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Soil ExplorationSoil Exploration

IntroductionIntroductionnn TheThe fieldfield andand laboratorylaboratory investigationsinvestigations requiredrequired toto

obtainobtain thethe necessarynecessary datadata forfor thethe soilssoils forfor properproperdesigndesign andand successfulsuccessful constructionconstruction ofof anyany structurestructureatat thethe sitesite areare collectivelycollectively calledcalled soilsoil explorationexploration..

nn TheThe choicechoice ofof thethe foundationfoundation andand itsits depth,depth, thethebearingbearing capacity,capacity, settlementsettlement analysisanalysis andand suchsuch otherotherimportantimportant aspectsaspects dependdepend veryvery muchmuch uponupon thethevariousvarious engineeringengineering propertiesproperties ofof thethe foundationfoundationsoilssoils involvedinvolved..

The primary objectives of soil exploration areThe primary objectives of soil exploration are

nn DeterminationDetermination ofof thethe naturenature ofof thethe depositsdeposits ofof soilsoil..nn DeterminationDetermination ofof thethe depthdepth andand thicknessthickness ofof thethe variousvarious

soilsoil stratastrata andand theirtheir extentextent inin thethe horizontalhorizontal directiondirection..nn TheThe locationlocation ofof groundground waterwater tabletable (GWT)(GWT)..nn ObtainingObtaining soilsoil andand rockrock samplessamples fromfrom thethe variousvarious stratastrata..nn TheThe determinationdetermination ofof thethe engineeringengineering propertiesproperties ofof thethe

soilsoil andand rockrock stratastrata thatthat affectaffect thethe performanceperformance ofof thethestructurestructure..

nn DeterminationDetermination ofof thethe inin--situsitu propertiesproperties byby performingperformingfieldfield teststests..

Soil data requiredSoil data required

vv Soil profileSoil profile

v Index properties

v Strength & compressibility characteristics

v Others (e.g., water table depth)

- layer thickness and soil identification

- water content, Atterberg limits (Liquid Limit,Plastic Limit, Shrinkage Limit) etc.

- c′, cu, φ′, Cc, OCR, …

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üü Aerial photographsAerial photographsüü Topographical mapsTopographical mapsüü Existing site investigation reports (for nearby sites)Existing site investigation reports (for nearby sites)üü Other information from local councils, literatureOther information from local councils, literature

First stage of site investigation. Negligible cost. Lookfor currently available information

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Site ReconnaissanceSite Reconnaissance

üü Site accessSite accessüü TopographyTopographyüü Site geologySite geologyüü Conditions of adjacent structuresConditions of adjacent structuresüü Any obvious problems foreseen?Any obvious problems foreseen?

A site visit and chat with locals.

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nn The methods available for soil exploration mayThe methods available for soil exploration maybe classified as followsbe classified as follows

nn Direct methods ... Test pits, trial pits or trenchesDirect methods ... Test pits, trial pits or trenchesnn SemiSemi--direct methods ... Boringsdirect methods ... Boringsnn Indirect methods ... Soundings or penetration testsIndirect methods ... Soundings or penetration tests

and geophysical methodsand geophysical methods

Test PitTest PitEnables visual inspection, locating strata boundaries, andaccess for undisturbed block samples.

URL: http://www.biblioresearch.com/images/Testpit.gif

Semi Direct MethodsSemi Direct Methods -- BoringBoring

nn BoringBoring:: MakingMaking oror drillingdrilling borebore holesholes intointo thethe groundgroundwithwith aa viewview toto obtainingobtaining soilsoil oror rockrock samplessamples fromfromspecifiedspecified oror knownknown depthsdepths isis calledcalled ‘‘boringboring’’

nn TheThe commoncommon methodsmethods ofof advancingadvancing borebore holesholes areare::nn Auger boringAuger boringnn Wash boringWash boringnn Rotary drillingRotary drillingnn Percussion drillingPercussion drilling

Auger boringAuger boring

Bowles, J.E, 1996

Wash BoringWash Boring

Bowles, J.E, 1996

Rotary DrillingRotary Drilling

Rotary DrillingURL:http://www.tpub.com/content/engine/14080/img/14080_204_1.jpg

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Percussion DrillingPercussion Drilling

Percussion DrillingURL:http://www.globalsecurity.org/military/library/policy/army/fm/5-484/Ch9.htm

Types of SamplesTypes of Samples

nn Samples of soil taken out of natural deposits for testingSamples of soil taken out of natural deposits for testingmay be classified as:may be classified as:DisturbedDisturbed samplesampleUndisturbedUndisturbed samplesample

nn AA disturbeddisturbed samplesample isis thatthat inin whichwhich thethe naturalnatural structurestructureofof thethe soilsoil getsgets modifiedmodified partlypartly oror fullyfully duringduring samplingsampling

nn AnAn undisturbedundisturbed samplesample isis thatthat inin whichwhich thethe naturalnaturalstructurestructure andand otherother physicalphysical propertiesproperties remainremainpreservedpreserved..

nn Disturbed but representative samples can generally beDisturbed but representative samples can generally beused forused for

vv GrainGrain--size analysissize analysisvv Determination of liquid and plastic limitsDetermination of liquid and plastic limitsvv Specific gravity of soil solidsSpecific gravity of soil solidsvv Organic content determinationOrganic content determinationvv Soil classificationSoil classification

qq Undisturbed samples must be used forUndisturbed samples must be used forvv Consolidation testConsolidation testvv Hydraulic conductivity testHydraulic conductivity testvv Shear strength testShear strength test

Split Spoon SamplerSplit Spoon Sampler

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URL; http://www4.ncsu.edu/~rcborden/Facilities/split_spoon_sampler.jpg

50.8 mm

Spring core catcher

Standard split-spoon sampler

Das, B. M. ,1999

In clay layers…

collect undisturbed claysamples in thin walledsampler(e.g. shelby tube)

Clay

bore hole Consolidation,triaxial tests in lab

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How many bore holes?How many bore holes?

The number of bore holes depends on:type and size of the project

soil variability

budget for site investigation

Locate the bore holes where the loads are expected.

proposed buildingSivakugan

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Spacing of BoringsSpacing of Borings

Type of project Spacing (m)

Multistory buildings 10 – 30One-story industrial plants 20 – 60Highways 250-500Residential subdivision 250-500Dams and dikes 40 - 80

Das, B. M. ,1999

nn The minimum depth of boring for a building with aThe minimum depth of boring for a building with awidth of 30.5 m (100 ft) will be as followswidth of 30.5 m (100 ft) will be as follows (Sowers and Sowers, 1970)(Sowers and Sowers, 1970)

No of storiesNo of stories Boring depthBoring depth11 3.5 m3.5 m22 6.0 m6.0 m33 10 m10 m44 16 m16 m55 24 m24 m

Standard Penetration TestStandard Penetration Test

URL: http://www.eng.fsu.edu/~tawfiq/geotech/spttoggle.jpg

StaticStatic Cone Penetration TestCone Penetration Test

10 cm2 cross section

cone resistance (qc) ortip resistance (qT)

sleeve friction (fs)

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× 100% c

cr q

fF,ratioFriction =

Pressuremeter TestPressuremeter TestExpand a cylindrical probe inside a borehole.Most rational of all in situ tests

cylindricalprobe guard

cell

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Dilatometer TestDilatometer Test

Advance @ 20 mm/s. Test every 200-300 mm.Nitrogen tank for inflating the membrane.

60 mm diameterflexible steelmembraneSivakugan

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Vane Shear TestVane Shear Test

bore hole

soft clay

measuring(torque) head

vane

vane

For clays, and mainly for soft clays.Measure torque required toquickly shear the vane pushedinto soft clay.

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Ground Water LevelGround Water Level

nn AA correctcorrect indicationindication ofof thethe generalgeneral groundground waterwaterlevellevel isis foundfound byby allowingallowing thethe waterwater inin thetheboringboring toto reachreach anan equilibriumequilibrium levellevel..

nn InIn sandysandy soils,soils, thethe levellevel getsgets stabilizedstabilized veryveryquicklyquickly -- withinwithin aa fewfew hourshours atat thethe mostmost..

nn InIn clayeyclayey soilssoils itit willwill taketake manymany daysdays forfor thisthispurposepurpose.. Hence,Hence, standpipesstandpipes oror piezometerspiezometers areareusedused inin claysclays andand siltsilt..

GPSGPSnn USUS DepartmentDepartment ofof DefenseDefense (DOD)(DOD) developeddeveloped

GPSGPS (Global(Global PositioningPositioning System)System)nn FirstFirst satellitessatellites werewere launchedlaunched inin 19781978nn SatellitesSatellites continuouslycontinuously broadcastbroadcast theirtheir ownown

positionposition inin spacespace andand useruser whowho hashas aa clock,clock,perfectlyperfectly synchronizedsynchronized toto thethe GPSGPS timetime system,system,isis ableable toto observedobserved thethe timetime delaydelay ofof aa GPSGPSsignalsignal fromfrom itsits ownown timetime ofof transmissiontransmission atat thethesatellitesatellite

nn TheThe timetime delay,delay, multipliedmultiplied byby thethe meanmean speedspeed ofoflightlight alongalong withwith thethe pathpath ofof thethe transmissiontransmission fromfromthethe satellitesatellite toto thethe useruser equipmentequipment willwill givegive thetherangerange fromfrom thethe satellitesatellite atat itsits knownknown positionposition totothethe useruser..

nn InIn practice,practice, satellitesatellite clocksclocks areare almostalmost perfectlyperfectlysynchronizedsynchronized toto GPSGPS timetime system,system, thethe useruser clockclockwillwill havehave anan errorerror ofof offsetoffset..

nn FourFour unknownunknown parametersparameters:: thethe threethree coordinatescoordinatesofof useruser positionposition andand thethe receiverreceiver clockclock offsetoffset..Thus,Thus, toto locatelocate thethe useruser positionposition atat leastleast fourfoursatellitessatellites areare requiredrequired..

nn Advantages:Advantages:üü No line of sight is requiredNo line of sight is requiredüü The equipment is suitably weatherproofThe equipment is suitably weatherproofüü One person operation with significant saving inOne person operation with significant saving in

time andtime and labourlabourüü Operation do not need high level of skillOperation do not need high level of skillüü Position may be fixed on land, air, seaPosition may be fixed on land, air, seaüü Baseline of hundreds of km can be measured toBaseline of hundreds of km can be measured to

accuracyaccuracy

nn DisadvantagesDisadvantagesüü AA goodgood viewview ofof skysky isis requiredrequiredüü ExpensiveExpensiveüü PositionsPositions ofof satellitessatellites areare globalglobal ratherrather thatthat locallocalüü TheThe heightheight determineddetermined byby satellitesatellite isis notnot whichwhich

wouldwould immediatelyimmediately recognizerecognize byby otherotherengineeringengineering surveyorsurveyor

GPS SegmentsGPS Segmentsnn 29 satellites29 satellitesnn Satellites are in almost circular orbitsSatellites are in almost circular orbitsnn 20200 km from earth (3 times the radius of earth)20200 km from earth (3 times the radius of earth)nn With orbit times just under 12 hrs.With orbit times just under 12 hrs.nn The six orbit planes are equally spacedThe six orbit planes are equally spacednn At least four satellite will always be in view at leastAt least four satellite will always be in view at least

1515°°above the horizontalabove the horizontalnn Weight of each satellite is 850 kgWeight of each satellite is 850 kgnn Design life from 7.5 years to 10 yearsDesign life from 7.5 years to 10 years

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Error SourcesError Sources

nn TheThe effecteffect ofof thethe atmosphericatmospheric refractionrefractionnn TheThe qualityquality andand quantityquantity ofof satellitesatellite datadata collectedcollectednn TheThe processingprocessing softwaresoftware usedusednn ToTo eliminateeliminate thisthis errorerror relativerelative positioningpositioning isis usedused

ratherrather thatthat singlesingle--pointpoint positioningpositioning (DGPS(DGPS::DifferentialDifferential GlobalGlobal PositioningPositioning System)System)

DGPS

ApplicationsApplicationsnn Plate tectonicsPlate tectonicsnn NavigationNavigationnn Geographical information system (GIS)Geographical information system (GIS)nn Deformation monitoringDeformation monitoring

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