc Schist (description) 48.2-48.4': Shear Zone (description)
Stratigraphic units should be colored to complete the log.Photograph the trench to complement the log or to recordspecific details within the trench.
Backhoe Trench Mapping
General
Backhoe trenches are excavated to expose rock orunconsolidated materials below surficial deposits andmajor surface creep. Generally, backhoe trenches areexcavated at sites which must be returned to near-original conditions and where dozer trenching wouldproduce unacceptable damage. Backhoe trenches oftenare excavated in the floor of an existing dozer trench todeepen the excavation. Walls should be excavatedvertically and free of narrow benches and loose debris.In most cases, the trench should be about 3 to 3-1/2 feetwide (1 m) (width of standard backhoe bucket), 10 to 12
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feet (3 to 3.6 m) deep, and slope at one end for easyaccess. Upon excavation completion, hydraulic trenchshores are placed and pressurized or wooden shoresconstructed to support the trench walls. Shoreconstruction and spacing must meet OSHA standardsand standards outlined in Reclamation's ConstructionSafety and Health Standards manual. At no time shouldpersonnel enter unshored portions of the trench over5 feet deep. The geologist who oversees the excavationof the backhoe trench is respon-sible for the constructionof a safe, stable trench.
After trench logging is completed, decide whether toleave the trench open or to backfill. At sites withcomplex geology, leave the trench open, if possible, asthis allows reinterpretation of the trench in light ofnewly acquired data. However, backhoe trenches areprone to sloughing with time, even when supported, andbackfilling of the trench may be necessary for safetyreasons. The coordi-nates and elevation of each end ofthe backhoe trench should be surveyed prior tobackfilling.
Suggested Equipment
Standard field equipment is used during backhoe trenchmapping. Additional equipment may include a hard hat,large knife, flat-blade pick or army trenching tool toclean off trench walls, putty knife, whisk broom, nails,flagging, twine, small string level, 100-foot (30-m) longsurveyor's chain or tape, and map board or log book. Thetype of backhoe needed depends on how consolidated orcemented the material is, site accessibility, and depth tobe excavated. Most of the larger, rubber-tired backhoesare suitable for excavation of typical trenches, but wellconsolidated or cemented material, steep site terrain, ortrench depths over about 12 feet (3.6 m) may require alarger track-mounted hydraulic excavator.
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Preparation
Each day prior to working in a backhoe trench, thetrench along both sides and the trench walls should beexamined for incipient fractures or loose materials,particularly within the surficial materials. These loosematerials should be removed before work starts.Hydraulic trench shores should be checked visually forleakage and for loss of pressure by pushing on them witha foot. Re-pressure any loose shores and replace leakingshores. The stability of each shore should be checkedbefore the mapper's weight is put on it, particularly ifthe shore is to be used to examine the upper trench wallor to climb out of the trench.
A backhoe trench must be cleaned prior to logging.During excavation, the backhoe bucket may smear clayand silt along the walls, obscuring structural and strati-graphic relationships. This smeared zone may be any-where from a fraction of an inch thick to several inchesthick, depending on the amount of fines and moisture inthe material excavated. The smeared material can beremoved by chipping or scraping with a large knife, flat-bladed pick, or army trenching tool. If the trench isexcavated in reasonably consolidated material and thetrench is free draining, a high pressure water and/or airjet will remove this material. Both walls should be spotcleaned and examined prior to major cleaning to deter-mine which wall exposes the best geologic data. Usuallyonly one wall is completely cleaned; the other wall is spotcleaned during trench logging to expose another view ofcritical features or relationships. After a wall is cleaned,a horizontal base line is established. The baseline is runat about eye level and constructed by stringing twinebetween nails driven into the cleaned trench wall. Thetwine can be leveled using a small string level (availablein most hardware stores) prior to driving nails. Whenthe baseline becomes either too high or too low for
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comfort-able measurements, a vertical offset of the stringline is made and the baseline continued at the newhorizon. In complex, critical areas where accuratelylocated contacts are needed, a string grid with horizontaland vertical elements can be constructed off the baselineto assist in mapping.
Documentation
The scale and format selected for logging a backhoetrench depends on the type of data needed and theamount of detail to be illustrated. Typical backhoetrench log scales are between 1 in = 5 ft (1:100) and 1 in= 10 ft (1 : 200), but scales of 1 in = 1 ft (1 : 50) may berequired in critical areas to adequately show structuraland stratigraphic details. If trench geology is notcomplex, a notebook is suggested. The log book shouldbe oriented so the sketch and description may be viewedtogether. The names of the field party, date, trenchnumber, location, and other pertinent data should berecorded. If trench geology is complex and a larger scaleis desired, cut sheets of grid paper attached to a mapboard may be used. These sheets are usually redraftedafter trench logging is completed. If the backhoe trenchis wet or wall material is sloughing down onto the mapboard, a blank grid sheet can be taped to the map boardand overlain by sheets of mylar. Trench data sketchedonto the mylar will not be smeared as easily, and thesheets can be erased without tearing. Prints of thesheets can be made for use in preliminary datatransmittal or as check prints for field checking. Figure6-3 shows a completed trench log.
Because the log sheets are separated easily, each sheetshould be marked with the names of the field party,date, trench number, location, and other pertinent data.
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165 Figure 6-3.—Sample completed trench log.
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Begin trench logging by recording the trench bearing.Begin at one end of the trench; place a surveyors chainor tape along the horizontal base line string. Verticaldistance of the trench wall above and below the base lineshould be measured every 10 feet (3 m) or so and thetrench outlines sketched. Sketches must be as accurateas possible to illustrate the field relationships of soil,geologic units, and structures. Use flagging to markobscure contacts or other features for easier logging.
Intervals for the various geologic units and features areto be noted where the contacts intersect the baseline.Contacts above and below the baseline are located by twomeasurements—the vertical distance from the baselineand baseline distance—and sketched onto the log.Geologic units should be designated by name or symbol.Symbols to illustrate the attitude of contacts, bedding,fol-iation or cleavage, faults, shear zones, and jointsshould be drawn at the point where determined and alsore-corded in the written description. Bedding or foliationshould be depicted and noted wherever relationships arecomplex and differ from the recorded attitude (i.e., wheresurface creep, drag folds, or disturbed zones are exposedin the wall). Attitudes on units that may have beenaffected by surface creep or slumping should also be sonoted.
Written descriptions of soil and rock units and structuralzones should be restricted to the area below the sketch.Main headings for written descriptions are restricted tomappable geologic units. Description format is similarto that discussed for dozer trench mapping. After trenchlogging is completed, geologic units should be colored tocomplete the log and the trench field checked. Photo-graph the trench to complement the trench log or torecord specific details within the trench. The limitedspace and poor lighting conditions in a backhoe trench
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many times make it difficult to obtain satisfactoryphotos. Generally, cameras capable of closeup focusingand loaded with fast film work best. Photographs takenwhile standing at the top of the trench generally aremarginal because of poor lighting and perspective. Theends of the trench should be located by GPS or survey.
Construction Geologic Mapping
Geologic mapping during construction is to: (1) identifyand delineate potential or actual construction-relatedneeds and problems; (2) verify and better define geologicinterpretations made during design studies, particularlyfor critical geologic features and properties;(3) determine if the geologic conditions are as interpretedduring the design phase and ensure that the actualconditions revealed are as interpreted. If thoseconditions are not as interpreted, design modificationsmay be required; and (4) provide a record of as-builtconditions in the event of litigation or operationalproblems.
To obtain meaningful data for mapping during con-struction, cooperation and coordination between theContractor and the construction staff is required. Thefield geologist prioritizes mapping; and when the specificarea is ready for mapping and approval, the staff andsurveyors (if required) should accomplish the work asquickly as possible. Photographs should be taken usingappropriate photographic equipment. All photographsshould be captioned and dated.
Possible safety hazards that might occur during mappingshould be evaluated, and appropriate precautions shouldbe taken.
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Large Excavation Mapping
General
Construction considerations prepared before constructionbegins should contain guidelines for the mapping of spe-cific features. The scope and detail of mapping requiredat each portion of the site should be determined andsuitable mapping scales determined. Suggested scalesfor detailed foundation mapping are 1 in = 5 ft to 1 in =50 ft (1:50 to 1: 600), generalized foundation invert mapscale 1 in = 20 ft to 1 in = 100 ft (1:20 to 1:1,000).Detailed, as-built foundation geology maps are used infinal design modification, as a final record, and for use inpossible future operation and maintenance problems.Mapping can be done on detailed topographic base mapsgenerated from survey control, GPS, or plane table.Preferably, geology points are flagged and surveyed by asurvey crew. Terrestrial photography, photogrammetry,and GPS can also be used to supplement mapping.Detailed photo-graphy of the entire foundation isimportant for inclusion in the final construction geologyreport and as a part of the construction record. Usestandard nomenclature and symbols both on maps andphotographs, but be consistent with those used in earlierstudies and specifications. Use a systematic method ofcollecting mapping data, then compile these data into auseful and accurate geologic map.
Detailed, as-built geology maps of cutslopes are requiredin delineating and solving major slope stability problemsand in selecting general slope support systems. Recom-mended scale selection for detailed cut-slope geologymaps are 1 inch = 10 feet to 1 inch = 50 feet (1:100 to1:600), generalized cutslope geology maps use a scale1 inch = 20 feet to 1 inch = 100 feet (1:200 to 1:1,000).Generally, maps are on detailed topographic base maps
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generated from survey control. Geologic points may beflagged for survey by survey crews. Detailedphotographs of the slopes are important.
Steep Slope Mapping
General
Define the purpose and goal for mapping and researchthe stratigraphy and structural geology prior to starting.Select scaling and safety equipment for specific areas.
Preparation
Special training is required for scaling. While scalingand mapping, a pocket tape recorder and camera areuseful for documentation.
Suggested Equipment
Use the appropriate scaling equipment and systems.Standard mapping equipment needs to be reviewed andmodified for scaling operations.
Documentation
Establish ground control for mapping including ter-restrial photo mapping. Data collected while scalingshould be based on the purpose of mapping and detailrequired. Establish general map controls such as gridcontrols.
Special Considerations
Select specific portions of an exposure to be mapped.
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Canal and Pipeline Mapping
General
In reconnaissance investigations, surface geologic map-ping is used to determine the most feasible alignment,which may be representative of the geologic conditions tobe encountered, the lining requirements, andconstruction materials available. Design datainvestigations along canal alignments must be detailedenough to determine the final alignment and allassociated requirements for specifications andconstruction.
Preconstruction investigations for canals and pipelinesare less detailed because of the long distances involved.Consequently, geologic construction mapping isnecessary to verify preconstruction assumptions,document changes from original assumptions, andprovide data for potential design changes or claimanalyses.
Preparation
General field mapping requirements.
Documentation
Pertinent geologic data that should be shown on the basemaps include: soil and geologic units, all natural andmanmade exposures, geologic structures, springs andseepage, surface channels, and potentially unstableareas. Where appropriate, photographs with overlays ordetailed site-specific drawings should be used to showsurface conditions in relation to the canal prism orassociated canal structures. Base maps should be planstrip topo-graphy or orthophotography with scales of 1 in= 20 ft (1:400) to 1 in = 100 ft (1:2,000) with associatedtopographic profiles.
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Underground Geologic Mapping
General
This is a general guide for recording tunnel geology anddescribes mapping requirements and procedures. Thisguide and the field geologist's judgement and experienceshould permit development of geologic data whichadequately document geologic factors that are significantto design, construction, and stability of tunnels andshafts. Some of the necessary data may be obtainedfrom other project personnel such as engineers,surveyors, and inspectors. The following items are ofprimary impor-tance during the construction orexploration for a wide range of tunnel and shaft types,excavation problems, geologic conditions, and contractadministration require-ments. The data recorded andthe emphasis given each item should be determined foreach specific tunnel. (Note: references to tunnels applyequally to shafts)
Three principal objectives are to:
• Acquire progressive, timely mapping of allsignificant geologic features as exposed during theadvance of the tunnel or shaft. These initial fea-tures are important for subsequent identification ofchanges which may take place, such as water flow,rock slaking, or support behavior, as the headingprogresses and before lining or other completionmeasures are undertaken.
• Facilitate periodic transmittal of these data in pre-liminary form to the office so that conditions beingencountered and their effect on the excavation canbe used in immediate evaluation of currentconstruction activities and anticipation of futureexcavation conditions.
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• Assure that a systematic, clear, record of geologicconditions is compiled for design reviews and use bythe project and contractor. These data should beincluded in the final construction geology report.These records may prove invaluable during subse-quent operation and maintenance and in theplanning and design of future tunnels and shafts. Ifgeologically related problems occur, these data willbe essential in evaluating the conditions.
Accuracy is essential, and consistency of data shown ontunnel maps is vital. If the maps are used in contractclaim negotiations or in litigation, even a few errors orinconsistencies may compromise the entire map.
The preparation of an adequate tunnel or shaft geologicmap requires a careful study of geologic structure, lith-ology, mineralogy, groundwater, and their effects on rockquality and behavior, tunneling methods, stability, andsupport. The preparation of a tunnel or shaft geologicmap is a geologic mapping process; geologic data shouldbe recorded directly on the map while making the obser-vations and not described in notes for subsequentdrafting in the office. An appropriately scaled tunnel orshaft mapping form, prepared prior to starting themapping, is essential to systematic data collection. One-matte-sided mylar tunnel forms should be used in wetexcavations and are recommended as a standard for alltunnel and shaft mapping. Figures 6-4 and 6-5 areexamples of field mapping forms. The use of mylars inall tunnels facili-tates copying and immediate use. Theextent or amount of mapping detail for a specific tunnelor shaft will depend on the driving method, geologicconditions, and design considerations. For example,tunnel face (head-ing) maps can be obtained under mostconditions when conventional excavation (drill/blast)methods are used but are difficult to obtain in tunnelsexcavated by tunnel
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173 Figure 6-4.—Tunnel mapping form with key alphanumeric descriptors and mapping data.
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Figure 6-5.—Tunnel mapping form with blocks for title and geologic data.
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boring machine (TBM). TBM excavated tunnels may bemore difficult to map than conventionally excavatedtunnels, depending on the level of detail required,machine configuration, and the support method.However, the key rock characteristics relative to tunnelstability must be mapped. In tunnels where shotcrete orprecast segments are used for support, detailed mappingmay be impossible; this does not cancel the requirementfor mapping and recording of important data on thegeologic conditions. The geologist must obtain requireddata with the available resources and under the specificconditions. These guidelines apply to all tunnel or shaftexcavations regardless of whether the mapping isperformed during project planning, design data acqui-sition, or construction.
Safety
Underground construction activities are inherently morehazardous than surface construction. Before workingunderground, the specific safety requirements for theparticular tunnel should be determined. Self-rescuertraining commonly is required, and the safety require-ments as described in the Reclamation Safety and HealthStandards [5] should be reviewed. Additional training oradditional requirements may exist under specialcircumstances such as gassy conditions. Beforebeginning work, a familiarization tour of the work site(including the underground workings) should be madewith project personnel, such as an inspector, intimatelyfamiliar with the job. Also, assume that every piece ofequipment and worker is out to get you; you shouldalways maintain an awareness of what the workers andequipment are doing around you.
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General Preparation
Tunnel construction is essentially a linear activity. Allaccess, equipment haulage, and work activities takeplace in a line. The mapping process should be plannedsuch that a minimum number of trips to the heading arerequired and a minimum amount of time is spent at theheading. Geologic mapping can usually be integratedinto an optimum part of the construction cycle.Unnecessarily spending time at the heading is not onlyinefficient but can interfere with the constructionprocess by adding to an already congested situation.
Available geologic data should be reviewed andestablished nomenclature used as appropriate. Geologicfeatures described in the available literature should bespecifically investigated while mapping, especially thosedescribed in specifications documents. Forms should bedesigned to expedite the work as much as possible(figures 6-4 and 6-5), required mapping equipment mustbe available, and the construction cycle should be ana-lyzed to determine the best and safest time to map.Tunnel map sheets should be a convenient size such as8.5 x 11 inches (A4) or 11 x 18 inches (A3). This permits100 feet (30 m) of tunnel on a scale of 1 inch = 10 feet(1:200) with sufficient space for concise explanations anda title block. The geology should be mapped in thetunnel directly on the matt side of mylar film. This map,developed in the tunnel, can be edited and copied forquick transmittal to the office. The value of current datacannot be overemphasized. Except under very specialconditions, the recording of geologic data in a notebookwithout mapping for subsequent preparation of a graphictunnel map is unacceptable. Without a graphicrepresen-tation during data acquisition, theinterrelationships of geologic data cannot be properlyevaluated, and data are missed or errors are introduced.Some items listed above will not apply to every tunnel,
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and some items may be shown more appropriately in asummary tunnel map (figure 6-6). This map presents asummary of essential engineering and geologicrelationships. Plotting engi-neering and geologic data asa time line permits direct comparison of geologicconditions, supports installed, overbreak, excavationrate, etc., for correlation. Sum-mary sheet scales mayrange from 1 inch = 10 to 100 feet (1:100 to 1:1,000)depending on amount of data and complexity of thegeology. Ongoing maintenance of these data avoidsexcessive compilation time after construction iscompleted. A summary tunnel map is required ontunnels for construction records.
When several individuals are mapping and/or contractrequirements hinge on geologic data, e.g., payment basedon ground classification, a project or specific mappingmanual may be necessary. A manual provides an easyreference for data requirements and format, reducesinconsistency between geologists, and sets a specificmapping standard.
Excavation Configuration
Conventionally excavated tunnels are usually a modifiedhorseshoe shape. Departures from this shape areusually for a special configuration or when groundconditions dictate a circular shape for optimizing support effective-ness. Machine-excavated tunnels are round if boredunless a road-header type machine is used. Road-headerexcavated tunnels are usually horseshoe shaped for con-struction convenience. Shafts are almost always roundfor optimizing support effectiveness and because mostare drilled or bored either from the surface or raise-boredfrom the bottom. Exploratory shafts may be sunkconven-tionally if shallow. Whatever the shape, the mapformat should be designed to minimize the amount ofprojection
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and interpretation required. Whenever possible, the fullperiphery mapping method should be employed.
Data Requirements
The relationship of the geology to the engineeringaspects of the tunnel or shaft is of primary importance.If geologi-cally related problems occur, the recorded datawill be valuable to the geologist and engineer inevaluating the conditions, the cause(s), and in devisingremedial measures. In most cases, geologicdiscontinuities, such as joints, faults, bedding, etc., arethe most important factors affecting excavation stability;and these data are of primary importance. Also, the rockstrength is important in high cover tunnels, and water isimportant in many situations. The following data aremost important:
1. Rock Classification.— Lithology and relatedfeatures such as foliation, schistosity, and flow structure.Rock descriptions should be concise; use standarddescriptors.
• Formation boundaries — describe beddingthick-ness and attitude, areas of soft, or unstablerock. Give dip and strike unless otherwise noted.Dips of planes (not necessarily true dip) into tunnelare desirable in cases where they may influenceexcavation stability.
• Physical properties of the rock — determinehardness by comparison with common or familiarmaterials, brittleness, reaction to pick or knife, andcolor.
• Alteration — describe degree, type, extent, andeffects on construction. Differentiate between wea-thering, other alteration, and cementation.
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179 Figure 6-6.—As-built summary geology tunnel map.
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• Features — describe the size, form (tabular,irregular), contacts (sharp, gradational, sheared),and mineralization, if any.
2. Conditions Which Affect Stability of the Rock.—
• Joints or joint systems — describe spacing,conti-nuity, length, whether open or tight,slickensides, planarity, waviness, cementation,fillings, dip and strike, and water.
• Shear zones — describe severity of shearing andphysical condition of rock in and adjacent to thezone, whether material is crushed or composed ofbreccia, gouge, or mylonite; describe gougethickness, physi-cal properties, mineralogy andalteration; dip and strike, and water.
• Faults — give dimensions of fault breccia and/orgouge and adjacent disturbed or fractured zones,amount of displacement, if determinable, and thefault's effect on stability of rock.
3. Effects of Tunneling on Rock.— Comment on: thecondition of rock after excavation, rate of air slaking orother deterioration of rock where appropriate, rockbursts, fallouts, development of squeezing or heavyground, and time interval between first exposure and thebeginning of these effects. Include the evidence used inevaluation, and the reaction of different rock types toconventional blasting or mechanical excavation method.
Periodic re-examination of the tunnel and comparison oforiginally mapped conditions with those existing later isrecommended.
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4. Tunnel Excavation Methods.—
Blast pattern — Give example of typical blast roundpattern, type of explosive and quantity per yard(powder factor) of rock blasted, size of rock fragments,ease or difficulty of rock breakage and condition of thewalls of the tunnel such as whether half-rounds (halfof peripheral shot holes) are visible. Some of thisinfor-mation should be obtainable from the inspectors.
Overbreak — Overbreak and fallout should be mea-sured as a peripheral average from "B" line (excavationpay line), where practical, and maximum at specificstations. Plot average overbreak on the section alongtunnel alignment. Relate this to geologic conditionsand construction methods, particularly blastingprocedure.
Ground behavior — Blockiness, caving, swelling,and/ or squeezing should be described with evidenceand effects.
Supports — Give size and spacing of ribs, size andtypes of struts, and behavior of supports in reaches ofbad ground. Where supports show distress or havefailed, give reason for failure, time after installationfor load to develop, the remedial measuresundertaken, and size and spacing of replaced supportsor jump sets. If a ground classification system is beingused, relate to geologic conditions and support used.Incorporate some reference to the actual need forsupport versus that installed. Use the properterminology when describing supports. A goodreference for tunnel supports (and conventionaltunneling) is Rock Tunneling with Steel Supports [6].
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Indicate where special supports such as mats, spiling,or breast boards are required and geologic reason.Where rock bolts (or split sets) are used, give spacing,size, length, type, anchor type, torque loading values,and quantities used. Note retorquing, if performed.Locations of rock bolts should be plotted on thegeologic maps.
Machine excavation — In machine-type excavations(in addition to appropriate items above) give: rate ofadvance, pressures used, and description of cuttings orrock breakage. Describe the effect of cutters andgrippers on rock walls, or other geologically relatedproblems such as abrasive rock wearing cutters.
5. Hydrogeology .—Water flows should be mapped andquantities estimated. Daily heading and portal measure-ments should be recorded. The location of all significantflows should be plotted on the tunnel map and changesin rate or duration of flow recorded. If the water ishighly mineralized, obtain chemical analyses of water forpos-sible effect on concrete or steel linings orcontamination of water being discharged or to beconveyed by the tunnel.
6. Gas.—The following should be done:
• Determine type, quantity, occurrence, geologic asso-ciations, and points of discharge should be mapped.
• Samples should be taken. This is usually done bysafety personnel.
• Record actions taken.
7. Instrumentation, Special Tests, Grout, andFeeler Holes.—Locations and logs (if available) shouldbe shown on the tunnel maps.
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8. Miscellaneous Excavations.—Geologic maps andsections of related excavations such as surge tanks, gateshafts, inlet and outlet portal open cuts are necessary.
Tunnel maps should include brief comments on thegeologic conditions being encountered and their possibleeffects.
9. Sampling.—A systematic sampling program of thetunnel rock is essential to adequately record tunnelgeology. These samples may be 2 in x 3 in (5 cm x 8 cm)or larger and should be secured in a labeled sample bagshowing station, date, and wall position with anappropriate description. Rock that easily deterioratesshould be protected with wax or plastic. Sampling atirregular (and locally close) intervals may be required toensure that all important rock, geologic, and physicalconditions are adequately represented. A representativestratigraphic series of samples should be collected. Thejudgement of the geologist who is familiar with thegeology is the best guide in determining the mostappropriate sampling interval.
Thorough photographic coverage provides a visual recordof construction and geologic conditions. Postconstructionevaluations use construction photographs extensivelyand are an important part of the construction record. Acamera should be part of the mapping equipment androutinely used. Photographs that show typical, as wellas atypical, geologic conditions should be takenroutinely. Identify photographs of significant features bynumber on the appropriate map sheet.
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Underground Geologic Mapping Methods
Full Periphery Mapping
The full periphery (or developed surface) mappingmethod is widely used in engineering practice andinvolves creating a map of the surface of theunderground excavation regardless of shape. Themethod produces a map which is virtually free fromdistortion and interpretation present in other methodswhere geologic features are projected onto a plane orsection. The method has been used successfully invarious types and shapes of excavations (Hatheway,1982 [7]; U.S. Army Corps of Engineers, 1970 [8];Proctor, 1971 [9]) and on numerous Reclamationprojects.
The method uses a developed surface created by"unrolling" or "flattening out" the circumference of thetunnel or shaft to form a "plan" of the entire wall surface(figure 6-7). The geologic features are plotted on thisplan. The method is especially effective in that geologicfeatures of all types can be plotted directly onto the mapregardless of orientation or location with no projectionrequired. The method is useful for plotting curving orirregular discontinuities which are difficult to project toa flat plane as in other methods.
Procedure.—Full periphery mapping generally requiresthe assembly of field sheets prior to the actual start ofmapping. This is done for drifts and tunnels by firstdrawing in the crown centerline of the plan (figure 6-7).The bases of the walls or the invert are then plotted at acircumferential distance from the crown centerline onthe plan. For instance, if the tunnel is 10 feet (3.048 m)in excavated diameter, the invert centerline will beplotted 15.71 feet (4.79 m) (in scale) from the crowncenterline. Plot springline at the appropriate circumferential
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distance from the crown centerline. This process is donefor both walls and produces a plan which represents theactual wall surface of the excavation. The map layout isdesigned to be viewed from above the tunnel. Shaft dataare plotted as viewed from inside the excavation. Thetunnel invert is not mapped because rock surfacesusually are covered with muck or invert segments. Plotscales on either side of the plan to provide distancecontrol while mapping. A longitudinal section view ofthe excavation may be added alongside the plan toprovide a space to record types and locations of support,overbreak, etc. Plot geologic features on the field sheets(figures 6-4 and 6-5) by noting where the featuresintercept known lines, such as where a particular jointintercepts the crown centerline, the spring line on bothwalls, or the base of either wall. The trace of the joint issketched to scale between these known points. Thestrike and dip of the discontinuity are recorded directlyon the field sheet adjacent to the trace. The locations ofsamples, photographs, water seeps, and flows are plottedon the map (figure 6-8).
The Brunton compass is used to measure dips on thevarious discontinuities; but due to the presence ofsupport steel, rock bolts, utilities, and any naturalmagnetism of the wall rock, a Brunton may not bereliable for deter-mining the strike of the feature. Inthis case, the strike may be determined by one of severalmethods. The first method is to align the map parallelto the tunnel where the feature is exposed in the walland plot the strike by eye on the sheet parallel to thestrike of the feature in the wall. The second method isto observe the strike of the feature on the map where itintersects the crown centerline. At this point, the crownis essentially hori-zontal, and the trace of the feature atthis point represents the strike. The third method isslightly more complex but is the most accurate methodof the three.
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Figure 6-8.—Full periphery geologic map example.
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This method requires locating where the feature inter-sects springline on each wall of the full periphery map.These points are projected to the corrected springline. Aline drawn between the projected points represents thestrike of the feature. Note that these methods assumethat the tunnel or drift is relatively horizontal. In somecases, if the excavation is inclined, the apparent strikecan be corrected for the amount of inclination. A fourthmethod is to use a gyroscopic compass.
Other Applications.—With minor variations in themethod described above, the full periphery method canbe used equally well in vertical or inclined shafts,horseshoe shaped drifts and tunnels, and other regularshaped excavations.
Advantages.—The full periphery method:
• Involves plotting the actual traces of geologicfeatures as they are exposed in the tunnel. Thiseliminates the distortion and interpretation introducedby other methods where the traces are projected backto a plane tangent to the tunnel.
• Allows the geologist to observe and plot irregu-larities in geologic features and make accurate three-dimensional interpretations of the features.
• Allows rapid and easy plotting of the locations ofsamples and photographs.
• Allows easy and rapid recording of the locations ofrock bolts and other types of rock reinforcement.
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Disadvantages.—
• Since the surface of the excavation is generally acurved surface, the trace of planar features, such asfractures, faults, and bedding planes, produce curveswhen plotted on the map.
• The full periphery method requires that the pointsat which features intersect springline be projected tothe original tunnel diameter in order to compute thetrue strike of the discontinuity (figure 6-7).
Plan and Section
The plan and section method has been used in engi-neering practice but has generally been replaced by thefull periphery mapping method. The plan and sectionmethod is still used where data interpretation isfacilitated by the flat plan and sections. The methodcreates vertical sections commonly coincident with a wallor walls of a tunnel or shaft, through centerline, or istangent to a curving surface commonly at springline oran edge of a shaft (figure 6-9). Geologic features areprojected to the sections and plotted as they are mapped.
The method produces a map which is a combination ofdirect trace and projection or a projection of the wallsexcept where the map is tangent to the excavation(figure 6-10). The plan through tunnel springline andcenterline or shaft centerline is a projection of thegeologic features exposed in the excavation.
Procedure.—The plan and section method generallyrequires the assembly of field sheets prior to the actualstart of mapping. This is done for drifts and tunnels bydrawing vertical sections the height of the excavation.
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Figure 6-9.—Map layout of a tunnel for geologic mapping.
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Figure 6-10.—Relationship of planar feature trace to map projections.
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The bases of the walls or the invert form the base of thesection with springline plotted and the crown formingthe top of the section. For instance, if the tunnel is 20feet (6 m) high, the crown will be 20 feet (6 m) from theinvert. Springline is plotted the appropriate verticaldistance from the crown or invert (figure 6-10). Thisprocess may be done for one or both walls, producing oneor two vertical representations of the wall/arch exposure.Shafts are similar, but the section corresponds to thewall of a rectangular shaft or is tangent to the shaft wallat a point, and the map is a projection of the shaft of onediameter.
A section through tunnel springlines produces a planprojection of the arch except at the plan intersection withthe wall at springline. The corresponding sectionthrough a shaft produces a vertical projection of thewall(s) through a shaft or along a diameter. The maprepresents the actual wall surface of the excavation onlywhere the projection intersects the wall.
Scales are added on either side of the sections to providedistance control while plotting. An additional longitu-dinal section view of the excavation may be added to pro-vide a space to record types and locations of support oroverbreak. Geologic features are then plotted on thefield sheets by noting where the features interceptknown lines, such as where a particular joint interceptsthe crown centerline, the spring line on both walls, or thebase of either wall. The trace of the joint is then pro-jected to the section between these known points. Theattitudes of features are recorded on the field sheet adja-cent to the trace. The location of samples, photographs,water seeps, and flows can be recorded by finding theirlocation on the wall and projecting that location to themap.
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Advantages.—The plan and section method:
• Produces two-dimensional sections and plans that donot require conversion. The sections and plans can beintegrated directly with other plans and sections. Thesections and plans are easily understood by individualsnot familiar with full periphery mapping or individualswho have difficulty visualizing structural features inthree-dimensions.
• Permits direct determination of strikes by spring-line intersections.
Disadvantages.—Since the surface of the excavation isgenerally a curved surface, the trace of planar features,such as fractures, faults, and bedding planes, are projec-tions to a plane. The only objective data is where themap is coincident or tangent to the excavation surface.
The plan and section method requires:
• Plotting and observing geologic features and makingaccurate three-dimensional interpretations of thefeatures by projecting locations to a plane.
• Plotting locations of samples and photographs byprojection.
• Recording locations of rock bolts and other types ofrock reinforcement by projection.
• Plotting is done after data collection and re-examination of the site is difficult or not practical.
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Face Maps
The geology exposed in an excavation face is plotteddirectly on a map. The purpose of the face map is toprovide a quick appraisal of rock conditions and providedata for special detailed studies. The combination ofwall and face maps will usually give an adequate andclear permanent record of any complex tunnel geology.Natural scales such as 1 inch = 1 to 2 feet (1:50) are themost satisfactory. All significant geologic features whichmay affect the stability of the tunnel must be mapped.
Photogrammetric Mapping
Photogrammetric geologic mapping is a specializedmethod consisting of the interpretation of close-rangestereophotography of excavation walls. Photogrammetriccontrol is provided by surveyed targets or by a gnomon orscale in the photographs. The stereophotos are inter-preted using photogrammetric software or an analyticalplotter. Feature location accuracy can vary from a fewinches (cm) to one-eighth of an inch (3mm) depending onequipment and survey control accuracy. The photogram-metric mapping can be combined with detail line surveysfor small-scale data collection and control.
Exploration Mapping Method Selection
The geologic mapping format for exploratory drifts andshafts should be determined by data uses. Directintegra-tion of excavation maps into composite maps ofa dam foundation is much easier if undistorted sectionsare available. The maps can be treated in the samemanner as drill hole logs. The disadvantages of plan andsection mapping may be offset by the advantages of easyinter-pretation and integration into other data bases.
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Construction Mapping.—Full periphery geologicmapping should be used for routine constructionactivities. The advantages of increased speed andaccuracy in production mapping and the reduction ofinterpretation offsets the disadvantages.
Summary
This guide to tunnel geologic mapping during construc-tion has been developed for general use and serves tostandardize procedures and data collection. Items ofprimary significance are included, but some are notadaptable to all tunnels or methods of tunnel excavation.The judgment of an experienced geologist is the bestguide to the specific items and amount of detail requiredto provide pertinent, informative data. To ensurereliable and useful tunnel geologic studies, all importantgeology and related engineering construction data whichmay be significant to tunnel construction as well asin the planning, designing, and constructing of futuretunnels should be considered for inclusion in the tunnelmap and report.
Photogeologic Mapping
General
Aerial photographs generally are used in reconnaissancegeologic mapping, geologic field mapping, and in gener-ation of photo-interpretive geologic maps. Various scalesof airphotos are valuable for regional and site studies, forboth detection and mapping of a wide variety of geologicfeatures important to engineering geology.
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Types of Aerial Photographs
Panchromatic (Black and White).—Panchromaticphotography records images essentially across the entirevisible spectrum, and with proper film and filters alsocan record into the near-infrared. In aerial photography,blue is generally filtered out to reduce the effects ofatmospheric haze.
Natural Color.—Images are recorded in the naturalcolors seen by the human eye in the visible portion of thespectrum.
False-Color Infrared.—Images are recorded using partof the visible spectrum and part of the near-infrared, butthe colors in the resultant photographs are not natural(false-color). Infrared film is commonly used and is lessaffected by haze than other types. False-color photo-graphy is not the same as thermal-infrared imagingwhich uses the thermal part of the infrared spectrum.
Multispectral.—Photographs acquired by multiplecameras simultaneously recording different portions ofthe spectrum can aid interpretation.
Photogrammetry and Equipment
Use stereoscopes to view aerial photographs formaximum utility and ease of interpretation. Pocketstereoscopes are useful in the field or office. Largemirror stereoscopes are useful for viewing largequantities of photos or photos in rolls. Know the photoscale, resolution, and exaggeration. Be aware of thetypes of distortions inherent in airphotos.
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Compilation of Photogeologic Map Data
Mapping should be done on transparent one-side-mattemylar overlays and not on the photographs. Any lines,even if erased, can confuse later interpretations usingthe photos. The mapping is then transferred to basemaps minimizing the effects of distortions in photos dueto the camera optics. Orthophoto quadrangles can helpreduce this distortion.
Analysis of Aerial Photographs
General Interpretive Factors
Analysis of aerial photographs involves interpretingindirect data. In most cases, several factors are used tointerpret geologic conditions. Interpretive factorsusually used in the analysis of aerial photographs are:
Sun Angle.—High or low illumination angles may bedesired, depending on the nature of the features to bedetected.
Photographic Tone.—Variations in color, intensity,shade and shadows.
Texture.—Frequency of change in tone, evident asroughness, smoothness.
Color.—True and false-color imagery may be easier tointerpret than panchromatic photographs, depending onfeatures being observed. For some applications (e.g., low sun angle photography), panchromatic photographyis better.
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Geomorphic Shape and Pattern.—Geologic conditionscan be identified by mapping various types of geomorphicfeatures related to drainage, bedding, and structure.
Vegetation.—Some types of vegetation and vegetal pat-terns can assist in interpreting geology. Vegetation mayindicate depth of soil, type of soil, available moisture,and type of bedrock.
Photoanalysis for ReconnaissanceGeologic Mapping
Photo-reconnaissance geologic mapping can be done toproduce a preliminary geologic map of the study areaprior to going into the field to check and verify theinterpreted geologic data or to produce a finishedgeologic map with little or no field checking. These mapsare called photo-reconnaissance geologic maps andphoto-interpretive geologic maps, respectively.
Photo-Reconnaissance Geologic Mapping
Photo-analysis prior to field work allows the mapper toform a preliminary concept of the geology of the studyarea and to select areas for detailed examination. Priorphoto-analysis is critical if available field time is limited,especially when a large area is involved, as in regionalstudies, reservoir area mapping, and pipeline or canalalignment studies.
Photo-Interpretive Geologic Mapping
Geologic maps produced solely from aerial photographswith little or no field checking are useful when time,funds, or access are limited or when adverse weatherprevents a more detailed field mapping program. The
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limitations of this form of geologic map are dependent onoutcrop density and degree of exposure, amount ofvegetative cover, contrast of the geologic units, and theskills of the photogeologic mapper. This type of map isuseful for preliminary or reconnaissance levelevaluations but should never be used for design levelwork.
Photoanalysis During Geologic Field Mapping
The location and verification of geologic features in thefield can usually be expedited by using aerial photo-graphs. Photographs often reveal landforms that aredifficult to see or interpret from the ground, such asland-slides. Photographs can be used to clarify andspeed up field mapping by allowing a comprehensiveview of the study site and the relationships of thevarious geologic features exposed. Alternately viewingphotos and exam-ining outcrops can greatly facilitatemapping.
Availability of Imagery
Aerial photography is available, commonly in a variety ofscales and types, for essentially the entire conterminousUnited States. The principal repositories of publiclyowned airphotos is the EROS Data Center, operated bythe U.S. Geological Survey and the AgriculturalStabilization and Conservation Service (ASCS) of theU.S. Department of Agriculture. The USGS has severalregional offices of the Earth Science Information Center(ESIC). The ESIC operates the Aerial PhotographySummary Record System (APSRS), which is a standardreference data base for users of aerial photographs. TheAPSRS lists aerial photography available from a largenumber of government agencies and commercial com-panies. The lists are comprehensive and categorized bystate and by latitude and longitude. APSRS data are
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available on request from ESIC. ESIC also providesinformation about cartographic products other thanimagery.
Some important addresses and telephone numbers are:
USDA-ASCS (801) 524-5856Aerial Photography Field OfficeCustomer Services2222 West 2300 SouthP.O. Box 30010Salt Lake City, UT 84130-0010
USGS (605) 594-6151EROS Data CenterSioux Falls, SD 57198
USGS (303) 202-4200ESICDenver Federal CenterDenver, CO 80225
USGS (650) 329-4309ESIC345 Middlefield RoadMenlo Park, CA 94025
Aerial Photography Flight Planning
If air photos are not available at the right scale, or of theright type for an area, specific flights can be made.Successful airphoto mission planning requires considera-tion of several factors, including film type, scale, time ofday (sun-angle), time of year, and the size of the area tobe covered. Mission planning should not be done bysomeone unfamiliar with the process without assistance.Specifications should be written to ensure that theresult-ing photographs will be appropriate for the
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intended purpose. Information critical to missionplanning is available from the references listed below.
Time and Cost Estimating
The cost of data acquisition is relatively easy to estimate.The cost of interpretation is much harder to estimate,being a function of the time required, which is related tothe size and complexity of the study area and the skill ofthe interpreter. The cost of a single drill hole will payfor a lot of aerial photography and interpretation.
References
A classic text on the use of airphotos in geology wasreprinted in 1985 and should be readily available. Someof the equipment described is obsolete and it isessentially limited to discussion of panchromaticphotography. The publication contains numerousstereopairs with geologic descriptions and is one of thebest works on airphoto interpretation for geologists:
Ray, R.G., Aerial photographs in geologic interpretationand mapping, USGS Professional Paper 373, 230 p.,1960.
Other useful references are:
Lattman, L.H., and Ray, R.G., Aerial photographs infield geology, Holt, Rinehart and Winston, New York, NY221 p., 1965.
Miller, V.C., Photogeology, McGraw-Hill, New York, NY,248 p., 1961.
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A reference containing no general discussion ofprinciples, but with excellent examples of stereopairs ofgeologic features, associated topographic maps, andgeologic annotations is:
Scovel, J.L., et al., Atlas of Landforms, Wiley & Sons,New York, NY, 164 p., 1965.
A broad and lengthy reference covering remote sensingin general, including much information about aerialphotography of all types, is:
Colwell, R.N., editor, Manual of remote sensing,2nd edition, American Society of Photogrammetry, FallsChurch, VA, 272 p., 1983.
BIBLIOGRAPHY
[1] U.S. Geological Survey, Map Projections - A WorkingManual, U.S. Geological Survey ProfessionalPaper 1395, 1987.
[2 ] Jackson, Julia A., editor, The Glossary of Geology,4th edition, American Geologic Institute,Alexandria, VA, 1997.
[3] Lahee, Frederic H., Field Geology, 6th edition,McGraw-Hill, Inc., New York, NY, 1961.
[4] Compton, Robert R., Geology in the Field, JohnWiley and Sons, New York, NY, 1985.
[5] Bureau of Reclamation, Division of Safety, Safetyand Health Standards, Denver Office, Denver, CO.
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[6] Proctor, M.E., and White, T.L., Rock Tunneling withSteel Supports, Commercial Shearing, Inc., Youngs-town, OH, 1977.
[7] Hatheway, A.W., “Trench, Shaft, and Tunnel Map-ping,” Bulletin of the Association of EngineeringGeologists, v. XIX, 1982.
[8] U.S. Army Corps of Engineers, “Engineering andDesign, Geologic Mapping of Tunnels and Shafts bythe Full Periphery Method,” Engineer TechnicalLetter No. 1110-1-37, Washington, DC, 1970.
[9] Proctor, R.J., “Mapping Geological Conditions inTunnels,” Bulletin of the Association of EngineeringGeologists, v. VIII, 1971.
Chapter 7
DISCONTINUITY SURVEYS
General
Physical properties of discontinuities generally controlthe engineering characteristics of a rock mass. Accurateand thorough description of discontinuities is an integralpart of geological mapping conducted for design andconstruction of civil structures. It is improbable that anysurvey will provide complete information on all thediscontinuities at a site. However, properly conductedsurveys will furnish data with a high probability ofaccurately representing the site discontinuities. Thischapter discusses discontinuity recording methodology.These recording methods can be applied to outcrops, drillholes, open excavations, and the perimeters of under-ground openings. The evaluation of discontinuity data iswell described in the literature. For example, plottingdiscontinuity data on stereograms, contouring to deter-mine prominent orientations, and subsequent wedgeanalyses are described in Rock Slope Engineering [1] andMethods of Geological Engineering in Discontinuous Rockand Introduction to Rock Mechanics [2,3]. “Chapter 5,Terminology and Descriptions for Discontinuities,” listsdata that are typically recorded in discontinuity surveys.
It is extremely important that the actual discontinuitydescriptors and measurement units be selected to supportthe anticipated rock mass classification system(s).Acquiring incomplete or excessive data may limit datausefulness in subsequent analyses, and result inexcessive costs due to repeating surveys or from collectingmore data than needed.
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Empirical Methods for Rock Mass Classification
A number of empirical methods have been developed topredict the stability of rock slopes and undergroundopenings in rock and to determine the supportrequirements of such features. A method for estimatingsteel-arch support requirements in tunnels was one of thefirst [4], and various methods which address open-cutexcavations and existing rock slopes have been usedsince. The Geomechanical Classification (Rock MassRating [RMR]) [5,6] and the Norwegian GeotechnicalInstitute (NGI) (Q-system Classification [Q]) [7] are com-monly used. Both of these methods incorporate RockQuality Designation (RQD) [8]. Since both the RMR andQ-system are based on actual case histories, both systemscan be somewhat dynamic, and refinements based on newdata are widely suggested. Additional information onRQD, RMR, and the Q-system is provided in chapter 2.
Other predictive methods include the Rock StructureRating (RSR) [9] and the Unified Rock ClassificationSystem (URCS) [10]. “Keyblock” analysis [11,12] is ameans of determining the most critical or “key” blocks ofrock formed by an excavation in jointed, competent rock.An excellent single source of information on the variousclassification systems is in American Society for TestingMaterials Special Technical Publication 984, RockClassification Systems for Engineering Purposes.
Data Collection
Discontinuity data can be collected using areal or detailline survey methods. The areal method, which consistsof the spot recording of discontinuities in outcrops withinan area of interest, is of limited use in geotechnicalanalyses. Areal surveys should be applied only forpreliminary scoping of a site or in cases where the lateral
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extent of exposed rock is inadequate to perform detail linesurveys. The detail line survey (DLS) method (DLS orline mapping) provides spacial control necessary to accu-rately portray and analyze site discontinuities. DLS map-ping was originally a method of mapping road cuts andopen pit excavations. DLS use has been expanded both inscope and types of exposures mapped. Each geologicfeature that intercepts a usually linear traverse isrecorded. The traverse can be a 100-ft (30 m) tape placedacross an outcrop, the wall of a tunnel, a shaft wall at afixed elevation, or an oriented drill core. In all cases, thealignment of the traverse and the location of both ends ofthe traverse should be determined. The mapper movesalong the line and records everything, as noted inchapter 5, or as needed to support analyses. Featurelocations are projected along strike to the tape, and thedistance is recorded. Regardless of the survey method,the mapper must obtain a statistically significant numberof observations. A minimum of 60 discontinuity measure-ments per rock type is suggested for confidence insubsequent analyses [14].
The orientation of a discontinuity can be recorded eitheras a strike azimuth and dip magnitude, preferably usingthe right-hand rule, or as a dip azimuth and magnitude(eliminating the need for dip direction and alphacharacters required by the quadrant system). Accordingto the right-hand rule, the strike azimuth is always to theleft of the dip direction. When the thumb of the righthand is pointed in the strike direction, the fingers pointin the dip direction. The selected recording methodshould be used consistently throughout the survey.
Data acquired in a single straight-line survey areinherently biased. The more nearly the strike of a discon-tinuity parallels the path of a line survey, the lessfrequently discontinuities with that strike will be
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recorded in the survey. This is called line bias. Thenumber of intersecting discontinuities is proportional tothe sine of the angle of intersection. In order to compen-sate for line bias, a sufficient number of line surveys at asufficient variety of orientations should be conducted toensure that discontinuities of any orientation are inter-sected by at least one survey at an angle of at least30 degrees. Common practice is to perform two surveysat nearly right angles or three surveys at radial angles of120 degrees. True discontinuity (set) spacing and tracelengths can be obtained by correcting the bias producedby line surveys [15, 16].
All discontinuities should be recorded regardless ofsubtlety, continuity, or other property until determinedotherwise. Data collection should be as systematic aspracticable, and accessible or easily measurable discon-tinuities should not be preferentially measured. Con-sistency and completeness of descriptions are alsoimportant. Consistency and completeness are best main-tained if all measurements are taken by the same mapperand data are recorded on a form that prompts the mapperfor the necessary descriptors. A form minimizes theprobability of descriptor omission and facilitates plottingon an equal area projection, commonly the Schmidt net(figure 7-1), or entering data for subsequent analysis.Computer programs are available that plotdiscontinuities in a variety of projections and perform avariety of analyses. Whether the plot format is the equalarea projection (Schmidt net) or equal angle projection(Wulff net), evaluation of the plotted data requires anunderstanding of the method of data collection, form ofpresentation, and any data bias corrections. References2 and 3 in the bibliography are good sources of dataanalysis background information.
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Figure 7-1.—Equatorial equal area net (Schmidt net).
Different rock types in the same structural terrain canhave different discontinuity properties and patterns, andthe host rock for each discontinuity should be recorded.This could be an important factor for understanding sub-sequent evaluations of tunneling conditions, rock slopes,or the inplace stress field in underground openings.
Figure 7-2 is a form that can be used to record the data inan abbreviated or coded format. Recording these datawill provide the necessary information for determiningRMR and Q. These codes are derived from the descriptorsfor discontinuities presented in chapter 5.
FIE
LD
MA
NU
AL
210
Figure 7-2.—Discontinuity log field sheet.
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BIBLIOGRAPHY
[1] Hoek, E., and J. Bray, Rock Slope Engineering, revised3rd edition, The Institute of Mining, London, 1981.
[2] Goodman, R.L., Methods of Geological Engineering inDiscontinuous Rock, 1976.
[3] Goodman, R.L., Introduction to Rock Mechanics, 1980.
[4] Terzaghi, K., “Rock defects and loads on tunnel sup-port,”Rock Tunneling with Steel Supports, CommercialShearing, Inc., Youngstown, OH, 1946.
[5] Bieniawski, Z.T., Engineering Rock Mass Classifica-tions, 1989.
[6] Bieniawski, Z.T.,and C.M. Orr, “Rapid site appraisalfor dam foundations by the geomechanics classification,”Proceedings 12th Congress Large Dams, ICOLD, MexicoCity, pp. 483-501, 1976.
[7] Barton, N., F. Lien, and J. Lunde, “Engineering classi-fication of rock masses for the design of tunnel support,”Rock Mechanics, v. 6, No. 4, pp. 189-236, 1974.
[8] Deere, D.U., A.J. Hendron, F.D. Patton, and E.J. Cord-ing, “Design of surface and near surface construction inrock,” Proceedings 8th U.S. Symposium Rock Mechanics,AIME, New York, pp. 237-302, 1967.
[9] Wickham, G.E., and H.R. Tiedemann, “Ground sup-port prediction model—RSR concept,” Proceedings RapidExcavation Tunneling Conference, AIME, New York,pp. 691-707, 1974.
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[10] Williamson, D.A., “Unified rock classificationsystem,” Bulletin of the Association of EngineeringGeologists, v. XXI, No. 3, pp. 345-354, 1984.
[11] Goodman, R.E., and Gen-Hua Shi, “Geology and rockslope stability—application of a “keyblock” concept forrock slopes,” Proceedings 3rd International Conference onStability in Open Pit Mining, Vancouver, June 1981.
[12] Goodman, R.E., and Gen-Hua Shi, Block Theory andIts Application to Rock Engineering, 1985.
[13] Piteau, D., “Geological factors significant to thestability of the slopes cut in rock,” Proceedings of the OpenPit Mining Symposium, South African Institute of Miningand Metallurgy, September 1970.
[14] Savely, J., “Orientation and Engineering Propertiesof Joints in Sierrita Pit, Arizona,” MS thesis, Universityof Arizona, 1972.
[15] Priest, S.D., and J.A. Hudson., “Estimation of discon-tinuity spacing and trace length using scanline surveys,”International Journal of Rock Mechanics-Mining Sciencesand Geomechanics Abstracts, v. 18, No. 3, pp. 183-197,1981.
[16] Terzaghi, R.D., “Sources of error in joint surveys,”Geotechnique, v. 15, No. 3, pp. 287-304, 1965.
Chapter 8
EXPLORATION DRILLING PROGRAMS
Introduction
This chapter is a guide for developing effective andefficient exploration drilling programs. Drillingprograms that involve extensive soil sampling, rockcoring, instrumentation installations, or in-place testingcommonly have excessive cost overruns and latecompletion times. The effort put into developing a wellorganized drilling program that explicitly defines drillingand sampling requirements can lower exploration costssignificantly by eliminating unnecessary or redundantwork and meeting schedules. Good references on drillingmethods and equipment are Groundwater and Wells,second edition, by Fletcher G. Driscoll, published byJohnson Division, St. Paul, Minnesota 55112, andDrilling: The Manual of Methods, Applications, andManagement, CRC Lewis Publishers, Boca Raton,Florida, 1996.
Planning the Exploration Drilling Program
Developing an exploration program requires a thoroughknowledge of the design requirements, site conditions,drilling equipment requirements and capabilities, andsoil or rock core testing. It is extremely important thatexploration needs be identified to avoid overdesign of aprogram by too many “it would be nice” requests.
A complete and detailed description of the drill sitelocation, accessibility, work requirements, geology, andother pertinent information should be made available toeither the drilling contractor or in-house drilling staff.This information is necessary for an effective andefficient drilling operation that will accomplish theprogram objectives. A major objective is to obtain themost information and samples possible from each hole by
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optimizing location, drilling and sampling methods,depth, and completion. For example, a drill hole on theintersection of dam and outlet works centerlines drilledto the depth of the deepest data requirement andsampled for both structures provides data for bothstructures.
Most exploration is done in phases, with subsequentexploration designed to refine the understanding of asite. Drill holes should be logged as the holes are drilled,so hole depths and subsequent hole locations can bechanged as exploration progresses. Because anexploration program evolves as data are acquired,information should be reviewed and added to maps andsections as the data become available.
Site Inspection
An onsite inspection of the drilling location should bemade by the geologist, designers, and other essentialmembers of the exploration team. The purpose of theonsite inspection is to determine the exploration neededto provide the data required for design. Data arerequired for several design disciplines with differentneeds. Having knowledgeable representatives see thesite is important when formulating an explorationprogram. Changes and additions to explorationprograms during or after exploration are expected butcan be minimized with careful planning.
During the site inspection, the geologist and designersshould discuss in detail all the design concerns that canonly be solved by analyzing the subsurface geology. Theteam should be explicit as to the size, quantity, type, andquality of soil or rock samples that are necessary todevelop an accurate evaluation of geologic conditions.The geologist can recommend the type of equipment and
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drilling procedures needed, based on the drilling andsampling requirements, and to address design concernsas well as to provide samples needed for laboratorytesting.
The onsite inspection should provide other pertinentinformation which is critical to the selection of specificequipment. The following factors should be addressedwhen preparing the exploration plan.
Topography-drill site accessibility.—The type ofdrilling equipment most suitable for the work needs tobe determined. Truck-mounted, all-terrain, skid-mounted, or a combination of several types may beappropriate. Heavy excavation and hauling equipmentmay be required to construct access roads, drill pads,stream crossings, temporary bridges, or pipe culverts forriver crossings. Explosives and track drills may berequired to prepare drill pads or remove unsafe rockoverhangs from drill sites, and roadbase or rockfill mayhave to be to be placed over soft mud or swamp.Helicopter support may be needed for fly-in rigs andheavy timber clearing. A source of water for drillingneeds to be identified. Other considerations are whetherthere is a relatively close and level area that may beused as a temporary drill yard/staging area and howclose equipment can be safely driven into the drill area.
Right-of-way, access permits, drilling permits,construction or clearing permits.—The drillinglocations, whether on public or private land, may requireaccess permits. Several different types of permits maybe needed, including archeological and environmentalpermits. These permits may take considerable time toobtain and should be acquired as soon as possible. Thelimitations of the permits should be determined.Construction or clearing permits may be needed. Most
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states require special licenses or permits for drill op-erators who perform water-well drilling and installation.
Protection of the Environment
Environmental, archeological, and biological factors mayplace restrictions or conditions on a site. Disposal of thecleared material should be arranged. The use of drillingmud requires planning and implementation prior todrilling. If the drill mud circulation pits can beexcavated, the mud pits may have to be enclosed withfencing to keep out animals. Drill mud and cuttings aswell as fuel and oil spills or oil change residue willrequire disposal. Some drill mud, cuttings, and watershould be stored because the material is considered ahazardous waste. These materials may have to bedisposed of at approved sites. Crossing shallow streamscan create contamination or turbidity problems. Drillhole completion and site restoration should beformulated. Dust abatement may be necessary for travelover the access roads. Routes through planted fieldsshould be arranged before travel.
Drilling
Many factors should be considered during thedevelopment of the exploration plan as listed below:
• Are the drill sites on rock
• Can downhole hammers be used to set collarcasing
• Are surficial materials suitable for hollow-stemauger use
• If the drill hole is to be water-pressure tested,may drilling mud or air foam be used
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• Are soil samples required
• Can casing or hollow-stem augers be advancedthrough the surficial deposits so that rock coringcan be performed
• Can the drill hole be used to combine geophysicaland in-place testing
• Will geophysical testing be required in the drillhole
• Are angle holes required
• Will the holes require directional drilling controland then be verified by survey
• Will polyvinyl chloride (PVC) casing have to beinstalled for survey confirmation
• Will water pressure tests or permeability tests berequired as the hole is drilled or can the testing beperformed after the hole is completed
• Will the permeability tests require packers andpressure testing or gravity head pressure
• Will the holes require instrumentation installation
• What are the requirements for the backfill in theinstrumentation drill hole and how is it to beplaced
• Will the outside annulus of the casing requiregrouting
• What are the hole completion requirements
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Equipment
• Are the requirements for soil sample and/or rockcore sizes compatible with existing commerciallyavailable equipment
• Will the samples or cores have to be transmittedto the testing laboratories in sealed liners, splittube liners, thin-wall steel tubes, or cheeseclothand wax seals in core boxes
• Are there special concerns for the samples andtheir delivery
• Will those concerns require them to betransported in vibration-free containers
• Should the samples be protected from freezing
• Should the samples be weighed in the field andthe density and moisture content determinedbefore delivery to the laboratories
• What is the minimum drill equipment that shouldbe specified considering the total hole depth, sizeof core or soil sample requirements, boreholediameter, and rod size
• What is the minimum mud pump or aircompressor rating that should be specified
• Where is the water source; will water have to behauled or can it be pumped to the drill site
• How much water line will have to be laid
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Traffic Control and Safety
• Will the drill locations require traffic control,detours, barricades, flag personnel, etc., for safetyand public protection
• Will road or highway travel require reroutingduring the drilling program
• Has permission been obtained from local, county,or state officials to close roads
• Will drilling be performed in high visibility areas
• Will equipment security and vandalism be enoughof a problem to warrant nighttime securitypersonnel or fencing
Special Considerations
• Will the drilling require excavating orconstructing ramps and drill pads on the slopeface of an earth embankment
• Will the embankment slope face drilling have tobe done with skid-rigs on timber cribbingplatforms or with specialized drills that arecapable of traversing and drilling intoembankment slope faces without excavatingramps or benches
• Will underground drilling be required
• Establish and include all underground safetyrequirements in the drilling specifications
• Size the underground drilling equipment so it willbe suitable for the height and width of the tunnelor drift
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• Is there potential for large water inflows
• Is there potential to intercept reservoir waterduring underground drilling operations
• Will the drilling program require drill setups onscaffolds or hanging platforms
• Are qualified personnel available to review thedesign of any scaffold or hanging platform drillsetup, and will they have the authority to acceptor reject the construction
• Will the drilling program require operation froma floating plant (barge) or a jack-up platform
• Obtain data for fluctuating river rises or falls,flow rate, and depth of water under normal flowconditions
• Will drilling be required in the vicinity of overheadtransmission lines, transformer boxes, or under-ground buried utilities
• Have all underground utilities been located andflagged
• Will the program require helicopter service for fly-in rigs
• Have fly-in hazards been identified prior to start,such as transmission lines, heavy timber,turbulent winds, and rough terrain
• Are artesian pressures anticipated
• Are circulation loss zones anticipated
• Have contingency plans been prepared to seal andcontain artesian water flow or large volume waterflow that may be encountered during any drillingoperations
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• Has it been determined how the drill holes are tobe completed, i.e., capped and locked collar casing,collar casing guard fixtures, or install piezometersor other monitoring instrumentation, or backfilledand grouted
Drilling in Dam Embankments
The Bureau of Reclamation's (Reclamation) embankmentdesign practice minimizes development of stress patternswithin an embankment. Stress patterns could lead tohydraulic fracturing by drill fluids during drilling.Certain embankment locations and conditions have ahigher potential for hydraulic fracturing than others, andimproper drilling procedures or methods will increasethe potential for hydraulic fracturing. Site locations andconditions where hydraulic fracturing by drilling mediaare more likely to occur and adversely affect a structure'sperformance include the following:
1. In impervious cores with slopes steeper than0.5H:1V, cut-off trenches, and upstream-inclinedcores.
2. Near abutments steeper than 0.5H:1V, whereabrupt changes in slopes occur, and above boundariesin the foundation which sharply separate areas ofcontrasting compressibility.
3. Near structures within embankments.
4. In impervious zones consisting of silt or mixturesof fine sand and silt.
Recommended procedures for developing exploration andinstrumentation programs and for drilling in theimpervious portion of embankment dams are as follows:
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1. The embankment design should indicate whethera hydraulic fracturing potential exists.
2. If a high potential for hydrofracturing exists, thetype of equipment and the method and technique tobe used for drilling must have the approval of theexploration team. Once drilling has commenced,drilling personnel are responsible for controlling andmonitoring drill media pressure, drill mediacirculation loss, and penetration rate to assure thatthe drilling operation minimizes the possibility forhydraulic fracturing.
3. If a sudden loss of drill fluid occurs during anyembankment drilling within the dam core, drillingshould be stopped immediately. Action should betaken to stop the loss of drill fluid. The reason forloss should be determined, and if hydraulic fracturingmay have been the reason for the fluid loss, thegeologist and designer should be notified.
With the exception of augering, any drilling method hasthe potential to hydraulically fracture an embankmentif care is not taken and attention is not paid to detail.Augering is the preferred method of drilling in the coreof embankment dams. Augering does not pressurize theembankment, and no potential for hydrofracturingexists. Use of a hollow-stem auger permits sampling inthe embankment and allows sampling/testing of thefounda-tion through the auger’s hollow stem, which actsas casing.
Drilling methods which may be approved for drilling inembankment dams if augering is not practical (i.e.,cobbly fill) are as follows:
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1. Cable tool
2. Direct rotary with mud (bentonite orbiodegradable)
3. Direct rotary with water
4. Direct rotary with air-foam
5. Down-hole hammer with reverse circulation
Selection of any one of the above methods should bebased on site-specific conditions, hole utilization,economic considerations, and availability of equipmentand trained personnel.
Any drilling into the impervious core of an embankmentdam should be performed by experienced drill crews thatemploy methods and procedures that minimize thepotential for hydraulic fracturing. It is essential thatdrillers be well trained and aware of the causes of andthe problems resulting from hydraulic fracturing.
Safety
Drilling safety requirements and safety requirements ingeneral are available in Reclamation Safety and HealthStandards, Bureau of Reclamation, United StatesDepartment of Interior, 1993.
Preparation of Drilling Specificationsand Format
The work requirements should be compiled in a clearand concise manner for use by the personnel who will
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perform and inspect the work. The following is asuggested specifications format for drilling contracts.
a. General Description of Exploration Program
(1) Available Geologic Data
(2) Identification of Design Concerns
(3) Generalized Exploration Drilling, Coring,Testing, Instrumentation Requirements
b. Location of Work
(1) Area Identification
(2) Nearest Community
(3) Emergency Facilities
(4) Nearest Living Quarters/Crew Camp Area
(5) Freight Facilities
(6) Fuel and Supply Business Locations
(7) Travel Routes/Road Restrictions
(8) Public/Private Land Access Routes/Restrictions
(9) Right-of-Way Permits
c. Site Location
(1) Hole Locations
(2) Topography/Accessibility
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(3) Protection of the Environment
(4) Water Source
(5) Waste Disposal Area/Acceptable Waste DisposalMethod
(6) Drill Yard Storage Area—Restrictions
d. Work Requirements
(1) Site Preparation
(2) Collaring Holes—Boring Size—Angle
(3) Casing Requirements
(4) Sample Requirements (Disturbed/Undisturbed)
(5) Sample Sizes and Intervals
(6) Care and Transportation of Samples
(7) Core Sizes and Intervals
(8) Care and Preservation of Rock Core
(9) In-Place Testing Requirements
(10) Instrumentation Requirements
(11) Hole Backfill and Completion
(12) Site Cleanup
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e. Equipment Requirements
(1) Drill Rig Capabilities
(2) Pump/Air Compressor Capabilities
(3) Drilling Media
(4) Sampling/Coring Equipment
(5) In Situ Testing Equipment
(6) Instrumentation Equipment
(7) Core Boxes/Sample Containers
f. Special Drilling Concerns
g. Potential for Program Change, Modification,or Extension
h. Safety Program/Safety Requirements/SafetyContingency Plans
i. Exploration Drilling Reports and Logs
j. Labor Checks/Equipment Checks/CostAccounting
Chapter 9
GROUNDWATER DATA ACQUISITION METHODS
Introduction
This chapter provides information that will help select,install, and operate appropriate groundwater instrumen-tation and to collect, establish, maintain, and present thegroundwater data. Most types of engineering geologyinvestigations require acquisition and use ofgroundwater data. The data required may vary fromsimple monthly verification of the water level elevationsalong a canal-axis profile to hourly monitoring ofpiezometric conditions in multiple zones within alandslide or embankment. Successful implementation ofa groundwater instrumen-tation program depends onknowledge of subsurface conditions, preliminaryidentification of all probable future uses of the data, andcareful planning of an instrumentation system and dataacquisition program to meet these data requirements.This chapter will provide the user with:
• A detailed description of methods employed indesigning and installing groundwater monitoringsystems.
• A detailed description of available manual andautomated methods and techniques used inmonitoring ground and surface water.
• A discussion of data base management and datapresentation.
• A listing of more detailed and specific sourcematerial on groundwater data acquisition methods.
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General
The importance of fully evaluating and understandinggeologic factors controlling groundwater flow—includingporosity, storativity, permeability, transmissivity, velo-city, recharge, and discharge—cannot beoveremphasized. This evaluation needs to be made at theonset of the exploration program and continuallyrepeated throughout the investigations. These factorswill ultimately control the type of groundwateracquisition methods required.
Geologic Controls on Groundwater
Geologic controls on groundwater flow impact the designof observation systems and must be identified in thepreliminary planning of the instrumentation program.For example:
1. Permeable materials, such as clastic sediments,karstic limestone, and fractured rock, control thetype and size of well point, well screen, orpiezometer to be used and must be accounted for indesigning instrumentation for the program.
2. Relatively impermeable materials, such as clays,silts, shales, siltstones, and massive rock presentspecial problems which must be accounted for inselecting the type and size of piezometer to beinstalled. Generally these materials require use ofthe smallest size piezometer practical becausechanges in water level and volume in the hole aresmall and require long periods of time to react. Porepressure measurements in this type of geologicenvironment should be considered, particularly ifshort-term periodic—daily or weekly—changes ingroundwater conditions are needed.
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3. Layering, attitude of layers, boundaries, weath-ering and alteration, and environment of depositionall influence selection of instrumentation.
Design and Installation of ObservationWells and Piezometers
Analysis of the Geologic Environment
The presence of variations in the geologic environmentmust be anticipated. Perched water tables, artesianaquifers, sources of recharge and discharge, knownboundaries and barriers, and structural controls such asfractures, joints, faults, shears, slides, folds, and strati-graphic contacts should be considered when selectinginstrument types and sizes. The preliminary instrumen-tation design should be advanced enough to allowprocurement of needed equipment, but flexible enough toadapt to changes in the environment.
Different types of groundwater observation instrumentsprovide different data types. Observation wells andpiezometers are selected in accordance with the datarequired and the aquifer material and type. To beuseful, reliable, and accurate, the well or piezometerdesign must be tailored to the subsurface conditions.Single or unconfined aquifer zones can be monitored byusing a screened or perforated standpipe or porous tubepiezometer, or by a pore-pressure transducer. Multiplezones may be monitored using multiple drill holes,multiple piezometers in a single drill hole, or multiplepiezometer ports in a single standpipe.
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Design
The most important aspect in the design of agroundwater monitoring well is the purpose and use ofthe well; whether for taking water samples, measuringwater levels, geophysical investigations, or a combinationof uses.
The hydrogeologic environment and the type of down-hole instruments that may be used in the well willinfluence the choice of well diameter, casing type, screento be used, and the interval to be monitored.
Components of a typical well include a screened intervalsurrounded by filter/gravel-pack material isolated by abentonite and/or cement grout seal, blank casing to thesurface, and a protective well cover.
PVC is the most widely used material for standpipes(casing and screens) in monitoring wells. It is relativelyinexpensive and presents few chemical interferences inwater quality sampling. Many other materials areavailable for specific uses, including galvanized andstainless steel, Teflon©, and other plastics.
The diameter of the well depends on the instrumentationto be installed and the intended use. If the well is to besampled, by either pump or bailer, a 3-inch (75-mm)diameter hole is the preferred size for accuracy and forcomplete development of the hole, but smaller sizes canbe used with small bailers and peristaltic pumps. Wellsused for measuring water levels only may be smallerdiameter or may have multiple small diameterstandpipes within a 4-inch (100-mm) to 8-inch (200-mm)diameter hole. A standpipe designed to accommodate anM-scope water level sensor can be ¾ inch (19 mm)diameter. However, if the standpipe is to be
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instrumented with a pneumatic or vibrating wirepiezometer or if a recorder and electric probe will be usedto monitor the water level, then the diameter of thestandpipe depends on the size of the instrument ortransducer to be installed. Lengths of well screen andcasing (PVC perforated and solid standpipe) must haveuniform inner and outer casing diameters. Inconsistentinner diameters cause problems when instruments withtight clearance are lowered into the well. The pipe mayneed to be reamed to remove the beads and burrs. Afilter pack is generally composed of washed sand andgravel and is placed within the screened interval. Theinterval may extend above the screen depending on thezone thickness. The pack is designed primarily to allowwater to enter the standpipe while preventing themovement of fines into the pipe through the slots, and toallow water to leave the standpipe when water levelsdrop. If the well is to be used for sampling, the packmaterial should be sterilized to prevent possiblecontamination before placement into the well. Thegravel pack should be tremied through a pipe to preventbridging. The top of the pack may be checked using asmall diameter tamping tool, or a properly weighted sur-veyor’s tape.
A seal is installed to create an impermeable boundarybetween the standpipe and the casing or drill hole wall.The seal should be placed in a zone of low permeability,such as a clay bed above the zone to be monitored. Thisensures that water will not travel vertically along thecasing or drill hole.
Cement grout can shrink due to temperature changesduring curing and may crack. This causes a poor bondbetween the grout and the standpipe. A 1-foot (0.3-m)bentonite seal should be placed preferably as pellets orby tremieing a bentonite slurry immediately below and
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above the cement grout seal. This helps ensure areliable plug. Any seal material (optional with bentonitepellets) should be tremied into place. This preventsbridging or caking along the hole wall. The seal must bereliable so that the screened interval monitors only thedesired groundwater zone.
A drill hole containing multiple standpipes, each mon-itoring a zone or distinct water bearing strata, may haveseveral isolating seals. To test the integrity of the seals,a gravity head test may be performed by adding water tothe shallowest standpipe and continuously measuringthe water level in the next lower piezometer to detectany leakage through or around the seals. If the waterleaks into the lower interval, the piezometric head willrise in the lower standpipe.
A protective cover helps prevent damage to the standpipeand reduces surface water drainage into the backfilledhole. The casing should extend 5 to 10 feet (1.5 to 3 m)below ground and be grouted into place. Uponcompletion of the monitoring well, standpipe should bebailed or blown dry and the water level allowed torecover to a static level. A completion log should beprepared using the drillers' records, geologic log, andmeasurements. The log should include the actual depthsand thicknesses of each component of the well; thestandpipe's total depth; the screened interval, theisolated interval; the type of filter pack; the depth,thickness, and type of isolating seals; and a referencepoint from which all measurements were taken, such astop of casing or ground surface. Many excellentreferences are available to design and installgroundwater monitoring wells for various purposes.Refer to these at the end of this chapter for moredetailed instructions.
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Construction Materials
Construction materials for observation wells andpiezometers are dictated by the projected use of theinstrument and the permeability of the aquifer. Thediameter of the standpipe, the type of standpipe used(metal versus plastic), screen slot size/porous tube type,and gravel pack material are all variables dictated byaquifer characteristics.
In a relatively permeable material, the diameter of astandpipe is not critical; sand or gravel pack around thewell tip may not be required, but the screen slot size maybe critical to the success of the installation. Too smallscreen or slot size may restrict instrument reaction tochanges in water levels.
In a relatively impermeable material, pipe diameter maybe critical, a pack material of select sand or fabric wrapusually is required, and a well point or screen assemblyusually is needed, (0.010-0.020-inch [0.0250.05centimeter (cm)] slot size). Generally, the smallestdiameter pipe practical should be used in this sort ofmonitoring application, keeping in mind that thestandpipe diameter must be large enough to install ameans of measuring water levels. If the volume of thehole is too large, too much water must move in and outof the hole to accurately reflect the water level. If rapidreaction to water level or changes is needed, a pressuretransducer may be more appropriate than an open-tubepiezometer or standpipe.
A variety of materials can be used as the standpipe.Polyvinyl chloride (PVC) plastic pipe is economical andeasy to install. Plastic pipe is fairly fragile, deformable,and can be destroyed accidentally during installation.Metal pipe is more durable for installation but generally
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costs more than plastic, rusts or corrodes, and is subjectto iron bacterial action. Generally, if grout plugs areused to isolate zones, black pipe is preferred because thezinc in galvanized pipe can react with the plug anddestroy the seal. The inside diameter (I.D.) of the pipedepends on the permeability of the aquifer material andcan vary from as small as ½ inch (13 millimeters [mm])to 2 inches (50 mm) or larger. The diameter of the riseris critical to instrumentation of the observation well orpiezometer. Generally, ¾-inch (19 mm) pipe is thesmallest practical size that can be used in automatedapplications. Reaming of the pipe prior to installation toremove burrs, weld seams, and blebs of galvanizingmaterial is a necessary precaution to ensure that thestandpipe will be usable if the pipe I.D. and measuringdevice outside diameter (O.D.) are close.
The screen assembly selected for an observation well orpiezometer can be a well point, well screen, porous tube,or perforated pipe (commercially manufactured or fieldfabricated). Screen should be PVC or corrosion-resistantmetal. Slot-size is determined by filter material size andaquifer material.
The gravel-pack material selected is determined by theparticle sizes of the aquifer material and the size of thewell screen. Concrete sand or reasonably well-gradedsand to pea gravel can be used.
Plug material used to isolate the interval to be monitoredcan be tremied cement grout, bentonite pellets, or a com-bination of the two. A bentonite slurry also may be usedin some instances but must be tremied in place.Bentonite pellets are preferred if only one isolationmethod is used.
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Methods Used to MeasureGroundwater Levels
General
Groundwater measurements (and any instrumentationreadings) should be interpreted concurrently with read-ing. Erroneous readings and faulty equipment need tobe detected as encountered, and timely interpretation isa reliable method of bad reading detection. Theperson(s) taking the readings must understand theequipment and gather reliable data from theinstruments. If bad read-ings or faulty equipment arenot detected by concurrent interpretation, months ofirretrievable data can be lost, and erroneousinterpretations or data impossible to inter-pret canresult.
Manual Methods Used to Measure GroundwaterLevels
Chalk and Surveyors' Chain.—Probably the oldestand one of the most reliable methods for measuring wellsis the surveyors' chain and chalk method. This methodis not recommended where water level depths exceedseveral hundred feet (300 m+).
A lead weight may (but not necessary) be attached to asteel measuring tape (surveyors' chain). The lower 5 feet(1.5 m) of the tape is wiped dry and covered with solidcarpenter's chalk if the water level is roughly known.The tape is lowered into the well, and one of the footmarks is held exactly at the top of the casing. The tapeis pulled up. The line can be read to a hundredth of afoot (0.003 m) on the chalked section. This reading issub-tracted from the mark held at the measuring point,and the difference is the depth to water.
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The disadvantage to this method is that the approximatewater depth must be known so that a portion of thechalked section will be submerged to produce a wettedline. Deep holes require a long surveyor’s chain whichcan be difficult to handle.M-Scope (Electric Sounder).—An M-scope is anelectric sounder or electrical depth gauge consisting of anelectrode suspended by a pair of insulated wires and amilliammeter that indicates a closed circuit and flow ofcurrent when the electrode touches the water surface.Usually, AA flashlight batteries supply the current. Theinsulated wire usually is marked off in 1-foot to 5-foot(0.3- to 1.5-m) intervals. The best devices have themeasuring marks embedded directly into the line.Markers that are attached to the line slip, making itnecessary to calibrate the instrument frequently.
With the reel and indicator wire in one hand and theother hand palm up with the index finger over the casingor piezometer pipe, the wire is lowered slowly over thefinger into the piezometer pipe or well casing. By slidingthe wire over the finger, the wire is not cut or damagedby the sharp casing or piezometer pipe. Several readingscan be taken to eliminate any errors from kinks or bendsin the wire. The water level depth can be measured fromthe top of casing using the mark-tags on the insulatedwire and a tape measure marked in tenths and hun-dredths of a foot. The advantage of this method is thatwater level depths in holes several hundred feet deep canbe measured fairly quickly and accurately. The disad-vantage to this method is that malfunctioning ormechanical problems develop in the instrument givinger-roneous water level readings. Before going into thefield, the instrument must be checked for low batteries,tears, scrapes on the insulated wires, and iron-calciumbuildup on the part of the electrode touching the watersurface.
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Airline and Gauge.—This method uses a smalldiameter pipe or tube inserted into the top of the wellcasing down to several feet below the lowest anticipatedwater level. The exact length of airline is measured asthe line is placed in the well. The airline must be airtight and should be checked. The airline must hangvertically and be free from twists and spirals inside thecasing. Quarter-inch (6.3 mm) copper or brass tubingcan be used. The upper end of the airline is fitted withsuitable connections and a Schraeder valve so that anordinary tire pump can be used to pump air into thetube. A tee is placed in the line so that air pressure canbe measured on a pressure gauge.
This device works on the principle that the air pressurerequired to push all the water out of the submergedportion of the tube equals the water pressure of a columnof water of that height. A reference point (e.g., top ofcasing or pipe) and the depth to the lower end of theairline must be known. Air is pumped into the airlineuntil the pressure on the gauge increases to a maximumpoint where all the water has been forced out of theairline. At this point, the air pressure in the tube justbalances the water pressure. The gauge reading showsthe pressure necessary to support a column of water ofa height equal to the distance from the water level in thewell to the bottom of the tube.
If the gauge reads the direct head of water, thesubmerged length of airline is read directly. The totallength of airline to the reference point, minus thesubmerged length gives the depth to water below themeasuring point. If the gauge reads in pounds persquare inch, multiply the reading by 2.31 to convert tofeet of water. An accurate, calibrated gauge and astraight, air-tight airline are important.
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Popper.—A simple and reliable method of measuringwater levels is with a popper. A tape with a popperattached to the bottom is lowered into the well or casinguntil the water is reached, as indicated by a pop. Thepopper is raised above and lowered to the water surfaceseveral times to accurately determine the distance. Apopper consists of a small cylinder closed at the top andopen at the bottom. The open bottom causes a poppingsound when the water surface is hit. A 1-inch (in) or1½-in (25- or 40-mm) pipe nipple 2 to 3 in (50 to 75 mm)long with a cap on top works satisfactorily.
Pressure Gauge for Monitoring Artesian Wells.—Additional standpipe or casing can theoretically be ex-tended to eventually equal the head of the water. Asimple method to determine the artesian head is toattach a pressure gauge to the casing or the piezometerpipe. The gauge selected may be read directly or in feet(meters) of water. Install a tee on the standpipe or onthe casing so that a pressure gauge and valve can beattached to the tee. The valve may be used to bleed thepressure gauge to see if the gauge is working and can beused to measure the flow on the artesian well. When apressure reading is taken, a flow measurement shouldalso be taken. During the winter months, the valveshould be cracked open to allow the well to flow slightlyto prevent the riser pipe from freezing and breaking.The line to the gauge should be bled of water. If thepressure gauge used is in lbs/in2, multiply the gaugereading by 2.31 to obtain the head of water above thevalve.
Continuous Recorders
Stevens Recorder.—The Stevens Recorder (producedby Stevens Water Resources Products) provides areliable and economical way to obtain continuous water
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level data. The recorder is a float type consisting of a 3-to 6-inch (76- to 152-mm) float connected to a pulleywhich turns a calibrated gear-driven drum. A powersource, such as a spring clock or small motor, rotates thedrum at a known rate giving a constant indication ofelapsed time. Gearing between the float pulley and the chart drumprovide a changeable ratio of water movement to penmovement on the chart. A time scale is available on thechart, and continuous recordings may be maintained forup to several months. When a Stevens recorder is usedin a well, the minimum diameter of the well casing is4 inches (100 cm). An advantage of the Stevens recorderis versatility. Hydrographs can be created with scales of1:1 to 1:20. Most recorders can be set from 4 hours toseveral months. Johnson-Keck has a water level sensinginstrument that can continuously record water levels in½-inch (13-mm) pipe and larger. Transistorized circuitryis used to control a battery powered motorized reel. Thesensing float is attached to one end of the control wire,and the other end of the wire is connected to the reel.The instrument is connected to a Stevens type F orStevens type A recorder. The control wire passes aroundthe recorder pulley, and the sensing device is placed inthe casing. The sensing device seeks the water surface;and once the water surface is found, the circuitry keepsthe sensing device at the water surface.
Many float recorders can be attached to digital recordersfor continuous records. Data from this type ofinstrument can be used and easily interfaced with acomputer system.
Bristol Recorders.—Recorders for monitoring contin-uous artesian pressures are produced by Bristol Instru-ment Systems. The Bristol and Stevens recorders aresimilar in that pressure and time are recorded on a
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chart. The instrument usually contains diaphragms thatcan be adjusted to varying pressure conditions. Thespring-driven clock usually is calibrated for 30 days. TheBristol recorder is very useful for observing pressurechanges in artesian wells but is limited by freezingconditions in northern climates. A pressure gaugeinstalled in the line between the artesian water and thepressure recorder is very useful. This gauge provides agood indication of the working condition of theinstrument.
Gas Bubbler Transducer.—Pneumatic or gas bubbletransducers are manufactured by many companies. Thetransducers vary from a single readout box to a compli-cated array of instruments that will measure severalwells at once. A gas is forced through a tube at aconstant rate past a diaphragm. When the pressure ofthe gas on the diaphragm and the water pressure on theother side of the diaphragm are equal, a constantreading is obtained. This reading equals the amount ofwater over the diaphragm. This number multiplied by2.31 will give the amount of water head over theinstrument. These instruments may be used as a singleunit or connected into an electronic data acquisitionsystem.
Maintenance.—A good maintenance program is neces-sary to ensure reliable performance of mechanicallyactuated recorders. The instruments and data collectedare only as good as the preventive maintenance. Aroutine preventive maintenance program should bescheduled for all the instruments. In some cases, dailyinspection of recorders is required; however, if theinstrument is working properly, weekly inspections maybe sufficient. Preventive maintenance can often beaccomplished when the charts are changed.
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Methods and Techniques Used to EstimateFlows from Seeps, Springs, and Small Drainages
A thorough and detailed discussion of weirs, flumes,stilling wells, and other techniques is presented inReclamation’s Water Measurement Manual [1]. Smallseeps, springs, and intermittent drainages are oftenencountered in field investigations. These features canprovide key information during design and constructionand may be key indicators of structure performance orenvironmental impacts that may affect the project. Thelocation of drainage features, the rate of flow, and thetime of year of the observation are importantinformation. Flow can be estimated accurately using themethods described below:
Estimate the rate of flow in an open channel usingQ=VA, where:
Q = rate of flowV = velocityA = cross sectional area of channel
The cross-sectional area is determined by direct meas-urements where possible. Where impractical, the cross-sectional area may be estimated or scaled from a topo-graphic map.
Velocity is determined using a float, a measuring tape,and a stop watch by timing how long a floating objecttakes to travel a given distance. This provides a crudebut reasonably accurate estimate of flow. Other methodsmay include a pitot tube or flow meter.
Substitute the values obtained into the Q=VA equationto obtain the volume of flow.
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Measure flow from small springs and seeps directly bydiverting the flow, or in some manner channel the flowto a point for collection in a container, such as a bucket.Determine the rate of flow by timing how long it takes tofill the container. Select points along a drainage whereabrupt dropoffs occur and use this method. It is betterto measure, however crudely; but if not possible,estimate the flow. Many more sophisticated methodscan be used to obtain more accurate flow measurements,if necessary. Determination of the most appropriatemethod can be made if preliminary data are available.
Computer-Based Monitoring Systems
General
Water level monitoring may be automated. Monitoringlandslides can require a great number of points andfrequent readings. A variety of data types may berequired, which may include measurements of not onlywater levels and pore pressure changes, but deformationand movement as well. Systems required to collect,store, format, and present these data are availableallowing realtime analysis of a wide variety of datatypes.
Components of a Computer-Based Monitoring System
1. Many types of instruments including inclinometers,pressure transducers, strain gauges, water level gauges,and flowmeters can be used in a monitoring system.Electronic instruments are available in many sizes andshapes; preliminary selection of the instrument type
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should be made during the initial design of the system.The inside diameter of the well must be sized to acceptthe transducer.
2. Acquired data is sent from the instrument at the wellto the data logger or processor. This is done by hardwirefrom the instrument, line-of-sight radio, satellite radio,or phone lines.
Data from the monitoring points may be preprocessed inthe field prior to transmittal to the central computer. Anumber of microprocessor data scanners that collect andreduce data can be installed at various field locations.The central computer queries the field scanners to obtainperiodic updates. The remote scanners can be interro-gated as frequently as desired. This may include acontinuous data scan mode.
3. Data scanners reduce the instrument output to usabledata. Data scanners can be the end destination for moresimple systems or can be part of a more elaboratesystem. Generally, two types of signals are generated byinstruments used in geotechnical monitoring: (a) digitaland (b) analog current or voltages. Data scanners whichaccept and reduce data from both types of signals areavailable.
Many manufacturers offer complete packages of auto-mated instrumentation systems, including computerhardware and software. If the initial observation wellprogram is designed for automation, most of thesesystems will provide the high quality data required.
Special Applications
Many types of instrumentation can be used in a singledrill hole. A multiple use casing collects groundwater
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data from a large number of horizons within a singledrill hole. Casing is available specifically for pore-pressure observations, or grooved casing can be used sothat the well can be completed for both pressure andinclinometer measurements. Isolation between horizonscan be accom-plished either by installing a bentonite sealor by using a packer assembly designed as an integralpart of a monitoring system. Use of a monitoring systemgreatly reduces drilling costs, provides detailedmonitoring of critical drill holes, and provides a greaterflexibility than systems previously available. Smalldiameter drill holes can be used to obtain a large numberof isolated water level intervals and, depending on theapplication, can be very cost effective.
Data Base Management and Data Presentation
Standard forms are available to record field data,although standard data sheets often must be modifiedfor specific applications. Data sheets must includeremarks and information that include the monitoringwell num-ber, location, elevation reference points, typeand size of well, dates and times the well was read,depth to water, and the elevation of the water surface.Periodic readings of these observation wells over longperiods of time generate numerous data sheets.Computerization of the data base very rapidly canbecome a necessity if data are to be readily available andeasily analyzed.
Data entry and storage in digital format allowselectronic transfer of data and greater flexibility indeveloping, analyzing, and presenting data. Data maybe tabulated or presented as time-depth/elevation plotsand interpre-tive drawings such as contours and otherthree dimensional plots. Tremendous volumes of data
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can be reduced quickly to a usable format. Use of acommer-cially available data base allows data use andmanipu-lation without specialized software or training.
Definitions
Aquifer—A body of soil or rock that is sufficientlypermeable to conduct groundwater and to yieldeconomically significant quantities of water to wells andsprings.
• Confined aquifer—An aquifer bounded aboveby impermeable beds, or beds of distinctly lowerpermeability than that of the aquifer itself. Anaquifer containing confined groundwater.
• Unconfined aquifer—An aquifer having awater table. An aquifer containing unconfinedground-water.
Artesian—An adjective referring to groundwaterconfined under hydrostatic pressure.
Artesian aquifer—An aquifer containing water underartesian pressure.
Aquitard—A confining bed that retards but does notprevent the flow of water to or from an adjacent aquifer;a leaky confining bed. An aquitard does not readily yieldwater to wells or springs but may serve as a storage unitfor groundwater.
Aquiclude—A body of relatively impermeable rock orsoil that is capable of absorbing water slowly butfunctions as an upper or lower boundary of an aquiferand does not transmit significant groundwater.
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Water table or water level—The surface between thezone of saturation and the zone of aeration; the surfaceof a body of unconfined groundwater at which thepressure is equal to atmospheric pressure.
Zone of aeration or Vadose zone—Subsurface zonecontaining water under pressure less than atmospheric,including water held by capillarity, and containing air orgases generally under atmospheric pressure. This zoneis limited above by the land surface and below by thesurface of the zone of saturation or water table.
Saturation—The maximum possible content of water inthe pore space of rock or soil.
Zone of saturation—A subsurface zone in which all ofthe interstices are filled with groundwater underpressure greater than atmospheric. The zone is stillconsidered saturated even though the zone may containgas-filled interstices or interstices filled with fluid otherthan water. This zone is separated from the zone ofaeration by the water table.
References
American Geological Institute, Glossary of Geology,4th edition, Alexandria, VI, 1997.
Bureau of Reclamation, Embankment DamInstrumentation Manual, U.S. Department of theInterior, United States Government Printing Office,Washington, DC, 1987.
Bureau of Reclamation, Ground Water Manual,2nd edition, A Water Resources Technical Publication,
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U.S. Department of the Interior, United StatesGovernment Printing Office, Washington, DC, 1995.
Driscoll, Fletcher G., Groundwater and Wells, 2ndedition, published by Johnson Division, St. Paul, MN55112, 1987.
Leupold and Stevens Inc., Stevens Water Resources DataBook, 3rd edition, P.O. Box 688, Beaverton, OR 97005.
Morrison, Robert D., “Equipment, and Application,”Ground Water Monitoring Technology Procedures, TimcoManufacturing Inc., Prairie du Sac, WI, 1983.
BIBLIOGRAPHY
[1] Bureau of Reclamation, Water MeasurementManual, 3rd edition, A Water Resources TechnicalPublication, U.S. Department of the Interior,United States Government Printing Office,Washing-ton, DC, 1997.
Chapter 10
GUIDELINES FORCORE LOGGING
These guidelines incorporate procedures and methodsused by many field offices and are appropriate for"standard" engineering geology/geotechnical log forms,computerized log forms, and many of the modified logforms used by various Bureau of Reclamation(Reclamation) offices.
General
Introduction
This chapter describes the basic methods for engineeringgeology core logging and provides examples andinstructions pertaining to format, descriptive data, andtechniques; procedures for working with drillers to obtainthe best data; caring for recovered core; and water testingin drill holes. The chapter also provides a reference forexperienced loggers to improve their techniques and trainothers. Most of the discussions and examples shownpertain to logging rock core, but many discussions applyto soil core logging, standard penetration resistance logs,and drive tube sample logging.
Purpose, Use, and Importance of Quality CoreLogging
The ability of a foundation to accommodate structureloads depends primarily on the deformability, strength,and groundwater conditions of the foundation materials.The remediation of a hazardous waste site can beformulated only by proper characterization of the site.Clear and accurate portrayal of geologic design andevaluation data and analytical procedures is paramount.Data reported in geologic logs not only must be accurate,
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consistently recorded, and concise, but also must providequantitative and qualitative descriptions.
Logs provide fundamental data on which conclusionsregarding a site are based. Additional exploration ortesting, final design criteria, treatment design, methodsof construction, and eventually the evaluation of structureperformance may depend on core logs. A log may presentimportant data for immediate interpretations or use, ormay provide data that are used over a period of years.The log may be used to delineate existing foundationconditions, changes over time to the foundation orstructure, serve as part of contract documents, and maybe used as evidence in negotiations and/or in court toresolve contract or possible responsible party (PRP)disputes.
For engineering geology purposes, the basic objectives oflogging core are to provide a factual, accurate, and conciserecord of the important geological and physical character-istics of engineering significance. Characteristics whichinfluence deformability, strength, and water conditionsmust be recorded appropriately for future interpretationsand analyses. Reclamation has adopted recognizedindexes, nomenclature, standard descriptors anddescriptive criteria, and alphanumeric descriptors forphysical properties to ensure that these data are recordeduniformly, consistently, and accurately. Use of alpha-numeric descriptors and indexes permits analysis of databy computer. These descriptors, descriptive criteria,examples, and supporting discussions are provided inchapters 3, 4, and 5.
Exploration should be logged or, as a minimum, reviewedby an experienced engineering geologist. The loggershould be aware of the multiple uses of the log and theneeds and interests of technically diverse users. The
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experienced logger concentrates on the primary purposesof the individual drill hole as well as any subordinatepurposes, keeping in mind the interests of others withvaried geological backgrounds including geotechnicalengineers, contract drillers, construction personnel, andcontract lawyers. An experienced logger tailors the log tomeet these needs, describing some seemingly minorfeatures or conditions which have engineeringsignificance, and excluding petrologic features or geologicconditions having only minor or academic interest. Lessexperienced loggers may have a tendency to concentrateon unnecessary garnishment, use irrelevant technicalterms, or produce an enormously detailed log whichignores the engineering geology considerations andperhaps the purpose for completing the drill hole.Adequate descriptions of recovered cores and samples canbe prepared solely through visual or hand specimenexamination of the core with the aid of simple field tests.Detailed microscopic or laboratory testing to define rocktype or mineralogy generally are necessary only in specialcases.
Empirical design methods, such as the Rock Mass RatingSystem Geomechanics Classification (RMR) and Q-systemClassification (Q), are commonly used for design of under-ground structures and are coming into common use forother structures as well. If these methods are used, thenecessary data must be collected during core logging.
If hazardous waste site characterization is the primarypurpose of the drilling, the log should concentrate onproviding data for that type of investigation.
Drilling and logging are to determine the in-placecondition of the soil or rock mass. Any core condition,core loss, or damage due to the type of bit, barrel, or otherequipment used, or due to improper techniques used in
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the drilling and handling processes should be described.Such factors may have a marked effect on the amount andcondition of the core recovered, particularly in soft,friable, weathered, intensely fractured materials or zonesof shearing. Geologic logs require the adequatedescription of materials; a detailed summary of drillingequipment, methods, samplers, and significantengineering conditions; and geologic interpretations.Complete geologic logs of drill holes require adequatedescriptions of recovered surficial deposits and bedrock,a detailed summary of drilling methods and conditions,and appropriate physical characteristics and indexes toensure that adequate engineering data are available forgeologic interpretation and analysis.
Format and Required Data for theFinal Geologic Log
Organization of the Log
The log forms are divided into five basic sections: aheading block; a left-hand column for notes; a center col-umn for indexes, additional notes, water tests andgraphics; a right-hand column for classification andphysical conditions; and a comments/explanation block atthe bottom. Data required for each column are describedin the following discussion and the referenced examplelogs. Log DH-123, figure 10-1, and log B-102, figure 10-2,are the most complete and preferred examples; othervariations are presented but in some cases are notcomplete.
Heading
The heading block at the top of the form provides spacesfor supplying project identifying information, feature,
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Figure 10-1.—Drill hole log, DH-123, sheet 1 of 2.
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Figure 10-1.—Drill hole log, DH-123, sheet 2 of 2.
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Figure 10-2.—Drill hole log, B-102, for StandardPenetration Test, sheet 1 of 3.
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Figure 10-2.—Drill hole log, B-102, for StandardPenetration Test, sheet 2 of 3.
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Figure 10-2.—Drill hole log, B-102, for StandardPenetration Test, sheet 3 of 3.
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hole number, location, coordinates, elevation, bearing andplunge of hole, dates started and completed, and thename(s) of the person(s) responsible for logging and re-view. Locations should preferably be in coordinatesunless station and offset are all that is available.
Provide both coordinates and station and offset ifavailable. The dip or plunge of the hole can be the anglefrom horizontal or from vertical, but the reference pointshould be noted on the log. Spaces for depth to bedrockand water levels are also provided. All this informationis important and should not be omitted. Below theheading, the body of the log form is divided into a seriesof columns covering the various kinds of informationrequired according to the type of exploratory hole.
Data Required for the "Drilling Notes" Column
Data for the left-hand column of all drill hole logs aresimilar whether for large-diameter sampling, StandardPenetration Tests, rock core, or push-tube sampling logs.These data are field observations and informationprovided by the driller on the Daily Drill Reports.Examples are provided for some of these data headings;a suggested guideline and preferred order is presented inthe following paragraphs but may differ depending on thepurpose and type of exploration. Headers for data canindicate whether depths are in feet (ft) or meters (m),eliminating the need to repeat "ft" or "m" for each intervalentry. An example of the Drilling Notes column isprovided on figures 10-1 through 10-4.
General Information.—This includes headers and datafor the hole purpose, the setup or site conditions, drillers,and drilling and testing equipment used.
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Figure 10-3.—Drill hole log, DH-SP-2, sheet 1 of 2.
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Figure 10-3.—Drill hole log, DH-SP-2, sheet 2 of 2.
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Figure 10-4.—Drill hole log, SPT-107-2, sheet 1 of 3.
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Figure 10-4.—Drill hole log, SPT-107-2, sheet 2 of 3.
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Figure 10-4.—Drill hole log, SPT-107-2, sheet 3 of 3.
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1. Purpose of hole — Includes reason for drillingthe hole, such as foundation investigation, materialsinvestigation, instrumentation, sampling, or testing.
2. Drill site or setup — Includes general physicaldescription of the location of the drill hole.Information on unusual setups, such as adjacent toa stream, or drilled from a barge, gallery, or adit,may help understand the unusual conditions.
3. Drillers — Names of drillers may be significantfor reference or for evaluating or interpreting corelosses, drilling rates, and other drilling conditions.
4. Drilling equipment —
• Drill rig (make and model)
• Core barrel(s), tube(s), special samplers (typeand size)
• Bits (type and size)
• Drill rods (type and size)
• Collar (type)
• Water test equipment (rod or pipe size, hosesize, pump type and capacity, and relativeposition and elevation of pressure gauges ortransducers), packers (type—mechanical orpneumatic)
Example: Skid-mounted Sprague and HenwoodModel 250. NWD3 bottom discharge bit with a5-ft (1.5-m), split-tube inner barrel. 5-ft (1.5-m)NW rods. Water tested with NX pneumatic
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packer No. 12 with 1-1/4-inch (in) (32-millimeter[mm]) pipe, Bean pump with 35-gallons perminute (gal/min) (159 liters per minute)maximum volume, and 1-in (25-mm) watermeter. (Water testing equipment can be aseparate heading if desired.)
Drilling Procedures and Conditions.—These headersand data should include methods, conditions, driller'scomments, and records for water losses, caving, or casing.
1. Drilling methods — Synopsis of drilling, sam-pling, and testing procedures, including proceduresand pressures for drive or push tubes used throughthe various intervals of the hole.
2. Drilling conditions and driller's comments — Note by interval the relative penetration rate andthe action of the drill during this process (i.e., 105.6-107.9: drilled slowly, moderate blocking off, holeadvancing 15 minutes per foot [.3 meter]). Unusualdrilling conditions should be summarized. Changesin drilling conditions may indicate differences inlithology, weathering, or fracture density. Thegeologist needs to account for variations in driller'sdescriptions; each driller may describe similarconditions with different adjectives or percentageestimates. Any other comments relative to ease ordifficulty of advancing or maintaining the holeshould be noted by depth intervals. Drillers'comments need to adequately describe conditionsencountered while advancing the hole. Statementssuch as "normal drilling" or "no problemsencountered" are not useful.
Differences in drilling speeds, pressures, andpenetration rates may be related to the relative
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hardness and density of materials. Abrupt changesin drilling time may identify lithologic changes orbreaks and also may pinpoint soft or hard interbedswithin larger units. Often, these may be correlatedwith geophysical logs. If the driller provides usefuland accurate records of drilling conditions andprocedures, an accurate determination of the top andbottom of key marker horizons can be made evenwithout core.
Drilling progress should be recorded while drilling;recovery can be improved by relating recovery tooptimum pressures and speeds, as well as providingdata for interpretation. For each run, the drillershould record the time when starting to drill andwhen stopping to come out of the hole. Most of thesedrilling progress data are qualitative rather thanquantitative values. Controlling factors are not onlythe type of materials encountered but also may bemechanical or driller variables. These variables mayinclude type and condition of the bit, rotation speed,drilling fluid pressure, etc. THE PURPOSE OF THEBORING IS TO OBTAIN THE HIGHEST QUALITYCORE AND MOST COMPLETE RECOVERY ANDINFORMATION, NOT JUST FEET PER HOUR ORSHIFT.
3. Drilling fluid — Type and where used (includingdrilling fluid additives). This may be combined withor discussed under the heading, drilling methods.
4. Drilling fluid return — Include interval/percentreturn. Drilling fluid return may be combined withcolor.
5. Drill fluid color — Include interval/color.
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6. Caving conditions — Intervals of cave with ap-propriate remarks about the relative amount ofcaving are to be noted. When possible, report theactual caving interval rather than the depth of thehole.
7. Casing record — Casing depth is the depth ofcasing at the start of the drilled interval (see theexample below).
8. Advancement (push-tube or StandardPenetration Test (SPT) applications) — Includedepth/ interval sampled.
9. Cementing record — Note all intervalscemented and if intervals were cemented more thanonce. This information may be combined with thecasing record, as shown below:
Example of casing and cementing record:
Interval drilled(feet)
Size(inch)
Casing depth(feet)
0.0-2.3 6 Cs 0.0
2.3-4.5 6 Cs 2.0
4.5-9.2 6 Cs 4.0
9.2-15.3 NxCs 8.0
15.3-18.7 NxCs 15.0
18.7-33.2 Cmt 12.1-18.7 Cmt
Hole Completion and Monitoring Data.—Data shownin this section of the left-hand column include holecompletion, surveys, water levels, drilling rates or time,and reason for hole termination.
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1. Borehole survey data — Include if obtained.
Example of survey data:
Depth Bearing Plunge
597999119Average
S 72EWS 75E WS 72E WS 72E W
90E1
90E89E89E89E
1 E = degrees.
2. Water level data — Note depths and/or eleva-tions, water quantities, and pressures from artesianflows. Water levels or flows should be recordedduring hole advancement, between shifts, or at thebeginning or end of a shift, but definitely should berecorded at completion of the hole and periodicallythereafter. It may be advantageous to leave space orprovide a note to refer the user to additional readingsprovided elsewhere on the log for subsequentmeasurements. Computer generated logs allowconvenient updating of water levels long after thehole is completed.
Examples of drill hole logs illustrate optional formatand subsequent readings. Examples of how to recorddata are:
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Date1981
Hole depth(feet)
Depth to water(feet)
11-02 25.0 6.0
Bailed 100 gal:Level beforeLevel after
6.021.0
or:
DateHole depth
(feet)
Depth towater(feet)
11-03-81 25.0 15.0
11-04-81 40.0 29.0
01-05-82 95.2 7.0
01-15-82 95.2 Flowing 25 gal/min
02-03-82 95.2 Flowing 5 gal/min at 5 pounds per square inch (lb/in2)
3. Hole completion — Indicate how hole was com-pleted or backfilled; if jetting, washing, or bailingwas employed; depth of casing left in hole or thatcasing was pulled; location and type of piezometers;location, sizes, and types of slotted pipes (includingsize and spacing of slots) or piezometer risers; typeand depth of backfill or depths of concrete and/orbentonite plugs; location of isolated intervals; andelevation at top of riser(s). Hole completion can beshown graphically (see figure 10-5).
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Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 1 of 3.
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Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 2 of 3.
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Figure 10-5.—Drill hole log, DH-DN/P-60-1, sheet 3 of 3.
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4. Reason for hole termination — State whetherthe hole reached the planned depth or reason whythe hole was stopped short.
5. Drilling time — Total time, setup time, drillingtime, and downtime should be recorded on drillers'daily sheets and should also be recorded on the drilllog. These records are essential for determiningexploration program costs.
Center Columns of the Drill Log
Computer Logs.—Computer-generated logs offer severaloptions for the content and format of the log such aspermeability, penetration resistance, or rock propertieswhich have some differences in format. Examples of eachare shown in figures 10-2 through 10-5. Standard Geologic Log Form.—The followingdiscussion pertains to the center columns for the standardReclamation log (form 7-1337). The columns shown onall figures are self-explanatory. The columns can be mod-ified or new columns added to the existing log form forrecording appropriate indexes or special conditions.
The percolation tests (water-pressure tests) columnshould record the general information of the tests.Additional data may be recorded on "water testing" logforms or drillers' reports.
Type and size of hole, elevation, and depth columns areself-explanatory.
Core recovery should be recorded in percent of recoveryby run. Although desirable, core recovery does notnecessarily require a visual graph. Core recovery shouldbe noted carefully by the driller for each run on the daily
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drill reports; however, this column should be the recordof those measurements determined by the geologistduring logging. Measuring the core while in the splittube or sampler, if possible, will produce the mostaccurate recovery records.
A hole completion column may be added whichgraphically portrays how the hole was completed. If used,an explanation of the graphic symbols should be providedon the log form.
Rock quality designation (RQD) should be reported bycore run. RQD should be included on the log in graph ortabular form regardless of the type project. RQD is usedin almost any engineering application of the hole data.Most contractors are interested in RQD as an index ofblasting performance, rippability, and stability. RQD isdescribed and explained in chapter 5.
A lithologic log or graphic column is helpful to quicklyvisualize the geologic conditions. Appropriate symbolsmay be used for correlation of units, shear zones, waterlevels, weathering, and fracturing (see figure 10-1).
The samples and testing column should include locationsof samples obtained for testing and can later have actualsample results inserted in the column, if the column isenlarged.
Modifications to Standard Log Form.—Modificationsor adaptations of the center columns are permissible and,in some instances, encouraged. Examples are:
1. The use of a continuation sheet for longer drilllogs saves time and is easier to type. The sheets mayhave only one column to continue the right-handnarrative, or may be divided into two or more
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columns. See sheets 2 and 3 for drill hole SPT-107-2,figure 10-4, for an example; also see sheet 3 of 3 fordrill hole DH-DN/P-60-1, figure 10-5.
2. The center column may be modified to portray ad-ditional data such as hole completion, variousindexes, alphanumeric descriptors, or laboratory testdata.
Standard penetration test hole SPT-107-2,figure 10-4, is a modified penetration resistance logwhich shows laboratory test results; a percentgravel/percent sand/ percent fines column; liquidlimit/plasticity index (LL/PI) column, a field moisturecolumn, and other modifications. Drill hole DH-SP-2,figure 10-3, has columns for reporting field densitytest results, moisture, porosity, percent saturation,percent fines/percent sand, LL/PI, and laboratoryclassification.
3. Another modification, shown on DH-SP-2,figure 10-3, is a drawing showing the location of thehole in relation to the structure being explored.Diagrams or graphs, such as water levels, mayillustrate data better than a column of figures.
Required Data and Descriptions for the Right-Hand "Classification and Physical Condition"Column
General.—An accurate description of recovered core anda technically sound interpretation of nonrecovered coreare the primary reasons for core logging. The loggerneeds to remember that any interpretation, such as ashear, must be based on observed factual data. Theinterpreted reason for the core loss is given, but usually
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it is best to define the area of core loss as the intervalheading. For example:
99.4. to 101.6: No Recovery. Interpreted to be in-tensely fractured zone. Drillers reported blocking off,core probably ground up during drilling.
103.4 to 103.7: Open Joint?. Drillers reported 0.3-ftdrop of drill rods during drilling and loss of all water.Joint surfaces in core do not match.
0.7 to 11.6: Silty Sand. Poor recovery, only 6.2 ftrecovered from interval. Classification based on re-covered material and wash samples.
0.9 to 3.2: Rockbitted. No samples recovered.(Usually this would be subheaded under a previousdescription, inferring the materials are the same asthe last recovered).
Descriptions of Surficial Deposits.—Surficial depositssuch as slope wash, alluvium, colluvium, and residual soilthat are recovered from drill holes are described usingUSBR 5000 and 5005. If samples cannot be obtained,then description of the cuttings, percent return and colorof drilling fluid, drilling characteristics, and correlation tosurface exposures is employed. Always indicate what isbeing described—undisturbed samples, SPT or washsamples, cuttings, or cores. Descriptors and descriptivecriteria for the physical characteristics of soils mustconform to the established standards. Chapter 11provides guidelines for soil and surficial depositdescriptions.
Extensive surficial deposits usually are described usinggeologic and soil classifications. Where surficial depositsare very shallow and not pertinent to engineeringapplications for design or remediation or where geologic
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classification such as landslides or talus is preferable,units may be given genetic or stratigraphic terms only.For example, Quaternary basin fill, recent streamchannel deposit, Quaternary colluvium, zone 3embankment, and random fill may be describedgenerally; or these may be unit headings with groupname subheadings. The format is:
Geologic and group name. i.e., Alluvium, (sandysilt). Field classification in parentheses if classified,refer to chapters 3 and 11 for exceptions.
Classification descriptions. Additionaldescriptors (particle sizes, strength, consistency,compactness, etc., from the USBR 5000 and 5005standards descriptive criteria).
Moisture. (dry to wet).
Color.
If cores or disturbed samples are not available, describeas many of the above items as can be determined fromcuttings, drill water color, drilling characteristics,correlation to surface exposures, etc. Remember that forrockbitted, no recovery, or poor recovery intervals, aclassification and group name should be assigned as aprimary identification.
Description of Rock.—Description of rock includes arock unit name based on general lithologic characteristicsfollowed by data on structural features and physicalconditions. Bedrock or lithologic units are to be delineatedand identified, not only by general rock types but by anyspecial geological, mineralogical features withengineering significance, or those pertinent tointerpretation of the subsurface conditions.
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Any information which is characteristic of all of the rockunits encountered normally is included under the mainheading, producing more concise logs. Differences can bedescribed in various subheadings. Rock core is to bedescribed in accordance with descriptors and descriptivecriteria presented in chapters 4 and 5. A suggestedformat is:
1. Rock name — A simple descriptive name,sufficient to provide others with possible engineeringproperties of the rock type; may include geologicalage and/or stratigraphic unit name.
2. Lithology (composition/grain sizes/texture/color) — Give a brief mineralogical description.Describe grain shape and size or sizes and textureusing textural adjectives such as vesicular,porphyritic, schistose. (Do not use petrographicterms such as hypidiomorphic, subidioblastic). Otherpertinent descriptions could include porosity,absorption, physical characteristics that assist incorrelation studies, and other typical and/or unusualproperties. Provide the wet color of fresh andweathered surfaces.
Contacts should be described here also. If thecontacts are fractured, sheared, open, or have othersignificant properties, the contacts should beidentified and described under separate subheadings.
3. Bedding/foliation/flow texture — Provide adescription of thickness of bedding, banding, orfoliation including the dip or inclination of thesefeatures.
4. Weathering/alteration — Use established de-scriptors which apply to most of the core or useindividual subheadings. For alteration other than
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weathering, use appropriate descriptors. These mayor may not be separate from weathering dependingupon rock type and type of alteration. Also, includeslaking properties if the material air or water slakes.(Weathering may be used as first or second orderheadings for some logs.)
5. Hardness — Use established descriptors.
6. Discontinuities — These include shears, joints,fractures, and contacts. Discontinuities control orsignificantly influence the behavior of rock massesand must be described in detail. Detailed discussionsof indexes and of descriptive criteria, descriptors, andterminology for describing fractures and shears areprovided in chapter 5 and 7.
Fractures or joints should be categorized into sets ifpossible, based on similar orientations, and each setshould be described. When possible, each set shouldbe assigned letter and/or number designations andvariations in their physical properties noted by depthintervals. Significant individual joints also may beidentified and described. Physical measurementssuch as spacing and orientation (dip or inclinationfrom core axis), information such as composition,thickness, and hardness of fillings or coatings;character of surfaces (smooth or rough); and, whenpossible, fracture openness should be recorded. Indrill core, the average length between fractures ismeasured along the centerline of the core forreporting any of the fracture indexes. However,when a set can be distinguished (parallel orsubparallel joints), true spacing is measured normalto the fracture surfaces.
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Description of Shears and Shear Zones.—Shears andshear zones should be described in detail, including datasuch as the percentage of the various components (gouge,rock fragments, and associated features such as dikes andveins) and the relationship of these components to eachother. Gouge color, moisture, consistency andcomposition, and fragment or breccia sizes, shape, surfacefeatures, lithology, and strengths are recorded. Thedepths, dip or inclination, and true thickness, measurednormal to the shear or fault contacts, also must bedetermined, if possible, along with healing, strength, andother associated features. A thorough discussion ofshears and shear zones is contained in chapter 5.
Description of Core Loss.—The significance of core lossis often more important than recovered core. Lost coremay represent the worst conditions for design concepts, orit may be insignificant, resulting from improper drillingtechniques or equipment. Core losses, their intervals,and the interpreted reason for the loss should be recordedon the log.
Written Description Form.—The written descriptionfor physical conditions consists of main headings,indented subheadings, and text which describes theimportant features of the core. Headings and indentedsubheadings divide the core into readily distinguishableintervals which are pertinent to an engineering geologystudy. Assigned unit names should correlate with thoseunit names used for surface mapping. These headingsmay describe portions of the core or the entire core,depending on how well the headings encompass overallcharacteristics. Items characteristic of the entire core inone hole may be stated under the major heading;however, in other holes, this same information may haveto be broken out into various subheadings because it isnot applicable to the entire core. In this discussion,
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several logs are referenced as examples. These logs donot necessarily reflect the established standards, andeach may be deficient in some format or context; they areexisting logs which are included as examples of differentsituations which may be encountered. A discussion ofheadings follows:
1. Main headings — The main heading usuallydivides surficial deposits from bedrock. However,other methods are also acceptable, for example, thesummary log in figure 10-5.
2. First order heading — The first order headingsmay be based on weathering or lithology. When theinitial rock type exhibits more than one weatheringbreak or the lithologic properties are mostsignificant, lithology would be the first orderheading. Weathering may be used as first orderheadings where significant. If a weathering breakcoincides with a lithologic break, or only oneweathering break is present, they may both beincluded in the main heading. Depending onlithologies present, for example, if there is only onerock type, the first order headings may be based onfracturing. Lithology, weathering, or fracturing canalso be the subject of the first order heading. Incertain circumstances, a shear or shear zone or otherfeature could be given a first order or any lower orderheading in order to emphasize a feature’s presence orimportance. The arrangement which will result inthe simplest log is usually the best and should beused. The following examples illustrate the use offirst, second, and third order headings. Theseexamples are not intended to represent examples ofcomplete logs.
An example in which weathering is preferred as thefirst order heading is:
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0.0-5.0: SLOPE WASH (main heading).—General de-scription could include the total description of theunit.
5.0-200.0: PALEOZOIC CALAVERAS GROUP (mainheading).
5.0-100.3: Moderately Weathered (first orderheading based on weathering; descriptions ofweathering applicable to all lithologies could bepresented here).
5.0-10.9: Basalt10.9-20.1: Limestone20.1-50.3: Shale50.3-100.3: Sandstone
100.3-150.0: Slightly Weathered100.3-120.2: Sandstone120.2-150.0: Shale
150.0-200.6: Fresh Shale
An example in which lithology is preferred as thefirst-order subheading is:
0.0-5.0: SLOPE WASH (main heading).—General de-scription, could include the total description of theunit.
5.0-200.6: PALEOZOIC CALAVERAS GROUP (mainheading).—General description applicable to alllithologies.
5.0-100.3: Sandstone (first order heading based onlithology)
5.0-10.2: Intensely weathered
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10.2-40.1: Moderately weathered
40.1-80.2: Slightly weathered
80.2-100.3: Fresh
100.3-150.1: Fresh Shale (first order heading whichcombines weathering and lithology)
150.1-200.6: Fresh Diabase
3. Second order heading — The second orderheading and the associated description contain thechar-acteristics of the rock that are unique to aninterval that is not described in the main and firstorder headings. The second order heading usually isbased on weathering if the first order heading isbased on lithology. If the first order heading is basedon weathering, the second order heading would usu-ally be based on lithology. Fracture data can bedescribed here if similar throughout the interval; ifnot, divide fracture data into third order headings.
4. Third order heading — The third order headingis usually based on fracture data, subordinatefeatures, variations in lithology, etc. This includesvariations of rock quality within a certain lithologydue to shears, joints, bedding or foliation joints, orother discontinuities. Core recovery lengths are anindicator of fracturing and should be described underthis heading, as in the interval from 87.2 to 101.2 inDH-123 figure 10-1. If the fractures are mainlyprominent joint sets or other discontinuities, thespacing and orientation of individual sets, along withthe overall fracture characteristics, should be noted.
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5. Additional indentations — Additionalindentations usually are used to describe importantaddi-tional subordinate features, such as veins orveinlets, variations in lithology, shears, and zones ofnon- or poor recovery.
In summary, any information consistent throughouta higher order heading, but usually included in alower one, should be described in the higher orderheading to prevent repetition.
Data Required for the Comments/ExplanationBlock
The comments/explanation block at the bottom of the logform is used for additional information. This may includeabbreviations used, gauge height for packer tests, andnotes. The hole start and completion date should be inthe heading, as well as the date logged. Revision dates ofthe log should be noted to ensure that the most recentversion of the log can be identified. (Date logged and anysubsequent revision dates should be entered in thisblock). The computer log file name can be recorded inthis block.
Method of Reporting Orientation of PlanarDiscontinuities and Structural Features
True dips can be measured directly in vertical holes. Thedips of planar features in vertical holes are recorded as"dips 60E”or "60E dip" (see drawing 40-D-6499, figure 5-9).True dip usually is not known in angle holes; and,orientation is measured from the core axis and calledinclination, i.e., "Joints are inclined 45E from the coreaxis" (figure 5-9). If dips are known from oriented core orother surveys, dips may be recorded instead of inclination
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in angle holes. Figure 5-9 demonstrates how misinter-pretations can occur; the inclination of a joint in the corefrom a 45E inclined angle hole can be interpreted as ahorizontal joint or as a vertical joint by rotating the core.
Core Recovery and Core Losses
Descriptions of core in the Classification and PhysicalCondition column should describe the recovered core, notonly by physical measurements (maximum, minimum,and mostly range or average), but should identify andinclude the interpretation for any core losses, especiallyif the losses are thought to represent conditions differentfrom the core recovered. Designers and other users of thecompleted log can incorporate into their design all thefactual data that are seen and recorded. What is not seenor reported (core losses) is more difficult to incorporateinto the design and may well be the most significantinformation. Also, core losses and interpretations of thereasons for their loss are significant engineering datathat may correlate open joints, soft zones, or shears fromboring to boring or from surface features to thesubsurface explorations.
Core losses can result from three generalized conditions:inaccurate measurements by the drillers; poor drillingtechniques, equipment, and handling; or geologicconditions. The geologist, using the depth of hole,recovered core, observations of the core, and drillersobservations, is the individual to make interpretations ofthe core loss. All core should be measured by the logger.If using a split-tube barrel, the core should be measuredwhile in the barrel and always after core segments arefitted together (using the midpoint of core ends). Unac-countable losses should be reconciled, and the location ofthe loss determined.
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Tape checks or rod checks are the most reliable and pre-ferred methods for knowing the exact location of geologicconditions (top of each run is known with certainty) andwhere losses occur. All core runs should be measured andrecorded; gains and losses can be transferred to adjacentruns and cancel out each other during the process ofdetermining where the core loss is located. Inaccuratedrillers’ measurements, or locations where portions of thepreviously drilled interval was left in the hole (pulled off,or fell back in and redrilled), can be determined byexamining and matching the end and beginning of eachcore run to see if they fit together or show signs of beingredrilled. Gains may be attributed to pulling out thebottom of the hole, mismeasurement, recovering core leftin the hole from the previous run, or recovery ofexpansive, slaking, or stress relieving materials.
Where unaccountable losses occur, the examination ofcore to determine the reason for that loss is critical. Poordrilling methods (excessive pressure, speed, excessivewater discharge from the drill bit, not stopping when fluidreturn plugs), inaccurate measurements, or geologicconditions responsible for core losses should bedetermined. Core may have spun in the barrel afterblocking; an intensely fractured zone may have beenground up; or a shear zone, open joint(s), solution cavity,or joint fillings may have been washed away. Geologicinterpretation of the core loss is based on examiningrecovered core and the fractures present in the core. Drillwater losses and color or changes in the drillingconditions noted by the driller may suggest aninterpretation of the core loss. Where losses occur near arecovered clay "seam," clay coats fracture surfaces,slickensides and/or breccia and gouge are present, thecore loss may be interpreted as a shear or shear zone.The description should include all the factualinformation—discontinuity surface orientations,slickensides, coatings, gouge and/or fractures; and the
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interpretation that the loss occurred in a shear.Depending on the confidence in the interpretation basedon the observed conditions, the description can be givenas "shear," or "shear?," or "probable shear zone." When aportion of a shear zone has been lost during drilling, theno recovery zone should be described as part of the shearand the loss or part of the loss included in the shear'sthickness.
Samples
If the geologist selects representative or special samplesfor laboratory testing, an appropriate space should be leftin the core box to ensure that when logs are reviewed orphotographs are taken, core recovery is not misleading.Either filler blocks or a spacer which indicates the topand bottom depths of the sample and a sample numbercan be used to fill the sample space. For N-size cores, alength of 2- by 2-inch (50- by 50-mm) block or otherspacers that fill the tray work well. These blocks alsoshould be used to separate core runs. The lettering onthe blocks should be easily readable at a distance. Spraypainting the blocks white or yellow and lettering themwith black waterproof pens enhances visibility andlegibility. The sample interval, and sample number ifdesired, must be recorded in the Samples for Testingcolumn on the log. Portions of the core may be preservedas representative samples or to protect samples fromslaking or other deterioration.
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Core Photography
General Photographic Methods
Transmittal of core photographs with the final logs is rec-ommended. The photos may be included in the datapackage or as an appendix to the data report. Coresshould be photographed while fresh. Before and afterphotographs of materials that slake or stress-relieve arerecommended. The importance of photographing the corebefore it has been disturbed in transit and before itsmoisture content has changed cannot be overemphasized.If proper precautions during transport are followed, andthe core is logged in a timely manner, reasonably goodphotographs can be obtained away from the drilling site.This permits the labeling of core features, if desired.
If possible, cores should be photographed in both colorand black and white at 8- by 10-inch (200- by 250-mm)size. Black and white photographs do not degrade overtime like color photographs. Core photographs should besubmitted with the final logs in the geology data report;color photographs are best for data analysis.
Many methods are employed for photographing core.Each box of core can be photographed separately as thebox is first filled or three or more boxes can bephotographed at a time. There are advantages to bothprocedures:
• Greater detail and photographs depicting fresherconditions are the major advantages of photo-graphing each box individually.
• When photographing several boxes at a time,transitional features, changes in weathering orfracturing, or large shear zones can be seen in onephotograph.
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The best method is a combination of the two. Pictures ofindividual boxes at the drill site and later pictures of theentire hole are the best of two worlds.
Individual Box Photography
Any portion of core that is in danger of altering or disag-gregating because of slaking or "discing" due to stressrelief, expansion, or shrinkage due to changes in moistureor confinement because of down time, ends of shifts, orweekends must be boxed and photographed. Under thesecircumstances, the core should be photographed while ator near the material natural condition (even if a box isonly partially filled).
Each photograph should be taken from approximately thesame distance so that the scale of each photograph isidentical. The box should fill the frame of the camera,thereby obtaining the highest quality resolution or coredetail, and the camera should be held as close to normalto the core as possible. A tripod should be used ifpossible. Tilting the core box and, if necessary, standingin a pickup bed or other vantage point may be helpful.Most core boxes can be tilted about 70 to 80E before anycore is in danger of spilling out, so very little additionalheight is required. A simple 2- by 4-foot (0.6- by 1.2-m)wood frame may be constructed, or the core box may beleaned against a tool box, pickup tailgate, or other stableobject. A Brunton compass can be used to ensure that thebox and the camera are placed at a consistent, uniformangle. Shadows should be eliminated as much aspossible.
All core should be photographed both wet and dry. In hotor dry weather, the unphotographed boxed core should becovered by moist cloth. When ready to photograph, anydry zones should be touched up using a wet cloth or
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paintbrush. In extremely hot weather, the boxed core canbe sprayed or sprinkled with water. A water hose, gardensprayer, or spray bottle works well for this operation.Wait for the water to be absorbed so that there is noobjectionable sheen or glare-producing film of water onthe core at the instant of film exposure.
A labeled lid, letter board, or another frame which showsfeature, drill hole number, photograph, or core boxnumber, and depths of the top and bottom of the coredinterval should be included in the photograph. A scale infeet and/or tenths of a foot or meters is helpful.
Photographing Multiple Boxes
As soon as possible after the core is removed from thebarrel and boxed, the core should be photographed. Tofacilitate the photography, construct a frame capable ofsupporting three or more boxes at a time for use at thedrill yard or core storage yard. Photograph the core drythen spray with water to bring back the natural moisturecolor. The same precautions about glare referred topreviously should be followed.
A frame which shows the project, feature, hole number,box __ of __boxes, and from—to, as a minimum, should beused for the photograph. Other optional butrecommended entries may include date photographed,and a scale.
Special Circumstances
Special photography such as closeups of shear zones orother special features may be worthwhile. When thesephotographs are taken, a common object or scale shouldbe included to provide the viewer with relative or actualdimensions.
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When cores are coated with drill mud, a brush, wet rag,or pocket knife should be used to wash or scrape off themud so that materials are their natural color and featuresof the core are not obscured. This step obviously must betaken prior to logging the material.
Photograph Overlays
Acetate or mylar overlays on photographs of core can helpinterpretation of exposed features. Details shown mayinclude labels for shears, weathering, lithologies, or itemsof special interest. Other items that may be shown onoverlays are joint sets, and they may be coded by an alphaor numeric character or by colored ink.
Equipment Necessary for Preparing Field Logs
The following equipment or supplies are necessary foradequately preparing geologic logs:
Core recovery sheets and rough log forms orcomputer data sheets.—For recording core recoveryand maintaining accurate depth measurements fordetermining core loss intervals.
Drillers' reports.—Daily drill reports (figure 10-6) tocheck measurements for core recovery, identifyingchanges in condition or contacts in intervals of poorrecovery, determining reasons for core loss, andevaluating openness of fractures.
Knife.—Core hardness/strength characteristics;cleaning or scraping drill mud from core to allowlogging and measurement of core recovery.
Hammer.—Core hardness/strength characteristics.
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Figure 10-6.—Daily drill report.
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Tape measure or folding ruler (engineering scalewith hundredths of feet or metric as appropriate).—Recovery measurements, thickness of units, shearsand fillings, and spacing of fractures.
Protractor.—Measuring orientation of contacts,bedding and foliation, and fracture orientation.
Hydrochloric acid.—Mineral or cementing agentidentification (3:1 distilled water to acid).
Hand lens.—Mineral or rock identification, minimum10X.
Marking pen.—Waterproof ink for marking core formechanical breaks, depth marks on core, samplemarking.
Paintbrush and/or scrub brush, and water.—Forcleaning core and for identifying wet color andincipient fractures.
Color identification charts (Munsel Color System orAmerican Geological Institute Rock Color Chart).
Filler block (spacer) material.—For identifying non-recovery intervals and location of samples and forrecording drill depths.
Sample preparation materials.—Wax, heater,container, brush, cheese cloth, etc.
Rock testing equipment.—Schmidt hammer, pointload apparatus, pocket penetrometer or torvane.
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Instruction to Drillers, Daily Drill Reports, andGeneral Drilling Procedures
Communication between the geologist and driller isextremely important. Establishment of lines ofcommunication, both orally and in writing, is key to asuccessful exploration program.
The role of the geologist in the drilling program is as anequal partner with the driller at the drill site.Establishment of this partnership at the beginning of thedrilling program will result in better data. Failure toestablish a good working relationship with the drill crewoften results in unanswered questions and a poor qualityend product. One way to establish good working rapportis to keep the drillers informed and to plan with them.
Drill Hole Plan
A suggested method for ensuring that a clearunderstanding of what the drilling requirements andexpectations are from the drill hole is the preparation ofa drill hole plan. The plan is prepared prior to startingthe hole and after the geologist has used availableinterpretive data and has determined whether specialtesting and procedures or deviations in standard practiceare required. This document provides the driller withinformation about safety, special site conditions, purposeof the hole, procedures to be followed, water testingrequirements, materials expected to be recovered, anyspecial sampling or geophysical testing required, and holecompletion requirements.
Guidelines for Drillers
The following guidelines provide a framework forpreparing written instructions for drill crews or for
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contract drill specifications. Also, the guidelines serve tohelp geologists correct poor drilling procedures, collectadditional data, or improve core handling and logging.
Drill Setup.—To ensure that drill holes are completed atthe desired location and along the correct bearing andplunge, the use of aiming stakes and a suitable device formeasuring angles should be provided by the geologist andused by the drill crews. Drillers should use aiming stakesset by the geologist or survey crew for the specifiedbearing of the drill hole. The rig must be anchoredproperly so that it will not shift. If stakes have beenremoved or knocked over, they should be replaced by thegeologist. Also, drillers must ensure the hole is drilled atthe designated angle. The geologist should check theplunge angle with Brunton compass, and/or the drillersshould use an appropriate measuring device.
Daily Drill Reports Preparation.—The drillers shouldprepare duplicate daily drill reports using carbon paper(additional copies of each report may be required oncontract rigs). All copies must be legible and preferablyprinted. One copy should be provided to the geologist formonitoring progress and for preparation of the geologiclog. The drill report has a space opposite each run foreach item of information required; each of these spacesneed to be filled out completely. Data should be added tothe report or recorded in a notebook after each run.Drillers should record data as it occurs. Seedrawing 40-D-6484 (figure 10-6) as an example forreporting daily drill activities. Many field offices havelocal forms on which these data can be recorded.Comments regarding specific items to be recorded on thedaily reports are contained in the following paragraphs.
1. Recording depths and core loss — Check foragreement on depths for intervals drilled by
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consecutive shifts. Depths should be recorded in feetand tenths of feet or to the nearest centimeter, asappropriate. Tape checks or rod checks may berequired at change of shift or more frequently whenrequested by the geologist. The section entitled“Core Recovery and Core Losses” containsinstructions for proper use of core measurements,filler blocks (spacers), and tape checks. The driller isresponsible for knowing the depth of the barrel andthe hole at all times. Discrepancies betweenintervals drilled and recovery need to be resolved.Only standard length drill rods should be used. Coreshould be measured while it is still in the innerbarrel and after it is placed in the core box.Record the most correct measurement of the two inthe report. In the event core is left in the hole, thenext run should be shortened accordingly; the leftamount and proper hole entry and startupprocedures should be followed to facilitate recovery.
2. Recording drilling conditions — Make suredrilling conditions, such as fast or slow, hard or soft,rough or smooth, even or erratic, moderately fast orvery slow, bit blocks off, etc., are indicated for eachrun. Record time in minutes per foot (meter) ofpenetration. Any changes in the drilling rate withina run also should be noted along with intervals ofcaving or raveling. If the bit becomes plugged orblocking off is suspected, the driller should stopdrilling and pull the core barrel. Also, when drillcirculation is lost, the driller should pull and ex-amine the core.
3. Drilling fluid return and color — The type,color, and estimated percent of drilling fluidsreturned should be recorded for each core run. Thedepth of changes in fluid loss or color is particularly
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important. If drilling mud is used, indicate numberof sacks used per shift. In case of total loss of drillingfluid, it may be necessary to pressure test theinterval.
4. Description of core — Drillers need to describethe core in general terms; i.e., moderately hard, veryhard, soft, clay seams, broken, color, etc. If familiarwith the rock types, drillers may report more thanjust general terminology.
5. Water-pressure testing — Holes in rock are typi-cally water tested in 10-foot (3-m) intervals atpressures of approximately ½ lb/in2 (3.5 kilopascals[kPa]) to 1 lb/in2 (6.90 kPa) per foot (1/3 m) of coverup to 100 lb/in2 (690 kPa). NOTE: Pressures may bemodified for each site. Factors such as density ofmaterials, "overburden pressure" or "cover," bedding,purpose of testing, distances from free faces, waterlevels, and artesian pressures all must be taken intoaccount so that pressure testing does notunintentionally hydrofracture the foundation or jackfoundation materials. Pressures should bedetermined by the geologist. If a range of pressuresis used, and disproportionately high water losses areobtained at the higher pressures, the pressuresshould be stepped down and water losses at thelower pressures recorded. Water test pressuresshould be stepped up 3 to 5 times and then steppeddown. Flow versus pressure should be plotted; andif the relationship is not linear or smoothly curved,hydrofracturing or jacking may be occurring. If thedecreasing pressure curve does not follow theincreasing pressure curve, washing, plugging, orhydrofracturing or jacking may be occurring withoutthe foundation materials returning to the prewatertest state. Intentionally increasing the pressureuntil the foundation is fractured or jacked is a good
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way to determine appro-priate grout pressures.Gravity tests, overlapping pressure tests, andvariations in the length of the interval tested may beused to ensure complete test data. For example, apacker interval of 8 feet (2.4 m) may be used if thehole is caving too badly to get 10 feet (3 m) of openhole. Also, if a packer will not seat at 10 feet (3 m)above the bottom of the hole and there is good rock at12 feet (3.66 m), a 12-foot test interval may be used.If losses are above 15 gal/min (1.146 liters persecond [L/sec]), exceed pump or system capacity, orwater is known to be bypassing the packer, reducethe length of the packer interval and retest.
Losses should be recorded in gallons and tenths ofgal/min (L/sec). The driller should record the watermeter reading at 1-minute intervals, and the testshould be run for a full 5 minutes at each pressureincrement after the flow has stabilized. The drillershould report the average flow in gal/min (L/sec) forthe 5-minute test. Each driller should keep his ownrecord of the packer data in case questions ariseconcerning the testing. A suggested form forrecording data is shown in figure 10-7.
6. Casing or cementing depths — The depth of thecasing or the cemented interval should be shown foreach core run. Do not cement any more of the holethan is necessary to repair a caving or ravelinginterval. The use of additives such as calciumchloride or aluminum powder, if permitted, willreduce the set time. These materials should beadded to the water and not to the cement.
7. Recording unusual conditions — All unusualconditions or events should be noted in the "Notes"
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299 Figure 10-7.—Water testing record.
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column of the report. This includes such items assudden changes in drilling speed, loss of circulation,drop of drill string (open joints or cavities), casingand cementing procedures, caving, squeezing, packerfailures, and gas.
8. Recording setups, drilling, and downtime —Time must be noted on reverse side of report. Type,number, and size of bit is indicated here also.
9. Recording water level measurements —Measurement should be recorded at the start of eachday shift and shown on the day shift report. Holesshould be jetted or bailed prior to completion of thehole to obtain reliable water level data. Immediatelyafter jetting or bailing, the depth to water should berecorded.
10. Care of core and core boxes — Split-tube(triple tube) core barrels should be used. If not used,the core should not be damaged when extracted fromthe core barrel. Do not beat on the barrel with ametal hammer; use a rubber mallet/hammer or apiece of wood. The best way to remove core from asolid barrel is by using a pump to pressurize theinside of the barrel and extrude the core (standback!). The mud pump will work satisfactorily forthis. Core should be extracted from the inner tubeand carefully placed into core boxes by hand. Theuse of cardboard or plastic halfrounds isrecommended (see figure 10-8. Core pieces shouldbe fitted into the core box and fragments shouldbe arranged to save space. Long pieces maybe broken for better fit in the core box, buta line should be drawn across the core to denote mechanical breaks. If 5-foot (1.5-m) core
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Figure 10-8.—Use of half-round to protect core.
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boxes are used, mechanical breaks to fit 5-foot runsin boxes are reduced. Figure 10-9 shows a typicalcore box for N-size core.
Core should be placed in the core box from left toright, with the top to the left, bottom to the right,starting at the top of the box so the core reads like abook. The ends and top of the box should be markedwith black enamel paint or indelible felt pen. Coreblocks, which mark the depths, are placed betweeneach run and the depth marked. Data on the outsideof the left end of the box should include the project,feature, drill hole number, box number, and depthinterval in the box.
Filler blocks (spacers) are necessary to properlyrecord information and minimize disturbance to thecore during handling. Blocks should be placed witha planed side marked with either black enamel paintor indelible felt-tip pen; 2- by 2-inch (50- by 50-mm)blocks work well for N-size core. All core runs mustbe separated with blocks properly labeled at the topand bottom of the run. Sample intervals should bemarked in the boxes using wooden blocks of lengthsequal to the missing core so that the sample may bereturned to the box. Gaps for core losses should notbe left in the core box. Core left in the hole andrecovered on the next run may be added to theprevious run. Filler blocks inserted whereunaccountable core losses occur should show thelength of loss in tenths of feet, as follows: LC (lostcore) 0.3 foot, or NR (no recovery) 0.3 foot. The coreloss block indicates that a certain length of core wasunaccountably lost within a run, and the blockshould be placed at the depth of the core loss. Ifthe point of core loss cannot be determined, the blockcan be placed in the core box at the bottom of
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303 Figure 10-9.—Standard N-size core
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the run, preceding the bottom of run block. Cavitiesmay be marked on the block. All spacer, sample,and core loss blocks should be nailed to the bottomor sides of the box to prevent movement of the core.
At the drill site, core boxes should be lined up,preferably on boards or planks, in order from top tobottom, with labels and up side to left, in a safe areaand kept covered with lids. While in the field, donot place boxes where sliding or caving of slopes islikely to occur and keep out of the way of vehiclesand equipment. Core boxes, especially thosecontaining soft, slaking, or intensely fractured corematerial, should be covered immediately to preventdamage by rain or drying. Tray partitions in boxesshould be nailed so that nails do not protrude frombottom of boxes.
When the core is moved, be careful to preventdisturbance, breakage, or spilling. Damage to thecore during transportation can be minimized byusing nailed-down spacers and a 3/4- to 1-inch thick(19-25-mm) foam-rubber pad placed between the topof the core and the secured core box lid.
Hole Completion.—Completion of the drill hole shouldmeet the requirements established by the explorationprogram and at the direction of the field geologist. Drillholes usually will be completed either with sufficientcasing or plastic pipe to assure that the hole will stayopen for later water level observations. In areas wherevandalism may occur or when long-term monitoring iscontemplated, a standpipe and suitable cap with lockshould be installed. Completion information should beindicated on the driller's report. The drill hole numbershould be stamped or welded into the casing. Ifgroundwater observation riser pipes have been installed,
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install a minimum 3-foot (1-m) length of surface casingwith a locking cap as a standpipe to mark the drill holeand protect the riser pipe. Grouted in place, thisstandpipe can also serve to protect the observation wellfrom infiltration by surface runoff.
Concrete Core Logging
Concrete structures are commonly cored to assess thequality of concrete or as part of foundation investigationson existing features. An early macroscopic assessmentof concrete core is warranted for the following reasons:
• Concrete physical condition may suggest changesin the drilling program or sampling techniquesthat would be difficult to modify after drilling iscomplete. A different approach in drilling orsampling techniques may be necessary todetermine the cause of distress or failure.
• Shipping, handling, and sample preparation maymodify the concrete core by inducing, modifying,or masking fractures or causing coredisintegration.
• Core could be lost or destroyed before reachingthe laboratory.
• Macroscopic examination may provide therequired information eliminating the need for apetrographic examination.
This section is based on American Society for TestingMaterials Designations (ASTM) C 823-83 and C 856-83.
Purposes of Examination.—Investigations of in-service concrete conditions are usually doneto: (a) determine the ability of the concrete to perform
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satisfactorily under anticipated conditions for futureservice; (b) identify the processes or materials causingdistress or failure; (c) discover conditions in the concretethat caused or contributed to satisfactory performance orfailure; (d) establish methods for repair or replacementwithout recurrence of the problem; (e) determineconformance to construction specification requirements;(f) evaluate the performance of the components in theconcrete; and (g) develop data for fixing financial andlegal responsibility.
In addition to the usual drill log information, thefollowing should be provided, if available:
• Reason for and objectives of the coring program.
• Location and original orientation of each core.
• Conditions of operation and service exposure.
• Age of the structure.
• Results of field tests, such as velocity andrebound or Schmidt hammer data.
Figure 10-10 is an example of a drill hole log showing thetypes of information that can be shown and a format fora log showing both rock and concrete core.
Examination.—Concrete core is commonly marked inthe field showing the top and bottom depths at theappropriate ends and at any of the following features.Below are listed the major items to examine and record:
Fractures — Cracks or fractures in core are bestseen on smooth surfaces and can be accented bywetting and partial drying of the surface. Old cracksurfaces are often different colors than freshfracture
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Figure 10-10.—Log of concrete and rock core.
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surfaces. Old fracture surfaces often have reactionproducts or alteration of the surfaces. Fracturesoften follow structural weaknesses.
Reacted particles — Rims on gravel or sand areoften caused by weathering processes unless otherfactors indicate chemical reactions with the cementpaste. Crushed aggregate with rims probably is dueto chemical reaction with the cement paste.
Reaction products — Crushed aggregate with rimsusually indicates alteration in the concrete, such asalkali-silica reaction or alkali-carbonate reaction.Rims in paste bordering coarse aggregate and lightcolored areas in the paste may be gel-soaked orhighly carbonated paste adjoining carbonateaggregate that has undergone an alkali-carbonatereaction. White areas of fairly hard, dry material orsoft, wet material that has fractured and penetratedthe concrete and aggregate or fills air voids shouldbe recorded. Alkali aggregate reaction products canbe differentiated from calcium carbonate deposits byusing hydrocloric acid. The reaction products do notfizz.
Changes in size or type of fine and coarseaggregate — Sizes, shapes, and types of aggregatecan vary in a structure due to changes in mixes,placement procedure, or sources and should belogged.
Voids — Voids (honeycomb, popcorn) are indicatorsof trapped air, inadequate vibration, or insufficientmortar to effectively fill the spaces among coarseaggregate particles. Voids should be described andthe volume percent estimated.
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Segregation of components — Concrete compo-nents can become segregated or concentrated duringplacement. Large aggregate sizes can separate fromfine aggregate, and paste can separate from theaggregate, especially near forms or finishedsurfaces.
Cold joints or lift lines — Weak joints or zonescan form in concrete due to long periods betweenbuckets or mixer loads. Poor vibration or poor orimproper preparation of previous lift surfaces canform zones of weakness or actual planes similar tojoints in rock. These surfaces, called lift lines,should be described and any material on thesurfaces described. Lift lines can be very subtle anddifficult to locate. Design or construction data oftenprovide clues as to where to look for lift lines andconstruction joints. The core should be examinedwet. Clues to lift line locations are: (1) alignedaggregate along the surfaces each side of a line,(2) coarser aggregate above the lift line than is belowthe line, (3) different shape, gradation, orcomposition of aggregate above and below the liftline, (4) a thin line of paste on the lift line, and(5) no aggregate crosses the lift line.
Steel or other imbedded items — Reinforcing steeland orientations should be described as well as othermaterials encountered such as timber, steel lagging,dirt, or cooling pipes.
Changes in color of the cement — Changes inpaste color can indicate reaction products or changesin cement type or cement sources and should belogged.
Aggregate-paste bond — The bond between theaggregate and cement should be described. A goodbond is characterized by concrete breaking through
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the aggregate and not around the particles. A fairbond is characterized by concrete breaking throughand around the aggregate. A poor bond has concretebreaking around the aggregate.
Aggregate rock type — The aggregate rock typecan be important in determining the causes ofconcrete problems. For example, limestone oftenhas chert inclusions suggesting an aggregatereaction, whereas an igneous rock such as graniteprobably will not react with cement. Both the coarseand fine aggregate should be examined.
Aggregate shape — Aggregate shape is usuallyunique to each source. Rounded or subroundedaggregate is probably natural. Angular (sharp)aggregate is probably crushed.
Mechanical breaks — Mechanical breaks in thecore and whether the break is around or through theaggregate should be noted.
Chapter 11
INSTRUCTIONS FORLOGGING SOILS
General
All subsurface investigations of soils for constructionmaterials and for most engineering purposes using testpits, trenches, auger holes, drill holes, or otherexploratory methods should be logged and describedusing the standards in USBR 5000 [1] and 5005 [1](Unified Soil Classification System [USCS]) in accordancewith the established descriptive criteria and descriptorspresented in chapter 3 and the guidelines presented inthis section.
All investigations associated with land classification forirrigation suitability, as well as data collection andanalyses of soil and materials related to drainage inves-tigations, should be logged and described using theU.S. Department of Agriculture terminology outlined inappendix I to Agriculture Handbook No. 436 (SoilTaxonomy), dated December 1975 [2].
Test pits and auger holes may be logged on a form(figure 11-1), or logs may be computer generated. Formetric design studies and specifications, information is tobe in metric units. For specifications using English units,the written soil description should use metric units forthe description of soil particle sizes (millimeters insteadof inches). Example word descriptions are shown infigures 11-2 through 11-11.
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Figure 11-1.—Log of test pit or auger hole.
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Figure 11-2.—Clean coarse-grained soils.
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Figure 11-3.—Fine-grained soils.
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Figure 11-4.—Soil classifications based on laboratory test data.
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Figure 11-5.—Auger hole with samples taken.
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Figure 11-6.—Reporting laboratory classification inaddition to visual classification.
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Figure 11-7.—Undisturbed soils.
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Figure 11-8.—Coarse-grained soils with fines.
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Figure 11-9.—Coarse-grained soils with dual symbols.
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Figure 11-10.—Reporting in-place density tests andpercent compaction.
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Figure 11-11.—Soil with measured percentages ofcobbles and boulders.
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Formats for Test Pits and Auger Hole Logs
General Instructions
The following subsection provides general instructions forlog format and descriptions. Refer to chapter 3 fordescriptive criteria, classification, and group names andsymbols.• Capitalize the group name. If cobbles and boulders arepresent, include them in the typical name.
• Describe plasticity of fines as:
“approximately 30 percent (%) fines with high plasticity”“approximately 60% fines with low to medium
plasticity”“approximately 10% nonplastic fines”
• Give results of hand tests when performed.
• Use “reaction with hydrochloric acid (HCl).”
• Do not give unnecessary information such as “no odor,”“no gravel,” and “no fines.”
However, the negative result of a hand test is positive in-formation and should be reported as “no dilatancy,”“nonplastic,” “no dry strength,” or “no reaction with HCl.”
For reporting maximum particle size, use the following:Fine sandMedium sandCoarse sand5-millimeter (mm) increments from 5 mm to 75 mm25-mm increments from 75 mm to 300 mm100-mm increments over 300 mm
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For example, “maximum particle size 35 mm” or“maximum particle size 400 mm” are the correct formatand size increment.
Table 11-1 is a checklist for log descriptors. Format fordescriptions, results, and other information are in thefollowing subsections.
Table 11-1.—Checklist for the description of soils in test pit and auger hole logs
1. Group symbol. - Capitalized and shown in the left-hand column.2. Depth. - Depths of interval classified, shown in eithermeters or feet and tenths of units in second column fromthe left.3. Identification of sample. - Type and size of sample andorigin of sample, shown in third column from the left.4. Classification and description column. -
a. First paragraph. -(1) Depth of interval classified(2) Group name capitalized(3) Percent of fines sand and gravel by weight
(include trace amounts but not added topercentage which must equal 100 percent)
(4) Description of particles(a) Particle size range: describe as either
gravel - fine or coarse, or sand—fine,medium, or coarse
(b) Hardness of particles (coarse sand andlarger)(c) Particle angularity (angular,
subangular, sub-rounded, or rounded)(d) Particle shape (flat, elongated, or flat
and elongated)(e) Maximum particle size or dimension
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(5) Description of fines(a) Plasticity (nonplastic, low, medium, or
high)(b) Dilatancy (none, slow, or rapid)(c) Dry strength (none, low, medium, high,
or very high)(d) Toughness (low, medium, or high)
(6) Moisture condition (dry, moist, or wet)(7) Color (moist color)(8) Odor (mention only if organic or unusual)(9) Reaction with HCl (none, weak, or strong)
b. TOTAL SAMPLE (BY VOLUME): second para-graph, if applicable - i.e., more than 50 per-cent plus 75-mm material(1) Percent of cobbles and percent of boulders (2) Same information as item 4.a (4)
c. IN-PLACE CONDITION: third paragraph(second paragraph if less than 50 percentoversize)(1) Consistency; fine-grained soils only (very
soft, soft, firm, hard, or very hard) (2) Structure (stratified, lensed, slickensided,
blocky, fissured, homogeneous)(3) Cementation (weak, moderate, strong)(4) Moisture (if an in-place condition
paragraph is included, moisture is notdescribed in the first paragraph)
(5) Color (if an in-place condition paragraph isincluded, color is not described in the firstparagraph)
(6) Result of in-place density and/or moisturetests
d. GEOLOGIC INTERPRETATION: (fourth para-graph) geologic description including geneticname, stratigraphic name if known, and anylocal name.
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5. Remarks block. - Provide additional description orremarks such as root holes, other debris found, caving,degree of difficulty to auger or excavate, reason forrefusal or reached predetermined depth, and waterlevel information or hole completion.
Figure 11-12 is a field form for logging soils.
Reporting by Method of Classification
Preparation of Logs Based on Visual Classifica-tion.—List fines, sand, and gravel in descending order ofpercent (must add up to 100 percent). For visual classi-fication, estimate percentages to the closest 5 percent.Precede the estimated percentages with “approx.,” not“about.” If a component is present but is less than5 percent of the total, use “trace.” “Trace” is not includedin the 100 percent.
Preparation of Logs Based on Laboratory Classifi-cation.—When logs are prepared using laboratoryclassifications (based on laboratory tests), the informationmust be presented on the log as shown in figure 11-4.The difference between a laboratory and a visualclassification is depicted in figure 11-6.
The visual classification should not be changed, norshould the estimated percentages, plasticity description,or the results of the hand tests (dry strength, dilatancy,and toughness) be changed to reflect laboratory testsresults. The visual classification is based on the totalmaterial observed; whereas, the laboratory classificationis based on a representative sample of the material.
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FIELD FORM—SOIL LOGGING HOLE NO. ____
DATE _______ PROJECT ___________________ FEATURE ___________________AREA _________________ DRILLER _________ LOGGED BY __________________
SAMPLE INTERVAL AND TYPE:Type MoistureSample SampleInterval _________ Sample Weight (Lbs) ______ Interval___________________
Typical Name __________________________________________________________Group Symbol _________________________________________________________
SIZE DISTRIBUTION, CHARACTERISTICS:(5-mm increments from 5 to 75 mm, 255-mm increments from 75 to 300 mm, 100mmincrements over 300 mm)
Boulders (>300 mm) __% (vol.) Max. size (mm) __ Hardness __ Angularity _____
Cobbles (75-300 mm) __% (vol.) Max. size (mm) ___ Hardness ___ Angularity ____
Gravel __% Coarse (20-75 mm) __ Fine (5-20 mm) ___ Hardness ___ Angularity __
Sand ___% Coarse ___ Medium ___ Fine ___ Hardness ___ Angularity _____
Fines _____%
Plasticity: Nonplastic _____ Low _____ Medium _____ High _____Dilatancy: No _____ Slow _____ Rapid _____Dry Strength: No ____ Low ____ Medium ____ High ____ Very High ____Toughness: Low _____ Medium _____ High _____
Maximum Size: Fine Sand ____ Medium Sand ____ Coarse Sand ____ ____mm
Moisture: Dry _____ Moist _____ Wet _____
Color _______________ Odor __________ Organic Debris and Type ___________
Reaction with HCl: None _____ Weak _____ Strong _____
EXCAVATING/AUGERING/DRILLING CONDITIONS:
Hardness: Very Soft _____ Soft _____ Hard _____ Very Hard _____
Penetration Action: Smooth ___ Mod. Smooth ___ Mod. Rough ___ Rough ____
Penetration Rate: Very Fast ____ Fast _____ Slow _____ Very Slow _____
PAGE ___ OF ___
Figure 11-12.—Field form - soil logging.
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The specimens for testing are to be samples that repre-sent the entire interval being described (see USBR 7000and 7010 [1]). The material collected must be split orquartered to obtain the specimen that is to be tested inthe laboratory.
Coefficients of uniformity and curvature (Cu and Cc) areto be calculated and reported on the logs for coarse-grained materials containing 12 percent or less fines.
Laboratory gradation percentages and Atterberg limitsare to be reported to the nearest whole number.
Procedures for Reporting Laboratory Data in Addi-tion to Visual Classification and Description.—Insome instances, gradation analyses and Atterberg limittests are performed on soil samples in conjunction withpreparation of logs of test pits or auger holes. These datashould be shown on the logs and clearly identified aslaboratory test data.
Specimens for testing are to be from samples thatrepresent the entire interval being described. If this isnot possible, the location of the sample should be given aspart of the word description. The sample taken should besplit or quartered to get the specimen size required fortesting (figure 11-5, interval 0.0 to 9.8 feet (ft).
Laboratory test data are to be presented in a separateparagraph. If the test results indicate a different classi-fication, and therefore different group symbol and/orgroup name than the visual classification, give thelaboratory classification symbol and name in thisparagraph (figure 11-6).
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Note: For logs which incorporate the testresults, the statement “Classification bylaboratory” should be placed in the “Remarks”portion of the log.
Coefficients of uniformity and curvature (Cu and Cc) areto be calculated and reported on the logs for coarse-grained materials containing 12 percent or less fines.
All laboratory gradation percentages and Atterberg limitsare to be reported to the nearest whole number.
Reporting Undisturbed (In-Place) Conditions
List in-place conditions on logs of test pits in a separateparagraph (figure 11-7). Do not give in-place soil condi-tions (consistency, compactness) on auger hole logs(unless the holes are large enough to inspect). Instead,describe difficulty of augering (figure 11-8). Also describecaving or any other unusual occurrences during drillingof the auger hole.
In-place density tests are often performed in test pits ortrenches. When a large quantity of logs are reviewed,density information on the log can save time, even thoughadditional time is required for preparation of the log.
Results of in-place density tests that are performed intest pits or trenches are to be included on the log in thedescriptive paragraph on in-place conditions, asillustrated in figure 11-10.
Results of any laboratory compaction tests (Proctor, mini-mum and maximum density) performed on the materialfrom the in-place density tests or from the pit or trenchare to be included on the log.
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For pipeline investigations, the percent of the maximumdry density or the percent relative density should be inparentheses on the logs (figure 11-10).
Densities are reported to the nearest 0.1 pound per cubicfoot (lb/ft3) or 1 kilogram per cubic meter (kg/m3).Moisture content is reported to the nearest 0.1 percent.Percent of laboratory maximum dry density or relativedensity is reported to the nearest whole number.
Geologic Interpretations
Geologic interpretations should be made by or under thesupervision of a geologist. Give geologic interpretation ina separate paragraph (figure 11-7). Interpretation shouldalso be included in the narrative section of the materialsportion of the design data submittals.
Description Formats on Test Pit and Auger HoleLogs for Soils with Cobbles and Boulders
If the soil has less than 50 percent cobbles and boulders(by volume), give the group name of the minus 75-mmportion and include cobbles and/or boulders in the groupname (figure 11-11). Use two paragraphs to describe soil.Refer to chapter 3 for a more complete discussion ofclassification and classification group names and symbols.
• Describe the minus 75-mm fraction in the first para-graph. These component percentages are estimated byweight.
• Describe the total sample in a second paragraph. Thesepercentages are estimated by volume. Even if thepercentage of cobbles and boulders is determined bymeasurement, use “approx.” in the word description.
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If the soil has more than 50 percent cobbles and boulders(by volume), list cobbles and boulders first in the name(figure 11-13). Do not give a group symbol or group name.
• Describe the total sample in the first paragraph.Percentages are estimated by volume.
• Describe the minus 75-mm fraction in a secondparagraph. Percentages are estimated by weight.
Angular particles larger than 75 mm are described as cob-bles and boulders, not as rock fragments. A descriptionof their shape should be provided in the word description.
Description of Materials Other than Natural Soils
Materials which are not natural soils are not described orclassified in the same manner as natural soils. Thesection titled “Use of Soil Classification as SecondaryIdentification Methods for Materials other than NaturalSoils”, chapter 3, outlines the criteria to be followed andprovides example descriptions for test pit and auger holelogs. Refer to appropriate sections in chapter 3 forexample format and descriptions. Figures 11-14 through11-17 show a variety of logs of test pits and auger holesreflecting miscellaneous conditions.
Format of Word Descriptions for Drill Hole Logs
The descriptions of surficial deposits and soil-likematerials in geologic logs of exploration holes should usesimilar descriptive criteria and format established for testpits and auger holes except as noted in the followingparagraphs.
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Figure 11-13.—Soil with more than 50 percent cobbles and boulders.
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Figure 11-14.—Borderline soils.
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Figure 11-15.—Test pit with samples taken.
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Figure 11-16.—Disturbed samples.
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Figure 11-17.—Two descriptions from the same horizon. (Top) Undisturbed soil containing estimated percent
of boulders. (Bottom) Disturbed soil containing trace of cobbles.
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Exceptions to Test Pit and Auger Hole Format and Descriptions for Drill Hole Logs
Unlike test pit logs where geologic interpretations may beprovided at the bottom of the log form, geologic inter-pretations are required on drill hole logs. The geologic classification (e.g., Quaternary Alluvium, QuaternaryGlacial Outwash, Quaternary Landslide, Tertiary BasinFill Deposits) should be provided as main headings on thegeological drill hole log.
Group names are capitalized in all test pit and auger holelogs. Where capitalization of the group name wouldconflict with main headings on drill hole logs, capitalizeonly the first letter of each word of the group name andthe group symbol. If the first letter of each word is notcapitalized, the group name is considered informal usageonly and not a classification. Classification and word description format for drill holelogs is similar to those used for test pit logs. Also,materials recovered from drill holes are generallyconsidered to represent in-place conditions. Thesecriteria do not apply when samples are not recovered orwhen poor recovery precludes classification (figure 11-18).
Samples Recovered from Wash Borings or asCuttings
When drill holes are advanced with a rock bit, water jet,or other nonsampling methods, a group symbol and nameor classification of the recovered materials should not beassigned, nor should in-place descriptions, such asconsistency, be used. However, descriptive criteria, suchas particle size, dry strength, and reaction with HCl,should be provided using the same terminology andformat used for auger holes.
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Figure 11-18.—Drill hole advanced by tri-cone rock bit.
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Descriptions should be preceded by “Recovered cuttingsas . . .” or “Recovered wash samples as. . .” (figure 11-18,interval 0.0-11.7 ft.
Poor or Partial Recovery
Where poor or partial recovery precludes accurate classi-fication, a primary classification should not be assigned,but as much descriptive information as possible should beprovided. Recovered materials, together with drillingconditions, cuttings, and drilling fluid color or losses, maybe used to interpret reasons for losses and types ofmaterials lost. However, an appropriate subheading (i.e.,“Poor Recovery”) should be used (figure 11-19, 2.1 to3.9 ft.
Materials Other Than Soils and Special Cases
As discussed in chapter 3, “Use of Soil Classification asSecondary Identification Methods for Materials OtherThan Natural Soils,” exceptions to the test pit and holeclassification and format are also applicable to hole logs.These special cases include processed or manmadematerials, shells, partially lithified or poorly cementedmaterials and decomposed bedrock, and shallow surficialdeposits or soils. Other special categories of soil-likematerials should be classified by USBR 5000 orUSBR 5005[1]. These are soil-like slide-failure zones orplanes; shear or fault zones; bedrock units which arerecovered as soil-like material or consist of soil-likematerial; and landslides and talus (figures 11-20, 11-21,and 11-22).
Format and classification for these exceptions aredescribed below.
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Figure 11-19.—Log showing poor recovery.
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Figure 11-21.—Log of landslide material (b).
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Processed or Manmade Materials.—Surficial depositssuch as tailings, crushed rock, shells, or slag are assigneda genetic name such as filter, bedding, drain material,shells, tailings, or road base, and a classification groupname and symbol are assigned in quotation marks, forexample: Filter material, “poorly graded sand (SP-SM).”Soil descriptors are then used to describe the materials.
Where drill holes penetrate embankment materials, mainheadings on the drill hole logs should be a classificationof the type of embankment, such as “Zone 3Miscellaneous Embankment.” The materials recovered ineach interval are classified, and group names andsymbols are provided as subheadings. See 1.0- to 3.9-ftand 3.9- to 15.4-ft intervals shown in figure 11-19.
Partially Lithified or Poorly Cemented Materialsand Decomposed Rock.—Descriptions of partiallylithified or poorly cemented materials such as siltstone,claystone, sandstone, and shale or decomposed rock whichare broken down during drilling or field classificationtesting should be classified by an appropriate rock unitname or by geologic formation name, if known, of the in-place materials. The materials are then described usingdescriptors for rock (chapter 4). A soil classification forthe broken down materials should be reported inquotation marks on the drill logs and all figures, tables,drawings, or narrative descriptions. The disaggregatingmechanism (e.g., drilling or testing) should be specified(figure 11-22, interval 17.3 to 67.9 ft).
Shallow Surficial Deposits.—Surficial deposits such asdrill pad or dozer trench fill for drill setups, shallow slopewash, or topsoil materials which will not be used in, orinfluence, design or construction may be classified bygenetic classification (e.g., “fill,” “slopewash,” or “topsoil”).Complete classification descriptions are not required ondrill hole logs; however, a classification name and/or
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symbol may be assigned and is often desirable. Althougha complete description is not required on each log, anadequate description of these materials should beprovided in a general legend or explanation drawing andin the narrative of the report, if not completely describedin drill hole logs.
Slide Failure Zones or Planes, Shear or FaultZones, and Interbeds Recovered as Soil-likeMaterials.—These features should be described usinggeologic names as well as behavior and soilclassifications.
Landslides and Talus.—Surficial deposits such aslandslides and talus should be assigned their geneticgeologic name in the main headings of the drill hole log.Landslide debris composed primarily of soils is classifiedas landslides in the main heading. Soil-like materialsshould be classified and group names and symbolsprovided in the headings. The materials are thendescribed using the descriptive criteria for drill hole logs.Where materials are predominantly rock fragments suchas talus and block slides, the materials should be loggedsimilar to the method used in figure 11-22.
Equipment Necessary forPreparing the Field Log
The following is a list of equipment for field testing anddescribing materials.
Required equipment:
• Small supply of water (squirt bottle)—forperforming field tests
• Pocket knife or small spatula• Materials for taking or preserving samples—sacks,
jars, labels, cloth, wax, heater, etc.
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• Hammer—for hardness descriptors• Tape measure and/or rule (engineer's scale and
metric scale)• Petrie dish for washing specimens• Small bottle of dilute hydrochloric acid [one part
HCl (10 N) to three parts distilled water. Whenpreparing the dilute HCl solution, slowly addacid into the water following necessary safetyprecautions. Handle with caution and storesafely. If solution comes in contact with skin,rinse thoroughly with water.]
• Rags for cleaning hands• Log forms
Optional apparatus:
• Small test tube and stopper or jar with lid• Plastic bags for “calibration samples”• Hand lens• Color identification charts• Paint brush and/or scrub brush and water for
cleaning samples• Marking pens• Protractor• Drillers' reports for drill holes• Comparison samples (in jars): fine gravel—3/4
inchto No. 4 sieve; medium sand—No. 4 to No. 10sieve; and coarse sand—No. 10 to No. 40 sieve
• Small No. 4 and 200 sieves
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Example Descriptions and Format
The examples which follow illustrate the preferredformat, description, and organization, and some of themore significant exceptions to typical standards.
Laboratory Classifications in Addition to Visual Classifications
In some instances, laboratory classifications may bedetermined in addition to the field visual classification.This may be done to confirm the visual classification,particularly when starting work in a new location orbecause the classification may be critical.
The laboratory data used must be reported in a separateparagraph at the end of the work description, as shown inthe examples in figure 11-23. If the laboratory clas-sification is different from the visual classification, as inthe upper example, give the group symbol in the left-hand column and the group name in the paragraph on thelaboratory data.
DO NOT CHANGE THE VISUAL CLASSIFICATION ORDESCRIPTION. The visual classification is based on awidely observed area in the excavation, whereas the labo-ratory classification is based on a sample of the material.
If the visual classification was the best judgment of anexperienced classifier, both are correct in what theyrepresent.
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Figure 11-23.—Geologic interpretation in test pit(sheet 1).
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Word Descriptions for Various SoilClassifications
Figures 11-6 to 11-17 illustrate some typical worddescriptions based on the soil classifications.
Logs are generally typed and single spaced. Theexamples in this manual are presented double spaced forlegibility.
Samples Taken
In addition to the brief description of the samples takenunder the “classification group symbol” column, a morecomplete description of any samples taken from eachdepth interval is included in the word descriptions. Thedescription should include the size of the sample, thelocation represented by the sample, and how the samplewas obtained (e.g., quartering and splitting).
Examples of how to report the sample information for apit or trench are shown in figures 11-24 through 11-33.
Some examples use the abbreviated method of indicatingthe group name with the group symbol. This abbreviatedmethod is described in appendix X5 in USBR 5000,“Determining Unified Soil Classification (LaboratoryMethod)” [1] and chapter 3.
Reporting Laboratory Data
Classifications Based on Laboratory Data
If the soil classification reported on the logs is based onlaboratory data and not a visual classification, this shouldbe clearly and distinctly reflected on the log.
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Figure 11-24.—Geologic interpretation in test pit(sheet 2).
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Figure 11-25.—Geologic interpretation in test pit using a geologic profile (1).
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Figure 11-26.—Geologic interpretation in test pit(sheet 3).
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Figure 11-27.—Geologic interpretation in test pit(sheet 4).
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Figure 11-28.—Geologic interpretation in test pit using a geologic profile (2).
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Figure 11-29.—Geologic interpretation in test pit(sheet 5).
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Figure 11-30.—Geologic interpretation in test pit (sheet 6).
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Figure 11-31.—Geologic interpretation in test pit(sheet 7).
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Figure 11-32.—Geologic interpretation in test pit (sheet 8).
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Figure 11-33.—Geologic interpretation in test pit using a geologic profile (3).
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The laboratory data should be reported on the log form asshown in the examples in figure 11-4.
The location of the sample and any laboratory testsperformed need to be clearly described.
The coefficients of uniformity and curvature (Cu, Cc) areto be calculated and reported for coarse-grained soilscontaining 12 percent fines or less.
Gradation percentages and Atterberg limits are to be re-ported to the nearest whole number.
The fact that the classification is a laboratory classi-fication needs to be indicated in the “classification groupsymbol” column.
The words “about” or “approximately” are not used in theword description.
Soils with More Than 50 Percent Cobbles andBoulders
If the soil contains more than 50 percent (by volume)cobbles and/or boulders:
1. The first paragraph describes the total sampleand includes the information on the cobbles andboulders. The information in the paragraph is thesame as described previously for cobbles andboulders.
2. The words “COBBLES” or “COBBLES ANDBOULDERS” are listed first in the classificationgroup name:
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COBBLES WITH POORLY GRADED GRAVELCOBBLES AND BOULDERS WITH SILTY GRAVEL
3. A classification symbol is not given. Where areport or form requires a classification symbol, usethe words “cobbles” or “cobbles and boulders”instead.
An example of a word description for a soil with morethan 50 percent cobbles and boulders is shown infigure 11-13.
Special Cases for USCS Classification
Some materials that require a classification anddescription according to USCS should not have a headingthat is a classification group name. When thesematerials will be used in, or have influence on, design andconstruction, they should be described according to thecriteria for logs of tests pits and auger holes, and theclassification symbol and group name should be inquotation marks. The heading should be as follows:
TOPSOILDRILL PADGRAVEL ROAD SURFACINGMINE TAILINGSUNCOMPACTED FILLFILL
For example:
Classification symbol Description
TOPSOIL 0.0 to 1.6-ft TOPSOIL—wouldbe classified as “ORGANICSOIL (OL/OH).” About 90%
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fines with low plasticity, slowdilatancy, low dry strength,and low toughness; about 10%fine to medium sand; soft, wet,dark brown, organic odor; rootspresent throughout strata;weak reaction with HCl.
Reporting In-Place Density Tests
In-place density tests are sometimes performed in testpits in borrow areas so that in-place densities can becompared with the expected compacted densities for theembankment. The required volume of material neededfrom the borrow area can also be calculated. The in-placedensity is also used to evaluate the expansion or collapsepotential for certain soils.
The density should be reported in the paragraph onin-place condition. Examples of the format are shown infigure 11-10. The upper example is used when only thedensity is determined. The lower example is used whena laboratory compaction test is also performed tocalculate the percent compaction (or D value if rapidmethod is used) (USBR 7240, [1]). For cohesionless soils,similar information is reported for the maximum indexdensity, the minimum index density, and the percentrelative density.
If the in-place density test hole spans two (or more) depthintervals of classification, the data and comments for thetest should be placed in the interval description corre-sponding to the top of the test hole. At the end of the in-formation reported, the comment (in all capital letters)must be added: “NOTE: TEST EXTENDED INTOUNDERLYING INTERVAL.” An in-place density testshould not span different materials or layers.
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Because the laboratory compaction test is generallyperformed on the material removed from the test hole,note that the data are for a mixture of intervals byadding, “NOTE: COMPACTION TEST PERFORMEDON MATERIAL MIXED FROM TWO DIFFERENTINTERVALS.”
The density units are lb/ft3 or kilonewtons per cubic meter(kN/m3).
Samples Taken
In addition to the brief description of the samples takenunder the “Classification Group Symbol” column, a morecomplete description of any samples taken from eachdepth interval is included in the word description. Thedescription should include the size of the sample, thelocation represented by the sample, and for each sample,how the sample was obtained (e.g., quartering andsplitting).
An example of how to report the sample information foran auger hole is shown in figure 11-17. An example ofhow to report the sample information for a test pit ortrench is shown in the section on word descriptions ofundisturbed samples.
The approximate weight of samples should be stated.
Measured Percentages of Cobbles and Boulders
If the percentages of the plus 3-inch particles are mea-sured, not estimated, the percentages are reported to
the nearest 1 percent. In the word description for theplus 3-inch particles, do not use the term “about” beforethe percentages.
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The procedure for measuring the percent by volume ofcobbles and boulders is given in the test procedure,USBR 7000, “Performing Disturbed Soil Sampling in TestPits”[1]. This method is rarely used; percentages areusually estimated. It is not recommended that thepercentages be measured for auger holes, since the massof material recovered is generally insufficient to obtain areliable gradation of plus 3-inch particles.
Figures 11-23 through 11-33 show a variety of logs of testpits using both the USCS and the geologic interpretationof the parent material. Note that USCS indicates thatbedrock has been altered or weathered to a soil-likematerial. For engineering considerations, use the USCSbut present the rock conditions as well.
BIBLIOGRAPHY
[1] Bureau of Reclamation, U.S. Department of theInterior Earth Manual, Part 2, third edition, 1990.
[2] U.S. Department of Agriculture, AgricultureHandbook No. 436, Appendix I (Soil Taxonomy),December 1975.
Chapter 12
HAZARDOUS WASTE SITEINVESTIGATIONS
General
Hazardous waste site investigations are geologic bynature. Site geology affects how the contaminants enterand migrate through the environment, controls theseverity of the contamination problem, and determines ifand how the contamination is remediated. An accuratecharacterization of site geology is critical for thesuccessful removal and/or remediation of hazardouswaste.
Investigations at hazardous waste sites use the samebasic tenets of geology commonly applied in other areasof engineering geologic exploration. Even though theseengineering geologic investigation techniques areuniversal, certain specialized criteria and regulations arerequired at hazardous waste sites which differ fromtraditional geologic work. This chapter assumes thataccepted geologic procedures and equipment are used athazardous waste sites and only discusses the variationsin the planning, implementation, and documentation ofgeologic field work required at such sites. Documentationat hazardous waste sites plays a very prominent role andinvolves much more effort than other geologicinvestigations.
This chapter provides a general overview of documents,terminology, processes, requirements, and site specificfactors for an investigation. This information can be usedto better prepare or conduct a field program. Muchinformation provided here is extracted from numerousEnvironmental Protection Agency (EPA) guidancedocuments. Hazardous waste investigations involve a
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myriad of documents and processes, mostly referred to byacronyms. See the appendix for an explanation of themore common acronyms.
In hazardous waste investigations, understanding thecontaminant’s physical and chemical properties is veryimportant. These properties are useful for predictingpathways that allow contaminant migration throughcomplex subsurface conditions. The understanding ofsubsurface conditions permits a program designed tobetter investigate and sample potentially contaminatedsoil, rock, and water.
Common Terminology and Processes
The "typical" hazardous waste site remediation processinvolves several investigation phases. Each phaseusually has a different emphasis and a different level ofdetail.
In general, there are two sets of regulations involved inhazardous waste site remediation: Resource Conserva-tion Recovery Act (RCRA) and Comprehensive Environ-mental Response, Compensation, and Liability Act(CERCLA). RCRA regulations are largely confined tooperators and generators of existing facilities, whereasCERCLA regulations are confined to the investigation ofabandoned sites (Superfund). Although most Bureau ofReclamation (Reclamation) activities involve CERCLAinvestigations, wastes generated during the investigationmay fall under RCRA regulations.
According to EPA guidelines (Guidance for PerformingPreliminary Assessments Under CERCLA, EPA/540/G-91/013), EPA uses a structured program to determineappropriate response for Superfund sites. The CERCLA/
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Superfund Amendments and Reauthorization Act of 1986(SARA) process ideally evolves through the followingphases: (1) discovery, (2) preliminary assessment, (3) siteinspection, (4) hazard ranking, (5) remedial investigation,(6) feasibility study, (7) record of decision, (8) remedialdesign, (9) remedial action, and (10) operation andmaintenance. Removal actions may occur at any stage.
Documentation
Proper documentation at jobs involving hazardous wasteis more important than at more "traditional" geologicinvestigation sites. The alleged low concentration valuesfor risks to human health and the associated costs forcontaminant testing are primary reasons for gooddocumentation. Soil contaminants are typically reportedin parts per million (ppm) (milligram per kilogram[mg/Kg]) and water contaminants are typically reportedin parts per billion (ppb) (microgram per liter [µg/L]).Since relatively low concentration levels may influence adecision for an expensive cleanup, the prevention of crosscontamination and proper testing procedures is anecessity. Also, proper documentation is necessary forlegally defensible data.
EPA has established documentation requirements forinvestigations. This chapter discusses the variousdocuments needed by EPA under the Superfund programwith an emphasis on the Sampling and Analysis Plan(SAP). Other documents such as the Health and SafetyPlan (HASP), Spill Prevention Plan, and CommunityRelation Plan are often pertinent to the field operation.
The SAP will assist in preparing the required documentsnecessary before actual site work begins. Specificrequirements for individual programs vary greatly, and
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common sense and regulatory concurrence dictate thelevel of detail needed. The EPA report Guidance forConducting Remedial Investigations and FeasibilityStudies Under CERCLA, Interim Final, October 1988(EPA/540/G-89/004) provides additional details regardingEPA-required documentation.
Work Plan (WP)
The WP includes a review of the existing data(background and study rationale), documents thedecisions to be made during the evaluation process, andpresents anticipated future tasks. The WP alsodesignates responsibilities and sets the project scheduleand cost. The primary use of the WP is to provide anagreed procedure to accomplish the work. The WP alsoprovides other interested agencies (such as localgovernment agencies) the opportunity to review proposedwork. The WP is placed in the Administrative Record.
The WP may include an analysis and summary of the sitebackground and physical setting, an analysis andsummary of previous studies and response actions, apresentation of the conceptual site model (including thenature and extent of contamination), a preliminaryassessment of human health and environmental impacts,additional data needs to conduct a baseline riskassessment, the preliminary identification of generalresponse actions and alternatives, and the data needs forthe evaluation of alternatives.
Sampling and Analysis Plan (SAP)
The SAP provides the "nuts and bolts" of the proceduresto be used at a site and must be site specific. The SAPshould consist of three parts:
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(1) A Field Sampling Plan (FSP) that providesguidance for all field work by defining in detail thesampling and data-gathering methods to be used on aproject.
(2) An Analysis Plan (AP) that describes analysis ofthe collected data, such as the contaminant chemicaldata, the groundwater quality, and the geologicsetting.
(3) A Quality Assurance Project Plan (QAPP) thatdescribes the quality assurance and quality controlprotocols necessary to achieve Data Qaulity Objectives(DQOs). Data Quality Objectives are qualitative andquantitative statements that clarify the studyobjective, define the type of data to collect, determinethe appropriate collection conditions, and specifytolerable decision error limits on the quality andquantity of data needed to support a decision.
The level of detail contained within the SAP varies.Depending on the WP, the testing, analysis, and qualitycontrol may be delegated to a differing lead agency orcontractor. Whether the SAP contains individual FSP,AP, and/or QAPP, the SAP indicates the field personnelroles and responsibilities, the acquired data goals, theanalytical methods, and how these methods meet theDQOs. Guidance for the selection and definition of fieldmethods, sampling procedures, and custody can beobtained from the EPA report Compendium of SuperfundField Operations Methods, December 1987(EPA/540/P-87/001 or National Technical InformationService [NTIS] publication PB88-181557). This report isa compilation of demonstrated field techniques that havebeen used during remedial response activities athazardous waste sites.
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The FSP specifies the actual data collection activities tobe performed. The AP provides the details if changes insampling methods or number of samples need to be made.If the AP is a separate document, the FSP should spellout in detail exactly how and why samples will becollected in the field.
Included with the SAP (sometimes as an appendix to theFSP) are the standard operating procedures (SOPs) to beused during the investigations. The SOPs describe, initem-by-item detail, the exact steps to be followed for eachsampling procedure. Included in the SOPs are calibrationand maintenance requirements for equipment to be used.Manufacturer's recommendations and usage manuals canserve as part of the individual SOPs. Further detailsregarding standardized tasks are given in the EPAQuality Assurance Technical Information BulletinCreating SOP Documents.
The QAPP is a companion document typically writtenwhen the FSP is final. The QAPP ensures that data andthe subsequent analyses are of sufficient quantity andquality to accurately represent the conditions at the site.The QAPP often describes policy, organization, andfunctional activities not addressed within the work plan.
The following is a suggested SAP format.
Example Sampling and Analysis Plan
FSP1. Site Background2. Sampling Objectives3. Sample Location and Frequency4. Sample Designation5. Sampling Equipment and Procedures6. Sample Handling and Analysis
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AP1. Objective(s) of the Data Collection2. Analytical Methods and Software3. Parameters Available and Required4. Analytical Assumptions (Boundaries, Estimated
Data)5. Data Management and Manipulation6. Evaluation of Accuracy (Model Calibration
and/or Sensitivity Analysis)
QAPP1. Project Organization and Responsibilities2. QA Objectives for Measurement3. Sample Custody4. Calibration Procedures5. Data Reduction, Validation, and Reporting6. Internal Quality Control7. Performance and System Audits8. Preventative Maintenance9. Data Assessment Procedures
10. Corrective Actions11. Quality Assurance Reports
Health and Safety Plan (HASP)
Each field activity will vary as to amount of planning,special training, supervision, and protective equipmentneeded. The HASP, prepared to support the field effort,must conform to the Reclamation “Safety and HealthStandards.” The site-specific HASP should be preparedconcurrently with the SAP to identify potential problemsearly in the planning stage, such as availability of trainedpersonnel and equipment. The HASP preparer shouldreview site historical information along with proposedactivities to identify potentially hazardous operations orexposures and to require appropriate protectivemeasures. Appendix B of the Occupational Safety and
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Health Guidance Manual for Hazardous Waste SiteActivities (National Institute for Occupational Safety andH e a l t h / O c c u p a t i o n a l S a f e t y a n d H e a l t hAdministration/U.S. Coast Guard/U.S. EnvironmentalProtection Agency, 1985) provides an example of a genericformat for an HASP. Commercial computer programsthat allow preparers to "fill in the blanks" to producerudimentary HASPs are also available.
A HASP should include, as appropriate, the followingelements:
1.Name of site health and safety officer and namesof key personnel and alternates responsible for sitesafety and health.
2. Listing of the potential contaminants at the siteand associated risk(s).
3. A health and safety risk analysis for existing siteconditions and for each site task and operation.
4. Employee training assignments.
5. A description of personal protective equipment tobe used by employees for each of the site tasks andoperations being conducted.
6. Medical surveillance requirements.
7. A description of the frequency and types of airmonitoring, personnel monitoring, and environ-mental sampling techniques and instrumentationto be used.
8. Site control measures.
9. Decontamination procedures.
10. Standard operating procedures for the site.
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11. A contingency plan that meets the requirements of29 CFR 1910.120(l)(1) and (l)(2).
12. Entry procedures for confined spaces.
13. Local emergency numbers, notification procedures,and a clear map (and written instructions) showingthe route to the nearest medical facility capable ofhandling emergencies arising from a hazardouswaste site.
Spill Prevention Plan (SPP)
All samples, equipment, cuttings, and other materialsthat have been exposed to potential contaminants mustbe decontaminated and/or tested and treated according toApplicable or Relevant and Appropriate Requirement(ARAR). Contingencies must be made for accidentallyreleasing and spreading contaminants into theenvironment during field activities at hazardous wastesites. Contaminants may originate from substancesbrought onto the site for specialized testing (e.g.,standards for chemical testing), from accumulations of"free" contaminants, or from contaminated natural waterwhich is released during sampling or investigations.Sufficient equipment (e.g., drums, absorbents, etc.) mustbe onsite to effectively control spills. In addition, keypersonnel should be identified for the control of spills.Paramount to such planning are spill preventionmeasures. Spill prevention plans may be incorporatedinto appropriate sections of a SAP or HASP, if desired.
Contaminant Characteristics and Migration
A primary difference between conventional engineeringgeology investigations and hazardous waste inves-tigations is that drilling methods may impact thecontaminant sampling results and increase migration
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paths. Lubricants, fuels, and equipment may maskspecific chemical testing or react with the contaminant ofconcern (COC). All samples, waste discharges, andequipment used in the investigations require evaluationin relation to the potential contaminant(s). The followingunique site factors are also important.
Contaminant Properties
Some contaminants are inherently mobile, for example,volatile organic compounds (VOCs). When released,VOCs can migrate rapidly through air, soil, andgroundwater. Other contaminants, such as heavy metalsolids, are less mobile. Heavy metals tend to accumulateon the surface of the ground. Although heavy metals maynot readily migrate into and through the subsurface,heavy metals may still migrate through the air asairborne particles. Understanding the behavior of COCsis very important because behavior will significantlyinfluence the ultimate design of the exploration program.For example, investigations to find gasoline, a lightnonaqueous phase liquid (LNAPL), should concentrate onthe water table surface. Dense, nonaqueous phase liquid(DNAPL) investigations should concentrate towards thebottom of the aquifer(s) or water table. Note that somecontaminants react with investigation materials; e.g.,TCE in high concentrations reacts with polyvinyl chloride(PVC) pipe.
When possible, the typical contaminant investigation willestimate the source type and location. The source typemay be barrels, storage tanks, pipelines, injection wells,landfills, or holding ponds. In investigations that involvegroundwater contamination, the investigation mustaddress collecting samples of material that may bemoving or have moved off site.
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Identifying the contaminant and its behavior within thehydrogeologic environment must be kept foremost inmind while developing the program. Hydrochemicalparameters such as density, diffusivity, solubility, soilsorption coefficient, volatilization (vapor pressure), andviscosity may impact the specific contaminant movement.Biological activities or meteoric waters may impactvarious COCs in the subsurface. Some contaminantsdegrade over time and under some environmentalconditions. In some instances, the degradation product(TCE to vinyl chloride) is worse than the original product.
A general introductory geological hazardous waste inves-tigation reference is the Standard Handbook for Solidand Hazardous Waste Facility Assessments, by Sara,1994. A general introductory reference for environ-mental chemistry is Fundamentals of EnvironmentalChemistry, by Manahan, 1993. A reference on DNAPLmaterials is DNAPL - Site Evaluation by Cohen andMercer, 1993. A reference for groundwater chemical andphysical properties is Groundwater Chemicals - DeskReference, by Montgomery, 1996. Toxicological ProfileSeries published by the U.S. Department of Health andHuman Resources describes physical, chemical, andbiological processes which effect contaminant fate andtransport.
Geologic Factors
The migration of contaminants is dependent on thesubsurface materials and water. The arrangement of thegeologic materials impacts the direction and flow rate ofthe contaminants and groundwater. Geologic factors suchas stratigraphy, structure, and lithology control theoccurrence and movement of water.
Various geologic factors to consider include: depth of soil,depth to bedrock, depth to the water table, seasonal
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variations in water table, water quality characteristics ofsite aquifers, mineralogic compositions of soil and rock,gradation, consolidation, and fracturing. Contaminantcharacteristics, such as property differences between solidor liquid materials, differences in liquid viscosity, ordifferences in liquid density relative to water, mayinfluence how the contaminants interact with geologicfactors and how the contamination plumes will behave.
Hydrologic Factors
Groundwater flow is a function of precipitation, runoff,and infiltration (figure 12-1).
Groundwater flow occurs through two zones: theunsaturated (vadose or aeration) zone and the saturatedzone. Each zone can be either soil or rock. Groundwatermovement is affected by the characteristics of thematerial pore spaces (porosity) and the interconnectivityof the pore spaces (permeability). Water movementoccurs under a hydraulic gradient.
Other terms often used in groundwater are transmissivityand storativity. Both terms are bulk terms used todescribe the water over the entire hydrologic unit. Trans-missivity is directly related to permeability. Storativityis a dimensionless value often incorrectly equated withspecific yield. For a more detailed description, see theBureau of Reclamation Water Resource Technical Publi-cation, Ground Water Manual, second edition, 1995 orGroundwater, by Freeze and Cherry, 1979.
An unconfined aquifer, often referred to as a "water table"aquifer, has no overlying confining layer. Water infiltrat-ing into the ground percolates downward through air-filled interstices of the vadose zone to the saturated zone.The water table, or surface of the saturated groundwater
HA
ZA
RD
OU
S W
AS
TE
379 Figure 12-1.—Aquifer types.
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body, is in contact with the atmosphere through the openpores of the material above and is in balance withatmospheric pressure.
A confined, or artesian, aquifer has an overlying,confining layer of lower permeability than the aquifer.Water in an artesian aquifer is under pressure, and whenthe confining layer is penetrated, the water will riseabove the bottom of the confining bed to an elevationcontrolled by the aquifer pressure. If the confining layertransmits some water into adjacent layers, the aquifer issaid to be a "leaky aquifer." A perched aquifer is createdby beds of clay or silt, unfractured rock, or other materialwith relatively lower permeability impeding thedownward percolation of water. An unsaturated zone ispresent between the bottom of the perching bed and theregional aquifer. Such an aquifer may be permanent ormay be seasonal.
Aquifers are typically anisotropic; i.e., flow conditionsvary with direction. In granular materials, the particleshapes, orientation, and the deposition process usuallyresult in vertical permeability being less than horizontalpermeability. The primary cause of anisotropy on amicroscopic scale is the orientation of platy minerals. Insome rock, the size, shape, orientation, and spacing ofdiscontinuities and other voids may result in anisotropy.These factors should always be considered when modelingcontaminant migration from hazardous waste sites.
After the natural flow conditions at a site are char-acterized, the presence of artificial conditions which maymodify the flow direction or velocity of groundwater isdetermined. Such items as surface water impoundmentsand drainages may influence overall groundwater flowmodels. Also, if existing water wells are present in thearea, pumping may be drawing the contaminants towardthe wells. All possible influences affecting the
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groundwater flow must be identified to modelcontaminant plume migration rates and paths.
Classification and Handling of Materials
Classification of soils for engineering properties isdescribed in chapter 3. “ Instructions for Logging Soilsand Surficial Deposits” (chapter 11) describes loggingprocedures, but there are two significant differences forhazardous waste investigations.
(1) Logging of the soil is often limited to visualinspection of cuttings. The sampling protocol mayprohibit the handling or poking of samples. Oftenthe samples are sealed for chemical testing, and timefor classification is restricted to the period when thesample is being packaged. Size of samples is kept toa minimum to reduce the amount of investigation-derived waste.
(2) All material recovered or generated during aninvestigation (samples, cuttings, water, etc.) shouldbe considered hazardous waste unless proven other-wise. Material removed should not be considered“normal” waste unless tested and permitted.
The RCRA “statutory” definition for hazardous waste isbroad and qualitative and does not have clear bounds.Hazardous waste is defined as material meeting theregulatory definition contained in 40 CFR 261.3.However, the definitions of solid and hazardous wastecontained in 40 CFR 261 are relevant only in identifyingthe waste. Material may still be considered solid orhazardous waste for purposes of other sections of RCRA.Some waste defined under the present regulatory statutescould become hazardous waste in the future.
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From the RCRA document, the definition of hazardouswaste is any
. . .solid waste or combination of solid wasteswhich because of its quantity, concentration, orphysical, chemical, or infectious characteristicsmay: (A) cause, or significantly contribute to, anincrease in mortality or an increase in seriousirreversible, or incapacitating reversible, illness;or (B) pose a substantial present or potentialhazard to humans or the environment whenimproperly treated, stored, transported, ordisposed of, or otherwise managed.
The level of contamination acceptable within the subsur-face is based on a complex formula that involves the riskof exposure; toxicity, mobility, and volume of contami-nants; and the cost of remediation. Soil and rock removedfrom a site cannot be returned to a site after theinvestigation has been completed.
Investigation waste water must be tested and handledunder a different set of rules. If the water is mixed withcuttings, the material is considered a combination of solidwastes. If the water is discharged on a site, the watertypically must meet drinking water standards. EPA cur-rently requires that sole source aquifers have specialproject review criteria for Federal actions possiblyaffecting designated aquifers. Water withdrawn forpublic drinking water supplies currently falls under theSafe Drinking Water Act (SDWA) (Public Law 93-523)regulations, as amended and reauthorized (1974). (See40 CFR 141 G for applicable water supply systems. See40 CFR 143 for applicable water supply systems.) Notethat the number of regulated constituents and theirrespective maximum contaminant levels (MCLs) arefrequently updated.
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Identifying and classifying hazardous waste is describedin Hazardous Waste, by Wagner, 1990. Procedures forsite evaluation are contained in EPA Guidance forConducting Remedial Investigation and FeasibilityStudies Under CERCLA, 1988.
Field Sampling Protocol
One of the most difficult parts of any investigation iscollecting representative samples. A sampling strategymust be efficiently and logically planned which delineatessite location, number of samples collected, types ofsamples collected, testing methods to be used, and theduration and frequency of sampling. The difficulties ofdrilling in the “right” location and the problemsassociated with collecting representative samples issimilar to traditional investigations. However, forhazardous waste investigation, the COC must be con-sidered in both time and space. Statistical considera-tions should be part of the sampling program. The follow-ing are references for sampling statistical considerations:
• Harvey, R.P. “Statistical Aspects of Air SamplingStrategies.” In: Detection and Measurement ofHazardous Gases; edited by C.F. Cullis andJ.G. Firth. Heineman Educational Books, London,1981.
• Mason, B.J. Protocol for Soil Sampling: Tech-niques and Strategies. EPA EnvironmentalSystems Laboratory, Contract No. CR808529-01-2.March 30, 1982. EPA-600/54-83-0020.
• Smith, R., and G.V. James. The Sampling of BulkMaterials. The Royal Society of Chemistry,London. 1981.
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• Environmental Protection Agency. Handbook forSampling and Sample Preservation of Water andWastewater. September 1982. EPA 600/4-82-029.
Sampling Strategies
Investigators must determine the correct number andtypes of samples to be collected, the proper chemicaltesting methods (analytical procedures), and the propersampling equipment before field activities begin. Samplecontainers, preservatives, sample quantities, and properholding times are also dictated by the chosen methods.
Table 12-1 is a list of recommended sampling containersand holding times for various classes of contaminants insoils.
Several sampling strategies are available, each withadvantages and disadvantages. Random sampling usesthe theory of random chance probabilities to choose repre-sentative sample locations. This is appropriate whenlittle information exists concerning the material, loca-tions, etc. Random sampling is most effective when thenumber of sampling locations is large enough to lendstatistical validity to the random selection.
Systematic random sampling involves the collection ofrandomly selected samples at predetermined, regularintervals (i.e., a grid). The method is a common samplingscheme, but care must be exercised to avoid over-sampling of one material or population type over others.
Stratified sampling is useful if data are available fromprevious investigations and/or the investigator hasexperience with similar situations. This scheme reducesthe number of samples needed to attain a specifiedprecision. Stratified sampling involves the division of the
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Table 12-1.—EPA recommended sampling containers, preservation requirements, and holding
times for soil samples
ContaminantContainer1
Preservation2Holding
time3
Acidity P, G 14 days
Alkalinity P, G 14 days
Ammonia P, G 28 days
Sulfate P, G 28 days
Sulfide P, G 28 days
Sulfite P, G 48 hours
Nitrate P, G 48 hours
Nitrate-Nitrite P, G 28 days
Nitrite P, G 48 hours
Oil and grease G 28 days
Organic carbon P, G 28 days
Metals
Chromium VI P, G 48 hours
Mercury P, G 28 days
Other metals P, G 6 months
Cyanide P, G 28 days
Organic compounds
Extractables
Including: Phthalates, nitro-samines, organic pesticides,PCBs, nitroaromatics, iso-phorone, polynuclear aroma-tics hydrocarbons, haloethers,chlorinated hydrocarbons, andtetrachlorodibenzo-p-dioxin(TCDD)
G, Teflon®-lined cap
7 days untilextraction
30 daysafterextraction
Footnotes at end of table.
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Table 12-1.—EPA recommended sampling containers, preservation requirements, and holding times for soil samples (continued)
ContaminantContainer1
Preservation2Holding
time3
Purgeables
Halocarbons andaromatics
G, Teflon®-linedseptum
14 days
Acrolein and acrylonitrate G, Teflon®-linedseptum
3 days
Orthophosphate P, G 48 hours
Pesticides G, Teflon®-linedcap
7 days untilextraction
30 days afterextraction
Phenols G 28 days
Phosphorus G 48 hours
Phosphorus, total P, G 28 days
Chlorinated organiccompounds
G, Teflon®-linedcap
7 days
1 P = polyethylene, G = glass. 2 All samples are cooled to 4 EC. Preservation is performedimmediately upon collection. For composites, each aliquot preservedat collection. When impossible to preserve each aliquot, samples maybe preserved by maintaining 4 EC until compositing and samplesplitting is completed. 3 Samples are analyzed as soon as possible. Times listed aremaximum holding if analysis is to be valid.
Source: Description and Sampling of Contaminated Soils,EPA/625/11-91/002 (1991).
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sample population into groups based on sample char-acteristics. The procedure involves handling each groupor division separately with a simple random samplingscheme.
Judgement sampling introduces a certain amount ofjudgment into the sampling approach and should beavoided if a true random sample is desired. Judgmentsampling allows investigator bias to influence decisions,which can lead to poor quality data or improper conclu-sions. If the local geology is fairly well understood,judgement sampling may provide the most efficient andcost-effective sampling scheme; however, regulatoryconcurrence, rationale, and proper documentation will benecessary.
Hybrid sampling is a combination of the types previouslydescribed. For example, an initial investigation of drumsmight be based on preliminary information concerningcontents (judgement, stratified) and then random sam-pling of the drums within specific population groups(random). Hybrid schemes are usually the method ofchoice for sampling a diverse population, reducing thevariance, and improving precision within each subgroup.
After the appropriate sampling scheme has been chosen,the specific type of samples necessary for characterizationmust be identified. The unique characteristics of the siteCOCs will play an important role in determining whichmedia will be sampled. Some sampling devices aredescribed in this manual or the Earth Manual, parts 1and 2, USBR, 1990 and 1999. A summary of samplingdevices is shown in table 12-2.
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Table 12-2.—Summary of soil sampling devices
Samplingdevice Applications Limitations
Hand-held samplers
Spoons andscoops
Surface soil samplesor the sides of pits ortrenches
Limited to relativelyshallow depths;disturbed samples
Shovels andpicks
A wide variety of soilconditions
Limited to relativelyshallow depths
Augers1
Screw auger Cohesive, soft, or hardsoils or residue
Will not retain dry,cohesionless, orgranular material
Standardbucket auger
General soil orresidue
May not retain dry,cohesionless, orgranular material
Sand bucketauger
Bit designed to retaindry, cohesionless, orgranular material(silt, sand, and gravel)
Difficult to advanceboring in cohesivesoils
Mud bucketauger
Bit and bucket de-signed for wet silt andclay soil or residue
Will not retain dry,cohesionless, orgranular material
Dutch auger Designed specificallyfor wet, fibrous, orrooted soils (marshes)
1 Suitable for soils with limited coarse fragments; only thestoney soil auger will work well in very gravelly soil.
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Table 12-2.—Summary of soil sampling devices (continued)
Samplingdevice Applications Limitations
Augers1
In situ soilrecoveryauger
Collection of soil sam-ples in reusable liners;closed top reduces con-tamination from cavingsidewalls
Similar to standardbucket auger
Eijkelcampstoney soilauger
Stoney soils andasphalt
Planer auger Clean out and flattenthe bottom of predrilledholes
Tube samplers2
Soil probe Cohesive, soft soils orresidue; representativesamples in soft tomedium cohesive soilsand silts
Sampling depthgenerally limited toless than 1 meter
Thin-walledtubes
Cohesive, soft soils orresidue; special tips forwet or dry soilsavailable
Similar toVeihmeyer tube
Soil recoveryprobe
Similar to thin-walledtube; cores arecollected in reusableliners, minimizingcontact with the air
Similar toVeihmeyer tube
1 Suitable for soils with limited coarse fragments; only the stoneysoil auger will work well in very gravelly soil. 2 Not suitable for soils with coarse fragments.
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Table 12-2.—Summary of soil sampling devices (continued)
Samplingdevice Applications Limitations
Tube samplers1 (continued)
Veihmeyertube
Cohesive soils orresidue to depth of10 feet (3 meters [m])
Difficult to drive intodense or hard mate-rial; will not retaindry, cohesionless, orgranular material;may be difficult topull from ground
Peat sampler Wet, fibrous, organicsoils
Power-driven samplers
Split spoonsampler
Disturbed samplesfrom cohesive soils
Ineffective in cohe-sionless sands; notsuitable for collectionof samples forlaboratory testsrequiringundisturbed soil
Thin-walled samplers
Fixed pistonsampler
Undisturbed samplesin cohesive soils, silt,and sand above orbelow water table
Ineffective incohesionless sands
Hydraulicpistonsampler(Osterberg)
Similar to fixed-pistonsampler
Not possible to limitthe length of push orto determine amountof partial samplerpenetration duringpush
1 Not suitable for soils with coarse fragments.
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Table 12-2.—Summary of soil sampling devices (continued)
Samplingdevice Applications Limitations
Thin-walled samplers (continued)
Free pistonsampler
Similar to stationarypiston sampler
Not suitable forcohesionless soils
Open drivesampler
Similar to stationarypiston sampler
Not suitable forcohesionless soils
Pitchersampler
Undisturbed samplesin hard, brittle, cohe-sive soils and ce-mented sands; repre-sentative samples insoft to medium cohe-sive soils, silts, andsome sands; variablesuccess with cohe-sionless soils
Frequentlyineffective incohesionless soils
Denisonsampler
Undisturbed samplesin stiff to hard cohe-sive soils, cementedsands, and soft rocks;variable success withcohesionless materials
Not suitable forundisturbedsampling of cohesionless soils orsoft cohesive soils
Vicksburgsampler
Similar to Denisonsampler except takeswider diametersamples
In addition, the following references may be consulted forsample collection methods:
• Environmental Protection Agency. Characterizationof Hazardous Waste Sites - A Methods Manual,Volume I - Site Investigations. April 1985. EPA600/4-84-075.
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• Environmental Protection Agency. Characterizationof Hazardous Waste Sites - A Methods Manual:Volume II. Available Sampling Methods. September1983. EPA 600/4-83-040, PB84-126929.
• Environmental Protection Agency. A Compendium ofSuperfund Field Operation Methods. December 1987.EPA 540/P-87-001, PB88-181557.
Samples can be either grab or composite samples. Grabsamples are collected at a discrete point, representing onelocation and/or time interval. Composite samples arecollected from several sources which are then accumu-lated to represent a broader area of interest. Therequirements for testing will often dictate which samplingmethod is used. For example, composite samples of soilcannot be used for volatile compounds because portions ofthe contaminants may easily volatilize during collection.
Many soil samples are collected as grab samples. Soilsamples should be collected from areas where dumping,spills, or leaks are apparent. Soil samples should becollected from areas upstream and downstream fromsuspected contaminant entry and in areas wheresediment deposition is significant. Samples can becollected readily from the first 18 inches (450 mm)(depending upon the soil type) by using relatively simpletools, such as spades, scoops, and dredge scoops. If scoopsare used for collecting surface soil samples, purchaseenough scoops to use a new scoop for each sample ratherthan decontaminating scoops between samples. Not onlyis time saved, but cross contamination is kept to aminimum. The COC must also be considered. Ifsampling for heavy metals, metal scoops should not beused, or if sampling for semivolatiles, plastic scoopsshould be avoided. Samples from greater depths usuallyrequire more elaborate methods or equipment, such astest pits, hand augers, thin-wall tube samplers, hand or
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power corers, bucket augers, cutting or wash samples,direct-push tools, etc. The nature of the geologic materialto be sampled will influence significantly the methods touse, but every effort should be made to reduce the amountof investigation-derived waste generated from thesampling method. Direct-push sampling (such as theGeoprobe®) is preferable in that drill cuttings and drillingfluids are not generated.
A useful field pocket guide is available from EPA:Description and Sampling of Contaminated Soils,EPA/625/12-9/002, November 1991. This guide addressessoil characterization, description, sampling, and samplehandling. Within this guide are general protocols for soilsample handling and preparation. The following areprocedures from the guide:
Soil Sample Collection Procedures for Volatiles.—
1. Tube samples are preferred when collecting forvolatiles. Augers should be used only if soil condi-tions make collection of undisturbed coresimpossible. Soil recovery probes and augers withdedicated or reusable liners will minimize contactof the sample with the atmosphere.
2. Place the first adequate grab sample, maintainingand handling the sample in as undisturbed a stateas possible, in 40-milliliter (mL) septum vials or ina 1-liter (L) glass wide mouth bottle with aTeflon®-lined cap. Do not mix or sieve soilsamples.
3. Ensure the 40-mL containers are filled to the top tominimize volatile loss. Secure the cap tightly, butdo not overtighten.
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4. Examine the hole from which the sample wastaken with an organic vapor instrument after eachsample increment. Record instrument readings.
5. Label and tag sample containers, and recordappropriate data on soil sample data sheets (depth,location, etc.).
6. Place glass sample containers in sealable plasticbags, if required, and place containers in icedshipping container. Samples should be cooled to4 degrees Centigrade (EC) as soon as possible.
7. Complete chain of custody forms and ship as soonas possible to minimize sample holding time.Scheduled arrival time at the analytical laboratoryshould give as much holding time as possible forscheduling of sample analyses.
8. Follow required decontamination and disposalprocedures.
Soil Sample Collection and Mixing Procedures forSemivolatiles and Metals.—
1. Collect samples.
2. If required, composite the grab samples or usediscrete grab samples.
3. If possible, screen the soils in the field through aprecleaned O-mesh (No. 10, 2-millimeter [mm])stainless steel screen for semivolatiles, or Teflon®-lined screen for metals.
4. Mix the sample in a stainless steel, aluminum (notsuitable when testing for aluminum), or glassmixing container using appropriate tool (stainlesssteel spoon, trowel, or pestle).
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5. After thorough mixing, place the sample in themiddle of a relatively inexpensive 1-meter (m)square piece of suitable plastic, canvas, or rubbersheeting.
6. Roll the sample backward and forward on thesheet while alternately lifting and releasingopposite sides or corners of the sheet.
7. After thorough mixing, spread the soil out evenlyon the sheet with a stainless steel spoon, trowel,spatula, or large knife.
8. Take sample container and check that a Teflon®liner is present in the cap, if required.
9. Divide the sample into quarters, and take samplesfrom each quarter in a consecutive manner untilappropriate sampling volume is collected for eachrequired container. Separate sample containerswould be required for semivolatiles, metals,duplicate samples, triplicate samples (split), andspiked samples.
10. Secure the cap tightly. The chemical preservationof solids is generally not recommended.
11. Label and tag sample containers, and recordappropriate data on soil sample data sheets (depth,location, etc.).
12. Place glass sample containers in sealable plasticbags, if required, and place containers in icedshipping container. Samples should be cooled to4 EC as soon as possible.
13. Complete chain of custody forms and ship as soonas possible to minimize sample holding time.Scheduled arrival time at the analytical laboratory
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should give as much holding time as possible for scheduling of sample analyses.
14. Follow required decontamination and disposalprocedures.
Water Quality Sample Collection Methods
Surface Water Collection.—Surface water on oradjacent to a suspected hazardous waste site can yieldsignificant information with minimal sampling effort.Surface water can reveal the presence of contaminationfrom several pathway mechanisms. If only a knowledgeof the presence or absence of contamination in the wateris needed, the collection of grab samples will usuallysuffice. If the water source is a stream, samples alsoshould be collected upstream and downstream from thearea of concern. Additional monitoring of surface wateris required of seeps, spills, surface leachates, etc. If thesite has National Pollutant Discharge EliminationSystem (NPDES) outfalls, the discharges should besampled.
Water quality samples are often the most importantmaterial collected at a site. Determining the appropriatenumber of samples and appropriate test method is criticalto a successful program. A good guidance document todevelop a water quality sampling program and providethe reasoning for collecting appropriate water samples isEPA’s Handbook, Ground Water, volumes I and II,EPA/625/6-90/016. There are several factors to considerin the selection of appropriate sampling devices. Timeand money are obvious factors; however, the data use,formation permeability, water depth, and contaminationtype are considerations. Water monitoring goals andobjectives should be addressed, such as:
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• Is the investigation to determine source(s)?
• Are the investigations included for a time criticalremoval action?
• Have the potential contaminants been identified?
• Will there be a follow up risk assessment and/orremediation?
• Are there potential responsible parties (PRPs)involved?
Water samples can be routinely analyzed for current EPAlisted priority pollutants. Alkalinity, acidity, totalorganic halogens, and chemical oxygen demand are oftenindicators of contamination. Routine tests can be used asscreening techniques before implementing more costlypriority pollutant analyses. Bioassessment samples, ifneeded, are described in Rapid Bioassessment Protocolsfor Use in Streams and Rivers, EPA/444/4-89-001. Iftechnical impracticability (Guidance for Evaluating theTechnical Impracticability, EPA Directive 9234.2-25, ornatural attenuation are potential remediation options,additional water quality parameters may need testingconsideration.
G r o u n d w a t e r C o l l e c t i o n . — G r o u n d w a t e rcontamination is usually difficult and costly to assess,control, and remove. Monitoring wells sample a smallpart of an aquifer, depending on screen size, length,placement depth, pumping rates, and other factors. Theuse of wells and piezometers can introduce additionalproblems due to material contamination, inadequateconstruction, and uncertainties of the water zonesampled. Guarding against cross contamination ofmultiple aquifers is important. Proper well constructionrequires significant skill. General guidelines for designand construction of monitoring wells can be found inAmerican Society for Testing Materials (ASTM)
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D5092-90, and guidelines for sampling can be found inRCRA Groundwater Monitoring Draft TechnicalGuidance, EPA/530-R-93-001. For general details ongroundwater quality monitoring well construction, seefigure 12-2. The location of the screen and designing anddevelopment of the screen and sand pack is extremelyimportant in hazardous waste wells. Meeting theturbidity requirement of less than five nephelometricturbidity units (NTUs) is difficult to achieve in the bestcircumstances. Drilling exploration and monitoring wellsin sequence from least to most contaminated areas isgood practice because this minimizes the possibility ofintroducing contaminants into cleaner aquifers or areas.
Although the Compendium of ERT GroundwaterSampling Procedures, EPA/540/P-91/007, providesstandard operating procedures for emergency responseteams, the recommended water quality samplingprocedures for groundwater should be in accordance withEPA’s Low-Flow (Minimal Drawdown) Ground-WaterSampling Procedures, EPA/540/S-95/504. The MinimalDrawdown (MD) method requires using a submersiblepump placed within a riser and not operated until thewell has stabilized. The use of bailers and hand pumps,including automated hand pump systems for waterquality sampling, is discouraged under the MD method.
Limiting water column disturbance is a primary reasonfor installing a dedicated submersible pump. Lowering atemporary sampling device into the water column createsa mini-slug test. The surge of water may induce sedi-ments into the monitoring well. As a result, the watermay not meet the five NTU limit that is part of therequirement for water quality monitoring wells.Sediments can significantly impact testing. If sediment
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Figure 12-2.—Typical monitoring wellconstruction for water quality sampling.
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content is great, additional tests, such as comparing totalversus dissolved solids, should be considered.
Some sampling devices may induce volatilization.Peristaltic pumps, bailers, or hand pumps in low-flowconditions can impact the test results for semi-volatileand volatile compounds. Peristaltic pumps may inducevolatilization if the samples are lifted from depths greaterthan about 25 feet.
The MD method is the preferred sampling collectionmethod because the method uses a low pumping rate (aslow as 0.1 liter per minute) and attempts to limitdrawdown to less than 0.3 foot. If the extraction rateexceeds the ability of the formation to yield water for lowpermeability wells, turbulent conditions can be inducedwithin the borehole. Water may trickle and fall down thecasing. This may potentially increase air exposure andcan entrain air in the water.
Although preferred water quality sampling uses theMD method, other methods may be acceptable to EPA orother regulatory agencies. Devices such as bailers orperistaltic and hand pumps are routinely used at somesites. However, if these devices are used and surge thewell, water sampling protocols often require that the wellbe purged of at least three well volumes of water prior tocollecting a sample.
Whatever sample device is selected, stabilization oftypical water quality parameters, such as pH, redoxpotential, conductivity, dissolved oxygen, and turbidity,are usually required. Which water quality parametersare specified may be dependent on the site conditions andregulatory requirements. The water extraction devicesand procedures should be specified in the FSP and
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correlated to match the site conditions, contaminants,and the regulatory agency requirements.
Vadose Zone.—In addition to sampling aquifers athazardous waste sites, significant information can beobtained by vadose zone sampling. Leachates from COCsmigrate through the vadose zone toward the water table.Samples collected from this zone can indicate the types ofcontaminants present and can aid in assessing thepotential threat to the aquifer below. The various typesof vadose zone monitors can be used to collect watersamples or interstitial pore space vapors for chemicalanalyses and to determine directional flow of COCs. Themain advantage is that such sampling is relativelyinexpensive, simple to do, and can begin supplyinginformation before aquifer monitoring is started. Thetypes of vadose zone monitors, their applications, andtheir use in satisfying the requirements of RCRA arediscussed in Vadose Zone Monitoring at Hazardous WasteSites, EMSL-LV KT-82-018R, April 1983.
Geophysical Methods
Geophysical methods can be used effectively at hazardouswaste sites to assist in defining the subsurface characterof the site, to assist in the proper placement of monitoringwells, to identify buried containers and debris, and todecrease the safety risks associated with drilling intounknown buried materials. A good overview of thesubject of geophysical methods for surveying hazardouswaste sites is: Geophysical Techniques for Sensing BuriedWastes and Waste Migration, prepared for EPA byTechnos, Inc., available from the National Water WellAssociation.
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Miscellaneous Methods
Ambient concentrations of volatile and semivolatileorganics, trace metals, and particulate matter in the aircan provide important data on the atmospheric migrationpath and the populations at risk and can be used forsource evaluations and personnel monitoring. Portablemonitoring devices such as organic vapor analyzers, staindetector tubes, or other monitors can detect the presenceof various atmospheric hazards. Other monitorscommonly used at hazardous waste sites are explosi-meters, oxygen indicators, and personal sampling pumps.
Other specialized sampling techniques may be necessaryat hazardous waste sites to sample media normally notfound in the geologic environment. Wipe samples may beused to document the presence of toxic materials and todetermine that site or equipment decontamination hasbeen adequate. Wipe sampling consists of rubbing amoistened filter paper, such as Whatman 541 filter paper,over a measured area of 15 in2 (100 cm2) to 10 ft2 (1 m2).The paper is then sent to a laboratory for analysis.
Sample Analysis
Onsite laboratories and field analytical equipment, suchas portable gas chromatographs (GCs) and immunoassaykits, can be very beneficial for rapid analyses. Rapid-analysis equipment, such as GCs, immunoassay, andcolorometric kits, are a cost-effective alternative forproviding qualitative and semi-quantitative chemicaldata and for screening large numbers of samples prior tosubmittals for laboratory testing. Another beneficial useof field screening techniques is to provide generalcontaminant level data for samples to be tested in thelaboratory. If a sample has a very high contaminant
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concentration, the sample may have to be diluted beforebeing analyzed to protect the laboratory instruments fromcostly contaminant saturation problems.
There are many standardized testing procedures andmethods for hazardous waste evaluation. Table 12-3 listssome common method series. Each series containsnumerous individual methods. There are over 25 series-500 (determination of organic compounds in drinkingwater) methods. Method 502.1 is for halogenated volatileorganics (purgeable halocarbons) by GC (48 compounds);Method 502.2 is for nonhalogenated volatile organics byGC (6 compounds); Method 503.1 is for aromatic andunsaturated volatile organics (purgeable aromatics) byGC (28 compounds); Method 507 is for nitrogen andphosphorus containing pesticides by GC (66 substances).
The following references discuss some of the commonmethods:
• Methods for the Determination of OrganicCompounds in Drinking Water. EPA-600/4-88/039, December 1988 (500 Series).
• Guidelines Establishing Test Procedures for theAnalysis of Pollutants Under the Clean Water Act.40 CFR Part 136, October 26, 1984 (600 Series,for effluent - wastewater discharged to a sewer orbody of water).
• Test Methods for Evaluating Solid Waste.SW-846, 2nd Edition, Revised, 1985 (8000 Seriesfor groundwater, soil, liquid, and solid wastes).
• Methods for Chemical Analysis of Water andWastes. EPA-600/4-79-020, March 1983.
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Table 12-3.—Common laboratory testing methods1
Method testing series Analytes
100 - EPA method Physical properties - water
200 - EPA method Metals - water
300 - EPA method Inorganic, non-metallics - water (i.e.,alkalinity)
400 - EPA method Organics - water (i.e., chemical oxygendemand, total recoverable petroleumhydrocarbons [TRPH])
500 - EPA method Organic compounds in drinking water
600 - EPA method Organic compounds in effluent
900 - EPA method Biologic - water (i.e., coliform, fecalstreptococcal)
1000 - SW-846 method Ignitability, toxicity characteristic leachingprocedure (TCLP), extractions, cleanup,headspace - solids
3000 - SW-846 method Acid digestion, extractions, cleanup,headspace - solids
4010 - SW-846 method Screening for pentachlorophenol byimmunoassay - solids
5000 - SW-846 method Organic (purge and trap, gaschromatograph/mass spectrometer[GC/MS], sorbent cartridges)
6000 - SW-846 method Inductively coupled plasma (spectrometry)
7000 - SW-846 method Metals - solid waste
8000 - SW-846 method Organic compounds in solid waste
9000 - SW-846 method Inorganics, coliform, oil and greaseextractions - solids
1 This list is not inclusive. Significant overlap and exceptions are present. Methods listed are basic guides to provide the investigator with the generalstructure of the testing method scheme. Numerous individual methods existwithin each series.
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• Standard Methods for the Examination of Waterand Wastewater, 19th edition, Greenberg;American Public Health Association, Washington,DC, 1995.
Reference guides are also available from several sources,such as the Trace Analysis Laboratory Reference Guidesfrom Trace Analysis Laboratory, Inc., 3423 InvestmentBoulevard, No. 8, Hayward, California 94545, telephone(415) 783-6960.
An important consideration in planning any fieldinvestigation program is scheduling the anticipatedactivities. Sufficient time must be allowed for thepeculiarities of hazardous waste work. Several factorsmust be considered: (1) time for establishing work zonesand erecting physical barriers, (2) time for establishingequipment, personnel, and vehicle decontaminationstations, (3) time needed to decontaminate equipmentand personnel, ( 4) loss of worker efficiency due to safetymonitoring, safety meetings, and the use of protectiveclothing, (5) documentation requirements and sample-handling procedures, and (6) inventory and procurementof specialized sample containers, preservative pre-paration, and reference standards, and equipmentcalibrations.
Safety at Hazardous Waste Sites
A major factor during hazardous waste site investigationsis the safety of both the general public and the siteinvestigators. The following references may be ofassistance:
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• Interim Standard Operation Safety Guides.Revised September 1982, U.S. EPA, Office ofEmergency and Remedial Response (OERR).
• Guidance Manual for Protection of Health andSafety at Uncontrolled Hazardous SubstancesSites. EPA, Center for Environmental ResearchInformation (ORD) (in draft, January 1983).
• Reclamation Safety and Health Standards.U.S. Department of the Interior, Bureau ofReclamation, Denver, Colorado, 1993.
• Chemical Substance Hazard Assessment andProtection Guide. OWENS/URIE Enterprises,Inc., Henehan, Urie, & Farlern, Wheat Ridge,Colorado, 1994.
Sample Quality Assurance and Quality Control
Sample QA procedures confirm the quality of the data bydocumenting that integrity is present throughout thesample history. Several sample types are used. Fieldblanks are samples of a "pure" substance, either water,solid, or air, which are collected in the field using thesame procedures as are used for actual environmentalsamples. The purpose of the field blank is to ensure thatoutside influences are not contaminating the truesamples (i.e., vehicular exhaust) during sampling. If"hits" are discovered in the field blank, the questionarises whether contamination not associated with the siteis affecting the true samples.
Trip blanks are samples of a "pure" substance (analyte-free deionized water which accompanies samples withvolatile contaminants) prepared in a laboratory or other
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controlled area and placed in a shipping container withenvironmental samples. The purpose of the trip blank isto ensure that samples were not cross contaminatedduring shipment and storage. "Hits" in a trip blankindicate that COCs were present in a container to adegree sufficient to infiltrate into the trip blank samplejar and, hence, possibly into true samples.
Equipment blanks are used when sampling equipment iscleaned and re-used for subsequent sample collection.The blanks verify the effectiveness of field cleaningprocedures. The final rinse for the sampling equipmentis often made with analyte-free deionized water. Therinse water is run on or through the sampling equipment,collected in appropriate containers and preserved. Thesesamples are usually collected on a schedule, such as onceevery 10 episodes.
Duplicates are samples collected at the same time, in thesame way, and contained, preserved, and transported inthe same manner as a corresponding duplicate.Duplicates are used to determine the precision of thelaboratory method and integrity of the sample fromcollection through testing. Duplicates are typicallycollected once every 10 samples.
Matrix spikes provide the best overall assessment ofaccuracy for the entire measurement system. For waterinvestigation episodes, a laboratory usually prepares thespike samples, sends them to the site, and the spikesample(s) are included in the sample handling andshipping process. The samples are analyzed blind by theoff-site laboratory. Matrix spikes can also be made fromcertified mixtures of a contaminant and clean soil in thefield.
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All types of blanks and duplicates must be prepared inthe same sample containers as actual samples includinglabeling and identification schemes so that the laboratoryanalyzes the sample without knowing that the samplesare quality control (QC) samples (blind testing).
In addition to field QC samples, the analytical laboratoryalso uses QC samples. Method blanks are organic-free ordeionized water carried through the analytical schemelike a sample. Method blanks measure contaminationassociated with laboratory activities. Calibration blanksare prepared with standards to create a calibration curve.Internal standards are measured amounts of certaincompounds added after preparation or extraction of asample. Surrogates are measured amounts of certaincompounds added before preparation or extraction of asample to determine systematic extraction problems.Duplicates and duplicate spikes are aliquots of samplessubjected to the same preparation and analytical schemeas the original sample. Laboratory control standards(LCSs) are aliquots of organic-free or deionized water towhich known amounts of analyte have been added. LCSsare subjected to the sample preparation or extractionprocedure and analyzed as samples.
Field, laboratory, data validation, and report presentationdocuments must be meticulously maintained duringhazardous waste site investigations. All field activitiesshould be recorded in bound, consecutively numbered logbooks. Each entry should be made with indelible ink, andall strike outs should be made by a single line whichallows the original error to be legible and initialed anddated by the person making the correction. Entriesshould include date, weather conditions, personnelinvolved with the activity, the type of activity beingperformed, unusual circumstances or variations made tothe SOPs, and data appropriate to the activity being
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performed. This is a diary of all activities on a site. Theinvestigator responsible for the activity is responsible formaintaining the field log book. An important purpose ofthe field log book is to document any changes made toSOPs. If such changes may affect data quality,concurrence with managers or regulatory personnel isrequired in writing. All records must be under control atall times. Unique project numbers should be assigned toall log books, documents, and reports. All records mustbe maintained and custody documented so thatunauthorized changes or tampering are eliminated. Logbook entries should be photocopied on a regular scheduleto ensure that field data are not lost if the original bookis lost or destroyed.
Activities during an investigation must be reviewed toensure that all procedures are followed. System auditsshould consist of inspections of training status, records,QC data, calibrations, and conformance to SOPs. Systemaudits are performed periodically on field, laboratory, andoffice operations. Each major investigation type shouldbe subject to at least one system audit as early aspracticable. Performance audits include evaluation andanalysis of check samples, usually from laboratoryactivities. Readiness reviews occur immediately prior tobeginning each type of field activity to assess thereadiness of the team to begin work. A checklist ofprerequisite issues, such as necessary equipment,controlled documents, training, assignments, spare parts,field arrangements, etc., are discussed and documented.
If any weaknesses or deficiencies are identified, theinvestigator must resolve them before field activitiesproceed.
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Sample Management
There must be control and documentation of all samplesafter the environmental samples are collected in the field.The proper quantity of a sample must be collected to havesufficient volume for the subsequent analysis. The propersample container and preservative must be used so thatsample integrity is not compromised. Many types ofsamples (e.g., volatiles) must be cooled, usually to 4 EC,throughout their history after collection. The properanalytical methods must be identified to obtain thedesired result. The laboratory must handle and track thereceived samples in a timely and accurate manner toensure that the results are correct.
Sample Custody
Sample custody is a prime consideration in the propermanagement of samples. Sample custody is designed tocreate an accurate, written, and verified record that canbe used to trace the possession and handling of thesamples from collection through data analyses andreporting. Adequate sample custody is achieved bymeans of QA-approved field and analyticaldocumentation. A sample is considered in custody if thesample is (1) in one's actual physical possession, (2) is inone's view after being in one's physical possession, (3) isin one's physical possession and then locked up orotherwise sealed so that tampering will be evident, or(4) is kept in a secure area restricted to authorizedpersonnel only. Personnel who collect samples arepersonally responsible for the care and integrity of thesecollected samples until the samples are properlytransferred or dispatched. To document that samples areproperly transferred or dispatched, sample identification
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and chain of custody procedures must be followed.Sample custody in the field and in transit involves thesteps described below.
Sample Identification.—The sample must first beproperly and uniquely identified. Sample identificationentails establishing a scheme which ensures that eachsample is identified in such a way that one sample cannotbe mistaken for another. Examples of sample labels areshown in figure 12-3. Labels must be filled outimmediately after the sample is collected to ensure thatcontainers are not later misidentified. Indelible ink mustbe used on all labels, and the writing must be legible. Forsamples which require preservation, the sample labelsmust have a space on the label reserved for noting thepreservative added, or other treatments, such as filtering,compositing, etc. Labels can be removed from a samplejar during shipment, especially if the accompanying icemelts and saturates the shipping labels. Double-labelsamples such as sacked soil whenever possible orcompletely wrap the label over the sample bottle withwide, water-proof tape. Also record the collection of eachsample in the field log book and chain of custody records. Chain of Custody.—Once all samples for a specific sam-pling task have been collected, the sampler(s) will com-plete the chain of custody record (figure 12-4). Specificprocedures for completing this form should be included inthe work plan documents specific to the project. Thisrecord accompanies the samples to their destination. Allsamples typically are transferred from the sampletransport container (e.g., cooler) and kept in the exclusionzone until transferred to a noncontaminated sampletransport container in the contamination reduction zone.The samples, with accompanying documentation, are
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Figure 12-3.—Soil and water sample identification labels.
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413 Figure 12-4.—Chain of custody record.
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then prepared for either distribution to the onsitelaboratory or shipment to an analytical laboratory in thesupport zone.
When transferring the possession of samples, theindividuals relinquishing and receiving the samples willsign, date, and note the time on the chain of custodyrecord. This record documents sample custody transferfrom the sampler to the analyst. Note that somecommercial shippers (such as Federal Express) do notsign chain of custody records but do prepare separateshipping documents which indicate receipt of thecooler(s). When samples are passed among fieldpersonnel while still onsite, chain of custody records donot need to be signed, as long as physical possession isretained by identified, responsible personnel duringtransit of the container(s). Packaging
Samples must be packaged properly for shipment anddispatched to the appropriate laboratory for analysis; aseparate record accompanies each shipment. Sampleswithin shipping containers will be sealed for shipment tothe laboratory by using custody seals (figure 12-5). Sealsare made of paper, with adhesive backing, so that theywill tear easily to indicate possible tampering. There aretwo methods of using custody seals. One method is toplace several sample containers in individual plastic bags(or boxes) within the shipping container and then placethe custody seal along the only opening of each bag. Anadvantage of this scheme is that the seal is not exposedto outside influences; but the disadvantages are that thebags are very pliable, and shifting may cause the seal tobreak, and the seal may become immersed in water if icemelts around the bags. The second method is to place thecustody seal on the outside of the cooler, along a seam of
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415 Figure 12-5—Custody seal.
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the lid. The advantage of this method is that the seal isstuck to the solid body of the cooler. The maindisadvantage is that the seal is exposed to handling bythe shipping company and other personnel from the fieldto the laboratory. The seal must not be broken acci-dentally because a broken seal will place all thesamples represented by the seal in jeopardy ofdisqualification due to tampering. An option may be toplace clear tape over the seal as added protection.
The samples within a container must be packed to avoidrattling and breakage. Styrofoam "popcorn" or bubblepack sheeting are acceptable packing materials. Organicpacking materials, including sawdust, should be avoideddue to the possibility of becoming wet from melting ice.Each sample jar should be wrapped such that jar-to-jarcontact is avoided. Also, it is usually desirable to placeice at the bottom of the container, and place the samplesabove the ice, with a water-proof barrier between the iceand samples. This way, if the ice melts, there is alessened probability of the samples becoming immersed.If time is available, ice should be double-wrapped, usingseveral "ice packages" to lessen spillage potential.Chemical ice packs and dry ice should be avoided, ifpossible, to lessen the chance of chemical contamination.The chain of custody record must accompany eachcontainer and list only the samples contained within thespecified cooler. The original chain of custody recordshould be sealed in a "zip-lock" plastic bag and taped tothe inside top of the cooler lid. When the laboratoryopens a cooler, the number and identification of eachsample contained within the cooler must exactly matchthe corresponding chain of custody record. A copy of thechain of custody record is to be retained by theinvestigator or site manager, and a copy is also retainedby the laboratory. A three-carbon copy type chain ofcustody record is best.
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The water drain at the lower edge of the cooler must besealed so there is no possibility of the drain opening. Ifany leakage occurs from a cooler containing environ-mental samples, the shipping company will cease ship-ment and delay the arrival of the samples, possiblyexceeding the holding times of the contained samples. Ashipping company may have unique requirements; but asa general rule, the weight of a cooler should not exceed50 to 70 pounds. If sent by mail, the package must bereceipt requested. If sent by common carrier, a govern-ment bill of lading can be used. Proper shipment trackingmethods must be in place. Copies of all receipts, etc.,must be retained as part of the permanentdocumentation.
Upon arrival at the laboratory, the containers will beopened, the custody seals inspected and documented, andany problems with chain of custody, temperature, orsample integrity noted. The laboratory custodian willthen sign and date the chain of custody record and enterthe sample identification numbers into a bound,paginated log book, possibly assigning and cross-referencing a unique laboratory number to each samplereceived. The laboratory then controls the samplesaccording to the SOPs specified in their work plandocuments.
Decontamination
Decontamination consists of removing contaminantsand/or changing their chemical nature to innocuoussubstances. How extensive decontamination must bedepends on a number of factors, the most important beingthe type of contaminants involved. The more harmful thecontaminant, the more extensive and thorough decon-tamination must be. Less harmful contaminants may
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require less decontamination. Only general guidance canbe given on methods and techniques for decontamination.The exact procedure to use must be determined afterevaluating a number of factors specific to the site.
When planning site operations, methods should bedeveloped to prevent the contamination of people andequipment. For example, using remote sampling tech-niques, using disposable sampling equipment, wateringdown dusty areas, and not walking through areas ofobvious contamination would reduce the probability ofbecoming contaminated and require a less elaboratedecontamination procedure.
The initial decontamination plan is usually based on aworst-case situation. During the investigations, specificconditions are evaluated including: type of contaminant,the amount of contamination, the levels of protectionrequired, and the type of protective clothing needed. Theinitial decontamination system may be modified byadapting it to actual site conditions.
Chapter 13
SURFACE GEOPHYSICALINVESTIGATIONS
Introduction
Surface geophysical surveys have been applied to mineraland petroleum exploration for many years. A magneticcompass was used in Sweden in the mid-1600s to find ironore deposits. The lateral extent of the Comstock ore bodywas mapped using self-potential methods in the 1880s. Avery crude type of seismic survey measured the energyresulting from blasting operations in Ireland in the late1800s. The idea that energy travels through a materialwith a certain velocity came from this survey. DuringWorld War I, geophysical techniques were used to locateartillery pieces. Anti-submarine warfare in World War IIled to magnetic and sonar surveys.
The main emphasis of geophysical surveys in theformative years was petroleum exploration. Technologydeveloped for oil and gas surveys led to the use of geo-physical surveys in many important facets of geotechnicalinvestigations. Geophysical surveys have been applied tocivil engineering investigations since the late 1920s, whenseismic and electrical resistivity surveys were used fordam siting studies. A seismic survey was performed inthe 1950s in St. Peter’s Basilica to locate buriedcatacombs prior to a renovation project. From the late1950s until the present time, geophysical techniques havehad an increasing role in both groundwater explorationand in geotechnical investigations. Geophysical surveysare now used routinely as part of geological investigationsand to provide information on site parameters (i.e., inplace dynamic properties, cathodic protection, depth tobedrock) that in some instances are not obtainable byother methods. Values derived from seismic geophysicalsurveys are obtained at strain levels different from somesite parameters obtained by other means.
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All geophysical techniques are based on the detection ofcontrasts in different physical properties of materials. Ifcontrasts do not exist, geophysical methods will not work.Reflection and refraction seismic methods contrast com-pressional or shear wave velocities of different materials.Electrical methods depend on the contrasts in electricalresistivities. Contrasts in the densities of differentmaterials permit gravity surveys to be used in certaintypes of investigations. Contrasts in magnetic suscepti-bilities of materials permit magnetic surveying to be usedin some investigations. Contrasts in the magnitude of thenaturally existing electric current within the earth can bedetected by self-potential (SP) surveys.
Seismic refraction surveys are used to map the depth tobedrock and to provide information on the compressionaland shear wave velocities of the various units overlyingbedrock. Velocity information also can be used to calcu-late in place small-strain dynamic properties of theseunits. Electrical resistivity surveys are used to provideinformation on the depth to bedrock and information onthe electrical properties of bedrock and the overlyingunits. Resistivity surveys have proven very useful indelineating areas of contamination within soils and rockand also in aquifer delineation. Gravity and magneticsurveys are not used to the extent of seismic andresistivity surveys in geotechnical investigations, butthese surveys have been used to locate buried utilities.Self-potential surveys have been used to map leakagefrom dams and reservoirs.
Geophysical surveys provide indirect information. Theobjective of these surveys is to determine characteristicsof subsurface materials without seeing them directly.Each type of geophysical survey has capabilities andlimitations and these must be understood and consideredwhen designing a geophysical investigations program.
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Geophysical interpretations should be correlatedwith real “ground-truth”data such as drill hole logs.It is very important that the results of geophysicalsurveys be integrated with the results of othergeologic investigations so that accurate interpre-tation of the geophysical surveys can be made.
The following sections provide the theory behind andguidelines for uses of geophysical surveys, particularly ingeotechnical investigations. Although this chapter doesnot provide all the detail necessary, the theory and inter-pretation methods involved in geophysical surveying areincluded in references in the bibliography. The referencesshould be used to supplement the materials presented inthis chapter.
Seismic Surveys
Seismic Refraction Surveys
Purpose.—Seismic refraction surveys are used to deter-mine the compressional wave velocities of materials fromthe ground surface to a specified depth within the earth.For most geotechnical investigations, the maximum depthof interest will be specified by the nature of the project.In many cases the objective of a seismic refraction surveyis to determine the configuration of the bedrock surfaceand the compressional wave velocities of the underlyingmaterials. Bedrock may be defined by compressionalwave velocities. The information obtained from a seismicrefraction survey is used to compute the depths to varioussubsurface layers and the configurations of these layers.The thickness of the layers and the velocity contrastsbetween the layers govern the effectiveness and the accu-racy of the survey. Seismic refraction surveys do notprovide all compressional wave velocities or delineate all
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Figure 13-1.—Simplified diagram of a seismic refraction test.
subsurface layers. Seismic refraction interpretationassumes that layer velocities increase with depth.
Applications.—Seismic refraction surveys have beenused in many types of exploration programs and geotech-nical investigations. The initial application of thesesurveys was mapping of salt domes in the early days of oilexploration. Seismic refraction surveys are now routinelyused in foundation studies for construction projects andsiting studies, fault investigations, dam safety analyses,and tunnel alignment studies. Seismic refraction surveysare also used to estimate rippability (Appendix C). Figure13-1 is a schematic of a seismic refraction test.
Seismic Reflection Surveys
Purpose.—Seismic reflection surveys have been usedsuccessfully in petroleum and geothermal explorationprojects and to investigate for shallow coal. The informa-tion obtained from seismic reflection surveys can be usedto define the geometry of the different subsurface layersand structural features.
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Applications.—High resolution seismic reflectionsurveys provide definitive information on the locationsand types of faults, as well as the location of buriedchannels. Shallow, high resolution seismic reflectionsurveys are playing an increasingly important role ingeotechnical investigations. When correctly used, seismicreflection surveys may provide data that seismicrefraction surveys can not (e.g., velocity reversalinformation). However, compressional (P) wave velocityinformation derived from reflection surveys may not be asaccurate as from refraction surveys. The compressionalwave velocities are needed for the analysis of thereflection records themselves and for seismic refractionsurveys, uphole velocity surveys, and sonic logs.
Shear Wave Surveys
Purpose.—Shear (S) waves travel through a medium ata slower velocity than compressional (P) waves and arriveafter compressional waves. Other types of secondaryarrivals also exist due to reflections, combinations ofreflections and refractions, and surface waves. Field sur-vey techniques are designed to suppress compressionaland unwanted reflected or refracted wave arrivals. Thefield procedure optimizes shear wave generation as wellas the polarity of the wave energy.
Applications.—For geotechnical investigations, shearwave velocities provide information on the low-straindynamic properties of a given material. The relationshipsbetween compressional wave velocity, shear wave velocity,density, and in place dynamic properties of materials areshown in table 13-1. The compressional wave velocity canbe determined from refraction surveys, the shear wavevelocity from shear wave surveys, and the density fromborehole geophysics or laboratory testing. The cross-holeseismic method is a common procedure used to determine
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Table 13-1.—Determining moduli and ratios for typicalvelocities of earth materials from refraction surveys
Vp = Compressional wave velocity (ft/s) (m/s)Vs = Shear wave velocity (ft/s) (m/s)E = Young's Modulus (lb/in2) (MPa)G = Shear Modulus (lb/in2) (MPa)K = Bulk Modulus (lb/in2) (MPa)µ = Poisson's Ratio� = Density (in situ) (lb/ft3) (kg/m3)
Shear Modulus: G = �Vs2
Young's Modulus: E = 2G(1+�) Bulk Modulus: K = �(Vp-4/3Vs
2)Velocity Ratio: Vp/Vs
Poisson's Ratio: µ = (.05) [Vp/Vs]2-2/[Vp/Vs]
2-1\
material dynamic properties. Compressional waves andshear waves are generated in one drill hole, and theseismic wave arrivals are received in companion drillhole(s). The seismic source(s) and receiver(s) are locatedat equal depths (elevations) for each recording. Drill holedeviation surveys are performed in each drill hole toaccurately determine the distances between each of thedrill holes at all recording intervals. For typical seismicvelocities of earth materials, see table 13-2.
Surface Wave Surveys
Purpose.—Surface wave surveys produce and recordsurface waves and their characteristics. Surface waveshave lower frequencies and higher amplitudes than otherseismic waves. Surface waves result from the construc-tive and destructive interference of refracted and reflectedseismic waves. Surface waves that travel along theboundaries of a body are called Stanley waves. Surfacewaves are the slowest type of seismic
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Table 13-2.—Typical velocities of earth materials
Material
Velocity
(feet per second)(meters per
second)
Dry silt, sand, loose gravel,loam, loose rock, talus, andmoist fine-grained topsoil
600-2,500 200-800
Compact till, induratedclays, gravel below watertable*, compact clayeygravel, sand, and sand-clay
2,500-7,500 800-2,300
Weathered, fractured, orpartly decomposed rock
2,000-10,000 600-3,000
Sound shale 2,500-11,000 800-3,400
Sound sandstone 5,000-14,000 1,500-4,000
Sound limestone, chalk 6,000-20,000 2,000-6,100
Sound igneous rock 12,000-20,000 3,700-6,100
Sound metamorphic rock 10,000-16,000 3,100-4,900
*Water (saturated materialsshould have velocities equalto or exceeding that ofwater)
4,700 1,400
wave, traveling along the boundaries between differentmaterials. The characteristics must be determined inaddition to recording the waves. Normally, surface wavesare filtered out of seismic data or are ignored. The term."ground roll," in the oil exploration industry denotessurface waves. Special care is taken in seismic reflectionsurveys to filter out surface waves because they caninterfere with desired reflections. The different types ofsurface waves and their characteristic motions are shownin figure 13-2.
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Figure 13-2.—Types of surface waves.
Applications.—The principal application of surface wavesurveying for geotechnical investigations is to determinethe type and characteristics of surface waves that canexist at a site. This information is used to determine pre-ferred site frequencies and for earthquake designanalysis.
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Vibration Surveys
Purpose.—Vibration surveys measure the vibrationlevels produced by mechanical or explosive sources. Oncethese levels are determined, structures can be designed toreduce the possibility of vibration damage.
Applications.—Vibration surveys have been performedfor quarrying and mining operations, excavations,measuring the effects of traffic on sensitive equipment,and measuring the effects of aircraft (sonic vibrations) onurban areas and historical buildings. Many manufactur-ing and research facilities contain extremely sensitiveequipment with very small vibration tolerances. Vibra-tion surveys can be very useful in determining the exactlevels of allowable vibration and in designing proceduresto reduce vibration levels produced by construction andblasting activities. The same type of vibration survey canbe used in quarrying and/or mining operations to reducevibration levels while maintaining rock breakage andfragmentation.
Electrical Resistivity Surveys
The electrical resistivity of any material depends largelyon its porosity and the salinity of the water in the porespaces. Although the electrical resistivity of a materialmay not be diagnostic, certain materials have specificranges of electrical resistivity. In all electrical resistivitysurveying techniques, a known electrical current is passedthrough the ground between two (or more) electrodes. Thepotential (voltage) of the electrical field resulting from theapplication of the current is measured between two (ormore) additional electrodes at various locations. Since thecurrent is known, and the potential can be measured, anapparent resistivity can be calculated. The separation
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between the current electrodes depends on the type ofsurveying being performed and the required investigationdepth.
For representatives values of resistivity, see table 13-3.
Table 13-3.—Representative values of resistivity
Material Resistivity (ohm-m)
Clay and saturated silt 1-100
Sandy clay and wet silty sand 100-250
Clayey sand and saturated sand 250-500
Sand 500-1,500
Gravel 1,500-5,000
Weathered rock 1,000-2,000
Sound rock 1,500-40,000
Electrical Resistivity Profiling Surveys
Electrical resistivity survey profiling is based on lateralchanges in the electrical properties of subsurfacematerials.
Purpose.—Electrical resistivity profiling is used to detectlateral changes in the electrical properties of subsurfacematerial, usually to a specified depth. Electrode spacingis held constant.
Applications.—Electrical resistivity has been used tomap sand and gravel deposits, determine parameters forcathodic protection, map contamination plumes inhazardous waste studies, and used in fault studies.
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Electrical Resistivity Sounding Surveys
Electrical resistivity sounding surveys measure verticalchanges in the electrical properties of subsurfacematerials. The electrode spacing used for resistivitysounding is variable, with the center point of the electrodearray remaining constant. The depth of investigationincreases as the electrode spacing increases.
Purpose.—Resistivity soundings are used to investigatevariations of resistivity with depth. Electrode spacing isvaried.
Applications.—Electrical resistivity soundings are com-monly used for aquifer and aquaclude delineation ingroundwater investigations. The technique has been usedfor bedrock delineation studies where there is not a suf-ficient velocity contrast to permit seismic surveying.Vertical electrical soundings have been used for largescale mineral investigations, geothermal investigations,cathodic protection and toxic waste studies, and inconjunction with self-potential surveys for seepageinvestigations.
Electrical Resistivity Dipole-Dipole Surveys
Dipole-dipole surveying potential electrodes may have anyposition with respect to the pair of current electrodes.When the current and potential electrodes are positionedalong the same line, the array is referred to as an axialdipole array (figure 13-3). The current electrodes areseparated from the potential electrodes by an interval, n,which is some multiple of the current and potential elec-trodes separation, a. The separation of the current andpotential electrodes is normally equal.
FIE
LD
MA
NU
AL
12
Figure 13-3.—Dipole resistivity array.
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Purpose.—Dipole-dipole arrays are used to determineboth the lateral and vertical changes in electricalproperties of subsurface materials with one electrodearray.
Applications.—The dipole-dipole array has limitedapplications in engineering and groundwater geophysics.This type of electrode array has been used primarily inmineral and geothermal exploration. The method hasbeen used to delineate abandoned mines, mappingsaltwater/fresh water interfaces, and mapping buriedstream channels.
Electromagnetic Conductivity Surveys
Electromagnetic Conductivity Profiling Surveys
Electromagnetic (EM) surveying uses time-varying, lowfrequency, electromagnetic fields induced into the earth.A transmitter, receiver, and a buried conductor arecoupled by electrical circuitry through electromagneticinduction. The characteristics of electromagnetic wavepropagation and attenuation by a material can permitinterpretation of the electrical conductivities of thesubsurface materials.
Purpose.—Since electrical conductivity is the reciprocalof electrical resistivity, electromagnetic surveys are usedto provide resistivity information on subsurface materials.Electromagnetic conductivity profiling surveys are spe-cifically used to determine lateral changes in conductivityof the subsurface materials.
Applications.—Electromagnetic surveys have been usedprimarily for mineral exploration; and with the exceptionof magnetic surveys, EM surveys are the most commonly
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used geophysical surveys for minerals. EM surveys havebeen used in engineering and groundwater investigations.The method is found to be particularly useful in mappingcontaminant plumes and buried metallic waste such asmetal drums containing hazardous chemicals. EM sur-veys are suited to hazardous waste studies because thesurveying procedure does not require equipment to touchpotentially contaminated ground. The method has beenused to locate buried pipes and cables and to locatelandmines.
Electromagnetic Conductivity Sounding Surveys
Purpose.—Electromagnetic conductivity sounding sur-veys are used to determine vertical changes in con-ductivity of subsurface material.
Applications.—Electromagnetic sounding surveys canlocate areas of permafrost, gravel deposits, map bedrocktopography, and provide general geological information.EM sounding and profiling surveys have been applied tomapping areas of salt water intrusion, archaeologicalinvestigations, and fault studies.
Ground Penetrating Radar Surveys
Purpose
Ground penetrating radar (GPR) surveys have the samegeneral characteristics as seismic surveys. The depth ofinvestigation with GPR is extremely shallow when com-pared to seismic surveys. This disadvantage is partiallyoffset by the much better resolution of GPR.
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Applications
Ground penetrating radar surveys can be used for avariety of very shallow geotechnical investigations,including the locations of pipes or other buried manmadeobjects such as timbers, very high resolution mapping ofnear-surface geology, and detecting cavities, piping, andleakage in dams. The applications are limited by the veryshallow penetration depth of the very high radarfrequencies. Silts, clays, salts, saline water, the watertable, and any other conductive materials in the sub-surface severely restrict or stop penetration of radar.
Self-Potential Surveys
Purpose
Self-potential ([SP] spontaneous potential or naturalpotential) is the natural electrical potential existingwithin the earth due to many causes. These causes can beclassified broadly into two groups (excluding manmadecauses):
Mineralization Potential.—Mineralization potential iscommonly the result of chemical concentration cellsformed when conductive mineral deposits, such asgraphite or sulfide, are intersected by the water table.Mineralization potentials are almost always negative andmay have values up to several hundred millivolts. Back-ground potentials can be either positive or negative andusually have values of only a few tens of millivolts.
Background Potential.—Background potential iscommonly the result of (a) two electrolytes of differentconcentration being in contact with one another,(b) electrolytes flowing through a capillary system or
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porous media, (c) an electrolyte in contact with a solid,and (d) electromagnetically induced telluric (large scaleflow in the earth’s crust) currents.
The background potentials developed by electrolytes flow-ing through a capillary system or porous media (calledelectro-filtration or streaming potentials) are used tostudy seepage. Water flowing through a capillary systemcollects and transports positive ions from the surroundingmaterials. The positive ions accumulate at the exit pointof the capillary, leaving a net positive charge. Theuntransported negative ions accumulate at the entrypoint of the capillary leaving a net negative charge. If thestreaming potentials developed by this process are ofsufficient magnitude to measure, the entry point and theexit point of zones of concentrated seepage may bedetermined from the negative and positive self potentialanomalies.
Applications
Self-potential surveys have been used to map the lateralextent of mineral deposits and, in some instances, provideinformation of the configuration of the deposits. Anotherexploration application has been to map the depth to andconfiguration of certain geothermal areas. Normally, ingeothermal applications, self-potential surveying is usedin conjunction with other geophysical surveys (gravity,seismic, and electrical).
In geotechnical investigations, self-potential surveys havebeen used to map leakage paths from dams. Self-potential surveying has also been used to map leaks fromcanals and buried pipelines that transport liquids.Detachment walls and lateral limits of some landslidemasses have been mapped with self-potential surveys.
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Self-potential surveying may play an important role inhazardous waste investigations and in monitoring leakagefrom dams.
Magnetic Surveys
Purpose
Magnetic surveys measure anomalous conditions withinthe Earth’s magnetic field. The Earth’s magnetic fieldresembles the field of a bar magnet. The field is twice asstrong in the polar regions than at the equator. Theintensity of the field in the polar regions is approximately60,000 gammas; while at the equator, the intensity isapproximately 30,000 gammas. The Earth’s magneticfield is not symmetrical but contains many large per-turbations due to local variations in magnetic materialsand larger magnetic features. Within the Earth’s field,anomalies on the order of one gamma to several thousandgammas are detected by magnetic surveys. The smalleranomalies can be detected with complex instruments, andthe larger anomalies can be detected with simpler instru-ments and field techniques.
Applications
Magnetic surveys have their widest applications in petro-leum and mineral exploration programs. For applicationsin petroleum exploration, the application is somewhatsimpler because the sources of most magnetic anomalieslie within the basement complex and the overlyingsediments are often "transparent" to magnetic surveys.
In geotechnical investigations, magnetic surveys havebeen used to detect buried barrels of contaminated
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materials and to detect and map buried pipelines.Magnetic surveys have also been used in archaeologicalinvestigations.
Gravity Surveys
Purpose
Gravity anomalies are the result of contrasts in densitiesof materials in the Earth. If all the materials within theEarth were layered horizontally and were of uniformdensity, there would be no density contrasts. Densitycontrasts of different materials are controlled by anumber of different factors; the most important are thegrain density of the particles forming the material, theporosity of the material, and the interstitial fluids withinthe material. Generally, soil and shale specific gravitiesrange from 1.7 to 2.2. Massive limestone specific gravitiesaverage 2.7. While this range of values may appear to befairly large, local contrasts will be only a fraction of thisrange. A common order of magnitude for local densitycontrasts is 0.25. Density contrasts can be determined bycalculating the gravity effect of a known model andcomparing that effect with the observed gravitydetermined from a gravity survey.
Applications
Gravity surveys provide an inexpensive determination ofregional structures that may be associated withgroundwater aquifers or petroleum traps. Gravity sur-veys have been one of the principal exploration tools inregional petroleum exploration surveys. Gravity surveyshave somewhat limited applications in geotechnicalinvestigations. Gravity surveys have been used to obtaininformation on bedrock depths and the top of rock
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configuration in areas where it has not been possible orpractical to use other geophysical techniques. Micro-gravity (high-precision) surveys have been used in a fewinstances to obtain information on the success of groutingprograms. In these cases, microgravity surveys are per-formed before and after grouting operations and densitycontrasts of the two surveys are compared. Microgravitysurveys have been used for archaeological investigations.
Glossary
A
Accelerometer – Transducer with output proportional toacceleration. A moving coil geophone (type oftransducer) with a response proportional tofrequency may operate as an accelerometer.
Acoustic Logging – borehole log of any of severalaspects of acoustic-wave propagation (e.g., a sonic,amplitude, character, or three-dimensional log).
Air Wave – Energy from a shot which travels in the airat the velocity of sound.
Amplitude – The size of a signal, either in the ground orafter amplification. Usually measured from the zeroor rest position to a maximum excursion. Theamplitude of a signal has units based on themeasurement of the signal (e.g., acceleration (inchper square second [in/sec2]), velocity (inches persecond [in/sec]) or displacement (inches [in]).
Analog – (1) A continuous physical variable (such as volt-age or rotation) that has a direct relationship toanother variable (such as acceleration) with one
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proportional to the other. (2) Continuous as opposedto discrete or digital.
Anomaly – A deviation from normal or the expected. Forexample, a travel time anomaly, Bouger anomaly,free-air anomaly.
Apparent Velocity – (1) The velocity that a wave-frontregisters on a line of geophones. (2) The inverseslope of a time-distance curve.
Automatic Gain Control (AGC) – The outputamplitude controls the gain of a seismic amplifier,usually individual for each channel; but sometimes,multi-channel devices are used.
B
Basement (Complex) – (1) generally of igneous andmetamorphic rocks overlain unconformably bysedimentary strata. (2) Crustal layer beneath asedimentary layer and above the Mohorovicicdiscontinuity.
Bedrock – Any solid rock exposed at the surface of theearth or overlain by unconsolidated material.
Bit – A binary digit; either a 1 (one) or 0 (zero).
Body Waves – The only waves that travel through theinterior of a body consisting of P-waves and S-waves.
Byte – Word.
C
Cable – The assembly of electrical conductors used toconnect geophone groups or other instruments.
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Casing – Tubing or pipe used to line drill holes or shot-holes to keep them from caving.
Cathodic Protection – Electrical corrosion protectionfor pile foundations, electrical grounding mats, bur-ied pipelines, or any metal subject to corrosion.
Channel – (1) A single series of interconnected devicesthrough which geophysical data can flow from sourceto recorder. (2) An elongated depression or geologicalfeature. (3) An allocated portion of the radio fre-quency spectrum.
Channel Wave – An elastic wave propagated in a layerof lower velocity than layers on either side. Energyis largely prevented from escaping from the channelbecause of repeated total reflection at the channelboundaries or because rays that tend to escape arerefracted back toward the channel.
Character. – (1) The recognizable aspect of a seismicevent, usually displayed in the waveform thatdistinguishes the event from other events. Usually,a frequency or phasing effect, often not definedprecisely and dependent upon subjective judgment.
Common Depth Point (CDP). – The same portion ofsubsurface that produces reflections at differentoffset distances on several profiles.
Compressional Wave – An elastic body wave withparticle motion in the direction of propagation.Same as P-waves, longitudinal wave, dilatationwave, irrotational.
Converted Wave – A wave that is converted fromlongitudinal to transverse, or vice versa, uponreflection or refraction at oblique incidence from aninterface.
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Critical Angle – Angle of incidence, �c, for which therefracted ray grazes the contact between two media(of velocities V1 and V2):
sin �c = V1/V2
Critical Distance – (1) The offset at which a refractedevent becomes the first break; cross-over distance.(2) The offset at which the reflection time equals therefraction time (i.e., the offset at which the reflectionoccurs at the critical angle).
Crossfeed (Crosstalk) – Interference resulting from theunintentional pickup of information or noise fromanother channel.
D
Datum – (1) The arbitrary reference level to which meas-urements are corrected. (2) The surface from whichseismic reflection times or depths are measured,corrections having been made for local topographicand/or weathering variations. (3) The reference levelfor elevation measurements, often sea level.
Delay Time – (l) In refraction work, the additional timetaken for a wave to follow a trajectory to and along aburied marker over that which would have beentaken to follow the same marker hypothetically atthe ground surface or at a reference level. Normally,delay time exists separately under a source andunder a detector and depends on the depth of themarker at wave incidence and emergence points.Shot delay time plus geophone delay time equalsintercept time. (2) Delay produced by a filter.(3) Time lag introduced by a delay cap.
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Diffraction – (1) Scattered energy which emanates froman abrupt irregularity, particularly common wherefaults cut reflecting interfaces. The diffracted energyshows greater curvature than a reflection (except incertain cases where there are buried foci), althoughnot necessarily as much as the curve of maximumconvexity. Diffraction frequently blends with areflection and obscures the fault location or becomesconfused with dip. (2) Interference produced byscattering at edges. (3) Causes energy to be trans-mitted laterally along a wave crest. When a portionof a wave train is interrupted by a barrier,diffraction allows waves to propagate into the regionof the barrier's geometric shadow.
Digital – Representation of quantities in discrete units.An analog system represents data as a continuoussignal.
Dipole – A pair of closely spaced current electrodes thatapproximates a dipole field from a distant pair ofvoltage detecting electrodes.
E
Elastic Constants –
(1) Bulk modulus, k. – The stress-strain ratio underhydrostatic pressure.
kP
V V= ∆
∆ /
where �P = pressure change, V = volume, and �V =volume change.
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(2) Shear modulus, �. – rigidity modulus, Lame'sconstant. The stress-strain ratio for simple shear.
µ = F A
L L
t /
/∆
where Ft = tangential force, A = cross-sectional area,L = distance between shear planes, and �L = sheardisplacement. Shear modulus can also be expressedin terms of other moduli as:
µσ
=+E
( )1
where E = Young's modulus, and � = Poisson's ratio.
(3) Young's modulus, E. – The stress-strain ratiowhen a rod is pulled or compressed.
EF A
L L= ∆
∆/
/
where �F/A = stress (force per unit area), L =original length, and �L = change in length.
(4) Lame' constant, �. – a tube is stretched in theup-direction by a tensile stress, S, giving an upwardstrain, s, and S’ is the lateral tensile stress needed toprevent lateral contraction, then:
λ = S
s
'
This constant can also be expressed in terms ofYoung’s modulus, E, and Poisson’s ratio, �:
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λ σσ σ
=+ −
E
( )( )1 1 2
Electromagnetic – Periodically varying field, such aslight, radio waves, radar.
End Line – Shotpoints that are shot near the end of thespread.
F
Fan Shooting – An early use of the refraction seis-mograph to find salt domes within a thick, low-velocity section; detectors located in widely spacedfan-like arrays radiating from the shot locations.
Filter – (1) A device that discriminates against some ofthe input information. The discrimination is usuallyon the basis of frequency, although other bases suchas wavelength or moveout (see velocity filter) may beused. The act of filtering is called convolution.(2) Filters may be characterized by their impulseresponse or, more usually, by their amplitude andphase response as a function of frequency. (3) Band-pass filters are often specified by successively listingtheir low-cutoff and high-cutoff points. (4) Notchfilters reject sharply at a particular frequency.(5) Digital filters filter data numerically in the timedomain. Digital filtering can be the exact equivalentof electrical filtering. Digital filtering is very versa-tile and permits easy filtering according toarbitrarily chosen characteristics.
First Break or First Arrival – The first recorded signalattributable to seismic wave travel from a source.First breaks on reflection records provide informa-tion about weathering. Refraction work is based
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principally on the first breaks, although secondary(later) refraction arrivals are also used.
Frequency – The repeat rate of a periodic wave,measured in hertz. Angular frequency, measured inradians per second.
G
Galvanometer – A coil suspended in a constant mag-netic field. The coil rotates through an angle propor-tional to the electrical current flowing through thecoil. A small mirror on the coil reflects a light beamproportional to the galvanometer rotation.
Geophone (Seismometer, Jug) – Instrument used toconvert seismic energy (vibration) into electricalenergy.
Geophone Station – Location of a geophone on aspread.
Gravimeter. – An instrument for measuring variationsin gravitational attraction.
Gravity Survey – A survey performed to measure thegravitational field strength, or derivatives, that arerelated to the density of different rock types.
Group Velocity – The velocity at which most of theenergy in a wave train travels. In dispersive mediawhere velocity varies with frequency, the wave trainchanges shape as it progresses so that individualwave crests appear to travel at velocities (the phasevelocity) different from the overall energy asapproximately enclosed by the envelope of the wavetrain. The velocity of the envelope is the groupvelocity. Same as dispersion.
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H
Head Wave – See refraction wave.
Hidden Layer – A layer that cannot be detected byrefraction methods; typically, a low velocity layerbeneath a high velocity layer.
Hydrodynamic Wave – A seismic surface wavepropagated along a free surface. The particle motionis elliptical and prograde (M2 type Rayleigh orSezawa) (e.g., Rayleigh-type wave dependent uponlayering).
Hydrophone (Pressure Detector) – A detector sensi-tive to variations in pressure, as compared to ageophone, which is sensitive to motion. Used whenthe detector can be placed below a few feet of watersuch as in marine or marsh applications or as a wellseismometer. The frequency response of the hydro-phone depends on the depth beneath the surface.
I
In-line Offset – Shot points that are in line, but offset toa spread.
L
Lead – An electrical conductor (wire cable) used toconnect electrical devices. Geophones are connectedto cables at the takeouts via leads on the geophones.
Love Wave – A surface seismic wave associated with lay-ering. This wave is characterized by horizontalmotion perpendicular to the direction of propagation,with no vertical motion.
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Low-velocity Layer (LVL) – The surface layer that haslow seismic velocity.
M
Magnetic Survey – A survey to measure the magneticfield or its components as a means of locatingconcentrations of magnetic materials or determiningdepth to basement.
Mis-tie – (1) The time difference obtained on carrying areflection event or some other measured quantityaround a loop; or the difference of the values atidentical points on intersecting lines or loops. (2) Inrefraction shooting, the time difference from reversedprofiles that gives erroneous depth and dipcalculations.
Multiple – Seismic energy that has been reflected morethan once (e.g., long-path multiple, short-pathmultiple, peg-leg multiple, and ghosts).
N
Noise – (1) Any undesired signal or disturbance that doesnot represent any part of a message from a specifiedsource. (2) Sometimes restricted to random energy.(3) Seismic energy that is not resolvable as re-flections. Noise can include microseisms, shot-generated noise, tape-modulation noise, andharmonic distortions. Sometimes divided into co-herent noise (including non-reflection coherentevents) and random noise (including wind noise,instrument noise, and all other energy which is non-coherent). (3) Random noise can be attenuated bycompositing signals from independent measure-ments. (4) Sometimes restricted to seismic energy
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not derived from the shot explosion. (5) Disturbancesin observed data due to more or less random inhomo-geneities in surface and near-surface material.
Noise Analysis – A profile or set of profiles used togather data for an analysis of coherent noise. Usedto design geophone arrays in reflection surveys.
Noise Survey (Ground Noise Survey) – A survey ofambient, continuous seismic noise levels within agiven frequency band. This technique is a useful toolfor detecting some geothermal reservoirs becausethey are a source of short-period seismic energy.
O
On-line – Shot points that are not at any point on aspread other than at the ends.
Original Data – (1) Any element of data generateddirectly in the field in the investigation of a site.(2) A new element of data resulting from a directmanipulation or compilation of field data.
Oscillograph – A device that records oscillations as acontinuous graph of corresponding variation in anelectric current or voltage.
Oscilloscope – A device that visually displays anelectrical wave on a screen (e.g., on a cathode raytube).
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P
Phase Velocity – The velocity of any given phase (suchas a trough or a wave of single frequency); it maydiffer from group velocity because of dispersion.
Plant – The manner in which a geophone is placed or thecoupling to the ground.
Primacord – An explosive rope that can be used to eitherconnect explosive charges or to detonate separatelyas a primary energy source.
Profile – The series of measurements made from severalshotpoints to a recording spread from which aseismic data cross section or profile can beconstructed.
R
Radar – An exploration method where microwaves aretransmitted into a medium and are reflected back byobjects or layers. The reflected microwaves are re-ceived and processed to provide an image of thesubsurface. May be used for shallow penetrationsurveys.
Rayleigh Wave – A seismic wave propagated along afree surface. The particle motion is elliptical andretrograde.
Ray Path – The path of a seismic wave. A line every-where perpendicular to wave-fronts (in isotropicmedia).
Reconnaissance – (1) A general examination of a regionto determine its main features, usually preliminaryto a more detailed survey. (2) A survey to determine
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regional geological structures or to determinewhether economically prospective features exist,rather than to map an individual structure.
Reflection Survey – A survey of geologic structure usingmeasurements made of arrival times of seismicwaves that have been reflected from acousticimpedance change interfaces.
Refraction Survey – A survey of geologic structureusing compressional or head waves. Head wavesinvolve energy that enters a high-velocity medium(refractor).
Refraction Wave (Headwave, Mintrop Wave,Conical Wave) – Wave travel from a point sourceobliquely downward to and along a relatively highvelocity formation or marker and then obliquelyupward. Snell's law is obeyed throughout the tra-jectory. Angles of incidence and of emergence at themarker are critical angles. Refracted waves typicallyfollowing successively deeper markers appear as firstarrivals with increasing range (shot to detectordistance). Refracted waves following differentmarkers may have different arrival times for anygiven range. Refracted waves cannot arise for anglesof incidence less than the critical angle for any givenmarker. At the critical angle, the refracted wavepath (and travel time) coincides with that of a wideangle reflection.
Refractor (Refraction Marker) – An extensive,relatively high-velocity layer underlying lower velo-city layers that transmits a refraction wave nearlyhorizontally.
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Resistivity – An electrical property of rock reflecting theconductivity of an electrical current. Resistivity isthe ratio of electric field intensity to current density.
Resistivity Meter – A general term for an instrumentused to measure the in place resistivity of soil androck materials.
Resistivity Survey – A survey that measures electricfields and earth resistivity of a current induced intothe ground.
Reverse Profile – A refraction seismic profile generatedby shooting both ends of a spread.
Roll-along – A mechanical or electrical switch thatconnects different geophones (or geophone groups) tothe recording instruments. The use of a roll-alongswitch permits common depth point reflection datato be easily acquired in the field.
S
Seismic Amplifier – An electronic device used to in-crease the electrical amplitude of a seismic signal.
Seismic Camera – A recording oscillograph used tomake a seismic record.
Seismic Cap – A small explosive designed to be deto-nated by an electric current that detonates anotherexplosive. These caps are designed to provide veryaccurate time control on the shot.
Seismic Velocity – The rate of propagation of seismicwaves through a medium.
Seismogram – A seismic record.
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Self-potential (Spontaneous Potential, NaturalPotential, SP) – The direct current or slowlyvarying natural ground voltage between nearby non-polarizing electrodes.
Shear Wave – A body wave with the particle motionperpendicular to the direction of propagation. (Sameas S-wave, equivoluminal, transverse wave.)
Shooter – The qualified, licensed individual (powder-man) in charge of all shot point operations andexplosives on a seismic crew.
Shot Depth – The distance from the surface down to theexplosive charge. The shot depth is measured to thecenter or bottom of the charge with small charges.The distances to both the top and bottom of thecolumn of explosives are measured with largecharges.
Shot Instant (Time Break, TB, Zero Time) – Theinstant at which a shot is detonated.
Shot Point – Location of the energy source used ingenerating a particular seismogram.
Signal Enhancement – A process used in seismographsand resistivity systems to improve the signal-to-noise ratio by real-time adding (stacking) ofsuccessive waveforms from the same source point.Random noise tends to cancel out, and the coherentsignal tends to add or stack.
Snell’s Law – When a wave crosses a boundary betweentwo isotropic mediums, the wave changes directionsuch that the sine of the angle of incidence of thewave divided by the velocity of the wave in the firstmedium equals the sine of the angle of refraction of
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the wave in the second medium divided by thevelocity of the wave in the second medium (seecritical angle).
Spread – The layout of geophone groups from which datafrom a single shot are simultaneously recorded.
Stanley Wave – A type of seismic surface wave prop-agated along an interface.
Surface Wave – Energy that travels along or near thesurface (ground roll).
T
Takeout – The connections on a multiconductor cable forconnecting geophones. May refer to the short cableleads from the geophones (pigtails).
Time Break – The mark on a seismic record that indi-cates the shot instant or the time the seismic wavewas generated.
Trace – A record of one seismic channel. This channelmay contain one or more geophones.
V
Vibration Monitor – A sensitive, calibrated recorder ofground and structural acceleration and velocity.Measurements are made to determine vibrationamplitudes and modal frequencies of buildings,towers, etc., under ambient conditions, as well as todetect potentially damaging vibrations caused byblasting, pile driving, etc.
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Vibroseis – A seismic energy source consisting of con-trolled frequency input into the earth by way of largetruck mounted vibrators. Trademark of ContinentalOil Company (Conoco).
W
Wave Length – The distance between successive similarpoints on two adjacent cycles of a wave measuredperpendicular to the wavefront.
Wave Train – (1) The sum of a series of propagatingwave fronts emanating from a single source. (2) Thecomplex wave form observed in a seismogramobtained from an explosive source.
Weathering Spread – A short-spaced geophone intervalrefraction spread used to provide corrections torefraction data caused by delay times in near-surface, low-velocity materials.
WWV(B) – The National Institute of Standards and Tech-nology (NIST) radio stations that broadcast time andfrequency standards.
For the definition of other geophysical terms used in thismanual, refer to: Glossary of Terms Used in GeophysicalExploration, Society of Exploration Geophysicists, Tulsa,Oklahoma, 1984.
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Bibliography
Mooney, H.M., Handbook of Engineering Geophysics,Volume 1: Seismic, Bison Instruments, Inc., Minneapolis,Minnesota, 1984.
Telford, W.M., et al., Applied Geophysics, CambridgeUniversity Press, New York, New York, 1976.
U.S. Corps of Engineers, Geophysical Exploration forEngineering and Environmental Investigations,Engineering Manual EM 111-1-1802, 1995.
U.S. Geological Survey, Application of Surface Geophysicsto Ground-Water Investigations, Chapter D1, Book 2,Techniques of Water-Resources Investigations of theUnited States Geological Survey, 1974.
Van Blaricom, R., compiler, Practical Geophysics II for theExploration Geologist, Second Edition, Northwest MiningAssociation, Spokane, Washington, 1992.
Ward, S.H., editor, Geotechnical and EnvironmentalGeophysics, Society of Exploration Geophysics, Tulsa,Oklahoma, 1990.
Chapter 14
BOREHOLE GEOPHYSICALAND WIRELINE SURVEYS
Introduction
Wireline surveys determine physical properties in andbeyond the wall of a borehole by devices attached to acable, or wireline. Subsurface geologic conditions andengineering characteristics can be derived directly orindirectly from the wide variety of measurable propertiesavailable by wireline surveying. Wireline logging tech-niques commonly are classified by the kind of energy thatis input (active systems) or received (passive systems),including electric, seismic or acoustic, nuclear, magnetic,gravity, or optical. Logging tools are also classifiedaccording to whether they are for use in open holes orcased holes. Data from several methods are oftencombined to evaluate a single geologic or engineeringcharacteristic. This chapter describes the methods anddiscusses the application of borehole wireline surveying togeotechnical exploration and investigation.
Electric Logging Techniques
An electric log is a continuous record of the electricalproperties of the fluids and geologic materials in andaround a borehole. Electric logging is performed in theuncased portion of a borehole by passing electric currentthrough electrodes in the logging device, or sonde, and outinto the borehole and the geologic medium. Otherelectrodes located on the surface or in the boreholecomplete the circuit to the source and recording device.Electric logging surveys are efficient and cost effectivebecause the process is automated and several electricalproperties are measured simultaneously by combiningseveral electrode configurations in the same tool.
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Electric logging techniques can be used in geotechnicalinvestigations to assess the variation with depth ofgeologic materials and associated fluids. Electric logsfrom two or more boreholes are used to correlate anddetermine the continuity of geologic strata or zones thathave similar electrical properties. Since the electricalproperties depend on physical characteristics, theporosity, mineral composition, water content (saturation),water salinity, lithology, and continuity of the beddingcan often be deduced. Borehole electric logs are also thebest source of control for surface electrical surveys byproviding subsurface layer resistivities. Electric logcorrelation of continuous layers from borehole to boreholeis relatively simple. The interpretation of physicalproperties from electric logs can be ambiguous andcomplicated. Different combinations of water content,salinity, mineralogy, porosity, and borehole peculiaritiescan produce similar electric logs.
Spontaneous Potential (SP) Log
The spontaneous potential or SP logging device recordsthe difference in potential in millivolts between a fixedelectrode at the surface and an electrode in a borehole(figure 14-1). The measured potential difference changesas the electrical potential between the borehole fluid andthe fluids in the various strata opposite the sondechanges. The spontaneous potential device commonly isincorporated into the multiple-electrode resistivity sondeso that resistivity and SP logs are acquired simulta-neously. Figure 14-2 illustrates a typical SP resistivitylog. The recording is a relative measurement of thevoltage in the borehole. Readings opposite shales or claysare relatively constant and form the shale baseline, or"shale line." The SP curve typically deflects to the left orright opposite permeable formations depending on thesalinity of the drilling mud. Sandstone and other porous
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Figure 14-1.—Spontaneous potential surveyelements.
and permeable strata allow the different fluids to mix andproduce salinity of the pore fluid with respect to theborehole fluid and the clay content of the strata. TheSP peaks are commonly displayed to the left of the shaleline because negative potentials are more commonlyencountered. In fresh water, SP anomalies are typicallyinverted (i.e., they appear to the right of the shalebaseline).
SP logs are used in combination with resistivity logs todefine strata boundaries for correlation and to infer thelithology of the strata as a function of permeability andresistivity. The shape of the SP curve depends on thedrilling mud used and the geologic strata encountered.For example, the SP curve for a shale bed would indicatezero deflection (the shale line in figure 14-2), and the
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Figure 14-2.—Electric log showing SP andresistivity in different beds.
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resistivity curve would indicate low resistivity because ofbound water in the clay and trapped water in the shale.Generally, the SP and resistivity curves converge oppositeshale strata (A in figure 14-2) and diverge oppositepermeable fresh water sands (B in figure 14-2). Alimestone bed, which usually is highly resistive butdevelops little spontaneous potential, would produce alarge resistivity deflection but a subdued SP peak (C infigure 14-2). A permeable sand bed with pore water ofhigh salinity typically would produce little resistivitydeflection but a large negative SP peak (D in figure 14-2).The determination of lithologies from SP logs should bedone cautiously because many factors contribute to themagnitudes and directions of the curve deflections. TheSP log is best used with resistivity and other logs to detectstrata boundaries and to correlate strata betweenboreholes. The SP log is also used to determine formationwater resistivities.
Single-Point Resistance Log
Single-point resistance loggers are the simplest electricalmeasuring devices. A current can flow between a singleelectrode placed in a borehole and another electrode at theground surface (figure 14-3). The earth between theelectrodes completes the circuit. Single-point resistancelogs are not commonly used in modern logging operationsbut illustrate the principal of down-hole electric logging.The resistance, R, of the circuit (electrodes plus earth) canbe calculated from Ohm’s Law, R = V/I, where V is themeasured voltage drop and I is the current through thecircuit. The resistance of a circuit is determined by theconductor’s size, shape, and resistivity, p, an intrinsicproperty of a material. Resistance of the conductor (theearth) is a convenient and useful property determined bypore fluid content, pore fluid composition, lithology, andcontinuity of strata. The resistivity of the measured
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Figure 14-3.—Single-point resistivity array.
section of earth is determined from p = KR, where K is ageometric factor which differs for different electrodeconfigurations and R is the measured resistance V/I. Asingle point resistance log measures an apparentresistance of a section made up of borehole fluid and thevarious individual strata between the borehole and theground surface electrode. The multiple electrode arraysdiscussed below are designed to narrow and better definethe measured sections so that individual strata arerepresented more accurately by the logs.
Multiple Electrode Array Log
Wireline electrical systems using multiple electrodearrays in the borehole provide better resolution of
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resistivity and associated properties of individual stratawithin the subsurface than can be achieved with thesingle-point array. Multiple electrode arrays include theshort- and long-normal array, lateral array, and focused-current or guard logging systems. Current electrodesusually are designated A and B, and potential electrodesare designated M and N. "Normal" arrays place the in-hole current electrode far away, at effective infinity(figure 14-4A). "Lateral" devices place the two potentialelectrodes close together with respect to the in-holecurrent electrode (figure 14-4B). Conventional modernlogging systems use a sonde made up of two normaldevices and one lateral device to produce three resistivitylogs and the SP log simultaneously.
The normal resistivity arrays (figure 14-4A) are calledshort normal or long normal depending on the spacing ofthe in-hole current (A and B) and potential (M and N)electrodes. The industry standard AM electrode spacingis 16 inches (in) for the short normal and 64 in for thelong normal. The normal arrays measure the electricalpotential at the in-hole electrode M. The greater thespacing between the current and measuring electrodes,the greater the effective penetration (effective penetrationdistance = ½ AM) of the device into the surroundinggeologic medium.
The lateral resistivity array is shown in figure 14-4B. Theactual positions of the electrodes may vary from thecircuit shown, but the resistivity measurements are thesame. The lateral array spacing is measured from theA current electrode to the center (0) of the potentialelectrode configuration and is called the AO spacing. Thelateral array measures the potential difference, orgradient, between the two in-hole potential electrodes andis also called the gradient array. The influence of the
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Figure 14-4.—Multiple-electrode resistivityarrays. (A and B are current electrodes.
M and N are potential electrodes.)
geologic medium away from the borehole (the effectivepenetration of the system) is greatest for the lateral arraywith an 18-foot 8-in spacing and least for a 16-in shortnormal array.
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The focused-current, or guard, resistivity device is a mod-ified single-electrode array in which "guard" current elec-trodes are placed above and below a central currentelectrode and two pairs of potential electrodes(figure 14-5). Current in the central and guard electrodesis adjusted so that zero potential exists between thepotential electrodes and the current is thus forced orfocused to flow out into the geologic medium in a narrowband. The device then measures the potential between thesonde electrodes and a reference electrode at the groundsurface. Focusing the current into a band ofpredetermined thickness gives the focused array muchgreater thin bed and stratum boundary resolution thanthe other arrays.
Geotechnical applications for multiple-electrode resistivityarrays include apparent resistivity and an approximationof true resistivities of individual strata or zones.Resistivity data aid in the interpretation of surfaceelectrical surveys, which generally are less expensive toconduct than down-hole surveys and can be applied overlarge areas. Since the depth of penetration of themeasuring circuit into the geologic medium varies withthe electrode spacing, logs of the various arrays (short-and long-normal and lateral) can be analyzed collectivelyto evaluate the effects of bed thickness, borehole fluids,drilling mudcake, variations in fluids, and permeabilitiesof strata at various distances from the borehole. Thecurve shapes of the logs for several boreholes permitcorrelation of strata and zones from borehole to borehole.Normal devices produce better boundary definition ofthick strata than do lateral devices, but lateral logs aremore effective in delineating thin strata and thin, highlyresistive zones. The focused logs discriminate moresharply between different strata, define strata boundariesbetter, and give a better approximation of true stratumresistivity than do normal or lateral logs. Porosity and
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Figure 14-5.— Focused current, or guard,
resistivity array.
water content of strata and salinity of pore fluids can becalculated from the logs if sufficient information isobtained.
Microlog
Special purpose electric logging devices are available tosupplement or, in some cases, replace standard resistivity
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logs. The microlog (also called contact log, microsurvey,and minilog) records variations in resistivity of a narrow,shallow zone near the borehole wall. The microlog sondeis equipped with three closely spaced electrodes placed ona rubber pad which is pressed against the borehole wall(figure 14-6). Microlog electrode spacings are about 1 to2 in (2.5 to 5 centimeters [cm]). Depth of investigation forthe microlog is about 3 in (7.5 cm) from the borehole wall.Normal, lateral, and guard arrays can be configured inthe microlog survey. Porous permeable zones allow themud cake to penetrate the strata, and the resultingmicrolog will indicate resistivities close to that of themud.
Induction Log
Induction logging is performed in dry boreholes orboreholes containing nonconducting fluids. Inductionlogging can be done in holes cased with polyvinyl chloride(PVC) casing. The induction logger is housed in a sondethat uses an induction coil to induce a current in thegeologic medium around a borehole. The induction loggeris a focused device and produces good thin-bed resolutionat greater distances from the borehole than can beachieved with normal spacing devices. A primaryadvantage over other devices is that the induction loggerdoes not require a conductive fluid in the borehole.
Nuclear Radiation Logging Techniques
A nuclear radiation log is a continuous record of thenatural or induced radiation emitted by geologic materialsnear the borehole. Nuclear radiation logging is performedby raising a sonde containing a radiation detector or a de-tector and a radioactive source up a borehole and record-ing electrical impulses produced by a radiation detector.
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Figure 14-6.—Microlog resistivity logging device.
Nuclear radiation logging can be used in geotechnicalinvestigations to correlate strata between boreholes, aidin determining lithology, and derive or measure directlymany physical parameters of the subsurface materials,
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including bulk density, porosity, water content, andrelative clay content. Most nuclear radiation loggingsystems can be operated in cased boreholes, giving theman advantage over electrical wireline logging systems.Nuclear logs can also be run in old boreholes, which aremore likely to be cased than recent boreholes. The logsare among the simplest to obtain and interpret, but thecalibrations required for meaningful quantitative inter-pretations must be meticulously performed. Nuclearradiation logging tools should be calibrated in controlledcalibration pits. Under favorable conditions, nuclearborehole measurements approach the precision of directdensity tests of rock cores. The gamma-gamma densitylog and the neutron water content log require the use ofisotopic sources of nuclear radiation. Potential radiationhazards necessitate thorough training of personnelworking around the logging sources.
Three common wireline nuclear radiation systems are thegamma ray or natural gamma logger, the gamma-gammaor density logger, and the neutron logger. The gamma-gamma and neutron devices require the use of aradioactive source material. The gamma ray device is apassive system and does not use a radioactive source. Allthe systems employ an in-hole sonde containing thesource and detector. Most devices require a boreholediameter of at least 2 in (5 cm) and investigate a zoneextending 6 to 12 in (15 to 30 cm) from the borehole.Applications differ for the three systems and depend onthe properties measured.
Gamma Ray (Natural Gamma) Log
The gamma ray or natural gamma radiation deviceprovides a continuous record of the amount of naturalgamma radiation emitted by geologic materials near thesonde. The gamma-ray detector converts incoming
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gamma radiation to electrical impulses proportional to thenumber of rays detected and sends the amplified electricalimpulses to the surface. Gamma ray logs generally revealthe presence of shale or clay beds because clay mineralscommonly contain the potassium isotope K40 ,which is theprimary source of natural gamma radiation in most sedi-ments. Shales and clays usually produce a high gammaray count, or a peak on the log.
The relative density of a stratum is also indicated bynatural gamma ray logs because gamma radiation isabsorbed more by dense materials than by less densematerials. Gamma ray logging can be conducted in casedboreholes and is sometimes used in place of SP logging todefine shale (clay) and non-shale (non-clay) strata. Thenatural gamma ray and neutron logs are usually runsimultaneously from the same sonde and recorded side-by-side. The gamma ray log also infers the effectiveporosity in porous strata with the assumption that highgamma counts are caused by clay filling the pores of thestrata. Gamma ray logs are used to correct gamma-gamma density logs. Gamma ray logs are standard inradiation logging systems.
Natural Gamma Spectral Log
Spectral logging permits the identification of thenaturally occurring radioactive isotopes of potassium,uranium, and thorium which make up the radiationdetected by the natural gamma ray detector. Spectrallogging technology allows the detection and identificationof radioactive isotopes that contaminate water resources,or are introduced as tracer elements in hydrologic studies.
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Figure 14-7.—Gamma-gamma logging sonde.
Density or Gamma-Gamma Log
The gamma-gamma or density logging device measuresthe response of the geologic medium to bombardment bygamma radiation from a source in the sonde. Electrons inthe atoms of the geologic medium scatter and slow downthe source gamma rays, impeding their paths to thedetector. Figure 14-7 illustrates the operation of thegamma-gamma device. Since electron density is propor-tional to bulk density for most earth materials, stratawith high bulk densities impede the source gamma raysmore than low density strata and produce correspondinglylower counts at the detector. The primary use of thegamma-gamma log is determining bulk density. If bulkdensity and grain density are known from samples and iffluid density can be determined, the porosity can becalculated. Gamma-gamma logs can also be used forcorrelation of strata between boreholes.
Gamma-gamma logging is best conducted in uncasedboreholes using decentralizing devices to keep the sonde
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against the borehole wall. The system is affected by bore-hole diameter and wall irregularities and must becarefully calibrated for the effects of hole diameter, decayof the strength of the radioactive source, natural gammaradiation in the geologic medium, and borehole fluid den-sity. A caliper log is commonly run to permit calibrationfor hole diameter. Some logging systems simultaneouslydisplay the gamma ray count on one side of the log andbulk density on the other side, with the bulk density logautomatically corrected for the effects of mud cake andwall irregularity.
Neutron Log
Neutron logging is an active system that measures theresponse of the geologic medium to emission of neutronradiation from a source located in the sonde. Neutronsemitted by the source are captured by certain atoms,especially hydrogen nuclei, in the strata near the sonde.Figure 14-8 illustrates the operation of the neutronlogging device. Collision of neutrons with atoms of thegeologic medium causes secondary emission of neutronsand gamma rays, a portion of which are picked up by thedetector. A high concentration of hydrogen atoms nearthe source captures a greater number of neutrons andproduces a smaller counting rate at the detector.
Neutron detectors may detect gamma (neutron-gamma) orneutron (neutron-neutron) radiation. Water and hydro-carbons contain high concentrations of hydrogen atoms.If the fluid in the strata is assumed to be water, theneutron log is an indicator of the amount of water present.Determination of volumetric water content (weight ofwater per unit volume measured) is a principal use ofneutron logging. In saturated materials, the neutron logcan be an indicator of porosity, the ratio of the volume ofvoid space to the total volume. Bulk densities fromgamma-gamma logs, grain densities from samples, caliper
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Figure 14-8.—Neutron logging sonde.
log data, and natural gamma log information can be com-bined with the volumetric water contents from neutronlogs to calculate the more commonly used geotechnicalparameters of water content by weight, wet and drydensity, void ratio, porosity, saturation, and lithology.
Neutron logs and natural gamma radioactive logs can beobtained through thick borehole casing and are usuallyrun together. Figure 14-9 illustrates the format of thetandem logs and typical responses for several lithologies.The response of different lithologies to the natural gammaand neutron devices is controlled directly by the amountof radioactive material present (especially the claycontent) and the fluid content and indirectly by theporosity and bulk density of the material. For example,the saturated sand of figure 14-9 absorbs neutronradiation, produces a correspondingly low neutron logcount, and produces a low natural gamma count becauseof the lack of clay in its pores.
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Figure 14-9.—Typical curve responsesfor nuclear radiation logs.
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Neutron activation or spectral logs provide spectral anal-yses of the geologic medium near the borehole to detectthe presence of certain elements. The spectral loggingsonde activates a neutron source in bursts of shortduration and activates the gamma ray detector onlyduring the source bursts. As a result, only certainradiation ("prompt" gamma rays) is detected. The systemproduces a plot of counts versus gamma ray energy.Peaks on the energy/count plot identify specific elements,for example carbon, silicon, magnesium, or chlorine.Spectral logs may have application to groundwaterquality investigations.
Neutrino Log
Neutrino logs are not necessarily a borehole log, but themethod can and often is performed in drill holes.Neutrino sources are located throughout the universewith the closest and most useful source being the sun.Using the sun as a neutrino source eliminates the needfor a special source, and there are no handling andlicensing problems that are often associated with othernuclear logs. Neutrinos penetrate the earth with little tono impediment, so neutrino logs can be run at any time ofday or night. Logging tools generally consist of strings ofwidely spaced photomultiplier tubes (PMT) placed intothe borehole. High-energy neutrinos passing through therock will occasionally interact with the rock and create amuon. These muons emit Cherenkov light when passingthrough the array and are tracked by measuring thearrival times of these Cherenkov photons at the PMTs.Resolution is high because the source (Sun) only subtendshalf a degree at this distance (93 million miles fromEarth). Neutrino logging is particularly useful in casedholes and when fluid in the hole is not a factor. New orold holes can be logged no matter what the hole contains.These logs are often used for tomography. Tomography is
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particularly useful and convenient because, as the Earthrotates, the source penetrates a full 360 degrees, similarto CAT scan or Magnetic Resonance Imaging. Adrawback is that 24 hours is required to run a completeneutrino tomography log.
Acoustic/Seismic Logging Techniques
Wireline acoustic/seismic logging systems use medium- tohigh-frequency acoustic (sonic) energy emitted from asonde to image the borehole wall or to obtain seismicvelocities of the geologic material in the wall or in theformation away from the borehole. Acoustic systems usesonic energy generated and propagated in a fluid such aswater. Seismic systems use sonic energy propagatedthrough the ground in geologic materials. The threesystems discussed in this section are the acoustic velocitylogger, an acoustic and seismic energy system; a boreholeimaging device, an acoustic system; and the cross-holeseismic technique, a seismic technique.
The borehole imaging and acoustic velocity systems areused in geotechnical investigations to evaluate geologicconditions including attitude and occurrence of dis-continuities and solution cavities and in determining theeffective porosity and elastic properties of rock. Thedown-hole systems also supply subsurface information forinterpreting surface-applied geophysical surveys. Thefrequency of the energy pulse produced by the sonde’stransducer determines whether the energy penetrates theborehole wall for acoustic/seismic velocity surveys.Medium frequencies are used in acoustic/seismic velocitysurveys. The energy is reflected from the wall for imagingsurveys. High frequencies are used in acoustic/seismicvelocity surveys. Borehole imaging velocity devicesgenerate compressional (P-wave) energy. The acoustic
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velocity device generates primarily compressional energybut also generates shear (S-wave) energy if the shearwave velocity exceeds the fluid velocity. The cross-holeseismic technique generates P- and S-wave energies anddetermines their velocities.
Acoustic Velocity Log
The continuous acoustic velocity (sonic) logger measuresand records the velocity of acoustic energy (seismic waves)in the material adjacent to the borehole. A transmitterlocated at one end of the sonde generates an electro-mechanical pulse that is transmitted through the bore-hole fluid into the borehole wall and by refraction to areceiver located at the other end of the sonde(figure 14-10). The propagation velocities of the seismicwaves can be calculated by travel times and distancetraveled from transmitter to receiver. The devices mustbe operated in a fluid-filled borehole. Compressionalwave oscillations set up by the sonde’s transmitter in theborehole fluid set up, in turn, oscillations in the boreholewall. Compressional, shear, and surface waves propagatein and along the wall and then, as compressional waves,back through the borehole fluid to the receiver.Compressional waves have the highest velocity and arrivefirst, followed by the shear waves and the surface waves.Devices with two receivers cancel the borehole fluid traveltimes so that only the refracted wave paths through theborehole wall are measured. Single-receiver devicesrequire the borehole fluid acoustic velocity and boreholediameter for calculation of seismic velocities. The acousticpulses generated at the transmitter are in the lowerultrasonic range around 20 kilohertz (kHz).
The simplest acoustic logging devices display a singlegraphical trace or waveform of the arrival of each pulse
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Figure 14-10.—Elements of a simple wirelineacoustic velocity device.
and are called amplitude-modulated devices. Intensity-modulated acoustic logging devices record the entirecontinuous acoustic wave (see figure 14-11). Intensity-modulated, or three-dimensional (3-D), devices expresswave frequency by the width of light and dark bands and
BO
RE
HO
LE
GE
OP
HY
SIC
AL
AN
D W
IRE
LIN
E S
UR
VE
YS59
Figure 14-11.—Acoustic log presentations. The intensitymodulated waveform wave frequency by the width of the
band, amplitude by the shading intensity of the band.
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amplitude by the degree of light or dark shading (figures14-11 and 14-12). The P-wave, S-wave, and surface wavearrivals can be discerned on the 3-D records. Strata orzones of different seismic velocity produce contrastingsignatures on the 3-D log. The phyllite zones infigure 14-12 represent softer materials of lower seismicvelocity than the metabasalts and produce correspond-ingly later arrival times. Fractures or other discon-tinuities can often be seen as disruptions in the bands.
Figure 14-12.—Sample of intensity modulatedacoustic log. Lithologies from core samples.
In addition to determining seismic velocities to aid inter-pretation of seismic surveys, 3-D logs show lithologiccontacts, geologic structure, and solution features. The P-and S-wave velocities can be used directly to calculate thedynamic elastic properties of rock, including Poisson’sratio, Young’s modulus, and bulk and shear moduli. Forexample, Poisson’s ratio is calculated using:
µ =−
−1 2 2 2
2 2
V V
V Vp s
p s
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where Vp and Vs are the compressional and shear wavevelocities, respectively. The effective porosity of the stratacan also be evaluated.
Acoustic velocity devices require a borehole diameter of3 in or greater. The in-place geologic materials must havecompressional wave velocities higher than the velocity ofthe borehole fluid (approximately 4,800 feet per second[ft/sec] [1,450 meters per second (m/sec)] for water) for thewaves to be refracted and detected. Soils generally do nothave sufficiently high seismic velocities for acousticvelocity logging. The wave train (trace) type velocityloggers often are equipped with a radiation logging deviceand caliper on the same sonde for simultaneous acousticand natural gamma ray logging and borehole diametermeasurement.
Acoustic Borehole Imaging Log
The acoustic borehole imaging device uses high-frequencyacoustic waves to produce a continuous 360-degree imageof the borehole wall. Physical changes in the boreholewall are visible as changes in image intensity or contrast.Proprietary trade names for the acoustic borehole imagingdevice include "Televiewer" and "Seisviewer."Figure 14-13 illustrates the operation of an acoustic bore-hole imaging device. A piezoelectric transducer and direc-tion indicating magnetometer are rotated by a motorinside the tool housing at approximately three revolutionsper second (rps). The transducer emits pulses of acousticenergy toward the borehole wall at a rate of about2,000 pulses per second at a frequency of about2 megahertz (MHz). The high-frequency acoustic energydoes not penetrate the borehole wall, and the acousticbeams are reflected from the borehole wall back to atransducer. The intensity of the reflected energy is afunction of the physical condition of the borehole wall,
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Figure 14-13.—Acoustic borehole imaging system.
including texture (rough or smooth) and hardness (afunction of the elasticity and density of the material). Theimage is oriented to magnetic north with every revolutionof the transducer. Fractures, cavities, and other opendiscontinuities produce low-amplitude acoustic reflectionsand are readily discerned in their true orientation, width,and vertical extent on the image.
The acoustic borehole imaging device can detect discon-tinuities as small as 1/8 in (3 millimeters [mm]) wide and
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Figure 14-14.—Traces of planar discontinuitiesintercepting the borehole (left) as they appear
on the acoustic borehole imaging record (right).
can sometimes distinguish contrasting lithologies.Discontinuities, contacts, and other linear featuresintercepting the borehole at an angle other than90 degrees produce a characteristic sinusoidal trace thatcan be used to determine the strikes and dips of thefeatures. Figure 14-14 shows how planar discontinuitiesof different orientations appear on the acoustic imaginglog. Vugs and solution cavities are displayed as black
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areas, and their traces can be analyzed to determine theirsize (in two dimensions) and percentage of the borehole.The device can also be used to inspect casing and wellscreens for defects. The acoustic imaging device must beoperated in a fluid-filled borehole.
Cross-Hole Seismic Test
Cross-hole tests are conducted by generating a seismicwave in a borehole and recording the arrival of theseismic pulse with geophones placed at the same depth inanother (receiver) borehole. Source and geophones areplaced at several regular depth intervals in the boreholesto determine seismic wave velocities of each material.Compressional and shear wave velocities can bedetermined with the cross-hole test. Figure 14-15 illu-strates the essential features of a cross-hole seismic test.The seismic source may be either an explosive or amechanical device. A vertical hammer device, clamped tothe borehole wall, is the typical source arrangement.Cross-hole geophones configured in triaxial arrays areused because directional detectors are necessary toidentify the S-wave arrival. Two or more receiver holesare sometimes used.
The raw data of cross-hole tests are the times required forP- and S-waves to travel from the seismic source in oneborehole to the detectors in the receiver hole or holes. Thecorresponding P- and S-wave arrival times can be used tocalculate seismic velocities as the ratios of distance totravel time, assuming the arrivals are direct (non-refracted) arrivals. If refraction through a faster zoneoccurs, true velocities must be calculated, similar to sur-face refraction seismic calculations.
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Figure 14-15.—Cross-hole seismic test.
Borehole spacing (distance) is critical in cross-hole tests.Generally, spacing should be no greater than 50 feet (ft)(15 meters [m]) or less than 10 ft (3 m). Borehole deviation surveys should be conducted prior to testing todetermine precise spacing between holes at each shotpointdepth.
Cross-hole tests have several applications in engineeringgeology. S-wave cross-hole tests provide data on materialproperties for static and dynamic stress analysis. In addi-tion to providing true P- and S-wave velocities at differentdepths, cross-hole surveys can detect seismic anomaliessuch as zones of low velocity underlying a zone of higher
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velocity or a layer with insufficient thickness or velocitycontrast to be detected by surface refraction tests.
Seismic Tomography
Tomography is a method of constructing an image of somephysical property inside an object from energy sentthrough the object in many directions. Much like medicaltomography (such as a CAT scan) is used to create imagesof features inside the human body; geophysical tomo-graphy is used to create images of features beneath theground or within engineered structures. There areseveral types of geophysical tomography. Cross-holeseismic tomography is one of the most common types ofgeophysical tomography. Cross-hole seismic tomographyinvolves sending seismic energy from one borehole toanother. A transmitter is lowered into one borehole, andthe transmitted seismic energy is recorded by a string ofreceivers located in the second borehole. The positions ofthe transmitter and receivers are varied so that theseismic energy is transmitted between the two boreholesover a large depth range and at many different angles.The arrival times of the transmitted seismic energy areused to construct an image of seismic P-wave velocity ofthe geologic materials between the two boreholes. Inaddition, the amplitudes of the transmitted signals maysometimes be used to construct an image of the apparentattenuation of the geologic materials. Attenuation is ameasure of the amount of energy loss of the seismic signaland is related to such factors as material type, degree ofcompaction or cementation, porosity, saturation, andfracturing. Cross-hole seismic tomography may be usedto image geologic features such as solution cavities,fracture zones, and lithologic contacts. Tomography mayalso be used to evaluate engineered structures such asconcrete cut-off walls, grout curtains, and concrete dams.
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Borehole Optical Systems
Borehole optical logging systems include borehole film-recording cameras and borehole television cameras.Optical logging systems permit viewing and recordingvisible features in the walls of dry or water-filledboreholes, wells, casing, pipelines, and small tunnels.
Borehole cameras are an important supplement togeotechnical drilling and sampling programs because thecameras show geologic and construction features in placeand in relatively undisturbed condition. The aperture(opening), true orientation (strike and dip), and frequency(number per foot of borehole) of discontinuities in the rockmass can be determined with optical logging systems.The effective or fracture porosity associated with opendiscontinuities can be derived also. The occurrence andsize of solution cavities, the rock type from visualexamination of rock and mineral textures and color of theborehole wall, and the location of stratigraphic contactscan be determined. Other geotechnical applicationsinclude inspecting contacts of rock or soil against concreteand of the interior of rock or concrete structures. Opticallogging systems permit viewing soft or open zones in rockthat may be overlooked in normal drilling and samplingoperations. Zones of poor sample recovery or of drillingfluid loss can be investigated.
Borehole Television Camera.—Borehole televisionsystems provide real-time viewing of the interior of a dryor water-filled borehole. The typical system (figure 14-16)consists of a down-hole probe and surface-mounted cablewinch, control unit, power supply, television monitor, andvideo tape unit. The down-hole probe contains atelevision camera facing vertically downward toward apartially reflecting mirror inclined 45 degrees to the axis
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Figure 14-16.—Borehole television logging system.
of the probe. A compass/clinometer used to determine theorientation of features in the borehole wall and theinclination of the borehole can be viewed selectivelythrough the mirror by varying the relative intensities oflamps located above and below the plane of the mirror. Amotor within the probe rotates the camera and mirrorassembly (or the mirror only) 380 degrees in areciprocating fashion (clockwise, then counterclockwise)as the probe is lowered or raised within the hole. The
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operator controls the motion and logging speed of theprobe. A full image of the borehole wall is obtained witheach rotation.
A viewing head can be attached to the probe to allow axialviewing of the hole directly ahead. The probe ascent ordescent and camera rotation can be slowed or stopped forexamination of borehole features. The entire viewingsequence is usually videotaped.
Borehole television systems are commonly used to inspectlarge concrete structures and rock for defects, determinethe effectiveness of grouting operations, check the con-dition of concrete joints, estimate the volume of cavitieswithin a rock or soil mass, and inspect the screens ofwater wells. Television images can be used to determineattitudes of discontinuities but are less effective forcomplete borehole mapping than the borehole film camerasystems that portray the borehole walls as discrete, full-color, separate images more suitable for detailed studyand measurement.
Borehole Film Camera.—The borehole film camera pro-duces consecutive, over-lapping, 16-mm color still photo-graphs of 360 degree, 1-in (25-mm) sections of the walls ofNX or larger boreholes. The system consists of a down-hole probe and surface- mounted lowering device,metering units, and power supply. Figure 14-17illustrates the down-hole probe. The probe consists of a16-mm camera mounted in line with the probe axis andfacing a truncated conical mirror, which is surrounded bya cylindrical quartz window. A film magazine and filmdrive mechanism are mounted above the camera in theprobe housing. A ring-shaped strobe illuminates the bore-hole wall in synchronization with the camera’s filmadvance. Film advance, probe movement, and strobelighting are synchronized to expose a frame every 3/4 in
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Figure 14-17.—Borehole film camera.
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(20 mm) along the hole, so that a photograph with 1/4-in(6-mm) overlap of every 360-degree, 1-in (25-mm) sectionis taken. The truncation of the conical mirror allows thecamera simultaneously to photograph acompass/clinometer located directly beneath the mirror.Photographs produced by the camera are viewedindividually (still frame) using a special projector. Theimage of the mirror face is projected onto a flat film plane.The outer ring of the image "doughnut" represents thebase, and the inner ring is the top of the 1-in section ofthe borehole wall. Planar discontinuities intersecting theborehole wall produce a trace on the image like theshaded curve of figure 14-18 (top). In a vertical borehole,the outer and inner rings of the image "doughnut" arehorizontal traces. Points of intersection of planardiscontinuities with a ring thus define the strike of thefeature in vertical boreholes. The compass area in thecenter of the image of figure 14-18 shows the bearing ofintersecting planes. The dip of the feature can bedetermined graphically by counting the number of succes-sive frames in which the feature appears. A steeplydipping plane intersects several frames, a gently dippingplane only a few frames, and a horizontal plane intersectsone frame. The thickness or width of the discontinuitycan also be measured directly from the image. Data frominclined boreholes must be corrected to true strike, dip,and width. The NX borehole film camera is a proven toolfor supplying subsurface data in difficult drilling andsampling situations and for providing completequantitative information on discontinuities and boreholeanomalies. Strike can be measured accurately to about 1degree, dip (or inclination) to about 5 degrees, andthickness or width of discontinuities to a hundredth of aninch (0.1 mm) or better.
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Figure 14-18.—Projection of borehole wall image into the film plane from the conical mirror of
the borehole film camera.
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In operation, the borehole film camera probe is lowered tothe bottom of the hole and raised by a hand-crankedwinch at a logging speed of between 5 and 10 feet perminute (ft/min). A single load of film can photograph75 to 90 ft of borehole. Since the camera has no shutteror light metering capability, the aperture must be presetto satisfy lighting requirements of hole diameter andreflectivity of the borehole wall. The lens aperture rangesfrom f 2.8 for dark rock to f 22 for light colored rock. Themaximum range (depth of field) is about 12 in. Boreholeslarger than NX require centering of the probe in the hole.
Borehole Image Processing System (BIPS)
The Borehole Image Processing System (BIPS) uses directoptical observation of the borehole wall in both air andclear-fluid filled holes. The BIPS tool has a smallfluorescent light ring that illuminates the borehole wall.A conical mirror in a clear cylindrical window projects a360-degree optical slice of borehole wall into the cameralens. The tool also contains a digital azimuth sensor thatdetermines the orientation of the image. The opticalimages are digitized and stored.
The BIPS analysis provides color images of the boreholewall. In a two-dimensional (2-D) projection, planarfeatures that intersect the borehole wall appear assinusoids. Processing allows the borehole wall to beviewed like a core, regardless of whether core was actuallyrecovered. Strike and dip of planar features intersectingthe borehole wall are determined during processing.
Other Wireline Systems
This section discusses wireline devices that are availablefor supplementary or special purpose applications. These
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systems include the borehole caliper log, directionalsurveys, borehole temperature log, borehole gravity log,magnetic log, and flowmeter log.
Borehole Caliper Log
The borehole caliper log provides a continuous record ofchanges in borehole diameter determined by a probeequipped with tensioned mechanical arms or an acoustictransducer. Caliper or borehole diameter logs are one ofthe most useful and simple of all logs obtained in boreholegeophysics. Caliper logs provide the physical size of adrill hole and should be run in all borings in which othergeophysical logging is anticipated. Caliper logs provideindirect information on subsurface lithology and rockquality. Borehole diameter varies with the hardness,fracture frequency, and cementation of the variousmaterials penetrated. Borehole caliper surveys can beused to accurately identify washouts or swelling or to helpdetermine the accurate location of fractures or solutionopenings, particularly in borings with core loss. Caliperlogs can also identify more porous zones in a boring bylocating the intervals in which excessive mud filter cakehas built up on the walls of the borehole. One of themajor uses of borehole caliper logs is to correct forborehole diameter effects. Caliper logs also can be used toplace water well screens, position packers for pressuretesting in foundation investigations for dams or otherlarge engineering structures, and help estimate groutvolumes in solution or washout zones.
Mechanical calipers are standard logging serviceequipment available in one-, two-, three-, four-, or six-armprobe designs. Multiple-arm calipers convert the positionof feelers or bow springs to electrical signals in the probe.The electrical signals are transmitted to the surfacethrough an armored cable. Some caliper systems average
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the movement of all the arms and record only the changein average diameter with depth, and others provide themovements of the individual arms as well as an averagediameter. The shape or geometry of the borehole crosssection can be determined with the individual caliper armreadings. A six-arm caliper capable of detecting diameterchanges as small as 1/4 inch in 6-in to 30-in diameterboreholes produces a record like that shown onfigure 14-19. The six arms are read as three pairs so thatthe diameter in three directions is recorded in addition tothe average diameter.
Mechanical calipers are lowered to the bottom of the bore-hole in closed position, the arms are released, and the toolis raised. The calipers must be calibrated against aknown minimum and maximum diameter before logging.
The acoustic caliper measures the distance from anacoustic transducer to the borehole wall. Individualdiameter readings for each of four transducers mounted90 degrees apart are obtained and also the average of thefour readings. A special purpose acoustic caliper designedfor large or cavernous holes (6 ft to 100 ft in diameter)uses a single rotating transducer to produce a continuousrecord of the hole diameter.
Directional Surveys
In some situations, borehole deviation must be accuratelydetermined. Several methods of accomplishing this havebeen devised. Borehole survey instruments initiallyconsisted of single or multiple picture (multishot) camerasthat photographed a compass and plumb bob at selectedlocations in the borehole. Depths were based on thelength of cable in the borehole. The camera was retrievedfrom the hole, and the film developed and interpreted.
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Figure 14-19.—Log of six-arm mechanical caliper.
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A fluxgate compass or gyroscope is commonly used todayto measure azimuth and an inclinometer to measuredeviation from vertical. The information is thenelectronically transmitted to the surface via a cable. Thismethod provides a continuous survey of the hole and notjust checks at intervals. Systems are also available thatuse accelerometers and gyroscopic sensors to surveyboreholes and provide real time data via a cable orultrasonically via the mud.
Borehole Fluid Temperature Log
The standard borehole fluid temperature logging devicecontinuously records the temperature of the water ordrilling fluid in an open or cased borehole as a sonde israised or lowered in the borehole. The standard, orgradient device uses a single thermistor (thermal resistor)that responds to temperature variations in the fluid. Asmall change in temperature produces a large change inresistance, which is converted to a change in electricalcurrent. A differential device is sometimes used to recorddifferences in temperature between two positions in theborehole by the use of two thermistors or one thermistorand a memory unit within the control module. The logproduced by the temperature device shows temperature asa function of depth.
Temperature logging is usually performed before standardgeophysical logging operations to permit correction ofother logs (e.g., the resistivity logs) for the effects of bore-hole fluid temperature. Temperature logs can also beused to locate the source and movement of fluids into orout of the borehole and identify zones of waste dischargeor thermal pollution in groundwater. Grouted zonesbehind casing can be located by the cement heat ofhydration.
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The temperature probe must be calibrated against a testfluid of known temperature immediately before tempera-ture logging. Borehole fluids must be allowed to reach astable temperature after drilling operations before loggingcan be conducted. Open boreholes take longer to stabilizebecause of the differences in thermal conductivity of thevarious materials encountered.
Borehole Gravity Log
A borehole gravity meter (or gravimeter) detects andmeasures variations in the force of gravity. The devicedetermines the bulk density of a large volume of soil orrock between a pair of measuring stations in the borehole(figure 14-20). The bulk density (�) is proportional to themeasured difference in gravity (G) between the twostations and inversely proportional to the verticaldistance (Z) between the stations:
∆G G G= −1 2 ρ = ∆∆G
Z
The borehole gravity meter has been used primarily bythe oil industry to determine the porosity (especiallyporosity because of fractures and vugs). Porosity iscalculated using standard equations relating bulkdensity, fluid density, and specific gravity of solids(matrix density). Although density and porosity are alsoprovided by the gamma-gamma density logger (see“Nuclear Radiation Logging Techniques”), because of thelarge volume and radius of investigation, gravity meterdata are less affected by borehole effects such as mudcakeand irregular hole diameter. Gravity meter densitydeterminations are more representative of the geologicmedium away from the borehole than are gamma-gamma
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logs. The radius of investigation of the gravity meter isan estimated five times the difference in elevationbetween the measuring stations (see figure 14-20).
The borehole gravity meter is not a continuous recordinginstrument. The tool must be positioned at a preselectedmeasurement station, allowed to stabilize, and then a
Figure 14-20.—Elements of borehole gravity logging.
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measurement taken. Instrument readings are convertedto gravity values using a conversion table. Bulk densityis then calculated using the difference in gravity valuesand depth between the two stations. Usually two or threetraverses are made in the hole at repeated stations andthe values averaged. The precision of the methodincreases with decreasing distance between measuringstations.
Surveys may be conducted in cased or uncased holes.Several corrections to the data are necessary, includingcorrections for earth-moon tides, instrument drift,borehole effects, subsurface structure, gravity anomalies,hole deviation from vertical, and the free-air verticalgravity gradient. The instrument should be calibrated tocorrect for drift and tides. The borehole gravity logger isavailable commercially but is not a standard log. Anapparent advantage over other bulk density/porosity log-ging methods is the reduction of borehole effects and thegreater sample volume.
Magnetic Log
The magnetic field in an uncased borehole is the result ofthe Earth’s magnetic field and any induced or remnantmagnetism. These fields can be directly measured.Magnetic susceptibility is the degree that a material iseffected by a magnetic field and is the basis for thelogging technique. Susceptibility logs measure the changeof inductance in a coil caused by the adjacent boreholewall. The magnetic susceptibility is proportional to theamount of iron-bearing minerals in the rock.
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Flowmeter Log
A flowmeter measures fluid flow in boreholes. A flow-meter log provides information about locations wherefluid enters or leaves the borehole through permeablematerial or fractures intersecting the borehole.
Conventional flowmeters employ a spinner or propellordriven by fluid moving through the borehole. High resolu-tion flowmeters such as the heat pulse flowmeter canmeasure very low flow rates. Heat pulse flowmeters havea heating element that heats borehole fluid. The flow rateand direction of the heated fluid pulse is measured bydetectors located above and below the heat element. Elec-tromagnetic flowmeters induce a voltage in electricallyconductive borehole fluid moving at a right angle througha magnetic field. The induced voltage is proportional tothe velocity of the conductive borehole fluid.
Bibliography
Hearst, J. R, and Nelson, P.H., Well Logging for PhysicalProperties, McGraw-Hill Book Co., New York, 1985.
Labo, J., A Practical Introduction to Borehole Geophysics,Society of Exploration Geophysicists, Tulsa, Oklahoma,1987.
Chapter 15
REMOTE SENSING TECHNIQUES
Introduction
This chapter briefly summarizes the capabilities,limitations, and requirements of typical remote sensingtechniques. Depending on the nature of the data and theobjective of the study, geologic interpretation of remotelysensed data may be simple or complicated. Remotesensing is a tool that makes some tasks easier, makespossible some tasks that would otherwise be impossible,but is inappropriate for some tasks. Depending on theindividual situation, remote sensing may be extremelyvaluable. Some remote sensing interpretations canstand on their own with confidence, but for most,establishing ground truth is essential.
Imaging Systems
There are three main types of imaging systems, two ofwhich are widely used in terrestrial applications:
Photographic.—Cameras and film are used.Photography provides the best spatial resolution but lessflexibility in spectral data collection and imageenhancement. Spatial resolution is dependent on alti-tude, focal length of lenses, and the types of film used. Spectral resolution is limited to visible and near infraredwavelengths.
Electronic Spectral Sensors.— Detectors are used,usually scanners, that may have less spatial resolutionthan photographs but can gather spectral data over widespectral ranges that enable a wide variety of imagingprocessing, mineral, and geologic identification. Theseremote sensing systems include satellites, such asLandsat, airborne sensors carried on aircraft, and
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spectrometers carried on the ground. This type ofremote sensing has several categories, including multi-spectral, hyperspectral, and imaging spectroscopy.
Vidicon. – A television-type system. Vidicon systemsgenerally are inferior to other types both spatially andspectrally. They are used mostly on space probesbecause of operational constraints.
Resolution
Two types of resolution are important to remote sensing.
Spatial.— The sharpness of an image and the minimumsize of objects that can be distinguished in the image area function of spatial resolution.
Spectral.—The width or wavelength range of the part ofthe electromagnetic spectrum the sensor or film canrecord and the number of channels a sensor uses definesspectral resolution. The electromagnetic spectrum is anordered array of electromagnetic radiation based onwavelength. Certain portions of the electromagneticspectrum, including the visible, reflective infrared,thermal infrared, and microwave bands, are useful forremote sensing applications. Rocks, minerals,vegetation, and manmade materials have identifyingspectral signatures and distinctive absorptive andreflective spectral characteristics. Given sufficientspectral data, digital image processing can generallyidentify unique spectral signatures. In practice,instrument limitations or cost limits on computerprocessing may preclude identification of somematerials.
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Photography
The uses of aerial photography in engineering geologyare discussed in Volume 1, chapter 6. A brief descriptionof types is presented below.
Panchromatic photography records images essentiallyacross the entire visible spectrum and, with proper filmand filters, also can record into the near-infraredspectrum. In aerial photography, blue generally isfiltered out to reduce the effects of atmospheric haze.
Natural color images are recorded in the natural colorsseen by the human eye in the visible portion of thespectrum.
False-color infrared images are recorded using part ofthe visible spectrum and part of the near-infrared, butthe colors in the resultant photographs are arbitrary andnot natural. Infrared film commonly is used and is lessaffected by haze than other types.
Multispectral photographs acquired by multiple camerassimultaneously recording different portions of thespectrum can facilitate interpretation.
Terrestrial photographs acquired on the ground or at lowaltitude with photogrammetric cameras can be used tomap geologic features such as strike and dip of joints,faults, and geologic contacts. This type of geologicphotogrammetry can also be done from historicconstruction photographs if enough survey controlfeatures can be located in the photographs and tied topresent control or known points. Terrestrial photogram-metry has proven useful on several dam projects inwhich mapping of geologic features by standard methodswas very difficult or impossible.
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Thermal Infrared Imagery
Thermal infrared systems create images by scanning andrecording radiant temperatures of surfaces. Somecharacteristics of thermal image data are generic todigital image data, and enable computer imageprocessing. Other characteristics are unique to thermalinfrared images and make thermal image data valuableinterpretive tools.
Thermal infrared imagery can be interpreted using con-ventional photogeologic techniques in conjunction withthe thermal properties of materials, instruments, andenvironmental factors that affect the data. Wherethermal characteristics of a material are unique, thermalinfrared imagery can be easy to interpret and can be agreat help in geologic studies. Thermal characteristicsof a material can vary with moisture content, differentialsolar heating, and topography making interpretationmore difficult and ambiguous.
Multispectral Scanner Imagery
Multispectral scanner (MSS) images are a series ofimages of the same target acquired simultaneously indifferent parts of the electromagnetic spectrum.MSS images are an array of lines of sequentially scanneddigital data. They may have unique distortions and mayor may not have high resolution or information content.Scanner systems consist of scanning mechanisms,spectral separators, detectors, and data recorders.
A digital image is actually an array of numerical dataand can be computer processed for a variety of purposes.Geometric distortions caused by sensor characteristicscan be removed or distortions can be introduced.
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Computer processing can be used to precisely register adigital image to a map or another image. Various typesof data (e.g., thermal and visible imagery or a digitalimage and digitized gravity data) can be merged into asingle image. Subtle information, difficult to interpret oreven to detect, can sometimes be extracted from animage by digital processing.
Airborne Imaging Spectroscopy
The “image,” or data, consist of an array of reflectedspectra collected in a two-dimensional array of pixels.Specific spectral features may be identified and pixelswith the same spectral wavelength feature may bemapped in colors. Different colors are assigned todifferent reflectance spectra, and an image is generatedfrom these classifications. A number of differentairborne systems are becoming available with variousspatial and spectral characteristics. A few commerciallyavailable systems are capable of recording 10 or morespectral bands simultaneously, ranging from ultravioletto thermal infrared wavelengths. The key factor inspectral identification of materials, geologic features, orvegetation is the system’s spectral resolution or numberof channels. Currently, the premier sensor for imagingspectroscopy is the National Aeronautics and SpaceAdministration (NASA) Jet Propulsion Laboratoryairborne visible and infrared imaging spectrometer(AVIRIS). AVIRIS simultaneously collects data over aspectral range of 0.4 micron to 2.4 microns in 224channels. The number of channels and very high qualityof data allow discrimination of very small spectralabsorption features and, therefore, the user candistinguish and map hundreds of types of minerals orvegetation. The AVIRIS instrument is operated by JetPropulsion Laboratory (JPL) onboard a NASA ER-2
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(modified U-2). Commonly operating at an altitude of63,000 feet, the spatial resolution is approximately20 meters. The AVIRIS instrument is also operated byJPL onboard a twin-engine aircraft at lower altitudes.The spatial resolution is approximately 1 meter. Thesize of data sets and the number of separate spectralbands on some airborne systems may require dataconsolidation or careful selection of data subsets forspecial processing. Because the Earth’s atmosphereintroduces it’s own spectral absorption features along thelight path from the ground to the sensor, removal ofatmospheric spectral features is essential to properanalysis of spectroscopy or hyperspectral data. Groundcalibration spectra using a field spectrometer operatingover the same wavelength ranges and resolutioncollected at the same time as the overflight is generallyrequired to achieve the highest quality mapping anddiscrimination of materials. Interpretation usually in-volves normal photogeologic techniques along withknowledge of spectral characteristics and the datamanipulations applied. The spectral imaging data canbe analyzed with specialized commercially availablesoftware, which relies primarily on statistical analysesand projection of a few spectral features in an image.Software being developed at the U.S. Geological Survey(USGS) Imaging Spectroscopy Laboratory is based on acomparison of laboratory spectral features of severalhundred minerals and materials in a spectral library.This software, known as “Tetracorder,” rapidly identifiesand maps all the key spectral features of knownminerals or materials in each pixel of an AVIRIS or otherhyperspectral image. The companion field spectrometercan also be used in its own right to collect bothlaboratory and field spectra of materials foridentification. Applications may include distinguishingdifferent types of clay minerals (e.g., expansive or not) asthe geologist maps in the field in real time.
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High resolution can be obtained and, with proper bandselection and processing, complex geochemistry, min-eralogy, vegetation, or other materials information canbe mapped from the imagery. These technologies havebeen used very successfully in mapping large areas forseveral environmental/engineering geology relatedprojects. Because of the complexity of the geology andthe size of the area studied, the calibration and analysisof imaging spectroscopy data is not trivial. The volumeof high quality data that can be collected using imagingspectroscopy over immense areas in one flight mayprovide an advantage over any other traditional methodof mapping in certain applications.
Satellite Multispectral Scanner Imagery
Landsat is the NASA satellite for civilian remote sensingof the Earth’s land surface. The Landsat MSS recordsseven bands at 30-meter resolution. The MSS is usefulfor some geological applications, although it is orientedprimarily toward agricultural uses. The Landsat 7 isequipped also with a thematic mapper (TM) that hasincreased spatial and spectral resolution compared to theMSS.
SPOT, a French satellite, provides panchromatic imagerywith up to 10-meter spatial resolution. MSS imagery iscapable at 20-meter resolution of stereo imaging. Othercommercially available satellites designed for rapid andrepeated imagery of customer-selected sites are alsobeing put in orbit to produce imagery of any area. Inaddition, archives of once classified satellite imagerygathered by United States spy satellites have becomeavailable to the public and government agencies and maybe a source of data and images.
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Satellite imagery provides a synoptic view of a large areathat is most valuable for regional studies. Withincreasing resolution and new sensors, site-specificgeologic mapping with satellite images is also of value toengineering geology.
Radar Imagery
Radar is an active remote sensing method (as opposed topassive methods like photography and thermal infrared)and is independent of lighting conditions and cloudiness.Some satellite radar imagery is available, like Landsat,and coverage may be useful for regional geologic studies.Side-looking airborne radar (SLAR) produces a radarimage of the terrain on one side of the airplaneequivalent to low-oblique aerial photography. Radarinterferometry is a quickly emerging field of radarremote sensing. Radar interferometry techniques willdetect very small changes in topography, such as thosecaused by landslide movements, fault displacements,erosion, or accretion, and can be mapped remotely overlarge areas.
Radar imagery has some unusual distortions thatrequire care in interpretation. Resolution is affected byseveral factors, and the reflectivity of target materialsmust be considered. The analysis and interpretation ofradar imagery requires knowledge of the imagingsystem, the look direction, and the responses of thetarget materials.
Radar can penetrate clouds and darkness and, to someextent, vegetation or even soil. Distortions, image geo-metry, and resolution can complicate interpretation, ascan a lack of multispectral information.
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Side Scan Sonar
Side Scan Sonar (SSS) is used for underwater surveysand not remote sensing in the typical sense of usingaerial or space platforms to image the Earth’s surface.SSS produces images underwater and may have usefulapplications to engineering geologic studies of reservoirs,dams, and other structures or surfaces hidden by water.SSS works by sending out acoustic energy and sensingthe return of the acoustic signal. Materials on the bottomsurface under water reflect the signal at differentstrengths depending on the material properties and theangles of incidence and reflection of the signal. Thevarying strength of signal return is then used to form animage. An image of the reflected signal that looks like ablack and white aerial photograph is the output. Theacoustic signal is generated by a torpedo-like instrumentthat is towed behind a boat by cable. Resolution ofobjects or features on the bottom of a reservoir varieswith the frequency of the signal generated and the heightof the torpedo above the bottom of the water body.
Single- and Multi-Beam Sonar
Other types of sonar devices that can be used to map thetopographic surface of a reservoir bottom include single-beam and multi-beam sonar. These devices send a directacoustic signal and measure the time of return. This istranslated to a depth to the bottom or feature. Bysending continuous signals along a line of survey, aprofile of the bottom is developed. When multiple linesare tied together in criss-crossing patterns with GlobalPositioning System (GPS) positions being recordedsimultaneously, a topographic map of the bottom can begenerated. Multi-beam systems send out multiple beams
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at different angles simultaneously, thereby generating atopographic surface over much larger areas in greaterdetail than single-beam systems.
Applications to Engineering Geology
The most useful form of remote sensing for engineeringgeology applications is aerial photography because of itshigh resolution, high information content, and low cost.Various scales of aerial photography are available forregional and site studies, for both detecting and mappinga wide variety of geologic features.
Applications of other forms of remote sensing toengineering geology depend on the nature of the problemto be solved and the characteristics of the site geology.Some problems can best be solved using remote sensing;for others, remote sensing is of little value. In somecases, the only way to find out if remote sensing can dothe job is to try it.
Appropriate remote sensing data are often not availablefor the area of interest, and the data must be acquiredspecifically for the project. Mission planning and timeand cost estimating are critical to a remote sensing datacollection program. Numerous factors make planning aremote sensing mission more complicated than planninga conventional aerial photographic mission. Remotesensing mission planning is best done in consultationwith someone with experience in the field.
Estimating the cost of data acquisition is relatively easy.Estimating the cost of interpretation is a function of thetime and image processing required and is much harder.Some forms of remote sensing are inexpensive to acquireand require little processing to be useful. Other forms
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may be expensive to acquire or may require muchprocessing, perhaps needing experimentation to deter-mine what will work in an untried situation. The costmust be weighed against the benefits.
Bibliography
Two excellent reference books on remote sensing andapplications to geology are:
Sabins, F.F., Remote Sensing Principles and Interpreta-tion, 2nd edition: Freeman, New York, 449 p., 1987.
Siegal, B.S., and Gillespie, A. R., editors, Remote Sensingin Geology, Wiley & Sons, New York, 702 p., 1980.
For a thorough treatment of remote sensing ("more thanyou ever wanted to know about remote sensing"),including a 287-page chapter on geological applicationswith abundant color images, see:
Colwell, R N., editor, Manual of Remote Sensing,2nd edition, Falls Church, Virginia, American Society ofPhotogrammetry, 2724 p., 1983.
Chapter 16
WATER TESTING FORGROUTING
Introduction
Water testing is necessary for evaluating seepagepotential and for determining whether grouting isnecessary or practical. Water testing for designing agrout program is often secondary to the main purpose ofthe water testing program, which is to determinepermeabilities for seepage evaluation or control. Designof an exploration program for water testing for groutingcan be significantly different from permeability testingfor the design of a dam or tunnel because of the desiredresults, the restricted area of a damsite, or the oftenhigh-cover linear tunnel site. Regardless of the mainreason for the investigations, design of a program forwater testing for grouting should consider:
(1) The type of structure to be built. Water testingfor evaluating and grouting a dam foundation issignificantly different than water testing for atunnel. More drill holes are generally available fortesting in dam foundations where seepage potentialis the primary concern and grouting is secondary.Relatively few drill holes are available forevaluating tunnel alignments because of the greatdepths often necessary and the linear nature of atunnel. A great deal of judgment is necessary inevaluating the data for tunnels because of the smallsample size. Ground conditions are of primaryinterest, and permeability and groutability aresecondary, especially if the tunnel will be lined.
(2) The geologic conditions at the site and thevariations between areas or reaches.Generalizations based on other sites are usuallyinaccurate because geologic conditions depend on the
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interrelationship of the local depositional, tectonic,and erosional history that uniquely determinegeologic conditions important to the permeabilityand groutability of a site. Damsite foundationpermeabilities can vary over short distances becauseof lithology and fracture changes, faults, or stressrelief in the abutments. Tunnel studies compoundthe difficulties because of the linear nature of thestructure, the often high cover, and access problems.Proper evaluation of water test results requires thatthe values be correlated with geologic conditions.The permeability values should be noted and plottedon the drill logs along with the water takes and testpressures. The test interval should be drawn on thelog so that the water test data can be related tofracture data.
(3) The level of seepage control desired. Seepagequantities beneath a dam in the arid West may beinsignificant compared to those in an area withabundant rainfall. Infiltration into a tunnel may beinsignificant in one area but, because of overlyingcultural and environmental features, may be thecontrolling factor in a dewatering, excavation, orlining design. The economic value of the water mayalso be a significant factor.
(4) Groutability and permeability are not necessarilyrelated. A highly fractured rock or a gravel may bevery permeable but essentially ungroutable usingstandard cement grout. Water test data must becorrelated with geologic data to properly assessgroutability.
(5) Groutability depends on fracture openness andnumber. Connectivity is not necessarily importantbecause of the relatively limited travel of grout.
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(6) Permeability depends on fracture openness,number, and connectivity. Highly fractured rockwith low connectivity will have low permeability,and a slightly fractured rock with high connectivitycan have high permeability.
(7) Exploratory drill hole orientations introduce asignificant bias into water test results. The orienta-tion of the drill hole relative to the fractures has adirect effect on the number of fractures interceptedby the hole. Vertical boreholes intercept very fewvertical fractures and can provide very misleadingwater test information on rock mass permeabilityand groutability. A vertical hole drilled in amaterial that has predominantly vertical fractureslike flat-bedded sediments will not intercept thefractures that control the rock mass permeability.Drill holes should be oriented to cross as manyfractures as possible not only for more meaningfulpermeability tests but also to get more meaningfulrock mass design parameters. If a preferred holeorientation is not practical, the results may beadjusted for the orientation bias.
(8) Water test calculation results can be verymisleading. Water test calculations based on a10-foot (3-meter [m]) interval with one 1/4-inch(6-millimeter [mm]) fracture taking water can havea significantly different seepage and grout potentialthan a 10-foot (3 m) interval with dozens ofrelatively tight fractures taking the same amount ofwater. Each water test must be evaluatedindividually to determine what the data reallymean.
(9) Different rock types, geologic structures, or insitu stresses have different jacking and
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hydrofracture potential and, therefore, differentmaximum acceptable water testing and groutingpressures. Dam foundations are more sensitive tojacking and hydro-fracturing than tunnels. Damfoundations can be seriously damaged by jackingand hydrofracturing. A dam foundation ininterbedded sedimentary rock with high horizontalin situ stresses is very sensitive to jacking. A damfoundation in hard, massive granite is almostunjackable and may have to be hydrofracturedbefore any movement can take place. Tunnels areless susceptible to jacking because of overburdendepth and may benefit from jacking open fracturesto provide grout travel and closure of ungroutedfractures.
(10) Rock mass permeability or groutability cannotbe determined by drill holes alone. Mapping andanalysis of the fractures are necessary factors indetermining seepage potential and groutability.Drill holes usually do not provide a realisticcharacterization of fracture orientations andconnectivity. All these data should be integrated todetermine rock mass permeability or groutability.
(11) Rules of thumb are not good substitutes forusing data and judgment in making decisions ingrouting unless specifically developed for the siteconditions.
(12) Hydraulic models are a tool that can be used toevaluate seepage potential and groutability butdepend on realistic design and data inputparameters. Water test-derived permeability andgroutability are important parameters for hydraulicmodels. Water tests must be carefully evaluated toensure that bad test data are not used in models.
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taketest pressure psi
× 155.
( )take
test
bar
pressure bars× 10
( )
Models large enough to approach characterizing asite are usually very large and expensive. Thetendency is to build models that are small andeconomical and, therefore, have a limited connectionwith reality. Realistic parameters are difficult toobtain in quality or quantity. Few explorationprograms provide a statistically significant samplesize to fully characterize a site, especially tunnels.Model input parameters and design should be partof any modeling report so the output can be properlyevaluated.
Procedure
Calculations
Permeabilities can be calculated in lugeons, feet per year(ft/yr), centimeters per second (cm/sec), or other unitsfrom the same basic field data. Lugeons are used in thefollowing discussion because these units are commonlyused in the grouting industry. Chapter 17 has athorough discussion of testing and calculating in otherpermeability units. One Lugeon equals:
(1) 1 liter per minute per meter (l/min/m) at apressure of 10 bars
(2) 0.0107 cubic feet per minute (ft3/min) at142 pounds per inch (psi)
(3) 1 x 10-5 cm/sec
(4) 10 ft/yr
The formula for calculating Lugeons (lu) is:
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Take is in liters per meter per minute or cubic feet perfoot per minute. One bar equals 14.5 psi. Takes shouldbe measured after flows have stabilized and should berun for 5-10 minutes at each pressure step.
Geologic Data
The geologic data should be examined to determine theoptimum drill hole orientations and locations. Geologicstructure, such as bedding and rock type, can be used toset the initial maximum water test pressures. Easilyjacked or hydrofractured rock should initially be watertested at a pressure of 0.5 psi per foot (2.2 kilogram persquare centimeter per meter [kg/cm2/m]) of overburdenand increased pressures based on stepped pressure testsor jacking tests.
Stepped Pressure Tests
Stepped pressure tests are the best method of conductingwater tests. Pressures are stepped up to the maximumpressure and then stepped down through the originalpressures. Comparison of the calculated permeabilityvalues and the pressure versus flow curves for the stepscan provide clues as to whether the flow is laminar, ifjacking or hydrofracturing is occurring, and if fracturesare being washed out or plugged. Single pressure testscan be misleading because of all the unknown pressureand flow variables affecting the test. The Lugeon valuefor the test interval should be determined by analysis ofthe individual test values and not necessarily by anaverage. The individual tests are used to determinewhat is happening in the rock, and one value of the fivetests is usually the appropriate value to use.
Figures 16-1 through 16-5 are bar chart plots showingthe relationship of pressure to Lugeon values for the
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0
20
40
60
80
100
PSI / Lugeons
Test
Laminar Flow
Pressure 25 50 100 50 25
Lugeons 21 23 22 23 22
1 2 3 4 5
Figure 16-1.—Bar chart showing relationshipof test pressure and Lugeons in laminar flow.
0
20
40
60
80
100
PSI / Lugeons
Test
Turbulent Flow
Pressure 25 50 100 50 25
Lugeons 38 28 15 27 39
1 2 3 4 5
Figure 16-2.—Bar chart showing relationshipof test pressure and Lugeons in turbulent flow.
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0
20
40
60
80
100
PSI / Lugeons
Test
Washing
Pressure 25 50 100 50 25
Lugeons 21 24 28 33 37
1 2 3 4 5
Figure 16-3.—Bar chart showing relationshipof test pressure and Lugeons when fractures
are washing out.
0
20
40
60
80
100
PSI / Lugeons
Test
Filling or Swelling
Pressure 25 50 100 50 25
Lugeons 32 28 21 16 12
1 2 3 4 5
Figure 16-4.—Bar chart showing relationshipof test pressure and Lugeons when fractures
are filling or swelling.
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0
10
20
30
40
50
60
70
80
90
100
PSI / Lugeons
Test
Jacking or Hydrofracturing
Pressure 25 50 100 50 25
Lugeons 23 21 43 22 21
1 2 3 4 5
Figure 16-5.—Bar chart showing relationshipof test pressure and Lugeons when rock ishydrofractured or joints are jacked open.
more common types of water test results. Figure 16-1is a plot of laminar flow in the fractures. Thepermeability is essentially the same no matter what thepressure and resultant water take. Figure 16-2 is a plotof turbulent flow in the fractures. Permeabilitydecreases as the pressure and resultant flow increasesbecause of the turbulent flow in the fractures. Figure 16-3 is a plot of flow in fractures that increase in size as thewater washes material out of the openings. Permeabilityincreases because fractures are enlarged by the test.Figure 16-4 is a plot of flow in fractures that are beingfilled and partially blocked as water flows or thefractures are in swelling rock that closes fractures overtime because of the introduction of water by the test.Figure 16-5 is a plot of testing in rock that is beingjacked along existing fractures or rock that is beingfractured by the highest water test pressure. Flow islaminar at the lower pressures.
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Hydrofracturing/Jacking Test
0
100
200
300
400
500
600
700
800
900
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Flow (Q)
Pre
ssu
re
Pressure - Hydrofrac
Pressure - Jacking
Figure 16-6.—Continuously recorded plotof pressure and flow.
Combinations of these types of flow can occur andrequire careful analysis. If the pressures are increasedto where jacking or hydrofracturing is occurring, thedesign grout pressures can be set as high as possible toget effective grout injection yet preclude fracturing or, ifappropriate, induce fracturing. Hydrofracture tests areeasier to analyze if a continuous pressure and flowrecording is obtained. The resolution of a step test maynot be adequate to separate hydrofracturing fromjacking. Figure 6 is a plot of a continuously recordedhydrofracture/jacking test.
Back Pressures
Back pressures should be measured after every test todetermine if the hole holds pressure and if fracturing orjacking has occurred. If the hole holds pressure andbackflow occurs while releasing the pressure, hydro-fracturing or jacking may have occurred at the testpressure.
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Test Equipment
Test equipment can affect the test results. At moderateto high flows, the friction loss caused by the piping andthe packer should be considered. Significant loss ofpressure occurs between the gauge and the packer. Athigh flows, the plumbing system “permeability” can bethe controlling factor and not the permeability of the testinterval. If meters and gauges are located in optimumrelation to each other and close to the hole, thearrangement of pipe, hose, etc., will not seriouslyinfluence shallow tests although sharp bends in hose, 90-degree fittings on pipes, and unnecessary changes in pipe and hose diameters should be avoided. Layingthe system out on the ground and pumping water through the plumbing to determine the capacity of the system is a good idea, especially if using small-diameter piping or wireline packers.
Water Takes Relative to Grout Takes
Water takes alone may be an indication of whethergrouting is necessary, and Lugeon calculations may notbe necessary after enough water tests with subsequentgrouting provide sufficient data to determine acorrelation. This shortcut is usually used during theactual grouting because not enough data are availablefrom exploration unless a test grout section isconstructed. The correlation can change if the geologicdomain in a foundation changes, so any correlation mustbe continuously checked.
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Depth of Grouting
Grouting depth for dam foundations is commonlydetermined by a rule of thumb related to dam height. Abetter method is to base the depth on water test dataand geologic data. Weathered rock and fracture surfacesare an indication of permeable rock. Grouting to tight,unweathered rock, where practical, makes more sensethan trying to grout tight, impermeable rock or notgrouting pervious rock because of a rule-of-thumbapproach.
Grouting in tunnels should be based on the thickness ofthe disturbed zone around the periphery of the tunneland the depth necessary to get the desired results whengrouting natural fractures. A machine-bored tunnel willhave a much shallower disturbed zone than aconventionally excavated (drill-blast) tunnel and mayrequire less or no grouting.
Bibliography
Ewart, Friedrich-Karl, Rock Permeability and Grouta-bility Related to Dams and Reservoirs, lecture notes,University of Paderborn, Germany, September 1994.
Water Resources Commission N.S.W., Grouting Manual,3rd edition, Australia, 1980.
Chapter 17
WATER TESTING FOR PERMEABILITY
General
Most rock and soil contains numerous open spaces wherewater may be stored and through which water can move.Permeability, or hydraulic conductivity, is a measure ofthe ease of movement of fluid and gas through the openspaces and fractures. The properties of soil and rockhave significant impact on water movement through theinterstitial spaces. Water movement through soil androck significantly impacts the ability to control waterduring construction. The movement of water throughslopes must be known to understand the stability ofslopes. Permeability in this chapter is consideredsynonymous with the term hydraulic conductivity and isa measurement of the groundwater flow through a cross-sectional area. This chapter discusses how to measurepermeability and how to best determine or estimateappropriate permeability values.
In addition to permeability, there are other hydrologicparameters that may impact the understanding ofgroundwater but are either more difficult to determineor are not a significant consideration in most engineeringsituations. These other hydraulic parameters ofsubsurface materials are transmissivity, porosity, andstorage. For a more detailed explanation of thesehydrologic parameters and the methods used to obtainedthe values, see chapters 5, 6, and 10 of the ReclamationGroundwater Manual.
Transmissivity
Transmissivity is the average permeability multiplied bythe saturated thickness. Transmissivity is particularlyimportant in areas with multiple aquifers. Determiningthe aquifer thickness may not be practical or necessary
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if permeability and recharge are relatively low and theneed for groundwater control is short term.Transmissivity values are often based on individualpermeability values or averaged permeability values. Itis important that any permeability value used with thesaturated thickness of an aquifer be appropriate andrepresentative. Since most aquifers are rarelyhomogeneous and isotropic, any field derived data mustbe qualified by indicating if averaging or selecting thehighest or lowest permeability value for a particular siteis appropriate.
Porosity
Porosity is the percentage of interstitial space within thesoil or rock relative to the total volume of soil or rock.Porosity is not necessarily directly proportional topermeability. Porosity is a significant factor inunderstanding the stability of soil and rock, but only theeffective porosity, the interconnected pores, contribute topermeability. Not all pores or interstitial spaces areconnected. Porosities are typically high for sands andgravels (30-40 percent) with high permeabilities (10 to10-2 cm/sec). Clays have higher porosities (45-55 percent)but have very low permeabilities (10-6 to 10-8 cm/sec).Effective porosity is important in high permeabilitymaterials, but the total porosity is rarely relevant exceptin contaminant transport modeling. In the field, porosityis typically estimated by borehole geophysics.
Storage
Storage is a dimensionless term defined as the volume ofwater released from or taken into interstitial spaces inthe soil or rock. Storage is often interchanged with theterms specific yield, effective porosity, coefficient ofstorage, and storativity. The water stored within theeffective porosity is controlled by the material’s ability to
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retain and to release water. Understanding storage isparticularly important in high permeability materials orlocalized zones connected with a large source of water.
A glossary of abbreviations and definitions is shown intable 17-1 that are used in the various permeabilitycalculations. Not all the parameters listed in the tableare necessary for every calculation. These parametersare derived from the Groundwater Manual, chapter 10.Abbreviations used in the figures and text of this chapterare consistent throughout the chapter. Definitions applyto angled holes as well as vertical wells.
Geologic Conditions
Understanding and measuring the above parameters isimportant, but understanding the hydrogeologicconditions is essential. Obtaining representative andappropriate hydrologic values is critical in any siteinvestigation. Identifying the water bearing zones andselecting the appropriate test method is very important.Improper test methods, poor well construction, andimproper isolation can significantly impact any testdesign. It is essential that the various aquifers andboundaries in heterogeneous settings be identified andthat the various water surfaces existing at the site belocated. Obtaining values without a good understandingof subsurface conditions can be misleading and canresult in surprises once the actual site conditions areexposed. Obtaining water level data and permeabilityvalues has little value without an understanding of thefactors controlling the groundwater. Proper evaluationof permeability values requires that the values becorrelated with geologic conditions.
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Table 17-1.—A glossary of abbreviations anddefinitions used in permeability calculations
K = Coefficient of permeability in feet (meters) per yearunder a unit gradient.
Q = Steady flow into the well in ft3/sec [m3/sec].
H = The effective head of water in the well in feet (m). Forpacker tests, determining the effective head is definedin figure 17-5. The effective head may be natural orinduced.
a = Exposed surface area of the test section in ft2 (m2). Notethat this area in an uncased borehole or using a singlepacker for some tests would include the exposed area atthe bottom of the borehole.
� = Length of test (packer tests) or screened (perforated)section of well isolated from the adjacent material infeet (m).
r = The radius to the borehole sidewall.re = The effective radius to borehole sidewall that is reduced
because of an obstruction such as a slotted riser(perforated casing), caved material, gravel, or sandpack.
r1 = The outer radius of a riser or casing.
rc = The inside radius of a riser or casing.D = Distance from the ground surface to the bottom of the
test section.U = Thickness of unsaturated materials above the water
surface, including the capillary zone.Tu = U-D+H = The distance from the induced water surface
in the well to the static natural water surface.S = Thickness of saturated material overlying a relatively
impermeable layer.Cu = Conductivity coefficient for unsaturated materials with
partially penetrating cylindrical test wells.Cs = Conductivity coefficient for saturated materials with
partially penetrating cylindrical test wells.
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Selecting the Appropriate Test
There are numerous ways to determine or estimatepermeabilities. The appropriate method for estimatingpermeabilities must be based on the subsurfaceconditions and how significantly the values obtained willimpact the project. The required level of understandingof the subsurface water conditions should be weighedrelative to the cost and the impact on stability andconstructability of the feature and on the changes inquality and quantity of water important to the site. Soilclassification and Standard Penetration Testing (SPT)blow counts provide crude estimates of soilpermeabilities. There are numerous geophysicalmethods for estimating permeabilities by usingflowmeters, acoustic velocities, and gamma boreholelogging techniques. The Reclamation Ground WaterManual, chapters 8 and 10, provides detailedexplanations of various test methods for determiningpermeabilities. Except for the aquifer tests, mostmethods described in this chapter determine the verticalor horizontal permeability.
The most accurate test method for determining per-meability is conducting a relatively long-term aquifertest. This method is not covered in this chapter. A full-term aquifer test (pumping test as described in chapter8 of the Reclamation Ground Water Manual) is rarelyjustified during initial site investigations because of thecost and time required to perform an aquifer test andpossibly handle the discharged water. This chapterdiscusses the less costly methods used to determinepermeability. These methods are less accurate,primarily because these tests are too short in durationand because the interval being tested is not necessarily“truly” undisturbed, open, dimensioned as assumed, andrepresentative.
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Stable Boreholes
Packer tests are commonly performed in boreholesbecause the tests are inexpensive and can be performedquickly, with minimal disruption to the primary task ofmost site investigations, which is determining thesubsurface materials and geology. The GravityPermeability Test Method 1 for consolidated material isused only within the vadose zone and is the preferredmethod if the packer test method cannot be used. Theprincipal problem of any gravity permeability testmethod is that a uniform supply of water is necessary sothat a constant head can be maintained above the staticwater surface. The falling head tests should be used instable boreholes if the packer test and gravity tests (bothabove and below the static water surface) cannot beperformed.
Unstable Boreholes
There are a number of permeability tests that can beused in unstable materials such as soils that arenoncohesive, uncemented, or unindurated or fracturedrock that collapses into the borehole. Slug tests are usedprimarily when water availability or usage is a problem.Piezometer tests are good where water surfaces are highand where water bearing units are relatively thinlayered but significant. Unfortunately, the piezometertest is limited to relatively shallow depths (around 20feet [6 m]) and is rarely successful in cohesionless orgravelly or coarser soils. Gravity permeability tests areused in unstable soils or in rock. Gravity permeabilitytests require costly construction techniques, delay orprevent further advancement of the borehole, andrequire a supply of water. Borehole permeabilities are appropriate for the intervaltested unless the test interval is greater than 10 feet
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113
(3 m). For intervals greater than 10 feet (3 m), the testmay not be an accurate reflection of the entire saturatedcolumn. The permeability values should be plotted onthe drill log, along with the water take and testpressures. The test interval should be drawn on the logso that the water test data can be related to fracturedata.
Permeability Testing in Rock
Permeability tests are routinely performed in rock,particularly by pressure or packer tests. Thepermeability calculation assumes laminar flow in anisotropic, homogeneous medium. In reality, the testwater take is effectively controlled by fractures becausethe intact rock permeability is effectively zero in mostcases. The water may be flowing into one or into manyfractures in the test interval, but the permeabilitycalculation assumes laminar flow in an isotropic,homogeneous medium. The length of the test interval isgoverned by the rock characteristics. Typically, the testinterval may be 10 feet (3 m) long, but the water can begoing into one ¼-inch (8-mm) fracture. Test intervalsgreater than 20 feet (6 m) are inadvisable because,typically, there are a few fractures or a relatively smallzone that controls the groundwater flow in bedrock. Thecalculated permeability of the packer test interval maybe a magnitude different from the actual rock masspermeability. Only in the case of a highly fractured rockmass is the calculated permeability relatively reliableand the result is still a relative or effective permeability.
Orientation.—The orientation of the drill hole relativeto the fractures significantly affects the number offractures intercepted by the hole and the perceivedpermeability. A vertical hole drilled in a material thathas predominantly vertical fractures such as flat-beddedsediments will not intercept the predominant control on
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the rock mass permeability. The drill holes should beoriented to cross as many fractures as possible not onlyfor more meaningful permeability tests, but also to getmeaningful rock mass design parameters. If holeorientation is not practical, the results may be correctedfor the orientation bias.
Jacking.—The pressure used for the water test shouldconsider geologic structure. Flat-lying, beddedsediments are very susceptible to jacking along beddingplanes. The combination of weak bedding planes,typically low vertical confining pressures, or highhorizontal in place stresses can result in jacking andapparently high permeabilities. Test pressures of halfthe typical pressure of 1 pound per square inch per foot(psi/ft) (0.2 kg/cm 2/m) of depth are often appropriate.
Hydrofracturing.—In place stresses in many areas arenot lithostatic and horizontal stresses are significantlylower than vertical stresses. The theoretical overburdenstress (roughly 1 pound per square inch per foot depth[0.2 kg/cm2/m]) is typically used to determine the testpressure. If the horizontal stress is much lower than thevertical stress, hydrofracturing can occur, resulting in aninduced high permeability value.
Stepped Pressure Tests.—Stepped pressure tests arean effective method of conducting water tests. Pressuresare stepped up to the maximum pressure and thenstepped down through the original pressures. Compari-son of the calculated permeability values and thepressure versus flow curves for the steps can tell youwhether the flow is laminar, if jacking or hydrofracturingis occurring, and if fractures are being washed out. Ifthe pressures are increased to where jacking orhydrofracturing is occurring, the design grout pressurescan be set as high as possible to get effective grout
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injection, yet preclude fracturing or induce fracturing ifdesired. Chapter 16 discusses these tests in detail.
Test Equipment.—The test equipment can affect thetest results. At moderate to high flows, the friction lossand restriction because of the piping (plumbing) and thepacker is important. Significant pressure loss occursbetween the gauge and the packer. At high flows, theplumbing system “permeability” can be the controllingfactor rather than the permeability of the test interval.If meters and gauges are located in relation to each otheras recommended, the arrangement of pipe, hose, etc.,will not seriously influence the tests, although sharpbends in hose, 90-degree fittings on pipes, andunnecessary changes in pipe and hose diameters shouldbe avoided. Laying the system out on the ground andpumping water through the plumbing to determine thecapacity of the system is a good idea, especially if usingsmall diameter piping or wireline packers.
In many investigations, information on the permeabilityof saturated or unsaturated materials is required.Permeability within the vadose zone, including thecapillary fringe, is typically estimated by permeameteror gravity permeability tests. Permeability tests withinsaturated materials are typically performed as a fallinghead, packer, or aquifer test. Water within theunsaturated zone is suspended within the material butis primarily moving downward by gravity. Inunsaturated conditions, the material permeabilities areobtained by one of several field permeameter tests.Since the material is not saturated, permeability testsrequire more equipment and a lot of water. These testsmeasure the volume of water flowing laterally whilemaintaining a constant head.
Laboratory permeability tests of subsurface materialsusually are not satisfactory. Test specimens are seldom
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undisturbed, and a specimen typically represents only alimited portion of the investigated material. Field testshave been devised that are relatively simple and lesscostly than aquifer pumping tests (although aquifer testsdo provide relatively accurate permeability values).These tests are usually conducted in conjunction withexploratory drilling or monitoring existing wells. Permeability testing of existing monitoring wells mayhelp determine material characteristics when evaluationof existing data indicates gaps or when it is necessary toconfirm previous assumptions. Properly conducted andcontrolled permeability tests will yield reasonablyaccurate and reliable data. Several locations may needto be tested to provide data on spatial variations ofsubsurface material characteristics.
The quality of water used in permeability tests isimportant. The presence of only a few parts per millionof turbidity or air dissolved in water can plug soil androck voids and cause serious errors in test results.Water should be clear and silt free. To avoid pluggingthe soil pores with air bubbles, use water that is a fewdegrees warmer than the temperature of the test section.
For some packer tests, pumps of up to 250 gallons perminute (gal/min) (950 liters per minute [L/min]) capacityagainst a total dynamic head of 160 feet (50 m) may berequired.
The tests described below provide semiquantitativevalues of permeability. There have been numerous typesof permeability tests devised with varying degrees ofaccuracy and usefulness. The tests described below arerelatively simple and generally provide usefulpermeability data. If the tests are performed properly,the values obtained are sufficiently accurate for someengineering purposes. The tests assume laminar flow
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and a homogeneous medium. These conditions are notoften encountered, and fracture flow is what usuallyoccurs in rock. The equations given for computingpermeability are applicable to laminar flow. The velocitywhere turbulent flow occurs depends, in part, on thegrain size of the materials tested. A maximum averagevelocity for laminar flow is about 0.1 foot per second(ft/sec) (25 millimeters per second [mm/sec]). If thequotient of the water intake in cubic units per seconddivided by the open area of the test section in squareunits times the estimated porosity of the tested materialis greater than 0.10, the various given equations may notbe accurate or applicable. The values obtained are notabsolute and can vary from the true permeability by plusor minus an order of magnitude.
Length, volume, pressure, and time measurementsshould be made as accurately as available equipmentwill permit, and gauges should be checked periodicallyfor accuracy. Keep the accuracy of the results in mindwhen determining the needed accuracy of the measure-ments. Results should be reported in feet per year orcentimeters per second for most engineering uses.
In an open hole test, the total open area of the testsection is computed by:
a = 2�r�+�r2
where:
a = total open area of the hole face plus the hole bottomr = radius of the hole� = length of the test section of the hole
When perforated casing is used and the open area issmall, the effective radius, re, is used instead of theactual radius, r.
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ap = total open area of perforationsa = area of each perforation
If fabricated well screens are used, estimates of the screenopen area generally can be obtained from the screenmanufacturer.
Permeability tests are divided into four types: pressuretests, constant head gravity tests, falling head gravitytests, and slug tests. In pressure tests and falling headgravity tests, one or two packers are used to isolate thetest section in the hole. In pressure tests, water is forcedinto the test section through combined applied pressureand gravity head or the tests can be performed usinggravity head only. In falling head tests, only gravity headis used. In constant head gravity tests, no packers areused, and a constant water level is maintained. Slug testsuse only small changes in water level, generally over ashort time.
Pressure Permeability Tests in Stable Rock
Pressure permeability tests are run using one or twopackers to isolate various zones or lengths of drill hole.The tests may be run in vertical, angled, or horizontalholes. Compression packers, inflatable packers, leathercups, and other types of packers have been used forpressure testing. Inflatable packers are usually moreeconomical and reliable because they reduce testing timeand ensure a tighter seal, particularly in rough-walled,oversize, or out-of-round holes. The packer(s) areinflated through tubes extending to a tank of compressedair or nitrogen at the surface. If a pressure sensinginstrument is included, pressure in the test section is
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transmitted to the surface. Although this arrangementpermits an accurate determination of test pressures,manual observations should still be made to permit anestimate of permeability if pressure sensors fail. Whendouble packers are used, the hole can be drilled to totaldepth and then tested. When a single packer is used, thehole is advanced and tested in increments.
Methods of Testing
In stable rock the hole is drilled to the total depthwithout testing. Two inflatable packers 5 to 10 feet (1.5to 3 m) apart are installed on the drill rod or pipe usedfor making the test. The section between the packers isperforated. The perforations should be at least ¼ inch(6 mm) in diameter, and the total area of all perforationsshould be more than two times the inside cross-sectionalarea of the pipe or rod. Tests are made beginning at thebottom of the hole. After each test, the packers areraised the length of the test section, and another test ismade of the appropriate section of the hole.
In unstable rock, the hole is drilled to the bottom of eachtest interval. An inflatable packer is set at the top of theinterval to be tested. After the test, the hole is thendrilled to the bottom of the next test interval.
Cleaning Test Sections
Before testing, the test section should be surged withclear water and bailed or flushed out to clean cuttingsand drilling fluid from the hole. If the test section isabove the water table and will not hold water, watershould be poured into the hole during the surging, thenbailed out as rapidly as possible. When a completed holeis tested using two packers, the entire hole can becleaned in one operation. Although cleaning the hole isfrequently omitted, failing to clean the hole may result
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in a permeable rock appearing to be impermeablebecause the hole wall is sealed by cuttings or drillingfluid.
Alternatives to surging and bailing a drill hole inindurated or consolidated material before pressuretesting include rotating a stiff bristled brush whilejetting with water. The jet velocity should be at least150 ft/sec (45 m/sec). This velocity is approximately1.4 gal/min per 1/16-inch- (5.3 L/min per 2-mm-)diameter hole in the rod. The drill hole should be blownor bailed out to the bottom after jetting.
Length of Test Section
The length of the test section is governed by thecharacter of the rock, but generally a length of 10 feet(3 m) is acceptable. Occasionally, a good packer sealcannot be obtained at the planned depth because ofbridging, raveling, fractures, or a rough hole. If a goodseal cannot be obtained, the test section length should beincreased or decreased or test sections overlapped toensure that the test is made with well-seated packers.On some tests, a 10-foot (3-m) section will take morewater than the pump can deliver, and no back pressurecan be developed. If this occurs, the length of the testsection should be shortened until back pressure can bedeveloped, or the falling head test might be tried.
The test sections should have an �/2r ratio greater than5, where r is the radius of the hole and � is the length ofthe test section. The packer should not be set inside thecasing when making a test unless the casing has beengrouted in the hole. Test sections greater than 20 feet(6 m) long may not allow sufficient resolution ofpermeable zones.
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Size of Rod or Pipe to Use in Tests
Drill rods are commonly used to make pressure andpermeability tests. NX and NW rods can be used if thetake does not exceed 12 to 15 gallons per minute (45 to60 liters per minute) and the depth to the top of the testsection does not exceed 50 feet (15 m). For general use,1¼-inch (32-mm) or larger pipe is better. Figures 17-1through 17-4 show head losses at various flow rates per10-foot (3-m) section for different sizes of drill rod and1¼-inch (32-mm) pipe. These figures were compiledfrom experimental tests. Using 1¼-inch (32-mm) pipe,particularly where holes 50 feet (15 m) or deeper are tobe tested, is obviously better than using smaller pipe.The couplings on 1¼-inch (32-mm) pipe must be turneddown to 1.8 inch (45 mm) outside diameter for use in AXholes.
Pumping Equipment
Mud pumps should not be used for pumping the waterfor permeability tests. Mud pumps are generally of themultiple cylinder type and produce a uniform but largefluctuation in pressure. Many of these pumps have amaximum capacity of about 25 gal/min (100 L/min), andif not in good condition, capacities may be as small as18 gal/min (70 L/min). Tests are often bad becausepumps do not have sufficient capacity to develop backpressure in the length of hole being tested. When thishappens, the tests are generally reported as “tookcapacity of pump, no pressure developed.” This resultdoes not permit a permeability calculation and onlyindicates that the permeability is probably high. Thefluctuating pressures of multiple cylinder pumps, evenwhen an air chamber is used, are often difficult to readaccurately because the high and low readings must beaveraged to determine the approximate true effective
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Figure 17-1.—Head loss in a 10-foot (3-m) section of AX (1.185-inch- [30.1-mm-] inside
diameter [ID] drill rod.
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Figure 17-2.—Head loss in a 10-foot (3-m) section of BX (1.655-inch
[42.0-mm] ID) drill rod.
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Figure 17-3.—Head loss in a 10-foot(3-m) section of NX (2.155-inch
[54.7-mm] ID) drill rod.
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Figure 17-4.—Head loss in a 10-foot(3-m) section of 1¼-inch (32-mm) steel pipe.
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pressure. In addition, mud pumps occasionally develophigh peak pressures that may fracture the rock or blowout a packer.
Permeability tests made in drill holes should beperformed using centrifugal or positive displacementpumps (Moyno type) having sufficient capacity to developback pressure. A pump with a capacity of up to250 gal/min (950 L/min) against a total head of 160 feet(48 m) is adequate for most testing. Head and dischargeof these pumps are easily controlled by changingrotational speed or adjusting the discharge valve.
Swivels for Use in Tests
Swivels used for pressure testing should be selected forminimum head losses.
Location of Pressure Gauges
The ideal location for a pressure gauge is in the testsection, but as close to the packer as possible.
Water Meters
Water deliveries in pressure tests may range from lessthan 1 gal/min (3.8 L/min) to as much as 400 gal/min(1,500 L/min). No one meter is sufficiently accurate atall ranges. Two meters are recommended: (1) a 4-inch(100-mm) propeller or impeller-type meter to measureflows between 50 and 350 gal/min (200 and 1,300 L/min),and (2) a 1-inch (25-mm) disk-type meter for flowsbetween 1 and 50 gal/min (4 and 200 L/min). Each metershould be equipped with an instantaneous flow indicatorand a totalizer. Water meters should be testedfrequently.
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Inlet pipes should be available to minimize turbulentflow into each meter. The inlet pipes should be at least10 times the diameter of the meter inlet.
Length of Time for Tests
The minimum length of time to run a test depends on thenature of the material tested. Tests should be run untilthree or more readings of water take and pressure takenat 5-minute intervals are essentially equal. In testsabove the water table, water should be pumped into thetest section at the desired pressure for about 10 minutesin coarse materials or 20 minutes in fine-grainedmaterials before making measurements.
Stability is obtained more rapidly in tests below thewater table than in unsaturated material. Whenmultiple pressure tests are made, each pressuretheoretically should be maintained until stabilizationoccurs. This procedure is not practical in some cases,but good practice requires that each pressure bemaintained for at least 20 minutes, and take andpressure readings should be made at 5-minute intervalsas the pressure is increased and for 5 minutes aspressure is decreased.
Pressures Used in Testing
The pressure used in testing should be based on the rockbeing tested. Relatively flat-lying, bedded rock should betested at 0.5 lbs/in2 per foot (0.1 kg/cm2/m) of depth tothe test interval to prevent uplift or jacking of the rock.Relatively homogeneous but fractured rock can be testedat 1 lb/in2 per foot (0.2 kg/cm2/m) of test interval depth.Relatively unfractured rock can be tested at 1.5 lb/in2 perfoot (0.3kg/cm2/m) of test interval depth.
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Arrangement of Equipment
The recommended arrangement of test equipmentstarting at the source of water is: source of water;suction line; pump; waterline to settling and storagetank or basin, if required; suction line; centrifugal orpositive displacement pump; line to water meter inletpipe; water meter; short length of pipe; valve; waterlineto swivel; sub for gauge; and pipe or rod to packer. Allconnections should be kept as short and straight aspossible, and the number of changes in hose diameter,pipe, etc., should be kept as small as possible.
All joints, connections, and hose between the watermeter and the packer or casing should be tight, andthere should be no water leaks.
Pressure Permeability Tests
A schematic of the following two methods is shown infigure 17-5.
Method 1: The hole is drilled, cleaned, the tools areremoved, a packer is seated the test interval distanceabove the bottom of the hole, water under pressure ispumped into the test section, and readings arerecorded. The packer is then removed, the hole isdrilled the test interval length deeper, cleaned, thepacker is inserted using the length of the newly drilledhole as the test section, and the test performed.
Method 2: The hole is drilled to the final depth,cleaned, and blown out or bailed. Two packers spacedon pipe or drill stem to isolate the desired test sectionare used. Tests should be started at the bottom of thehole. After each test, the pipe is lifted a distance equalto l, shown on figure 17-5, and the test is repeated untilthe entire hole is tested.
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Figure 17-5.—Permeability test for use in saturated or unsaturated consolidated rock and well indurated soils.
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Data required for computing the permeability may not beavailable until the hole has encountered the water tableor a relatively impermeable bed. The required data foreach test include:
• Radius, r, of the hole, in feet (meters).
• Length of test section, �, the distance between thepacker and the bottom of the hole, Method 1, orbetween the packers, Method 2, in feet (meters).
• Depth, h1, from pressure gauge to the bottom of thehole, Method 1, or from gauge to the upper surface oflower packer in Method 2. If a pressure transducer isused, substitute the pressure recorded in the testsection before pumping for the h1 value.
• Applied pressure, h2, at the gauge, in feet (meters), orthe pressure recorded during pumping in the testsection if a transducer is used.
• Steady flow, Q, into well at 5-minute intervals, incubic feet per second (ft3/sec) (cubic meters per second[m3/sec]).
• Nominal diameter in inches (mm) and length of intakepipe in feet (m) between the gauge and upper packer.
• Thickness, U, of unsaturated material above the watertable, in feet (m).
• Thickness, S, of saturated material above a relativelyimpermeable bed, in feet (m).
• Distance, D, from the ground surface to the bottom ofthe test section, in feet (m).
• Time that the test is started and the time measure-ments are made.
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Figure 17-6.—Location of zone 1 lowerboundary for use in unsaturated materials.
• Effective head, the difference in feet (m) between theelevation of the free water surface in the pipe and theelevation of the gauge plus the applied pressure. If apressure transducer is used, the effective head in thetest section is the difference in pressure before wateris pumped into the test section and the pressurereadings made during the test.
The following examples show some typical calculationsusing Methods 1 and 2 in the different zones shown infigure 17-5. Figure 17-6 shows the location of the zone 1lower boundary for use in unsaturated materials.
Pressure permeability tests examples using Methods 1and 2:
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Zone 1, Method 1
Given: U = 75 feet, D = 25 feet, � = 10 feet, r =0.5 foot, h1 = 32 feet, h2 = 25 lb/in2 = 57.8 feet, and Q = 20 gal/min = 0.045 ft3/sec
From figure 17-4: head loss, L, for a 1¼-inch pipe at20 gal/min is 0.76 foot per 10-foot section. If thedistance from the gauge to the bottom of the pipe is22 feet, the total head loss, L, is (2.2) (0.76) = 1.7 feet.
H = h1 + h2 - L = 32 + 57.8 - 1.7 = 88.1 feet of effectivehead, Tu = U - D + H = 75 - 25 + 88.1 = 138.1 feet
The values for X and Tu/� lie in zone 1 (figure 17-6). To determine the unsaturated conductivitycoefficient, Cu, from figure 17-7:
then:
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Figure 17-7.—Conductivity coefficientsfor permeability determination in
unsaturated materials with partiallypenetrating cylindrical test wells.
Zone 2
Given: U, �, r, h2, Q, and L are as given in example1, D = 65 feet, and h1 = 72 feet
If the distance from the gauge to the bottom of theintake pipe is 62 feet, the total L is (6.2) (0.76) =4.7 feet.
H = 72 + 57.8 - 4.7 = 125.1 feet
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Figure 17-8.—Conductivity coefficientsfor semispherical flow in saturated
materials through partially penetratingcylindrical test wells.
Tu = 75 - 65 + 125.1 = 135.1 feet
The test section is located in zone 2 (figure 17-6). Todetermine the saturated conductivity coefficient, Cs,from figure 17-8:
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Method 1:
Method 2:
Zone 3
Given:
U,�, r, h2, Q, and L are as given in example 1, D =100 feet, h1 = 82 feet, and S = 60 feet
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If the distance from the gauge to the bottom of theintake pipe is 97 feet, the total L is (9.7) (0.76) =7.4 feet.
H = 82 + 57.8 - 7.4 = 132.4 feet
Method 1:
Method 2:
Multiple Pressure Tests
Multiple pressure tests are pressure permeability teststhat apply the pressure in three or more approximatelyequal steps. For example, if the allowable maximumdifferential pressure is 90 lb/in2 (620 kilopascal [kPa]), thetest would be run at pressures of about 30, 60, and90 lb/in2 (210 kPa, 415 kPa, and 620 kPa).
Each pressure is maintained for 20 minutes, and watertake readings are made at 5-minute intervals. The
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pressure is then raised to the next step. After thehighest step, the process is reversed and the pressuremaintained for 5 minutes at the same middle and lowpressures. A plot of take against pressure for the fivesteps is then used to evaluate hydraulic conditions.These tests are also discussed in chapter 16.
Hypothetical test results of multiple pressure tests areplotted in figure 17-9. The curves are typical of thoseoften encountered. The test results should be analyzedusing confined flow hydraulic principles combined withdata obtained from the core or hole logs.
Probable conditions represented by plots in figure 17-9are:
1. Very narrow, clean fractures. Flow is laminar,permeability is low, and discharge is directlyproportional to head.
2. Practically impermeable material with tightfractures. Little or no intake regardless of pressure.
3. Highly permeable, relatively large, open fracturesindicated by high rates of water intake and no backpressure. Pressure shown on gauge caused entirelyby pipe resistance.
4. Permeability high with fractures that are relativelyopen and permeable but contain filling materialwhich tends to expand on wetting or dislodges andtends to collect in traps that retard flow. Flow isturbulent.
5. Permeability high, with fracture filling materialwhich washes out, increasing permeability with time.Fractures probably are relatively large. Flow isturbulent.
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Figure 17-9.—Plots of simulated, multiplepressure permeability tests.
6. Similar to 4, but fractures are tighter and flow islaminar.
7. Packer failed or fractures are large, and flow isturbulent. Fractures have been washed clean; highlypermeable. Test takes capacity of pump with little orno back pressure.
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8. Fractures are fairly wide but filled with clay gougematerial that tends to pack and seal when underpressure. Takes full pressure with no water intakenear end of test.
9. Open fractures with filling that tends to first blockand then break under increased pressure. Probablypermeable. Flow is turbulent.
Gravity Permeability Tests
Gravity permeability tests are used primarily in uncon-solidated or unstable materials. Gravity tests areperformed in unconsolidated materials but are typicallyperformed at greater depths. Gravity tests can be runonly in vertical or near-vertical holes. A normal testsection length is 5 feet (1.5 m). If the material is stable,stands without caving or sloughing, and is relativelyuniform, sections up to 10 feet (3 m) long may be tested.Shorter test sections may be used if the length of thewater column in the test section is at least five times thediameter of the hole. This length to diameter ratio isused in attempting to eliminate the effect of the bottomof the borehole. The diameter of the borehole sidewallsis the outside of any screen and annular packing of sandand or gravel. After each test, the casing for open holetests is driven to the bottom of the hole, and a new testsection is opened below the casing. If perforated casingis used, the pipe can be driven to the required depth andcleaned out, or the hole can be drilled to the requireddepth and the casing driven to the bottom of the hole andthe hole cleaned out.
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Cleaning and Developing Test Sections
Each newly opened test section should be developed bysurging and bailing. Development should be done slowlyand gently so that a large volume of loosely packedmaterial is not drawn into the hole and only thecompaction caused by drilling is broken down and thefines will be removed from the formation.
Measurement of Water Levels Through Protective Pipe
Measuring water depths inside a ¾- to 1½-inch- (20- to40-mm-) small-diameter perforated pipe in the holedampens wave or ripple action on the water surfacecaused by the inflow of water resulting in more accuratewater level measurements. Water may also beintroduced through the pipe and water levelmeasurements made in the annular space between thepipe and the casing.
In an uncased test section in friable materials liable towash, the end of the pipe should rest on a 4- to 6-inch(100- to 150-mm) cushion of coarse gravel at the bottomof the hole. In more stable material, the pipe may besuspended above the bottom of the hole, but the bottomof the pipe should be located at least 2 feet (0.6 m) belowthe top of the water surface maintained in the hole.
Pumping Equipment and Controls
Pressure is not required in the test, but pump capacityshould be adequate to maintain a constant head duringthe test.
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Accurate control of the flow of water into the casing is aproblem on many gravity tests. The intake of the testsection necessary to maintain a constant head issometimes so small that inflow cannot be sufficientlycontrolled using a conventional arrangement. A precisemethod of controlling low flows, such as using needlevalves, is important. Many meters are inaccurate atvery low flows.
Water Meters
Water deliveries in gravity tests may range from lessthan 1 gal/min (3.8 L/min) to several hundred gallons perminute. No one meter is sufficiently accurate at allranges. Two meters are recommended: (1) a 4-inch(100-mm) propeller- or impeller-type meter to measureflows between 50 and 350 gal/min (200 and 1,300 L/min)and (2) a 1-inch (25-mm) disk-type meter for flowsbetween 1 and 50 gal/min (4 and 200 L/min). Each metershould be equipped with an instantaneous flow indicatorand a totalizer. Water meters should be testedfrequently.
Length of Time for Tests
As in pressure tests, stabilized conditions are veryimportant if good results are to be obtained from gravitytests. Depending on the type of test performed, one oftwo methods is used. In one method, the inflow of wateris controlled until a uniform inflow results in a stabilizedwater level at a predetermined depth. In the othermethod, a uniform flow of water is introduced into thehole until the water level stabilizes.
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Arrangement of Equipment
A recommended arrangement of test equipment, startingat the source of water, is: suction line; pump; waterlineto settling and storage tank or basin, if required; suctionline; centrifugal or positive displacement pump; line towater meter inlet pipe; water meter; short length of pipe;valve; and the waterline to the casing. All connectionsshould be kept as short and straight as possible, and thechanges in diameter of hose, pipe, etc., should be kept toa minimum. If a constant head tank is used, the tankshould be placed so that water flows directly into thecasing.
Gravity Permeability Test - Method 1
For tests in unsaturated and unstable material usingonly one drill hole, Method 1 is the most accurateavailable. Because of mechanical difficulties, this testcannot be economically carried out at depths greaterthan about 40 feet (12 m) when gravel fill must be usedin the hole. When performing the test, after theobservation and intake pipes are set, add gravel in smallincrements as the casing is pulled back; otherwise, thepipes may become sandlocked in the casing. For tests inunsaturated and unstable material at depths greaterthan about 12 meters (40 feet), Method 2 should be used(described later).
The procedures for testing soil conditions are:
Unconsolidated Materials – A 6-inch (150-mm) orlarger hole is drilled or augered to the test depth andthen carefully developed. A cushion of coarse gravelis placed at the bottom of the hole, and the feed pipe
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(I) and the observation pipe (O) are set in position(figure 17-10). After the pipes are in position, thehole is filled with medium gravel to a depth at leastfive times the diameter of the hole. If the drill holewall material will not stand without support, the holemust be cased to the bottom. After casing, the gravelcushion and pipes are put in, and the casing is pulledback slowly as medium gravel is fed into the hole.The casing should be pulled back only enough toensure that the water surface to be maintained in thehole will be below the bottom of the casing. About 4inches (100 mm) of the gravel fill should extend upinto the casing.
A metered supply of water is poured into the feedpipe until three or more successive measurements ofthe water level taken at 5-minute intervals throughthe observation pipe are within 0.2 foot (5 mm). Thewater supply should be controlled so that thestabilized water level is not within the casing and islocated more than five times the hole diameter abovethe bottom of the hole. The water flow generally hasto be adjusted to obtain the required stabilized level.
Consolidated Materials – The gravel fill and casingmay be omitted in consolidated material orunconsolidated material that will stand withoutsupport even when saturated. A coarse gravelcushion is appropriate. The test is carried out as inunconsolidated, unstable materials.
Tests should be made at successive depths selected sothat the water level in each test is located at or above thebottom of the hole in the preceding test. Thepermeability coefficients within the limits ordinarily
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employed in the field can be obtained from figures 17-7and 17-8. The test zone and applicable equations areshown in figures 17-6 and 17-10.
Data required for computing the permeability may not beavailable until the hole has penetrated the water table.The required data are:
• Radius of hole, r, in feet (meters)
• Depth of hole, D, in feet (meters)
• Depth to bottom of casing, in feet (meters)
• Depth of water in hole, H, in feet (meters)
• Depth to top of gravel in hole, in feet (meters)
• Length of test section, �, in feet (meters)
• Depth-to-water table, Tu, in feet (meters)
• Steady flow, Q, introduced into the hole to maintain auniform water level, in ft3/sec (m3/sec)
• Time test is started and time each measurement ismade
Some examples using Method 1 are:
Zone 1, Method 1
Given:
H = � = 5 feet,�� = 0.5 foot, D = 15 feet, U = 50 feet, andQ = 0.10 ft3/sec
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145 Figure 17-10.—Gravity permeability test (Method 1).
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Tu = U-D + H = 50 - 15 + 5 = 40 feet, also Tu /� = 40/5 = 8
The values for X and Tu /� lie in zone 1 (figure 17-6). Todetermine the unsaturated conductivity coefficient, Cu,from figure 17-7:
Zone 2, Method 1
Given:
H, �, r, U, and Q are as given in example 1, D = 45 feet
Points Tu /� and X lie in zone 2 on figure 17-6.
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To determine the saturated conductivity coefficient, Cs,from figure 17-8:
From figure 17-10:
Gravity Permeability Test - Method 2
This method may give erroneous results when used inunconsolidated material because of several uncontrollablefactors. However, it is the best of the available pump-intests for the conditions. The results obtained areadequate in most instances if the test is performedcarefully. When permeabilities in streambeds or lakebedsmust be determined below water, Method 2 is the onlypractical gravity test available.
A 5-foot (1.5-m) length of 3- to 6-inch- (75- to 150-mm-)diameter casing uniformly perforated with the maximumnumber of perforations possible without seriouslyaffecting the strength of the casing is best. The bottom ofthe perforated section of casing should be beveled on theinside and case hardened for a cutting edge.
The casing is sunk by drilling or jetting and driving,whichever method will give the tightest fit of the casingin the hole. In poorly consolidated material and soilswith a nonuniform grain size, development by filling thecasing with water to about 3 feet (1 m) above theperforations and gently surging and bailing is advisable
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before making the test. A 6-inch (150-mm) coarse gravelcushion is poured into the casing, and the observationpipe is set on the cushion.
A uniform flow of water sufficient to maintain the waterlevel in the casing above the top of the perforations ispoured into the well. The water should be pouredthrough a pipe and measurements made between thepipe and casing or reversed if necessary. Depth of watermeasurements are made at 5-minute intervals untilthree or more measurements are within ±0.2 foot(60 mm) of each other.
When a test is completed, the casing is sunk anadditional 5 feet (1.5 m), and the test is repeated.
The test may be run in stable consolidated materialusing an open hole for the test section. Because thebottom of the casing is seldom tight in the hole andsignificant error may result from seepage upward alongthe annular space between the casing and the wall of thehole, this is not recommended. Measurements should bemade to the nearest 0.01 foot (3 mm). The values of Cu
and Cs within the limits ordinarily employed in the fieldcan be obtained from figures 17-7 and 17-8. The zone inwhich the test is made and applicable equations can befound in figures 17-6 and 17-11, respectively.
Some data required for computing permeability are notavailable until the hole has encountered the water table.
The recorded data are supplemented by this informationas the data are acquired. The data recorded in each testare:
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149 Figure 17-11.—Gravity permeability test (Method 2).
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• Outside radius of casing, r1
• Length of perforated section of casing, �
• Number and diameter of perforations in length �
• Depth to bottom of hole, D
• Depth-to-water surface in hole
• Depth of water in hole, H
• Depth-to-water table, U
• Thickness of saturated permeable material aboveunderlying relatively impermeable bed, S
• Steady flow into well to maintain a constant waterlevel in hole, Q
• Time test is started, and measurement is made
Some examples using Method 2 are:
Zone 1, Method 2
Given:
H = 10 feet, � = 5 feet, r1 = 0.25 foot, D = 20 feet,U = 50 feet, Q = 0.10 ft3/sec, 128 0.5-inch-diameterperforations, bottom of the hole is sealed
Area of perforations = 128� r1 2 = 128� (0.25)2 =
25.13 in2 = 0.174 ft2
Area of perforated section = 2�r� = 2� (0.25) (5) =
7.854 ft2
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Points Tu /� and X lie in zone 1 on figure 17-6.
Find Cu from figure 17-7:
then, Cu = 1,200
From figure 17-11:
Zone 2, Method 2
Given:
Q, H, �, r1, re, U, �/H, and H/re same as Zone 1,Method 2, D = 40 feet
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Points Tu /� and X lie in zone 2 on figure 17-6.
Find Cs from figure 17-8:
From figure 17-11:
Zone 3, Method 2
Given:
Q, H, �, r1, re, �/H, H/re, U, Cs, and �/re are as given inZone 2, Method 2, S = 60 feet
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From figure 17-11:
Gravity Permeability Test - Method 3
This method is a combination of gravity permeability testMethods 1 and 2. The method is the least accurate, but isthe only one available for gravelly or coarse soils(figure 17-12).
In some materials, a casing that is beveled and casehardened at the bottom will not stand up to the driving.This is particularly true in gravelly materials where theparticle size is greater than about 1 inch (25 mm). Underthese conditions, Method 3 would probably not besatisfactory because a drive shoe must be used. Using adrive shoe causes excessive compaction of the materialsand forms an annular space around the casing.
On completion of each test, a 3- to 6-inch-diameter (90-to 150-millimeter) perforated casing is advanced 5 feet(1.5 m) by drilling and driving. After each new testsection is developed by surging and bailing, a 6-inch(150-mm) gravel cushion is placed on the bottom tosupport the observation pipe. A uniform flow of watersufficient to maintain the water level in the casing just atthe top of the perforations is then poured into the well.The water is poured directly into the casing, andmeasurements are made through a 1¼-inch (32-mm)observation pipe. The test should be run until three or
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Figure 17-12.—Gravity permeability test (Method 3).
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more measurements taken at 5-minute intervals arewithin ±0.2 foot (60 mm) of the top of the perforations.
The values of Cu and Cs, within the limits ordinarilyemployed in the field, can be obtained from figures 17-7and 17-8. The zone in which the test is made andapplicable equations can be found on figures 17-6 and17-12, respectively.
The data recorded in each test are:
• Outside radius of casing, r1, in feet (meters)
• Length of perforated section of casing, �, in feet(meters)
• Number and diameter of perforations in length �
• Depth to bottom of hole, D, in feet (meters)
• Depth-to-water surface in hole, in feet (meters)
• Depth of water in hole, in feet (meters)
• Depth-to-water table, in feet (meters)
• Steady flow into well to maintain a constant waterlevel in hole, Q, in ft3/sec (m3/sec)
• Time test is started and time each measurement ismade
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Zone 1, Method 3
Given: Q = 10.1 gal/min = 0.023 ft3/sec, H = � = 5 feet,D = 17 feet, U = 71 feet, Tu = 54.5 feet, re = 0.008 foot,and r1 = 1.75 inches = 0.146 foot (nominal 3-inch casing)
These points lie in zone 1 (figure 17-6).
Find Cu from figure 17-7:
then, Cu = 640
From figure 17-12:
Zone 2, Method 3
Given: Q, H, �, U, re, and r1 are as given in Zone1,Method 3, D = 66 feet and Tu = 10 feet
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These points lie in zone 2 (figure 17-6).
Find Cs from figure 17-8:
From figure 17-12:
Gravity Permeability Test - Method 4
This method can be used to determine the overall averagepermeability of unsaturated materials above a widespreadimpermeable layer. The method does not detect perme-ability variations with depth. The method is actually anapplication of steady-state pumping test theory.
A well, preferably 6 inches (150 mm) or larger indiameter, is drilled to a relatively impermeable layer ofwide areal extent or to the water table. If the saturatedthickness is small compared to the height of the watercolumn that can be maintained in the hole, a water tablewill act as an impermeable layer for this test. The well isuncased in consolidated material, but a perforated casing
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casing or screen should be set from the bottom to about5 feet (1.5 m) below the ground surface in unconsolidatedmaterial. The well should be developed by pouring waterinto the hole while surging and bailing before testing.
Before observation wells are drilled, a test run of theintake well should be made to determine the maximumheight, H, of the column of water that can be maintained(figure 17-13) above the top of the impermeable layer. A1- to 1¼-inch (25- to 32-mm) observation pipe should beinserted to near the bottom of the intake well to forwater-level measurements. The spacing of theobservation wells can be determined from this test run.
A minimum of three observation wells should beinstalled to the top of the impermeable layer or watertable. Suitable pipe, perforated for the bottom 10 to 15feet (3 to 4.5 m), should be set to the bottom of thesewells. The observation wells should be offset from theintake well by distances equal to multiples of one-halfthe height, H, of the water column that will bemaintained in the intake well.
The elevations of the top of the impermeable layer orwater table in each well are determined, and the test isstarted. After water has been poured into the intake ata constant rate for an hour, measurements are made ofwater levels in the observation wells. Measurements arethen made at 15-minute intervals, and each set ofmeasurements is plotted on semi-log paper. The square
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Figure 17-13.—Gravity permeability test(Method 4).
of the height of the water level above the top of theimpermeable bed, h2, is plotted against the distance fromthe intake well to the observation holes, d, for each hole(figure 17-14). When the plot of a set of measurementsis a straight line drawn through the points within thelimits of plotting, conditions are stable and thepermeability may be computed.
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Figure 17-14.—Plot of h2 versus d for gravitypermeability test (Method 4).
The data recorded in each test are:
• Ground elevations at the intake well and theobservation wells
• Elevations of reference points at the intake well andthe observation wells, in feet (meters)
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• Distances from center of the observation wells to centerof the intake well, d1, d2, and d3, in feet (meters)
• Elevation of top of impermeable bed at the intake welland the observation wells, in feet (meters)
• Depths of water below reference point in the intake welland the observation wells at 15-minute intervals, infeet (meters)
• Uniform flow of water, Q, introduced into well, in ft3/sec(m3/sec)
• Time pumping is started and time each measurementis made
Method 4
Given: U = 50 feet, Q = 1 ft3/sec, H = 30 feet, d1 =15 feet, d2 = 30 feet, d3 = 60 feet, h1 = 23.24 feet, h2 = 17.89 feet, h3 = 10.0 feet, h1
2 = 540 ft2, h22 = 320 ft2,
and h32 = 100 ft2
A plot of d against h2, as shown on figure 17-14, showsthat a straight line can be drawn through the plottedpoints, meaning that stable conditions exist and thepermeability may be computed.
From figure 17-13:
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Falling Head Tests
Falling head tests are used primarily in open holes inconsolidated rock. Falling head tests use inflatablepackers identical to those used for pressure testing andcan be used as an alternate method if the pressuretransducer or other instrumentation fails. The method ofcleaning the hole is the same as that described underpressure testing.
Tests Below the Static Water Level
Tests below the static water level should be done asfollows:
• Use inflatable straddle packers at 10-foot (3-m) spacingon a 1¼-inch (32-mm) drop pipe (inside diameter =1.38 inches [35 mm]). Set packers initially at thebottom of the hole and inflate to 300 lb/in2 (2,000 kPa)of differential pressure.
• After packers are inflated, measure the water level inthe drop pipe three or more times at 5-minute intervalsuntil the water level stabilizes. The stabilized level willbe the static water level in the test section.
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• Pour 2 gallons (8 liters [L]) or more of water as rapidlyas possible into the drop pipe after the water levelstabilizes. One gallon (4 l) of water will raise the waterlevel in a 1¼-inch (32-mm) pipe 13 feet (4 m) if thesection is tight.
• Measure the water level as soon as possible after thewater is poured in. Measure the initial depth to water,record the time as soon as possible, and repeat twice at5-minute intervals. If the rate of decline exceeds 15 feet(4.5 m) in 13 minutes, the transmissivity of a 10-foot (3-m) test section is greater than 200 ft2 (18 m2) per year,and the average permeability is greater than 20 feet(6 m) per year.
The transmissivity value determined is only anapproximation, but the value is sufficiently accurate formany engineering purposes.
The equation for analysis is:
where:
T = transmissivity of test section, in ft2/sec (m2/sec)
V = volume of water entering test section in period�t, in ft3 (m3). (A 1-foot [30-cm] decline in1¼-inch [32-mm] pipe = 0.01 ft3 [0.000283 m3])
s = decline in water level in period �t, in feet(meters)
�t = period of time, in seconds, between successivewater level measurements (i.e., t1 - to, t2 - t1, etc.)
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• If the log indicates the test section is uniform andwithout obvious points of concentrated leakage, theaverage permeability of the test section, in feet persecond (m/sec), can be estimated from K = T/�, where� is the length of the test section, in feet (m). If the logindicates a predominantly impervious test section, butincludes a zone or zones of concentrated flow, theaverage K of the zones can be estimated from K = T/��,where �� is the thickness of the permeable zone orzones, in feet (m).
• After each test, deflate the packers, raise the teststring 10 feet (3 m), and repeat the test until theentire hole below the static water level has beentested.
Tests Above the Water Table
Tests above the water table require different proceduresand analyses than tests in the saturated zone. Testsmade in sections straddling the water table or slightlyabove the water table will give high computed values ifthe equations for tests below the static water level areused and low computed values if the following equationsare used. For tests above the water table, the followingprocedure is used:
• Install a 10-foot- (3-m-) spaced straddle packer at thebottom of the hole, if the hole is dry, or with the top ofthe bottom packer at the water table if the holecontains water. Inflate the packer.
• Fill the drop pipe with water to the surface, if possible,otherwise, to the level permitted by pump capacity.
• Measure the water level in the drop pipe and recordwith time of measurement. Make two or more similarmeasurements while the water-table declines.
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• Upon completion of a test, raise the packer 10 feet (3 m)and repeat this procedure until all of the open orscreened hole is tested.
The equation for analysis is:
where:
r1 = inside radius of drop pipe, in feet���������������� ����������� ��������������������
��
� �������� �������� ����� ������ � ��� ���� ������ �����������������������������������!��
�� � ������������!�������
� ��
���
�� ����������
������ � ���������"���#!�������
�� � ������!�!$������
� � !��$��� � %����� �!���� ��� #���� � �����������!���%������������������������ ���������) (H0, H1, H2 lengths at time ofmeasurements t0, t1, t2, etc.)
• For the particular equipment specified and a 10-foot(3-m) test section, the equation may be simplified to:
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Slug Tests
Slug tests are performed by “rapidly” changing waterlevels in a borehole. The rapid change is induced byadding or removing small quantities of water, air, or anobject that displaces the groundwater. The timerequired to restore the water level to its original level isused to calculate the permeability. Slug tests aretypically performed in areas where access or budget islimited or the extraction or addition of water has apotential impact to the surrounding area. Slug tests areappropriate where the aquifer will not yield enoughwater to conduct an aquifer test or the introduction ofwater could change or impact the water quality. A majorfactor in conducting slug tests is ensuring that the waterlevel during the test reflects the aquifer characteristicsand is not unduly affected by the well construction.Where the water surface is shallow and clean water isreadily available, water injection or bailing is often theeasiest method. The displacement or air injectionmethod may be desirable at locations where the waterlevel is deep and rapid injection or removal of water isdifficult.
A number of slug test methods exist. The choice dependson the hydrologic and geologic conditions and the wellsize and construction.
Selecting the Slug Test
The method of inducing a rise or fall in the water surfacedepends on the purpose of the test and conditions at thesite. Where the water level is shallow and clean wateris readily available, water injection or bailing is often theeasiest method. One limitation of the test accuracy isthe initial water flowing down the inside wall of the well.Causing a rapid rise by displacing water in the well by
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dropping a pipe or weight or injecting air may bepreferable at remote sites where water may not bereadily available. The displacement or air injectionmethod may also be desirable at locations where thewater level is deep and rapid injection or removal ofwater may require collection and treatment or at wellsites that are being used for water chemistry studies.
Conducting the Slug Test
Before introducing the slug, the well’s sidewall, screen,or filter pack needs to be clear of any obstructions thatwill impede the movement of water from the riser to thesurrounding materials. The riser diameter and lengthneed to be measured as accurately as possible, and thewater level must be stabilized and recorded as accuratelyas possible. The water level measurements must beginimmediately following the introduction of the slug.Where the water level changes slowly, measurementsmay be made by using a water level indicator. For mosttests, water levels should be recorded by a pressuretransducer and automatic data logger.
Hvorslev Slug Test
The Hvorslev slug test is the simplest method ofanalysis. This analysis assumes a homogeneous,isotropic, infinite medium in which both the soil andwater are incompressible. It neglects well bore storageand is not accurate where a gravel pack or thick sandpack is present. Figure 17-15 is a sketch of the geometryof this test and the method of analysis. This method isused where the slug test is conducted below an existingwater surface.
The test analysis requires graphing the change in headversus time. Head changes are given by (H-h)/H-H0 and
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Figure 17-15.—Hvorslev piezometer test.
should be plotted semi-log against time. The graphshould approximate a straight line; and at the point 0.37,the T0 value is defined as the basic time lag. Using thegraphical solution for T0, the dimension of the cavity, andthe appropriate shape factor, F, a solution forpermeability can be found by:
Figure 17-16 provides shape equations for various wellgeometries.
Bouwer Slug Test
The Bouwer slug test assumes no aquifer storage andfinite well bore storage. The well can be partiallypenetrating and partially screened. The method was
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Figure 17-16a.—Shape factors for computing permeability from variable head tests.
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Figure 17-16a (cont.).—Shape factors for computing permeability from variable head
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Figure 17-16b.—Shape factor coefficient Fs.
originally developed for unconfined aquifers but can alsobe used for confined or stratified aquifers if the top of thescreen or perforated section is located some distancebelow the upper confining layer. The analysis is basedon the Thies equation and determines permeability, K, ofthe aquifer around the well from the equation:
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where:
� = length of the perforated section of the casing orriser
s0 = the vertical difference between the water surfaceinside the well and the static water level at timezero
st = s at time t
t = time of reading
rc = inside radius of the riser or casing
r = the effective radius of the well, including theperforated casing, sand or gravel pack, and anyremaining annular space to the sidewall of theborehole
de = effective radial distance; the distance between
the well and the observation well; the distanceover which the water level, s, returns to thestatic level
H = the height of water within the well
S = aquifer thickness
See figure 17-17 for the configuration definition.
The values of de were determined using an electricalresistance analog network. The effective radial distanceis influenced by the well diameter, well screen length,well depth, and the aquifer thickness. Various values forrc, �, H, and S were used in the analog network foranalysis of their impacts on de.
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Figure 17-17.—Slug test on partially penetrating,screened well in unconfined aquifer with gravel
pack and developed zone around screen.
The term, ln (de/r), is related to the geometry of the testzone and the amount of aquifer penetration of the well.Two separate solutions are required to address partiallypenetrating wells and fully penetrating wells. For
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partially penetrating wells, an empirical equation relatingln (de/r) to the geometry of the test zone is:
In this equation, A and B are dimensionless coefficientsthat can be read on figure 17-18. An effective upper limitof ln[(S-H)/r] is 6. If the computed value of ln[(S-H)/r] isgreater than 6, then 6 should be used in the equation forln(de /r). When S = H, the well is fully penetrating, andthe value of C should be used from figure 17-18 in theequation.
Values of the field test data should be plotted as recovery,s, versus time for each data point reading. The value sshould be plotted on a y-axis log scale, and values forcorresponding time should be plotted on the x-axis. Thepoints should approximate a straight line, which indicatesgood test data. Areas of the data that plot as curves(usually at the beginning of the test or near the end of thetest) should not be used in the computation.
Piezometer Test
The piezometer test measures the horizontal permeabilityof individual soil layers below a water surface. This test
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Figure 17-18.—Dimensionless parameters A, B,and C as a function of �/re (F for calculation
of ln(de/re)).
surface. This test may apply to large diameter directpush technology, as well as to any depth that an openhole can be maintained. This test is preferred over theauger-hole test described in section 10-6 of the GroundWater Manual, especially when the soils tested are lessthan 1.5 feet (0.5 m) thick and are below the water table.This method is particularly good for determining whichlayer below the capillary zone is an effective barrier.
Equipment
The following items are suggested equipment for thepiezometer test.
• Riser between 1- to 2-inch (24- to 50-mm) insidediameter for a depth of around 15 feet (4.5 m) andblack iron pipe with smooth inside wall for depthsgreater than 15 feet (4.5 m)
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• Equipment capable of installing the riser and cavitybelow the riser
• Pump with hose and controller or bailer that will fitinside the casing
• Bottle brush for cleaning soil film from the inside ofthe test riser if the riser is driven without a protectivepoint that can prevent soils from filling the inside ofthe tube
• Water level detector, stop watch, and transducer anddata logger
Procedure
The test layer should be at least 1 foot (30 cm) thick sothat a 4-inch (10-cm) length of cased hole or cavity can belocated in the middle of the layer. This placement isespecially important if a marked difference in the layersexists above and below the test layer. The differencesmay be changes in the percentages of fines (>15 percent),overall changes in the soil gradations, soil structure, ordegree of cementation or induration within the soilhorizon. After selecting an appropriate interval based onthe soil investigation, an adjacent hole within 2 feet(0.6 m) of the test hole is advanced to around 2.0 feet(0.6 m) above the bottom of the 4-inch (10-cm) testinterval, if using direct push technology, or to the top ofthe 4-inch (10-cm) interval. Then use a smaller diameterauger to ream the final 4-inch (10-cm) interval for theriser pipe. The final 2.0 feet (0.6 m) are driven to ensurethat a reasonably good seal is obtained and also tominimize the disturbance. The lower 4 inches (10 cm) ofthe borehole are exposed, and the cavity must remainopen. After some recovery has occurred, the riser shouldbe cleaned with a brush to remove any soil film unless
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should be screened within the lower cavity and thencleaned out by gently pumping or bailing water andsediment from the piezometer.
After the water surface has stabilized, the transducer isinstalled. The riser is bailed or pumped, depending on thediameter of riser and the depth to water. It is notnecessary to remove all the water in the screened interval,but the water level should be lowered enough that at leastthree readings during the first half of the water rise willgive consistent results.
Calculations
After completing the piezometer test, the permeability iscalculated from:
where:
s1 and s2 = distance from static water level at times t1
and t2, in inches (cm)
t2 - t1 = time for water level change from s1 to s2,in seconds
Ca = a constant for a given flow geometry, ininches (cm)
� = length of open cavity, in inches (cm)
d = H-�, distance from the static water level tothe top of the cavity, in inches (cm)
b = distance below the bottom of the cavity tothe top of next layer, in inches (cm)
A sample calculation using this equation is shown infigure 17-19. The constant, Ca, may be taken from curves
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A sample calculation using this equation is shown infigure 17-19. The constant, Ca, may be taken fromcurves shown in figures 17-19 or 17-20. The curve onfigure 17-19 is valid when d and b are both largecompared to �. When b = 0 and d is much greater than�, the curve will give a Ca factor for � = 4 and d = 1 thatwill be about 25 percent too large.
The chart on figure 17-20 is used for determining Ca
when upward pressure exists in the test zone. Whenpressures are present, additional piezometers must beinstalled. The tip of the second piezometer should beplaced just below the contact between layers in layeredsoil (figure 17-21). In deep, uniform soils, the secondpiezometer tip should be placed an arbitrary distancebelow the test cavity.
After installing the second piezometer, the followingmeasurements should be made:
• Distance, �d, in feet (m), between the ends of the riserpipes
• Difference, �H, in feet (m), between water surfaces inthe two piezometers at static conditions
• Distance, d’, in feet (m), between the center of thelower piezometer cavity and the contact between soillayers in the layered soils
The Ca value from figure 17-20 is used in the equation todetermine the permeability.
Limitations
Installation and sealing difficulties encountered in coarsesand and gravel are the principal limitations of the
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179 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �
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Figure 17-20.—Chart for determining Ca if upward pressure exists in the test zone.
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Figure 17-21.— Sample calculation for the piezometer test with upward pressure
in the test zone.
piezometer test for permeability. Also, when the riserbottoms in gravel, a satisfactory cavity cannot beobtained. The practical limit of hole depth is about20 feet (6 meters). Deeper holes require largerdiameters (greater than 2 inches [5cm]), and driving theriser deeper is difficult.
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Details on the equipment requirements and proceduresare provided in chapter 3 of the Drainage Manual.Permeameter tests are typically restricted to shallowboreholes or excavations and require time to set up theequipment and perform the test. Where thepermeability is relatively high (>1,000 feet per year [10-3
cm per second]), these tests require large amounts ofwater. With material having permeability values greaterthan 106 feet per year (10 cm/sec), laboratorypermeability testing is more cost effective. The samplesare collected and tested in the laboratory in accordancewith Reclamation Procedure 5605.
Bibliography
Bureau of Reclamation, U.S. Department of the Interior,Drainage Manual, 1993.
Bureau of Reclamation, U.S. Department of the Interior,Ground Water Manual, 1995.
Figure 18-1.—Riprap properly placed on bedding. The riprap is angular, quarried rock, and the
bedding is rounded stream gravel. The backhoe is placing and arranging the rock on the bedding.
Chapter 18
RIPRAP
Introduction
Riprap is preferably a relatively thin layer of large,approximately equidimensional, durable rock fragmentsor blocks placed on bedding to dissipate water energy andprotect a slope, channel bank or shore from erosion causedby the action of runoff, currents, waves or ice (figure 18-1).Bedding is usually a layer of sand and gravel placedunder the riprap to prevent erosion of the material fromunder the riprap. Most dam embankments contain atleast one zone that uses rock. Rock is used as riprap forprotection against erosion or as rockfill and filter zonesthat strengthen or drain the embankment.
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The terms “slope protection” and “riprap” are often usedinterchangeably, but not all slope protection is riprap.Soil cement is also commonly used as slope protection.Riprap is an assemblage of rocks “nested” together toprotect a structure or area from the action of water. Thestability of an assemblage of rocks is a function of theindividual rock’s size, shape, weight, and durability. Anassemblage of rocks depends on the individual rockcharacteristics for stability and also on the site conditions,grading, and thickness. The assemblage of rocks isdesigned to minimize voids and thickness of the ripraplayer to keep the volume of material as low as possible.Proper placement interlocks the individual fragments intoa layer of rocks that resists the action of water.Figure 18-2 shows what can happen if riprap is notdesigned, obtained, and placed properly.
Riprap should be “hand” placed to reduce the void spaceand maximize the interlocking arrangement, but rarely isthis economical (figure 18-3). Most riprap is dumped andfalls into place by gravity with little or no additionaladjustment (figure 18-4). Because of this, individualpieces of riprap must have appropriate characteristics sothat the rocks can be processed, handled, and placed sothat the layer remains intact for the life of the project.
This chapter discusses: (1) riprap source evaluation,(2) onsite inspection to ensure that the samples are appro-priate and that specified material is being produced fromthe source, (3) presentation of information to designersand estimators, and (4) waste factors in riprap produc-tion. A geologic background, a knowledge of blastingmethods and types of explosives, and an understanding ofthe equipment involved in the processing, hauling, andplacing of riprap is important to riprap evaluation,production, and placement. Most of the following discus-sion applies to rock adequate for aggregate and to larger
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Figure 18-2.—Improperly designed, obtained, and placed riprap.
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Figure 18-3.—Hand-placed riprap.
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187
Figure 18-4.—Dumped riprap.
rock fragments used for roads, breakwaters, and jetties.However, this chapter is oriented toward acquiringsuitable material for riprap.
This chapter should be used in conjunction withUSBR Procedure 6025, Sampling and Quality EvaluationTesting of Rock for Riprap Slope Protection, and
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USBR Design Standard No. 13 for Embankment Dams(DS13). Riprap design is discussed in “Chapter 7, RiprapSlope Protection,” of USBR Design Standard DS13. Otherdocuments, such as the U.S. Army Corps of Engineers’Engineering Manual 1110-2-2301, Engineering andDesign - Test Quarries and Test Fills, and EngineeringManual 1110-20-1601, Engineering and Design -Hydraulic Design of Flood Control Channels, also provideinformation on design and source evaluation. Note: Testprocedures developed to test similar riprap characteristicsby different organizations are not necessarily the same.The appropriate test procedure should be selected basedon the actual test and the available test equipment.
Evaluation
Much of the following discussion is more guidance thanhard and fast rules or requirements. What is unac-ceptable riprap at one location may be acceptable atanother site. Remember that a riprap source must becapable of providing suitable material in sufficientquantities at a reasonable cost. The three elements inevery source evaluation are: quality, quantity, and cost.
Quality
Rock quality is determined by laboratory testing, but fieldpersonnel input and selection of the samples for testingare critical in determining the riprap quality. There arenumerous quarries and pits capable of producingaggregate, but not all sources are suitable for theproduction of riprap. Riprap sources must produce riprapof the necessary weight, size, shape, gradation, anddurability to be processed and placed and then remain“nested” for the life of the project. Performance on
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189
existing structures is a valuable method of assessingriprap quality from a particular source.
Shape
The shape of individual rock fragments affects theworkability and nesting of the rock assemblage. Natural“stones” from alluvial and glacial deposits are usuallyrounded to subrounded and are easier to obtain, handle,and place and, therefore, are more workable. Roundedstones are less resistant to movement.
The drag force on rounded stones is less than betweenangular rock fragments. Rounded stones interlock morepoorly than do equal-sized angular rock fragments. As aresult, a rounded stone assemblage is more likely to bemoved or eroded by water action. Angular-shaped rocksnested together resist movement by water and make thebest riprap. The rock fragments should have sharp, angu-lar, clean edges at the intersections of relatively flat faces.
Glacial or alluvial deposits are used as riprap sources onlyif rock quarries are unavailable, too distant, or incapableof producing the appropriate sizes. Unless the designslope is at an angle to the wave direction or wave energyand the erosive action of water on the slope is low,rounded to subrounded stones are typically used only onthe downstream face of embankments, in underlyingfilters, or as the packing material in gabions.
No more than 30 percent of the riprap fragments shouldhave a 2.5 ratio of longest to shortest axis of the rock.Stones having a ratio greater than 2.5 are either tabularor elongated. These tabular or elongated particles(figure 18-5) tend to bridge across the more blocky piecesor protrude out of the assemblage of rocks. Duringhandling, transporting, and placement, these elongated or
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Figure 18-5.—Tabular rock fragment.
tabular rock fragments tend to break into smaller frag-ments and could significantly change the gradation orthickness of the protective layer.
Nearly all durable rock types can provide appropriatelyshaped material, but not all rock types can be blasted andprocessed economically into suitable shapes. Mineralalignment and fractures within the rock mass are theprimary factors affecting the development of the shape.Most igneous and some sedimentary rocks are capable ofmaking suitably shaped fragments. However, secondaryfracturing or shearing will affect the shape. Rocks havingclosely spaced discontinuities tend to produce fragmentsthat are too small. Sedimentary rocks that have beddingplane partings tend to produce flat shapes. Metamorphicrocks tend to break along jointing, rock cleavage, ormineral banding and often produce elongated shapes.
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Weight and Size The weight and size of individual riprap pieces areessential factors in resisting erosive water forces. Theweight of the rock fragment is one design element forriprap but is difficult to obtain in the field for the largersizes. The relationship between weight and size isapproximately:
Wn = 0.75 �Dn3
where: Wn - Percentage of total weight of rock wheren percent is smaller
� - Unit weight of rockDn - Representative diameter of rock where
n percent is smaller
This formula assumes the shape of the rock fragment isbetween a sphere and a cube. The weight and size may bedetermined in the laboratory or in the field. The unitweight of riprap generally varies from 150 to 175 poundsper cubic foot (2.4 to 2.8 g/cm3) and correlates with surfacesaturated dry specific gravity (SSSG). Rock having anSSSG above 2.6 is typically suitable for riprap.
Determination of the relationship between weight andsize is difficult. Rock is either graded by size or countedand weighed, but rarely are weight and size correlated.Rarely does rock break into perfect cubical shapes; andbecause of the various shapes and sizes, weighing andsorting the individual pieces is difficult. The AmericanSociety for Testing and Materials Procedure D-5519 pro-vides three methods for obtaining size and weight data.
Typically, for sizes up to 36 inches (1 meter) minimumdiameter, rock pieces are sorted by size with a sieve ortemplate, and the number of individual pieces is counted
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within each group. These piles can then be weighed andindividual pieces adjusted to determine size. For indi-vidual pieces larger than 36 inches, the size is typicallydetermined by using a tape to measure the maximum andminimum size of each piece. The weight is determinedfrom a chart that assumes the shape is between a cubeand sphere.
Most rock sources are capable of producing suitableweights and sizes. The size rarely impacts use as a riprapsource unless more than 30 percent of the rocks areelongated or flat. In special circumstances, the rockmineralogy and porosity control the weight. The porosityof some sedimentary and extrusive volcanic rock couldaffect the weight. Rock having an SSSG under 2.3 istypically not considered for riprap. Generally, rockhaving a low unit weight is weak and tends to break downwith handling.
Gradation
The desired gradation consists of size fractions of theindividual particles that will nest together and withstandenvironmental conditions. The gradation design is basedon the ability of the source(s) to produce appropriate sizes.Inherent rock mineralogy, cleavage, and fractures controlthe size of the rock fragments. Blasting, excavating, andprocessing also affect the size. Most acceptable riprapgradations are obtained by understanding the inherentrock characteristics, by proper blasting techniques, and byprocessing. Rarely can blending rock sizes achieve anappropriate grading for riprap because the larger frag-ments tend to separate from the smaller fragments duringhandling and processing. Processing is typically limitedto running the rock fragments over a stationary grizzly(figure 18-6) or sorting with a rock bucket or rock rake(figure 18-7). Rarely is rock processed with jaw or
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Figure 18-7.—Rock rake. A dozer-mounted rock rake separates the larger fragments
from the smaller material.
Figure 18-6.—Stationary grizzly. Rock is dumped on the sloping rails, and the larger material slides
off and is separated from the smaller material which falls through.
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gyratory crushers except for testing. Segregation of largeand small sizes is controlled by reducing the number andamount of drops during handling and processing.Handling should be kept to a minimum.
Most coarse-grained sedimentary and igneous rockquarries are capable of producing suitable riprapgradations. The range of gradations from sedimentarysources depends on the depositional environment. Rockderived from rapid depositional environments is morelikely to produce well-graded riprap.
Size range is controlled by discontinuities in the rock.Columnar basalt, some fine-grained sedimentary rock,and metamorphic rock commonly have inherent planes ofweakness that limit larger riprap sizes. Intensely tomoderately fractured rock rarely produces suitable riprapgradations.
Durability Riprap durability affects the ability of a source to providea consistent shape, size, and gradation and the ability toresist weathering and other environmental influences.Durability is typically determined by laboratory test; butdurability can be assessed by observing surface exposures,talus, and waste piles or by examining riprap applicationsalready using the potential source or similar sourcematerials. Cracking, spalling, delaminating, splitting,disaggregating, dissolving, and disintegrating arecommon forms of rock deterioration. Durability is afunction of the rock’s mineralogy, porosity, weathering,discontinuities, and site conditions. In rare instances,environmental considerations such as abnormal pH of thewater may be a controlling factor in selecting anappropriate riprap source. A high or low pH mayaccelerate disintegration of the rock.
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Alteration of minerals, such as feldspars to softer clays,will impact rock durability. Fine-grained rock types,rocks having high porosity, and chemically altered rocksmay tend to slake after cyclic wetting and drying orfreezing and thawing. Some rocks tend to break upbecause of discontinuities such as bedding plane parting,cementation or secondary mineralization, unstableminerals, banding, or foliation. Jointing, rock cleavage,and bedding plane partings often result in excessive finersizes or tabular and elongated rock fragments.
Rock that breaks down either physically or chemicallyshould be avoided. Obvious examples are most weatheredor altered rocks, rock containing soluble or expansiveminerals, vesicular basalts, shale, claystone, siltstone,weakly cemented or porous sandstone, schist, or phyllite.Even durable rocks such as slate and some gneisses maygenerally be unusable because other physicalcharacteristics (cleavage and foliation) will not allowproduction of large, nearly equidimensional blocks.
Mechanical breakdown and weathering may beaccelerated by microfracturing from the blasting,handling, weak cementation or may be the result ofalteration of more stable minerals to clay. In addition,there appears to be a significant correlation betweenporosity, absorption, and durability of rock. Rock that hasmore than 2 percent absorption is commonly impacted byfreezing and thawing and by wetting and dryingprocesses.
Quantity
Every riprap source investigation must provide theestimated quantity required. Estimating realisticquantities depends on an understanding of subsurfacegeologic conditions. The uniformity of rock and
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discontinuities within a source area must be assessed.This estimate (often referred to as the reserve) providesnot only the amount of riprap available but also providesan understanding of wastage resulting from blasting,handling, processing, haulage, and placement. In strati-fied deposits such as limestones or sandstones, uniformitymust be evaluated because individual beds often differ incharacter and quality. The dip of stratified rocks andcontacts between dissimilar rock types, such as igneousintrusions, must also be considered. The larger theindividual pieces required, the more difficult it is for anyrock type to supply suitable quantities. Zones or layers ofundesirable clay or shale seams may be so large orprevalent that selective quarrying or wasting ofundesirable material is required. The geologic conditions,ability of the rock to produce suitable sizes, and thepotential reserve should be determined.
Existing commercial sources may be capable of producingriprap but may not be capable of expanding their opera-tion into similar quality rock. In any new source, theamount of burden that must be removed, stability of thecutslopes, uniformity of the rock, depth to water, andability to blast or process the rock into the appropriategradation must be evaluated. Since riprap is a surfacelayer, a smaller sized riprap of increased thickness maybe acceptable, or a less durable riprap may be used withthe understanding that the riprap may requirereplacement.
Cost
A primary factor in determining a suitable riprap sourceis cost. Design and environmental requirements, access,subsurface conditions, testing, depth to water, quantity ofsuitable rock, and location also affect the cost and shouldbe assessed early in any source investigation.
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Producing sources should be located first. Using existingquarries or pits is generally cheaper because there isconsiderably less cost associated with permitting,developing, and evaluating an existing source. Anexisting source provides easier access to rock; a history ofthe source provides an understanding of the source’sability to provide suitable rock; regulatory requirementsare often more easily met; development and processingcosts are often known; and often, some testing of materialhas been performed so that the quality is known.Although existing sources may be known, each of theseelements should be evaluated to ensure that informationis representative and appropriate for the particularrequirement. In areas where existing sources are not economical,evaluating the surrounding undeveloped areas orabandoned pits or quarries should be considered.Evaluating new or abandoned sources typically involvesconsiderable expense. A new quarry or pit investigationinvolves understanding subsurface conditions; obtaining,evaluating, and testing subsurface samples; andevaluating subsurface conditions to determine ifappropriate riprap can be produced. Factors such as thehaul distance, grade, width, and type of roadway shouldalso be assessed.
Investigation Stages
The complexity of investigations for suitable sources ofriprap is governed by the development stage and designrequirements of the project. Projects are normallydeveloped in four stages: reconnaissance, feasibility,design, and construction.
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Reconnaissance
Initial exploration involves field surface reconnaissanceusing topographic maps, geologic and groundwater mapsand reports, and aerial photographs. Supplemental infor-mation is provided by records of known developed sourcesof material. Areas having steep topography could havethe best rock exposures. Geology maps providegeneralized locations of rock types. Groundwater mapsprovide indications of rock permeability, depths to water,and information on the need for dewatering or unwateringwithin the source area. During field reconnaissance, thecountryside should be examined for exposed rock outcropsor talus piles. Roadcuts and ditches may also provideuseful exposures. Existing sources and any projects thatpreviously used the rock source should be examined.
Service records are an excellent indication of the potentialdurability of rock. Federal (Reclamation, U.S. ArmyCorps of Engineers, Department of Transportation), State(highway, environmental quality), and county or local(highway or building) agencies usually maintain lists ofsources. The local telephone "Yellow Pages," Internet,and construction companies may also provide information.
Data obtained should define the major advantages ordisadvantages of potential material sources withinreasonable haul distance. A reconnaissance constructionmaterial report should be prepared at this stage.
Feasibility
Information acquired during the feasibility stage is usedto prepare preliminary designs and cost estimates.Sufficient information concerning potential sources shouldbe gathered to determine whether the rock should beobtained from an existing source or a new source.
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Selection of sources should be limited to those that mayeventually be used in specifications. Core drilling andblast tests may be required to confirm fragment size andquantity of material available in each source. Thepotential material sources should be examined todetermine size and character, and particularly to observejoint and fracture spacing, resistance to weathering, andvariability of the rock. The spacing of joints, fractures,schistosity, banding, bedding, and other planes ofweakness may control the rock fragment sizes andshapes. Weathering resistance of the rock will provide agood indication of durability. Quarry or pit developmentand the impacts of groundwater should be addressed.Particular attention should be given to location anddistribution of unsound seams or beds that must beavoided or wasted during the quarry operation. A generallocation map and detailed report describing the potentialsources and containing estimates of available quantities,overburden, haul roads, and accessibility should beprepared. Representative samples of riprap materialfrom the most promising potential sources should be sub-mitted to the laboratory for testing. A feasibility con-struction material report should be prepared at this stage.
Design
Investigations during the design stage furnish data andinformation required for the specifications. Sources indi-cated by feasibility investigations to be suitable arefurther investigated to establish quantities, determine thecapability to produce the required gradation, and to deter-mine uniformity. Depending on project needs, servicerecords may be used in conjunction with or instead oflaboratory testing. Blast and processing testing should beconsidered for new sources. All sampling and testing andthe laboratory’s Riprap Quality Evaluation Report shouldbe completed at this stage. If additional sources are
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necessary, the new sources must be investigated asthroughly as the original sources.
Construction
Investigations during construction provide field anddesign personnel with additional detailed information forproper source development. This information should beobtained sufficiently ahead of quarrying or excavating toprovide for proper processing and placing of material. Ifunforeseen changes occur in the quality of material in thesource, sampling and quality evaluation testing of thematerial may be required to confirm material suitabilityor to delineate unsuitable areas.
Reports Reporting the results of any investigation is important.The level of detailed information requirements increaseswith each successive stage. Adequate information mustbe available by the feasibility stage to develop realisticcost estimates and to properly select sources. A suggestedoutline for reports for rock or riprap obtained from anypotential quarry or pit is as follows:
a. Ownership
b. Location of source and project shown on a map
c. General description of site
d. General hydrologic and geologic descriptions
e. Structural geology information (distribution andarrangement of rock types and discontinuitieswithin the deposit.)
f. Manner and sizes of rock breakage
g. Estimate of uniformity and wastage
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h. Shape and angularity of source material
i. Hardness and density of source material
j. Degree and extent of weathering
k. Any abnormal properties or conditions not coveredabove
l. Estimate of extent, volume, and depth of suitabledeposit(s)
m. Accessibility
n. Photographs
o. Geophysical and geologic data (e.g., drill logs,borehole geophysical logs, and seismic refraction orreflection survey data)
If commercial quarry or pit deposits are considered,obtain, as appropriate, the following information in addi-tion to the data needed for a new source.
• Name, address, and phone number of the plantoperator
• Location of the plant relative to quarry
• Description of the operation and plant withemphasis on capabilities for additional riprapproduction and maintaining current operationcapabilities
• Blasting methods and problems related to produc-tion of riprap
• Transportation facilities and any potentialdifficulties
• Actual or estimated riprap gradations achieved orachievable by current or adjusted operations
• Location of scales
• Estimate of reserve and wastage
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• Approximate prices of riprap material
• Service history of material produced
• Any other pertinent information
Sampling Sampling is often the weak link in any source evaluation.The samples should represent the nature and condition ofthe materials and be appropriate for testing. Sampling isinitiated at the specifications stage of the project.Sampling should cover the entire riprap source. Thesample size should be at least 600 pounds (275 kilograms)and represent the quality range from poor to best as foundat the source in the same proportions as the source cansupply. If the material quality is quite variable, it may bepreferable to obtain three samples that represent thepoorest to best quality material available. The minimumsize of individual fragments selected should be at least0.5 foot (15 cm) square. An estimate of the relativepercentages of material at each quality level should bemade.
Representative samples may be difficult to obtain.Overburden may limit the areas where material can beobtained and obscure the true characteristics of thedeposit. Outcrops will often be more weathered than thesubsurface deposits. Samples obtained from talus piles orouter surfaces of rock outcrops are seldom representativeof quality, quantity, or gradation. Fresh material may beobtained by breaking away the outer surfaces, or bytrenching, blasting, or core drilling. If coring is the onlymethod of obtaining samples, the preferred size is6 inches (15 cm).
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Shipping
Samples of rock fragments can be shipped by conventionaltransport such as motor freight. Large rock fragmentsshould be securely banded to shipping pallets. Smallerfragments should be transported in bags or containers topreclude loss, contamination, or damage frommishandling during shipment.
Testing
The Riprap Quality Evaluation Report is based onlaboratory testing of the shipped representative samples.The quality evaluation tests include detailed petrographicexamination, determination of physical properties andabsorption, and a rapid freeze-thaw durability evaluation.
Petrographic Examination.—The petrographic exami-nation follows USBR Procedure 4295 or ASTM ProcedureC 295, which were developed for concrete aggregate. Thedecisions concerning specific procedural methods andspecimen preparation depend on the nature of the rockand the intended use of the rock.
The rock pieces are visually examined and the differentrock facies and types are segregated for individualevaluation. The following are evaluated:
• Size range
• Fragment shape
• Shape and size control by discontinuities such asjoints, banding, or bedding
• Surface weathering
• Secondary mineralization or alteration
• Hardness, toughness, and brittleness
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• Voids and pore characteristics and their variations
• Texture, internal structure, grain size, cementation,and mineralogy of the various facies and rock types
• Thin sections, sometimes supplemented by X-raydiffraction as required
Freeze-Thaw Test.— For freeze-thaw durability testing,two 7/8-inch (73 millimeter) cubes are sawed from rockfragments selected by visual inspection to represent therange from poorest to best quality rock for each rock faciesor type. Because the rock pieces could have significantphysical or structural discontinuities, the number ofcubes obtained for testing will vary from sample tosample. The samples are photographed, the cubes areimmersed in water for 72 hours, and specific gravities(bulk, SSSG, and apparent) and absorptions aredetermined by USBR Procedure 4127 or ASTM ProcedureC 127. The cubes are reimmersed in water to maintain asaturated condition for freeze-thaw testing.
Rapid freezing and thawing durability tests areperformed on riprap samples according to USBRProcedure 4666 or ASTM Procedure D5312. The rockfailure criterion is 25 percent loss of cube mass calculatedfrom the difference in mass between the largest cubefragment remaining after testing and the initial cubemass.
Sodium Sulfate Soundness Test.—Sodium sulfatesoundness tests are performed on riprap samplesaccording to USBR Procedure 4088 or ASTM ProcedureD5240. The loss after an interval of screening isdetermined after at least five cycles of saturation anddrying of the samples. The test is a good indicator ofresistance to freeze-thaw deterioration.
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Physical Properties.—Material remaining after thepetrographic examination and freeze-thaw testing iscrushed into specific size fractions (USBR Procedure4702). Representative samples of each size fraction aretested for bulk, SSGS, and absorption followingUSBR Procedure 4127 or ASTM Procedure C 127; abra-sion is tested using the Los Angeles abrasion testfollowing USBR Procedure 4131 or ASTM ProcedureC 535. Both the Los Angeles abrasion and sodium sulfatesoundness tests are durability tests. The Los Angelesabrasion test is used to determine the ability of the rockto withstand handling and processing and water action.The sodium sulfate soundness test simulates weatheringof the rock pieces.
Waste in Riprap Production
Production of riprap generally requires drilling, blasting,and processing to obtain the desired sizes. This section isa guide to help estimate the amount of waste that can beexpected from riprap production.
Numerous factors in the parent rock contribute to wastein quarrying operations. The natural factors include:
• Weathering• Fracturing (joints, shears, and faults)• Bedding, schistosity, and foliation• Recementing of planar features
Other important, somewhat controllable contributors towaste are:
• Construction inspection• Size and gradation requirements• Drilling and blasting• Processing, hauling, and placement
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Factors a through d relate to the geology in the quarryand probably are the most important factors that governwhat sizes can be produced. Weathering can extend 20 to60 feet (6 to 18 meters) below the original ground surface.Weathering breaks down the rock and weakens existingplanar features such as bedding, schistosity, and jointing.In rocks such as limestone and dolomite, secondarydeposits of calcium carbonate can cement existing joints.When first examined, this cementation appears to besound; but processing the rock can refracture theseplanes. Existing quarries, or quarries that have been inoperation for many years, probably will produce materialwith less waste because excavations are partly orcompletely through the zone of weathering. Newquarries, or quarries where rock production has beenlimited, must contend with the weathered zone and willlikely produce a less desirable product.
Gradation Requirements
Gradation requirements and inspection control aregoverned by the agency issuing the constructionspecifications. Adjustments in gradation or inspectionrequirements can drastically change the waste quantitiesproduced. Except in isolated cases, it becomes moredifficult to produce riprap when rock sizes are increasedand gradations are tightly controlled.
Production Methods
Production methods that include drilling, blasting, pro-cessing, and hauling also play an important role in thesizes that can be obtained. Rock that is well-graded andhas a large maximum size can be produced more readilywhen using large diameter, widely spaced shot holes.Close spaced, small diameter shot holes tend to maximizefragmentation. Blasting agents, delays, and loading
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methods vary considerably and have a significant effecton how the rock fractures. The most efficient andeconomical drilling and blasting methods must bedetermined by test blasting and performing gradations onthe blasted product. Test shots should be modified toachieve the desired product. Production should not startuntil it is proven that the required product can beproduced with a minimum of waste.
Many rock types, especially those that are banded (beddedor schistose) or contain healed joints, can break downsignificantly during processing. Some limestones areespecially susceptible to breakdown when the rock isdropped during blasting and processing operations. Rockfrom most quarries will fracture badly when droppedmore than 50 feet (15 meters).
Quarries must tailor their blasting techniques to get therequired gradations. Quarries that normally produceaggregates for concrete, road metal, and base courseusually have a very difficult time producing a reasonablywell-graded riprap. This is because their normal opera-tion already has shattered the face at least 100 feet back.To obtain good riprap, a working face or ledge should bereserved for riprap production.
The quantity of quarry waste shown in table 18-1 istypical of riprap quarries. Items that should be con-sidered when using the table include:
• Waste includes undersize and excessive intermediatesizes. Oversize riprap is reprocessed to the propersize.
• Rock produced is reasonably well graded from 6± to36± inches (.15 to 1 m), and the inspection control isvery strict. Much less waste will be incurred ifsmaller rock sizes
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Table 18-1.—Rock types and typical usable quantities of riprap
Rock type
Estimated percentwaste to producesuitable riprap Remarks
IGNEOUS
Intrusive 25 to 75%Average 50%±
Extrusive 40 to 85%Average 60%±
METAMORPHIC
Gneiss 40 to 75%Average 55%±
Based on limited data
Schist 50 to 75%Average 65%±
Based on limited dataVery little riprapwould be salvaged inthe weathered zone
SEDIMENTARY
Limestone/Dolomite
55 to 85 %Average 65%±
Based on several goodquarry sites
Sandstone Average 60%± Based on limited data
are required or if the deposit is shot for rockfill or thespecific rock product.
• Drilling, blasting, processing, hauling, and placingare accomplished by a typical contractor.
• Rock quarried is the best material available and isnot severely fractured or weathered.
• Riprap production is generally limited to newquarries or unshot ledges or benches.
Chapter 19
BLAST DESIGN
Introduction
This chapter is an introduction to blasting techniquesbased primarily on the Explosives and BlastingProcedures Manual (Dick et al., 1987) and the Blaster’sHandbook (E.I. du Pont de Nemours & Co., Inc., 1978).Blast design is not a precise science. Because of widelyvarying properties of rock, geologic structure, and explo-sives, design of a blasting program requires field testing.Tradeoffs frequently must be made when designing thebest blast for a given geologic situation. This chapterprovides the fundamental concepts of blast design. Theseconcepts are useful as a first approximation for blastdesign and also in troubleshooting the cause of a badblast. Field testing is the best tool to refine individualblast designs.
Throughout the blast design process, two overriding prin-ciples must be kept in mind:
(1) Explosives function best when there is a free faceapproximately parallel to the explosive column atthe time of detonation.
(2) There must be adequate space for the broken rockto move and expand. Excessive confinement ofexplosives is the leading cause of poor blastingresults such as backbreak, ground vibrations,airblast, unbroken toe, flyrock, and poorfragmentation.
Properties and Geology of the Rock Mass
The rock mass properties are the single most criticalvariable affecting the design and results of a blast. The
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rock properties are very qualitative and cannot be suffi-ciently quantified numerically when applied to blastdesign. Rock properties often vary greatly from one endof a construction job to another. Explosive selection, blastdesign, and delay pattern must consider the specific rockmass being blasted.
Characterizing the Rock Mass
The keys to characterizing the rock mass are a good geol-ogist and a good blasting driller. The geologist must con-centrate on detailed mapping of the rock surface for blastdesign. Jointing probably has the most significant effecton blasting design. The geologist should document thedirection, density, and spacing between the joint sets. Atleast three joint sets—one dominant and two lesspronounced—are in most sedimentary rocks. The strikeand dip of bedding planes, foliation, and schistosity arealso important to blast design and should be documentedby the geologist. The presence of major zones of weaknesssuch as faults, open joints, open beds, solution cavities, orzones of less competent rock or unconsolidated materialare also important to blast design and must beconsidered. Samples of freshly broken rock can be used todetermine the hardness and density of the rock.
An observant blasting driller can be of great help inassessing rock variations that are not apparent from thesurface. Slow penetration, excessive drill noise, andvibration indicate a hard rock that will be difficult tobreak. Fast penetration and a quiet drill indicate a softer,more easily broken zone of rock. Total lack of resistanceto penetration, accompanied by a lack of cuttings orreturn water or air, means that the drill has hit a void.Lack of cuttings or return water may also indicate thepresence of an open bedding plane or other crack. Adetailed drill log indicating the depth of these various
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conditions can be very helpful in designing and loadingthe blast. The log should be kept by the driller. Thedriller should also document changes in the color ornature of the drill cuttings which will tell the geologistand blaster the location of various beds in the formation.
Rock Density and Hardness
Some displacement is required to prepare a muckpile forefficient excavation. The density of the rock is a majorfactor in determining how much explosive is needed todisplace a given volume of rock (powder factor). Theburden-to-charge diameter ratio varies with rock density,changing the powder factor. The average burden-to-charge diameter ratio of 25 to 30 is for average densityrocks similar to the typical rocks listed in table 19-1.Denser rocks such as basalt require smaller ratios (higherpowder factors). Lighter materials such as somesandstone or bituminous coal can be blasted with higherratios (lower powder factors).
The hardness or brittleness of rock can have a significanteffect on blasting results. If soft rock is slightly under-blasted, the rock probably will still be excavatable. If softrock is slightly overblasted, excessive violence will notusually occur. On the other hand, slight underblasting ofhard rock will often result in a tight muckpile that isdifficult to excavate. Overblasting of hard rock is likely tocause excessive flyrock and airblast. Blast designs forhard rock require closer control and tighter tolerancesthan those for soft rock.
Voids and Zones of Weakness
Undetected voids and zones of weakness such as solutioncavities, “mud” seams, and shears are serious problems in
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Table 19-1.—Typical rocks, densities, and unit weights
Rock type
Densityrange
(g/cm3)1
Range of unit weights
U.S.customary
(lb/ft3)2Metric
(kg/m3)3
Limestone 2.5 to 2.8 156 to 174.7 2,500 to 2,800
Schist 2.6 to 2.8 162.2 to 174.7 2,600 to 2,800
Rhyolite 2.2 to 2.7 137.2 to 168.5 2,200 to 2,700
Basalt 2.7 to 2.9 168.5 to 181 2,700 to 2,900
Sandstone 2/0 to 2.6 124.8 to 162.2 2,000 to 2,600
Bituminous coal
1.2 to 1.5 74.9 to 93.6 1,200 to 1,500
1 Grams per cubic centimeter. 2 Pounds per cubic foot. 3 Kilograms per cubic meter.
blasting. Explosive energy always seeks the path of leastresistance. Where the rock burden is composed ofalternate zones of hard material, weak zones, or voids, theexplosive energy will be vented through the weak zonesand voids resulting in poor fragmentation. Depending onthe orientation of zones of weakness with respect to freefaces, excessive violence in the form of airblast and flyrockmay occur. When the blasthole intersects a void,particular care must be taken in loading the charge, orthe void will be loaded with a heavy concentration ofexplosive resulting in excessive air-blast and flyrock.
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If these voids and zones of weakness can be identified andlogged, steps can be taken during borehole loading toimprove fragmentation and avoid violence. The best toolfor this is a good drill log. The depths of voids and zonesof weakness encountered by the drill should bedocumented. The geologist can help by plotting the trendsof “mud” seams and shears. When charging the blasthole,inert stemming materials rather than explosives shouldbe loaded through these weak zones. Voids should befilled with stemming. Where this is impractical becauseof the size of the void, it may be necessary to block thehole just above the void before continuing the explosivecolumn.
If the condition of the borehole is in doubt, the top of thepowder column should be checked frequently as loadingproceeds. A void probably exists if the column fails to riseas expected. At this point, a deck of inert stemmingmaterial should be loaded before powder loadingcontinues. If the column rises more rapidly thanexpected, frequent checking will ensure that adequatespace is left for stemming.
Alternate zones of hard and soft rock usually result in un-acceptably blocky fragmentation. A higher powder factorseldom will correct this problem; it will merely cause theblocks to be displaced farther. Usually, the best way to al-leviate this situation is to use smaller blastholes withsmaller blast pattern dimensions to get a better powderdistribution. The explosive charges should be concen-trated in the hard rock.
Jointing
Jointing can have a pronounced effect on both fragmenta-tion and the stability of the perimeter of the excavation.Close jointing usually results in good fragmentation.
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Figure 19-1.—Effect of jointing on the stability of an excavation (plan view).
Widely spaced jointing, especially where the jointing ispronounced, often results in a very blocky muckpilebecause the joint planes tend to isolate large blocks inplace. Where the fragmentation is unacceptable, the bestsolution is to use smaller blast holes with smaller blastpattern dimensions. This extra drilling and blastingexpense will be more than justified by the savings inloading, hauling, and crushing costs and the savings insecondary blasting.
Where possible, the perimeter holes of a blast should bealigned with the principal joint sets. This produces amore stable excavation, whereas rows of holesperpendicular to a primary joint set produces a moreragged, unstable perimeter (figure 19-1). The jointing willgenerally determine how the corners at the back of theblast will break out. To minimize backbreak and flyrock,tight corners, as shown in figure 19-2, should be avoided.
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Figure 19-2.—Tight and open cornerscaused by jointing (plan view).
The open corner at the left of figure 19-2 is preferable.Given the dominant jointing in figure 19-2, more stableconditions will result if the first blast is opened at the farright and designed so that the hole in the rear insidecorner contains the highest numbered delay.
Bedding/Foliation
Bedding has a pronounced effect on both the fragmen-tation and the stability of the excavation perimeter. Openbedding planes, open joints, or beds of weaker materialsshould be treated as zones of weakness. Stemming,rather than explosive, should be loaded into the boreholeat the location of these zones as shown in figure 19-3. Ina bed of hard material (greater than 3 feet [1 m] thick), itis often beneficial to load an explosive of higher densitythan is used in the remainder of the borehole. To breakan isolated bed or zone of hard rock (3 feet [1 m] thick orgreater) near the collar of the blasthole, a deck charge isrecommended, as shown in figure 19-4, with the deckbeing fired on the same delay as the main charge or onedelay later. Occasionally, satellite holes are used to helpbreak a hard zone in the upper part of the burden.Satellite holes (figure 19-4) are short holes, usuallysmaller in diameter than the main blastholes drilledbetween the main blastholes.
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Figure 19-3.—Stemming through weakmaterial and open beds.
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Figure 19-4.—Two methods of breakinga hard collar zone.
A pronounced foliation, bedding plane, or joint isfrequently a convenient location for the bench floor. It notonly gives a smoother floor but also may reducesubdrilling requirements.
Dipping beds frequently cause stability problems anddifficulty in breaking the toe of the excavation. Whenbedding or foliation dip into the excavation wall, thestability of the slope is enhanced. When the dip is out ofthe wall, slip planes exist that increase the likelihood ofslope deterioration or failure. Blasthole cutoffs (part of acolumn of explosives not fired) caused by differential bedmovement are also more likely. Beds dipping out of thefinal slope should be avoided wherever possible.
Although beds dipping into the face improve slopestability, the beds can create toe problems because the toerock tends to break along the bedding or foliation planes.
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Dipping beds such as these require a tradeoff, dependingupon which is the more serious problem—a somewhatunstable slope or an uneven toe. In some cases,advancing the opening perpendicular to dipping beds maybe a compromise.
Many blasting jobs encounter site-specific geologic condi-tions not covered in this general discussion. Goodblasting techniques require constant study of the geologyto make every effort to advantageously use the geology, orat least minimize its unfavorable effects in blast designs.
Surface Blasting
Blast Hole Diameter
The blast hole size is the first consideration of any blastdesign. The blast hole diameter, along with the type ofexplosive being used and the type of rock being blasted,determines the burden (distance from the blast hole to thenearest free face). All other blast dimensions are afunction of the burden. This discussion assumes that theblaster has the freedom to select the borehole size. Manyoperations limit borehole size based on available drillingequipment.
Practical blasthole diameters for surface constructionexcavations range from 3 (75 mm) to approximately15 inches (38 cm). Large blasthole diameters generallyyield low drilling and blasting costs because large holesare cheaper to drill per unit volume, and less sensitive,cheaper blasting agents can be used in larger diameterholes. Larger diameter blastholes also allow large bur-dens and spacings and can give coarser fragmentation.Figure 19-5 illustrates this comparison using 2- (50-mm)and 20-inch (500-mm)-diameter blastholes as an example.
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Figure 19-5.—The effect of large and smallblast holes on unit costs.
Pattern A contains four 20-inch (500-mm) blast boles, andpattern B contains 400 2-inch (5-mm) blast holes. In allbench blasting operations, some compromise betweenthese two extremes is chosen. Each pattern representsthe same area of excavation—15,000 square feet(1,400 m2)—each involves approximately the same volumeof blast holes, and each can be loaded with about the sameweight of explosive.
As a general rule, large diameter blast holes (6 to15 inches [15 to 38 cm]) have limited applications on mostconstruction projects because of the requirements for finefragmentation and the use of relatively shallow cuts.However, borehole size depends primarily on localconditions. Large holes are most efficient in deep cutswhere a free face has already been developed.
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In most construction projects, small diameter drillingwith high-speed equipment provides relatively low unitcosts and permits fairly close spacing of holes. This closespacing provides better distribution of explosives through-out the rock mass, which in turn produces betterbreakage. An additional advantage of small diameterblast holes is that the reduction in the amount of eachexplosive used in each hole reduces ground vibrations.Construction blast hole diameters usually vary from 3.5 to4.5 inches (90 to 114 mm), and the normal drilling depthis less than 40 feet (12 m). Reclamation generally limitsblast hole diameters for structural excavation drilling to3.5 inches (90 mm). Blasting patterns usually range from6 by 8 feet (1.8 by 2.4 meters) to 8 by 15 feet (2.4 by 4.6 m)and are usually rectangular with the burden being lessthan the spacing.
In a given rock type, a four-hole pattern will giverelatively low drilling and blasting costs. Drilling costs forlarge blastholes will be low, a low-cost blasting agent willbe used, and the cost of detonators will be minimal. In adifficult blasting situation, the broken material will beblocky and nonuniform in size, resulting in higherloading, hauling, and crushing costs as well as requiringmore secondary breakage. Insufficient breakage at thetoe may also result.
The 400-hole pattern will yield high drilling and blastingcosts. Small holes cost more to drill per unit volume,powder for small diameter blastholes is usually moreexpensive, and the cost of detonators will be higher. Thefragmentation will be finer and more uniform, resultingin lower loading, hauling, and crushing costs. Secondaryblasting and toe problems will be minimized. Sizeof equipment, subsequent processing required for theblasted material, and economics will dictate the type offragmentation needed and the size of blast hole to beused.
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Figure 19-6.—The effects of jointingon selection of blast hole size.
Geologic structure is a major factor in determining theblast hole diameter. Planes of weakness (i.e., joints,shears, or zones of soft rock) tend to isolate large blocks ofrock in the burden. The larger the blast pattern, the morelikely these blocks are to be thrown unbroken into themuckpile. Note that in the top pattern in figure 19-6,some of the blocks are not penetrated by a blast hole. Inthe smaller bottom pattern, all the blocks contain at leastone blast hole. Because of the better explosivesdistribution, the bottom pattern will give betterfragmentation.
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Airblast and flyrock often occur because of an insufficientcollar distance (stemming column) above the explosivecharge. As the blast hole diameter increases, the collardistance required to prevent violence increases. The ratioof collar distance to blast hole diameter required toprevent violence varies from 14:1 to 28:1, depending onthe relative densities and velocities of the explosive androck, the physical condition of the rock, the type ofstemming used, and the point of initiation. A larger collardistance is required where the sonic velocity of the rockexceeds the detonation velocity of the explosive or wherethe rock is heavily fractured or low density. A top-initiated charge requires a larger collar distance than abottom-initiated charge. As the collar distance increases,the powder distribution becomes poorer, resulting inpoorer fragmentation of the rock in the upper part of thebench.
Ground vibrations are controlled by reducing the weightof explosive fired per delay interval. This is done moreeasily with small blast holes than with large blast holes.In many situations where large diameter blast holes areused near populated areas, several delays, along withdecking, must be used within each hole to controlvibrations.
Large holes with large blast patterns are best suited to anoperation with: (1) a large volume of material to bemoved, (2) large loading, hauling, and crushingequipment, (3) no requirement for fine, uniform fragmen-tation, (4) an easily broken toe, (5) few ground vibrationor airblast problems (few nearby buildings), and (6) arelatively homogeneous, easily fragmented rock withoutmany planes of weakness or voids. Many blasting jobshave constraints that require smaller blast holes.
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Figure 19-7.—Three basic types of drill patterns.
The final selection of blast hole size is based oneconomics. Savings realized through inappropriate costcutting in the drilling and blasting program may well belost through increased loading, hauling, or crushing costs.
Blast Patterns
The three drill patterns commonly used are square,rectangular, and staggered. The square drill pattern(figure 19-7) has equal burdens and spacing, and therectangular pattern has a larger spacing than burden. Inboth the square and rectangular patterns, the holes ofeach row are lined up directly behind the holes in thepreceding row. In the staggered pattern (figure 19-8), theholes in each are positioned in the middle of the spacingsof the holes in the preceding row. In the staggeredpattern, the spacings should be larger than the burden.
Square or rectangular drilling patterns are used for firingV-cut (figure 19-9) or echelon rounds. The burdens andsubsequent rock displacement are at an angle to theoriginal free face either side of the blast round in V-cut orechelon patterns. The staggered drilling pattern is usedfor row-on-row firing where the holes of one row are firedbefore the holes in the row immediately behind them asshown in figure 19-9. Looking at figure 19-9, with theburdens developed at a 45-degree angle to the original
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Figure 19-9.—V-Echelon blast round(true spacing, S, is twice the true burden, B).
Figure 19-8.—Corner cut staggered pattern withsimultaneous initiation within rows (blast hole
spacing, S, is twice the burden, B).
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Figure 19-10.—Isometric view of a bench blast.
free face, the original square drilling pattern has beentransformed to a staggered blasting pattern with aspacing twice the burden. The three simple patternsdiscussed here account for nearly all the surface blasting.
Burden
Figure 19-10 is an isometric view showing therelationship of the various dimensions of a bench blast.The burden is defined as the distance from a blast hole tothe nearest free face at the instant of detonation. Inmultiple row blasts, the burden for a blast hole is notnecessarily measured in the direction of the original freeface. The free faces developed by blast holes fired onlower delay periods must be taken into account. As an
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example, in figure 19-8, where one entire row is blastedbefore the next row begins, the burden is measuredperpendicular between rows.
In figure 19-9, the blast progresses in a V-shape. Thetrue burden on most of the holes is measured at an angleof 45 degrees from the original free face.
It is very important that the proper burden be calculated,accounting for the blast hole diameter, relative density ofthe rock and explosive, and, to some degree, the depth ofthe blast hole. An insufficient burden will cause excessiveairblast and flyrock. Too large a burden will produceinadequate fragmentation, toe problems, and excessiveground vibrations. If it is necessary to drill a roundbefore the previous round has been excavated, it isimportant to stake out the first row of the second roundbefore the first round is fired. This will ensure a properburden on the first row of blast holes in the second blastround.
For bulk-loaded charges (the charge is poured down thehole), the charge diameter is equal to the blast holediameter. For tamped cartridges, the charge diameterwill be between the cartridge diameter and the blast holediameter, depending on the degree of tamping. Foruntamped cartridges, the charge diameter is equal to thecartridge diameter. When blasting with ANFO(ammonium nitrate/fuel oil mixture) or other low densityblasting agents with densities near 53 lb/ft3 (0.85 g/cm3),in typical rock with a density near 170 lb/ft3 (2.7 g/cm3,the normal burden is approximately 25 times the chargediameter. When using denser products such as slurries ordynamites with densities near 75 lb/ft3 (1.2 g/cm3), thenormal burden is approximately 30 times the chargediameter. These are first approximations, and fieldtesting usually results in adjustments to these values.
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The burden-to-charge-diameter ratio is seldom less than20 or seldom more than 40, even in extreme cases. Forinstance, when blasting with a low density blasting agentsuch as ANFO in a dense formation such as basalt, thedesired burden may be about 20 times the chargediameter. When blasting with denser slurries ordynamites in low density formations such as sandstones,the burden may approach 40 times the charge diameter.Table 19-2 summarizes these approximations.
Table 19-2.—Approximate burden charge diameter ratios for bench blasting
Material Ratio
ANFO (density 53.1 lb/ft3, 0.85 g/cm3)Light rock (density ~ 137.3 lb/ft3, 2.2 g/cm3)Average rock (density ~ 168.6 lb/ft3, 2.7 g/cm3)Dense rock (density ~ 199.8 lb/ft3, 3.2 g/cm3)
282523
Slurry, dynamite (density ~ 199.7 lb/ft3, 3.2 g/cm3)Light rock (density ~ 137.3 lb/ft3, 2.2 g/cm3,)Average rock (density ~ 168.6 lb/ft3, 2.7 g/cm3)Dense rock (density ~ 199.8 lb/ft3, 3.2 g/cm3)
333027
High-speed photographs of blasts show that flexing of theburden plays an important role in rock fragmentation. Arelatively deep, narrow burden flexes and breaks moreeasily than a shallow, wider burden. Figure 19-11 showsthe difference between using a 6-inch (150-mm) blast holeand a 12.25-inch (310-mm) blast hole in a 40-foot (12-m)bench with a burden-to-charge-diameter ratio of 30 andappropriate subdrilling and stemming dimensions. Notethe inherent stiffness of the burden with a 12.25-inch(310-mm) blast hole as compared to a 6-inch (150-mm)
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Figure 19-11.—Comparison of a 12¼-inch- (300-mm) diameter blast hole (stiff burden)
on the left with a 6-inch- (150-mm) diameter blast hole (flexible burden) on the right
in a 40-foot (12-m) bench.
blast hole. Based on this, lower burden-to-charge-diameter ratios should be used as a first approximationwhen the blast hole diameter is large in comparison to thebench height. Care must be taken that the burden ratiois not so small as to create violence. Once the ratio hasbeen determined, it becomes the basis for calculatingsubdrilling, collar distance (stemming), and spacing.
Subdrilling
Subdrilling is the distance drilled below the floor level toensure that the full face of rock is removed. Where thereis a pronounced parting at floor level for the explosivecharge to conveniently break, subdrilling may not berequired. In coal strip mining, it is common practice to
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drill down to the coal and then backfill a foot or two beforeloading explosives, resulting in a negative subdrill. Inmost surface blasting jobs, some subdrilling is necessaryto make sure the shot pulls to grade. In most constructionblasting, subdrilling is generally limited to 10 percent orless of the bench height. In blasting for civil engineeringstructures where a final grade is specified, subdrilling ofthe final lift is severely restricted. The final lift instructural excavations is usually limited to 5 or 10 feet(1.5 to 3 m). Subdrilling is not allowed in a 5-foot (1.5-m)lift and is limited to 2 feet (0.6 m) for the 10-foot (3-m) lift.To prevent damage to the foundation, the diameter of theblast hole is limited to 3.5 inches (90 mm).
Priming the explosive column at the toe level (bottom ofthe drill hole) gives maximum confinement and normallygives the best breakage. Toe priming usually requires lesssubdrilling than collar priming. Toe priming should berestricted in structural foundations because of thepotential damage to the unshot rock.
Excessive subdrilling is unnecessary, expensive, and maycause excessive ground vibrations because of the highdegree of confinement of the explosive in the bottom of theblast hole, particularly when the primer is placed in thebottom of the hole. In multiple-bench operations,excessive subdrilling may cause undue fracturing in theupper portion of the bench below, creating difficulties incollaring holes in the lower bench. Insufficient sub-drilling causes a high bottom, resulting in increased wearand tear on equipment and expensive secondary blastingor hand excavation in structural foundations.
Collar Distance (Stemming)
Collar distance is the distance from the top of theexplosive charge to the collar of the blast hole. This zone
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usually is filled with an inert material called stemming togive some confinement to the explosive gases and toreduce airblast. A well-graded, crushed gravel works bestas stemming, but it is common practice to use drillcuttings because of availability and economics. Collar dis-tances that are too short result in excessive violence in theform of airblast and flyrock and may cause backbreak(breaking beyond the back wall). Collar distances thatare too long create large blocks in the upper part of themuck pile. The selection of a collar distance is often atradeoff between fragmentation and the amount ofairblast and flyrock that can be tolerated. This is trueespecially where the upper part of the bench contains rockthat is difficult to break or is of a different type. Thedifference between a violent blast and one that fails tofragment the upper zone properly may be a matter of onlya few feet of stemming. Collar or direct priming (placingthe primer at or near the collar of the blast hole with theblasting cap pointing toward the bottom of the hole) ofblast holes normally causes more violence than center ortoe priming and requires the use of a longer collardistance.
Field experience has shown that a collar distance equal to70 percent of the burden is a good first approximation.Careful observation of airblast, flyrock, and fragmen-tation will enable further refinement of this dimension.Where adequate fragmentation in the collar zone cannotbe attained while still controlling airblast and flyrock,deck charges or satellite (mid-spaced) holes may berequired (figure19-4).
A deck charge is an explosive charge near the top of theblast hole, separated from the main charge by inert stem-ming. If large blocky materials are being created in thecollar zone and less stemming would cause excessiveairblast or flyrock, the main charge should be reduced
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slightly and a deck charge added. The deck charge isusually shot on the same delay as the main charge or onedelay later. Do not place the deck charge too near the topof the blast hole, or excessive flyrock may result.Alternatively, short satellite holes between the main blastholes can be used. The diameter of the satellite holes isusually smaller than the main blast holes, and thesatellite holes are loaded with a light charge of explosives.
Collar distance is a very important blast design variable.One violent blast can permanently alienate neighbors. Ina delicate situation, it may be best to start with a collardistance equal to the burden and gradually reduce this if,conditions warrant. Collar distances greater than theburden are seldom necessary.
Spacing
Spacing is defined as the distance between adjacent blastholes, measured perpendicular to the burden. Where therows are blasted one after the other as in figure 19-8, thespacing is measured between holes in a row. Where theblast progresses at an angle to the original free face, as infigure 19-9, the spacing is measured at an angle from theoriginal free face.
Spacing is calculated as a function of the burden and alsodepends on the timing between holes. Spacing that is tooclose causes crushing and cratering between holes, largeblocks in the burden, and toe problems. Spacing that istoo wide causes inadequate fracturing between holes, toeproblems, and is accompanied by humps on the face(figure 19-12).
When the holes in a row are initiated on the samedelay period, a spacing equal to twice the burden usuallywill pull the round satisfactorily. The V-cut round in
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Figure 19-12.—Effects of too small and too large spacing.
figure 19-9 illustrates simultaneous initiation within arow, with the rows being the angled lines of holes fired onthe same delay. The true spacing is twice the trueburden, even though the holes originally were drilled ona square pattern.
Field experience has shown that the use of millisecond(ms) delays between holes in a row results in betterfragmentation and also reduces ground vibrationsproduced by the blast. When ms delays are used betweenholes in a row, the spacing-to-burden ratio must be
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Figure 19-13.—Staggered blast pattern withalternate delays (blast hole spacing, S, is
1.4 times the burden, B).
reduced to somewhere between 1.2 and 1.8, with 1.5 beinga good first approximation. Various delay patterns maybe used within the rows, including alternate delays(figure 19-13) and progressive delays (figure 19-14).Generally, large diameter blast holes require lowerspacing-to-burden ratios (usually 1.2 to 1.5 with msdelays) than small diameter blast holes (usually 1.5 to1.8). Because of the geology complexities, the interactionof delays, differences in explosive and rock strengths, andother variables, the proper spacing-to-burden ratio mustbe determined through onsite experimentation, using thepreceding values as first approximations.
Except when using controlled blasting techniques such assmooth blasting and cushion blasting, described later, thespacing should never be less than the burden.
Hole Depth
In any blast design, the burden and the blast hole depth(or bench height) must be reasonably compatible. Therule of thumb for bench blasting is that the hole depth-to-burden ratio should be between 1.5 and 4.0. Hole depths
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Figure 19-14.—Staggered blast pattern withprogressive delays (blast hole spacing, S, is
1.4 times the burden, B).
less than 1.5 times the burden cause excessive air blastand fly rock and, because of the short, thick shape of theburden, give coarse and uneven fragmentation. Whereoperational conditions require a ratio of less than 1.5, aprimer should be placed at the toe of the bench to assuremaximum confinement. Keep in mind that placing theprimer in the subdrill can cause increased groundvibrations and unacceptably irregular final grades forengineering structures. If the use of a hole depth-to-burden ratio of less than 1.5 is necessary or specified,consideration should be given to increasing the benchheight or using smaller drill hole diameters.
Hole depths greater than four times the burden are alsoundesirable. The longer a hole is with respect to itsdiameter, the more error there will be in the hole locationat toe level (hole wandering), the most critical portion ofthe blast. A poorly controlled blast will result. Extremelylong, slender holes have been known to intersect.
High benches with short burdens can also create safetyhazards, such as small equipment having to drill the front
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235
row of holes near the edge of a high ledge or a smallshovel having to dig at the toe of a precariously high face.The obvious solution to this problem is to use a lowerbench height. There is no real advantage to a high bench.Lower benches yield more efficient blasting results, lowerdrilling costs, less chance of cutoffs, and are safer. If it isimpractical to reduce the bench height, larger rockhandling and drilling equipment should be used,effectively reducing the blast hole depth-to-burden ratio.
A major problem with long slender charges is the greaterpotential for cutoffs in the explosive column. If it isnecessary to use blast designs with large hole depth-to-burden ratios, multiple priming should be used asinsurance against cutoffs.
Delays
Millisecond delays are used between charges in a blastround to:
• To ensure that a proper free face is developed to en-able the explosive charge to efficiently fragment anddisplace the rock
• To enhance fragmentation between adjacent holes
• To reduce the ground vibrations created by the blast
Numerous delay patterns exist, several of which are cov-ered in figures 19-8, 19-9, 19-13, and 19-14. Keep in mindthe following:
• The delay time between holes in a row should be be-tween 1 and 5 ms per foot (0.3 m) of burden. Delaytimes less than 1 ms per foot of burden causepremature shearing between holes, resulting in
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coarse fragmentation. If an excessive delay time isused between holes, rock movement from the firsthole prevents the adjacent hole from creatingadditional fractures between the two holes. A delayof 3 ms per foot (0.3 m) of burden gives good resultsin many types of rock.
• The delay time between rows should be two to threetimes the delay time between holes in a row. Toobtain good fragmentation and to control fly rock, asufficient delay is needed so that the burden frompreviously fired holes has enough time to moveforward to accommodate moving rock from subse-quent rows. If the delay between rows is too short,movement in the back rows will be upward ratherthan outward (figure19-15).
• Where airblast is a problem, the delay between holesin a row should be at least 2 ms per foot of spacing.This prevents airblast from one charge from addingto that of subsequent charges as the blast proceedsdown the row.
• For controlling ground vibrations, most regulatoryauthorities consider two charges to be separateevents if they are separated by a delay of 9 ms ormore.
These rules-of-thumb generally yield good blastingresults. When using surface delay systems such as deto-nating cord connectors and sequential timers, the chancesfor cutoffs will be increased. To solve this problem, in-hole delays should be used in addition to the surfacedelays. When using surface detonating cord connectors,the use of 100-ms delays in each hole is suggested. Thiswill cause ignition of the in-hole delays well in advance of
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Figure 19-15.—The effect of inadequatedelays between rows.
rock movement, thus minimizing cutoffs. The same effectcan be accomplished with a sequential timer by avoidingthe use of electric caps with delays shorter than 75 to100 ms.
It is best if all the explosive in a blast hole is fired as asingle column charge. When firing large blast holes inpopulated areas, two or more delays within a blast holecan be used to reduce ground vibrations. Blast rounds ofthis type can become quite complex.
All currently used delay detonators employ pyrotechnicdelay elements that depend on a burning powder train fortheir delay. Although these delays are reasonablyaccurate, overlaps have been known to occur. When it isessential that one charge fires before an adjacent charge,such as in a tight corner of a blast, it is a good idea to skipa delay period.
Powder Factor
Powder factor, or pounds of explosive per cubic yard(kg/m3) of rock, is not the best tool for designing blasts.
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( )( )P F
L d D
BSH. .
.=
0 340
27
2
Blast designs should be based on the dimensionsdiscussed earlier in this chapter. Powder factor is anecessary calculation for cost accounting purposes. Inconstruction blasting where the excavated material haslittle or no inherent value, powder factor is usuallyexpressed in pounds of explosives per cubic yard ofmaterial broken. Powder factors for surface blasting canvary from 0.25 to 2.5 pounds per cubic yards (lb/yd3 [0.1 to1.1 kg/m3]), with 0.5 to 1.0 lb/yd3 (0.2 to 0.45 kg/m3) beingmost typical.
Powder factor for a single blast hole is calculated by thefollowing:
P.F. = Powder factor in pounds of explosive per cubic yard of rockL = Length of explosive charge in feetd = Density of explosive charge in grams per cubic
centimeterD = Charge diameter in inchesB = Burden in feetS = Spacing in feetH = Bench height
A comparable formula can be developed for metricequivalents. Many companies that provide explosives alsopublish tables that give loading densities in pounds perfoot of blast hole for different combinations of d and D. Acommon nomograph found in most blasting handbookscan be used to calculate the density in pounds per foot ofborehole. The powder factor is a function of the explosivetype, rock density, and geologic structure. Table 19-3includes typical powder factors for surface blasting.
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Table 19-3.—Typical powder factors for surface blasting
Rock breakagedifficulty
Powder factor
(lb/yd3) (kg/m3)
Low 0.25-0.40 0.1-0.18
Medium 0.40- 0.75 0.18-0.34
High 0.75-1.25 0.34-0.57
Very high 1.25-2.50 0.57-1.14
Higher energy explosives, such as those containing largeamounts of aluminum, can break more rock per unitweight than lower energy explosives. Most of thecommonly (lower energy) used explosive products havesimilar energy values and, thus, have similar rockbreaking capabilities. Soft, low density rock requires lessexplosive than hard, dense rock. Large hole patternsrequire less explosive per volume of rock because a largerportion of stemming is used. Poor powder distribution inlarger diameter blast holes frequently results in coarserfragmentation. Massive rock with few existing planes ofweakness requires a higher powder factor than a rock unitwith numerous, closely spaced joints or fractures. Themore free faces a blast has to break to, the lower thepowder factor requirement. A corner cut (figure19-8),with two vertical free faces, requires less powder than abox cut (figure19-9) or angled cuts (figure19-16) with onlyone vertical free face, which, in turn, will require lesspowder than a shaft sinking type or parallel cut(figure19-16) where there are no free faces. In a shaftsinking cut, it is desirable to open a second free face by
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Figure 19-16.—Types of opening cuts.
creating a V-cut somewhere near the center of the round.V-cuts are discussed in the “Underground Blasting”section of this chapter.
When blasted materials have an inherent value per ton,such as aggregate or ore, powder factors are expressed asunit weight of explosives per ton of rock or tons of rock perunit weight of explosive.
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Secondary Blasting
Some primary blasts will result in fragments too large tobe handled efficiently by the loading equipment and willcause plugging of crushers or preparation plants.Secondary fragmentation techniques must be used tobreak these oversize fragments. If fragments are too largeto be handled, the loader operator will set the rock asidefor treatment. Identifying material large enough to causecrusher plugging is not always easy. The loader operatormust be knowledgeable enough to watch for material thatis small enough for convenient loading but that is toolarge for the crusher.
Secondary fragmentation can be accomplished by:
• A heavy ball (headache ball) suspended from a cranemay be dropped repeatedly on the oversize fragmentuntil it breaks. This is a relatively inefficientmethod, and breaking a large or tough (nonbrittle)rock may take considerable time. This method isadequate where the number of oversize fragments issmall.
• A hole may be drilled into the oversize fragment anda hydraulic wedging device inserted to split the rock.This is also a slow method but may be satisfactorywhere a limited amount of secondary fragmentationis necessary. An advantage to this method is that itdoes not create the flyrock associated with explosivesand, to some degree, with the headache ball method.
• An explosive may be packed loosely into a crack ordepression in the oversize fragment then coveredwith a damp earth material and fired. This type ofcharge is called a mudcap, plaster, or adobe charge.This method is inefficient because of the limited
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explosive confinement and the relatively largeamount of explosives required. Other results areexcessive noise, flyrock, and often, inadequatefragmentation. This method is also hazardousbecause the primed charge lying on the surface isprone to accidental initiation by external impactsfrom falling rocks or equipment. External chargesshould be used to break boulders only where drillingis impractical.
• The most efficient method of secondary fragmenta-tion is through the use of small (1- to 3-inch [25- to75-mm]) blast holes. The blast hole is normallycollared at the most convenient location, such as acrack or depression in the rock, and is directedtoward the center of the mass. The hole is drilledtwo-thirds to three-fourths of the way through therock. Because the powder charge is surrounded byfree faces, less explosive is required to break a givenamount of rock than in primary blasting. One-quarter pound per cubic yard (0.1 kg/m3) usually isadequate. Careful location of the charge is moreimportant than its precise size. When in doubt, it isbest to estimate on the low side and under load thehole. For larger fragments, it is best to drill severalholes and distribute the explosive charge rather thanplace the entire charge in a single hole. All secondaryblast holes should be stemmed. Usually, secondaryblasts are more violent than primary blasts. Anytype of initiation system may be used to initiate asecondary blast and for connecting large numbers ofoversize fragments. Detonating cord often is usedwhere noise is not a problem.
Although secondary blasting employs relatively smallcharges, the potential safety hazards must not be under-
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estimated. Usually, there is more flyrock, and the flyrockis less predictable than with primary blasting.
Underground Blasting
Underground blast rounds are divided into two basiccategories:
(1) Heading, drift, or tunnel rounds, where the onlyfree face is the surface from which the holes aredrilled
(2) Bench or stope rounds, where there is one or morefree faces in addition to the face where the blastholes are drilled.
In the second category, blast rounds are designed in thesame manner as surface blast rounds. Only the blastrounds that are in the first category (those with only oneinitial free face) are discussed below.
Opening Cuts
The initial and most critical part of a heading round is theopening cut. The essential function of this cut is toprovide additional free faces where the rock can bebroken. Although there are many specific types ofopening cuts and the terminology can be quite confusing,all opening cuts fall into one of two classifications—angledcuts or parallel hole cuts (figure 19-16).
An angled cut, also referred to as a V-cut, draw cut, slabcut, or pyramid cut, breaks out a wedge of rock to createan opening that the remaining burden can move into.Angled cuts are very difficult to drill accurately. Thebottoms of each pair of cut holes should be as close
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together as possible but must not cross. If they cross, thedepth of round pulled will be less than designed. If thehole bottoms are more than a foot or so apart, the roundmay not pull to the proper depth. The angle between thecut holes should be 60 degrees or more to minimizebootlegging. One method to ensure getting a standardangle cut is to supply the drillers with a template with theproper spacing and angles for the angled holes. Theselection of the specific type of angled cut is a function ofthe rock, the type of drilling equipment, and thephilosophy of the blasting supervisor. A considerableamount of trial and error usually is involved indetermining the best angle cut for a specific site. In smalldiameter tunnels with narrow headings, it is oftenimpossible to position the drill properly to drill an angledcut. In this case, a parallel hole cut must be used.
Parallel hole cuts, also referred to as Michigan cuts,Cornish cuts, shatter cuts, burn cuts, or Coromant cuts,are basically a series of closely spaced holes, some loadedand some unloaded (figure 19-17) that, when fired,pulverize and eject a cylinder of rock to create an openingwhere the remaining burden can be broken. Because theyrequire higher powder factors and more drilling pervolume of rock blasted, the use of parallel hole cutsusually is restricted to narrow headings where there isnot enough room to drill an angled cut.
Parallel hole cuts involve more drilling than angled cutsbecause the closely spaced holes break relatively smallvolumes of rock. Parallel cuts are relatively easy to drillbecause the holes are parallel. Like angled cuts, accu-rately drilled parallel hole cuts are essential if the blastround is to be effective. Some drill jumbos have automaticcontrols to ensure that holes are drilled parallel. Drilljumbos of this type are a good investment where parallelhole cuts will be drilled routinely. A template also may
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Figure 19-17.—Six designs for parallel hole cuts.
be used in drilling a parallel hole cut. The selection of thetype of parallel hole cut also depends on the rock, the typeof drilling equipment, and the philosophy of the blastingsupervisor. As with angled cuts, trial and error usually isinvolved in determining the best parallel hole cut for aspecific site.
All types of opening cuts must pull to the planned depthbecause the remainder of the round will not pull moredeeply than the opening cut. In blasting with burn cuts,care must be exercised to prevent overloading of the burnholes because overloading may cause the cut to “freeze” ornot pull properly. The design of the cut depends on thetype of rock and often must be designed and refined bytrial and error.
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The advantage of a large central hole is that the holegives a dependable free face where succeeding holes canbreak. This free face is not always obtained withstandard burn cuts. The large central hole ensures amore dependable and deeper pull of the blast round. Thedisadvantages of a large central hole are the requirementsfor the proper equipment to drill the large central hole aswell as extra time. Intermediate-sized holes, usually 4 to5 inches (100-130 mm) in diameter, are sometimes drilledusing the standard blast hole equipment as a compromise.
In some soft materials, particularly coal, the blasted cutis replaced by a sawed kerf, usually at floor level(figure 19-18). In addition to giving the material adependable void to break into, the sawed cut ensures thatthe floor of the opening will be smooth.
Blasting Rounds
Once the opening cut has established the necessary freeface, the remainder of the blast holes must be designed sothat the burden successively breaks into the void space.The progression of the blast round should provide aproper free face parallel or nearly parallel to the hole atits time of initiation. Figure 19-19 gives the typicalnomenclature for blast holes in a heading round.
The holes fired immediately after the cut holes are calledthe relievers. The burden between these holes must beplanned carefully. If the burden is too small, the chargeswill not pull their share of the round. If the burden is toolarge, the round may freeze because the rock will haveinsufficient space to expand. After several relievers havebeen fired, the opening usually is large enough to permitthe remainder of the blast to be designed, as discussedunder “Surface Blasting.” Where heading rounds arelarge, the burden and spacing ratio usually is slightly less
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Figure 19-18.—Blast round for soft rock using sawed kerf (numbers on loaded
holes show delay in milliseconds.)
than that for surface blasts. In small headings wherespace is limited, the burden and spacing ratio will be stillsmaller. Trial and error plays an important part in thistype of blast design.
The last holes to be fired in an underground round are theback holes at the top, the rib holes at the sides, and thelifters at the bottom of the heading. Unless controlledblasting is used (discussed below), the spacing betweenthese perimeter holes is about 20 to 25 blast holediameters. Figure 19-20 shows two typical angled cutblast rounds. After the initial wedge of rock is extractedby the cut, the angles of the subsequent blast holes are
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Figure 19-19.—Nomenclature for blast holesin a heading round.
Figure 19-20.—Angled cut blast rounds.
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Figure 19-21.—Parallel hole cut blast rounds.
reduced progressively until the perimeter holes areparallel to the heading or looking slightly outward. Indesigning burden and spacing dimensions for angled cutblast rounds, the location of the bottom of the hole isconsidered rather than the collar.
Figure 19-21 shows two typical parallel hole cut blastrounds. These rounds are simpler to drill than angled cutrounds. Once the central opening has been established,the round resembles a bench round turned on its side.Figure 19-22 shows a comparison of typical muckpilesobtained from V-cut and burn-cut blast rounds. Burn cutsgive more uniform fragmentation and a more compactmuckpile than V-cuts. V-cut muckpiles are more spreadout and vary in fragmentation. Powder factors and theamount of drilling required are higher for burn cuts.
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Figure 19-22.—Fragmentation and shape of muckpile as a function of type of cut.
Delays
Two series of delays are available for undergroundblasting—millisecond delays, the same as those used insurface blasting; and slow, or tunnel delays. The choiceof delay depends on the size of the heading being blastedand on the fragmentation and type of muckpile desired.Slow delays give coarser fragmentation and a morecompact muckpile. Millisecond delays give finer fragmen-tation and a looser muckpile (figure19-23). In smallheadings where space is limited, particularly when usingparallel hole cut rounds, slow delays are necessary toensure that the rock from each blast hole has time to beejected before the next hole fires. Where delays inter-mediate between millisecond delays and slow delays isdesired, use millisecond delays and skip delay periods.
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Figure 19-23.—Fragmentation and shape ofmuckpile as a function of delay.
In an underground blast round, the delay pattern must bedesigned so that at the time of firing each hole has a goodfree face where the burden can be displaced. Figure 19-24shows a typical delay pattern for a burn cut blast roundin a heading in hard rock. Figure 19-25 shows a delaypattern for a V-cut blast round.
The shape of the muckpile is affected by the order that thedelays are fired (figure19-26). If the blast is designed sothat the back holes at the roof are fired last, a cascadingeffect is obtained, resulting in a compact muckpile. If thelifters are fired last, the muckpile will be displaced awayfrom the face.
Powder Factor
As with surface blasting, powder factors for undergroundblasting vary depending on several things. Powderfactors for underground blasting may vary from 1.5 to
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Figure 19-25.—Typical V-cut blast rounddelay pattern (numbers on loaded holes
show delay in milliseconds).
Figure 19-24.—Typical burn cut blast round delay pattern (numbers on loaded
holes show delay in milliseconds).
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Figure 19-26.—Shape of muckpile as a function of firing order.
12 lb/yd3 (0.7 to 5.5 kg/m3). Soft, light weight rock,headings with large cross sections, large blast holes, andangle cut rounds all tend to require lower powder factorsthan hard, dense rock, small headings, small blast holes,and parallel hole cuts.
Controlled Blasting Techniques
The term, controlled blasting, is used to describe severaltechniques that limit damage to the rock at the perimeterof the excavation by preventing the force of a blast fromcontinuing into the side walls. Normal blasting propa-gates cracks into the surrounding rock. These cracks canreduce the stability of the opening. The purpose of con-trolled blasting is to reduce this perimeter cracking and,
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thus, increase stability of the final surface. Much of thefollowing discussion on controlled blasting techniques hasbeen determined through years of on-the-job testing andevaluation. The results of controlled blasting are afunction of the geology, especially the number andorientation of joint and fracture planes and the quality ofthe final rock surface that is required.
Line Drilling
Line drilling consists of drilling a row of closely spacedholes along the final excavation limits and not loading theholes with explosive. The line-drilled holes provide aplane of weakness to which the final row of blast holescan break and also reflect a portion of the blast’s shockwave. Line drilling is used mostly in small blastingoperations and involves small holes in the range of 2 to3 inches (50-75 mm) in diameter. Line drilling holes arespaced (center to center) two to four diameters apart butare more closely spaced at the corners. The maximumpractical depth to which line drilling can be done isgoverned by how accurately the alignment of the holes canbe held at depth (seldom more than 30 feet [10 m]).
To further protect the final perimeter, the blast holes ad-jacent to the line drill are spaced more closely and loadedmore lightly than the rest of the blast, and deck chargesare used as necessary. Best results are obtained in ahomogeneous rock with few joints or bedding planes orwhen the holes are aligned with a major joint plane. Linedrilling is sometimes used in conjunction with presplittingwhere the corners are line drilled and the remainder ofthe perimeter is presplit.
The use of line drilling is limited to jobs where even alight load of explosives in the perimeter holes would causeunacceptable damage. The results of line drilling are
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often unpredictable, the cost of drilling is high, and theresults depend on the accuracy of the drilling.
Presplitting
Presplitting, sometimes called preshearing, is similar toline drilling except that the holes are drilled slightlyfarther apart and are loaded very lightly. Presplit holesare fired before any of the adjacent main blast holes. Thelight explosive charges propagate a crack between theholes. In badly fractured rock, unloaded guide holes maybe drilled between the loaded holes. The light powderload may be obtained by using specially designed slendercartridges, partial or whole cartridges taped to a deto-nating cord downline, an explosive cut from a continuousreel, or heavy grain detonating cord. A heavier charge oftamped cartridges is used in the bottom few feet of hole.Figure 19-27 shows three types of blast hole loads used forpresplitting. Cartridges ¾ or � inch by 2 feet (19 or22 mm by 0.6 m) connected with couplers are available.Manufacturers now produce continuous, small diameter,long-tubular water gel columns for loading presplit holes.The diameter of these continuous tubular columns usuallyis 1 inch (25 mm), and they come with a built-in downline.They can be loaded easily in rough and inclined holes.The continuous column presplit explosives produceincreased loading rates and reduced labor costs.
If possible, stem completely around and between thecartridges in the blast hole; and, although not essential,fire in advance of the main blast. The maximum depthfor a single presplit is limited by the accuracy of thedrillholes and is usually about 50 feet (15 m). Depthsbetween 20 and 40 feet (6 and 12 m) are recommended.A deviation of greater than 6 inches (152 mm) from thedesired plane or shear will give inferior results. Avoidpresplitting too
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Figure 19-27.—Typical presplit blast hole loading.
far ahead of the production blast. If possible, presplit ashort section and dig that section out so that the qualityof the presplit can be checked. If the presplit results areunsatisfactory, adjustments can be made in subsequentblasts.
Presplitting is usually done in a separate operation andwell in advance of drilling and loading the main blast.The presplit holes can be fired with the main blast by
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firing the presplit holes on the first delay period. Theincreased hole spacing compared with line drillingreduces drilling costs. Table 19-4 gives parameters forpresplitting.
Smooth Blasting
Smooth blasting, also called contour blasting, perimeterblasting, or sculpture blasting, is the most widely usedmethod of controlling overbreak in underground openingssuch as drifts and stopes (benches). Smooth blasting issimilar to presplitting in that an additional row of holesis drilled at the perimeter of the excavation. These holescontain light loads and are more closely spaced than theother holes in the round (figure19-28). The light powderload usually is continuously “string loaded” (loaded endto end) with slender cartridges or continuous reel explo-sive is used as shown in figure 19-27. Unlike presplitting,the smooth blast holes are fired after the main blast.Usually, this is done by loading and connecting the entireround and firing the perimeter holes one delay later thanthe last hole in the round. The burden on the perimeterholes should be approximately 1.5 times the spacing.Table 19-5 gives parameters for smooth blasting.
A compromise for smooth wall blasting is to slightlyreduce the spacing of the perimeter holes, compared to astandard design, and “string load” regular cartridges ofexplosive. The explosive column should be sealed with atamping plug, clay plug, or other type of stemming toprevent the string-loaded charges from being extractedfrom the hole by charges on earlier delays. Smoothblasting reduces overbreak and reduces the need forground support. These advantages usually outweigh thecost of the additional perimeter holes.
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Hole diameter Spacing Explosive charge
(inch) (mm) (feet) (m) (lb/ft) (kg/m)
1.50-1.75 38-44 1.00-1.50 0.3-0.46 0.08-0.25 0.03-0.1
2.00-2.50 50-64 1.50-2.00 0.46-0.6 .08-0.25 0.03-0.1
3.00-3.50 75-90 1.50-3.00 0.6-1.0 0.13-0.50 0.05-0.23
4.00 100 2.00-4.00 0.6-1.2 0.25-0.75 0.23-0.34
Table 19-5.—Parameters for smooth blasting
Hole diameter Spacing Burden Explosive charge
(inch) (mm) (feet) (m) (feet) (m) (lb/ft) (kg/m)
1.50-1.75 38-44 2.00 0.6 3.00 1 0.12-0.25 0.05-0.55
2.0 50 2.50 0.75 3.50 1.06 0.12-0.25 0.05-0.55
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Figure 19-28.—Typical smooth blastingpattern (Burden, B, is larger than spacing, S). Numbers on holes show delay in milliseconds.
Cushion Blasting
Cushion blasting, also called trimming, slabbing, orslashing, is the surface equivalent of smooth blasting.Like other controlled blasting techniques, cushionblasting involves a row of closely spaced, lightly loadedholes at the perimeter of the excavation. Holes up to
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Figure 19-29.—Cushion blasting techniques.
6½ inches (165 mm) in diameter have been used incushion blasting. Drilling accuracy with this larger sizeborehole permits depths of up to 90 feet (27 m) for cushionblasting. After the explosives have been loaded, stem-ming is placed in the void space around the charges forthe entire length of the column. Stemming “cushions” theshock from the finished wall minimizing the stresses andfractures in the finished wall. The cushion blast holes arefired after the main excavation is removed (figure19-29).A minimum delay between the cushion blast holes is
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desirable. The same loading techniques that apply to pre-splitting are used with cushion blasting. The burden onthe cushion holes should always be less than the width ofthe berm being removed.
The large diameter holes associated with cushion blastingresult in larger spacings as compared with presplittingreducing drilling costs. Better results can be obtained inpoorly lithified and weathered formations than withpresplitting, and the larger holes permit better alignmentat depth. Table 19-6 gives parameters for cushionblasting.
Riprap Blasting Techniques
Riprap blasting follows the usual rules for blast designs.A few special techniques can aid production of qualityriprap.
Powder distribution is the key to satisfactory results. Ifthe above principles of good blast design are followed,satisfactory results should be achieved. The blast designmust be monitored continually and changed to producethe best results.
Full column loading is usually the best for initial shots.The starting burden for riprap production should belarger than predicted from table 19-1. If a burden of7 feet (2.1 m) is predicted, a starting burden ofapproximately 9 feet (2.7 m) should be tried. Furtheradjustments can be made to optimize the breakage.
In typical quarry blasting, a spacing of 1.5 times theburden is a good first estimate. The spacing should beabout equal to the burden but not smaller than theburden for riprap. Either a square or a staggered drill
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Table 19-6.—Parameters for cushion blasting
Hole diameter Spacing Burden Explosive charge
(inch) (mm) (feet) (m) (feet) (m) (lb/ft) (kg/m)
2.00-2.50 50-64 3.00 1.0 4.00 1.2 0.08-0.25 0.03-0.1
3.00-3.50 75-90 4.00 1.2 5.00 1.5 0.13-0.5 0.05-0.2
4.00-4.50 100-115 5.00 1.5 6.00 1.8 0.25-0.75 0.1-0.3
5.00-5.50 127-140 6.00 1.8 7.00 2.1 0.75-1.00 0.3-0.45
6.00-6.50 152-165 7.00 2.1 9.00 2.7 1.00-1.50 0.45-0.7
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pattern should be used. The square pattern often gives acoarser product but also may give more erratic toeconditions. Where possible, rows of blast holes should beperpendicular to the major vertical plane of weaknesssuch as the primary vertical joint set.
If a reasonably well graded riprap is specified, it will benecessary to perform test or trial blasts. The productshould be analyzed for gradation, and further test blastsmade and gradations checked until the specifications havebeen met. If insufficient coarse product is produced, theburden and spacing of subsequent rounds should beincreased by 1 foot (0.3 m) per round until the amount ofcoarse product is adequate. If toe problems occur beforethe amount of coarse product is adequate, reduce theburden and spacing again and increase the stemming ortry deck loading in the upper part of the lift.
If too much coarse product is produced, determinewhether the material comes from the top or bottom partof the bench face. If the material comes from the bottomor is generally well-distributed, decrease the burden andspacing in 1-foot (0.3-m) increments until the oversize iscontrolled. If the oversize comes from the top, try usingsatellite holes (short, smaller diameter holes between themain blast holes, figure19-4) or less stemming.
It is essential that each blast be laid out accurately anddrilled and loaded so that there is a known baseline toadjust from if early results are not good. Keeping goodrecords is essential for later adjustments to the blastdesign. Single row firing, at least for the early shots, alsosimplifies blast pattern adjustments.
In dry conditions, ANFO will work well. A good, fast,bottom primer should be used. In wet conditions, anemulsion, water gel, slurry, or gelatin dynamite should be
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used. The bottom of the blast hole should be primed.Excessive orange smoke from a blast indicates the needfor a water resistant product or for a better proportionalmix of the ANFO.
Bibliography
Dick, R.A., L.R. Fletcher, and D.V. Andrea, Explosivesand Blasting Procedures Manual. Bureau of MinesInformation Circular 8925, pp. 57-74, 1987.
E. I. du Pont de Nemours & Co., Inc., Blaster’s Handbook.16th edition, pp. 494, Wilmington, Delaware, 1978.
Glossary
A
Acoustical impedance - The mathematical expressioncharacterizing a material energy transfer property.The product of a material unit density and sonicvelocity.
Adobe charge - See mud cap.
Airblast - An airborne shock wave resulting from thedetonation of explosives; may be caused by burdenmovement or the release of expanding gas into the air.Airblast may or may not be audible.
Airdox - System that uses 10,000 lb/in2 compressed air tobreak undercut coal. Airdox will not ignite a gassy ordusty atmosphere.
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Aluminum - A metal commonly used as a fuel or sen-sitizing agent in explosives and blasting agents;normally used in finely divided particle or flake form.
American Table of Distance - A quantity-distancetable published by the Institute of Makers ofExplosives (IME) as pamphlet No. 2, which specifiessafe explosive storage distances from inhabitedbuildings, public highways, passenger railways, andother stored explosive materials.
Ammonium nitrate (AN) - The most commonly usedoxidizer in explosives and blasting agents, NH4NO3.
ANFO - An explosive material consisting of a mixture ofammonium nitrate and fuel oil. The most commonlyused blasting agent.
ATF - Bureau of Alcohol, Tobacco and Firearms,U.S. Department of the Treasury, which enforcesexplosives control and security regulations.
Axial priming - A system for priming blasting agentswhere a core of priming materials extends throughmost or all of the blasting agent charge length.
B
Back break - Rock broken beyond the limits of the lastrow of holes.
Back holes - The top holes in a tunnel or drift round.
Base charge - The main explosive charge in a detonator.
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Bench - The horizontal ledge in a quarry face alongwhere holes are drilled. Benching is the process ofexcavating where terraces or ledges are worked in astepped sequence.
Binary explosive - An explosive based on twononexplosive ingredients, such as nitromethane andammonium nitrate. Materials are shipped and storedseparately and mixed at the jobsite to form a highexplosive.
Black powder - A low energy explosive consisting ofsodium or potassium nitrate, carbon, and sulfur.Black powder is seldom used today because of the lowenergy, poor fume quality, and extreme sensitivity tosparks.
Blast - The detonation of explosives to break rock.
Blast area - The area near a blast within the influence offlying rock or concussion.
Blaster - A qualified person in charge of a blast. Also, aperson (blaster-in-charge) who has passed testapproved by Office of Surface Mining (OSM) whichcertifies the blaster’s qualifications to superviseblasting activities.
Blasters’ galvanometer - Blasters' multimeter; seegalvanometer, multimeter.
Blast hole - A hole drilled in rock or other material forthe placement of explosives.
Blasting agent - An explosive that meets prescribedcriteria for insensitivity to initiation. For storage, anymaterial or mixture consisting of a fuel and oxidizer,
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intended for blasting, not otherwise defined as anexplosive, provided that the finished product, as mixedand packaged for use or shipment, cannot be detonatedby means of a No. 8 test blasting cap when unconfined(ATF). For transportation, a material designed forblasting that has been tested in accordance with theCode of Federal Regulations (CFR) Title 49, Section173.14a, and found to be so insensitive that there isvery little probability of accidental initiation toexplosion or transition from deflagration to detonation(Department of Transportation [DOT]).
Blasting cap - A detonator that is initiated by safety fuse(Mine Safety and Health Administration [MSHA]).See detonator.
Blasting circuit - The circuit used to fire one or moreblasting caps.
Blasting crew - A crew whose job is to load explosivecharges.
Blasting machine - Any machine built expressly for thepurpose of energizing blasting caps or other types ofinitiators.
Blasting mat - See mat.
Blasting switch - A switch used to connect a powersource to a blasting circuit.
Blistering - See mud cap.
Blockhole - A hole drilled into a boulder to allow theplacement of a small charge to break the boulder.
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Booster - A unit of explosive or blasting agent used forperpetuating or intensifying an explosive reaction. Abooster does not contain an initiating device but isoften cap sensitive.
Bootleg - That portion of a borehole that remains rela-tively intact after having been charged with explosiveand fired. A bootleg may contain unfired explosiveand may be hazardous.
Borehole (blast hole) - A drilled hole, usually in rock,that is loaded with explosives.
Borehole pressure - The pressure that the hot gases ofdetonation exert on the borehole wall. Boreholepressure is primarily a function of the density of theexplosive and the heat of explosion.
Bridge wire - A very fine filament wire imbedded in theignition element of an electric blasting cap. An electriccurrent passing through the wire causes a sudden heatrise, causing the ignition element to be ignited.
Brisance - A property of an explosive roughly equivalentto detonation velocity. An explosive with a high deto-nation velocity has high brisance.
Bubble energy - The expanding gas energy of anexplosive, as measured in an underwater test.
Bulk mix - An explosive material prepared for usewithout packaging.
Bulk strength - The strength of an explosive per unitvolume.
Bulldoze - See mud cap.
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Burden - The distance to the nearest free or open facefrom an explosive charge. There may be apparentburden and a true burden, the latter being measuredin the direction broken rock will be displaced followingfiring of the explosive charge. Also, the amount ofmaterial to be blasted by a given hole in tons or cubicyards (m3).
Burn cut - A parallel hole cut employing several closelyspaced blast holes. Not all of the holes are loaded withexplosive. The cut creates a cylindrical opening byshattering the rock.
Bus wires - The two wires joined to the connecting wirewhere the leg wires of the electric caps are connectedin a parallel circuit. Each leg wire of each cap isconnected to a different bus wire. In a series-in-parallel circuit, each end of each series is connected toa different bus wire.
Butt - See bootleg.
C
Cap - See detonator.
Capped fuse - A length of safety fuse with an attachedblasting cap.
Capped primer - A package or cartridge of cap-sensitiveexplosive that is specifically designed to transmitdetonation to other explosives and which contains adetonator (MSHA).
Cap sensitivity - The sensitivity of an explosive to initia-tion, relative to an IME No. 8 test detonator.
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Carbon monoxide - A poisonous gas created bydetonating explosive materials. Excessive carbonmonoxide is caused by an inadequate amount ofoxygen in the explosive mixture (excessive fuel).
Cardox - A system that uses a cartridge filled with liquidcarbon dioxide, which when initiated by a mixture ofpotassium perchlorate and charcoal, creates a pressureadequate to break undercut coal.
Cartridge - A rigid or semirigid container of explosive orblasting agent of a specified length or diameter.
Cartridge count - The number of 1¼- by 8-inch (32- by203-mm) cartridges of explosives per 50-pound(22.7-kg) case.
Cartridge strength - A rating that compares a givenvolume of explosive with an equivalent volume ofstraight nitroglycerin dynamite expressed as apercentage.
Cast primer - A cast unit of explosive, usually pentoliteor composition B, commonly used to initiate detonationin a blasting agent.
Chambering - The process of enlarging a portion of blasthole (usually the bottom) by firing a series of smallexplosive charges. Chambering can also be done bymechanical or thermal methods.
Chapman-Jougeut (C-J) plane - The plane that definesthe rear boundary of the primary reaction zone in adetonating explosive column.
Circuit tester - See galvanometer or multimeter.
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Class A explosive - Defined by the U.S. Department ofTransportation (DOT) as an explosive that possessesdetonating or otherwise maximum hazard; such as,but not limited to, dynamite, nitroglycerin, lead azide,black powder, blasting caps, and detonating primers.
Class B explosive - Defined by DOT as an explosive thatpossesses flammable hazard, such as, but not limitedto, propellant explosives, photographic flash powders,and some special fireworks.
Class C explosive - Defined by DOT as an explosive thatcontains Class A or Class B explosives, or both, ascomponents but in restricted quantities. For example,blasting caps or electric blasting caps in lots of lessthan 1,000.
Collar - The top or opening of a borehole or shaft. To“collar” in drilling means the act of starting a borehole.
Collar distance - The distance from the top of thepowder column to the collar of the blast hole, usuallyfilled with stemming.
Column charge - A long, continuous charge of explosiveor blasting agent in a borehole.
Commercial explosives - Explosives designed and usedfor commercial or industrial, rather than militaryapplications.
Composition B - A mixture of RDX and TNT that has adensity of 1.65 g/cm3 and a velocity of 25,000 feet persecond (7,622 m/sec), when cast. It is useful as aprimer for blasting agents.
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Condenser-discharge blasting machine - A blastingmachine that uses batteries or magnets to energizeone or more condensers (capacitors) whose storedenergy is released into a blasting circuit.
Confined detonation velocity - The detonation velocityof an explosive or blasting agent under confinementsuch as in a borehole.
Connecting wire - A wire, smaller in gage than the leadwire, used in a blasting circuit to connect the capcircuit with the lead wire or to extend leg wires fromone borehole to another. Usually consideredexpendable.
Connector - See MS connector.
Controlled blasting - Techniques used to control over-break and produce a competent final excavation wall.See line drilling, presplitting, smooth blasting, andcushion blasting.
Cordeau detonant fuse - A term used to definedetonating cord.
Cornish cut - See parallel hole cut.
Coromant cut - See parallel hole cut.
Coupling - The degree that an explosive fills the bore-hole. Untamped cartridges are decoupled; alsocapacitive and inductive coupling from power lines toan electric blasting circuit.
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Coyote blasting - The practice of driving tunnelshorizontally into a rock face at the foot of the shot.Explosives are loaded into these tunnels. Coyoteblasting is used where it is impractical to drillvertically.
Critical diameter - The minimum diameter of anyexplosive for propagation of a stable detonation.Critical diameter is effected by confinement,temperature, and pressure on the explosive.
Crosslinking agent - The final ingredient added to awater gel or slurry, causing the material to changefrom a liquid to a gel.
Current limiting device - A device used to preventarcing in electric blasting caps by limiting the amountor duration of current flow. Also used in a blasters’galvanometer or multimeter to ensure a safe currentoutput.
Cushion blasting - A surface blasting technique used toproduce competent slopes. The cushion holes, firedafter the main charge, have a reduced spacing andemploy decoupled charges.
Cushion stick - A cartridge of explosive loaded into asmall diameter borehole before the primer. The use ofa cushion stick is not generally recommended becauseof possible bootlegs.
Cut - An arrangement of holes used in undergroundmining and tunnel blasting providing a free face forthe remainder of the round to break.
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Cutoffs - A portion of a column of explosives that hasfailed to detonate owing to bridging or a shifting of therock formation, often due to an improper delay system;also a cessation of detonation in detonating cord.
D
Dead pressing - Desensitization of an explosive causedby pressurization. Tiny air bubbles required for sensi-tivity are literally squeezed from the mixture.
Decibel - The unit of sound pressure commonly used tomeasure airblast from explosives. The decibel scale islogarithmic.
Deck - A small charge or portion of a blast hole loadedwith explosives that is separated from other chargesby stemming or an air cushion.
Decoupling - The use of cartridged products significantlysmaller in diameter than the borehole. Decoupledcharges are normally not used except in cushionblasting, smooth blasting, presplitting, and othersituations where crushing is undesirable.
Deflagration - A subsonic but extremely rapid explosivereaction accompanied by gas formation and boreholepressure but without shock.
Delay blasting - The use of delay detonators orconnectors that cause separate charges to detonate atdifferent times rather than simultaneously.
Delay connector - A nonelectric, short-interval delaydevice for use in delaying blasts that are initiated bydetonating cord.
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Delay detonator - An electric or nonelectric detonatorwith a built-in element that creates a delay betweenthe input of energy and the explosion of the detonator.
Delay electric blasting cap - An electric blasting capwith a built-in delay that delays cap detonation inpredetermined time intervals from milliseconds up toa second or more.
Delay element - The portion of a blasting cap thatcauses a delay between the application of energy to thecap and the time of detonation of the base charge ofthe cap.
Density - The weight per unit volume of explosive,expressed as cartridge count or grams per cubiccentimeter. See loading density.
Department of Transportation (DOT) - A Federalagency that regulates safety in interstate shipping ofexplosives and other hazardous materials.
Detaline System - A nonelectric system for initiatingblasting caps where the energy is transmitted throughthe circuit by a low-energy detonating cord.
Detonating cord - A plastic covered core of high-velocityexplosive, usually PETN, used to detonate explosives.The plastic covering is covered with various combi-nations of textiles and waterproofing.
Detonation - A supersonic explosive reaction where ashock wave propagates through the explosiveaccompanied by a chemical reaction that furnishesenergy to sustain stable shock wave propagation.Detonation creates both a detonation pressure and aborehole pressure.
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Detonation pressure - The head-on pressure created bythe detonation proceeding down the explosive column.Detonation pressure is a function of the explosivedensity and the square of the explosive velocity.
Detonation velocity - See velocity.
Detonator - Any device containing a detonating chargethat is used to initiate an explosive. Includes, but isnot limited to, blasting caps, electric blasting caps, andnonelectric instantaneous or delay blasting caps.
Ditch blasting - See propagation blasting.
DOT - See Department of Transportation.
Downline - The line of detonating cord in the boreholethat transmits energy from the trunkline down thehole to the primer.
Drilling pattern - See pattern.
Drop ball - Known also as a headache ball. An iron orsteel weight held on a wire rope that is dropped froma height onto large boulders to break them intosmaller fragments.
Dynamite - The high explosive invented by Alfred Nobel.Any high explosive where the sensitizer is nitrogly-cerin or a similar explosive oil.
E
Echelon pattern - A delay pattern that causes the trueburden at the time of detonation to be at an obliqueangle from the original free face.
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Electric blasting cap - A blasting cap designed to beinitiated by an electric current.
Electric storm - An atmospheric disturbance of intenseelectrical activity presenting a hazard in all blastingactivities.
Emulsion - An explosive material containing substantialamounts of oxidizers dissolved in water droplets sur-rounded by an immiscible fuel. Similar to a slurry.
Exploding bridge wire (EBW) - A wire that explodesupon application of current. The wire takes the placeof the primary explosive in an electric detonator. Anexploding bridge wire detonator is an electricdetonator that employs an exploding bridge wirerather than a primary explosive. An exploding bridgewire detonator is instantaneous.
Explosion - A thermochemical process where mixtures ofgases, solids, or liquids react with the almost instan-taneous formation of gas pressures and sudden heatrelease.
Explosion pressure - See borehole pressure.
Explosive - Any chemical mixture that reacts at highvelocity to liberate gas and heat causing very highpressures. ATF classifications include high explosivesand low explosives. Also, any substance classified asan explosive by DOT.
Explosive materials - A term that includes, but is notnecessarily limited to, dynamite and other high explo-sives, slurries, water gels, emulsions, blasting agents,black powder, pellet powder, initiating explosives,detonators, safety fuses, squibs, detonating cord,igniter cord, and igniters.
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Extra dynamite - Also called ammonia dynamite, adynamite that derives the major portion of its energyfrom ammonium nitrate.
Extraneous electricity - Electrical energy other thanactual firing current that may be a hazard withelectric blasting caps. Includes stray current, staticelectricity, lightning, radio frequency energy, andcapacitive or inductive coupling.
F
Face - A rock surface exposed to air. Also called a freeface, a face provides the rock with room to expandupon fragmentation.
Firing current - Electric current purposely introducedinto a blasting circuit for initiation. Also, the amountof current required to activate an electric blasting cap.
Firing line - A line, often permanent, extending from thefiring location to the electric blasting cap circuit. Alsocalled lead wire.
Flash over - Sympathetic detonation between explosivecharges or between charged blast holes.
Flyrock - Rock that is propelled through the air from ablast. Excessive flyrock may be caused by poor blastdesign or unexpected weak zones in the rock.
Fracturing - The breaking of rock with or without move-ment of the broken pieces.
Fragmentation - The extent that a rock is broken intopieces by blasting. Also the act of breaking rock.
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Fuel - An ingredient in an explosive that reacts with anoxidizer to form gaseous products of detonation.
Fuel oil - The fuel in ANFO, usually No. 2 diesel.
Fume Classification - An IME quantification of theamount of fumes generated by an explosive or blastingagent.
Fume quality - A measure of the toxic fumes to beexpected when a specific explosive is properlydetonated. See fumes.
Fumes - Noxious or poisonous gases liberated from ablast. May be due to a low fume quality explosive orinefficient detonation.
Fuse - See safety fuse.
Fuse lighter - A pyrotechnic device for rapid and depend-able lighting of safety fuse.
G
Galvanometer - (More properly called blasters’ galva-nometer.) A measuring instrument containing asilver chloride cell and/or a current limiting devicethat is used to measure resistance in an electricblasting circuit. Only a device specifically identifiedas a blasting galvanometer or blasting multimetershould be used for this purpose.
Gap sensitivity - The gap distance an explosive canpropagate across. The gap may be air or a definedsolid material. Gap sensitivity is a measure of thelikelihood of sympathetic propagation.
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Gas detonation system - A system for initiating capswhere the energy is transmitted through the circuit bya gas detonation inside a hollow plastic tube.
Gelatin - An explosive or blasting agent that has a gelati-nous consistency. The term is usually applied to agelatin dynamite but may also be a water gel.
Gelatin dynamite - A highly water-resistant dynamitewith a gelatinous consistency.
Generator blasting machine - A blasting machineoperated by vigorously pushing down a rack bar ortwisting a handle. Now largely replaced by condensordischarge blasting machines.
Grains - A weight measurement unit where 7,000 grains
equal 1 pound.
Ground vibration - Ground shaking caused by theelastic wave emanating from a blast. Excessivevibrations may cause damage to structures.
H
Hangfire - The detonation of an explosive charge afterthe designed firing time. A source of serious accidents.
Heading - The working face or end of an excavationdriven in an underground mine.
Hercudet - See gas detonation system.
Hertz - A term used to express the frequency of groundvibrations and airblast. One hertz is one cycle persecond.
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High explosive - Any product used in blasting that issensitive to a No. 8 test blasting cap and reacts at aspeed faster than that of sound in the explosivemedium. A classification used by ATF for explosivestorage.
Highwall - The bench, bluff, or ledge on the edge of asurface excavation. This term is most commonly usedin coal strip mining.
I
Ignitacord – A cordlike fuse that burns progressivelyalong its length with an external flame at the zone ofburning and is used for lighting a series of safety fusesin sequence. Burns with a spitting flame similar to aFourth-of-July sparkler.
IME - The Institute of Makers of Explosives. A tradeorganization dealing with the use of explosives andconcerned with safety in manufacture, transportation,storage, handling, and use. The IME publishes aseries of blasting safety pamphlets.
Initiation - The act of detonating a high explosive bymeans of a cap, mechanical device, or other means.Also the act of detonating the initiator.
Instantaneous detonator - A detonator that contains nodelay element.
J
Jet 1oader - A system for loading ANFO into smallblastholes where the ANFO is sucked from a containerand blown into the hole at high velocity through aloading hose.
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Jumbo - A machine designed to mount two or moredrilling units that may or may not be operatedindependently.
K
Kerf - A slot cut in a coal or soft rock face by amechanical cutter to provide a free face for blasting.
L
Lead wire - The wire connecting the electrical powersource with the leg wires or connecting wires of ablasting circuit. Also called a firing line.
LEDC - Low-energy detonating cord used to initiatenonelectric blasting caps.
Leg wires - Wires connected to the bridge wire of an elec-tric blasting cap and extending from the waterproofplug. The opposite ends are used to connect the capinto a circuit.
Lifters - The bottom holes in a tunnel or drift round.
Line drilling - An overbreak control method where aseries of very closely spaced holes are drilled at theperimeter of the excavation. These holes are notloaded with explosive.
Liquid oxygen explosive - A high explosive made bysoaking cartridges of carbonaceous materials in liquidoxygen. This explosive is rarely used today.
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Loading density - The pounds of explosive per foot ofcharge of a specific diameter.
Loading factor - See powder factor.
Loading pole - A pole made of nonsparking materialused to push explosive cartridges into a borehole andto break and tightly pack the explosive cartridges intothe hole.
Low explosive - An explosive where the speed ofreaction is slower than the speed of sound, such asblack powder. A classification used by ATF forexplosive storage.
LOX - See liquid oxygen explosive.
M
Magazine - A building, structure, or container speciallyconstructed for storing explosives, blasting agents,detonators, or other explosive materials.
Mat - A covering placed over a shot to hold down flyingmaterial. The mat is usually made of woven wirecable, rope, or scrap tires.
Maximum firing current - The highest current(amperage) recommended for the safe and effectiveinitiation of an electric blasting cap.
Metallized - Sensitized or energized with finely dividedmetal flakes, powders, or granules, usually aluminum.
Michigan cut - See parallel hole cut.
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Microballoons - Tiny hollow spheres of glass or plasticthat are added to explosive materials to enhancesensitivity by assuring adequate entrapped aircontent.
Millisecond (ms) - Short delay intervals equal to 1/1,000of a second.
Millisecond delay caps - Delay detonators that havebuilt-in time delays of various lengths. The intervalbetween the delays at the lower end of the series isusually 25 ms. The interval between delays at theupper end of the series may be 100 to 300 ms.
Minimum firing current - The lowest current(amperage) that will initiate an electric blasting capwithin a specified short interval of time.
Misfire - A charge or part of a charge that has failed tofire as planned. All misfires are dangerous.
Monomethylaminenitrate - A compound used to sensi-tize some water gels.
MS connector - A device used as a delay in a detonatingcord circuit connecting one hole in the circuit withanother or one row of holes to other rows of holes.
MSHA - The Mine Safety and Health Administration. Anagency under the Department of Labor that enforceshealth and safety regulations in the mining industry.
Muckpile - A pile of broken rock or dirt that is to beloaded for removal.
Mud cap - Referred to also as adobe, bulldoze, blistering,or plaster shot. A charge of explosive fired in contact
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with the surface of a rock usually covered with aquantity of mud, wet earth, or similar substance. Noborehole is used.
Multimeter - A multipurpose test instrument used tocheck line voltages, firing currents, current leakage,stray currents, and other measurements pertinent toelectric blasting. (More properly called blasters’multimeter.) Only a meter specifically designated asa blasters’ multimeter or blasters’ galvanometershould be used to test electric blasting circuits.
N
National Fire Protection Association (NFPA) - Anindustry/government association that publishesstandards for explosive material and ammoniumnitrate.
Nitrocarbonitrate - A shipping classification once givento a blasting agent by DOT.
Nitrogen oxides - Poisonous gases created by detonatingexplosive materials. Excessive nitrogen oxides may becaused by an excessive amount of oxygen in theexplosive mixture (excessive oxidizer) or by inefficientdetonation.
Nitroglycerin (NG) - The explosive oil originally used asthe sensitizer in dynamites, C3H5(ONO2)3.
Nitromethane - A liquid compound used as a fuel in two-component (binary) explosives and as rocket anddragster fuel.
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Nitropropane - A liquid fuel that can be combined withpulverized ammonium nitrate prills to make a denseblasting mixture.
Nitrostarch - A solid explosive similar to nitroglycerinused as the base of “nonheadache” powders.
Nonel - See shock tube system.
Nonelectric delay blasting cap - A detonator with adelay element capable of being initiatednonelectrically. See shock tube system; gas detonationsystem; Detaline System.
No. 8 test blasting cap - See test blasting cap No. 8.
O
OSHA - The Occupational Safety and Health Administra-tion. An agency under the Department of Labor thatenforces health and safety regulations in theconstruction industry, including blasting.
OSM - The Office of Surface Mining Reclamation andEnforcement. An agency under the Department of theInterior that enforces surface environmentalregulations in the coal mining industry.
Overbreak - Excessive breakage of rock beyond thedesired excavation limit.
Overburden - Worthless material lying on top of adeposit of useful materials. Overburden often refers todirt or gravel but can be rock, such as shale overlimestone or shale and limestone over coal.
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Overdrive - Inducing a velocity higher than the steadystate velocity in a powder column by the use of apowerful primer. Overdrive is a temporary pheno-menon, and the powder quickly assumes its steadystate velocity.
Oxides of nitrogen - See nitrogen oxides.
Oxidizer - An ingredient in an explosive or blastingagent that supplies oxygen to combine with the fuel toform gaseous or solid detonation products. Ammo-nium nitrate is the most common oxidizer used incommercial explosives.
Oxygen balance - A mixture of fuels and oxidizers wherethe gaseous products of detonation are predominantlycarbon dioxide, water vapor (steam), and free nitrogen.A mixture containing excess oxygen has a negativeoxygen balance.
P
Parallel circuit - A circuit where two wires, called buswires, extend from the lead wire. One leg wire fromeach cap in the circuit is hooked to each of the buswires.
Parallel hole cut - A group of parallel holes, some ofwhich are loaded with explosives, used to establish afree face in tunnel or heading blasting. One or more ofthe unloaded holes may be larger than the blast holes;also called Coromant, Cornish, burn, shatter, orMichigan cut.
Parallel series circuit - Similar to a parallel circuit butinvolving two or more series of electric blasting caps.
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One end of each series of caps is connected to each ofthe bus wires; sometimes called series-in-parallelcircuit.
Particle velocity - A measure of ground vibration.Describes the velocity of particle vibration whenexcited by a seismic wave.
Pattern - A drill hole plan laid out on a face or bench tobe drilled for blasting.
Pellet powder - Black powder pressed into 2-inch-long,1¼- to 2-inch diameter cylindrical pellets.
Pentaerythritoltetranitrate (PETN) - A militaryexplosive compound used as the core load of detonatingcord and the base charge of blasting caps.
Pentolite - A mixture of PETN and TNT used as a castprimer.
Permissible - A machine, material, apparatus, or devicethat has been investigated, tested, and approved bythe Bureau of Mines or MSHA maintained inpermissible condition.
Permissible blasting - Blasting according to MSHAregulations for underground coal mines or other gassyunderground mines.
Permissible explosives - Explosives that have been ap-proved by MSHA for use in underground coal mines orother gassy mines.
PETN - See pentaerythritoltetranitrate.
Plaster shot - See mud cap.
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Pneumatic 1oader - One of a variety of machinespowered by compressed air used to load bulk blastingagents or cartridged water gels.
Powder - Any solid explosive.
Powder chest - A strong, nonconductive portable con-tainer equipped with a lid used at blasting sites fortemporary explosive storage.
Powder factor - A ratio between the amount of powderloaded and the amount of rock broken, usuallyexpressed as pounds per ton or pounds per cubic yard.In some cases, the reciprocals of these terms are used.
Preblast survey - A documentation of the existing condi-tion of a structure. The survey is used to determinewhether subsequent blasting causes damage to thestructure.
Premature - A charge that detonates before intended.
Preshearing - See presplitting.
Presplitting - Controlled blasting where decoupledcharges are fired in closely spaced holes at theperimeter of the excavation. A presplit blast is firedbefore the main blast. Also called preshearing.
Pressure vessel - A system for loading ANFO into smalldiameter blast holes. The ANFO is contained in asealed vessel where air pressure forces the ANFOthrough a hose and into the blast hole; also known aspressure pot.
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Prill - A small porous sphere of ammonium nitratecapable of absorbing more than 6 percent by weight offuel oil. Blasting prills have a bulk density of 0.80 to0.85 g/cm3.
Primary blast - The main blast executed to sustainproduction.
Primary explosive - An explosive or explosive mixturesensitive to spark, flame, impact, or friction used in adetonator to initiate the explosion.
Primer - A unit, package, or cartridge of cap-sensitiveexplosive used to initiate other explosives or blastingagents and that contains a detonator.
Propagation - The detonation of explosive charges by animpulse from a nearby explosive charge.
Propagation blasting - The use of closely spaced,sensitive charges. The shock from the first chargepropagates through the ground, setting off theadjacent charge and so on. Only one detonator isrequired; primarily used for ditching in damp ground.
Propellant explosive - An explosive that normallydeflagrates and is used for propulsion.
Pull - The quantity of rock or length of advance excavatedby a blast round.
R
Radio frequency energy - Electrical energy travelingthrough the air as radio or electromagnetic waves.Under ideal conditions this energy can fire an electricblasting cap. IME Pamphlet No. 20 recommends safedistances from transmitters to electric blasting caps.
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Radio frequency transmitter - An electric device, suchas a stationary or mobile radio transmitting station,that transmits a radio frequency wave.
RDX - Cyclotrimethylenetrinitramine, an explosivesubstance used in the manufacture of compositions B,C-3, and C-4. Composition B is useful as a castprimer.
Relievers - In a heading round, holes adjacent to the cutholes, used to expand the opening made by the cutholes.
Rib holes - The holes at the sides of a tunnel or driftround that determine the width of the opening.
Riprap - Coarse rocks used for river bank or dam stabili-zation to reduce erosion by water flow.
Rotational firing - A delay blasting system where eachcharge successively displaces its burden into a voidcreated by an explosive detonated on an earlier delayperiod.
Round - A group or set of blast holes used to produce aunit of advance in underground headings or tunnels.
S
Safety fuse - A core of potassium nitrate black powder,enclosed in a covering of textile and waterproofing,used to initiate a blasting cap or a black powdercharge. Safety fuse burns at a continuous, uniformrate.
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Scaled distance - A ratio used to predict ground vibra-tions. Scaled distance equals the distance from theblast to the point of concern in feet divided by thesquare root of the charge weight of explosive per delayin pounds. When using the equation, the delay periodmust be at least 9 ms.
Secondary blasting - Using explosives to break bouldersor high bottom resulting from the primary blast.
Seismograph - An instrument that measures and maysupply a permanent record of earthborne vibrationsinduced by earthquakes or blasting.
Semiconductive hose - A hose used for pneumaticloading of ANFO that has a minimum electricalresistance of 1,000 ohms per foot, 10,000 ohms totalresistance, and a maximum total resistance of2,000,000 ohms.
Sensitiveness - A measure of an explosive’s ability topropagate a detonation.
Sensitivity - A measure of an explosive’s susceptibility todetonation by an external impulse such as impact,shock, flame, or friction.
Sensitizer - An ingredient used in explosive compoundsto promote greater ease in initiation or propagation ofthe detonation reaction.
Sequential blasting machine - A series of condenserdischarge blasting machines in a single unit that canbe activated at various accurately timed intervalsfollowing the application of electrical current.
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Series circuit - A circuit of electric blasting caps whereeach leg wire of a cap is connected to a leg wire fromthe adjacent caps so that the electrical current followsa single path through the entire circuit.
Series-in-parallel circuit - See parallel series circuit.
Shatter cut - See parallel hole cut.
Shock energy - The shattering force of an explosivecaused by the detonation wave.
Shock tube system - A system for initiating caps wherethe energy is transmitted to the cap by a shock waveinside a hollow plastic tube.
Shock wave - A pressure pulse that propagates at super-sonic velocity.
Shot - See blast.
Shot firer - Also referred to as the shooter. The personwho actually fires a blast. A powderman may chargeor load blast holes with explosives but may not fire theblast.
Shunt - A piece of metal or metal foil that short circuitsthe ends of cap leg wires to prevent stray currentsfrom causing accidental detonation of the cap.
Silver chloride cell - A low-current cell used in ablasting galvanometer and other devices to measurecontinuity in electric blasting caps and circuits.
Slurry - An aqueous solution of ammonium nitrate, sen-sitized with a fuel, thickened, and crosslinked toprovide a gelatinous consistency. Sometimes called a
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water gel. DOT may classify a slurry as a Class Aexplosive, a Class B explosive, or a blasting agent. Anexplosive or blasting agent containing substantialportions of water (MSHA). See emulsion; water gel.
Smooth blasting - Controlled blasting used undergroundwhere a series of closely spaced holes is drilled at theperimeter, loaded with decoupled charges, and fired onthe highest delay period of the blast round.
Snake hole - A borehole drilled slightly downward fromhorizontal into the floor of a quarry face. Also, a holedrilled under a boulder.
Sodium nitrate - An oxidizer used in dynamites andsometimes in blasting agents.
Spacing - The distance between boreholes or charges ina row measured perpendicular to the burden andparallel to the free face of expected rock movement.
Specific gravity - The ratio of the weight of a givenvolume of any substance to the weight of an equalvolume of water.
Spitter cord - See Ignitacord.
Springing - See chambering.
Square pattern - A blast hole pattern where the holes insucceeding rows are drilled directly behind the holes inthe front row. In a truly square pattern, the burdenand spacing are equal.
Squib - A firing device that burns with a flash. Used toignite black powder or pellet powder.
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Stability - The ability of an explosive material tomaintain its physical and chemical properties over aperiod of time in storage.
Staggered pattern - A blast hole pattern where theholes in each row are drilled between the holes in thepreceding row.
Static electricity - Electrical energy stored on a personor object in a manner similar to that of a capacitor.Static electricity may be discharged into electricalinitiators, detonating them.
Steady state velocity - The characteristic velocity atwhich a specific explosive, under specific conditions ina given charge diameter, will detonate.
Stemming - The inert material such as drill cuttingsused in the collar portion (or elsewhere) of a blast holeto confine the gaseous products of detonation; also, thelength of blast hole left uncharged.
Stick count - See cartridge count.
Stray current - Current flowing outside the desiredconductor. Stray current may come from electricalequipment, electrified fences, electric railways, orsimilar sources. Flow is facilitated by conductivepaths such as pipelines and wet ground or other wetmaterials. Galvanic action of two dissimilar metals incontact or connected by a conductor may cause straycurrent.
Strength - An explosive property described variously ascartridge or weight strength, seismic strength, shockor bubble energy, crater strength, or ballistic mortar
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strength. Not a well-defined property. Used to ex-press an explosive’s capacity to do work.
String 1oading - Loading cartridges end-to-end in aborehole without deforming them. Used mainly incontrolled blasting and permissible blasting.
Subdrill - To drill blast holes beyond the planned gradelines or below floor level to insure breakage to theplanned grade or floor level.
Subsonic - Slower than the speed of sound.
Supersonic - Faster than the speed of sound.
Swell factor - The ratio of the volume of a material in anundisturbed state to that when broken. May also beexpressed as the reciprocal of this number.
Sympathetic propagation (sympathetic detonation)- Detonation of an explosive material by an impulsefrom another detonation through air, earth, or water.
T
Tamping - Compressing the stemming or explosive in ablast hole. Sometimes used synonymously withstemming.
Tamping bag - A cylindrical bag containing stemmingmaterial used to confine explosive charges inboreholes.
Tamping pole - See loading pole.
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Test blasting cap No. 8 - A detonator containing 0.40 to0.45 g of PETN base charge at a specific gravity of 1.4g/cm3 primed with standard weights of primer,depending on the manufacturer.
Toe - The burden or distance between the bottom of aborehole and the vertical free face of a bench in an ex-cavation. Also the rock left unbroken at the foot of aquarry blast.
Transient velocity - A velocity different from the steadystate velocity that a primer imparts to a column ofpowder. The powder column quickly attains steadystate velocity.
Trinitrotoluene (TNT) - A military explosive compoundused industrially as a sensitizer for slurries and as aningredient in pentolite and composition B. Once usedas a free-running pelletized powder.
Trunkline -A detonating cord line used to connect thedownlines of other detonating cord lines in a blast pat-tern. Usually runs along each row of blast holes.
Tunnel - A basically horizontal underground passage.
Two-component explosive - See binary explosive.
U
Unconfined detonation velocity - The detonationvelocity of an explosive material not confined by aborehole or other confining medium.
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V
V-cut - A cut employing several pairs of angled holesmeeting at the bottoms used to create free faces for therest of the blast round.
Velocity - The rate that the detonation wave travelsthrough an explosive. May be measured confined orunconfined. Manufacturer’s data are sometimesmeasured with explosives confined in a steel pipe.
Venturi 1oader - See jet loader.
Volume strength - See cartridge strength or bulkstrength.
W
Water gel - An aqueous solution of ammonium nitrate,sensitized with a fuel, thickened, and crosslinked toprovide a gelatinous consistency; also called a slurry;may be an explosive or a blasting agent.
Water stemming bags - Plastic bags containing a self-sealing device that are filled with water. Classified asa permissible stemming device by MSHA.
Weight strength - A rating that compares the strengthof a given weight of explosive with an equivalentweight of straight nitroglycerin dynamite or otherexplosive standard, expressed as a percentage.
Chapter 20
WATER CONTROL
Introduction
This chapter discusses site conditions that needdewatering and the extent and basic requirements forconstruction dewatering. A more comprehensive discus-sion of technical requirements and methods for con-structing dewatering facilities is available in theReclamation Ground Water Manual. The subjects thatare discussed include:
� Site review
� Site investigations
� Data collection
� Data interpretation, evaluation, and presentation
� Specifications paragraphs
� Construction considerations
� Supervision and oversight
� Documentation of results (final construction report)
Water control is lumped into two categories—dewateringand unwatering. Water control is the removal or controlof groundwater or seepage from below the surface(dewatering) or the removal or control of ponded orflowing surface water by ditches, surface drains, or sumps(unwatering). Excavation of materials or constructionnear or below the water table or near surface water bodiesusually requires control of the groundwater or seepage.Control may involve isolation with cutoffs, stabilization byfreezing, grouting, or other methods, or by a combinationof methods. Control of groundwater and seepage usuallyinvolves installation and operation of wells or drains. Akey operation in most water control in unstable materialsis the removal of water from below the ground surface inadvance of excavation and maintaining the water level at
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a suitable depth below the working surface. These stepspermit construction “in the dry,” unhampered by theadverse effects of water.
Understanding what factors control water is critical forensuring short-term stability during construction of anyfacility and for the long-term stability of any structure.This chapter discusses what should be considered. Ifwater is considered a potential problem, any fieldinvestigation must obtain information on the site’svarious potential water sources including seasonalprecipitation and runoff periods and the identification andunderstanding of the water bearing zones within a site.This means not only identifying and determining thedepths and extent of the various water bearing zones andtheir water surfaces but also understanding the formationhydraulic parameters (porosity, permeability, and, whennecessary, storage).
Figure 20-1 illustrates the importance of understandingthe site hydraulic parameters in selecting the appropriatedewatering method. Using the wrong method for the sitematerials can result in a totally ineffective dewateringsystem. Figure 20-1 can be used to assess what is theappropriate dewatering method based on the sitematerials.
In excavations in rock, cemented granular materials,clays, and other stable materials, water removal orunwatering may be by draining to sumps and usingsurface pumps concurrently with or following completionof the excavation. Subsurface cutoffs such as sheet pilingand slurry walls in soil or soft rock and grouting in rockare also used to control ground and surface water and forground support. Cutoffs are seldom 100-percent effective,and supplementary dewatering or unwatering is usuallyrequired. Soils are frozen for short periods such as for a
WA
TE
R C
ON
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OL
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Figure 20-1.—Limits of dewatering methods for different materials.
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temporary excavation, especially in clayey or silty soilsthat have low permeability and are difficult to drain.
Unwatering methods are commonly used in soils thathave high porosity but low permeabilities (clayey or siltysoils), bedrock that has solution cavities, and lava tubesthat carry large volumes of water in isolated areas.Unwatering methods are commonly used to controlsurface water.
Unwatering usually is performed in conjunction withdewatering to ensure control of surface water and topermit dewatering to proceed unaffected by recharge orflooding from nearby surface water. Failure to properlyremove or control water during unwatering or dewateringmay result in:
• Unstable natural or excavated slopes
• Unstable, unworkable, or unsuitable subgrade
• Boils, springs, blowouts, or seeps on slopes or in thesubgrade
• Flooding of excavations or structures
• Uplift of constructed features such as concrete slabs
• Dilution, corrosion, or other adverse effects on con-crete, metals, or other construction materials
• Instability of nearby structures
• Draining surrounding surface water and ground-water
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• Instability of cutoff facilities such as cofferdams
• Loss of fines from the foundation
• Safety problems
• Delays in construction
• Increased construction costs
Water control may vary widely in scope, magnitude, anddifficulty. Some controlling factors related to theconstructed feature include footprint, foundation depth,and construction time. Factors related to site conditionsare:
• Subsurface geology including general material types;bedding, attitudes and lateral extent of bedding; andattitudes, continuity, and apertures of fractures
• Subsurface hydraulic conditions including permea-bilities and thicknesses of different materials,groundwater occurrence, and levels
• Recharge conditions including proximity to surfacewater bodies and precipitation
• Other facilities including cofferdams and site access
Conditions that may indicate the need for dewatering andthe possibility for difficult dewatering include:
• Site location adjacent to a large body of surfacewater, a stream, a marshy area, or an area subject toflooding
• An excavation significantly below the water table
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• Complex foundation geology
• An artesian zone immediately below grade
• Existing structures or facilities
• Existing use of groundwater
• Poor quality groundwater
• Presence of hazardous materials
• Thick zones of saturated, low-strength materials suchas silt or soft clay, especially under artesianconditions
• Presence of cofferdams or other similar features forwhich dewatering is needed for stability
• Conditions where failure of dewatering facilitiescould result in catastrophic failure of protective orother features and a hazard to life or property
Sites requiring groundwater or seepage control forconstruction or proper operation of a facility should beidentified as early in the planning or design process aspossible.
Exploration Program
Investigations for water control should be part of thegeneral exploration and design data collection program.Advantages of conducting investigations together include:
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• Maximizing the use of design data collection andlowering exploration costs
• Providing dewatering data early in the program
• Using field personnel efficiently
Water control investigations generally cannot beestablished in detail until some reconnaissance leveldrilling has been done and general subsurface geologicand hydrologic conditions are determined. Generalsurface conditions including topography and surfacehydrology should be known. A specialist should beconsulted as early in the program as possible to maximizethe benefits of the obtained data.
Design Data Requirements, Responsibilities,and Methods of Collection and Presentation
Adequate surface and subsurface data are essential to theproper design, installation, and operation of water controlfacilities. The amount of data required for water controlfacilities design may equal or exceed the foundation datarequired for design of the structure. Water controlfacilities may be designed in-house or by the contractor;but investigations may be extensive, complex, timeconsuming, and beyond the capability of a contractor toaccomplish in the bidding period. An in-house design isgenerally better because the time is usually available todo the job right, the designer has control over the designdata, responsibility for the water control design is clear tothe owner and the contractor, and the contractor can bidthe water control installation more accurately.
Design data for water control facilities should be obtainedregardless of who is ultimately responsible for the design.
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The extent and level of data should be appropriate for theanticipated water control requirements and facilities. Allsubsurface investigations should be sufficiently detailedto determine the groundwater conditions, including thedepth of the vadose zone and the various potentiometricwater surfaces; and the investigations should provide atleast enough data to estimate the permeability of the soilor rock. Crude soil permeabilities can be estimated fromblow counts and the visual or laboratory soilclassification. Permeability tests should be considered inany exploration program. If aquifer tests are required,the test wells should approximate the size and capacity ofanticipated dewatering wells. Facilities should bepreserved and made available to prospective contractorsfor their testing or use, if appropriate.
If the contractor is responsible for the dewatering design,all field design data should be included in theconstruction specifications. Data include details ofdrilling and completion of exploratory drill holes, wells,piezometers, and other installations as well as test data.Data should be as concise as possible and clearly show thehistory, sequence, and location of all exploration. Designdata for water control facilities should be obtained con-currently with feature design data if possible. Specialistsshould be consulted when preparing design dataprograms, especially programs for foundation drilling andaquifer testing. Water control data are an essential partof the design data package and must be given therequired priority in funds, time, and personnel tominimize problems such as construction delays andclaims. Where dewatering may have impacts on existingadjacent structures, wells, facilities, or water resources,a study of the area surrounding the site may be necessaryto determine and document impacts. In addition to datainvolving the constructed feature such as a structure
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layout, excavation depth, and time to construct, otherinformation is required on site conditions such as:
Surface Data
• Site and surrounding topography at an appropriatescale and contour interval
• Cultural features on and off site
• Site and surrounding surface geology with descrip-tions of materials
• Site and adjacent surface water features such aslakes, streams, swamps, bogs, and marshes
• Plan map of all data points, including locations ofdrill holes, test holes, piezometers, observation wells,test wells, and overlays on the plan of the proposedfeature
Surface information should include data on soil erosion orresistance or how erosion relates to runoff or the potentialrecharge of the groundwater system. Soil infiltration datafrom Natural Resource Conservation Service mappingshould be included if available.
Subsurface Data
Subsurface data should include representativepermeabilities, a real distribution of permeabilities, lo-cation and potential recharge sources or barriers, andanticipated seasonal changes in the groundwater system.When a project has a relatively high soil or rockpermeability and the permeable formation extendslaterally over a large area, storage (storativity, effective
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porosity) of the aquifer requires evaluation. Specific datathat may be necessary include:
• General geology of the site and surrounding areaincluding geologic cross sections that show verticaland lateral variations in materials
• Logs of drill holes, test holes, and piezometersshowing depths and thicknesses of materials,descriptions of materials, and results of testing
• Results of material sampling including depths,descriptions, mechanical analyses, and hydrometeranalyses
• Geophysical logs
• Aquifer or permeability test results including yieldsand drawdown with time and static water levels
• Layout of test holes and depths and designs of wellsand piezometers
• Water quality analyses
Other Data
• Climatic data for the nearest station including dailytemperature and precipitation and details on theoccurrence of severe storms
• Streamflow and elevation, lake or reservoir depth,elevation, and other similar data
• Groundwater levels for monitored observation wells,piezometers, test wells, drill holes, and pits
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• If a nearby surface water body and the groundwaterare connected, continuous monitoring of both featuresfor a typical hydrologic cycle
Presentation of Data
The presentation of dewatering data may differ from thepresentation of conventional geologic data because watercontrol data are subject to a variety of quantitativeinterpretations and because water levels, flow, and waterquality vary with time.
Because of the potential for different interpretations, mostdewatering data such as those from aquifer tests andpacker tests are presented as observed field data and asinterpretations. A complete description of the site,subsurface conditions, and test facilities should be givenalong with the data (figures 20-2 and 20-3).
Where time related data are presented, the informationshould be in a form that will ensure maximum recognitionand proper interpretation. Hydrographs that plot timeversus water levels mean a lot more than a table ofreadings.
Monitoring
Water control activities must be monitored duringconstruction and, in some cases, up to a year or morebefore and following completion of the facility. Details ofthe monitoring program including design and layout ofthe system, the responsibilities for installing the system,and monitoring and maintaining records must be includedin the specifications and construction considerations toensure adequate reliable data and inform constructionpersonnel of monitoring requirements.
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Figure 20-3.—Aquifer test data.
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Monitoring is intended to:
• Provide data on base level conditions
• Confirm that the specifications requirements arebeing met
• Maintain a general data base on conditions andimpacts resulting from the dewatering
• Alert personnel to unsuitable, hazardous, or poten-tially hazardous conditions
• Document conditions in the event of claims orlitigation
• Provide background data for a followup analysis inthe event of a slope, foundation, or structural failure
Monitoring of water control parameters, activities, andfeatures should include:
• Groundwater levels
• Discharges
• Sediment content of discharges
• Chemical and biologic quality of water discharged
• Horizontal and vertical control on constructedfeatures and natural and excavated slopes
• Levels and sizes of nearby surface water bodies
• Stability of nearby structures
The monitoring facilities may range from a fewobservation wells to a complex system involving sophisti-cated equipment and continuous and possibly remotemonitoring. The extent, complexity, and capability ofwater control facilities depend on the size and complexity
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of the facilities and the hydrologic and geologic conditionsand excavation depths.
Groundwater Monitoring
Monitoring during construction should include ground-water levels in excavations, areas surrounding theexcavations, and off-site locations. Excavations of anysubstantial width (other than trenches) and a depth ofmore than a few feet below the anticipated water levelmay need groundwater monitoring instrumentation in-stalled directly in the excavation. Excavations underlainat shallow depths by artesian conditions may need to bemonitored because of the potential for blowout.
Groundwater Monitoring Locations
Groundwater monitoring instrumentation located withinan excavation may interfere with the contractor duringconstruction, but monitoring groundwater levels withinan excavation generally justifies inconveniences. Becausethe most difficult area to dewater is usually the center ofthe excavation, groundwater monitoring instrumentsshould be located near the center. Special provisions maybe necessary to ensure continued groundwater monitoringof the facilities during all stages of the excavation. Insome cases, groundwater monitoring instrumentationmay be incorporated into the structure. This may requirethat the monitoring instrument be embedded in concretesuch as a wall or pier to permit continuous monitoringand simplify backfill operations.
Water level monitoring instrumentation should be locatedin areas surrounding the excavation to monitor represen-tative areas and specific problem areas. Groundwaterlevels in off-site locations should be monitored tomaintain a general record of conditions and to document
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dewatering. Off-site monitoring is especially important inareas where groundwater is widely used, wheregroundwater levels are crucial to existing activities, orwhere there might be subsidence or groundwater leveldecline.
Locations of individual water level monitoring instru-ments must be based on conditions encountered at thesite, construction activities, and the dewatering facilities.Monitoring instrumentation locations generally will haveto be selected after other features such as dewatering sys-tems and roads have been located to avoid conflicts and toensure representative and reliable monitoring. Instru-mentation should be installed and functioning long beforeconstruction to obtain trends and base level conditions.Existing instrumentation may be used for monitoring; butunless the instrumentation construction and other detailsare known, instrumentation designed specifically for theconditions of the site should be installed as a part ofconstruction.
Groundwater Monitoring Instrumentation
Instrumentation for monitoring groundwater levels usu-ally consists of several observation wells or piezometers.The type of instrumentation, depth, and riser and holediameter depends primarily on subsurface conditions,desired operating life, and type of monitoring. The designof the instrumentation should be tailored to thesubsurface and data requirements so that measurementsare a true indication of in place conditions.
Observation wells intended to monitor general ground-water levels can be used in areas where the foundationmaterial is relatively uniform in depth, there is little or nolayering, and groundwater levels do not vary appreciably
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with depth. Piezometers should be used where layeringexists or perching, artesian, or complex conditions areexpected.
Observation wells and piezometers usually consist of asection of well screen, perforated pipe, or porous tubeisolated in the zone to be monitored and connected to alength of standpipe, riser, or casing extending to thesurface. The section of well screen, perforations, or poroustube must be isolated with a watertight grout or bentoniteseal, and a watertight riser must be used. The diameterof the screen and standpipe should conform to ASTMD-5092. Water levels are measured directly in the well orpiezometer by use of tape or electric sounder (M-scope).Float-type recorders can be used to continuously recordwater level fluctuations but may require a minimum 4- to6-inch (10- to 15-cm) diameter casing or standpipe. Awide range of electronic and pneumatic instruments isavailable for monitoring and recording groundwaterlevels.
Special types of monitoring wells or piezometers may benecessary if hazardous materials are present.
Monitoring Discharges From Dewatering Systems
The discharge from dewatering facilities such as wells,well point systems, drains, and sump pumps should bemonitored to provide a record of the dewatering quan-tities. Data should include starting and stopping times,instantaneous rates of discharge, changes in rates,combined daily volumes, and, in some cases, waterchemistry, turbidity, and biologic content.
Discharge rates can be monitored by flow meters(propeller, pitot tube, and acoustic), free discharge
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orifices, weirs, flumes, and volumetric (tank-stopwatch)methods. Meters must be calibrated using a volumetrictest before flow testing. Measuring devices generallymust be accurate within 10 percent.
Sediment content of dewatering facilities including wells,well point systems, and drains should be monitored.Sediment can damage pumping equipment, cause deteri-oration of water quality in a receiving water body, andcreate voids in the foundation that result in well collapseand foundation settlement.
Sediment content usually is measured in parts per millionby volume of water or in nephelometric turbidity units(NTU) in water taken directly from the discharge.Measurement requires special equipment. If the limitsare 50 parts per million or less, a special centrifugalmeasuring device is required. If the limits are more than50 parts per million, an Imhoff cone can be used. A tur-bidity meter typically measures values less than2,000 NTUs. Values less than 200 NTUs are generallyacceptable for discharge. If sediment yield increasesrapidly, the facility may need to be shut down to avoidserious damage or contamination.
The chemical and biologic content of water dischargedfrom dewatering systems should be monitored by periodiccollection and analysis of samples taken directly from thesystem discharge. A single representative sample is ade-quate if there are a number of discharges from the samesource. If there is pumping from different sources,multiple samples may be needed. The initial samplesshould be taken shortly after startup of the dewateringsystem (or during any test pumping done duringexploration) and periodically during operation. Eachsample may need biologic and chemical analyses forheavy metals, organics, and pesticides. More frequent
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sampling and analyses may be made to determine totaldissolved solids, conductivity, pH, and sediment contentor turbidity.
Monitoring Water and Ground Surfaces andStructures
Well or Piezometer Design.—Most groundwater moni-toring for water control investigations is to collect waterlevel information, but some monitoring is to obtain waterquality information. All monitoring wells should beconstructed according to ASTM D-5092 and constructedfor site conditions and purposes. Geologic conditions,available drilling equipment, depth to water, and thefrequency of the readings should be factored into thedesign of a monitoring well. If a monitoring well requiresdaily or weekly readings, the well may requireinstallation of an automated water level monitoringsystem. The type and diameter of riser should be basedon the intended use of the monitoring well. If monitoringis to continue into construction, protecting the well shouldbe part of the design. Too often, a piezometer orobservation well is constructed without any seriousattempt to design the well. Typically, monitoring wellsare constructed using 1-inch (2.5-cm) diameter PVC riserswith a screen slot size of 0.010 inch (0.25 mm) or with orwithout a 10/20 sand pack. This “low permeability”monitoring well design is appropriate if the well ismonitored only for water levels and the adjacent sourcesof recharge due to precipitation, dewatering, unwateringactivities, or other water bodies is not changing rapidly.
All monitoring wells should be completed using theappropriate seals, risers, and openings to allow the waterlevel in the riser or piezometer to respond to the formationrather than to the water within the riser, the screen, orthe sand pack. Improper or inadequate removal of
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cuttings and drill fluids, or too fine a slot or sand pack,can delay the response of groundwater within a riser. Toolarge openings can result in clogging of the monitoringwell and impact the chemistry of the groundwater. Awater quality monitoring well in soils or decomposed tointensely weathered bedrock should have a minimum of2-inch (5-cm) risers with an annular space of at least2 inches (5 cm). All wells with screen or slots should bedeveloped, especially if the well is being used to obtainwater quality samples. Clays and humic materials ofcolloidal sizes can skew water quality tests.
Ground Surface Monitoring.—The ground surface andother pertinent points should be monitored for settlementduring dewatering activities. Use standard surveyingmethods (at least third order) and temporary benchmarksor other facilities to maintain survey control. Horizontalcontrol is necessary in large or deep excavations that maybe susceptible to slope failure. Special instrumentationwith alarm warning capability may be necessary if groundfailure might endanger life or property.
Water Surface Monitoring.—Nearby surface waterbodies, swamps, drains, and other similar features shouldbe monitored, if appropriate, for elevation and dischargechanges and environmental changes.
Structural Monitoring.—Nearby structures that maybe influenced by settlement or horizontal displacementcaused by groundwater withdrawal should be monitored.Both horizontal and vertical measurements should beacquired to detect movement.
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Performance Evaluation During Construction
The performance of the water control facilities should beevaluated and documented periodically during construc-tion. This will ensure that the specifications are beingmet and that unusual or unexpected conditions areproperly accommodated. Charts and diagrams such ashydrographs or plots of well or system discharge ratesshould be prepared at the start of dewatering operationsand updated throughout the construction period. Anevaluation, along with tables and graphs, should beincluded in monthly reports to provide essential data forfinal reports. The evaluation should be coordinated withthe design staff to ensure complete understanding ofconditions.
Final Reporting
The final construction report should include a section onwater control. This section should include a chronology ofdewatering and an evaluation of the performance of thefacilities as well as contractor compliance with thespecifications. Problem areas and unusual events such aspump or slope failures should be documented. Mon-itoring results, including groundwater levels anddischarge rates, should be presented in the form ofhydrographs and other similar plots or tabulated data.
Bibliography
Bureau of Reclamation, U.S. Department of the Interior,Ground Water Manual, 2nd Edition, 1995.
Cedergren, Harry R., Seepage, Drainage and Flow Nets,John Wiley and Sons, Inc., New York, New York, 1967.
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Driscoll, Fletcher, G., Ground Water and Wells, JohnsonDivision, St. Paul, Minnesota, 1986.
Joint AEG-ASCE Symposium, Practical ConstructionDewatering, Baltimore, Maryland, May 16, 1975.
Leonards, G.A., Editor, Foundation Engineering,McGraw-Hill Book Co., Inc., New York, New York, 1962.
Powers, J. Patrick, Construction Dewatering, John Wileyand Sons, New York, New York, 1981.
U.S. Departments of the Army, the Navy, and the AirForce, Dewatering and Groundwater Control for DeepExcavations, TM5-818-5, NAVFAC P-418, AFM 88-5,Chapter 6, April 1971.
Chapter 21
FOUNDATION PREPARATION,TREATMENT, AND CLEANUP
This chapter discusses foundation preparation for and theplacement of the first several layers of earthfill andconcrete. Preparation includes excavating overburden;shaping the foundation surface with dental concrete;filling surface irregularities with slush grout (usually acement/water mixture poured in cracks) or dental concrete(conventional concrete used to shape surfaces, fillirregularities, and protect poor rock); treating faults,shears, or weak zones; and cleanup.
Earthfill Dams
Shaping
Shape the foundation to ensure proper compaction of filland to prevent stress anomalies in the overlyingembankment. Fractures and resultant seepage problemsin embankment dams may be caused by irregularities inthe foundation such as stepped surfaces, abrupt changesin slope, and excessively steep surfaces. Embankmentzones may differentially settle adjacent to these areas,resulting in cracks. Arching occurs near stepped surfacesresulting in a zone of low horizontal stress adjacent to thesteep surface. Preventing arching is more important inthe upper 1/6 to 1/4 of a dam or in low dams wherestresses are low and tension zones develop along steep ordiverging abutments. Tension zones or areas of lowstresses are susceptible to hydraulic fracturing. Thefoundation surface should be shaped by excavating or byusing concrete to obtain a smooth, continuous surface thatminimizes crack potential. When an inclined core is usedin a rockfill dam, the core derives support from the
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underlying filter and transition material. The zonebeneath the filter and transition should be shaped usingcore contact criteria.
Foundation outside the core contact must be shaped tofacilitate fill placement and compaction, and unsuitableweak or compressible materials must be removed.Impervious materials beneath drainage features whichwould prevent drainage features from properlyfunctioning must also be removed. Materials may moveinto the foundation, and erodible foundation materialsmay move into the embankment. Appropriately gradedfilters between the drainage materials and foundationmay be necessary.
The minimum treatment of any foundation consists ofstripping or removing organic material such as roots andstumps, sod, topsoil, wood, trash, and other unsuitablematerials. Cobbles and boulders may also requireremoval depending on the type of embankment materialto be placed.
The weak points in earthfill dams are generally withinthe foundation and especially at the contact of thefoundation with the embankment. Foundation seepagecontrol and stability features must be carefully supervisedby the inspection force during construction to ensureconformance with the design, specifications, and goodpractice. Water control methods used in connection withexcavating cutoff trenches or stabilizing the foundationsshould ensure that fine material is not washed out of thefoundation because of improper screening of wells andthat the water level is far enough below the foundationsurface to permit construction “in the dry.” Wheneverpossible, locate well points and sumps outside the area tobe excavated to avoid loosening soil or creating a "quick"bottom caused by the upward flow of water or equipment
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vibration. Avoid locating sumps and associated drainagetrenches within the impervious zone because of thedifficulty in properly grouting them after fill placementand the danger of damaging the imperviouszone/foundation contact.
Found cutoff walls or concrete grout caps in the best rockavailable. Prohibit or strictly control blasting for theexcavation of these structures to avoid damaging thefoundation. If the material cannot be excavated with ahydraulic excavator fitted with a rock bucket, a grout capor cutoff wall is probably not needed and grout nipplescan be set directly in the foundation. A highly weatheredzone can be grouted effectively by:
• Leaving the foundation high.
• Setting grout nipples through the unsuitablematerial. Long grout nipples may be necessary inpoor rock.
• Excavating to final foundation grade aftergrouting.
In hard, sound rock, neither a grout cap nor a high foun-dation is necessary.
When overburden is stripped to rock, carefully clean therock surface and all pockets or depressions of soil and rockfragments before the embankment is placed. This mayrequire compressed air or water cleaning and handwork.Rock surfaces that slake or disintegrate rapidly onexposure must be protected or covered immediately withembankment material or concrete. Foundation rockshould be shaped to remove overhangs and steep surfaces(figure 21-1). High rock surfaces must be stable duringconstruction and should be cut back to maintain a
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Figure 21-1.—Example foundation treatmentdetails from specifications.
smooth, continuous profile to minimize differentialsettlement and stress concentrations within theembankment. Final slopes should be 0.5:1 (horizontal tovertical [H:V]) or flatter. Beneath the impervious zone,all overhangs should be removed; stepped surfaces steeperthan 0.5:1 and higher than 0.5 foot (15 cm) should beexcavated or treated with dental concrete to a slope of0.5:1 or flatter. Outside the impervious zone, alloverhangs should be removed, and stepped surfacessteeper than 0.5:1 and higher than 5 ft (1.5 m) (should beexcavated or treated with dental concrete to a slope of0.5:1 or flatter.
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Slush grout or joint mortar should be used to fill narrowcracks in the foundation (figure 21-1). However, theyshould not be used to cover exposed areas of thefoundation. Slush grout and joint mortar are composed ofPortland cement and water or, in some cases, Portlandcement, sand, and water. The slush grout is preferablyused just before fill placement to eliminate any tendencyfor hardened grout to crack under load. Dental concreteshould be used to fill potholes and grooves created bybedding planes and other irregularities such as previouslycleaned shear zones and large joints or channels in rocksurfaces. Formed dental concrete can be used to filletsteep slopes and fill overhangs.
Care should be used during all blasting to excavate or toshape rock surfaces. Controlled blasting techniques, suchas line drilling and smooth blasting, should be used.
Soil Foundations
When the foundation is soil, all organic or otherunsuitable materials, such as stumps, brush, sod, andlarge roots, should be stripped and wasted. Strippingshould be performed carefully to ensure the removal of allmaterial that may be unstable because of saturation,shaking, or decomposition; all material that may interferewith the creation of a proper bond between the foundationand the embankment; and all pockets of soil significantlymore compressible than the average foundation material.Stripping of pervious materials under the pervious orsemipervious zones of an embankment should be limitedto the removal of surface debris and roots unless materialremoval is required for seismic stability. Test pits shouldbe excavated if the stripping operations indicate the pres-ence of unstable or otherwise unsuitable material.
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Before placing the first embankment layer (lift) on anearth foundation, moistening and compacting the surfaceby rolling with a tamping roller is necessary to obtainproper bond. An earth foundation surface sometimesrequires scarification by disks or harrows to ensure properbonding. No additional scarification is usually necessaryif the material is penetrated by tamping rollers.
All irregularities, ruts, and washouts should be removedto provide a satisfactory foundation. Cut slopes should beflat enough to prevent sloughing, and not steeper than1:1. Material that has been loosened to a depth of lessthan 6 in (15 cm) may be treated by compaction.Loosened material deeper than 6 in (15 cm) cannot beadequately compacted and should be removed.
Foundation materials at the core/foundation contact mustbe compacted to a density compatible with the overlyingfill material. A fine-grained foundation should be com-pacted and disked to obtain good mixing and bondbetween the foundation and the first lift of core material.
Fine-grained foundations should be compacted with aroller. If the foundation is too firm for the tamping feet topenetrate, the foundation surface should be disked to adepth of 6 in and moistened before compaction. Smoothsurfaces created by construction traffic on a previouslycompacted foundation surface should be disked to a depthof 2 in (5 cm).
Coarse-grained foundations should be compacted byrubber-tired or vibratory rollers. Vibratory compactorscreate a more uniform surface for placement of the firstearthfill and are the preferred method of compaction.
Cemented and highly overconsolidated soils that breakinto hard chunks should not be reworked or disked to mix
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foundation and core material. The first lift ofembankment material should be placed in a mannersimilar to that required for rock foundations as describedabove.
Soil foundation compaction requirements beneath filterand shell zones should be the same as those outlinedabove, except bonding the foundation to the overlying fillis not required.
The moisture content of the upper 6 in (15 cm) of a fine-grained soil foundation should be within 2 percent dryand 1 percent wet of the Proctor optimum moisturecontent for adequate compaction. Coarse-grainedfoundation materials should be just wet enough to permitcompaction to the specified relative density, butsaturation is not permitted. Dry materials must bedisked and moistened to provide a homogeneous moisturecontent within the specified limits in the upper 6 in(15 cm) of the foundation. Wet materials must be dried bydisking to bring the upper 6 in of foundation materia1within the specified moisture content limits. Wetfoundations should be unwatered or dewateredsufficiently to prevent saturation of the upper 6 in (15 cm)of foundation material due to capillary rise or pumpingcaused by construction equipment travel.
All embankment materials should be protected fromeroding into coarser soil zones in the foundation bytransitions satisfying filter criteria or by select zones ofhighly plastic, nonerodible material. Transition zones orfilters on the downstream face of the cutoff trench andbeneath the downstream zones should prevent movementof fine material in the foundation into the embankment.Dispersive embankment materials must be protected frompiping into coarse material in the foundation by placingselect zones of nondispersive material between the
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embankment and foundation. Lime-treated or naturallynondispersive earthfill is appropriate for the first severallifts of fill material or filters. Except for areas where animpervious seal between the embankment and foundationis required, filter zone(s) are the preferred method.
Rock Foundations
Rock foundation surfaces should be moistened, but nostanding water should be permitted when the first lift isplaced. The use of very wet soil for the first lift againstthe foundation should generally be avoided, but havingthe soil slightly wet of optimum moisture content isbetter. Any material more plastic than what is typicallyavailable for embankment construction is commonly usedon the first few lifts. The foundation should be properlymoistened to prevent drying of the soil. On steep,irregular rock abutments, material slightly wetter thanoptimum may be necessary to obtain good workability anda suitable bond. Be careful when special compaction isused to ensure that suitable bonds are created betweensuccessive layers of material. This usually requires lightscarification between lifts of compacted material. Wherea rock foundation would be damaged by penetration of thetamping roller feet, the first compacted lift can be thickerthan that specified. The first lift thickness should neverexceed 15 in (40 cm) loose for 9-in-long (23-cm) tamperfeet, and additional roller passes are probably required toensure proper compaction. Special compaction methods,such as hand tamping, should be used in pockets thatcannot be compacted by roller instead of permitting anunusually thick initial lift to obtain a uniform surface forcompaction. Irregular rock surfaces may prevent propercompaction by rollers, and hand compaction may benecessary. However, where foundation surfaces permit,a pneumatic-tire roller or pneumatic-tire equipmentshould be used near foundation contact surfaces. An
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alternative to using thick lifts is using a pneumatic-tireroller or loader with a full bucket and disking orscarifying the lift surfaces to obtain a bond between lifts.The tamping roller can be used when the fill is sufficientlythick and regular to protect the foundation from thetamping feet. Unit weight and moisture should becarefully monitored in the foundation contact zone, andplacing and compacting operations should be carefullyinspected.
On steep surfaces, ramping the fill aids compaction; abouta 6:1 slope should be used for ramping the fill. Thesurfaces of structures should be sloped (battered) at about1:10 to facilitate compaction.
The basic objectives of foundation surface treatmentwithin the impervious core are:
• Obtain a good bond between the impervious corematerials and the foundation. The foundationsurface must be shaped by excavation or concreteplacement to provide a surface suitable forearthfill compaction. Compaction techniques usedfor initial earthfill placement should result inadequately compacted embankment material inintimate contact with and tightly bonded to thefoundation without damaging the foundationduring placement of the first lifts. A plasticmaterial is preferred next to the foundation, andspecial requirements on the plasticity, gradation,and moisture content are commonly specified.
• Defend against erosion of embankment materialsinto the foundation by filling or covering surfacecracks in the foundation, using blanket grouting,protective filters, and nonerodible embankment
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materials (natural or manufactured) at thefoundation contact.
• Remove erodible, weak, unstable, compressible,loose, or pervious materials to ensure afoundation of adequate strength and appropriatepermeability. When in doubt, take it out. In rockfoundations, defects such as faults, fractures,erosion channels, or solution cavities or channelssometimes cannot be completely removed.Material defects in the rock mass include faultgouge, rock fragments, soft or pervious soil, orsolutioned rock. These materials require removalto an adequate depth and replacement with slushgrout, dental concrete, or specially compactedearthfill.
How the exposed rock surface is treated after removal ofunsuitable overlying materials depends on the type ofrock and the irregularities present. Construction activ-ities such as using tracked equipment on soft rocksurfaces, using rippers near foundation grade, or nearbyblasting may loosen rock or open joints in originallysatisfactory rock. This type of damage should and can beavoided to limit excavation and cleanup. Theconfiguration of exposed rock surfaces is controlled largelyby bedding, joints, other discontinuities, and excavationmethods. Depending on discontinuity orientations, thesefeatures can result in vertical surfaces, benches,overhangs, or sawteeth. Features such as potholes,buried river channels, solution cavities, and shear zonescan create additional irregularities requiring treatment.Unsuitable material must be removed from theirregularities, and the foundation surface must be shapedto provide a sufficiently regular surface that earthfill canbe placed without differential settlement. If theirregularities are small enough and discontinuous both
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horizontally and vertically, overexcavation can beappropriate. Generally, the foundation surface can beshaped adequately by conventional excavation or smoothblasting. When smoothing of irregularities requiresexcessively large quantities of excavation or requiresblasting that may damage the foundation, shaping withdental concrete may be appropriate.
High rock surfaces must be stable during constructionand must be laid back to maintain a smooth, continuousprofile to minimize differential settlement and stressconcentrations. Slopes should be 0.5:1 (H:V) or flatter,depending on the fill material.
Remove overhangs. Stepped surfaces that are steeperthan 0.5:1 and higher than 1 foot (30 cm) should beexcavated or treated with dental concrete to a resultantslope of 0.5:1 or flatter, depending on the fill material(figure 21-1). In the lower portions of a high dam, thisrequirement may be relaxed. For example, a verticalsurface less than 20 ft (6.1 m) long and 5 ft (1.5 m) highmight be tolerated if the surface is well within theimpervious zone.
Remove all overhangs under the outer zones of earthfilldams and under transitions and filters of rockfill dams.Stepped surfaces that are steeper than 0.5:1 and higherthan 5 ft (1.5 m) should be flattened or treated withdental concrete to a slope of 0.5:1 or flatter. Beneath theouter rockfill zones of rockfill dams, nearly verticalabutment contact slopes have been permitted in high,steep-walled canyons. Overhangs should be trimmed orthe undercut below the overhang filled with concrete.
If shaping requires blasting, proper blasting proceduresare essential to ensure that the permeability and strengthof the rock is not adversely affected and that the rock can
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stand on the slopes and handle the imposed loads.Existing fractures and joints in a rock mass, as well aspoor blasting, often result in unacceptable excavatedsurfaces. Prior competent review, approval, and enforce-ment of the Contractor’s blasting plan, control of blastingdetails, requirements for acceptabi1ity of the excavatedsurface, and control of vibration levels can help obtain thedesired excavation surface.
All loose or objectionable material should be removed byhandwork, barring, picking, brooming, water jetting, orair jetting. Remove accumulated water from cleaningoperations. When the rock surface softens or slakes bywater washing, compressed-air jetting or jetting with asmall amount of water added to the air should be used.Loose or unsuitable material in cavities, shear zones,cracks, or seams should be treated as follows (figure 21-1):
• Openings narrower than 2 in (5 cm) should becleaned to a depth of three times the width of theopening and treated.
• Openings wider than 2 in (5 cm) and narrowerthan 5 ft (1.5 m) should be cleaned to a depth ofthree times the width of the opening or to a depthwhere the opening is 0.5 in (12mm) wide or less,but not to a depth exceeding 5 ft (5 cm) andtreated.
• Openings wider than 5 ft (1.5 m) are a special casewhere the required depth of cleaning andtreatment is determined in the field.
Special cleanup procedures are required for foundationmaterials that deteriorate when exposed to air or water(slake). The foundation must be kept moist if deteriora-tion is caused by exposure to air and kept dry if
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deterioration is caused by exposure to water. Spraycoating with material (similar to concrete curingcompound) designed to reduce slaking may (but probablywill not) be effective. Cleanup and placing a lean concrete“mud slab” approximately 4 in (15 cm) thick may beeffective. Usually, removing the last few inches ofmaterial and doing final cleanup just before firstplacement of fill is the best approach. A maximum timeinterval may also be specified between the time ofexposure of the final grade and the time that thefoundation is protected with earthfill or a suitableprotective coating.
Cleanup outside the core is normally less critical. Loosematerial should be removed so that the embankment is indirect contact with suitable rock. If defects are containedwithin the foundation area, they may not require cleaningand refill. If a defect crosses the entire foundation area,it may require cleaning similar to the foundation beneaththe core.
Dental concrete is used to fill or shape holes, grooves,extensive areas of vertical surfaces, and sawteeth createdby bedding planes, joints, and other irregularities such aspreviously cleaned out solution features, shear zones,large joints, or buried channels. Formed dental concretecan be used to fillet steep slopes and fill overhangs.Placing a concrete mat over a zone of closely spacedirregularities is appropriate in local areas that are notlarge in relation to the core dimensions. Dental concreteshaping can be used instead of excavation by blasting orwhen excessive amounts of excavation would otherwise berequired.
Slabs of dental concrete should have a minimumthickness of 6 in (15 cm) if the foundation is weak enoughto allow cracking of the concrete under load (figure 21-1).
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Thin areas of dental concrete over rock projections on ajagged rock surface are likely places for concrete crackingand should be avoided by using a sufficient thickness ofdental concrete or by avoiding continuous slabs of concreteover areas containing numerous irregularities on weakfoundations. Feathering at the end of concrete slabs onweak foundations should not be permitted, and the edgesof slabs should be sloped no flatter than 45 degrees.Formed dental concrete should not be placed on slopesgreater than 0.5:1 (H:V). When dental concrete fillets areplaced against vertical or nearly vertical surfaces in weakrock, feathering should not be permitted, and a beveledsurface with a minimum thickness of 6 in (15 cm) isrequired at the top of the fillet.
Concrete mix proportions should provide a 28-daystrength of 3,000 pounds per square inch (21 MPa). Themaximum aggregate size should be less than one-thirdthe depth of slabs or one-fifth the narrowest dimensionbetween the side of a form and the rock surface. Cementtype will depend on the concentration of sulfates in thefoundation materials and groundwater. Low-alkalicement is required for alkali-reactive aggregates. Cementtype should be the same as used in structural concrete onthe job. Aggregate and water quality should be equal tothat required in structural concrete.
The rock surface should be thoroughly cleaned, asdescribed below, and moistened before concrete placementto obtain a good bond between the concrete and the rocksurface. When overhangs are filled with dental concrete,the concrete must be well bonded to the upper surface ofthe overhang. The overhang should be shaped to allow airto escape during concrete placement to prevent air pocketsbetween the concrete and the upper surface of theoverhang. The concrete must be formed and placed sothat the head of the concrete is higher than the upper
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surface of the overhang. If this is impractical, grout pipesshould be installed in the dental concrete for later fillingof the air voids. If grouting through dental concrete isdone, pressures should be closely controlled to preventjacking the concrete or fracturing the fill.
Finished horizontal dental concrete slabs should have aroughened, broomed finish for satisfactory bonding of fillto concrete. Dental concrete should be cured by water oran approved curing compound for 7 days or covered byearthfill. Earthfill placement may not be permitted overdental concrete for a minimum of 72 hours or more afterconcrete placement to allow concrete time to developsufficient strength to withstand stress caused by placingearthfill. Inadequate curing may result in the concretecracking.
Slush grout is a neat cement grout or a sand-cementslurry that is applied to cracks in the foundation. Cracksor joints are filled with grout rather than spreading grouton the surface (figure 21-1). Slush grout should be usedto fill narrow surface cracks and not used to cover areasof the foundation. Slush grout may consist of cement andwater, or sand, cement, and water. To ensure adequatepenetration of the crack, the maximum particle size in theslush grout mixture should be no greater than one-thirdthe crack width. Generally, neat cement grout is used.The consistency of the slush grout mix may vary from avery thin mix to mortar as required to penetrate thecrack. The grout preferably should be mixed with amechanical or centrifugal mixer, and the grout should beused within 30 minutes after mixing.
The type of cement required will depend on theconcentration of sulfates in the foundation materials andgroundwater. Low-alkali cement is required for alkalisensitive aggregates. Cement type should be that
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specified for structural concrete. Sand and water qualityshould be equal to that required for structural concrete.
Clean out cracks as described above. All cracks should bewetted before placing slush grout. Slush grout may beapplied by brooming over surfaces containing closelyspaced cracks or by troweling, pouring, rodding, orfunneling into individual cracks. Slush grout is bestapplied just before material placement so cracking willnot occur during compaction.
Shotcrete is concrete or mortar that is sprayed in place.The quality of the shotcrete depends on the skill andexperience of the crew, particularly regarding the amountof rebound, thickness, feather edges, and ensuringadequate thickness over protrusions on irregular surfaces.Untreated areas can be inadvertently covered because ofthe ease and rapidity of placement. Shotcrete should beused beneath impervious zones only when site conditionspreclude using dental concrete. If shotcrete is used, closeinspection and caution are necessary. Shotcrete is anacceptable alternative to dental concrete outside the corecontact area.
The fill compaction method used depends on the steepnessof the surface, the nature of the irregularities in thefoundation surface, and the soil material.
A hand tamper may be used to compact earthfill in oragainst irregular surfaces on abutments, in potholes anddepressions, and against structures not accessible toheavy compaction equipment. Hand-tamped, speciallycompacted earthfill is typically placed in 4-in (10-cm)maximum compacted lifts with scarification between lifts.
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Site-specific conditions determine whether hand-compacted earthfill or filling with dental concrete is thebest solution.
The feet of the roller must not penetrate the first layer ofearthfill and damage the foundation. Penetration can beprevented by using a rubber-tired roller or loader tocompact the first few lifts above the foundation surfacewith scarification between lifts. Earthfill speciallycompacted by pneumatic-tired equipment is typicallyplaced in 6-in (15-cm) maximum compacted lifts.Placement of horizontal lifts against mildly sloping rocksurfaces can result in feathering of the earthfill lift nearthe rock contact. Placement of the initial lift parallel tothe foundation surface (as opposed to a horizontal lift) forfoundation surfaces flatter than 10:1 (H:V) is acceptableif the compactor climbing up the slope does not loosen ordisturb the previously compacted earthfill.
Core material compacted against steep surfaces istypically placed in 6-in (15-cm) compacted lifts withscarification between lifts. Earthfill 8 to 10 ft (2.4 to 3 m)from a steep surface should be ramped toward the steepsurface at a slope of 6:1 to 10:1 so that a component of thecompactive force acts toward the steep surface.
Earthfill placed against irregular surfaces should beplastic and deformable so that the material is forced(squished) into all irregularities on the foundation surfaceby compaction or subsequent loading. The first layer soilmoisture contents should range from 0 to 2 percent wet ofoptimum. Select material with a required plasticity rangeis commonly specified. A soil plasticity index rangingfrom 16 to 30 is preferred although not absolutelynecessary.
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Core materials that are erodible include low plasticity ornonplastic, silty materials and dispersive clays.Preventing erosion of embankment materials into thefoundation includes sealing cracks in the foundation withslush grout and dental concrete and using filter zone(s)between the fine-grained material and the foundation.Sealing cracks is not totally reliable because concrete andmortar can crack due to shrinkage or loading. Usingnatural or manufactured nonerodible material for the firstseveral lifts of embankment at the core-foundation contactis good practice.
If erosion-resistant plastic materials are available, thesematerials should be used for the first several lifts alongthe foundation contact to avoid placing erodible nonplasticmaterials directly against the rock surface. If plasticmaterials are not available, the natural soil can be mixedwith sodium bentonite to produce core material to beplaced against the foundation. Laboratory testing shouldestablish the amount of sodium bentonite required to givethe soil the characteristics of a lean clay.
If nondispersive material is available, it should be usedinstead of dispersive material, at least in critical locationssuch as along the core-foundation contact. In depositscontaining dispersive material, the dispersion potentialgenerally varies greatly over short distances. Selectivelyexcavating nondispersive material from a depositcontaining dispersive materials is frequently difficult andunreliable. Lime can be added to dispersive materials toreduce or convert the soil to a nondispersive material.The amount of lime required to treat the dispersive soilshould be established by performing dispersivity tests onsamples of soils treated with varying percentages of lime.Adding lime to a soil results in reduced plasticity and amore brittle soil. The lime content should be the
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minimum required to treat the soil. Do not treatmaterial that has naturally low plasticity with lime if itis not necessary.
Concrete Arch Dams
The entire area to be occupied by the base of a concretearch dam should be excavated to material capable ofwithstanding the loads imposed by the dam, reservoir,and appurtenant structures. Blasting operations mustnot damage the rock foundation. All excavations shouldconform to the lines and dimensions shown on theconstruction drawings, where practical, but it may benecessary to vary dimensions or excavation slopes becauseof local conditions.
Foundations containing seams of shale, siltstone, chalk,or mudstone may require protection against air and waterslaking or, in some environments, against freezing.Excavations can be protected by leaving a temporarycover of unexcavated material, by immediately coveringthe exposed surfaces with a minimum of 12 in (30 cm) ofconcrete, or by any other method that will preventdamage to the foundation.
Shaping
Although not considered essential, a symmetrical ornearly symmetrical profile is desirable for an arch dam forstress distribution. However, asymmetrical canyonsfrequently have to be chosen as arch dam sites. Theasymmetry may introduce stress problems, but these canbe overcome by proper design. Abutment pads betweenthe dam and foundation may be used to overcome some ofthe detrimental effects of asymmetry or foundationirregularities. Thrust blocks are sometimes used at
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asymmetrical sites. The primary use of a thrust block isnot to provide symmetry but to establish an artificialabutment where a natural one does not exist.Overexcavation of a site to achieve symmetry is notrecommended. In all cases, the foundation should beexcavated in such a way as to eliminate sharp breaks inthe excavated profile because these may cause stressconcentrations in both the foundation rock and the dam.The foundation should also be excavated to about radialor part radial lines.
Dental Treatment
Exploratory drilling or final excavation often uncoversfaults, seams, or shattered or inferior rock extending todepths that are impracticable to remove. Geologicdiscontinuities can affect both the stability and thedeformation modulus of the foundation. In reality, thefoundation modulus need not be known accurately if theratio of the foundation modulus Ef to the concretemodulus Ec of the dam is known to be greater than 1:4.Canyons with extensive zones of highly deformablematerials and, consequently, Ef /Ec ratios less than 1:4should still be considered potential arch dam sites. Thedeformation modulus of weak zones can be improved byremoving sheared material, gouge, and inferior rock andreplacing the material with backfill concrete.
Analytical methods can provide a way to combine thephysical properties of different rock types and geologicdiscontinuities such as faults, shears, and joint sets intoa value representative of the stress and deformation in agiven segment of the foundation. This also permitssubstitution of backfill concrete in faults, shears, andzones of weak rock and evaluates the benefit contributedby dental treatment.
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Data required for analysis are the dimensions andcomposition of the lithologic bodies and geologicdiscontinuities, deformation moduli for each of theelements incorporated into the study, and the loadingpattern imposed by the dam and reservoir.
Dental treatment concrete may also be required toimprove the stability of a rock mass. By using datarelated to the shear strength of faults, shears, joints,intact rock, pore water pressures induced by the reservoirand/or groundwater, the weight of the rock mass, and thedriving force induced by the dam and reservoir, a safetyfactor for a particular rock mass can be calculated.
Frequently, relatively homogeneous rock foundations withonly nominal faulting or shearing do not require thesophisticated analytical procedures described above. Thefollowing approximate formulas for determining the depthof dental treatment can be used:
d = 0.002 bH + 5 for H >_ 150 ft
d = 0.3b+5 for H<150 ft
where:
H = height of dam above general foundation level inft
b = width of weak zone in ftd = depth of excavation of the weak zone below the
surface of adjoining sound rock in ft. In claygouge seams, d should not be less than 0.1 H.
These rules provide an estimate of how much should beexcavated, but final decisions must be made in the fieldduring actual excavation.
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Protection Against Piping
The methods described in the preceding paragraphs willsatisfy the stress, deformation, and stability requirementsfor a foundation, but the methods may not providesuitable protection against piping. Faults, shears, andseams may contain pipable material. To protect againstpiping, upstream and downstream cutoff shafts may benecessary in each seam, shear, or fault, and the shaftsbackfilled with concrete. The dimension of the shaftperpendicular to the seam should be equal to the width ofthe weak zone plus a minimum of 1 foot on each end tokey the concrete backfill into sound rock. The shaftdimension parallel to the seam should be at least one-halfthe other dimension. In any instance a minimum shaftdimension of 5 ft (1.6 m) each way should be used toprovide working space. The depth of cutoff shafts may becomputed by constructing flow nets and computing thecutoff depths required to eliminate piping.
Other adverse foundation conditions may be caused byhorizontally bedded clay and shale seams, caverns, orsprings. Procedures for treating these conditions willvary and will depend on the characteristics of theparticular condition to be remedied.
Foundation Irregularities
Although analyses and designs assume relatively uniformfoundation and abutment excavations, the finalexcavation may vary widely from that which wasassumed. Faults or crush zones are often uncoveredduring excavation, and the excavation of the unsound rockleaves depressions or holes which must be filled withconcrete. Unless this backfill concrete has undergonemost of its volumetric shrinkage at the time overlyingconcrete is placed, cracks can occur in the overlying
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concrete near the boundaries of the backfill concrete asloss of support occurs because of continuing shrinkage ofthe backfill concrete. Where dental work is extensive, thebackfill concrete should be placed and cooled beforeadditional concrete is placed over the area.
Similar conditions exist where the foundation has abruptchanges in slope. At the break of slope, cracks oftendevelop because of the differential movement that takesplace between concrete held in place by rock and concreteheld in place by previously placed concrete that has notundergone its full volumetric shrinkage. A forced coolingof the concrete adjacent to and below the break in slopeand a delay in placement of concrete over the break inslope can minimize cracking at these locations. Ifeconomical, the elimination of these points of high stressconcentration is worthwhile. Cracks in lifts near theabutments very often develop leakage and lead to spallingand deterioration of the concrete.
Concrete Gravity Dams
The entire base area of a concrete gravity dam should beexcavated to material capable of withstanding the loadsimposed by the dam, reservoir, and appurtenantstructures. Blasting should not shatter, loosen, orotherwise adversely affect the suitability of the foundationrock. All excavations should conform to the lines anddimensions shown on the construction drawings, wherepracticable. Dimensions or excavation slopes may varybecause of local conditions.
Foundations such as shale, chalk, mudstone, and siltstonemay require protection against air and water slaking or,in some environments, against freezing. These excava-tions can be protected by leaving a temporary cover of
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unexcavated material, by immediately applying a mini-mum of 12 in (30 cm) of mortar to the exposed surfaces, orby any other method that will prevent damage to thefoundation.
Shaping
If the canyon profile for a damsite is relatively narrowand the walls are steeply sloping, each vertical section ofthe dam from the center towards the abutments is shorterin height than the preceding one. Consequently, sectionscloser to the abutments will be deflected less by thereservoir load, and sections toward the center of thecanyon will be deflected more. Since most gravity damsare keyed at the contraction joints, a torsional effect onthe dam is transmitted to the foundation rock.
A sharp break in the excavated profile of the canyon willresult in an abrupt change in the height of the dam. Theeffect of the irregularity of the foundation rock causes amarked change in stresses in the dam and foundation andin stability factors. For this reason, the foundation shouldbe shaped so that a uniform profile without sharp offsetsand breaks is obtained.
Generally, a foundation surface will appear as horizontalin the transverse (upstream-downstream) direction.However, where an increased resistance to sliding isdesired, particularly for structures founded onsedimentary rock foundations, the surface can be slopedupward from heel to toe of the dam.
Dental Treatment
Faults, seams, or shattered or inferior rock extending todepths that are impractical to remove require specialtreatment by removing the weak material and backfilling
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the resulting excavations with dental concrete. Generalrules for how deep transverse seams should be excavatedhave been formulated based on actual foundationconditions and stresses in dams. Approximate formulasfor determining the depth of dental treatment are:
d = 0.002 bH + 5 for H >_ 150 ft
d = 0.3 b + 5 for H < 150 ft
where:
H = height of dam above general foundation level infeet
b = width of weak zone in feet
d = depth of excavation of weak zone below surface ofadjoining sound rock in feet. In clay gougeseams, d should not be less than 0.1 H.
These rules provide guidance for how much should beexcavated, but actual quantities should be determined inthe field during excavation.
Although the preceding rules are suitable for foundationswith a relatively homogeneous rock foundation andnominal faulting, some damsites may have severaldistinct rock types interspersed with numerous faults andshears. The effect on the overall strength and stability ofthe foundation of rock differences complicated by largezones of faulting may require extensive analysis. Datarequired for analysis include the dimensions andcomposition of the rock mass and geologic discontinuities,deformation moduli for each of the elements incorporatedinto the study, and the loading pattern imposed on thefoundation by the dam and reservoir.
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Dental treatment may also be required to improve thestability of the rock mass. A safety factor for a particularrock mass can be calculated using data related to thestrength of faults, shear zones, joints, intact rock, porewater pressures induced by the reservoir and/orgroundwater, the weight of the rock mass, and the drivingforces induced by the dam and reservoir.
Protection Against Piping
The methods discussed above can satisfy the stress,deformation, and stability requirements for a foundation,but they may not provide suitable protection againstpiping. Faults and seams may contain pipeable material,and concrete backfilled cutoff shafts may be required ineach fault or seam. The dimension of the shaftperpendicular to the seam should be equal to the width ofthe weak zone plus a minimum of 1 foot (0.3 m) on eachend to key the concrete backfill into sound rock. The shaftdimension parallel to the seam should be at least one-halfthe other dimension. A minimum shaft dimension of 5 ft(1.6 m) each way should be provided for working space.The depth of cutoff shafts may be computed byconstructing flow nets and calculating the cutoff depthsrequired to eliminate piping.
Other adverse foundation conditions may be caused byhorizontally bedded clay and shale seams, caverns, orsprings. Procedures for treating these conditions willvary and will depend on field studies of the characteristicsof the particular condition to be remedied.
Foundation Irregularities
Although analyses and designs assume relatively uniformfoundation and abutment excavations, the final excava-tion may vary widely from that which was assumed.
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Faults or crush zones are often uncovered duringexcavation, and the excavation of the unsound rock leavesdepressions or holes that must be filled with concrete.Unless this backfill concrete has undergone most of itsvolumetric shrinkage at the time overlying concrete isplaced, cracks can occur in the overlying concrete near theboundaries of the backfill concrete. Shrinkage of thebackfill concrete results in loss of support. Where dentalwork is extensive, the backfill concrete should be placedand cooled before additional concrete is placed over thearea.
Similar conditions exist where the foundation has abruptchanges in slope. At the break of slope, cracks oftendevelop because of the differential movement that takesplace between concrete held in place by rock and concreteheld in place by previously placed concrete that has notundergone its full volumetric shrinkage. A forced coolingof the concrete adjacent to and below the break in slopeand a delay in placement of concrete over the break inslope can be employed to minimize cracking at theselocations. If economical, the elimination of these points ofhigh stress concentration is worthwhile. Cracks in liftsnear the abutments very often leak and lead to spallingand deterioration of the concrete.
Cleanup
Proper cleaning and water control on a foundation beforeplacing fill or concrete allows the structure and soil orrock contact to perform as designed. Good cleanup allowsthe contact area to have the compressive and shearstrength and the permeability anticipated in the design.Poor cleanup reduces the compressive and shear strengthresulting in a weak zone under the structure andproviding a highly permeable path for seepage.
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Cleaning
Foundation cleanup is labor intensive and costly, so it isroutinely neglected. The result is substandard founda-tions that do not meet design requirements. Rock founda-tions should be cleaned by:
• Barring and prying loose all drummy rock
• Using an air/water jet to remove as much loosematerial and fluff as possible
• Removing by hand loose material that anair/water jet misses
Soil foundations should be cleaned by removing materialmissed by machine stripping that will not be suitablefoundation after compaction.
Foundations of weak rock or firm soil can be cleaned byplacing a steel plate (butter bar) across the teeth of abackhoe or hydraulic excavator and “shaving” or “peeling”objectionable material off the surface, leaving a cleanfoundation requiring very little hand cleaning.
Water Removal
Water in small quantities can be removed by vacuuming(with a shop vac or air-powered venturi pipe) or blottingwith soil and wasting the wet material just before fillplacement. Larger water quantities from seeps can beisolated in gravel sumps and pumped. Grout pipes shouldbe installed; the sumps covered with fabric or plastic; fillplaced over the fabric; and after the fill is a few feet abovethe sump, the sump should be cement grouted by gravitypressure. Seeps in concrete foundations can be isolatedand gravel sumps constructed and subsequently grouted
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as described above or if the seeps are not too large, theconcrete can be used to displace the water out of thefoundation during placement.
Bibliography
Abutment and Foundation Treatment for High Embank-ment Dams on Rock, Journal of the Soil Mechanics andFoundations Division, Proceedings of the AmericanSociety of Civil Engineers, Vol. 98, No. SM10, pp.1017-1032, October 1972.
Current Practice in Abutment and Foundation Treatment,Journal of the Soil Mechanics and Foundations Division,Proceedings of the American Society of Civil Engineers,Vol. 98, No. SM10, pp. 1033-1052, October 1972.
Earth and Rockfill Dams, New York, John Wiley andSons, Inc., 1963.
Foundations and Abutments - Bennett and Mica Dams,Journal of the Soil Mechanics and Foundations Division,Proceedings of the American Society of Civil Engineers,Vol. 98, No. SM10, pp. 1053-1072, October 1972.
Foundation Practices for Talbingo Dam, Australia,Journal of the Soil Mechanics and Foundations Division,Proceedings of the American Society of Civil Engineers,Vol. 98, No. SM10, pp. 1081-1098, October 1972.
Foundation Treatment for Embankment Dams on Rock,Journal of the Soil Mechanics and Foundations Division,Proceedings of the American Society of Civil Engineers,Vol. 98, No. SM10, pp. 1073-1080, October 1972.
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Foundation Treatment for Rockfill Dams, Journal of theSoil Mechanics and Foundations Division, Proceedings ofthe American Society of Civil Engineers, Vol. 98,No. SM10, pp. 995-1016, October 1972.
Preparation of Rock Foundations for Embankment Dams,Embankment Dams Engineering, New York, John Wileyand Sons, Inc., pp. 355-363, 1973.
Treatment of High Embankment Dam Foundations,Journal of the Soil Mechanics and Foundations Division,Proceedings of the American Society of Civil Engineers,Vol. 98, No. SM10, pp. 1099-1113, October 1972.
Chapter 22
PENETRATION TESTING
Introduction
This chapter discusses the Standard Penetration Test(SPT), Becker Penetration Test (BPT), and Cone Penetra-tion Test (CPT). Penetration tests are used to determinefoundation strength and to evaluate the liquefactionpotential of a material. SPTs for liquefaction evaluationsare stressed in the discussion. The significant aspects ofthe tests and the potential problems that can occur areincluded.
History
Penetration resistance testing and sampling with an openended pipe was started in the early 1900s. The RaymondConcrete Pile Company developed the Standard Penetra-tion Test with the split barrel sampler in 1927. Sincethen, the SPT has been performed worldwide. The SPT orvariations of the test are the primary means of collectinggeotechnical design data in the United States. Anestimated 80-90 percent of geotechnical investigationsconsist of SPTs.
Standard Penetration Testing
Equipment and Procedures
The SPT consists of driving a 2-inch (5-cm) outsidediameter (OD) “split barrel” sampler (figure 22-1) at thebottom of an open borehole with a 140-pound (63.6-kg)hammer dropped 30 inches (75 cm). The “N” value is thenumber of blows to drive the sampler the last 1 foot(30 cm), expressed in blows per foot. After the penetration
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Figure 22-1.—ASTM and Reclamation SPT sampler requirements.
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test is completed, the sampler is retrieved from the hole.The split barrel is opened, the soil is classified, and amoisture specimen is obtained. After the test, theborehole is extended to the next test depth and theprocess is repeated. SPT soil samples are disturbedduring the driving process and cannot be used asundisturbed specimens for laboratory testing.
The American Society of Testing and Materials standard-ized the test in the 1950s. The procedure required a freefalling hammer, but the shape and drop method were notstandardized. Many hammer systems can be used toperform the test, and many do not really free fall. Thepredominant hammer system used in the United Statesis the safety hammer (figure 22-2) that is lifted anddropped with the a rope and cat head. Donut hammers(figure 22-3) are operated by rope and cat head ormechanical tripping. Donut hammers are not recom-mended because the hammers are more dangerous tooperate and are less efficient than safety hammers. Auto-matic hammer systems are used frequently and arepreferred because the hammers are safer and offer closeto true free fall conditions, and the results are morerepeatable.
The SPT should not be confused with other thick-walldrive sampling methods such as described inASTM Standard D 3550 which covers larger ring-linedsplit barrel samplers with up to 3-inch (7.6-cm) OD.These samplers are also know as “California” or “Dames& Moore” samplers. These drive samplers do not meetSPT requirements because they use bigger barrels,different hammers, and different drop heights to advancethe sampler.
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Figure 22-2.—Safety hammer.
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Figure 22-3.—Donut hammer.
The energy delivered to the sampler can vary widelybecause of the wide variety of acceptable hammersystems. Numerous studies of SPT driving systemsindicate that the energy varies from 40 to 95 percent ofthe theoretical maximum energy. The “N” value isinversely proportional to the energy supplied to the
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sampler, and the energy delivered to the sampler iscritical. Because of energy losses in the impact anvil,energy from the hammer should be measured on the drillrod below the impact surface. Drill rod energy ratio isdetermined by measuring the force-time history in thedrill string. Both acceleration and force-time history canbe measured and are important in determining thenormalized penetration resistance of sands forliquefaction resistance evaluations (ASTM D 6066).Common practice is to normalize the SPT N value to a60-percent drill rod energy ratio. Adjustment factors canbe as large as 20 to 30 percent.
The largest cause of error in the SPT is drillingdisturbance of the material to be tested. This is especiallytrue when testing loose sands below the water table.Field studies have shown that “sanding in” can beprevented by using rotary drilling with drill mud andupward-deflected-discharge bits and by maintaining thefluid level in the drill hole at all times. Hollow-stemaugers are especially popular for drilling in theimpervious zones in dams but can cause problems whenloose sand is encountered below the water table. Manyother drilling methods are available for performing SPTs,and each should be evaluated relative to potentialproblems and how the data will be used.
Information Obtainable by SPT
The SPT does provide a soil sample. Sampling is notcontinuous because the closest recommended test intervalis 2.5 feet (75 cm). Typical sampling is at 5-foot (1.5-m)intervals or at changes in materials. The test recovers adisturbed soil sample that can be classified on site, or thesample can be sent to the laboratory for physicalproperties tests.
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SPT N values have been correlated to numerous soilproperties. In cohesionless soils (sands), the SPT can beused to predict the relative density of sands (i.e., veryloose, loose, medium, etc.) (table 22-1).
Table 22-1.—Penetration resistance and soilproperties based on the SPT (Peck, et al.)
Sands(Fairly reliable)
Clays(Rather reliable)
Number ofblows per
foot (30 m), N
Relativedensity
Number ofblows per
foot (30 cm), N Consistency
Below 2 Very soft
0-4 Very loose 2-4 Soft
4-10 Loose 4-8 Medium
10-30 Medium 8-15 Stiff
30-50 Dense 15-30 Very stiff
Over 50 Very dense Over 30 Hard
The SPT has been widely used to predict the allowablebearing capacity of footings on sand. There are severalempirical methods that are based either on case historiesor on drained modulus of deformation predictions. Theapplication of these predictions should be tempered bylocal experience. There are many proposed methods forestimating bearing capacity. The methods are probablyslightly conservative and should be applied carefully.
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SPT N values must be corrected for overburden pressuresand the location of the water table.
For clays, the SPT is less reliable for predicting strengthand compressibility, especially for weaker clays. The SPTis commonly used to assess the consistency of clays bygrouping clays as very soft, soft, medium, etc. Predictionsof undrained strengths should be used with extremecaution, especially in weak clays, because the SPT barrelremolds the clay, and the penetration resistance is morea measure of remolded strength. For evaluatingundrained strength in clays, vane shear, unconfinedcompression, or CPTs are better than SPTs. SPT datashould not be used to estimate the compressibility ofclays. To evaluate compression behavior of clays, useeither empirical factors based on water content andatterberg limits or obtain undisturbed samples forlaboratory consolidation testing.
SPT data routinely have been used for predictingliquefaction triggered by earthquake loading. Ifliquefaction is predicted, the SPT data can be used toestimate the post-earthquake shear strengths. Extensivecase history data have been collected to evaluateliquefaction; however, the data are subject to drillingdisturbance errors and the energy delivered by thehammer system must be known. If drilling disturbanceis evident or suspected, the CPT is an alternative becausethe soil can be tested in place. Procedures for evaluatingliquefaction from SPTs are given in Reclamation’s DesignStandards No. 13, Embankment Dams, “Chapter 13,Seismic Design and Analysis.” SPT N data can be usedto estimate the shear modulus of clean sands, but themethod is approximate. If the shear modulus is needed,directly measuring the shear wave velocity is preferred.
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Liquefaction occurs when water pressure builds up ingranular soils during an earthquake. Soils mostlysusceptible to liquefaction are “cohesionless” soils,primarily clean sands and gravels (GP, SP, GW, SW, GP-GM, SP-SM) and silty sands and gravels (SM, GM). Theterm, “sands,” in the following discussion refers to allthese soils. The water pressure buildup results instrength loss and possibly deformation, slippage, andfailure. Data collected at liquefaction sites have beenused to assess whether a deposit is liquefiable.
Testing Cohesionless Soils
Earthquake induced liquefaction is commonly associatedwith sands below the water table. Good drilling techniqueis critical to ensuring that the sands are undisturbedprior to the SPT. Unfortunately, loose sand is one of themost difficult materials to drill.
If disturbed sands are present, take measures to avoidcontinued disturbance. Perform depth checks to assessthe sand depth at the bottom of the drill hole. Thesedepth checks are made by seeing exactly where thesampler rests before testing. Depth checks that can bemade during drilling will be discussed below. Do not drillat excessive rates. Signs of disturbance are excessiveslough in the SPT barrel, drill fluid in the sample, andfailure of the sampler to rest at the proper cleanout depth.Slough is the disturbed material in the drill hole thatcaves from the sidewalls but can include disturbed sandthat heaves or flows upward into the drill hole. Sloughcan also consist of cuttings which settle from the drillfluid before testing.
The SPT sampler must rest at the intended depth. Thisdepth is to the end of the cleanout bit or the end of thepilot bit in hollow-stem augers. If the sampler rests at an
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elevation that is 0.4 foot (12 cm) different from thecleanout depth, disturbance of the soil may be occurring,and the hole must be recleaned. There are a number of advantages to the SPT:
(1) The test is widely used, and often local experienceis well developed.
(2) The test is simple, and many drillers can performthe test.
(3) The SPT equipment is rugged, and the test can beperformed in a wide range of soil conditions.
(4) There are numerous correlations for predictingengineering properties with a good degree ofconfidence.
(5) The SPT is the only in place test that collects a soilsample.
Although the SPT is commonly used and is a flexible inplace test, there are significant disadvantages. The testdoes not provide continuous samples. Different soils inthe SPT interval tend to be logged as one soil, especiallyif the soil core is combined into one laboratory testspecimen and laboratory data are used in the logs.Hollow-stem augers can give disturbed samples betweentest intervals, and the intervals between tests can belogged. The greatest disadvantage to SPTs is the lack ofreproducibility of the test results. Drilling disturbance,mechanical variability, and operator variability all cancause a significant variation in test results. The SPTshould not be used unless the testing is observed andlogged in detail. Old data where drilling and testprocedures are not documented should be used with
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extreme caution. Another disadvantage to SPTs is thatprogress is slower than other in place tests because ofincremental drilling, testing, and sample retrieval, andSPTs may be more expensive than other in place tests.The SPT is influenced by more than just overburdenstress and soil density. The soil type, particle size, soilage, and stress history of the soil deposit all influenceSPT results.
Drilling Methods
Fluid Rotary Drilling
Rotary drilling with clear water results in N values thatare much lower than N values that are obtained whendrilling mud is used. Two factors are involved: (1) thewater from drilling can jet into the test intervaldisturbing the sand, and (2) the water level in theborehole can drop and the sand can heave up the boreholewhen the cleanout string is removed. These two factorsmust be minimized as much as is practical.
The best way to drill loose, saturated sands is to usebentonite or polymer-enhanced drill fluid and drill bitsthat minimize jetting disturbance. Also when drillingwith fluid, use a pump bypass line to keep the hole fullof fluid as the cleanout string is removed from the drillhole. The lack of fluid in the hole is one of the mostfrequent causes of disturbed sands. If the soils arefine-grained, use a fishtail-type drag bit with baffles thatdeflect the fluid upwards. A tricone rockbit is acceptableif gravels or harder materials are present, but adjust theflow rates to minimize jetting.
Casing can help keep the borehole stable, but keep thecasing back from the test interval a minimum of 2.5 feet
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(75 cm) or more if the hole remains stable. Using abypass line to keep the hole full of fluid is even moreimportant with casing because the chance of sand heaveup into the casing is increased if the water in the casingdrops below natural groundwater level. The imbalance isfocused at the bottom, open end of the casing. In extremecases, the casing will need to be kept close to the testinterval. Under these conditions, set the casing at thebase of the previously tested interval before drilling to thenext test interval. Intervals of 2.5 feet (75 cm) arerecommended as the closest spacing for SPTs.
Use drilling mud when the SPT is performed forliquefaction evaluation when rotary drilling. Abentonite-based drilling mud has the maximumstabilizing benefit of mud. Bentonite provides themaximum weight, density, and wall caking propertiesneeded to keep the drill hole stable. When mixing mud,use enough bentonite for the mud to be effective. Thereare two ways to test drill mud density or viscosity—aMarsh Funnel or a mud balance. A mud sample is pouredthrough a Marsh Funnel, and the time needed to passthrough the funnel is a function of the viscosity. Waterhas a Marsh Funnel time of 26 seconds. Fine-grainedsoils require mud with Marsh Funnel times of 35 to50 seconds. Coarser materials such as gravels mayrequire funnel times of 65 to 85 seconds to carry thecuttings to the surface. If using a mud balance, typicaldrill mud should weigh 10-11 pounds per gallon (lbs/gal)(1-1.1 kilograms per liter [kg/L]). Water weighs about8 pounds per gallon (0.8 kg/L).
Exploration holes are often completed as piezometers.Revertible drilling fluids have been improved, and thereare synthetic polymers that break down more reliably. Ifnecessary, specific “breaker” compounds can be used tobreak down the mud and clean the borehole. If the
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borehole cannot be kept stable with polymer fluid,bentonite mud should be used and a second hole drilledfor the piezometer installation. Do not combine drill holepurposes if the data from SPTs or piezometers arecompromised.
Drilling sands with clear water is possible, but only if thedriller is very experienced. As long as drilling is carefullyperformed, drilling with water can result in SPT N valuesclose to those obtained using mud. Disturbance can beavoided; but without drill mud, jetting disturbance, cave,and sand heave caused by fluid imbalance are likely.
If the water level in the sand layer is higher than theground surface, sand heave is really going to be aproblem. Under these conditions, heavy bentonite mud(80 to100 sec on the Marsh Funnel) is required. A fluidbypass to keep the hole full of mud is required, and anelevated casing or drill pad to hold down the sand can beused. Some successful mud improvement is possible withBarite or Ilmenite additives. Mud can be weighted toabout 15 lb/gal with these additives. Sodium or calciumchloride can be used to give polymer fluid better gelstrength. In artesian conditions, it may not be possible tokeep the sand stable. In these cases, other tests such asthe CPT can be used to evaluate the sand.
When using fluid rotary drilling, circulate the drill fluidto remove the cuttings. Pull back the cutting bit severalfeet, cut fluid circulation, and then slowly and gentlylower the bit to rest on the bottom of the hole. Check tosee if the depth is within 0.4 foot (10 cm) of the cleanoutdepth. This check determines if there is cuttingssettlement, wall cave, or jetting disturbance.
The bottom of the borehole normally heaves when thecleanout drill string is pulled back creating suction. Fluid
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should be added to the drill hole as the cleanout string isremoved to help avoid problems. Once the sampler isplaced, check the sampler depth and compare it to thecleanout depth. A difference of 0.4 foot (10 cm) isunsatisfactory. If sands or silty sands heave up into theborehole, the SPT sampler will often sink through most ofthe slough. The only way to check for this situation is tocarefully inspect the top of the sampler and the ball checkhousing for slough or cuttings. If the ball check area isplugged with cuttings, the SPT N value may have beenaffected. A thin plastic cover is sometimes used to keepthe slough out of the sampler. The cover is either shearedoff at the first blow or it is shoved up into the sampler.
The fluid rotary method is probably the best method fordetermining SPT N values in saturated sands. In thefollowing sections, two other acceptable drilling methodsare discussed. If these methods do not work, use the fluidrotary method.
Hollow-Stem Augers
Hollow-stem augers (HSA) have been used successfully todo SPTs in loose saturated sands. With the properprecautions, hollow-stems can be used reliably in sands,but there are some problems with HSAs. The primaryproblem with the HSA in loose sands is sand heaving intothe augers. This occurs when the pilot bit or the HSAsampler barrel is removed in preparation for the SPT.Sometimes, sand can heave 5 to 10 feet (1.5 to 3 m) upinside the augers. SPT N values taken with this amountof disturbance are unacceptable. These problems can beovercome in most cases by using water-filled augers andremoving the pilot bit or HSA sampler slowly to avoid thesuction. Drilling mud is not usually required and cancause sealing problems.
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There are two types of HSA systems shown infigure 22-4—wireline and rod type. With either type ofsystem, removal of the pilot bit or HSA sampler barrel canresult in sand heaving into the augers. The rod typesystem is best at preventing sample barrel rotationduring soil sampling. In sanding conditions, the wirelinesystem is sometimes harder to operate because thewithdrawal rate of the bit or HSA sampler is harder tocontrol. Sanding-in also prevents re-latching of thewireline barrel. Rod type systems are recommended whendrilling in heaving sands. If sand heaves a considerableheight into the augers, the auger will need to be cleanedor retracted in order to continue drilling using eithersystem. If the augers have to be pulled up 3 feet (1 m) tore-latch a pilot bit or sampler barrel, tremendous suctionoccurs at the base of the boring, which can disturb thenext SPT test interval.
When using HSAs below the water table, the hole must bekept full of fluid, just like it must when using fluid rotarymethods. A water or mud source and a bypass lineare required. Some successful techniques for hollow-stem drilling in flowing sands are:
� When approaching the test interval, slow the augerrotation to just enough to cut the soil; do not continueto rotate without advancement near the test interval.In flowing sands, continued rotation near the testinterval will create a large void around the holeannulus and increase the chance of caving anddisturbance of the test interval. If high down pres-sure is used with wireline systems, the pressureshould be relaxed; and the augers should be slightly
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Figure 22-4.—Example of rod-type and wireline-type hollow-stem augers.
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retracted ½ inch (1 cm) or so to re-latch bits orbarrels. There is no need to release down pressure orretract the augers with rod-type systems.
� Add water to a level higher than the surroundinggroundwater level before pulling the pilot bit orsampling barrel. In most cases, water can be addedto the top of the augers without concern fordisturbance. Add water by removing the drive capusing a hose from the bypass line. When removingthe drive cap on rod-type systems, be careful todisconnect the drive cap bearing from the inner rods,or the pilot bit or sampler will be pulled prematurelybefore adding water. When using a wireline system,the latching device can be sent down the hole andlatched before adding water.
The water level is not always maintained at the top of thecolumn, especially if there is a thick layer of unsaturatedsoil above the test zone. Water can leak through theauger joints, and it may be necessary to add a lot of water.
Pulling the Sampler Barrel.—The sample barrelassembly is generally 5 feet (1.5 m) long. This barrel doesnot have much clearance with the inside of the augers,especially in the bushing at the base of the augers. Withthe augers full of water, reconnect the drive cap to theinner rods. Pull the barrel slowly up 0.1 to 0.3 foot (3 to10 cm) and observe the water level in the augers. If waterflows upward, out of the augers, there is a seal betweenthe augers and the sampler, and the sampler barrel isacting like a syringe. If water flows from the top with rodtype systems, rotate the barrel or work the barrel slightlydown and up to try to break the seal and vent. Forwireline systems, release the pulling force and re-apply.Pull slowly and attempt to break the seal. Once the sealis broken, remove the sampler slowly. Remember, with
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rapid withdrawal rates, suction can be created anywherein the auger column. For rod systems, add water duringpulling to account for water level drop. The same ruleapplies for wireline systems, but less water is needed.
Pulling the Pilot Bit.—Most pilot bits are seated flushin a brass bushing in the end (crown) of the augers. Thepilot bit cutting teeth should be set to a lead distance thesame as the outer cutting teeth, so that the body of thepilot bit sits correctly in the bushing. Do not drill withthe pilot bit in advance of the outer cutting teeth. Auseful procedure in heaving sands is to use a pilot bit onesize smaller than the augers being used. For example, ifa 4.25-inch (11-cm) inside diameter (ID) HSA is used, a3.75-inch (9.5-cm) ID HSA pilot bit can be used to reducevacuum and suction effects.
When drilling with the pilot bit, pull the bit back slowlyabout 0.1 to 0.2 foot (3 to 6 cm) to allow any seal in thebushing to vent. If the bit is withdrawn quickly, suctionwill likely occur. If water flows out the top of the augers,suction is occurring. If suction is occurring, rotate thepilot bit and work it down and up to try to break the seal.Once the bit clears the bushing, the tendency to bind isreduced. Withdraw the pilot bit slowly and add water, toaccount for water level drop as the rods are removed.Remember, with rapid withdraw rates, suction effects canbe created anywhere in the auger column.
If sanding-in cannot be controlled with fluid or slowpulling, there are special flap valves that can be placed inthe pilot bit seat. Drill without the pilot bit with flapvalves.
Once the sampler has been inserted to the base of theboring, determine the depth to the sampler tip as aquality check. If there is more than 0.4 foot (12 cm) of
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slough or heave, the test may not be acceptable. Thisguideline is arbitrary, and it is possible to get a reliabletest with as much as 0.5 foot (15 cm) or more slough aslong as the vent and ball check of the sampler are notplugged. If the SPT barrel is used to test the bottom ofthe hole, the sampler will often penetrate loose slough orheave. Checks with a weighted tape may be moreaccurate in determining the depth to the slough. Whenusing the HSA sampler barrel to core before testing, sandfalling out of the barrel could be the cause of slough insidethe auger. To avoid this problem, use catcher baskets inthe HSA sampler barrel.
When testing at close intervals of 2.5 feet (75 cm) or less,it may be necessary to add water to the augers as theSPT sampling string is removed to avoid water levelimbalance and possible heave.
It’s a good idea to combine the continuous sampler of theHSA with SPT operations. If SPTs are at 2.5-foot (75-cm)intervals, perform the SPT and then sample the 2.5-foot(75-cm) and over-sample the 1.5-foot (45-cm) test interval.This adds some time, but allows continuous sampling.This sampling method provides a look at the soils betweenthe test intervals. It is also helpful if recovery is low.
Rotary Casing Advancers
Rotary casing advancers can provide good SPT N valuesin sands. The casing advancer method uses drilling fluid(bentonite and water) as a circulation medium and is afluid rotary drilling method. This method is successfulbecause the large diameter outer rods remain filled withdrill fluid and keep the sand down. The casing advancernormally has a diamond bit but can be equipped withtungsten carbide drag bits on the outside edge to over-cutsoil. Typically, an HQ- or HW-size casing advancer is
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used with or without a pilot bit. The pilot bit can be atricone bit removed via wire line. Suction is possiblewhen a pilot bit is removed. If suction occurs, drillingwithout a pilot bit should be tried. An advantage ofdrilling with a wireline is that when the pilot bit isremoved, the line takes up little volume and results in aminor drop in fluid level inside the rod column. Since agood fluid column remains in the rods, a fluid bypass isnot needed. The only problem is that whenever addingrods to the SPT drill string, fluid flows out of theadvancer.
The casing advancer must be operated very carefully toavoid sand disturbance. Fluid is pumped down the casingand up a narrow annulus along the exterior of the casing.A casing advancer, especially without a pilot bit, isequivalent to a bottom discharge bit. If excessive fluidpressures are used or if circulation is lost, jetting orhydraulic fracturing the material in the SPT test intervalis possible. Drilling the material with a slow advancerate and with low pressure while maintaining circulationis necessary to drill successfully with this system. Ifcirculation return stops, blockage may be occurring; andif pump pressures increase, hydraulic fracturing couldoccur. If the advance rate is too fast, circulation will beblocked. Water is not an acceptable drill fluid with thismethod, and drill mud must be used.
Summary of Drilling Effects
Table 22-2 illustrates the effects of different drilling andmechanical variables on the SPT N value (items 1through 5). A typical N value in clean quartz sand is20 blows per foot (30 cm). The possible range of N for thematerial is shown if the material is subject to errors intesting.
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Table 22-2 shows that drilling disturbance can havedrastic effects on the N value. In fact, zero blows can beobtained. Zero blows may not be realistic because, inmany cases, loosened sand settles back to the bottom ofthe hole. Also, very loose sand normally does not allowthe sampler to settle under the weight of the assembly.Drilling disturbance usually results in a low N value.Low blow counts indicate loose, weak soils, and a weakfoundation may be assumed. Erroneous low disturbedN values can result in costly over design of structures.The most important aspect of SPT testing is the way thehole is drilled.
Procedure Variables
The recommended 2.5-foot (75-cm) interval is to ensurethat the next interval is not disturbed. If material thatonly has a few thin layers of sand is drilled, continuoussampling is possible, but difficult, and should not beattempted unless necessary.
Hammer Blow Rate
The blow count rate is important when soil drainageneeds to be considered. Most test standards requestSPT blows at a rate of 20 to 40 blows per minute (bpm).Blows at 55 bpm are not likely to have an effect on cleansand; but at some fines content, blows will be reduced bythe lack of drainage. Blows should be between 20 and40 bpm if a hammer with a controllable rate is used.Some hammer systems are designed to deliver blows at afaster rate. The automatic hammer is designed to deliverblows at a rate of 50 to 55 bpm. The hammer can be setto run at 40 bpm by adding a spacer ring to the impactanvil. If a hammer rate differs from 50 bpm, clearly noteit on the drill logs.
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372 Table 22-2.—Estimated variability of SPT N Values
CauseTypical rawSPT value inclean sand
N = 20
Typical rawSPT value
in clayN=10Basic Description
Drillingmethod
1. Using drilling mud and fluid bypass 20 10
2. Using drill mud and no fluid bypass 0-20 8-10?
3. Using clear water with or without bypass 0-20 8-10?
4. Using hollow-stem augers with or withoutfluid
0-20 8-10?
5. 8-inch (20-cm) diameter hole compared to4 inches (10 cm)
17 8-10?
Sampler 6. Using a larger ID barrel, without the liners 17 9
7. Using a 3-inch (7.6-cm) OD barrel versus a2-inch (5-cm) barrel
e25-30 10
Procedure 8. Using a blow count rate of 55 blows perminute (bpm) as opposed to 30 bpm
e120 e110
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Table 22-2.—Estimated variability of SPT N Values (continued)
CauseTypical rawSPT value inclean sand
N = 20
Typical rawSPT value
in clay N=10Basic Description
Energy Transmission Factors
Drill rods 9. AW rod versus NW rod e218-22 e28-10
10. SPT at 200 feet (60 m) as opposed to 50 feet (30 m) 422 e35
11. SPT at less than 10 feet (3 m) as opposed to 50 feet(30 m) with AW rods
30 15
12. SPT at less than 10 feet (3 m) as opposed to 50 feet (30 m)with NW rods
25 12
Hammeroperation
13. Three wraps versus two wraps around the cathead 22 11
14. Using new rope as opposed to old rope 19 9
15. Free fall string cut drops versus two wrap on cathead 16 8
16. Using high-efficiency automatic hammer versus twowrap safety hammer
14 7
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374 Table 22-2.—Estimated variability of SPT N Values (continued)
CauseTypical rawSPT value inclean sand
N = 20
Typical rawSPT value
in clay N=10Basic Description
Energy Transmission Factors (continued)
HammerOperation
17. Using a donut hammer with large anvil as opposed tosafety hammer
24 12
18. Failure to obtain 30-inch (75-cm) drop height (28 inches[70 cm])
22 11
19. Failure to obtain 30-inch (75-cm) drop height (32 inches[80 cm])
18 9
20. Back tapping of safety hammer during testing 25 12
e = Estimated value. 1 = Difference occurs in dirty sands only. 2 = It is not known whether small drill holes are less or more efficient; with larger rods, N may be less in clay because ofthe weight. 3 = N in clay may be lower because of the weight of the rods. 4 = Actual N value will be much higher because of higher confining pressure at great depth. The difference shown hereis from energy only and confining pressure was not considered.
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Limiting Blow Counts
The Reclamation test procedure calls for stopping the testat 50 blows per foot (30 cm). Other agencies sometimes goto 100 blows per foot (30 cm) because the ASTM teststandard D 1586 sets a 100-blow limit. The Reclamationstandard is lower to reduce equipment wear. Using the soil liquefaction criteria for sand at a depth of100 feet (30 m), 50 blows would not be consideredliquefiable. SPT data are corrected to a stress level of1 ton per square foot (ton/ft2). In a typical ground mass,a 1 ton/ft2 stress level occurs at a depth of 20 to 30 feet(6 to 9 m), depending on the location of the groundwatertable. Blow counts in a sand of constant density increasewith depth. A correction factor is used to adjust for thisoverburden effect. In earthquake liquefaction clean sandN160 values greater 30 blows per foot (bpf) are notliquefiable. A blow count of 50 bpf at 100 feet (30 m)corrects to about 30 bpf at 1 ton/ft2. Higher blow countswould not be considered liquefiable. If testing is deeperthan 100 feet (30 m) it will be necessary to increase thelimiting blow counts to 100. The refusal rule still applies;if there is no successive advance after 10 blows, the testcan be stopped.
SPT N values in gravels generally are much higher thanin sands. Liquefaction criteria for sands are not reliablecriteria for gravels.
Penetration per Blow or Blows per 0.1 Foot (3 cm)
Penetration for each blow should be recorded whendrilling in gravelly soils. If penetration per blow isrecorded, sand layers can be resolved, and the N value ofthe sand can be estimated. The blow count in sand can beestimated from a graph of penetration per blow. The
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extrapolation is generally reliable if the blows start insand. If the interval starts with gravel and then pene-trates into sand, the extrapolation is less reliable becausethe sampler could be plugged by gravel.
The number of blows for 0.1 feet (3 cm) is the minimumpenetration rate data that should be collected. If threepeople are present, it is very easy to record “penetrationper blow,” and these data are preferred over the coarserblows per 0.1 feet (3 cm). To record penetration per blow,make a form with three columns. In one column, list theblows 1 through 100. Mark the drill rods in 0.1-foot(3-cm) intervals or use a tape starting at zero from theedge of a reference point. In the second column, recordthe total penetration as the test is performed. This willrequire a reader to call off the total penetration. Thereader can interpolate between the 0.1-foot (3-cm)increments, or the penetration can be read directly froma tape. After the test is done the incremental penetrationcan be calculated from the cumulative penetration dataand recorded in the third column.
Equipment and Mechanical Variables
Sampler Barrel
The standard sampler barrel is 2 inches (5.1 cm) in ODand is the barrel that should be used. In private industry,2.5- (6.4-cm) and 3-inch (7.6-cm) OD barrels areoccasionally used. If sample recovery in coarse materialsis poor, it is acceptable to re-sample with a 3-inch (7.6-cm)barrel equipped with a catcher.
Gravelly soils generally do not provide reliable SPT datafor liquefaction evaluations that are based on sands.Other methods use larger samplers and hammers to
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evaluate the liquefaction potential of gravelly soils. TheBPT is used at gravel sites. Often, the BPT is used atgravel sites after a first round of SPT testing showsconsiderable gravels present.
Sampler Shoe
The dimensions of the sampler shoe should meet ASTM D1586 requirements. Some drill equipment catalogs claimto have special “heavy duty” sample barrels and shoes.The “Terzaghi” style does not meet the ASTM andReclamation requirements. When buying shoes, checktheir dimensions to be sure they meet test requirements.Figure 22-1 shows both Reclamation and ASTM samplerrequirements.
Shoe ruggedness can be improved by “carburizing” themetal. This is a process where the shoe is heated in acarbon gas to improve the surface hardness of the steel.This makes the shoe more rugged but also more brittle.Most drill manufacturers supply untreated low carbonsteel such as 1040 alloy. Generally, a local machine shopcan “carburize” the shoe, an inexpensive process.
Sample Retainers
A sample retainer should not be used for liquefactionstudies except in desperation because the effects areunknown. If the sample cannot be retained, a samplemay be taken with a large diameter split barrel samplerwith a retainer re-driven through the test interval. Theover coring procedure discussed earlier using HSAs couldalso be used.
There are several types of retainers available and sometypes are better than others. There is a flap valve devicethat actually looks like a toilet seat (a small one) that
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places a large constriction inside the barrel. This deviceis the least desirable of the retainers if the N value isimportant. The basket type catcher is made of curvedfingers of steel, brass, or plastic. This type of retainer isonly a minor constriction because the holding ring fitsinto the recessed area between the shoe and the barrel.The problem with this catcher is that the fingers may notalways fall back into position to hold the core. A bettervariation of this catcher is the “Ladd” type retainer thatcombines the finger basket with a plastic sleeve. Thisretainer is the most successful at retaining flowing sandbecause the bag adds extra retaining capability.
Sampler Liners
Most of the SPT samplers in the USA accept liners, butthe liner is usually omitted. To determine if the samplerwill accept a liner, feel for an offset (increased diameter)inside the shoe. If an offset is present, the barrel is1½-inch (3.8-cm) ID. Log whether a constant diameter oran enlarged diameter barrel is used because the sampletype can effect recovery. For liquefaction evaluation, aconstant ID barrel is recommended.
A sampler used without liners is actually better forrecovery. Average recovery of a constant ID barrel isabout 60 percent, and the average for the barrel withoutliners is about 80 percent. The difference in N valuebetween constant and enlarged diameter barrels is notknown, but an increase in blows in the range of 1 to 4 islikely with a constant ID barrel.
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Sampler Length
A 24-inch- (61-cm-) long split barrel can normally accom-modate any slough in the drill hole without plugging theball check device.
Sampler Vent Ports
The required vent ports for the sampler top subassemblyin ASTM and Reclamation test procedures are inadequatewhen drilling with mud. The ASTM standard requirestwo �-inch (1-cm) diameter vents above the ball check.When drilling with mud, the fluid gets loaded with sandand can easily plug these ports. The sampler and rods fillwith mud as they are lowered into the drill hole. A bigcolumn of drill mud may try to push the sample out if theball check does not seat. Drill larger vent ports in the topsubassembly to avoid this problem. Some drillers use a0.5- to 1-foot (15- to 30-cm) drill rod sub just above thesampler with extra holes drilled in it to easily drain drillfluid from the rod column.
Hammers, Anvils, Rods, and Energy Effects
The variables in energy transmission are hammer type,hammer drop height, hammer drop friction, energy lossesin impact anvil(s), and energy losses in rods. The energyin the drill rods is called the “Drill Rod Energy Ratio” orERi.
Some hammers, especially donut (casing type) hammerswith large anvils, deliver approximately 50 percent of thetotal potential energy of a 140-lb (63.6-kg ) hammerdropping 30 inches (75 cm). The N value is proportionalto the energy delivered, and the N values can be adjustedto a common energy delivery level. The current practiceis to adjust SPT N values to 60-percent drill rod energy.
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Safety Hammers
There are many kinds of SPT hammers. Pin-guided anddonut type hammers were common in the past, but thesehammers have generally been replaced by the “safety”hammer which has an enclosed anvil (figure 22-2). Thereare also new automatic hammers that improve therepeatability of delivered hammer energy to the sampler.
The safety hammer provides an economical and safemethod of performing the SPT. The enclosed anvilremoves hazards from flying metal chips, and operatorscannot get their hands in the impact surface. Due to theirinherent geometry, safety hammer energy transmissioncan vary only by about 20 percent as long as the hammersare operated correctly and consistently.
Safety hammers should be designed with a total stroke ofabout 32 inches (80 cm), and there should be a mark onthe guide rod so the operator can see the 30-inch (75-cm)drop. The hammer weight should be 140 pounds(63.6 kg). These characteristics should be verified on thehammer. An easy way to weigh the hammer is to placethe total assembly on a platform scale, get the totalweight, then lift the outer hammer off the anvil, andweigh the guide rod and anvil. The difference in the twoweights is the hammer weight. The hammer weightshould be 140 +/- 2 lb (63.6 kg +/- 0.9 kg). Hammersshould be stamped with an ID number. It is best to keepa given hammer for a specific drill, especially if the energytransmission of the drill has been measured in the past.
The assumption is that safety hammers deliver60-percent drill rod energy with two wraps of rope aroundthe cathead. Actually, the hammers deliver about 60 to75 percent depending on their construction. The guiderod is one factor that affects the energy transmission.
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Some safety hammers come with a solid steel guide rod,and others use a hollow AW drill rod. The solid guide rodabsorbs energy, and the solid steel guide rod safetyhammer will deliver lower energy than the hollow guiderod safety hammer. These differences are not enough torecommend one design over another. Another variablewith safety hammers is a vent. Some hammers havevents near the top of the hammer. A vent allows some airto escape as the anvil moves toward the impact surface.These vents allow the best free fall possible.
Donut Hammers
These hammers are not recommended except in specialcases such as when clearance is a problem. If the testingis for liquefaction evaluation, it may be necessary tomeasure the energy of the donut hammer used. Thedonut hammer is supposed to be inefficient, but if thehammer has a small anvil, efficiencies may be similar tothe safety hammer. The larger anvil absorbs part of thehammer energy.
Rope and Cathead Operations
Most SPTs are performed using the rope and catheadmethod. In this method, the hammer is lifted by acathead rope that goes over the crown sheaves. ASTMand Reclamation standards require two wraps of ropearound the cathead. After the hammer is lifted to the30-inch (75-cm) drop height, the rope is thrown towardthe cathead, allowing the hammer to drop as freely aspossible.
Three wraps will reduce the drill rod energy by about10 percent and will result in a higher N value. As therope gets old, burned, and dirty, there is more friction onthe cathead and across the crown sheaves. New rope is
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stiffer and is likely to have higher friction than a ropethat has been broken in. A wet rope may have lessfriction, but the energy differences are small enough thatit is not necessary to stop testing in the rain. Rain shouldbe noted on the drill report and log. Frozen rope mayhave considerably more friction. Under wet and freezingconditions, exercise the rope and warm it up prior totesting.
Consistent rope and cathead operations depend on havingwell maintained crown sheaves on the mast. Crownsheaves should be cleaned and lubricated periodically toensure that they spin freely.
Automatic Hammers
Automatic hammers are generally safer and provide goodrepeatability. Central Mine Equipment (CME) made oneof the first automatic hammers commercially available inthe United States. This hammer uses a chain cam to lifta hammer that is enclosed in a guide tube. The chain camis driven with a hydraulic motor. The drop height of thishammer depends on the chain cam speed and the anvillength. Problems with this hammer system primarilyresult from the speed not being correctly adjusted. Thehammer should be run at 50 to 55 bpm to obtain a 30-inch(75-cm) drop. There are blow control adjustments on thehammer, and there is a slot on the side of the hammercasing to observe the hammer drop height. Be sure thehammer is providing a 30-inch (75-cm) drop by adjustingthe blow control.
The CME automatic hammer is designed to exert a downforce on the rods. This down force from the assembly isabout 500 lbs (227 kg). A safety hammer assemblyweighs from 170 to 230 pounds (77 to 104 kg). In very
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soft clays, the sampler will more easily sink under theweight of the assembly, and with the automatic hammer,the blow counts will be lower.
The Foremost Mobile Drilling Company hammer “floats”on a wireline system. The drop mechanism does notdepend on rate. Energy transfer is about 60 to 70 percent.
Energy transfer of some automatic hammers is signi-ficantly higher than rope and cathead operated hammers.The CME hammer can deliver up to 95 percent energy.This could result in very low blow counts in sands.Energy corrections are usually required for automatichammers. The Mobile Drilling Company hammer is lessefficient because of a large two-piece anvil.
If an automatic hammer is used, report detailedinformation on the hammer use. Report make, model,blow count rates, and any other specific adjustments onthe drilling log. In liquefaction investigations, the energytransfer must be known. For some hammer systems, suchas the CME and Mobile Drilling Company, the energytransfer is known if the hammers are operated correctly,but for some systems, energy measurements may berequired.
Spooling Winch Hammers
Mobile Drilling Company developed a hammer called the“Safety Driver.” This hammer system used a steel wire-line cable connected to an automated spooling winch withmagnetic trip contacts. The contacts sensed when thehammer was lifted 30 inches (75 cm), and the hammerthen dropped with the spool unrolling at the correct ratefor the dropping hammer.
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Energy measurements of this hammer system show someextreme energy variations. Apparently, the contacts andspooling systems require continual adjustment to operatecorrectly. This type of hammer system is not recom-mended because of energy transmission problems.
Drill Rods
Any rod from AW to NW size is acceptable for testing.There is some concern about whipping or buckling ofsmaller AW rods at depths greater than 75 feet (23 m). Inthese cases, use BW rods or larger. There is not muchdifference in energy transfer between AW and NW rods.The type of rod changes a blow count in sand only byabout two blows and maybe less.
SPT drill rods should be relatively tight during testing.Energy measurements on differing locations of the drillrods do not show significant energy loss on joints that areloose. There has to be a real gap on the shoulders tocause significant energy loss. This is because when therod is resting in the hole, the shoulders of the joints are incontact. There is no need to wrench tighten joints unlessrod joints are really loosening during testing. Be sure tofirmly hand tighten each joint.
Drill Rod Length
When using very short rods, energy input to the sampleris attenuated early because of a reflected shock wave. Thedriller can usually hear this because there is a secondhammer tap. The early termination of energy is aproblem to depths of 30 feet (9 m), but the correction issmall and is often ignored. The energy termination is alsoa function of the size of the drill rods. There is someenergy loss for drill rod strings longer than 100 feet(30 m), and a correction is necessary. A constant density
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sand will have an increasingly higher penetrationresistance as depths increase. This is because theconfining pressure increases in the ground mass withdepth.
Summary How Good is the SPT Test
Figure 22-5 is a summary graph of a study performed inSeattle by the American Society of Civil Engineers(ASCE). In this study, several private geotechnical firmsand agencies drilled SPTs at the same site. Six drillswere used. Some had safety hammers, and others hadautomatic hammers. One drill was equipped with a300-lb (136-kg) safety hammer.
The graph shows a wide variation in raw N value versusdepth. The soil conditions at the site are not welldocumented. Some gravel layers are present. Note thatthe spooling winch system resulted in unreliably highSPT N values.
The variability of SPT drilling can be reduced if drillersare aware of the problems inherent to the SPT. Inter-pretation of the data improves if all unusual occurrencesduring SPTs are reported. Drill logs should clearlydescribe in detail the equipment used.
Liquefaction studies are done in loose sands below thewater table. Unfortunately, this material is the hardestto drill without disturbance. Fluid rotary drilling is thepreferred approach for keeping the sand stable. HSAsand casing advancer systems have also been successfullyused.
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Figure 22-5.—Results of SPT with six different drills—ASCE Seattle study.
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The drilling part of SPTs is the most important.Generally, disturbance from improper drilling techniqueresults in lower N values.
Energy transfer effects can be important, especially ifhighly efficient automatic hammers are used.
Becker-Hammer Penetration Testing for Gravelly Soils
Introduction
The BPT is used to test the density of materials that aretoo coarse for the SPT or the CPT. Gravel can causemisleading results in the SPT and CPT. Because thediameter of the BPT penetrometer tip is much larger thanthat of the SPT sampler or the cone penetrometer, gravel-sized particles do not seriously affect the BPT.
The BPT consists of driving a plugged steel casing intothe ground using a diesel pile-driving hammer. The blowsper foot (30 cm) of penetration are recorded and adjustedfor driving conditions. An empirical correlation is thenused to estimate equivalent SPT values. The BPT isperformed with a Becker Drills, Ltd. model AP-1000 orB-180 drill rig, equipped with an InternationalConstruction Equipment (ICE) model 180 closed-enddiesel hammer. The standard configuration uses 6.6-inch(16.8-cm) OD double-wall casing and a plugged “crowd-out” bit. Some ICE 180 hammers are marked “Linkbelt.”
The BPT is rapid and economical to perform. Productioncan reach 500 feet (150 m) per day. A disadvantage isthat no sample is retrieved with the BPT, so othersampling, such as SPT or coring, is also required.Another disadvantage is the uncertainty in interpretation
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of the data. Since the BPT is generally used to estimateequivalent SPT blow counts, significant uncertainty isintroduced by that step, in addition to the uncertaintythat exists in predictions of soil behavior from N values.
The penetration resistance of soils is influenced by a largenumber of factors, including soil type (grain-sizedistribution, plasticity, particle sizes, particle shapes),density, confining stress, energy delivered to thepenetrometer, size and shape of the penetrometer, andfriction on the sides of the penetrometer. The BPT differsfrom the SPT test in many ways, and correlation betweenBPT and SPT data is not consistent. The BPT is notperformed in an open hole with a diameter greater thanthe rod diameter, and the penetrometer tip is not openlike a SPT tip, so there is substantial friction on the drillstring. This greatly complicates the analysis. Like theSPT, the BPT may give misleading results in soilscontaining boulders, cobbles, or even large amounts ofgravel coarser than about 1½ inches (4 cm).
The effect of fines in the relationship between Beckerpenetration resistance and liquefaction potential has notbeen established by experiment or field performance. Theeffect of fines is generally assumed to be similar to whatoccurs with the SPT. Since the BPT does not return asample, it is often necessary to estimate the fines contentfrom nearby drill holes or to neglect the potential benefitof fines.
Role of BPT in Exploration
In soils containing gravel, measured SPT or CPT resist-ance may be misleadingly high, and there is potential fordamage to CPT equipment. CPT equipment generallycannot be advanced through thick gravel layers with morethan about 30 percent gravel, depending on the size of the
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gravel and the density of the soil. Results may bemisleading with smaller gravel contents. BPTs are rarelyperformed at the start of an investigation and aregenerally done after SPTs or CPTs have been attemptedand found to be inappropriate because of too much gravel.BPT testing generally should not be relied on as the solebasis for liquefaction evaluation without site-specificverification of the SPT-BPT correlation, corroboration byshear-wave velocities, or other liquefaction resistancepredictors.
A Becker drill can also be used for other tasks such asinstallation of instrumentation or holes for geophysicaltesting. Some soil is compacted around each Becker hole,and the holes may be more prone to deviate from verticalthan holes drilled by conventional methods. The extent ofdensification is not known, so if the holes are to be usedfor geophysical measurements (such as shear-wavevelocity), vary the spacings to evaluate the effect ofcompaction around the hole. Rotary drilling can also bedone inside the double-wall Becker casing to socketinstallations such as inclinometers into bedrock. This ismore expensive than standard Becker testing because ofdelays and the need for a second rig. Becker rigs do nothave rotary drilling capability.
Equipment
Becker drills can be operated with a variety of equipmentconfigurations, but for penetration testing, the standardtesting setup is as follows:
• Drill rig: Becker Drills, Ltd. model AP-1000 rig
• Hammer: Supercharged ICE model 180 dieselhammer
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• Casing (rods): 168-mm (6.6-in) OD, double-wall
• Drive bit: Crowd-out plugged bit
The correlation between BPT and SPT data proposed byHarder and Seed relies on the use of the standardequipment configuration. The method proposed by Syrequires that at least the last two conditions be met. Allfour conditions should be met because analyses by theSy method would probably be duplicated by the Harder-Seed method for preliminary calculations and/orverification. Harder and Seed determined that open-bittests were inconsistent and erroneously low relative to theclosed-bit standard. The older model B-180 and HAV-180rigs, equipped with the same hammer, transfer about50 percent more of the energy to the drill string than doAP-1000 rigs. This factor has been tentatively confirmedby energy measurements, but it is preferable to avoid theissue by specifying the use of AP-1000 rigs only.
The diesel hammer does not provide consistent energy tothe drill string. This is because the energy depends oncombustion conditions, which are affected by fuelcondition, air mixture, ambient pressure, drivingresistance, and throttle control. The closed-end diesel pilehammer is equipped with a “bounce chamber” where airis compressed by the rising ram after each blow; the airacts as a spring to push the ram back down for the nextblow (unlike the more common open-ended diesel hammerthat uses gravity alone to return the ram). Measuring thebounce-chamber pressure provides an indirect measure ofcombustion energy.
Harder-Seed Method of BPT Interpretation
The Harder-Seed method of interpreting the BPT usesmeasurements of bounce-chamber pressure as an
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indication of the energy imparted to the rods by eachblow. The bounce-chamber pressure is used to adjust theblow count for the actual combustion condition to thatproduced by a hypothetical constant combustioncondition. The measured bounce-chamber pressure mustbe adjusted at altitudes above 1000 feet (300 m). Thethrottle should be kept wide open and the superchargershould be operated any time data are being recorded.Some drillers prefer to use a smaller throttle opening orno supercharger at the beginning of driving when theblowcounts are smaller, producing high blow counts. Ifthe blowcounts required for analysis are near the surface,the driller should be instructed to keep the throttle wideopen. Instances where full throttle and supercharger arenot used should be recorded in the field notes.
The bounce chamber pressure needs to be monitoredcontinuously during testing. An electronic recordingsystem is available to monitor the bounce chamber. Thepressure gauge provided by the hammer manufacturercan be used to record the data manually, but the gaugereading is sensitive to the length of hose used to connectthe gauge to the hammer.
If a B-180 or HAV-180 rig is used, the data can beadjusted by multiplying by the factor 1.5 to account forthe difference in energy transmitted to the rods. Thisfactor is supported by few data and is consideredapproximate. An AP-1000 rig is preferred.
Testing for the Harder-Seed Method of Interpretation
The Harder-Seed method requires that the number ofblows to drive BPT rods each foot (30 cm) of depth andbounce-chamber pressure during that interval be
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recorded. Record the driving conditions and note if thedrillers pull the rods back to loosen them up to reduce thedriving friction.
Sy Method of BPT Interpretation
The method proposed by Sy and Campanella is morerigorous, but more costly and time-consuming. Frictionon the sides of the rods may contribute a substantialportion of the driving resistance. A pile-driving analyzer(PDA) is used to record acceleration and rod force duringindividual blows of the hammer. The PDA also measuresthe driving energy for each blow. The force and accelera-tion histories are then analyzed to separate the resistanceto driving contributed by the bearing capacity of the tipand by the side friction using a computer program calledCAPWAP. PDA operation and CAPWAP analyses areusually done by the contractor.
The PDA measurement eliminates concern about theperformance of the hammer, effects of altitude, or loss ofenergy between the hammer and the rods. At least intheory, analyses should eliminate the effects of varyingamounts of side friction on the blow count. The primarydrawback is the need for PDA measurements and specialanalyses. These substantially increase the cost of thetesting program and slow the process of testing andinterpretation.
The side friction can also be measured directly bypullback tests, where the force required to pull the rodsback a few inches is measured by a load cell. Thismeasurement can be substituted for some of the CAPWAPdata, but it is not recommended that CAPWAP calcu-lations be completely eliminated. CAPWAP data is thestandard from which the method was developed.
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Testing for the Sy Method of Interpretation
The Sy method requires:
Using the PDA, record rod force, acceleration, andtransmitted energy. Record the number of blows for each1-foot (30-cm) interval of BPT driving. Record drivingconditions, and note if the drillers pull the rods back toloosen them up to reduce the driving friction.
Discussion of Methods
For routine investigations of typical alluvial materialsthat do not have dense material overlying them, a PDA isgenerally not necessary, and the Harder-Seed approachshould usually be sufficient. In cases where drill rodfriction is likely to be a problem (penetration throughcompacted fill or deep deposits), the Sy method may bebetter. BPTs can be done after pre-drilling and casing orafter pre-driving the BPT with an open bit throughcompacted fill overlying the tested layers. This reducesthe friction but does not necessarily provide validpredictions of SPT N60 with the Harder-Seed method andmay cause them to be low.
With either method, the field notes should mention anytime that the drillers pull back the rods to reduce thefriction. There is no way to explicitly account for this inthe Harder-Seed method. When using the Sy method, thelocations for calculations should be selected with thepullbacks in mind. Ideally, pullbacks should be done onlybefore and after critical layers are penetrated. This way,the rod friction can be interpolated between analyzedzones with no pullbacks between them to invalidate theinterpolation. Zones to be tested and pullbacks should bediscussed with the drillers prior to each hole. Substantialuncertainties exist both in the correlations to estimate the
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equivalent SPT N60 and in the correlations to estimate soilbehavior from the SPT blow count.
Contracting for Becker Drilling Services
In addition to the usual specifications requirements, thework statement for BPT should address:
� Work requirements — explain general workrequirements.
� Purpose and scope — state which portions of the workare for liquefaction assessment and which are forinstrumentation or other purposes.
� Local conditions and geology — describe anticipateddrilling conditions and potential problem areas.
� Equipment and personnel to be furnished by the con-tractor — specify complete details on the equipment:rig model numbers, hammers, superchargers, anddouble wall pipe for rods. See above for details.
� Drilling requirements — list special considerationssuch as staking, calibration requirements, andrefusal criteria.
� Hole completion — describe all hole completion orabandonment procedures.
� Driller’s logs — list requirements for the driller’sreport, including forms to be used.
� Field measurement — specify method of measure-ment of depths for payment.
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In the contract for PDA work, specify the following:
� Purpose and scope of testing.
� Estimated number of feet of driving to be monitoredby PDA.
Cone Penetration Test
Test History
The CPT was introduced in northern Europe in the 1930sto facilitate the design of driven pile foundations in softground. Early devices were mechanical penetrometersthat incrementally measured the cone tip resistance. Inthe 1960s, mechanical cones, known as Begemann frictioncones, were developed. This penetrometer measured boththe tip resistance and the side resistance along a sleeveabove the cone tip (figure 22-6). At about this same time,the CPT was introduced in North America. Usingtechnology from the rapidly advancing electronicsindustry, an electric cone penetrometer was developedthat used electrical transducers to measure the tip andside resistance (figure 22-7). Most of the work today isperformed with electronic cone penetrometers, and themanual does not discuss mechanical systems. The use ofelectronics allows the incorporation of additional sensorsin the cone system, including those for pore water stress,temperature, inclination, acoustic emissions, down-holeseismic, and resistivity/conductivity. In the 1990s,sensors such as laser or other energy-induced fluorescencespectroscopy sensors, membrane interface probes, andeven video cameras have been added to detectgroundwater contamination. Penetrometers capable ofmeasuring dynamic or static pore water pressures arecalled piezometric cones or piezocones (CPTU). CPT
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Figure 22-6.—Mechanical conepenetrometers.
Figure 22-7.—Typical electrical cone penetrometers.
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has continued to gain wide acceptance as an effective siteinvestigation tool in North America.
Test Procedure
The procedures for performing CPTs are standardized inReclamation procedures USBR 7020 and 7021 andASTM D-5778 and D-6067. The test is highlyreproducible as opposed to SPTs. Test standards call fora cone tip 35.7 mm in diameter with a 10-square-centimeter (cm2) projected area and an apex angle of60 degrees. The friction sleeve is 150 cm2. Largerdiameter penetrometers of 15-cm2 projected area aresometimes used in very soft soils. Smaller diameterpenetrometers are sometimes used for laboratory studiesof soils.
The cone is advanced at a constant rate of 20 mm persecond. Since the penetration resistance dependssignificantly on the advance rate, the push rate must bechecked in the field. The basic equipment required toadvance any cone penetrometer is a hydraulic jackingsystem. Trucks or vehicles built for CPT are typicallyused; but, in some cases, the hydraulics of rotary drill rigsare used. Semi-portable equipment has been developedfor remote site testing. Rigs can be mounted on trucks,tracked vehicles, trailers, barges, or diving bells,depending on accessability. The capacity of cone rigsvaries from 100 to 200 kilonewtons (kN) (11.2 to22.4 tons). The upper bound is the maximum allowablethrust on the cone penetration rods.
Electronic cone penetrometers have built in load cells tomeasure the tip and side resistance simultaneously(Figure 22-7). Bonded strain gauges typically are used inthe load cells because of their simplicity and ruggedness.The load cells commonly have a range of 90 kN (10 tons)
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for tip resistance and 9 kN (1 ton) for side resistance. Theload cell capacity can be varied, depending on thestrength of the soils to be penetrated. The load cells areusually connected by an electric cable passing through thedrill rods to a data acquisition system at the surface.Cordless models are also available that transmit sonicallyand “Memo” cones that store the data internally untilretrieved at the surface. Data are recorded digitally,which greatly enhances the use of CPT results inengineering applications. The data can be sent in daily bye-mail to the engineer and geologist.
Nearly all electronic cone penetrometers are equippedwith a pore pressure element. This pore pressure sensoris typically located between the tip and the friction sleeve.The element can record dynamic water pressure as thecone is being pushed, as well as static water pressuresduring pauses in testing. The typical capacity of thewater pressure transducer is 2.2 kN (500 lb/in2), and theaccuracy of water pressure head is about ± 3 cm (0.1 foot).Cones are almost always equipped with inclinometers.The inclinometers are used to monitor rod bending duringpush and are an essential part of protecting the cone fromdamage. The inclinometer can be monitored by computer,and pushing can be stopped if bending is excessive. Conerods can bend as much as 10 to 20 degrees. If the cone isused to detect bedrock or hard layers, this error can besignificant. The inclinometer is not directional, so theerror from bending can only be estimated.
Advantages and Disadvantages
The CPT has several advantages over other routine inplace tests. The tests are rapid and inexpensive comparedto other geotechnical profiling techniques. Penetrationrates of 3 feet (1 m) per minute are common in many soils.Penetration is stopped only to add sections of push rods,
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except when pore water stress dissipation measurementsare made with the piezocone. With electrical equipment,continuous profiles are recorded and plotted aspenetration progresses, and operator effects areminimized. As discussed below, the test results have beencorrelated to a variety of soil properties. Digital dataacquisition with electrical cones enhances interpretationand provides continuous profiles of soil propertyestimates.
Although the tests are applicable to a wide range of soilconditions, penetration is limited in certain groundconditions. Well-cemented soils, very stiff clays, and soilscontaining gravel and cobbles may cause damage to thepenetrometer tips.
The CPT can be used at nearly any site because portabledevices are available. Portable hydraulic jacking systemscan be used for soft soils in locations not accessible tostandard rigs.
The CPT has several disadvantages. The test does notprovide soil samples. The test is unsuited for well-cemented, very dense and gravelly soils because thesesoils may damage the relatively expensive penetrometertips.
Local experience with this test is less than that with theSPT. Although the test is rapidly gaining acceptance inthe United States, some drilling contractors do not havethe equipment or experience necessary to perform thetest. The equipment is expensive and may not beavailable in some locations. Maintaining the electronicsfor the CPT and CPTU equipment may be a problem insome test locations.
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Data Obtainable
The CPT is primarily a logging tool and provides some ofthe most detailed stratigraphic information of anypenetration test. With electronic cones, data are typicallyrecorded at 5-cm-depth intervals, but data can be recordedat closer spacings. Layers as thin as 10 mm can bedetected using the CPT, but the tip resistance can beinfluenced by softer or harder material in the layer belowthe cone. Full tip resistance of an equivalent thicker layermay not be achieved. The penetration resistance of thesoil is a function of the drainage conditions duringpenetration. In sands that are drained, the penetrationresistance is high, but in clays that are undrained, thepenetration resistance is low.
A typical CPT data plot is shown in figure 22-8.CPT plots should show all recorded data (i.e., TipResistance, qc , Sleeve Resistance, fs , Pore pressure, u,and for this example, cone inclination and temperature).CPT data should be plotted to consistent scales on a givenproject so that the plots can be more easily evaluated.
The CPT does not obtain a soil sample. However, the soilsmay be classified by comparing the tip resistance to theratio of tip to sleeve resistance which is known as thefriction ratio, Fr . Friction ratio should also be shown onthe summary plots. Figures 22-9 and 10 show commonlyused relationships to estimate the “soil behavior type.”Clay soils have low tip resistance and high friction ratio,while sands have high tip resistance and low frictionratio. Mixed soils fall in zones 4 through 7. There arealso classification methods that incorporate the dynamicpore water pressure generation. The CPT cannot exactlyclassify soil according to the Unified Soil ClassificationSystem. Experience at many sites shows that soils giveconsistent signatures; and even though the soil behavior
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Figure 22-8.—Example CPT data plot.
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Figure 22-9.—Chart for estimatingthe soil behavior type.
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Figure 22-10.—Chart for estimating the soilbehavior type and the coefficient of permeability.
type is generally correct, the soil types should beconfirmed with a sample boring. Soil behavior typeprediction in the unsaturated zone is less reliable butoften still useful. The summary plot in figure 22-8 alsoshows the soil behavior group on the right side bar.
Soil permeability can be estimated from CPT because thetip resistance is a function of drainage during penetra-tion. The permeability estimate is generally within anorder of magnitude, which is suitable for mostgroundwater and seepage studies (figure 22-10).
Numerous correlations of CPT data to strength andcompressibility of soils have been developed. Thesecorrelations are based primarily on tip resistance but arealso supplemented by sleeve friction and dynamic porewater pressure data.
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Figure 22-11.—Relationships between cone tipresistance, relative density, and effective
vertical stress.
CPTs in clean sands have been performed in largecalibration chambers where the density and confiningpressure have been controlled. Based on the chamberdata, the relative density and friction angle of sand can beestimated using relationships such as those shown infigure 22-11. The tip resistance at a constant relativedensity increases with increasing confining pressure.Once the relative density is estimated, the friction angle
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Figure 22-12.—Empirical cone factor, Nk , for clays.
can be estimated. The compressibility of the sanddepends on the mineralogy of the sand particles. Highlycompressible sands may contain soft particles. If mica ispresent in the sand at percentages as low as 5 percent,the compressibility will increase. Samples of the sand todetermine mineralogy may be necessary. These estimatesfor sands are not applicable to sands containing morethan 10 percent fines.
The CPT can be used to estimate the undrained strength,Su, for clays because the CPT is like a cone bearing test inrapid, undrained loading. Figure 22-12 shows that thecone factor, Nk, must be estimated for clay. Typically, afactor of 12 to 15 is used. The factor can be refined bycross correlating with sampling and unconfinedcompression testing or by vane shear testing.
Compressibility of soils can be estimated by the CPT test,but the consolidation behavior should be confirmed bysampling and laboratory testing.
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Figure 22-13.—Comparison of various cyclicresistance ratio (CRR) curves and field data.
The CPT is the best method for estimating theliquefaction resistance of sandy soils. The SPT is alsoused but has many problems in drilling and withequipment. The CPT tests the sand in place withoutdisturbance, and the test is highly repeatable.Figure 22-13 shows the chart used to estimateliquefaction triggering. The chart is based on “cleansands,” but the method includes conversion of dirty sandsfor evaluation. If the CPT can be used for liquefactionevaluation, it should definitely be considered in theexploration plan. SPT should still be performed at a fewsites, but the CPT can be used to rapidly and economically
PENETRATION TESTING
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map the extent of liquefiable strata. CPT is also usedextensively for evaluating ground improvement ofliquefiable deposits.
The cone is like a miniature pile and is used forevaluating pile capacity. CPT tests are often performedat the abutments of bridges for pile design. Numerousmethods exist for estimating pile capacity.
Economics
Equipment costs for CPT range from low for mechanicaldevices to high for piezocones, and generally twotechnicians are required to perform CPTs. Thesepersonnel should have a working knowledge of theequipment, but highly trained technicians are notrequired. The equipment mobilization is similar to thatrequired for the SPT, but portable devices can be used forremote locations. Unit costs are difficult to estimatebecause the tests provide continuous or nearly continuousmeasurements. Rig costs are comparable to costs for theSPT, with an added capital cost to convert a conventionaldrilling rig for CPT testing. However, 200 feet (60 m) ofpenetration per day is typical; and in some cases,maximum production of 400 feet (120 m) per day ispossible. This cost is the lowest of any geotechnicaldrilling, sampling, and logging method.
Bibliography
Harder, L.F., Application of the Becker Penetration Testfor Evaluating the Liquefaction Potential of Gravelly Soils,NCEER Workshop on Evaluation of LiquefactionResistance, held in Salt Lake City, Utah, 1997.
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Harder, L.F. and Seed, H.B., Determination of PenetrationResistance for Coarse-Grained Soils Using the BeckerHammer Drill, Report No. UC/EERC-86-06, NTIS PB87-124210, Earthquake Engineering Research Center,College of Engineering, University of California, Berkeley,California, May 1986.
Peck, Ralph B., Foundation Engineering, Second Edition,John Wiley & Sons, 1973.
Rausche, F., Goble, G.G., and Likins, Jr., G.E., DynamicDetermination of Pile Capacity, Journal of GeotechnicalEngineering, ASCE, Vol. 111, No. 3, pp. 367-383, 1985.
Sy, A. and Campanella, R.G., Becker and StandardPenetration Tests (BPT-SPT) Correlations withConsideration of Casing Friction, Canadian GeotechnicalJournal, 31(3): 343-356, 1994.
Sy, A., Campanella, R.G., and Stewart, R.A., BPT-SPTCorrelations for Evaluation of Liquefaction Resistance ofGravelly Soils, Static and Dynamic Properties of GravellySoils, ASCE Special Publication 56, M.D. Evans and R.J.Fragazy, Editors, American Society of Civil Engineers,New York, New York, 1995.
Chapter 23
HANDLING AND TRANSPORTINGROCK AND SOIL SAMPLES
Introduction
Subsurface sampling is expensive and time consuming, soit makes sense to obtain all information possible from theinvestigative process and the retrieved samples. Afterexpending the money and effort to obtain subsurfaceinformation, the samples should not be subjected tounacceptable temperature, rough handling, shoddypackaging, or harsh transportation methods. Any type ofmishandling of a sample may make the sample useless fortesting or logging, and the investigation may have to berepeated.
There are certain procedures in the handling andtransporting of samples that should be a part of everyinvestigation. However, some programs might requiremore demanding techniques in the handling of samplesthan others, depending on the types and ultimate uses ofthe samples. Proper handling results in lower overallcosts when the cost of repeating an investigation isconsidered.
The care and handling required for samples collected forhazardous or toxic material investigations can varyconsiderably, and details for this type of sampling are notprovided in this chapter. Information on requiredvolumes of material, types of storage containers, methodsof collection and preservation, and maximum holdingperiods should be obtained from the appropriateregulatory agency.
Poor samples are sometimes the result of poor drillingpractices rather than mishandling. Compressionfracturing of core, "spun" core, or uneven or wavy coresurfaces may indicate that drilling techniques are
FIELD MANUAL
410
inappropriate for the conditions. Problems should benoted in the logs and corrections or improvements shouldbe made immediately, if practicable, to the drillingprocedures.
When samples requiring extreme care are obtained,personnel involved in the investigation must be totallyfamiliar with the following procedures, and they musthave a clear understanding of which geologic features areto be sampled and why they are to be sampled.
The geologic characteristics and the intended use of therock and soil samples determine the extent and type ofcare required. If engineering properties are to bedetermined, the sample must be handled and preservedso that the properties are not significantly influenced bymechanical damage, changes in chemistry, andenvironmental conditions such as moisture andtemperature.
Design requirements for samples range from geologiclogging to complex and critical testing in the laboratory.Priorities for multiple uses or different types of tests mustsometimes be established when available samples arelimited and when a use or test precludes another test.When the required level of protection is unknown,overprotection is better than underprotection. If thesample is intended for geologic logging only, the care andpreservation may be entirely different from that whichwould be needed if testing in the laboratory is required.Even though the sample has been geologically logged,other studies might be necessary, and continuous care inhandling and proper storage may be required.
Samples can range from highly disturbed to relativelyundisturbed. The methods of obtaining soil samples varyand may range from "grab" samples to samples obtained
HANDLING AND TRANSPORTING SAMPLES
411
by highly refined drilling and sampling techniques. Soilcan be difficult to sample whether by drilling or test pits,and obtaining an “undisturbed” sample of soil can be anordeal. To obtain good “undisturbed” (minimally-disturbed) soil samples, extensive knowledge and exper-ience with numerous types of soil sampling equipment,drilling methods, and drilling fluid additives is necessary.
Specific procedures for the disposal of rock core andsamples depend on several factors; see chapter 24 forguidelines.
Sample Protection
The following describes recommended procedures forhandling rock and soil samples (samples). The samplegroupings are based on the type of testing to beperformed, rather than any physical condition of thesamples, and generally conform with ASTM Standards.Groups 1 through 4 deal with rock core, but note that thechange to soil-like characteristics is transitional ratherthan abrupt. Table 23-1 summarizes the procedures.
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HANDLING AND TRANSPORTING SAMPLES
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Figure 23-1.—Properly boxed and labeled core.
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FIELD MANUAL
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Figure 23-2.—Core storage area with boxes neatly arranged and separated by spacers for
ventilation. Note core photography frame in center of photograph.
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HANDLING AND TRANSPORTING SAMPLES
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Storage Containers
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FIELD MANUAL
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HANDLING AND TRANSPORTING SAMPLES
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FIELD MANUAL
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Transportation Requirements and Procedures
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FIELD MANUAL
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Upright Handling and Shipping of Samples
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Chapter 24
CARE, RETENTION, AND DISPOSALOF DRILL CORE, SOIL, AND
ROCK SAMPLES
General
These guidelines for the care, retention, and disposal ofdrill core, soil, and rock samples apply to (1) foundationexploration for structures, such as dams, canals, tunnels,powerplants and pumping plants, (2) constructionmaterials investigations including riprap and borrow, and(3) safety of existing structures investigations. Sampleretention and disposal guidelines for concrete aggregate,pozzolan, land classification, drainage (except fordrainage structures), and hazardous waste studies areexcluded.
These guidelines are intended to maximize care ofsamples and cores, minimize storage costs, meet mini-mum technical requirements, and avoid unnecessarilylong storage periods. Special circumstances or needs mayrequire modification of the guidelines.
These guidelines apply to rock and soil core and samplestaken without special sampling sleeves, tubes, or con-tainers. When undisturbed samples taken in sleeves orcontainers or undisturbed hand-cut samples arespecifically intended for laboratory examination or testingto supply design data, the samples should be taken,prepared, cared for, and handled in accordance withUSBR 7100 [1] and USBR 7105 [2]. Undisturbed samplesshould be shipped immediately to avoid deterioration andchanges in physical properties. Chapter 23 describesproper procedures for protecting and shipping samples.Appropriate logs, sample data sheets, or other pertinentinformation should be submitted with the samples.
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Location of Storage Facilities
The preparation of an adequate log or description of thecore or samples should be done before storing and sub-sequently disposing of samples. If the sampled material,such as slaking shales, breaks down upon drying andloses in-place characteristics during storage, it may bebetter to drill new holes than to store large quantities ofcore that will seldom be looked at or will lead to wronginterpretations if inspected or tested after years ofstorage.
The following are the general requirements for storage ofcore and samples:
1. Provide minimum storage conditions. (See thenext section, “Conditions of Storage.”)
2. Eliminate unsupervised storage. The storagefacility should be at or near the site of a project orinvestigation.
3. Minimize transferring core and samples from onestorage facility to another because work on astructure site or project progresses through suc-cessive stages of investigation and construction.
4. Provide accessibility so that minimum travel isrequired for examination of the core and samples.Frequent inspection may be necessary for designpurposes and for prospective bidders on construc-tion specifications.
5. Survey existing unused space before constructingor acquiring new space or use space initiallyprovided for other purposes but adaptable to coreand sample storage. For example, the lower
CARE, RETENTION AND DISPOSAL
433
floors and galleries of many powerplants andsome pumping plants or buildings erected fortemporary use during construction have storagespace.
Storage During Investigations
Core and samples should be kept at the nearest existingstorage facility. A new storage facility should be estab-lished only if required by the location, the amount of coreand number of samples anticipated, and the duration ofinvestigation or access convenience. In some instancesduring periods when actual drilling and sampling opera-tions are in progress, temporary storage at the site maybe required to facilitate logging, selection of samples, orready reference while geologic, soils, or other field studiesare in progress. Temporary onsite storage should belimited to short periods of actual need and should preventdamage or deterioration of the core and samples.
When a field office maintaining core storage facilities isclosed following preliminary investigations, core and sam-ples no longer required should be discarded (see sectionentitled Retention of Rock Core and Samples), and theremaining core and samples should be transferred to anappropriate location. When exploration is resumed, thecore should be examined to determine whether thesamples are still useful or whether redrilling is necessary.
Storage During Construction
Core and samples should be stored locally during con-struction. The core and samples provide foundation andmaterials data to geologists, designers, and constructionpersonnel during construction and claim processing.
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At the close of construction, special samples should beselected for possible future testing (See the section on“Retention of Rock Core and Samples”). Sample selectionis better when personnel familiar with the core, samples,and foundation conditions are available.
At the close of construction, arrangements should be madefor continued storage of core and samples until applicablecore and sample retention criteria have been met. Thecore and samples should remain at the local storagefacility, if practical.
Storage During Operation and Maintenance
Any transfer of a structure from one organization toanother should include arrangements for core and samplestorage until the applicable standard core and sampleretention periods are met.
Conditions of Storage
The minimum conditions for core and sample storage are:
1. Protection against wetting and drying but notagainst temperature changes. Cores that mightbe damaged by drying or freezing should beappropriately protected.
2. Protection against unauthorized access, damage,vandalism, and snake or rodent infestation.
3. Grouping core boxes and samples by drill holenumber, investigation site, and project and stack-ing to permit reasonably easy access and exami-nation. The core and samples should beaccessible without excessive unstacking andmoving of adjacent core boxes and samples. The
CARE, RETENTION AND DISPOSAL
435
safe height of core box or sample stacks dependson the strength of the boxes and reasonable easeof handling. Core box racks should be providedonly when repeated reexamination and study areanticipated and when the time saved by havingthe boxes separated in units of four or five boxeswould be cost effective.
4. The office responsible for storage should maintainadequate records including copies of final logs,photographs, inventory, and location map of thecore and samples stored at each core and samplestorage location. The records should include thename of the feature or investigation site, drillhole number, number of boxes and samples, andwhether the cores or samples have been tested.
Length of Storage
Proposed Structures or Projects
All core and samples collected during site investigationsshould be kept until the proposed structure, unit, or pro-ject is built and has performed satisfactorily for a periodof time or is abandoned. The following are exceptions.
Appraisal.—Core and samples obtained in investigationsfor dams, canals, etc., should be disposed of at the end ofappraisal stage investigations, such as the abandonmentof a proposed structure site or completion of recon-naissance designs and estimates, except in special cases.
Feasibility.—Disturbed soil samples from borrow pitinvestigations obtained during feasibility stage investiga-tions and not used for testing should be discarded at theend of the investigations unless interest in the project is
FIELD MANUAL
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sufficient to ensure continuing development. If, at theend of 1 year, further development work has notmaterialized, the samples should be discarded on theassumption that deterioration makes tests on the samplesunreliable.
Undisturbed soil samples can be discarded after 1 year.
Design Investigations and Completed Structuresor Projects
Requirements for length of storage for various types ofsamples and core are as follows:
Borrow Pit Investigations for Design.—Borrow pitsoil samples collected for design investigations should beretained until construction is complete and all claims aresettled except as the samples are consumed in routinetesting.
Borrow Investigations for Construction Control.—Soil samples collected for construction control investiga-tions and field laboratory testing should be discardedafter completion of the field laboratory testing and allclaims are settled.
Record Samples from Fill.—Samples collected forrecord tests and not consumed should be retained unlessthe number of samples is more than necessary to repre-sent the materials used for construction.
Foundation Core and Samples.—Foundation core andsamples obtained during design and construction investi-gations and not consumed in testing may be disposed ofwhen the following requirements are met:
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1. Canals and distribution systems including pipe-lines, minor or small engineering structures, andlow dikes or embankments are trouble free for1 year.
2. Large or major engineering structures such asdams, powerplants or pumping plants, mainfeeder canals, and main power conduits aretrouble free for 5 years. The 5-year time periodshould begin after operating level reservoir fillingfor large dams. Representative core and samplesfrom a few representative drill holes should bekept for the life of the structure.
3. Contractual negotiations and settlement of claimswhich might involve reinspection or testing of thecore or samples are complete.
4. Initial safety of dams analysis, modification, andconstruction activities are complete.
Disposal of Core and Samples
Photographs and an adequate log or description of thecore and samples should be available before disposal.When the minimum retention periods and otherrequirements outlined above have been met, concurrenceof the design and operation and maintenance (O&M)offices should be obtained by the office responsible for thecore or samples before any core or samples are discarded.
The responsible office should consider giving the StateGeologist’s Office, technical schools, colleges, museums, orsimilar groups the opportunity to select samples or retainthe core.
The recommended disposal procedure is to place per-manent markers in the core boxes, wrap the boxes inplastic, and bury the boxes in a marked location.
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Retention of Rock Core and Samples
If selected cores or samples are retained as representativeof the foundation and dam, appropriate assistance inselecting the samples is necessary. Assistance canusually be obtained from the design office.
To facilitate storage, handling, and inspection, standardcore box sizes and labeling procedures should be used.Core boxes should withstand a reasonable amount ofcareful handling, stacking, and shipping when filled withrock core.
To help identify the boxes when stacked, informationshould be shown on one end and the top of each core box.Temporary labeling of core boxes used while drilling ahole should be replaced with permanent labeling of coreboxes which will remain legible after handling, stacking,or storing for long periods. A map or an index file of drillhole core should be maintained which shows the locationof drill hole core if the boxes are stored in a large or con-gested storage area.
Bibliography
Bureau of Reclamation, U.S. Department of theInterior, USBR-7100, “Obtaining Undisturbed BlockSamples by the Hand and Chain Saw Methods,” EarthManual, Part II, 3rd edition, 1990.
Bureau of Reclamation, U.S. Department of theInterior, USBR-7105, “Performing Undisturbed SoilSampling by Mechanical Drilling Methods),” EarthManual, Part II, 3rd edition, 1990.
Chapter 25
GLOBAL POSITIONINGSYSTEM
System Description
The Navigation Satellite Time and Ranging (NAVSTAR)Global Positioning System (GPS) is a space-based satelliteradio navigation system developed by the U. S. Depart-ment of Defense (DoD). GPS receivers provide land,marine, and airborne users with continuous three-dimensional (3D) position, velocity, and time data (PVT).This information is available free of charge to anunlimited number of users. The system operates underall weather conditions, 24 hours a day, anywhere onEarth. The Union of Soviet Socialist Republics developeda similar system that is generally not used because it is aduplication of the NAVSTAR function.
GPS System Design
The GPS system consists of (1) the space segment, (2) thecontrol segment, and (3) the user segment.
Space Segment.—The space segment consists of anominal constellation of 24 operational satellites(including 3 spares) that have been placed in 6 orbitalplanes 10,900 miles (20,200 kilometers [km]) above theEarth’s surface. The satellites are in circular orbits witha 12-hour orbital period and an inclination angle of55 degrees. This orientation provides a minimum of fivesatellites in view at any time anywhere on Earth. Eachsatellite continuously broadcasts two low-power, spread-spectrum, RF Link signals (L1 and L2). The L1 signal iscentered at 1575.42 megahertz (MHz), and the L2 signalis centered at 1227.6 MHz.
Control Segment.—The control segment consists of aMaster Control Station (in Colorado Springs) and a
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number of monitor stations at various locations aroundthe world. Each monitor station tracks all the GPS satel-lites in view and passes the signal measurement databack to the Master Control Station. Computations areperformed at the Master Control Station to determine aprecise satellite ephemeris and satellite clock errors.These data are then uplinked to the individual satellitesand, subsequently, rebroadcast by the satellite as part ofa navigation data message.
User Segment.—The user segment is all GPS receiversand their application support equipment such asantennas and processors. This equipment allows users toreceive, decode, and process the information necessary toobtain accurate position, velocity, and timing measure-ments. These data are used by the receiver’s supportequipment for specific application requirements.
GPS Basic Operating Concepts
Satellite Signals.—The satellites transmit their signalsusing spread-spectrum techniques that employ twodifferent spreading functions: a 1.023-MHZ coarse/acquisition (C/A) code on L1 only and a 10.23-MHzprecision (P) code on both L1 and L2. The two spreadingtechniques provide two levels of GPS service: PrecisePositioning Service (PPS) and Standard PositioningService (SPS). SPS uses C/A code to derive position, whilePPS uses the more precise P-code (Y-code).
C/A Code.—The C/A code is a 1,023 bit nonrepeating codesequence with a clock rate of 1.023 MHZ. The satelliterepeats the code once every millisecond. Each satellite isassigned a unique C/A code that is chosen from a set ofcodes known as Gold Codes.
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Figure 25-1.—Satellite signal structure.
P(Y)-Code.—The P-code consists of a 2.36e+14 bitnonrepeating code sequence with a clock rate of10.23 MHZ. The entire code would take 267 days beforea repetition occurs; however, each satellite is assigned aunique 1-week segment of this code that restarts everySaturday/Sunday midnight.
The P-code has a number of advantages over C/A code.(1) The P-code rate is 10 times faster; therefore, thewavelength is 1/10th as long, giving the P-code a muchhigher resolution. (2) The higher rate spreads the signalover a wider frequency range (see figure 25-1). Thisfrequency spreading makes the P-code much moredifficult to jam. (3) By encrypting the P-code (creatingY-code), the receiver is not susceptible to spoofing (falseGPS signals intended to deceive the receiver).
The drawback of P-code is that it is relatively difficult toacquire because of its length and high speed. For thisreason, many PPS receivers first acquire C/A code, thenswitch over to the P(Y)-code. Y-code is an encrypted
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version of P-code that is used for anti-spoofing (A-S).Because of the similarity of these two codes, they arereferred to collectively as P(Y)-code.
Navigation (NAV) Message
Superimposed on both the P-code and the C/A code is anavigation (NAV) message containing satellite ephemerisdata, atmospheric propagation correction data, satelliteclock-bias information, and almanac information for allsatellites in the constellation.
The navigation message consists of 25 1,500-bit framesand is broadcast at 50 bits per second. It takes 30 secondsto receive a data frame or 12.5 minutes to receive all25 data frames. Each satellite repeats its own ephemerisdata and clock bias every frame along with a portion ofthe almanac. The receiver will receive the critical acquisi-tion information within 30 seconds, but a full almanacwill require 12.5 minutes to download.
Signal Acquisition.—The GPS satellites use Bi-PhaseShift Keyed (BPSK) modulation to transmit the C/A andP(Y)-codes. The BPSK technique involves reversal of thecarrier phase whenever the C/A or P(Y)-code transitionsfrom 0 to 1 or from 1 to 0.
To the casual observer, the very long sequence of ones andzeros that make up the C/A and P-codes appears randomand blends into the background noise. For this reason,the codes are known as pseudo-random noise (PRN).
In actuality, the C/A and P-codes generated are preciselypredictable to the start time of the code sequence and canbe duplicated by the GPS receiver. The amount thereceiver must offset its code generator to match the
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Figure 25-2.—Satellite ranging intersections.
incoming code from the satellite is directly proportional tothe range between the GPS receiver antenna and thesatellite.
By the time the spread-spectrum signal arrives at theGPS receiver, the signal power is well below the thermalnoise level. To recover the signal, the receiver uses acorrelation method to compare the incoming signals withits own generated C/A or P(Y) codes. The receiver shiftsits generated code until the two codes are correlated.
Satellite Ranging.—The receiver continuously deter-mines its geographic position by measuring the ranges(the distance between a satellite with known coordinatesin space and the receiver’s antenna) of several satellitesand computes the geometric intersection of these ranges.To determine a range, the receiver measures the timerequired for the GPS signal to travel from the satellite tothe receiver antenna. The resulting time shift ismultiplied by the speed of light, arriving at the rangemeasurement.
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Because the resulting range measurement containspropagation delays caused by atmospheric effects as wellas satellite and receiver clock errors, the measurement isreferred to as a "pseudorange." A minimum of fourpseudorange measurements are required by the receiverto mathematically determine time and the three compo-nents of position (latitude, longitude, and elevation). Thesolution of these equations may be visualized as thegeometric intersections of ranges from known satellitelocations (see figure 25-2). If one of the variables, such aselevation, is known, only three satellite pseudorangemeasurements are required for a PVT solution, and onlythree satellites would need to be tracked.
GPS Accuracy
GPS accuracy has a statistical distribution that dependson a number of important factors, including dilution ofprecision (DOP) satellite position and clock errors,atmospheric delay of the satellite signals, selectiveavailability (SA), signal obstruction, and multipatherrors.
Dilution of Precision
Geometric Dilution of Precision (GDOP) is a measure ofthe amount of error due to the geometry of the satellites.The errors in the range measurements that are used tosolve for position may be magnified by poor geometry.The least error results when the lines of sight have thegreatest angular separation between satellites.
There are four other DOP components that indicate howthe geometry specifically affects errors in horizontalposition (HDOP), vertical position (VDOP), position(PDOP), and time (TDOP). DOPs are computed based on
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the spatial relationships between the satellites and theuser and vary constantly due to the motion of thesatellites. Lower DOPs mean more accurate estimates.A PDOP less than six is necessary for accurate GPSpositioning.
Satellite Position and Clock Errors
Each satellite follows a known orbit around the earth andcontains a precise atomic clock. The monitor stationsclosely track each satellite to detect any errors in the orbitor the clock. Corrections for errors are sent to eachsatellite as ephemeris and almanac data. The ephemerisdata contain specific position and clock correction data foreach satellite while the almanac contains satelliteposition data for all satellites. The NAV set receives theephemeris and almanac data from the satellites and usesthese data to compensate for the position and clock errorswhen calculating the NAV data.
Atmospheric Delay of Satellite Signals
Electromagnetic signals (such as GPS signals) travel atthe speed of light, which is always a constant in a vacuumbut not in the atmosphere. There are two layers of theEarth’s atmosphere that affect satellite signals, theionosphere and the troposphere.
The ionosphere is a 90-mile (150-km) thick layer of theupper atmosphere in which ultraviolet radiation from thesun has ionized a fraction of the gas molecules, therebyreleasing free electrons (ions). The shape of the iono-sphere and its electron density varies with latitude, timeof day, time of year, number of sunspots, solar flares, andother cosmic activity. The magnitude of the error causedby ionospheric effects can translate to a position error aslarge as 130 ft (40 m).
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The troposphere is the dense, humid layer of atmospherenear the surface of the Earth. This layer refracts thesatellite signals in proportion to the humidity and densityof the air. The magnitude of the tropospheric error can beas small as 8 ft (2.3 m) at the zenith, or as large as 65 ft(20 m) at 10 degrees above the horizon.
There are two ways to compensate for the atmosphericdelays: modeling and direct measurement. The iono-spheric and tropospheric delays are inversely proportionalto the square of the frequency. If a receiver can receive L1and L2 frequencies, it can measure the difference betweenthe two signals and calculate the exact atmospheric delay.
Most receivers currently use mathematical models toapproximate the atmospheric delay. The troposphericeffects are fairly static and predictable, and a model hasbeen developed that effectively removes 92-95 percent ofthe error. This reduces the total two-dimensional (2D)position error caused by the troposphere to around 8 ft(2.0 m).
The ionosphere is more difficult to model because of itsunusual shape and the number of factors that affect it. Amodel has been developed that requires eight variablecoefficients. Every day, the control segment calculates thecoefficients for the ionospheric model and uplinks them tothe satellites. The data are then rebroadcast in the NAVmessages of the C/A and P(Y)-codes. This model caneffectively remove 55 percent of the ionospheric delay,reducing the total 2D position error caused by theionosphere to around 25 ft (7.5 m).
Selective Availability and Anti-Spoofing
GPS satellites provide two levels of navigation service:Standard Position Service and Precise Position Service.
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SPS receivers use GPS information that is broadcast inthe clear and is available to anyone in the world. Thisinformation may contain built-in errors that limit theaccuracy of the receiver. This is a security techniquecalled Selective Availability (SA). These SA errors arevariable. In normal conditions, the U.S. Governmentguarantees that these errors do not exceed 100 mhorizontal, 140 m vertical, and time accuracy of340 nanoseconds, 95 percent of the time. There are timeswhen an SPS receiver error exceeds these limits.SPS receivers are for civil use, and SA may or may not beon.
PPS receivers use the same information as SPS receivers.PPS receivers also read encoded information that containsthe corrections to remove the intentional SA errors. Onlyusers who have crypto keys to decode this information getthe PPS accuracy. U.S. Government agencies and someAllies are authorized to have these crypto keys. Areceiver with valid crypto keys loaded and verified is aPPS receiver.
To protect authorized users from hostile attempts toimitate the GPS signals, a security technique called anti-spoofing is also used. This is an encrypted signal from thesatellites that can be read only by PPS receivers.SPS receivers are not capable of using anti-spoofing. Areceiver with valid crypto keys loaded and verified readsthis encrypted signal and operates in a spoofingenvironment.
GPS Signal Obstruction
Normal operation of the GPS receiver requiresundisturbed reception of signals from as few as foursatellites (in normal 3D mode) or three satellites in fixed-
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elevation mode. The signals propagating from thesatellites cannot penetrate water, soil, walls, or othersimilar obstacles.
The antenna and the satellites are required to be in "line-of-sight" with each other. GPS cannot be used for under-ground positioning in tunnels, mines, or subsurfacemarine navigation. In surface navigation, the signal canbe obscured by buildings, bridges, trees, and other matterthat might block an antenna’s line-of-sight from theGPS satellites. In airborne applications, the signal can beshaded by the aircraft’s body during high banking angles.For moving users, signal shading or temporary outagesare generally transitory and should not degrade theoverall positioning solution.
The GPS receiver uses five channels to minimize theeffects of obstruction. During normal operation, fourchannels track the four primary GPS satellites while thefifth channel tracks the remaining visible satellites andrecovers the ephemeris data for each satellite. If one ormore of the primary satellites are obscured, the receivercontains the data to support rapid acquisition ofalternative satellites.
If only three satellites can be tracked, receivers may fea-ture an “Elevation Hold” mode and continue to navigateas previously noted. The accuracy of the PVT in thismode will not be greatly affected unless the elevationchanges. The receiver will use either the last computedelevation or an elevation provided by the user or hostsystem. The accuracy of the “Elevation Hold” modedepends on the accuracy of the elevation provided to thereceiver.
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Multipath Interference
Multipath errors result from the combination of data frommore than one propagation path. These errors distort thesignal characteristics of the range measurements andresult in pseudorange errors. These errors depend on thenature and location of a reflective surface peculiar to eachuser location. The effects are less detrimental for amoving user because small antenna movements cancompletely change the multipath characteristics.
The receiver is designed to reject multipath signals. First,the active patch antennas are designed to have a sharpgain roll-off near the horizon while providing nominalgain for the primary satellite signal. Since most multi-path signals are reflected from ground structures, theytend to be attenuated. Second, the antenna is right-handpolarized. When a right-hand polarized GPS signal isreflected off a conductive surface, the signal becomes left-hand polarized and rejected by the antenna. The receiveralso has hardware and software designed to reduce theeffects of any multipath interference errors.
Differential GPS
Differential GPS (DGPS) may be used to eliminate theeffects of SA and correct certain bias-like errors in theGPS signals. A Reference or Base Station Receivermeasures ranges from all visible satellites to its surveyedposition. Differences between the measured andestimated ranges are computed and saved for postprocessing or transmitted by radio or other signals todifferential equipped receivers. Sub-meter to centimeterposition accuracy is possible using local base stationdifferential GPS.
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Quality of Measurement
The accuracy with which positions are determined usingGPS depends on two factors—satellite geometry and usermeasurement accuracy.
Satellite Geometry
Satellite geometry effects on specific position solutionscan be expressed as dilution of precision. DOP is used todescribe the contribution of satellite geometry to totalpositioning accuracy. An ideal satellite constellationwould not dilute the positioning accuracy.
Ideal Satellite Constellation
The term, “current satellite constellation,” refers to thesatellites being used in the current position solution.When the current satellite constellation geometry is ideal,the DOP value is 1. This means the current satellite con-stellation contributes a “dilution factor” of 1 to positioningaccuracy. Most of the time, the satellite geometry is notideal, which means the current satellite constellationgeometry "dilutes the precision" of the positioningaccuracy. As the satellite constellation becomes less ideal,the adverse effect on positioning accuracy is greater. Thedilution will change over time as satellites travel alongtheir orbits, as different satellites are used to solve forGPS position, and as the user moves.
DOP Effects
The effect of satellite geometry is not equally distributedin all three positional vectors (x, y, and z in Earth-centered, Earth-fixed coordinates). Several DOP relatedvalues are commonly used. Table 25-1 shows expectedvalues for HDOP, VDOP, and others. The range given for
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Table 25-1.—Expected values of dilution of precision
DOP Description
68-percentprobability of
obtaining
95-percentprobability
of obtaining
HDOP Horizontal DOP is thesatellite geometryfactor in the 2D hori-zontal position solution.
1.50 1.78
VDOP Vertical DOP is thesatellite geometryfactor in the verticalposition (elevation)solution.
2.08 2.70
PDOP Positional DOP is thesatellite geometryfactor in the 3D positionsolution.
2.56 3.23
PDOP HDOP VDOP=
+2 2
TDOP Time DOP is thesatellite geometryfactor in the timesolution.
N/A N/A
HTDOP Horizontal and timeDOP is the satellitegeometry factor in the2D horizontal positionand time solutions.
N/A N/A
HTDOP = SQRT (HDOP2 + TDOP2)
GDOP Geometrical DOP is thesatellite geometryfactor in the 3D positionand time solutions.
2.79 3.61
GDOP = SQRT (HDOP2 + VDOP2 + TDOP2)
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VDOP, HDOP, GDOP, and PDOP assumes a 5-degreeantenna mask (signals 5 degrees or more above thehorizon) and a 24 satellite constellation.
Unique user conditions, such as more than 5 degrees ofantenna masking (e.g., in deep canyons), satellite outages,and poor constellation choice may result in a degradedDOP.
Quality Indicators
The indicators of solution quality are computed based onseveral things. These include uncertainties in receivermeasurement processes, current satellite constellationgeometry, and errors as reported by the satellites, such asthe User Range Accuracy (URA) index. There are dif-ferent measures of quality. A quality indicator must beselected based on the requirements of the application andhow meaningful that measure will be. Some measures ofquality indicators are shown below.
Circular Error Probable.—Circular Error Probable(CEP) is an estimate of horizontal accuracy that expressesthe radius of a circle in the horizontal plane that willcontain at least 50 percent of the GPS 2D positionalsolutions. CEP is generally expressed in meters; asmaller value indicates a higher quality 2D positionsolution. CEP is not desirable as a quality measure fornavigation systems because a 50-percent probability is toosmall. This measure can be useful in some applications,for example, a bombing run where a better than50-percent chance of hitting a target is required. CEP isnot available from all GPS units. However, CEP may beestimated by the following equation.
CEP = 0.8323* EHE
EHE is the expected horizontal error.
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R95.—R95 is similar to CEP except that the circlecontains at least 95 percent of the GPS 2D positionalsolutions. R95 is generally expressed in meters, and asmaller value indicates a higher quality 2D position. R95is better than CEP as a measure for navigation systemsbecause a 95-percent probability is more commonlyassociated with navigation requirements. R95 is notavailable from all GPS units. However, it may beestimated by the following equation.
R95 = 1.731 * EHE
Spherical Error Probable.—Spherical error probable(SEP) is an estimate of 3D accuracy that is the radius ofa sphere that will contain at least 50 percent of the GPS3D positional solutions. SEP is generally expressed inmeters, and a smaller value indicates a higher quality 3Dposition solution. SEP is not desirable as a quality mea-sure for navigation systems for the same reason that CEPis not; a 50-percent probability is too small. A sphericalmodel of errors is not well suited to the GPS modelbecause error probabilities in the horizontal plane are ofa smaller scale than those in the vertical plane (compareHDOP to VDOP). This leads to more of a football shapederror distribution than a spherical distribution. SEP isnot available from all GPS units.
Expected Position Error.—Expected position error(EPE) is a 1-sigma calculation of 3D position solutionestimate of error. EPE is expressed in meters, and asmaller EPE indicates a higher quality position solution.Similarly computed values are often referred to,including:
EHE, Expected Horizontal Error (1-sigma estimate of 2D error)
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( )EPE EHE EVE= +2 2
EVE, Expected Vertical Error (1-sigma estimate of one-dimensional error)
EPE is one of the best available indicators of quality fornavigation systems.
EPE can also be output as Figure of Merit (FoM). (Seebelow.)
Root Mean Square.—Root Mean Square (RMS) is a1-sigma calculation of error in position. Horizontal RMSis equivalent to EHE, vertical RMS is equivalent to EVE,and 3D RMS is equivalent to EPE.
The above is true only if the mean values of the errorcomponents are zero or the biases of the errors can beindependently determined and removed.
Figure of Merit.—Figure of Merit (FOM) is anexpression of EPE, as shown in table 25-2.
From a historical perspective, FOM was created at theinception of GPS to provide users with a simple and quickmethod of indicating the solution accuracy; it is stillwidely used in many military applications today. It doesnot have the granularity to take advantage of thesignificant improvements in accuracies that may beachieved today. FOM is available from some GPS unitson the display.
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Table 25-2.—FOM related to EPE
FOMEPE
(meters)
1 < 25
2 < 50
3 < 75
4 < 100
5 < 200
6 < 500
7 < 1,000
8 < 5,000
9 5,000
Expected Time Error.—Expected Time Error (ETE) isa calculation of time error that is computed similarly toEPE. ETE is a 1-sigma estimate of time solution error.ETE is expressed in seconds, and a lower ETE indicatesa higher quality time solution. Some GPS units calculateand output EPE in the form of Time Figure of Merit.
Time Figure of Merit.—Time Figure of Merit (TFOM)is an expression of ETE as shown in table 25-3.
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Table 25-3.—TFOM related to ETE
TFOM ETE
1 < 1 nanosec
2 < 10 nanosec
3 < 100 nanosec
4 < 1 microsec
5 < 10 microsec
6 < 100 microsec
7 < 1 millisec
8 < 10 millisec
9 10 millisec
User Measurement Accuracy
Several factors are involved in the receiver’s ability toaccurately measure the distance to the satellites. Themost significant factors in user measurement accuracyare space and control segment errors, atmospherics, anduser equipment (UE) errors. These errors are generallygrouped together and referred to as User EquivalentRange Error (UERE).
≥
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User Equivalent Range Error
User Equivalent Range Error represents the combinedeffect of space and control segment errors (satellite vehicleposition [ephemeris] and clock errors), atmospherics(ionospheric and tropospheric), and user equipmenterrors (receiver measurement uncertainties). UEREcannot be broadcast by the satellites and can be estimatedonly at the receiver. The point that sets UERE apart fromother measures of error is that UERE does not take intoaccount any satellite geometry effects, such as HDOP orVDOP. Table 25-4 shows a typical error budget for aP(Y)-code GPS receiver.
Table 25-4.—Typical GPS receiver error budget
Accuracy factor Error
Space and control segment 4.0 m
Ionospheric 5.0 m
Tropospheric 2.0 m
Receiver noise 1.5 m
Multipath 1.2 m
Miscellaneous 0.5 m
( )UERE = + + + + +4 5 2 15 12 0 52 2 2 2 2 2. . . 7.0 m
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Space and Control Segment Errors
Satellites provide an estimate of their own satelliteposition and clock errors. Each satellite transmits anindication of these errors in the form of User RangeAccuracy (URA).
URA is a value transmitted by each GPS satellite that isa statistical indicator (1-sigma estimate) of rangingaccuracies obtainable from that satellite. URA includesall errors that the space and control segments areresponsible for—for example, satellite clock error andSA error. URA has very coarse granularity, however.
The URA value is received in the form of an index relatedto URA as shown in table 25-5.
The URA index broadcast by each satellite will changeover time. In practice, the control segment will uploadcorrection data to each satellite at least once every 24hours. When a satellite first receives its upload, it shouldhave a very low URA index. The amount of error willincrease over time, because of things such as satelliteclock drift, and the URA index for that satellite will grow.Some satellites’ URA index will grow more rapidly thanothers.
In practice, authorized PPS users should expect to seeURA index values in the range of 0 to 5. More commonly,values of 2-4 should be expected. The values depend onthe length of time since the last control segment upload tothat satellite.
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Table 25-5.—URA index and values
URA index
URA(meters)
1 0.00 < URA <= 2.40
2 2.40 < URA <= 3.40
3 3.40 < URA <= 4.85
4 6.85 < URA <= 9.65
5 9.65 < URA <= 13.65
6 13.65 < URA <= 24.00
7 24.00 < URA <= 48.00
8 48.00 < URA <= 96.00
9 96.00 < URA <= 192.00
10 192.00 < URA <= 384.00
11 384.00 < URA <= 768.00
12 768.00 < URA <= 1,536.00
13 1,536 < URA <= 3,072.00
14 3,072.00 < URA <= 6,144
15 6,144 < URA (or no accuracy prediction available)
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Wide Area GPS Enhancement
Wide Area GPS Enhancement (WAGE) is a featureavailable in Precise Positioning Service PLGR+96receivers. The WAGE feature uses encrypted satellitedata to reduce some space and control segment errors.
Each satellite broadcasts WAGE data that are valid for6 hours after that satellite receives a data upload. Thesedata may be used to correct satellite clock errors on othersatellites that have not received an upload recently.These clock corrections are used to reduce the errorcaused by satellite clock biases when a period of time haspassed since the last upload to those satellites. It takesapproximately 12.5 minutes to download a completeWAGE data set. Only WAGE data from the most recentlyupdated satellite are used in PLGR.
Atmospheric Errors
Atmospheric errors are those caused by the satelliteRF signal passing through the earth’s atmosphere. Theseerrors include ionospheric and tropospheric delays.
Ionospheric delay affects the GPS signal as it passesthrough the earth’s ionosphere. The ionospheric delay toGPS signals is very dynamic and depends on the time ofday, the elevation angle of the satellites, and solar flareactivity. Single frequency receivers use a modeledestimate of the range error induced by GPS navigationsignals passing through the Earth’s ionosphere. It is verydifficult, however, to estimate the error in this model.
Dual frequency receivers measure this delay by trackingboth the GPS L1 and L2 signals. The magnitude ofthe delay is frequency dependent, and the absolute
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delay on either frequency can be scaled from thedifferential delay between L1 and L2.
Tropospheric delay is the expected measure of range errorinduced by GPS navigation signals passing through theEarth’s troposphere. This measure is based on satelliteelevation. Unlike the ionospheric delay, the troposphericdelay is very predictable, and there is very little error inthe compensation.
User Equipment Errors
User equipment errors are those uncertainties in themeasurements that are inherent in the receiver’scollection and computation of measurements. Severalfactors influence these uncertainties, including the GPShardware, the design of the tracking loops, the code typebeing tracked (C/A or P(Y)), and the strength of thesatellite signals. These uncertainties are taken intoaccount in the Kalman filter processing done in a PLGRwhen computing EPE and ETE.
Multipath effects are caused by a signal arriving at thereceiver site over two or more different paths. The dif-ference between the path lengths can cause them tointerfere with one another in the receiver. Buildings,parking lots, or other large objects may reflect a signalfrom a satellite, causing multipath effects. Signal aver-aging can be used to minimize the effects of multipathsignals.
Error Source Summary
There are many factors that influence the accuracy ofGPS measurements. Many of the factors do notcontribute large errors but cumulatively are important.
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In practice, the three major sources of error are(1) performing the survey when satellite geometry is poor,(2) using equipment not designed to provide the desiredaccuracy, and (3) mixing datums and coordinate systems.
Satellite Geometry
The most useful error measurement available is positiondilution of precision (PDOP). PDOP is a number derivedfrom the geometry of the visible satellites and changes asthe satellites move in their orbits. The smaller the PDOPnumber, the better the satellite geometry. The PDOPvalue should be six, or preferably less, for accurate GPSwork. Some GPS units display the PDOP or an accuracyestimate in real time. Software is available that calcu-lates the PDOP for any planned GPS survey and shouldbe used before conducting the survey to determinewhether accurate GPS work is possible at the plannedlocation and time. The software also can be used todetermine satellite positions and whether terrain or otherobstructions will affect the survey. Presurvey planning,especially relative to PDOP, can make the differencebetween a mediocre or failed GPS survey and a successfulsurvey.
Equipment
Using inappropriate equipment is another major factor inGPS survey problems. The accuracy of the equipmentmust be known, and the equipment must be usedproperly. A small, inexpensive hand-held GPS unit canprovide an accuracy of 10s of feet when selectiveavailability is off and approximately 100 feet (30 m) whenSA is on. A PLGR (military GPS) can provide similaraccuracy when SA is on. A mapping grade GPS unit canprovide 1- to 2-ft (0.5-m) accuracy if the data are post-processed and 3-ft (1-m) real-time accuracy if a satellite
GLOBAL POSITIONING SYSTEMS
463
differential correction signal is available. Centimeter orsurvey-grade accuracy is possible with a local differentialbase station providing real-time or post-processingcorrection of rover data. Do not expect more accuracythan the equipment can deliver. Manufacturer estimatesof accuracy are generally better than what is commonlyencountered in the field.
The equipment must be well maintained. Many appar-ently satellite related problems are caused by equipmentmalfunctions, poorly charged batteries, or faulty cableconnections.
Datums and Coordinate Systems
An apparent GPS problem is introduced by collecting orcomparing position data based on different datums orcoordinate systems. Many old topographic maps andsurveys use the 1927 North American Datum (NAD27),and most new survey data are based on the 1983 NorthAmerican Datum (NAD83). Also, some sites use a localreference system that is not related to a regional datumor coordinate system. Systematic errors are a good indica-tion of a datum problem. Software is available that veryaccurately converts between datums and coordinatesystems and is very useful for diagnosing and correctingproblems. Chapter 6 of Volume 1 contains a discussion ofdatums, map projections, and coordinate systems.
APPENDIX
ABBREVIATIONS AND ACRONYMSCOMMONLY USED IN
BUREAU OF RECLAMATIONENGINEERING GEOLOGY
AND RELATED TO HAZARDOUS WASTE
(Many are modified from A.A.P.G. Committeeon Stratigraphic Correlations)
Acronyms and Abbreviations Commonly Used in Bureau of Reclamation Engineering Geology
A Apparent trace
acre-ft Acre-feet
acre-ft/d Acre-feet per day
acre-ft/yr Acre-feet per year
AGI American Geological Institute
AP Analysis Plan
APSRS Aerial Photography Summary RecordSystem
ARAR Applicable or Relevant and AppropriateRequirement
ASCS Agricultural Stabilization andConservation Service
ASTM American Society for Testing Materials
FIELD MANUAL
420
ASTM/USCS American Society for Testing Materials/Unified Soil Classification System
b As a suffix, with boulders
BJ Bedding joint
c As a suffix, with cobbles
CADD Computer assisted design and drafting
CERCLA Comprehensive EnvironmentalResponse, Compensation, andLiability Act
CH Fat clay
CL Lean clay
CL Cleavage
CL-ML Silty clay
cm Centimeter
cm2 Square centimeter
cm/s Centimeter per second
COC Contaminant of concern
D Dip trace
DI Durability Index
DLS Detail line survey
DNAPL Dense, nonaqueous phase liquid
DQOs Data Quality Objective
ABBREVIATIONS
421
EPA Environmental Protection Agency
ft Foot
ft2 Square foot
ft3 Cubic foot
ft3/s Cubic foot per second
ft/yr Feet per year
FJ Foliation joint
FSP Field Sampling Plan
FZ Fracture zone
g As a prefix, gravelly; as a suffix, withgravel
gal Gallon
gal/min Gallon per minute
GC Clayey gravel
GC-GM Silty, clayey gravel
GC/MS Gas chromatograph/mass spectrometer
GC Gas chromatograph
GM Silty gravel
GP Poorly graded gravel
GP-GC Poorly graded gravel with clay
GP-GM Poorly graded gravel with silt
FIELD MANUAL
422
GPS Global Positioning System
GW Well graded gravel
GW-GC Well graded gravel with clay
GW-GM Well graded gravel with silt
H1 Extremely hard
H2 Very hard
H3 Hard
H4 Moderately hard
H5 Moderately soft
H6 Soft
H7 Very soft
HASP Health and Safety Plan
HCl Hydrochloric acid
ID Inside diameter
IF Incipient fracture
IJ Incipient joint
in Inch
in2 Square inch
in3 Cubic inch
JT Joint
ABBREVIATIONS
423
k Hydraulic conductivity
kPa Kilopascal
kg/cm2 Kilogram per square centimeter
km Kilometer
kN Kilonewton
kN/m3 Kilonewton per cubic meter
L Liter
lbf/in2 Pound-force per square inch
lb/in2 Pounds per square inch
lb/ft3 Pounds per cubic foot
LCS Laboratory control standard
LL/PI Liquid limit/plasticity index
LNAPL Light nonaqueous phase liquid
L/sec Liter per second
m Meter
m2 Square meter
m3 Cubic meter
m3/s Cubic meter per second
m3/yr Cubic meter per year
MB Mechanical break
FIELD MANUAL
424
MCL Maximum contaminant level
mg/Kg milligram per kilogram
MH Elastic silt
mi Mile
ML Silt
mm Millimeter
NAD North American Datum
NASC North American Stratigraphic Code
NCC National Cartographic InformationCenter
NGI Norwegian Geotechnical Institute
NPDES National Pollutant DischargeElimination System
NTIS National Technical Information Service
NTU Nephelometric turbidity unit
OD Outside diameter
OERR Office of Emergency and RemedialResponse
OH Organic clay
OL Organic silt
OSHA Occupational Safety and Health Administration
ABBREVIATIONS
425
Pa Pascals
PRP Possible responsible party
PCB Pentachlorobenzene
ppb Part per billion
ppm Part per million
PSI Pound-force per square inch
PT Peat
PVC Polyvinyl chloride
QAPP Quality Assurance Project Plan
QC Quality control
RCRA Resource Conservation Recovery Act
Reclamation U.S. Bureau of Reclamation
RF Random fracture
RMR Rock Mass Rating System GeomechanicsClassification
RQD Rock Quality Designation
RSR Rock Structure Rating
S Strike trace
s As a prefix, sandy; as a suffix, with sand
SAP Sampling and Analysis Plan
SC Clayey sand
FIELD MANUAL
426
SC-SM Silty, clayey sand
SDWA Safe Drinking Water Act
SM Silty sand
SOP Standard operating procedures
SP Poorly graded sand
SP-SC Poorly graded sand with clay
SPT Standard Penetration Test
SP-SM Poorly graded sand with silt
SW Well graded sand
SW-SC Well graded sand with clay
SW-SM Well graded sand with silt
TBM Tunnel boring machine
TCE Trichloroethlyene
TCLP Toxicity characteristic leachingprocedure
TRPH Total recoverable petroleumhydrocarbons
URCS Unified Rock Classification System
USCS Unified Soil Classification System
USDA United States Department of Agriculture
USGS United States Geological Survey
ABBREVIATIONS
427
VOC Volatile organic compound
WP Work plan
yd3 Cubic yard
µg/L microgram per liter
µm Micrometer
EC degrees Centigrade
EF degrees Fahrenheit
Commonly Used Acronyms and AbbreviationsRelated to Hazardous Waste
ARAR Applicable or relevant and appropriaterequirement
AST Above ground storage tank
AP Analysis plan
BADT Best available demonstrated technology
BAT Best available technology or bestavailable treatment
CAA Clean Air Act
CERCLA Comprehensive Environmental Response,Compensation, and Liability Act(Superfund)
FIELD MANUAL
428
CERCLIS Comprehensive Environmental Response,Compensation, and LiabilityInformation System
COD Chemical oxygen demand
CRP Community Relations Plan
CRZ Contaminant reduction zone
CWA Clean Water Act (aka FWPCA)
DQO Data quality objectives
EPA Environmental Protection Agency
FS Feasibility study
FSP Field sampling plan
HASP Health and safety plan
HRS Hazard ranking system
HS Head space (analysis)
IDL Instrument detection limit
IDLH Immediately dangerous of life andhealth
LEL Lower explosive limit
LFL Lower flamability limit
LUST Leaking underground storage tank
MCL Maximum contaminant level (SDWA)
MDL Method detection limit
ABBREVIATIONS
429
MSDS Material safety data sheet
NCR Nonconformance report
ND Nondetect
NFRAP No further remedial action planned
NPDES National Pollutant Discharge EliminationSystem
NPL National Priority List
NTIS National Technical Information Service
OSWER Office of Solid Waste and EmergencyResponse
PA Preliminary assessment
PCB Polychlorinated biphenyl
PEL Permissible exposure limit or personalexposure limit
PPB Parts per billion
PPM Parts per million
PPT Parts per trillion
PPTh Parts per thousand
PRP Potentially responsible party
PS Point source
PVC Polyvinyl chloride
FIELD MANUAL
430
PWS Public water supply or public water system
QA Quality assurance
QAPP Quality assurance project plan
QC Quality control
QL Quantitation limit
RA Remedial action or removal action or riskassessment
RCRA Resource Conservation Recovery Act
RD Remedial design
RfD Reference dose
RI Remedial investigation
RMCL Recommended maximum contaminantlevels
RME Reasonable maximum exposure
ROD Record of decision
RP Responsible party
RPM Remedial project manager
RQ Reportable quantity
SAP Sampling and analysis plan
SAR Start action request
ABBREVIATIONS
431
SARA Superfund Amendments andReauthorization Act of 1986
SAS Special analytical services
SDWA Safe Drinking Water Act
SF Slope factor
SI Site inspection
SOP Standard operating procedures
SQG Small quantity generator
STEL Short-term exposure limit
STP Sewage treatment plant
SVOC Semivolatile organic chemical(Compound)
SWDA Solid Waste Disposal Act
TCE Trichloroethylene
TCL Target compound list
TCLP Toxicity characteristic leaching procedure
TD Toxic dose
TDS Total dissolved solids
THC Total hydrocarbons
TIC Tentatively identified compound
TLV Threshold limit value
FIELD MANUAL
432
TOA Trace organic analysis
TOC Total organic carbon or total organiccompound
TOX Total organic halogens
TPY Tons per year
TRPH Total recoverable petroleumhydrocarbons
TSCA Toxic Substances Control Act
TSDF Treatment, storage, and disposal facility
TSS Total suspended solids
UEL Upper explosive limit
UFL Upper flamability limit
UST Underground storage tank
VOC Volatile organic chemical (compound)
WP Work plan
WSRA Wild and Scenic Rivers Act
WWTP Wastewater treatment plan
APPENDIX A
ABBREVIATIONS AND ACRONYMSCOMMONLY USED IN
BUREAU OF RECLAMATIONENGINEERING GEOLOGY
AGC automatic gain controlAN ammonium nitrateA-S anti-spoofingASCE American Society of Civil EngineersASTM American Society for Testing
MaterialsATF Bureau of Alcohol, Tobacco, and
FirearmsAVIRIS Airborne Visible and Infrared Imaging
SpectrometerBIPS Borehole Image Processing Systembpf blow per footbpm blow per minuteBPSK bi-phase shift keyedBPT Becker Penetration TestC/A coarse/acquisitionCDP common depth pointCFR Code of Federal Regulationscm centimetercm2 centimeter squaredCME Central Mine Equipmentcm/sec centimeter per secondCPE Circular Probable ErrorCPT Cone Penetration TestCPTU piezometric cones or piezoconesCRR cyclic resistance ratioDGPS differential GPS
FIELD MANUAL
466
DoD U.S. Department of DefenseDOP dilution of precisionDOT Department of TransportationDS13 U.S. Bureau of Reclamation Design
Standard No. 13 for EmbankmentDams
EBW exploding bridge wireEHE expected horizontal errorEM electromagneticEPE expected position errorERi drill rod energy ratioETE expected time errorEVE expected vertical errorFoM Figure of MeritFr friction ratiofs sleeve resistanceft feetft/sec feet per secondft3/min cubic feet per minuteft3/sec cubic feet per secondgal/min gallons per minuteGDOP geometric dilution of precisiong/cm3 grams per cubic centimeterGPR ground penetrating radarGPS Global Positioning SystemHDOP horizontal dilution of precisionHSA hollow-stem augerICE International Construction EquipmentID inside diameterIME Institute of Makers of Explosivesin inch
APPENDIX A
467
in/sec inch per secondJPL Jet Propulsion Laboratorykg kilogramkg/cm2/m kilograms per square centimeter per
meterkg/L kilogram per literkg/m3 kilogram per cubic meterkHz kilohertzkm kilometerkPa kilopascalL literlb/ft3 pounds per cubic footlb/in2 pounds per square inchlb/gal pounds per gallonlb/yd3 pounds per cubic yardLEDC low-energy detonating cordL/min liter per minuteL/min/m liter per minute per meterlu LugeonLVL low-velocity layerm meterm2 square metersMHz megahertzmL millilitermm millimetermm/sec millimeters per secondm/sec meters per secondm3/sec cubic meters per secondms millisecondMSHA Mine Safety and Health
Administration
FIELD MANUAL
468
MSS multispectral scannerNAD27 1927 North American DatumNAD83 1983 North American DatumNASA National Aeronautics and Space
AdministrationNAV navigationNAVSTAR Navigation Satellite Time and
RangingNFPA National Fire Protection AssociationNG nitroglycerinNIST National Institute of Standards and
Technology NTU nephelometric turbidity unitOD outside diameterO&M operation and maintenanceOSHA Occupational Safety and Health
AdministrationOSM Office of Surface MiningP compressional wavePDA pile-driving analyzerPDOP position dilution of precisionPETN pentaerythritoltetranitratePMT photomultiplier tubePPS Precise Positioning ServicePRN pseudo-random noisepsi pounds per square inchpsi/ft pounds per square inch per footPVC polyvinyl chloridePVT position, velocity, and time dataqc tip resistanceRMS root mean square
APPENDIX A
469
rps revolutions per secondS shear waveSA selective availabilitySEP spherical error probableSLAR side-looking airborne radarSP self-potential, spontanious potentialSPS Standard Positioning ServiceSPT Standard Penetration TestSSS side scan sonarSSSG surface saturated dry specific gravityTDOP time dilution of precisionTFOM Time Figure of MeritTM thematic mapperTNT trinitrotolueneton/ft2 ton per square footUE user equipmentUERE User Equivalent Range ErrorURA User Range AccuracyUSGS U.S. Geological SurveyVDOP vertical position dilution of precisionWAGE Wide Area GPS Enhancement° C degrees Centigrade° F degrees Fahrenheit3D three-dimensional2D two-dimensional
“Column Diameter” equals hole diameter for poured and pumped blastingproducts. (For cartridged products, estimate the explosives columnaverage diameter, based upon cartridge diameter and amount of tampingor slump.) For example: a line drawn through the 0.8 gm/cc point (forANFO) and the 3-inch column diameter point intersects the “weight” line atabout 2.5 lb/ft.
APPENDIX B
NOMOGRAPH RELATING THEDENSITY OF AN EXPLOSIVE IN G/CC,
THE DIAMETER OF THE EXPLOSIVE IN INCHES, AND THE POUNDS OF
EXPLOSIVE PER LINEAL FOOT
APPENDIX C
CHART SHOWING RIPABILITY VERSUS SEISMIC VELOCITY FOR
A D11N BULLDOZER
APPENDIX D
CHARTS SHOWING WEIGHT OF MATERIALS REQUIRED FORTYPICAL LABORATORY TESTS
FIE
LD
MA
NU
AL
478
Weight of material required for individual soil tests - sheet 1 of 7(footnotes are at the end of the table)
DesignationNo.
Nominaldescription
of testMaximum particle
size1,2,3
Practical fieldsample4
Recommendedminimum test sample4 Required
minimumtest specimen CommentsEnglish Metric English Metric
USBR 5300ASTM D 2216
USBR 5305ASTM D 4959
USBR 5310ASTM D 4944
USBR 5315ASTM D 4643
Moisturecontent
No. 40 (425 µm) 0.1 lb 40 g
Same as test specimen
10 g
No. 4 2 lb 800 g 200 g
� in 9 lb 4 kg 2.2 lb, 1 kg
¾ in 18 lb 8 kg 4.4 lb, 2 kg
1½ in 26 lb 12 kg 6.6 lb, 3 kg
3 in 26 lb 12 kg 6.6 lb, 3 kg**Or more to obtain arepresentative sample
USBR 5320Method A
ASTM D 854
Specificgravityminus No. 4
No. 4 5 lb 2.3 kg 1.1 lb 500 g100 g ovendried
AP
PE
ND
IX D
479
Weight of material required for individual soil tests - sheet 2 of 7(footnotes at end of table)
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical field sample4Recommended minimum
test sample4 Requiredminimum test
specimen CommentsEnglish Metric English Metric
USBR 5320Method B or C
ASTM C 127
Specificgravity andabsorptionplus No. 4
� in 20 lb** 9.1 kg**
Same astest
specimen
4.4 lb, 2 kg****Requiredweight of plusNo. 4 particles,air dried
¾ in 30 lb** 14 kg** 6.6 lb, 3 kg**
1½ in 50 lb** 23 kg** 11 lb, 5 kg**
3 in 200 lb** 91 kg** 40 lb, 18 kg**
USBR 5330 orUSBR 5335
ASTM D 2487
Gradation:minus No. 4
No. 4 5 lb 2.3 kg 1.1 lb 500 g100 g oven dried
*10 lbrecommendedfor largemechanicalsieve shakers
**Air dried
USBR 5325
ASTM D 2487
Gradation:gravel sizes
� in 5 lb* 2.3 kg*If not air dried, need testspecimen weight plusamount equivalent toweight of moisture content
200 g*, **
¾ in 15 lb 6.8 kg2.4 lb,1.1 kg*, **
1½ in 100 lb 45 kg 20 lb, 9.1 kg**
3 in 200 lb 4n/a 91 kg 150 lb, 68 kg**
FIE
LD
MA
NU
AL
480
Weight of material required for individual soil tests - sheet 3 of 7(footnotes at end of table)
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical field sample4Recommended minimum
test sample4 Requiredminimum
test specimen CommentsEnglish Metric English Metric
USBR 5350
ASTM D 4318LL - 1 point
No. 4 5 lb* 2 kg* 1.1 lb*, ** 500 g*, **
100 g***Or more, asrequired, to have120 g of air-dried soil(150 g if shrinkagelimit is included)
**Air dried
USBR 5355
ASTM (none)LL - 3 point 100 g**
USBR 5360
ASTM D 4318Plastic limit 20 g**
Two 8-g wet-weightspecimens
USBR 5365
ASTM D 427
Shrinkagelimit
30 g**
AP
PE
ND
IX D
481
Weight of material required for individual soil tests - sheet 4 of 7(footnotes at end of table)
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical field sample4Recommended minimum
test sample4 Requiredminimum
test specimen CommentsEnglish Metric English Metric
USBR 5400ASTM (none)
USBR 5405ASTM D 4647
USBR 5410ASTM D 4221
Dispersivity (crumb,
pinhole,
doublehydrometer)
No. 4 5 lb 2.3 kg 1.1 lb 500 g 500 g
USBR 5525and/or
USBR 5530
ASTM D 4564
Minimumand/ormaximumindex unitweight(wet or drymaximum)
No. 4, � or¾ in
100 lb 45 kg 25 lb 12 kg 25 lb, 12 kg
1½ or 3 in 150 lb 68kg 75 lb 34 kg 75 lb, 34 kg
(Wet anddrymaximum)
No. 4, � or¾ in
100 lb 45 kg 50 lb 23 kg 50 lb, 23 kg
1½ or 3 in 200 lb 91 kg 150 lb 68 kg 150 lb, 68 kg
FIE
LD
MA
NU
AL
482
Weight of material required for individual soil tests - sheet 5 of 7 (footnotes at end of table)
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical fieldsample4
Recommended minimumtest sample4 Required
minimumtest specimen CommentsEnglish Metric English Metric
USBR 5500
ASTM D 2937
Laboratorycompaction:minus No. 4
No. 4 200 lb 91 kg 50 lb** 23 kg** 50 lb, 23 kg** **Air dried
USBR 5515
ASTM (none)
Laboratorycompaction:gravelly soils(one specimen)
3 in350 lb* 159 kg* 350 lb* 159 kg* 225 lb, 102 kg
*Or more as neededto have at least 50 lbof minus No. 4 and atleast 50 lb of plusNo. 4
3 specimens 900 lb 409 kg 900 lb 409 kg 900 lb, 409 kg
USBR 5600
ASTM D 2434
Permeabilityminus No. 4
No. 4 50 lb 23 kg 15 lb 7 kg 15 lb, 7 kg
Permeabilitygravelly soils
3 in 350 lb* 159 kg* 350 lb* 159 kg* 225 lb, 102 kg
AP
PE
ND
IX D
483
Weight of material required for individual soil tests - sheet 6 of 7(footnotes at end of table)
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical fieldsample4
Recommended minimumtest sample4 Required
minimumtest specimen CommentsEnglish Metric English Metric
USBR 5700ASTM D 2435
USBR 5705ASTM D 3877
USBR 5715ASTM D 3877
One-dimensionalconsolidation,
Expansion or
Uplift
No. 4 15 lb 7 kg 3 lb 1.4 kg 1.5 lb, 0.7 kg
FIE
LD
MA
NU
AL
484
Weight of material required for individual soil tests - sheet 7 of 7
DesignationNo.
Nominaldescription
of test
Maximumparticle size1,2,3
Practical fieldsample4
Recommended minimumtest sample4 Required
minimumtest specimen CommentsEnglish Metric English Metric
USBR 5740ASTM D 2850
USBR 5745ASTM D 2850
USBR 5740ASTM D 2850
USBR 5755ASTM (none)
Triaxial K0 (usu-ally performed inconjunction withother triaxialtests)
UU
CU or
CD
No. 4 20 lb 9.1 kg 4 lb 1.8 kg 2 lb, 0.9 kg One 2-in-dia specimen
¾ in 100 lb 45 kg 50 lb 23 kg 45 lb, 20 kg One 6-in-dia specimen
1½ in 200 lb 91 kg 170 lb 77 kg 150 lb, 68 kg One 9-in-dia specimen
No. 4 65 lb 30 kg 16 lb 7.3 kg 8 lb, 3.6 kg Four 2-in-dia specimens
¾in 200 lb 91 kg 200 lb 91 kg 180 lb, 82 kg Four 6-in-dia specimens
1½ in 700 lb 318 kg 700 lb 318 kg 600 lb, 273 kg Four 9-in dia specimens
1 Maximum particle size present in original sample. 2 No. 4 fraction means either maximum particle in original sample was No. 4 or smaller or a representative portion of the minus No. 4fraction of the original sample is required. 3 Metric equivalents are: No. 4 sieve - 4.75 mm, � inch - 9.5 mm, ¾ inch - 19.0 mm, 1½ inch - 37.5 mm, 3 inch - 75 mm and 5 inch - 125 mm. 4 To permit quartering, the field sample should be � 4 times the required weight of the test sample. The test sample is sized to yield therequired number of prepared test specimens.
APPENDIX D
485
Weight of material required for combinations of soil tests -sheet 1 of 1
Test combinations1Maximum
particle size2,3
Minimum samplerequired
English Metric
Laboratoryclassification(gradation, Atterberglimits)
No. 4
50 lb 23 kg� in
¾ in
1½ in 100 lb 46 kg
3 in 200 lb 91 kg
Physical properties -Cohesive soil(gradation, Atterberglimits, specificgravity, laboratorycompaction
No. 4 50 lb 23 kg
� in
100 lb4 46 kg4¾ in
1½ in
3 in 200 lb4 91kg4
Physical properties -Cohesionless soil(gradation, Atterberglimits, specificgravity, maximumand minimum indexunit weight)
No. 4100 lb 46 kg
� in
¾ in
200 lb 91 kg1½ in
3 in
Soil-cement (for3 cement contents)
1½ in 2,000 lb 908 kg
1 Assumes field sample will be used for more than onetest. If sample is divided to provide separate test samples,add up values for individual soil tests. 2 Maximum particle size present in original sample. 3 Metric equivalents are: No. 4 sieve - 4.75 mm, � inch -9.5 mm, ¾ inch - 19.0 mm, 1½ inches - 37.5 mm, 3 inches -75 mm, and 5 inch - 125 mm. 4 Or more, as needed to have 50 lb of minus No. 4.
FIELD MANUAL
486
In place density test requirements - test apparatus andminimum excavation
Cohesive materials
Maximumparticle size
(in)
Minimumrequiredvolume
(ft3)Apparatus and template
opening
¾ 0.25 8-in sand cone
1½ 0.5 12-in sand cone
3 120-in sand cone or24-in-square frame
5 2 30-in square frame
8 8 4-ft-diameter ring
12 27 6-ft-diameter ring
18 90 9-ft-diameter ring
>18 Determine on a case-by-case basis
Cohesionless materials
¾ 0.25 20-in sand cone
1½ 0.5 24-in-square frame
3 1 33-in-square frame
5 2 40-in-diameter ring
8 8 62-in-diameter ring
>8 Determine on a case-by-case basis
APPENDIX D
487
Weight of material required for slope protection tests
Reclamation designation
No.
Minimum requiredsample
CommentsEnglish Metric
6025Design
Standard No. 13
600 lb 275 kg
The minimum dimensionof individual rockfragments selectedshould be at least 0.5 feet(15 cm). If sourcematerial quality isvariable, the sampleshould include rockfragments representingthe quality range of thesource material.
APPENDIX E
USEFUL CONVERSION FACTORSMETRIC AND ENGLISH UNITS
(INCH-POUND)
To convert units in column 1 to units in column 4, multiply column 1 by the factor in column 2.To convert units in column 4 to units in column 1, multiply column 4 by the factor in column 3.
Column 1 Column 2 Column 3 Column 4
Lengthinch (in) 2.540 X 10 1 3.937 X 10-2 millimeter (mm)hundredths of feet 3.048 X 102 3.281 X 10 -3 millimeter (mm)foot (ft) 3.048 X 10 -1 3.281 meter (m)mile (mi) 1.6093 6.2137 X 10-1 kilometer (km)
Areasquare inch (in2) 6.4516 X 10-4 1.550 X 10-3 square meter (m2)square foot (ft2) 9.2903 X 10 -2 1.0764 X 101 square meter (m2)acre 4.0469 X 10 -1 2.4711 hectaresquare mile (mi2) 0.386 X 10 -2 259.0 hectares
Volumecubic inch (in3) 1.6387 X 10-2 6.102 X 10-2 cubic centimeter (cm2)cubic feet (ft3) 2.8317 X 10-2 3.5315 x 101 cubic meter (m3)
cubic yard (yd3) 7.6455 X 101 1.3079 cubic meter (ms)cubic feet (ft3) 7.4805 1.3368 x 10-1 gallon (gal)gallon (gal) 3.7854 2.6417 X 10-1 liter (L)acre-feet (acre-ft) 1.2335 X 103 8.1071 X 10 -4 cubic meter (m3)
Flowgallon per minute (gal/min) 6.309 X 10-2 1.5850 X 101 liter per second (L/s)cubic foot per second (ft3/s) 4.4883 X 102 2.228 X 10-3 gallons per minute (gal/min)
1.9835 5.0417 X 10-1 acre-feet per day (acre-ft/d)cubic foot per second (ft3/s) 7.2398 X 102 1.3813 X 10-3 acre-feet per year (acre-ft/yr)
2.8317 X 10-2 3.531 X 101 cubic meters per second (m3/s)8.93 X 105 1.119 X 10-6 cubic meters per year (m3/yr)
Permeabilityk, feet/year 9.651 X 10-7 1.035 X 106 k, centimeter per second
(cm/sec)Density
pound-mass per cubic foot 1.6018 X 101 6.2429 X 10-2 kilogram per cubic meter (lb/ft3) (kg/m3)
Unit Weightpound force per cubic foot 0.157 6.366 kilonewton per cubic meter
(lb/ft3) (kN/m3)
Pressurepounds per square inch (psi) 7.03 X 10-2 1.4223 X 101 kilogram per square
centimeter (kg/cm3)
6.8948 0.145 kiloPascal (kPa)
Forceton 8.89644 1.12405 X 10-1 kilonewton (kN)
pound-force 4.4482 X 10-3 224.8096 kilonewton (kN)
Temperature °C = 5/9 (°F - 32 °) °F = (9/5 °C) + 32 °
GroutingMetric bag cement per meter 3.0 0.33 U.S. bag cement per foot
Water:cement ratio 0.7 1.4 water:cement ratio by weight
by volume
pounds per square inch 0.2296 4.3554 kilogram per square centi-
per foot meter per meter (kg/cm2/m)k, feet/year 0.1 10 Lugeon
Index
A
abandoned mines, 13absorption, 87, 88, 195, 203, 205abutment contact slopes, 331abutment pads, 339accelerometers, 77acoustic
beams, 61borehole imaging device, 61, 62caliper, 75energy, 57, 61, 91energy (seismic waves), 57imaging, 63, 64imaging device, 64logging, 19, 57, 58logging devices, 57, 58signal, 91transducer, 74, 75velocity devices, 61velocity logger, 56waves, 61
active remote sensing, 90adjusting the blow control, 382adobe charge, 241, 264aerial photography, 85, 90, 92, 198aggregate, 184, 188, 203, 207, 240, 334, 335, 431air injection method, 166, 167air jetting, 332air/water jet, 348air-powered venturi pipe, 348alkali sensitive aggregates, reactive, 334, 335alteration of minerals, 195alternate delays, 233aluminum foil wrapping, 415American Society of Testing and Materials, 353amplitude-modulated devices, 58ANFO (ammonium nitrate/fuel oil mixture), 226angled cut, 239, 243, 244, 245, 247, 249
FIELD MANUAL
492
angular-shaped rocks nested together, 189anti-spoofing, 442, 446, 447aperture, 67, 73apparent
attenuation, 66resistance, 42resistivity, 9, 45
appraisal stage investigations, 435aquaclude delineation, 11aquifer, 2, 11, 108, 111, 115, 116, 166, 168, 171-173,
306, 308, 309, aquifer tests, 111, 116, 306, 309archaeological investigations, 14, 18, 19arch dam sites, 339, 340arching, 321arrival times, 31, 55, 60, 64, 66artesian conditions, 304, 313, 363artificial abutment, 340ASTM D 1586, 377ASTM D-5778, 397ASTM D 3550, 353atmospheric delay, 444-446atmospheric spectral features, 88automated spooling winch, 383automated water level monitoring system, 317automatic data logger, 167automatic hammer, 371, 373, 380, 382, 383, 385, 387axial dipole array, 11
B
backfill concrete, 340, 342, 343, 347backflow, 104background potentials, 15, 16backhoe, 183, 348ball check housing, 364
INDEX
493
bar magnet, 17Barite, 363barring, 332, 348basement complex, 17basket type catcher, 378Becker Drills, Ltd. model AP-1000, 389Becker Penetration Test (BPT), 351bedding, riprap, 183, 190, 195bedding planes, 114, 210, 215, 254, 325, 333bedrock
delineation studies, 11depths, 18topography, 14
Begemann friction cones, 395bench blasting, 219, 227, 233bench floor, 217benches, 234, 235, 257, 298, 330bentonite, 315, 338, 361-363, 369BIPS analysis, 73blanket grouting, 329blast and processing testing, 199blast hole size, 218, 221, 223blast tests, 199blasthole cutoffs, 217blasting procedures, techniques, 192, 207, 209, 218,
233, 253, 254, 259, 261, 264, 325, 331blotting with soil, 348blow count rate, 371, 372blow counts, 111, 306, 371, 375, 383, 388, 391blowout, 302, 313boils, 302bond, 325, 326, 328, 329, 334bonding of fill to concrete, 335borehole
caliper log, surveys, 74deviation, 75diameter, 49, 52, 57, 61, 74
FIELD MANUAL
494
effects, 74electric logs, 38film camera probe, 73film camera systems, 69fluid, 38, 39, 42, 45, 52, 57, 61, 77, 78, 81
acoustic velocity, 57temperature, 77
gravity log, 74, 78gravity logger, meter, 78, 79, 80imaging, 56, 61-63
device, 56, 61, 62velocity devices, 56
mapping, 69peculiarities, 38permeabilities, 112spacing (distance), 65television systems, 69temperature log, 74wireline surveying, 37
bounce chamber, 390, 391bounce-chamber pressure, 390, 391bound water, 41boundary definition of thick strata, 45Bouwer slug test, 168box cut, 239brooming, 332, 336buckling of smaller AW rods, 384bulk and shear moduli, 60bulk density, 49, 51-53, 78, 80, 290
log, 52bulk density/porosity logging methods, 80bulk-loaded charges, 226burden-to-charge diameter ratio, 211buried
channels, 5, 333manmade objects, 15metallic waste, 14
INDEX
495
pipelines, 14, 16, 18, 21stream channels, 13
burning powder train, 237bypass line, 361, 362, 365, 367
C
calcium chloride, 363calculated permeability values, 100, 114calibration
chambers, 404for hole diameter, 52pits, 49
caliper, 52, 61, 74-76caliper log, 52, 74camera, 32, 67-73, 75, 85, 395, 413canals (and distribution systems), 16, 431, 435, 437canyon profile for a damsite, 344capillary
fringe, 115rise, 327system, 15, 16zone, 110, 175
CAPWAP, 392carburizing, 377care of samples, 431cased boreholes, 37, 49, 50, 55casing advancer method, 369casing advancer systems, 385cat head, 353cathodic protection, 1, 10, 11, 21cavities, 15, 56, 62, 63, 66, 67, 69, 210, 211, 302,
330, 332cement, 77, 96, 184, 206, 321, 325, 334, 335, 348cementation, 66, 74, 176, 195, 204, 206centrifugal mixer, 335
FIELD MANUAL
496
channels, 5, 13, 84, 87, 188, 325, 330, 333, 448channels in rock surfaces, 325cheese cloth, 415-417chemical and biologic
content of water, 316quality of water discharged, 312
chemical concentration cells, 15Cherenkov
light, 55photons, 55
chronology of dewatering, 319claims, 306, 312, 433, 436, 437clay plug, 257cleanout bit, 359cleanup procedures, 332clock errors, 440, 444, 445, 457, 458, 460closed-end diesel pile hammer, 390CME automatic hammer, 382coefficient of storage, 108cofferdams, 303, 304cold protection, 412collar distance, 222, 228-231, 271color of the borehole wall, 67commercial
quarry or pit deposits, 201sources, 196
compaction, 66, 140, 153, 321, 322, 326-329, 336, 337,348, 389, 417
techniques, 329compass/clinometer, 68, 71compressed air or water cleaning (air jetting), 323, 332compression fracturing of core, 409compression packers, 118compressional
energy, 57(P) wave velocity, 5wave oscillations, 57
INDEX
497
wave velocities, 3, 5, 61waves, 5, 6, 57
concrete, 66, 67, 69, 203, 207, 302, 313, 321, 323-325,329-331, 333-343, 345-349, 351, 431
backfill, 342, 346backfilled cutoff shafts, 346cracking, 334, 335grout caps, 323joints, 69modulus, 340
conductive fluid in the borehole, 47conductivity, 13, 14, 32, 78, 107, 110, 132, 134, 146,
147, 317, 395cone tip resistance, 395connectivity, 96-98cone tip resistance, 395construction
specifications, 206, 306traffic, 326
contact log, 46contacts of rock or soil against concrete, 67contaminant plumes, 10, 14continuity of geologic strata, 38continuity of the bedding, 38continuous acoustic velocity (sonic) logger, 57continuously recorded hydrofracture/jacking test, 104contour blasting, 257contrasting lithologies, 63contractor compliance, 319contractual negotiations, 437control segment, 439, 446, 456-458, 460controlled blasting techniques, 233, 253, 254, 259, 325conventional flowmeters, 81conventionally excavated (drill-blast) tunnel, 106core
box, 411, 412, 413, 415, 416, 420-423, 434, 435, 437, 438
FIELD MANUAL
498
contact area, 336contact criteria, 322drilling, 199, 202materials, 329, 338storage facilities, 433
core/foundation contact, 326, 338coring, 202, 377, 387corner cut, 239cornish cuts, 244correlate strata, 41, 45, 48, 51corrosion, 21, 302CPT, 351, 358, 363, 387, 388, 395, 397-401, 403,
405-407crack potential, 321cracks in the foundation, 325, 329, 335, 338cross-hole
geophones, 64seismic tomography, 66test(s), 64, 65
crowd-out plugged bit, 390crown sheaves, 381, 382crypto keys, 447curing compound, 333, 335curve shapes, 45cushion blasting, 233, 259-262, 272-274cushion holes, 261, 273cushioning material, 416, 420cutoff
depths, 342, 346facilities, 303shafts, 342, 346trench(s), 322, 327wall, 323
cutoffs, 217, 235-237, 274, 299, 300cylindrical and cube samples, 417-419
INDEX
499
D
daily drill report, 423dam foundation, 95, 98, 106, 350dam height, 106damp sawdust, 419damsite foundation permeabilities, 96deck charge, 215, 230, 231deck of inert stemming material, 213deformation, 340-342, 345, 346, 357, 359
moduli, 340, 341, 345degree of compaction, 66delay
interval, 222pattern, 210, 251, 252, 276
delineating thin strata, 45densities of materials in the Earth, 18density
contrasts, 18, 19logger, 49, 78logging device, 51
dental concrete, 321, 324, 325, 330, 331, 333-338, 345
fillets, 334treatment, 340, 341, 344-346
concrete, 341work, 343, 347
depth of geologic materials, 38of investigation, 11, 14, 47of investigation for the microlog, 47of penetration, 45
design data, 304-306, 351, 431collection program, 304
Design Standards No. 13, Embankment Dams, 358detecting cavities, 15
FIELD MANUAL
500
determination, 18, 41, 52, 119, 133, 191, 203, 408, 417of lithologies from SP logs, 41of physical properties, 38, 203of the relationship between weight and size, 191of volumetric water content, 52
detonating cord, 236, 242, 255, 272, 274-277, 282, 284,connectors, 236
deviation surveys, 6, 65, 288, 297dewatering, 96, 198, 299, 300, 302-306, 309, 312,
314-320design, 306facilities, 299, 304, 314-316wells, 306
diesel pile-driving hammer, 387differential GPS (DGPS), 449differential
movement, 343, 347settlement, 324, 330, 331
digital processing, 84, 87dilution, 302, 444, 450, 451, 462
factor, 450of precision (DOP), 444
direct (non-refracted) arrivals, 64directional
detectors, 64surveys, 74, 75
discontinuity (discontinuities), 20, 56, 62, 63, 67, 69, 71,190, 194-196, 200, 203, 204, 330, 340, 341, 345
disk-type meter, 126, 141disks, 326, 418, 428disturbed zone, 106dispersive clays, 338dispersive
embankment materials, 327material(s), 338soil, 338
dispersivity tests, 338
INDEX
501
disposal guidelines, 431disposing of samples, 432ditches, 198, 299double packers, 119down-hole probe, 67, 69drag force, 189drainage trenches, 323draining, 300, 302
surrounding surface water and groundwater, 302drawdown with time, 308draw cut, 243drill hole deviation surveys, 6drill jumbos, 244drill rod energy ratio, 356, 379drilling
fluid loss, 67mud, 38, 39, 361, 362, 364, 372mudcake, 45
drive cap, 367drive shoe, 153driving friction, 392, 393drop pipe, 162-165drummy rock, 348dry boreholes, 47dual frequency receivers, 460durability tests, 204, 205durable rock types, 190dynamic elastic properties of rock, 60dynamites, 226, 227, 285, 294D-6067, 397
E
earthquake design analysis, 8liquefaction, 375
FIELD MANUAL
502
Earth’s magnetic field, 80effective porosity, 50, 56, 61, 108, 308effects
of bed thickness, 45of mud cake, 52of traffic, 9
on sensitive equipment, 9EHE, 452-454electric
log, 37, 38log correlation, 38sounder (M-scope), 315
electrical current, 9, 26, 32, 77, 292, 293field, 9properties, 2, 10, 11, 13, 37, 38resistivity, 1, 2, 9-11, 13surveys, 38, 45
electrode(s), 9-11, 23, 33, 37, 41, 43-45, 47 array, 11, 13, 42, 45spacing, 10, 11, 43, 45
electrolyte, 16electromagnetic (EM)
conductivity, 13, 14profiling surveys, 10, 13, 14
induction, 13radiation, 84spectrum, 84, 86surveying, 13wave propagation, 13
electromagnetically induced telluric, 16(large scale flow in the earth’s crust) currents, 16
electron density, 51, 445electro-filtration, 16electro-mechanical pulse, 57embankment, 183, 188, 321-329, 333, 338, 349,
350, 358
INDEX
503
embankment layer (lift), 326embankment zones, 321energy
losses in rods, 379transfer effects, 387
energy/count plot, 55EPE, 453-455, 461erodible
foundation materials, 322nonplastic materials, 338
erosion, 90, 183, 291, 307, 329, 330, 338channels, 330
erosional history, 96erosive
action of water, 189water forces, 191
erosion-resistant plastic materials, 338ETE, 455, 456, 461evaluating
an existing source, 197subsurface conditions, 197
excavated slopes, 302, 312excavating, 192, 200, 266, 321-323, 338excavation, 96, 211, 213-215, 217, 220, 229, 253, 254,
257, 259, 260, 272, 280-282, 286, 289, 297, 299,300, 302, 303, 307, 313, 323, 329-333, 339-343,345, 347
existing quarries, 197, 206expandable packers, 418, 426exploration program(s), 4, 17, 95, 99, 304, 306
F
fabricated well screens, 118falling head test(s), 112, 118, 120, 162false-color infrared images, 85
FIELD MANUAL
504
fault(s), 5, 23, 85, 96, 205, 210, 321, 330, 340-342,344-347
investigations, 4studies, 10, 14
feasibility stage, 198, 200, 435feathering (edges), 334, 336, 337feathering of the earthfill lift, 337feeder canals, 437field
laboratory testing, 436spectra, 88spectrometer, 88surface reconnaissance, 198
fill material, 326, 328, 331fillet steep slopes, 325, 333film, 67, 69-73, 75, 83-85, 176, 412, 415, 417, 419, 427film-recording cameras, 67filter(s), 25, 85, 189, 322, 327-329, 331
criteria, 327pack, 167zone(s), 328, 338
first lift, 326-328fishtail-type drag bit, 361flap valves, 368flooding, 302, 303flow in fractures, 103flow nets, 319, 342, 346flowing sands, 365flowmeter(s), 74, 81, 111
log, 74, 81fluff, 348fluid
content, 41, 53density, 51, 78flow, 81temperature logging device, 77velocity, 57
INDEX
505
fluid-filled borehole, 57, 64fluxgate compass, 77focused
device, 47logs, 45
focused-current, or guard, resistivity device, 43, 45foliation, 195, 205, 210, 215, 217FOM, 454, 455forced cooling, 343, 347Foremost Mobile Drilling Company hammer, 383formation water resistivities, 41foundation
and abutment excavations, 342, 346contact surfaces, 328data, 305depth, 303materials, 322, 326, 327, 332, 334, 335modulus, 340strength, 351studies, 4surface, 321, 322, 326, 329-331, 336, 337, 344
fracture(s), 60, 62, 74, 78, 81, 97, 98, 100, 103, 106, 107,113, 114, 120, 137-139, 190, 192, 199, 207, 236,239, 260, 303, 321, 330, 332
changes, 96orientations, 98zones, 66
fracturing, 66, 98, 104, 115, 190, 205, 229, 231, 278,321, 335, 370, 409
the fill, 335fragmentation, 9, 206, 209, 212-214, 218-222, 226, 227,
230, 232, 234-236, 239, 241, 242, 249, 250, 278free face, 209, 218, 219, 223, 225, 226, 231, 235, 239,
243, 246, 251, 273, 276, 278, 282, 287, 294, 297
FIELD MANUAL
506
freeze-thaw deterioration, 204durability testing, 204testing, 204, 205
freezing, 195, 204, 299, 339, 343, 382, 420-422, 424,426, 428, 434
French satellite, 89frequency
(number per foot of borehole) of discontinuities, 67fresh water, 13, 39, 41
sands, 41friction
loss, 105, 115ratio, Fr, 400sleeve, 397, 398
frozen rope, 382fs, 171, 400full column loading, 261fully penetrating wells, 173
G
gabions, 189gamma
radiation, 49-52ray(s), 49, 50-52, 55, 61
gamma borehole, 111logging techniques, 37, 38, 47, 56, 78, 111
gamma raycount, 50, 52detector, 50, 55energy, 55logs, 50
gamma-gammadensity log(s), 49, 50
INDEX
507
density logger, 78logs, 51, 52
gelatin dynamite, 263, 280geologic photogrammetry, 85geologic structure, 31, 60, 100, 114, 209, 238Geometric Dilution of Precision (GDOP), 444geometric distortions, 86geophones, 20, 27, 32, 34, 64geophysical
surveys, 1-3, 14, 16, 56tomography, 66
geotechnical exploration, 37investigations, 1-3, 5, 8, 15-18, 38, 48, 56, 351
geothermal applications, 16areas, 16exploration, 4, 13investigations, 11
glacial or alluvial deposits, 189Global Positioning System (GPS), 91, 439-450, 452-455,
457, 458, 460-463GPR, 14gradation requirements, 205, 206grading for riprap, 192grain density, 18, 51graphite, 15gravel
deposits, 10, 14sumps, 348
gravimeter, 26, 78gravity
anomalies, 18, 80effect, 18meter, 78, 79meter density, 78
FIELD MANUAL
508
permeability test, 112, 142, 147, 153, 157values, 80
grizzly, 192ground
conditions, 95, 399failure, 318roll, 7, 34support, 257, 300surface electrode, 42
groundwater aquifers, 18geophysics, 13investigations, 11, 14levels, 308, 312-315, 318 in excavations, 300, 313maps, 198monitoring, 313, 314monitoring instrumentation, 313, 314occurrence, 303quality investigations, 55withdrawal, 318
ground-truth, 3grout
cap, 323injection, 104, 114nipples, 323pipes, 335, 348potential, 97program, 95travel, 98
groutability, 95-98grouting, 19, 69, 95, 98, 99, 105, 106, 299, 300, 323,
329, 335depth, 106in rock, 300in tunnels, 106
INDEX
509
operations, 19, 69pressures, 98
guard arrays, 47gyratory crushers, 194gyroscope, 77gyroscopic sensors, 77
H
hammer drop friction, 379height, 379, 382
hammer type, 379hammers, 379
(casing type) hammers, 379hand
cleaning, 348compaction, 328tamper(tampering), 328, 336tighten each joint, 384
Harder-Seed method, 390, 391, 393harrows, 326haul distance, 197, 198hauling, 184, 205, 206, 208, 214, 220, 222, 223HAV-180 rig, 391hazardous materials (chemicals), 14, 275, 304, 315, 424hazardous waste studies (investigations), 10, 14, 17,
431HDOP, 444, 450-453, 457headache ball, 241, 276heading round, 243, 246, 248, 291heat pulse flowmeter, 81heavy grain detonating cord, 255high resolution seismic reflection, 5high-energy neutrinos, 55high-frequency acoustic energy, 61
FIELD MANUAL
510
hole wandering, 234hollow
AW drill rod, 381guide rod safety hammer, 381
hollow-stem, 356, 359, 360, 364-366, 372augers (HSAs), 364, 365, 377, 385
horizontal displacement, 318permeability, 111, 174plane, 71, 452, 453
hydraulic conductivity, 107excavator, 323, 348fracturing, 321, 370models, 98wedging device, 241
hydrofracture tests, 104hydrofractured rock, 100hydrofracturing, 98, 100, 104, 114hydrogen atoms (nuclei), 52hydrologic studies, 50hyperspectral data, 88hydrographs, 309, 319
I
igneous rock, 194Ilmenite additives, 363Imhoff cone, 316impact anvil, 356, 371, 379impeller-type meter, 126, 141impervious materials, 322impervious zone(s), 323, 324, 331, 336, 356
foundation contact, 323inclined core, 321inclinometer, 398
INDEX
511
inert stemming materials, 213infiltration, 307inflatable (straddle) packers, 118, 119, 162initial lift, 328, 337inspection control, 206, 207investigations during the design stage, 199ionosphere, 445, 446, 460irregular rock surfaces, 328
J
jacking, 97, 98, 100, 104, 114, 127, 335, 397, 399tests, 100
jetting and driving, 147joint
mortar, 325sets, 210, 214, 340
K
kerf, 246, 247, 282
L
Landsat, 83, 89, 90lateral, 1, 10, 13, 16, 24, 43-45, 47, 303, 308
array (resistivity), 43, 44array spacing, 43device(s), 43, 45logs, 45
lava tubes, 302layer velocities, 4leakage paths, 16leather cups, 118left-hand polarized, 449
FIELD MANUAL
512
lifts, 328, 329, 336-338, 343, 347lime, 328, 338, 339line drilling, 254, 255, 257, 272, 282, 325linear features, 63lining design, 96liquefaction, 351, 356, 358, 359, 362, 375-378, 381, 383,
385, 388, 389, 394, 406-408evaluation(s), 351, 362, 376, 378, 381, 389, 406resistance, 356, 389, 406-408resistance evaluations, 356triggering, 406
lithologic contacts, 60, 66lithology, 38, 39, 41, 48, 53, 74, 96litigation, 312load cells, 397, 398local differential base station, 463location
map of the core and samples, 435of drill hole core, 438of stratigraphic contacts, 67
logging tools, 37, 49, 55long-normal, 43, 45loss of fines, 303low
permeabilities, 108, 302plasticity, 338, 339
low-alkali cement, 334, 335Lugeon value, 100
M
machine stripping, 348machine-bored tunnel, 106magnetic
features, 17log, 74, 80
INDEX
513
materials, 17, 28north, 62surveys, 2, 13, 17, 18susceptibility, 80
material properties for static and dynamic stressanalysis, 65
mechanical breakdown, 195calipers, 74, 75penetrometers, 395
metal expandable packers, 418methods for obtaining size and weight data, 191Michigan cuts, 244microlog, 46, 47
electrode spacings, 47sonde, 47survey, 47
microsurvey, 46microwave bands, 84military GPS, 462millisecond delays, 235, 250mineral
composition, 38deposits, 15, 16exploration, 13, 17textures, 67
mineralogy, 38, 192, 194, 204, 405minilog, 47model input parameters, 99monitoring
during construction, 313leakage, 17of water control parameters, 312well design, 317wells, 116, 315, 317
mortar, 295, 325, 335, 336, 338, 344movement by water, 189
FIELD MANUAL
514
ms delays, 232, 233, 236MSS, 86, 89mud cake, 47, 52mud pumps, 121mud slab, 333mudcap, 241multiple
aquifers, 107electrode arrays, 42, 43pressure tests, 127, 136, 137
multiple-arm calipers, 74multiple-electrode resistivity
arrays, 45sonde, 38
multispectral photographs, 85multi-beam sonar, 91multi-beam systems, 91muon, 55
N
N value, 356, 364, 370, 371, 374, 375, 378, 379, 381,385
NAD27, 463NAD83, 463natural color images, 85natural electrical potential, 15natural gamma
log, 53logger, 49radiation, 49, 50, 52ray detector, 50ray logging, 61ray logs, 50
natural potential, 15, 33
INDEX
515
Navigation Satellite Time and Ranging (NAVSTAR), 439
near infrared wavelengths, 83near-infrared spectrum, 85neat cement grout, 335needle valves, 141negative subdrill, 229nephelometric turbidity units (NTU), 316neutron
activation, 55detectors, 52devices (source), 49, 53, 55log(s), 50, 52, 53logger, 49radiation, 52, 53water content log, 49
new quarry or pit investigation, 197Nk, 405nonconducting fluids, 47nondispersive earthfill (material), 327, 328, 338nonerodible embankment materials, 330normal
array(s), 43, 44devices, 43, 45resistivity arrays, 43spacing devices, 47
NTU, 316nuclear borehole measurements, 49nuclear logs, 49, 55nuclear radiation logging
systems, 49tools, 49
FIELD MANUAL
516
O
objectives of foundation surface treatment, 329observation well(s), 158, 160, 161, 172, 307, 308, 312,
314, 315, 317observed gravity, 18office responsible for the core or samples, 437oil exploration, 4, 7open discontinuities, 62, 67open holes, 37, 162open-ended diesel hammer, 390optical logging systems, 67optimum
drill hole orientations, 100moisture content, 327, 328
orange smoke, 264organic material, 322orientation of the drill hole relative to the fractures, 113outcrops, 198, 202overburden (depth), 98, 100, 114, 199, 202, 286, 321,
323, 358, 361, 375overexcavation, 331, 340overhangs, 323-325, 330, 331, 333, 334
P
packer, 105, 110, 112, 113, 115, 116, 118-120, 126, 128,130, 138, 164, 165, 309
packer(s), 74, 105, 115, 118-120, 128, 130, 162, 164,418, 426
seal, 120test(s), 110, 112, 113, 116, 309
packing material, 189, 418, 421, 428pails, 417-419, 428panchromatic photography, 85parallel hole cuts, 243-245, 253partially penetrating wells, 173, 174
INDEX
517
PDA measurement, 392PDOP, 444, 445, 451, 452, 462peeling, 348penetration
per blow, 375, 376resistance, 351, 356, 358, 385, 388, 397,
400, 408penetrometer, 387, 388, 395, 397, 399
tip, 387, 388perforated pipe, 140, 315performance, 188, 319, 388, 392
on existing structures, 189performing gradations on the blasted product, 207perimeter
blasting, 257cracking, 253holes of a blast, 214
permafrost, 14permanent
labeling, 438markers, 437
permeabilities, 45, 95, 96, 99, 108, 111, 112, 114, 115,147, 302, 306, 307
permeabilities of strata, 45permeability, 39, 95-100, 103, 105, 106, 107-119, 121,
126, 128, 130, 131, 133, 136-139, 142-145,147-149, 153, 154, 157, 159-161, 163, 164, 166,168, 170, 171, 174, 177-179, 181, 182, 198, 300,302, 306-308, 316���330, 331, 347������������������
coefficients, 143of the soil, 306test(s), 97, 112-116, 118, 121, 126, 128, 131, 138,
139, 142, 145, 147, 149, 153, 154, 157, 159, 160,179, 306, 308
FIELD MANUAL
518
permeable, 38, 39, 41, 47, 81, 96, 106, 120, 137, 138,150, 164, 307, 347
path, 347sand bed, 41
permeameter, 115, 182pervious rock, 106petrographic examination, 203, 205petroleum
exploration, 1, 17, 18traps, 18
pH, 194, 317photographs, 69, 71, 83, 85, 198, 201, 227, 435, 437photography, 83, 85, 90, 92, 411, 414
frame, 414photomultiplier tubes, 55physical properties, 2, 37, 38, 81, 203, 205, 340, 356,
431piezoelectric transducer, 61piezometer(s), 178, 306-308, 314, 315, 362, 363
permeability test, 179pile-driving analyzer, 392pilot bit, 359, 364, 365, 367, 368, 370
cutting teeth, 368seat, 368
pipable material, 342pipelines, 16, 18, 21, 67, 295piping, 15, 105, 115, 327, 342, 346 pit development, 199planar discontinuities, 63, 71plastic
bags, 298, 417, 419material, 329pails, 418, 428
plasticity, 329, 337-339, 388, 415PLGR, 460-462PLGR+96 receivers, 460PMT, 55
INDEX
519
pneumatic instruments, 315pneumatic-tire(d)
equipment, 328, 337roller, 328, 329
points of high stress concentration, 343, 347Poisson’s ratio, 24polar regions, 17polymer-enhanced drill fluid, 361(poly)urethane foam, 416pore
fluid content, 41spaces, 9water, 41, 341, 346, 395, 399, 400, 403water stress, 395, 399
dissipation measurements, 399porosity, 9, 18, 38, 45, 49-53, 56, 61, 66, 67, 78, 80, 107,
108, 117, 192, 194, 195, 300, 302, 308porous
media, 16permeable zones, 47tube, 315
position dilution of precision (PDOP), 462positive ions, 16potassium isotope K40, 50potential electrodes, 11, 43-45power conduits, 437powerplants, 431, 433, 437powder factor, 211, 213, 237-239, 251, 283, 289PPS accuracy, 447precipitation, 300, 303, 308, 317Precise Position (Positioning) Service (PPS), 440, 446,
460preferred site frequencies, 8presentation of information, 184preshearing, 255, 289presplitting, 254-258, 261, 272, 274, 289
FIELD MANUAL
520
pressure transducer, 130, 131, 162, 167, 398versus flow curves, 100, 114
principal joint sets, 214production blast, 256progressive delays, 233, 234propagation velocities, 57protecting and shipping samples, 431Protection against wetting and drying, 434protective
filters, 329outer box, 422
pseudorange, 444, 449pseudo-random noise (PRN), 442pump bypass line, 361pumping caused by construction equipment travel, 327pyramid cut, 243pyrotechnic delay elements, 237P- and S-wave energies, 57P- and S-waves, 64P-code, 440-442P-wave, 56, 60, 66
R
R95, 453radar
interferometry, 90remote sensing, 90
radiation detector, 47logging device, 61logging systems, 49, 50
radioactiveisotopes, 50
INDEX
521
material, 53source (material), 47, 49, 52
ramping the fill, 329rapid freeze-thaw durability evaluation, 203real-time viewing, 67rebound, 336receiver measurement uncertainties, 457recharge conditions, 303record tests, 436rectangular pattern, 223reference electrode, 45reflectance spectra, 87reflected shock wave, 384refraction, 2-6, 21, 22, 25-28, 31-33, 35, 57, 64, 66, 201refusal rule, 375relationship between weight and size, 191relative
clay content, 49density, 50, 226, 327, 357, 404, 417
remote sensing, 83, 84, 89-93interpretations, 83
representative permeabilities, 307samples, 199, 202, 203, 205
requirements for length of storage, 436for storage of core and samples, 432
reservoir load, 344resistance
of a circuit, 41of the conductor, 41
resistivity, 1, 2, 9-11, 13, 32, 33, 38-48, 77, 395deflection, 41logs, 39, 43, 46, 77measurements, 43
revertible drilling fluids, 362RF Link signals, 439
FIELD MANUAL
522
right-hand polarized, 449rippers, 330rippability, 4riprap, 183-189, 191, 192, 194-197, 199-208, 261, 263,
291, 298, 431characteristics, 188durability, 194evaluation, production, and placement, 184fragments, 189quality, 188, 189, 199, 203Quality Evaluation Report, 199, 203quarries, 207source(s), 184, 188, 189, 192, 194-196, 202
evaluation, 184investigation, 195
riser and hole diameter, 314rock
abutments, 328breakage, 9, 200, 239bucket, 192, 323characteristics, 113, 184, 192durability, 195failure criterion, 204foundation(s), 327, 328, 330, 339, 341, 344, 345,
350surfaces, 328
fragments, 183, 187, 189, 190, 192, 195, 203, 204,323, 330
mass design parameters, 97, 114permeability, 97, 98, 113, 114
quarries, 189, 194rake, 192, 193
rockfill dams, 331, 349, 350roller, 326, 328, 329, 337
passes, 328
INDEX
523
rotary casing advancers, 369drilling, 356, 361-363, 369, 385, 389
rounded stone assemblage, 189rover data, 463rubber-tired roller, 337
S
SA, 444, 447, 449, 458, 462Safety Driver, 383safety
hammer, 353, 373, 374, 380-382, 385of dams analysis, 437
saline water, 15salinity, 9, 38, 39, 41, 46
of pore fluids, 46salt water intrusion, 14saltwater/fresh water interfaces, 13sample
data sheets, 431retention (criteria), 431, 434selection, 434size, 95, 99, 202
sampler shoe, 377tip, 368
sand heave, 362, 363pack, 110, 167, 317, 318
sanding in (sandlocked), 142, 356sand-cement slurry, 335satellite(s), 83, 89, 90, 215, 230, 231, 263, 317, 318,
439-452, 456-458, 460-463differential correction signal, 463vehicle position, 457
FIELD MANUAL
524
saturatedlow-strength materials, 304materials, 7, 52, 110, 115sand, 10, 53
saturation, 38, 53, 66, 204, 325, 327sawdust, 416, 419, 427sawed kerf, 246, 247sawteeth, 330, 333scarification, 326, 328, 336, 337scarifying the lift surfaces, 329schistosity, 199, 205, 206, 210screen slot size, 317screening of wells, 322screens of water wells, 69sculpture blasting, 257sealing samples, 415secondary arrivals, 5
blasting, 214, 220, 229, 241, 242, 292emission of neutrons and gamma rays, 52fragmentation, 241, 242fragmentation techniques, 241
sediment content, 312, 316, 317seepage, 11, 16, 95-98, 148, 299, 304, 319, 321, 322,
347, 403control, 96, 304, 322evaluation, 95
investigations, 11potential, 95, 98quantities, 96seeps, 302, 348, 349seismic
anomalies, 65energy, 26, 28, 29, 35, 56, 66pulse, 64P-wave velocity, 66refraction interpretation, 4signal, 32, 66
INDEX
525
source, 6, 64stability, 325surveys, 3, 14, 60tomography, 66velocities, 6, 56, 57, 60, 61, 64wave(s), 6, 25, 27, 30, 31, 32, 34, 57, 64, 288
velocities, 64Seisviewer, 61Selective Availability (SA), 444, 446, 447, 462selective quarrying, 196self-potential surveys, 2, 11, 15, 16sequential timers, 236service history of material produced, 202settlement during dewatering activities, 318settlement of claims, 437shaft sinking cut, 239shale baseline (line), 38, 39shape of individual rock fragments, 189shatter cuts, 244shaving, 348shear wave velocity (velocities), 2, 5, 6, 57, 61, 64, 358shear waves, 6, 57shell zones, 327shipping containers, 420-422, 429shop vac, 348short normal array, 44short rods, 384shotcrete, 336shotpoint depth, 65shrinkage, 338, 342, 343, 347Side Scan Sonar (SSS), 91side-looking airborne radar (SLAR), 90single
column charge, 237frequency receivers, 460packer, 110, 119
single-beam systems, 92
FIELD MANUAL
526
single-electrode array, 45single-point array, 43single-receiver devices, 57siting studies, 1, 4slab cut, 243slabbing, 259slake (slaking), 195, 323, 332, 333, 339, 343, 432slashing, 259slope
failure, 318protection, 184, 187, 188
sloughing, 139, 326slug tests, 112, 118, 166slush grout, 321, 325, 330, 335, 336, 338
mix, 335small-strain dynamic properties, 2smooth blasting, 233, 257-259, 272, 274, 294, 325, 331sodium sulfate soundness test, 204, 205soil
cement, 184foundation compaction requirements, 327infiltration data, 307liquefaction criteria, 375
solar flare(s) activity, 445, 460solid steel guide rod, 381solution
cavities, 56, 63, 66, 67, 210, 211, 302, 330features, 60, 333
sonde, 37, 38, 43, 45, 47, 49-53, 55-57, 61, 77electrodes, 45
sonic energy, 56vibrations, 9
SP log (logging), 38, 41, 43, 50SP peak, 41space segment, 439
INDEX
527
spacer blocks, 423ring, 371
spacing-to-burden ratio, 232, 233spalling, 194, 343, 347special purpose electric logging devices, 46specific gravity (gravities), 18, 78, 191, 204, 294, 297spectral
analyses, 55bands, 87, 88data, 83, 84logging sonde, 55logs, 55ranges, 83resolution, 83, 84, 87, 89signatures, 84
spectrometers, 84spontaneous potential, 15, 33, 38, 41spoofing, 441, 442, 446, 447
environment, 447spray coating, 333spring suspension system, 422springs, 74, 302, 342, 346, 439square drill pattern, 223SSGS, 205SSSG, 191, 192, 204stability requirements, 342, 346staggered pattern, 223, 224, 295Standard Penetration Test (SPT), 351Standard Position Service, 446standard surveying methods, 318standing water, 328standpipe, 165, 315Stanley waves, 6static
pore water pressures, 395water levels, 308
FIELD MANUAL
528
Station Receiver, 449statistically significant sample size, 99steeply dipping plane, 71stemming, 213, 215, 222, 227-230, 239, 257, 260, 263,
271, 274, 295, 296, 298stemming column, 222stepped
pressure tests (step test), 100, 104, 114surfaces, 321, 324, 331
stereo imaging, 89storage, 107-109, 128, 142, 167, 168, 265, 266, 281, 283,
289, 295, 300, 307, 409, 410, 414, 415, 418, 420,424, 427, 431-436, 438
costs, 431facility, 432-434of core, 432, 434periods, 431
storativity, 108, 307stove to melt wax, 427straddle packer, 164strain gauges, 397strata boundaries, 39, 41, 45stratum boundary resolution, 45stream gravel, 183stress
anomalies, 321caused by placing earthfill, 335concentrations, 324, 331, 340relief, 96
strike and dip of planar features (strikes and dips), 63,73
string loaded, 257stripping, 322, 325, 348
of pervious materials, 325operations, 325
structural concrete, 334, 336Su, 405
INDEX
529
subdrilling requirements, 217subsurface cutoffs, 300subsurface
geologic conditions, 37, 195, 305hydraulic conditions, 303, 305layer resistivities, 38materials, 2, 10, 11, 13, 48, 107, 112, 115
suitable riprap source, 196sulfates, 334, 335sulfide, 15sump pumps, 315sumps, 299, 300, 322, 323, 348sunspots, 445supplementary dewatering, 300surface
and subsurface data, 305cracks, 329, 335
in the foundation, 329drains, 299electrical surveys, 38, 45saturated dry specific gravity (SSSG), 191water, 299, 300, 302, 303, 307, 309, 312, 318wave(s), 5-8, 27, 34, 57, 60
surveying, 8survey control, 85, 318susceptibility logs, 80swelling rock, 103swivels, 126S-wave, 33, 57, 60, 64, 65
arrival, 64cross-hole tests, 65
Sy method, 390, 392, 393synthetic polymers, 362
FIELD MANUAL
530
T
talus, 7, 194, 198, 202piles, 198, 202
Televiewer, 61tamped cartridges, 226, 255tamping (tamper)
feet, 326, 328, 329plug, 257roller(s), 326, 328, 329roller feet, 328
TDOP, 444, 451television cameras, 67temperature
changes, 426, 434device, 77logging, 77, 78probe, 78variations in the fluid, 77
temporary labeling, 438storage, 433
tension zones, 321tensioned mechanical arms, 74test
blasting (blasts), 207, 263, 267, 281, 286, 297grout section, 105pressure(s), 96, 100, 103, 104, 113, 114, 119wells, 110, 133, 134, 306-308
testing subsurface samples, 197TFOM, 455, 456theoretical overburden stress, 114thermal
infrared, 84, 86, 87, 90systems, 86wavelengths, 87
properties of materials, 86
INDEX
531
thermistor (thermal resistor), 77thick-wall, 353thickness of the riprap, 184thrust blocks, 339tight, impermeable rock, 106timbers, 15time-varying, low frequency, electromagnetic fields, 13top of rock configuration, 19topographic maps, 198, 463total dissolved solids (TDS), 317total porosity, 108toxic waste studies, 11tracer elements, 50tracked equipment, 330tracking, 424, 460, 461transferring core, 432trapped water, 41travel times, 57trial blasts, 263triaxial arrays, 64tricone
bit, 370rockbit, 361
trimming, 259troposphere, 445, 446, 461true orientation (strike and dip), 67true P- and S-wave velocities, 65true velocities, 64tunnel alignments, 95tunnel delays, 250tunnel studies, 96tunnels, 67, 95, 98, 99, 106, 244, 273, 291, 431, 448turbidity, 116, 315-317turbulent flow, 103, 117, 127two-dimensional (2-D) projection, 73
FIELD MANUAL
532
U
UERE, 456, 457ultraviolet radiation, 445uncased boreholes, 51unconfined compression, 358, 405underground blast rounds, 243underwater surveys, 91undisturbed soil samples, 436undrained strength in clays, 358uniformity of rock, 195unsaturated conductivity coefficient, 132, 146unsuitable subgrade, 302unsupervised storage, 432unwatering (methods), 198, 299, 300, 302, 317uplift of constructed features, 302URA, 452, 458, 459USBR 7020, 397user
equipment (UE) errors, 456Equivalent Range Error (UERE), 456Range Accuracy (URA), 452, 458segment, 439, 440
V
vacuuming, 348vadose zone, 112, 115, 306vane shear, 358, 405
testing, 405variable head tests, 170variations in fluids, 45VDOP, 444, 450-453, 457velocity
contrast, 11, 66reversal, 5
INDEX
533
vertical electrical soundings, 11hammer device, 64surfaces, 330, 333, 334
very high resolution mapping of near-surface geology,15
vibration damage, 9levels, 9, 332protection, 412
vibratory compactors (rollers), 326videotaped, 69vinylidene chloride, 415, 427visible spectrum, 85void ratio, 53vugs, 63, 78
W
WAGE, 460wall
irregularity (irregularities), 52of a borehole, 37
washout zones, 74wastage, 196, 200, 201waste piles, 194water
action, 189, 205content, 38, 46, 49, 52, 53, 358, 417content (saturation), 38
by weight, 53of strata, 46
control, 299, 303-306, 309, 312, 317, 319, 322, 347data, 306, 309facilities, 305, 306, 312, 319
FIELD MANUAL
534
investigations, 305, 317methods, 322
energy, 183gel columns, 255jetting, 332level monitoring instrumentation, 313meters, 126, 141quality, 166, 308, 309, 316-318, 334, 336
analyses, 308removal, 300, 348salinity, 38table, 7, 15, 119, 127, 130, 144, 148, 150, 155, 157,
158, 164, 175, 299, 303, 356, 358, 359, 365, 385take(s), 96, 103, 105, 113, 127, 136test(s), 98, 100, 105, 114
calculation, 97data, 96, 106, 113information, 97pressure, 103results, 96, 97, 103
washing, 332watertight riser, 315wavelength range, 84wavy core surfaces, 409wax, 412, 415-419, 427waxed wood disks, 418weight of the rock fragment, 191well(s), 67, 69, 109, 110, 116, 133, 134, 158, 160, 161,
173, 174, 299, 306-308, 312, 314-318, 322 collapse, 316point systems, 315, 316points, 322screen(s), 64, 74, 118, 172, 315
well-graded riprap, 194, 207wet
and dry density, 53
INDEX
535
foundations, 327rope, 382
whipping, 384Wide Area GPS Enhancement (WAGE), 460wireline (wire line), 370
acoustic/seismic logging systems, 56devices, 73electrical systems, 42nuclear radiation systems, 49packers, 105, 115
wood shipping containers, 422workability and nesting of the rock assemblage, 189
Y
Young’s modulus, 24