2nd lecture ,lecture on site investigation for handout...

Dr. Hussein M. Al.Khuzaie; hma@mu.edu.iq 1

FoundationEngineering,2018-2019

Dr.HusseinM.AshourAl.KhuzaieProfessor,CivilEngineering,CollegeofEngineering,Al-MuthannaUniversity

Syllabus of Foundation DesignSite Investigation, Bearing capacity of Soil, Settlement,

Foundation Design, Piles, Lateral Earth Pressure, slope Stability.

SITEINVESTIGATION

2Dr. Hussein M. Al.Khuzaie; hma@mu.edu.iq

Definition

Theprocessofdeterminingthelayersofnaturalsoildepositsthatwillunderlieaproposedstructureandtheirphysicalpropertiesisgenerallyreferredtoassiteinvestigation.

SITEINVESTIGATION

Thepurposeofasoilinvestigationprogram

1. Selectionofthetypeandthedepthoffoundationsuitableforagivenstructure.

2. Evaluationoftheload-bearingcapacityofthefoundation.3. Estimationoftheprobablesettlementofastructure.4. Determinationofpotentialfoundationproblems(for

example,expansivesoil,collapsiblesoil,sanitarylandfill,andsoon).

5. Establishmentofgroundwatertable.6. Predictionoflateralearthpressureforstructureslike

retainingwalls,sheetpilebulkheads,andbracedcuts.7. Establishmentofconstructionmethodsforchanging

subsoilconditions.

EXPLORATIONPROGRAM

Thepurposeoftheexplorationprogramistodetermine,withinpracticallimits,thestratificationandengineeringpropertiesofthesoilsunderlyingthesite.Theprincipalpropertiesofinterestwillbethestrength,deformation,andhydrauliccharacteristics.Theprogramshouldbeplannedsothatthemaximumamountofinformationcanbeobtainedatminimumcost.

Stepsofsubsurfaceexplorationprogram[Stage1]

1. Assemblyofallavailableinformationondimensions,columnspacing,typeanduseofthestructure,basementrequirements,andanyspecialarchitecturalconsiderationsoftheproposedbuilding.Foundationregulationsinthelocalbuildingcodeshouldbeconsultedforanyspecialrequirements.Forbridgesthesoilengineershouldhaveaccesstotypeandspanlengthsaswellaspierloadings.Thisinformationwillindicateanysettlementlimitations,andcanbeusedtoestimatefoundationloads.

2.Reconnaissanceofthearea:Thismaybeintheformofafieldtriptothesitewhichcanrevealinformationonthetypeandbehaviorofadjacentstructuressuchascracks,noticeablesags,andpossiblystickingdoorsandwindows.Thetypeoflocalexistingstructuremayinfluence,toaconsiderableextent,theexplorationprogramandthebestfoundationtypefortheproposedadjacentstructure.

3.Apreliminarysiteinvestigation:Inthisphaseafewboringsaremadeoratestpitisopenedtoestablishinageneralmannerthestratification,typesofsoiltobeexpected,andpossiblythelocationofthegroundwatertable.Oneormoreboringsshouldbetakentorock,orcompetentstrata,iftheinitialboringsindicatetheuppersoilislooseorhighlycompressible.Thisamountofexplorationisusuallytheextentofthesiteinvestigationforsmallstructures.

4.Adetailedsiteinvestigation:Wherethepreliminarysiteinvestigationhasestablishedthefeasibilityoftheproject,amoredetailedexplorationprogramisundertaken.Thepreliminaryboringsanddataareusedasabasisforlocatingadditionalborings,whichshouldbeconfirmatoryinnature,anddeterminingtheadditionalsamplesrequired.

DepthofBoring

Theapproximaterequiredminimumdepthoftheboringsshouldbepredetermined.Theestimateddepthscanbechangedduringthedrillingoperation,dependingonthesubsoilencountered.Todeterminetheapproximateminimumdepthofboring,engineersmayusethefollowingrule:

DepthofBoring1. Determinethenetincreaseofstress,Ds underafoundation

withdepthasshownintheFigure.2. Estimatethevariationoftheverticaleffectivestress,s'u,with

depth.3. Determinethedepth,D=D1,atwhichthestressincreaseDs

isequalto(1/10)q(q=estimatednetstressonthefoundation).

4. Determinethedepth,D=D2,atwhichDs/s'u =0.05.5. Unlessbedrockisencountered,thesmallerofthetwodepths,

D1 andD2,justdeterminedistheapproximateminimumdepthofboringrequired.Tableshowstheminimumdepthsofboringsforbuildingsbasedontheprecedingrule.

DepthofBoring

Determination of the minimum depth of boring

Dr. Hussein M. Al.Khuzaie; hma@mu.edu.iq

Effective overburden pressure

DepthofBoring

Depth of Boring

DepthofBoringForhospitalsandofficebuildings,thefollowingrulecouldbeusedtodetermineboringdepth

Db = 3S0.7 (for light steel or narrow concrete buildings)

Db = 6S0.7 (for heavy steel or wide concrete buildings)

where:Db = depth of boring, in metersS= number of stories

DepthofBoring

Whendeepexcavationsareanticipated,thedepthofboringshouldbeat,least1.5timesthedepthofexcavation.Sometimessubsoilconditionsaresuchthatthefoundationloadmayhavetobetransmittedtothebedrock.Theminimumdepthofcoreboringintothebedrockisabout3m.Ifthebedrockisirregularorweathered,thecoreboringsmayhavetobeextendedtogreaterdepths.

SpacingofBoring

Therearenohardandfastrulesforthespacingoftheboreholes.Thefollowingtablegivessomegeneralguidelinesforboreholespacing.Thesespacingcanbeincreasedordecreased,dependingonthesubsoilcondition.Ifvarioussoilstrataaremoreorlessuniformandpredictable,thenumberofboreholescanbereduced.

SpacingofBoring

Approximate Spacing of Boreholes

Type of Project Spacing (m)Multistory Building 10-30

One story Industrial Plants 20-60Highways 250-500

Residential Subdivision 250-500Dams and Dikes 40-80

Example:

For a 4-story residential building of plan area 270 m2 with pressure is equal to 150 kPa at the level of the foundation base (q) that transferred from the superstructure. The expected unit weight of the soil under the foundation is 15.5 kN/m3 Calculate the approximate depth of boring and the required boreholes number for reporting the soil investigation program thoroughly.

SOILBORING

Theearliestmethodofobtainingatestholewastoexcavateatestpitusingapickandshovel.Becauseofeconomics,thecurrentprocedureistousepower-excavationequipmentsuchasabackhoetoexcavatethepitandthentousehandtoolstoremoveablocksampleorshapethesiteforinsitutesting.Thisisthebestmethodatpresentforobtainingqualityundisturbedsamplesorsamplesfortestingatotherthanverticalorientation.

SOILBORING

Boringtools

Auger boring Power drills

Boringtools

Wash boring rig

Rotary Drilling rig

Boringtools

PreparationofBoringLogs1.Nameandaddressofthedrillingcompany2.Driller’sname3.Jobdescriptionandnumber4.Number,type,andlocationofboring5.Dateofboring6.Subsurfacestratification,whichcanheobtainedbyvisual

observationofthesoilbroughtoutbyauger,split-spoonsampler,andthin-walledShelbytubesampler

7.Elevationofwatertableanddateobserved,useofcasingandmudlosses,andsoon

8.StandardpenetrationresistanceandthedepthofSPT9.Number,type,anddepthofsoilsamplecollected10.Incaseofrockcoring,typeofcorebarrelusedand,foreach

run,theactuallengthofcoring,lengthofcorerecovery,andROD

Boring Logs

Examplesheet

SOILSAMPLINGTwotypesofsoilsamples canbeobtainedduringsamplingdisturbed and undisturbed.Themostimportantengineeringpropertiesrequiredforfoundationdesignarestrength,compressibility,andpermeability.Reasonablygoodestimatesofthesepropertiesforcohesive soilscanbemadebylaboratorytestson undisturbed sampleswhichcanbeobtainedwithmoderatedifficulty.Itisnearlyimpossibletoobtainatrulyundisturbedsampleofsoil;soingeneralusagetheterm"undisturbed"meansasamplewheresomeprecautionshavebeentakentominimizedisturbanceorremoldingeffects.Inthiscontext,thequalityofan"undisturbed"samplevarieswidelybetweensoillaboratories.

SoilsInvestigation

Disturbed vsUndisturbed

(%) 100..

DIDOAR

Good quality samples necessary.

AR<10%

sampling tube

area ratio

Thicker the wall, greater the disturbance.Dr. Hussein M. Al.Khuzaie; hma@mu.edu.iq

Disturbed vsUndisturbed

CommonSamplingMethods

ROCKSAMPLING

• Rockcoresarenecessaryifthesoundnessoftherockistobeestablished.

• smallcorestendtobreakupinsidethedrillbarrel.

• Largercoresalsohaveatendencytobreakup(rotateinsidethebarrelanddegrade),especiallyiftherockissoftorfissured.

Rockcoring

ROCKSAMPLING- Definition

RockCoreDrilling

• Donewitheithertungstencarbideordiamondcorebits

• Useadoubleortripletubecorebarrelwhensamplingweatheredorfracturedrock

• UsedtodetermineRockQualityDesignation

41core barrelDr. Hussein M. Al.Khuzaie; hma@mu.edu.iq

RockQualityDesignation(RQD)

RockQualityDesignation

RQDRock Quality Designation (RQD) is defined as the percentage of rock cores that have length equal or greater than 10 cm over the total drill length.

ExampleonCoreRecovery&RQD

• Corerunof150cm• Totalcorerecovery=125cm

• Corerecoveryratio=125/150=83%

• Onmodifiedbasis,95cmarecountedRQD =95/150=63%

GROUNDWATERTABLELEVEL

Groundwaterconditionsandthepotentialforgroundwaterseepagearefundamentalfactorsinvirtuallyallgeotechnicalanalysesanddesignstudies.Accordingly,theevaluationofgroundwaterconditionsisabasicelementofalmostallgeotechnicalinvestigationprograms.Groundwaterinvestigationsareoftwotypesasfollows:

• Determinationofgroundwaterlevelsandpressures.• Measurementofthepermeabilityofthesubsurfacematerials.

FIELDSTRENGTHTESTSThefollowingarethemajorfieldtestsfordeterminingthesoilstrength:1. Vanesheartest(VST).2. StandardPenetrationTest(SPT).3. ConePenetrationTest(CPT).4. TheBoreholeShearTest(BST).5. TheFlatDilatometerTest(DMT).6. ThePressure-meterTest(PMT).7.ThePlateLoadTest(PLT).

FIELDSTRENGTHTESTS

StandardPenetrationTest(SPT)

CorrectionsarenormallyappliedtotheSPTblowcounttoaccountfordifferencesin:•energyimpartedduringthetest(60%hammerefficiency)

•thestresslevelatthetestdepthThefollowingequationisusedtocompensateforthetestingfactors(Skempton,1986):

Cone PenetrationTest(CPT)

ThePlateLoadTest(PLT)

ThePlateLoadTest(PLT)ScaleEffectinFoundationDesign

GeotechnicalDesignReports• Attheendofallsubsoilexplorationprograms,thesoiland/orrockspecimenscollectedfromthefieldaresubjectedtovisualobservationandappropriatelaboratorytesting.Afterthecompilationofalloftherequiredinformation,asoilexplorationreportispreparedfortheuseofthedesignofficeandforreferenceduringfutureconstructionwork.Althoughthedetailsandsequenceofinformationinthereportmayvarytosomedegreeisdependingonthestructureunderconsiderationandthepersoncompilingthereport.

SubsoilExplorationReport1.Adescriptionofthescopeoftheinvestigation2.Adescriptionoftheproposedstructureforwhichthesubsoil

explorationhasbeenconducted3.Adescriptionofthelocationofthesite,includinganystructures

nearby,drainageconditions,thenatureofvegetationonthesiteandsurroundingit,andanyotherfeaturesuniquetothesite

4.Adescriptionofthegeologicalsettingofthesite5.Detailsofthefieldexploration—thatis,numberofborings,depths

ofborings,typesofboringsinvolved,andsoon6.Ageneraldescriptionofthesubsoilconditions,asdeterminedfrom

soilspecimensandfromrelatedlaboratorytests,standardpenetrationresistanceandconepenetrationresistance,andsoon

7.Adescriptionofthewater-tableconditions8.Recommendationsregardingthefoundation,includingthetypeof

foundationrecommended,theallowablehearingpressure,andanyspecialconstructionprocedurethatmayheneeded;alternativefoundationdesignproceduresshouldalsobediscussedinthisportionofthereport

9.Conclusionsandlimitationsoftheinvestigations

SubsoilExplorationReport

Thefollowinggraphicalpresentationsshouldheattachedtothereport:

1.Asitelocationmap2.Aplanviewofthelocationoftheboringswithrespecttotheproposedstructuresandthosenearby

3.Boringlogs4.Laboratorytestresults5.Otherspecialgraphicalpresentations

Example: Table of Contents for a Geotechnical Investigation (Data) Report

1.Compare the advantages and disadvantages between in-situ tests and drilling and lab testing. 2.Provide your recommendation of drilling/sampling, in-situ testing procedures for each of the following purposes, and state your assumptions for your answer if necessary:

1. Determine the soil stratigraphy within the top 5 m, at 200 test locations along a proposed 20 km-long highway.

2. Determine the compressibility of an overconsolidated clay layer at 5–15 m below ground surface.

3. Determine the compressibility of a sand deposit at 5–15m below ground surface.

4. Determine the groundwater table distribution within a 300-acre project site.

5. Determine the type(s) and quality of rock from 50 to 100 m below ground surface.

3. Describe the possible procedures to determine the groundwater table in the field.

Questions for Review

Assignment

Write a report including the following field tests:1- Soil resistivity2- Dynamic test for a soil, as megaphone 3- Pressure meter4- Vane shear test5- Ground penetration radar

2nd lecture ,lecture on site investigation for handout...

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