general & geotechnical considerations for pile design

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Page 1: General & geotechnical considerations for pile design
Page 2: General & geotechnical considerations for pile design

GENERAL & GENERAL & GEOTECHNICAL GEOTECHNICAL

CONSIDERATIONS CONSIDERATIONS FOR PILE DESIGNFOR PILE DESIGN

Presented By;Presented By;

ZAHID UMAIRZAHID UMAIR

2007-MS-GEO-112007-MS-GEO-11

Page 3: General & geotechnical considerations for pile design

CONTENTSCONTENTS General ConsiderationsGeneral Considerations Design ConsiderationsDesign Considerations Nature of LoadingsNature of Loadings Foundation MaterialFoundation Material Identification & Evaluation of Pile Identification & Evaluation of Pile

AlternativesAlternatives Subsurface Investigations and GeologySubsurface Investigations and Geology Laboratory and Field TestingLaboratory and Field Testing Foundation ModificationFoundation Modification Groundwater StudiesGroundwater Studies Dynamic ConsiderationsDynamic Considerations Subsurface ConditionsSubsurface Conditions Pile Load TestPile Load Test Selection of Shear Strength ParametersSelection of Shear Strength Parameters Field Responsibilities for Design Field Responsibilities for Design

EngineerEngineer Pile InstrumentationPile Instrumentation

Page 4: General & geotechnical considerations for pile design

PILESPILES

The purpose of a pile foundation is The purpose of a pile foundation is to transfer and distribute load to transfer and distribute load through a material or stratum with through a material or stratum with inadequate bearing, sliding or uplift inadequate bearing, sliding or uplift capacity to a firmer stratum that is capacity to a firmer stratum that is capable of supporting the load capable of supporting the load without detrimental displacement.without detrimental displacement.

Page 5: General & geotechnical considerations for pile design

GENERAL GENERAL CONSIDERATIONSCONSIDERATIONS

Many factors must be considered while Many factors must be considered while selecting an appropriate foundation. The selecting an appropriate foundation. The final selection should be based on;final selection should be based on;

Evaluation of Engineering FeasibilityEvaluation of Engineering Feasibility Comparative Costs for the Potential Comparative Costs for the Potential

AlternativesAlternatives Factors of SafetyFactors of Safety ReliabilityReliability ConstructabilityConstructability Life Cycle PerformanceLife Cycle Performance

Page 6: General & geotechnical considerations for pile design

Structural & Geotechnical Structural & Geotechnical Coordination Coordination

Some of the critical aspects of the design Some of the critical aspects of the design process which require coordination are:process which require coordination are:

Preliminary and Final Selection of Pile TypePreliminary and Final Selection of Pile Type Preliminary Evaluation of Geotechnical Data Preliminary Evaluation of Geotechnical Data

and Subsurface Conditionsand Subsurface Conditions Selection of Loading Conditions, Loading Selection of Loading Conditions, Loading

Effects, Potential Failure Mechanisms for Effects, Potential Failure Mechanisms for Analytical Model.Analytical Model.

Minimum Pile SpacingMinimum Pile Spacing Lateral Resistance of SoilLateral Resistance of Soil Required Pile Length and Axial CapacityRequired Pile Length and Axial Capacity Drivability of the Pile to the Selected Drivability of the Pile to the Selected

CapacityCapacity

Page 7: General & geotechnical considerations for pile design

DESIGN CONSIDERATIONSDESIGN CONSIDERATIONS

The pile foundation analysis is based The pile foundation analysis is based upon several simplifying assumptions upon several simplifying assumptions which affect the accuracy of the which affect the accuracy of the results. The computed results must results. The computed results must always be reviewed with Engineeringalways be reviewed with Engineering JudgementJudgement by the design engineer to by the design engineer to assure that the values are reasonable. assure that the values are reasonable. Also, the analysis results should be Also, the analysis results should be compared with load test results.compared with load test results.

Page 8: General & geotechnical considerations for pile design

Functional Significance of Functional Significance of StructureStructure

The type, purpose, and function of the The type, purpose, and function of the structure affect decisions regarding;structure affect decisions regarding;

Subsurface Investigation ProgramsSubsurface Investigation Programs Analytical MethodsAnalytical Methods Construction Procedures and InspectionConstruction Procedures and Inspection Performance MonitoringPerformance Monitoring

Generally, the proposed structure should Generally, the proposed structure should be evaluated on the basis of the be evaluated on the basis of the consequences of failure, that is, the consequences of failure, that is, the potential for loss of lives and property, potential for loss of lives and property, economic losses both local and national, economic losses both local and national, compromising the national defense, and compromising the national defense, and adverse public opinion. adverse public opinion.

Page 9: General & geotechnical considerations for pile design

Definitions of FailureDefinitions of FailureStructure or foundation failures can be Structure or foundation failures can be categorized as:categorized as: Functional FailureFunctional Failure Actual CollapseActual CollapseFunctional failure can be due to Functional failure can be due to

Excessive DeflectionExcessive Deflection Unacceptable Differential MovementsUnacceptable Differential Movements Excessive VibrationExcessive Vibration Premature Deterioration due to Environmental Premature Deterioration due to Environmental

FactorsFactorsFor critical structures, failure to meet functional For critical structures, failure to meet functional requirements may be as serious as the actual requirements may be as serious as the actual collapse of a lesser structure. The designers collapse of a lesser structure. The designers should be aware of the degree of safety against should be aware of the degree of safety against collapse but also of effects of settlement and collapse but also of effects of settlement and vibration on the functional performance.vibration on the functional performance.

Page 10: General & geotechnical considerations for pile design

Factors of SafetyFactors of SafetyIn order to reduce the potential for failure and In order to reduce the potential for failure and to minimize the cost, the designer must apply to minimize the cost, the designer must apply appropriate FOS to the design. These FOS are appropriate FOS to the design. These FOS are based on;based on;

Functional Significance of the StructureFunctional Significance of the Structure Level of Confidence in the Foundation Level of Confidence in the Foundation

ParametersParameters Adequacy of the Analysis ToolsAdequacy of the Analysis Tools Level of Construction ControlsLevel of Construction Controls

Uncertain design parameters and loads, require Uncertain design parameters and loads, require a higher FOS.a higher FOS.For less significant structures, it is permissible For less significant structures, it is permissible to use larger FOS if it is not economical to to use larger FOS if it is not economical to reduce the uncertainty in the analysis and reduce the uncertainty in the analysis and design by performing additional studies, testing design by performing additional studies, testing etc.etc.

Page 11: General & geotechnical considerations for pile design

Soil-Structure Considerations for Soil-Structure Considerations for AnalysisAnalysis

Foundation Testing Program should clearly Foundation Testing Program should clearly define soil types and profiles, soil strengths etc.define soil types and profiles, soil strengths etc.

A well-planned and monitored Pile Load Test A well-planned and monitored Pile Load Test Program will allow the designer to utilize a Program will allow the designer to utilize a lower FOS or by modifying the required number lower FOS or by modifying the required number or length of piles required.or length of piles required.

Depending upon the type of foundation Depending upon the type of foundation material, the nature of the loading, the location material, the nature of the loading, the location of the ground water, and the functional of the ground water, and the functional requirements of the structure, a Detailed requirements of the structure, a Detailed Seepage Analysis and/or Pile Settlement Seepage Analysis and/or Pile Settlement Analysis may also be required to define Analysis may also be required to define adequately the PILE-SOIL LOAD TRANSFER adequately the PILE-SOIL LOAD TRANSFER MECHANISMMECHANISM and the resulting parameters and the resulting parameters necessary for an adequate pile design.necessary for an adequate pile design.

Page 12: General & geotechnical considerations for pile design

Construction & Service Construction & Service ConsiderationsConsiderations

The designer prepares the specifications and instructions The designer prepares the specifications and instructions for field personnel to assure the proper execution of the for field personnel to assure the proper execution of the design.design.

For critical structures a representative of the design For critical structures a representative of the design office should be present in the field on a continuous basis.office should be present in the field on a continuous basis.

Designers should make frequent visits to the construction Designers should make frequent visits to the construction site not only to ensure that the design objective is being site not only to ensure that the design objective is being fulfilled but also to familiarize themselves with fulfilled but also to familiarize themselves with construction procedures and problems to improve on construction procedures and problems to improve on future designs.future designs.

Once the project is in operation, the designer should Once the project is in operation, the designer should obtain feedback on how well the structure is fulfilling its obtain feedback on how well the structure is fulfilling its operational purposes. This may require that operational purposes. This may require that instrumentation or may be from operating personnel and instrumentation or may be from operating personnel and periodic inspections.periodic inspections.

Page 13: General & geotechnical considerations for pile design

NATURE OF LOADINGSNATURE OF LOADINGS

Usual Loading:Usual Loading: Usual loads refer to conditions which are Usual loads refer to conditions which are

related to the primary function of a related to the primary function of a structure and can be reasonably expected structure and can be reasonably expected to occur during the economic service life.to occur during the economic service life.

The loading effects may be of either a The loading effects may be of either a long term, constant or an intermittent, long term, constant or an intermittent, repetitive nature.repetitive nature.

Pile allowable loads and stresses should Pile allowable loads and stresses should include a conservative safety factor for include a conservative safety factor for such conditions.such conditions.

Page 14: General & geotechnical considerations for pile design

Unusual Loading:Unusual Loading: Unusual loads refer to construction, Unusual loads refer to construction,

operation or maintenance conditions operation or maintenance conditions which are of relatively short which are of relatively short duration or infrequent occur rence.duration or infrequent occur rence.

Only minor cosmetic damage to the Only minor cosmetic damage to the structure may occur during these structure may occur during these conditions. Lower factors of safety conditions. Lower factors of safety may be used for such loadings.may be used for such loadings.

A less efficient pile layout is A less efficient pile layout is acceptable for these conditions.acceptable for these conditions.

Page 15: General & geotechnical considerations for pile design

Extreme Loading:Extreme Loading: Extreme loads refer to events which Extreme loads refer to events which

are highly improbable and cause are highly improbable and cause significant structural damage which significant structural damage which requires major rehabilitation or requires major rehabilitation or replacement of the structure.replacement of the structure.

Designing for pile ductility in high Designing for pile ductility in high risk seismic regions is very important risk seismic regions is very important because it is very difficult to assess because it is very difficult to assess pile damage after earthquakes and pile damage after earthquakes and the potential repair costs are very the potential repair costs are very large.large.

Page 16: General & geotechnical considerations for pile design

FOUNDATION MATERIALFOUNDATION MATERIALData Collection:Data Collection:The designer should make a site visit to examine;The designer should make a site visit to examine;

Topography at the SiteTopography at the Site An Examination of Existing Structures in the An Examination of Existing Structures in the

Vicinity.Vicinity. A Visit to the Local Building Department may A Visit to the Local Building Department may

provide Foundation Information and Boring Logs provide Foundation Information and Boring Logs for nearby Buildings.for nearby Buildings.

Valuable Soil and Geological Information can be Valuable Soil and Geological Information can be obtained from other Governmental Agencies.obtained from other Governmental Agencies.

Colleagues may be able to provide information on Colleagues may be able to provide information on projects they have worked on in the area. Check projects they have worked on in the area. Check the files for previous jobs your office might have the files for previous jobs your office might have built or explored in the area.built or explored in the area.

Page 17: General & geotechnical considerations for pile design

Exploration RequirementsExploration RequirementsThe designer must lay out an The designer must lay out an exploration and testing program that exploration and testing program that will identify;will identify;

Various Material Zones and their Various Material Zones and their PropertiesProperties

Groundwater TableGroundwater Table Water QualityWater Quality Existing AquifersExisting Aquifers Information relating to FaultsInformation relating to Faults

Page 18: General & geotechnical considerations for pile design

IDENTIFICATION & IDENTIFICATION & EVALUATION OF PILE EVALUATION OF PILE

ALTERNATIVESALTERNATIVESAfter obtaining a general evaluation of the After obtaining a general evaluation of the subsurface conditions the engineer should subsurface conditions the engineer should attempt to identify all potential useful attempt to identify all potential useful foundation alternatives for a structure.foundation alternatives for a structure.Three basic types of foundations are Three basic types of foundations are available: soil-founded, various types of available: soil-founded, various types of piles, and piers or caissons.piles, and piers or caissons.Types of Piles:Types of Piles:

Steel H-PilesSteel H-Piles Steel Pipe PilesSteel Pipe Piles Precast ConcretePrecast Concrete Cast-in-Place ConcreteCast-in-Place Concrete TimberTimber

Page 19: General & geotechnical considerations for pile design
Page 20: General & geotechnical considerations for pile design

Evaluation of Pile TypesEvaluation of Pile TypesLoad Capacity and Pile SpacingLoad Capacity and Pile Spacing

For capacity of a pile foundation, consider the pile For capacity of a pile foundation, consider the pile spacing along with the capacity of individual piles.spacing along with the capacity of individual piles.

The lateral load resistance of the piles is also The lateral load resistance of the piles is also important since lateral loads can induce high important since lateral loads can induce high bending stresses.bending stresses.

ConstructabilityConstructability Piles susceptible to damage during hard driving Piles susceptible to damage during hard driving

are less likely to penetrate hard strata or gravel are less likely to penetrate hard strata or gravel and boulder zones.and boulder zones.

Soil disturbance or vibrations during construction Soil disturbance or vibrations during construction may damage adjacent piles or structures.may damage adjacent piles or structures.

The ease of cutting or splicing a pile may also The ease of cutting or splicing a pile may also affect constructability.affect constructability.

Page 21: General & geotechnical considerations for pile design

PerformancePerformance The pile foundation must perform as The pile foundation must perform as

designed for the life of the structure.designed for the life of the structure. Structural displacements should not Structural displacements should not

cause actual pile failure.cause actual pile failure. The load capacity should not degrade The load capacity should not degrade

over time due to deterioration of the over time due to deterioration of the pile material.pile material.

AvailabilityAvailability Piles must be available in the lengths Piles must be available in the lengths

required, or they must be spliced or required, or they must be spliced or cut off.cut off.

Page 22: General & geotechnical considerations for pile design

CostCost For comparisons between types of piles, For comparisons between types of piles,

calculate the Pile Cost per Load Capacity. calculate the Pile Cost per Load Capacity. It will lead to an obvious exclusion of It will lead to an obvious exclusion of certain pile typescertain pile types

The cost evaluation should include all The cost evaluation should include all expenses related to pile foundation like;expenses related to pile foundation like;

Additional Expense for Storage or Additional Expense for Storage or SplicingSplicing

Pressure-Relief Systems used to reduce Pressure-Relief Systems used to reduce Uplift Pressures and thus control Pile Uplift Pressures and thus control Pile LoadsLoads

Any Required Modifications to the Any Required Modifications to the Structure to Accommodate the PilesStructure to Accommodate the Piles

Page 23: General & geotechnical considerations for pile design

Preliminary EvaluationsPreliminary Evaluations

All identified foundation alternatives All identified foundation alternatives should first be evaluated for;should first be evaluated for;

Suitability for the Intended ApplicationSuitability for the Intended Application EconomyEconomy CapacityCapacity AvailabilityAvailability ConstructabilityConstructability Expected PerformanceExpected Performance

This will limit further studies to those This will limit further studies to those foundation alternatives which are foundation alternatives which are reasonably feasible.reasonably feasible.

Page 24: General & geotechnical considerations for pile design

Final EvaluationsFinal Evaluations

Final evaluation should include;Final evaluation should include; Costs of Structural or Site Modifications Costs of Structural or Site Modifications

Required to Accommodate Foundation Required to Accommodate Foundation TypeType

CostCost Differences in Delivery or Installation Differences in Delivery or Installation

SchedulesSchedules Levels of Reliability of PerformanceLevels of Reliability of Performance Potential Construction ComplicationsPotential Construction Complications

Page 25: General & geotechnical considerations for pile design

SUBSURFACE SUBSURFACE INVESTIGATIONS AND INVESTIGATIONS AND GEOLOGYGEOLOGY

The investigation program should cover the The investigation program should cover the area of the foundation and, as a very area of the foundation and, as a very minimum, extend 20 feet below the tip of minimum, extend 20 feet below the tip of the longest pile anticipated to identify any the longest pile anticipated to identify any soft, settlement-prone layerssoft, settlement-prone layers

The type of soil-boring will be determined by The type of soil-boring will be determined by the type of soil profile that existsthe type of soil profile that exists

In a clay layer, sufficient undisturbed In a clay layer, sufficient undisturbed samples should be obtained to determinesamples should be obtained to determine Shear StrengthShear Strength Consolidation CharacteristicsConsolidation Characteristics Sensitivity of the ClaySensitivity of the Clay Shrink-Swell CharacteristicsShrink-Swell Characteristics In-situ Soil Confining PressureIn-situ Soil Confining Pressure

Page 26: General & geotechnical considerations for pile design

Where gravels or cobbles are expected, some Where gravels or cobbles are expected, some large diameter soil borings should be made large diameter soil borings should be made in order to collect representative samples to in order to collect representative samples to determine their properties.determine their properties.

An accurate location of the soil borings An accurate location of the soil borings should be made in the field and a map should be made in the field and a map provided in the designprovided in the design

An engineering geologist should be present An engineering geologist should be present during the drilling operation to provide field during the drilling operation to provide field interpretation.interpretation.

Geologic interpretations should be provided Geologic interpretations should be provided in the design documents in the form of in the design documents in the form of geologic maps and/or profiles. The profiles geologic maps and/or profiles. The profiles should extend from the ground surface to should extend from the ground surface to well below the deepest foundation element. well below the deepest foundation element. The accompanying text and/or maps should The accompanying text and/or maps should fully explain the stratigraphy of the subgrade fully explain the stratigraphy of the subgrade as well as its engineering geology as well as its engineering geology characteristics.characteristics.

Page 27: General & geotechnical considerations for pile design

LABORATORY AND FIELD LABORATORY AND FIELD TESTINGTESTINGLaboratory DeterminationsLaboratory Determinations of the shear of the shear strength and consolidation properties of the clay strength and consolidation properties of the clay should be performed.should be performed. For the construction case in clay, UU triaxial For the construction case in clay, UU triaxial

shear (Q) test should be performed.shear (Q) test should be performed. In silts, CU triaxial shear (R) test, with pore In silts, CU triaxial shear (R) test, with pore

pressure recorded, should be performed In pressure recorded, should be performed In sands if samples can be collected, CD triaxial sands if samples can be collected, CD triaxial shear test or direct shear test (S) should be shear test or direct shear test (S) should be used to predict the shear strength.used to predict the shear strength.

The sensitivity of these soils should be The sensitivity of these soils should be estimated and the appropriate remolded triaxial estimated and the appropriate remolded triaxial shear test performedshear test performed

Shrink-swell tests is performed, if appropriateShrink-swell tests is performed, if appropriate Consolidation tests should be performed Consolidation tests should be performed

throughout the profile so that settlement of the throughout the profile so that settlement of the structure may be estimated.structure may be estimated.

Page 28: General & geotechnical considerations for pile design

Field TestingField Testing should include; should include;In-situ Ground-water EvaluationIn-situ Ground-water EvaluationStandard Penetration TestStandard Penetration TestElectronic Cone Penetration TestElectronic Cone Penetration TestVane ShearVane ShearPressure MeterPressure Meter

Geophysical TechniquesGeophysical Techniques of logging of logging the soil boring, electric logging, the soil boring, electric logging, should be employed wherever should be employed wherever possible if highly stratified soils are possible if highly stratified soils are encountered or expected or if faults encountered or expected or if faults need to be located.need to be located.

Page 29: General & geotechnical considerations for pile design

FOUNDATION MODIFICATIONFOUNDATION MODIFICATION Installation of piles will densify loose, Installation of piles will densify loose,

granular materials and may loosen dense, granular materials and may loosen dense, granular materials. This should be taken granular materials. This should be taken into consideration by the designer.into consideration by the designer.

For homogeneous stratifications, the best For homogeneous stratifications, the best pile foundations would tend theoretically pile foundations would tend theoretically toward longer piles at a larger spacingtoward longer piles at a larger spacing

In silty subgrades, the foundations may In silty subgrades, the foundations may dilate and lose strength which will not be dilate and lose strength which will not be regained.regained.

Piles can be used to modify foundation Piles can be used to modify foundation soils by densificationsoils by densification

In soft clay soils piles could be used to In soft clay soils piles could be used to achieve some slight gain in shear strengthachieve some slight gain in shear strength

Page 30: General & geotechnical considerations for pile design

GROUNDWATER STUDIESGROUNDWATER STUDIES The groundwater should be evaluated in each of The groundwater should be evaluated in each of

the soil borings during the field investigation.the soil borings during the field investigation. Piezometers and/or monitoring wells should be Piezometers and/or monitoring wells should be

installed and monitored during the various installed and monitored during the various weather cycles.weather cycles.

A determination should be made of all of the A determination should be made of all of the groundwater environments beneath the groundwater environments beneath the structure, i.e. perched water tables, artesian structure, i.e. perched water tables, artesian conditions and deep aquifers, excess pore water conditions and deep aquifers, excess pore water pressurepressure

For the design of pile foundations the highest For the design of pile foundations the highest groundwater table elevation should prove to be groundwater table elevation should prove to be the worst case for analysis of pile capacity. the worst case for analysis of pile capacity. However, significant lowering of the water table However, significant lowering of the water table during construction may cause installation and during construction may cause installation and later service problems by inducing densification later service problems by inducing densification or consolidation.or consolidation.

Page 31: General & geotechnical considerations for pile design

DYNAMIC DYNAMIC CONSIDERATIONSCONSIDERATIONS Liquefaction is most commonly induced by Liquefaction is most commonly induced by

seismic loading and rarely by vibrations seismic loading and rarely by vibrations due to pile driving during construction or due to pile driving during construction or from vibrations occurring during from vibrations occurring during operations.operations.

If soils in the foundation or surrounding If soils in the foundation or surrounding area are subject to liquefaction, the area are subject to liquefaction, the removal or densification of the liquefiable removal or densification of the liquefiable material should be considered, along with material should be considered, along with alternative foundation designs.alternative foundation designs.

The first few natural frequencies of the The first few natural frequencies of the structure-foundation system should be structure-foundation system should be evaluated and compared to the operating evaluated and compared to the operating frequencies to assure that resonance (not frequencies to assure that resonance (not associated with liquefaction) is not associated with liquefaction) is not induced.induced.

Page 32: General & geotechnical considerations for pile design

SUBSURFACE SUBSURFACE CONDITIONSCONDITIONS Skin Friction and End Bearing are Skin Friction and End Bearing are

dependent on the subsurface conditions dependent on the subsurface conditions and soil type.and soil type.

In soil deposits that contain layers of In soil deposits that contain layers of varying stiffness, the ultimate axial pile varying stiffness, the ultimate axial pile capacity cannot be equal to the sum of the capacity cannot be equal to the sum of the peak strength of all the materials in peak strength of all the materials in contact with the pile because the peak contact with the pile because the peak strengths are not reached simultaneously. strengths are not reached simultaneously. Failure is likely to be progressive.Failure is likely to be progressive.

The existence of boulders or cobbles The existence of boulders or cobbles within foundation layers can present within foundation layers can present driving problems and hinder determination driving problems and hinder determination of ultimate axial capacity of a single pile.of ultimate axial capacity of a single pile.

Page 33: General & geotechnical considerations for pile design

PILE LOAD TESTPILE LOAD TEST The pile load test is intended to validate the The pile load test is intended to validate the

computed capacity and to provide computed capacity and to provide information for the improvement of design. information for the improvement of design. Therefore, a test to soil/ pile failure should be Therefore, a test to soil/ pile failure should be conducted in lieu of testing to a specified conducted in lieu of testing to a specified load of termination.load of termination.

Data from a test should not be used to Data from a test should not be used to lengthen or shorten piles to an extent that lengthen or shorten piles to an extent that their new capacities vary more than 10% their new capacities vary more than 10% from the test load.from the test load.

Shortening the service piles may place the Shortening the service piles may place the tips above a firm bearing stratum into a soft tips above a firm bearing stratum into a soft clay layer. Then Consolidation and loss in BC clay layer. Then Consolidation and loss in BC may occur.may occur.

Extending tips deeper into a firmer bearing Extending tips deeper into a firmer bearing may cause driving problems.may cause driving problems.

At the end of test, the test piles should be At the end of test, the test piles should be extracted and inspectedextracted and inspected

Page 34: General & geotechnical considerations for pile design

Greater reliance can be placed upon future Greater reliance can be placed upon future results when using the analyzer for verifying results when using the analyzer for verifying the driving system efficiency, capacity, and the driving system efficiency, capacity, and pile integrity for production piles.pile integrity for production piles.

A pile loading test is necessary if a sufficient A pile loading test is necessary if a sufficient number of piles are to be driven or a reduced number of piles are to be driven or a reduced FOS will result in a sufficient shortening of the FOS will result in a sufficient shortening of the piles to improve economy.piles to improve economy.

In highly stratified soils where some pile-tip In highly stratified soils where some pile-tip capacity is used in design computations, care capacity is used in design computations, care should be taken to keep at least 5 feet or 8 pile should be taken to keep at least 5 feet or 8 pile tip diameters of embedment into the bearing tip diameters of embedment into the bearing stratum.stratum.

The jack and reference beam should be in the The jack and reference beam should be in the same plane with the axis of the test pile since same plane with the axis of the test pile since deviations will result in erroneous pile load deviations will result in erroneous pile load tests.tests.Cautions. A poorly performed pile load test Cautions. A poorly performed pile load test may be worse than having no test at all.may be worse than having no test at all.

Page 35: General & geotechnical considerations for pile design

SELECTION OF SHEAR SELECTION OF SHEAR STRENGTH PARAMETERSSTRENGTH PARAMETERSThe two allowable pile capacities obtained for The two allowable pile capacities obtained for undrained and drained soil conditions should be undrained and drained soil conditions should be compared and the lower of the two cases selected for compared and the lower of the two cases selected for use for any tip penetration.use for any tip penetration.

In cases where the S case governs, then the classic In cases where the S case governs, then the classic slow pile test should be selected.slow pile test should be selected.

The designer should also consider using 24-hour load The designer should also consider using 24-hour load holding periods at 100, 200, and 300 percent of holding periods at 100, 200, and 300 percent of design load especially when foundation soils are design load especially when foundation soils are known to exhibit a tendency to creep.known to exhibit a tendency to creep.

When the design is verified by pile load test, the pile When the design is verified by pile load test, the pile load test will take precedence in the selection of load test will take precedence in the selection of ultimate pile capacity and pile tip over the predicted ultimate pile capacity and pile tip over the predicted theoretical value in most cases.theoretical value in most cases.

Page 36: General & geotechnical considerations for pile design

FIELD RESPONSIBILITIES FIELD RESPONSIBILITIES FOR DESIGN ENGINEERFOR DESIGN ENGINEER

Loading TestLoading Test On all major structures with significant On all major structures with significant

foundation costs, pile load tests are required foundation costs, pile load tests are required while minor structures may not required.while minor structures may not required.

Load tests of piles should be performed to Load tests of piles should be performed to finalize pile lengths and to provide finalize pile lengths and to provide information for improving design procedures.information for improving design procedures.Field VisitsField Visits

Field visits should be made to view critical Field visits should be made to view critical construction phases and to discuss progress construction phases and to discuss progress and potential changes in procedures with the and potential changes in procedures with the construction representative.construction representative.

Critical items include monitoring and Critical items include monitoring and maintaining detailed records of driving maintaining detailed records of driving operations, especially:operations, especially:

Page 37: General & geotechnical considerations for pile design

Driving reports for individual pilesDriving reports for individual piles - Date - Date and times, placement position and alignment; and times, placement position and alignment; blow counts, difficulties and interruptions blow counts, difficulties and interruptions during driving; installation and location of any during driving; installation and location of any pile splices.pile splices.

General driving dataGeneral driving data - Complete descriptions - Complete descriptions of driving equipment, adjustments and of driving equipment, adjustments and changes (leads, hammer, anvil, cap, cushions changes (leads, hammer, anvil, cap, cushions etc.); pile storage and handling procedures; etc.); pile storage and handling procedures; pile interference; pile heave.pile interference; pile heave.

Driving restrictionsDriving restrictions - existing structures in - existing structures in vicinity; driving near new concrete; limiting vicinity; driving near new concrete; limiting water elevation.water elevation.

Instructions to the FieldInstructions to the Field

Instructions Report to the field should Instructions Report to the field should include the following information;include the following information;

Page 38: General & geotechnical considerations for pile design

Present the design concepts, special Present the design concepts, special details and assumptions made details and assumptions made regarding interpretation of subsurface regarding interpretation of subsurface investigation data and field conditions.investigation data and field conditions.

The concepts, assumptions, and special The concepts, assumptions, and special details of the design.details of the design.

Assistance to field personnel in Assistance to field personnel in interpreting the plans and interpreting the plans and specifications.specifications.

Information to make field personnel Information to make field personnel aware of critical areas in the design aware of critical areas in the design which require additional control and which require additional control and inspection.inspection.

Provide guidance for use of pile driving Provide guidance for use of pile driving analyzer to monitor driving operations.analyzer to monitor driving operations.

Page 39: General & geotechnical considerations for pile design

PILE INSTRUMENTATIONPILE INSTRUMENTATION Pile instrumentation have three categories:Pile instrumentation have three categories:

Instrumentation used during Pile Load Tests to Instrumentation used during Pile Load Tests to obtain Design Dataobtain Design Data

Pile Driving Analyzer used to control Quality of Pile Driving Analyzer used to control Quality of Pile InstallationPile Installation

Permanent Instrumentation used to gather Permanent Instrumentation used to gather Information during the Service LifeInformation during the Service Life

The designer should select instrumentation The designer should select instrumentation that has sufficient accuracy to measure the that has sufficient accuracy to measure the required data.required data.

Permanent instrumentation is used to Permanent instrumentation is used to gather data relating to the state of stress gather data relating to the state of stress and behavior of the pile under service load and behavior of the pile under service load conditions, the behavior of a particular pile conditions, the behavior of a particular pile foundation and about analysis and design foundation and about analysis and design assumptions in general.assumptions in general.

Page 40: General & geotechnical considerations for pile design

THANKS FORTHANKS FOR

YOURYOUR

ATTENTION!ATTENTION!