Geotechnical Engineering_Site Investigations

Geotechnical investigation is a critical aspect of engineering geology that involves the study of the physical properties and behaviour of earth materials, such as soil and rock, at a specific site.
This investigation is essential in the planning, design, and construction of civil engineering projects, including buildings, bridges, dams, highways, and tunnels.
This investigation helps engineers and geologists understand the site's subsurface conditions and assess its suitability for various construction projects.

1. SUBSURFACE
INVESTIGATIONS
Engineering Geology
Francis W.

2. Geotechnical site Investigations
▪Geotechnicalinvestigationisacriticalaspectofengineeringgeologythatinvolvesthestudy
ofthephysicalpropertiesandbehaviorofearthmaterials,suchassoilandrock,ataspecific
site.
▪Thisinvestigationisessentialintheplanning,design,andconstructionofcivilengineering
projects,includingbuildings,bridges,dams,highways,andtunnels.
▪Thisinvestigationhelpsengineersandgeologistsunderstandthesite'ssubsurfaceconditions
andassessitssuitabilityforvariousconstructionprojects.

3. SUBSOIL EXPLORATION
Theprocessofdeterminingthelayersofnaturalsoildepositsthatwillunderliea
proposedstructureandtheirphysicalproperties

4. Objectives of site investigation
Followingaretheobjectivesofsiteinvestigationorsubsurfaceexploration
1.Determinationofthenatureofthedepositsofsoil.
2.Determinationofthedepthandthicknessofvarioussoilstrataandtheirextentinhorizontal
direction.
3.Locationofgroundwaterandfluctuationsingroundwaterlevel.
4.Obtainingsoilandrocksamplesfromthevariousstrata.
5.Determinationofengineeringpropertiesofsoilandrockstratathataffectstheperformance
ofthestructure.
6.Determinationofin-situpropertiesbyperformingfieldtests.
7.Toknowabouttheorderofoccurrenceofsoilandrockstrata.

5. Objectives of site investigation
9.Toselectasuitabletypeoffoundation.
10.Toestimatetheprobableandmaximumdifferentialsettlements.
11.Tofindthebearingcapacityofthesoil.
12.Topredictthelateralearthpressureagainstretainingwallsandabutments.
13.Toselectsuitablesoilimprovementtechniques.
14.Toselectsuitableconstructionequipment.
15.Toforecastproblemsoccurringinfoundationsandtheirsolutions.

6. Planning of Subsurface investigation (SI)
Toobtainthemostusefulinformationatminimumcostandeffort,properplanningof
subsurfaceinvestigationprogramisessential.
Forplanningoftheprogram,thesoilengineer-in-chargeoftheprogramshouldincludethe
followingsteps:
○Completelyfamiliarwiththekindofinformationrequiredfromtheinvestigation.
○Knowledgeoftype,sizeandimportanceoftheproject.
○Preparationoflayoutplanoftheproject,
○Preparationofboreholelayoutplanwhichincludesthenumberandspacingof
boreholes,depthandfrequencyofsampling.
○Selectionofproperdrillingandsamplingequipment.
○Selectionofpersonneltosupervisethefieldinvestigation.
○Markingonthelayoutplananyadditionaltypesofsoilinvestigation.
○Preparationofguidelinesforlaboratorytestingofcollectedsamples.

7. The purpose of a soil investigation program
▪Selectionofthetypeandthedepthoffoundationsuitableforagivenstructure.
▪Evaluationoftheload-bearingcapacityofthefoundation.
▪Estimationoftheprobablesettlementofastructure.
▪Determinationofpotentialfoundationproblems(forexample,expansivesoil,collapsible
soil,sanitarylandfill,andsoon).
▪Establishmentofgroundwatertable.
▪Predictionoflateralearthpressureforstructureslikeretainingwalls,sheetpilebulkheads
andbracedcuts.
▪Identificationofconstructionproblemsandtheirsolution(sheeting,dewatering,rock
excavation,etc.)
▪Identificationofproblemsconcerningadjacentexistingbuildings(settlement,damages)
▪Conductingfieldteststomeasurerelevantengineeringpropertiesofsoils.

8. The purpose of a soil investigation program
Thenatureandextentofsoilexplorationdependsupontheultimateusetowhichtheresultsof
theinvestigationwillbeapplied.Forexample,forstructureswhichtransmitheavyloadonthe
soil,theaimofsoilexplorationistoprovidedatawhichwillhelpintheselectionofpropertypes
offoundation,itslocationanddesignoffoundations.

9. Factors affecting exploration program
Soilexplorationprogramareinfluencedbyanumberoffactorssomeoftheseare:
▪Sizeandtypeoftheproject;
▪Generalcharacteristicsofthesoilsintheworkarea;
▪Timeavailableforexploration;and
▪Degreeofriskorsafetyinvolved.

10. General considerations for SI
Mainlytworequirementsshouldalwaysbeobservedinplanning/conductingSI
▪Accuracy/reliabilityofworkperformed,carelessnessorlackofexperiencemay
produceinconclusiveresultsleadingtowronginterpretations
▪TimelinessofperformingSI

11. Exploration program
•Thepurposeoftheexplorationprogramistodetermine,withinpracticallimits,the
stratificationandengineeringpropertiesofthesoilsunderlyingthesite.
•Theprincipalpropertiesofinterestwillbethestrength,deformation,andhydraulic
characteristics.
•Theprogramshouldbeplannedsothatthemaximumamountofinformationcanbeobtained
atminimumcost.

12. Phases of SI
ProjectAssessment:
ForaffectiveplanningofSIprogram,theGeotechnicalengineermustassessthefollowing
aspectsoftheproposeddevelopment.
○Thetype,purpose,locationandappropriatedimensionoftheproposedfacility,number
ofstorey,typeoffoundation,provisionbasementetc.
○Thetypeofconstruction,structuralloads,allowablesettlementsetc.
○Theexistingtopographyandanyproposedgrading
○Thepresenceofvariousdevelopmentsinthesitearea.
AllthefactorshaveanimpactandthoroughnessonSIprogram,e.g.,aproposednuclearpower
planttobebuiltondifficultgroundwouldrequireanextensiveSIprogramandcharacterization,
whileaonestoreywoodframebuildingonagoodsitemayrequireonlyminimaleffort.

13. Phases of SI
Framework/StagesofSI
SIprogrammayconsistsofthefollowingstages
○DeskStudyorLiteratureSearch
○Reconnaissance
○PreliminaryInvestigation
○DetailedInvestigation

14. Phases of SI
1.DeskStudy:
Assemblyofallavailableinformationregardingthesite,itmayinclude
▪Theinformationabouttheproposeddevelopment:dimensions,columnspacing,type
anduseofthestructure,basementrequirements,andanyspecialarchitectural
considerationsoftheproposedbuilding.Foundationregulationsinthelocalbuilding
codeshouldbeconsultedforanyspecialrequirements.Forbridgesthesoilengineer
shouldhaveaccesstotypeandspanlengthsaswellaspierloadings.Thisinformation
willindicateanysettlementlimitations,andcanbeusedtoestimatefoundationloads.
▪Sitehistory---earliersiteuse—mining---industrialcomplexes—Ancientmonuments
▪Geologicalmaps
▪Soilsurveyreports
▪Geotechnicalinvestigationreportofnearbysites
▪Historicgroundwater
▪Remotesensingdata,aerialphotographs,nowdayssatelliteimagerymaps

15. Phases of SI
2.Reconnaissanceofthearea:
Thismaybeintheformofafieldtriptothesite
whichcanreveal
▪Informationonthetypeandbehaviorof
adjacentstructuressuchascracks,noticeable
sags.Thetypeoflocalexistingstructuremay
influence,toaconsiderableextent,the
explorationprogramandthebestfoundation
typefortheproposedadjacentstructure.
▪Includesmarkingthelocationofproposed
exploratoryborings/trenches/testpits
▪Theexposedrockandthesurfacesoilsare
mapped
▪Markingofdifficultareaslikecoveredwith
organicsoil,sanitaryfilletc.
▪Approximatemapofthesiteareashowingthe
relativepositionofvariousexistingfeaturesin
thesitearea
▪Furtherfocusonvariousaspectslike:
✓Anyevidenceofpreviousdevelopment
onthesite
✓Anyevidenceofpreviousgradingon
site
✓Anyevidenceoflandslidesorstability
problem
✓Performanceofnearbystructure
✓Accesstothesite
✓Effectsofanyoffsiteconditionse.g.
flooding,mudfloworrockfallsetc.

16. Phases of SI
3.Preliminarysiteinvestigation:
▪Inthisphaseafewboringsaremadeoratestpitisopenedtoestablishinageneralmanner
thestratification,typesofsoiltobeexpected,andpossiblythelocationofthegroundwater
table.
▪Oneormoreboringsshouldbetakentorock,orcompetentstrata,iftheinitialborings
indicatetheuppersoilislooseorhighlycompressible.
▪Geophysicalmethodsmaybeusedtoestablishthetentativeboundarybetweenthestrata,
especiallythelocationofbedrock.
▪Laboratorytestingonlimitedsoilsamplestoevaluatethesoilparameters.
Thisamountofexplorationisusuallytheextentofthesiteinvestigationforsmallstructuresand
helpformulatingthescopeofSIforlargeprojectatdetailedSIstage.

17. Phases of SI
3.Preliminarysiteinvestigation:
Followingaresomeofthegeneralinformationobtainedthroughprimarysiteexploration.
▪Approximatesvaluesofsoil'scompressivestrength.
▪Positionofthegroundwatertable.
▪Depthandextentofsoilstrata.
▪Soilcomposition.
▪Depthofhardstratumfromgroundlevel.
▪Engineeringpropertiesofsoil(disturbedsample)

18. Phases of SI
4.Detailedsiteinvestigation:
Indetailedsoilinvestigation,boring,samplingandtestingisdonetoobtaintheengineering
propertiesofsoil.
▪Detailedexplorationispreferredforcomplexprojects,majorengineeringworks,heavy
structureslikedams,bridges,highrisebuildings,etc.Ahugeamountofcapitalisrequired
foradetailedsiteexplorationhence,itisnotrecommendedforminorengineeringworks
wherethebudgetislimited.Forsuchtypeofworks,datacollectedthroughpreliminarysite
explorationisenough.
▪Inthisstage,numerousfieldtestssuchasin-situvanesheartest,plateloadtest,etc.and
laboratorytestssuchaspermeabilitytests,compressivestrengthtestonundistractedsoil
samplesareconductedtogetexactvaluesofsoilproperties.

19. Phases of SI
4.Detailedsiteinvestigation:
Wherethepreliminarysiteinvestigationhasestablishedthefeasibilityoftheproject,amore
detailedexplorationprogramisundertaken.Thepreliminaryboringsanddataareusedasabasis
forlocatingadditionalborings,whichshouldbeconfirmatoryinnature,anditmayalsoinclude:
▪In-situtesting
▪Procuringsoilsamplesandcomprehensivelabtesting
▪Comprehensiveanalysesandreporting.

20. Phases of SI
5. During Construction Soil Investigation
If during excavations, the geotechnical condition may change from the established condition,
more soil investigation may be required to explore the extent of the changed conditions.

21. Subsurface Exploration Program

22. Planning/Scope of SI
WhiledecidingfieldworkofSI,threeaspectsareimportant
1.Locations2.Spacing3.DepthOfInvestigation/Boring
Location:Theboringshouldbeplacedatpointsofstrategicimportance
▪Atpointswhereheavyloadsareanticipated
▪Atabutmentsandatpointswhereintermediatepierswillcomeincaseofbridges
▪Fordams,usuallyalongthecentrelinebutsomelateralboringshouldbeplacedon
bothsidesofC/L
▪Forbuildingunits,atcornersandatcentreoftheplan

23. Planning/Scope of SI
Spacing:
▪Nohardandfastrule
▪Forstructuresusually10-30m
▪Forsmallstructures,minof3borings
▪Structuresconsistingofseparateunits,oneboringforeachunit
▪ForDams,tunnelsandotherexcavationsmaybecloselyspacedtogetbettergeology.

24. Planning/Scope of SI
Determiningthenumberofboring:
oThereisnohard-and-fastruleexistsfordeterminingthenumberofboringsaretobe
advanced.
oFormostbuildings,atleastoneboringateachcornerandoneatthecentershouldprovidea
start.
oSpacingcanbeincreasedordecreased,dependingontheconditionofthesubsoil.
oIfvarioussoilstrataaremoreorlessuniformandpredictable,fewerboreholesareneeded
thaninnonhomogeneoussoilstrata.

25. Planning/Scope of SI
In practice:
onumber of boreholes and the depth of each borehole
will be identified according to the type of project
and the subsoil on site.
oExample for a 5-story residential building with
dimensions of (40 x 70) m:
oThe required number of boreholes = 5
oboreholes (one at each corner and one at the center)
as mentioned previously.
oThe figure shows the distribution of boreholes on
the land

26. Planning/Scope of SI
Depth:
▪Uptodepthswhichareaffectedbyloadings,uptoinfluencezone
▪Explorationshouldbeextendedbelowalldepositsunsuitableforfoundationpurposes,e.g.
madeground,compressiblesoilsetc.
▪Uptohardstratum,min3minrocks

27. Planning/Scope of SI
Morespecifically:AsperBS-5930-1981
ForShallowFoundations:
Toadepthatleast1.5timestheloadedarea,andtheloadedareamaybe:
A.theareaoftheindividualfootingsiffootingwidelyspaced
B.wherespacingbetweentheindividualfootingislessthan3timesfootingwidthorwhere
floorloadingissignificant,theloadedareashouldbetheplanarea
C.Theareaofafoundationraft
ForPiles
▪Uptohardstratum
▪Uptoatleast4-5timesofthepilediameterbelowtheintendedpilelength

28. Planning/Scope of SI
DepthofBoringasPerASCE(1972)
Theapproximaterequiredminimumdepthoftheboringsshouldbepredetermined.The
estimateddepthscanbechangedduringthedrillingoperation,dependingonthesubsoil
encountered(e.g.,Rock).
Todeterminetheapproximaterequiredminimumdepthofboring,engineersmayusetherules
establishedbytheAmericanSocietyofCivilEngineers(ASCE1972):
1.Determinethenetincreaseofstress,underafoundationwithdepthasshowninthe
Figure.
2.Estimatethevariationoftheverticaleffectivestress,??????
�
′
,withdepth.
3.Determinethedepth,D=D
1,atwhichthestressincreaseΔ??????isequalto(1/10)q
o(q
o=
estimatednetcontactstressonthefoundation).
4.Determinethedepth,D=D
2,atwhichΔ??????/??????
�
′
=0.05.
5.Determinethedepth(D=D
3)whichisthedistancefromthelowerfaceofthefoundation
tobedrock(ifencountered).
6.Thesmallerofthethreedepths(D
1,D
2,andD
3)istheapproximaterequiredminimum
depthofboring.

29. Depth of Boring

31. Depth of Boring
Determining the value of vertical effective stress (??????�′):
●The value of (σo′) always calculated from the ground surface to the required depth
Determining the increase in vertical effective stress(Δ??????′):
●The value of (Δσ′) always calculated from the lower face of the foundation
●An alternative approximate method can be used (2:1 Method). According to this method, the value
of (Δσ′) at depth (D) is:
P = the load applied on the foundation (kN).
A = the area of the stress distribution at ���????????????(??????).
Notethattheaboveequationisbasedontheassumption
thatthestressfromthefoundationspreadsoutwitha
vertical-to-horizontalslopeof2:1.

32. Depth of Boring
If the foundation is circular, the value of (Δσ′) at depth (D) can be determined as following:
P = the load applied on the foundation (kN).
A = the area of the stress distribution at ���????????????(??????).

33. Example
Site investigation is to be made for a structure of 100 m length and 70 m width. The soil profile
is shown below, if the structure is subjected to 200 kN/m
2
. What is the approximate depth of
borehole. (Take ??????
w=10 kN/m
3
).

34. Solution
1.DeterminationofthedepthD1)atwhichtheeffectiveincreaseΔ??????
′
=Τ110??????
Δ??????
′
=Τ110×200=20??????????????????
Δσ
??????=
??????
??????
=
1.4×10
6
70+??????
1100+??????
1
=20
??????
1=180??????
2.DeterminationofthedepthD
2,atwhichΔ??????/??????
�
′
=0.05.
??????
�
′
=??????
2??????
�??????�−??????
�=??????
218−10=8??????
2
Δσ
??????=0.05??????
�
′
=0.4??????
2
Δσ
??????=
??????
??????
=
1.4×10
6
70+??????
2100+??????
2
=0.4??????
2
??????
2=101.4??????
??????
1=180??????;??????
2=101.4??????and??????
3=130??????
D=101.4m(thesmallest)

35. Sowers Methods for number and depth of Borings

36. Sowers Methods for number and depth of Borings

37. Sowers Methods for number and depth of Borings
●If the preceding rules are used, the depths of boring for a building with a width of 30 m will
be approximately the following, according to Sowers and Sowers (1970):

38. Method Proposed by Cernica

39. Planning/Scope of SI
Embankments:ASCErecommends
▪1.5to2timestheheightofembankments
▪Depthshouldbesufficienttopossibleshearfailureandprobablesettlement
Dams:depthshouldbesuchtoexploreallstratathroughwhichpipingandseepagemayoccur
andsomeboringsuptorockbed(min3mintotherock)
Roads:Explorationupto2-3mbelowtheformationlevel
Runways:5-6mbelowtheformationlevel
PipeLines:Depthbelowinvertleveloftheorderof1.5-2mmaybesufficient
Tunnels:Relativelytodeeperdepthasthelevelofthetunnelmaybelowered.

40. Example of Planning SI program

41. Economics of SI

42. Methods of Eploration

43. Open Methods
TestPits:
▪Openexcavation(1.5-2.5deep&approximate1mwide)
▪Suitablefornearsurfaceevaluation,samplingandtesting
▪Visualinspection
▪Excavatedbyhandormachine
▪Forsmallprojectswherefoundationlevel<2m
▪Blocksamples
▪Forpreliminaryinvestigation
▪Itisrelativelyfastandinexpensive

44. Open Methods

45. Methods of Boring
Theboringmethodsareusedforexplorationatgreaterdepthswheredirectmethodsfail.
Theyprovidebothdisturbedaswellasundisturbedsamplesdependinguponthemethodof
boring.
Inselectingtheboringmethodforaparticularjob,considerationshouldbemadeforthe
following:
▪Thematerialstobeencounteredandtherelativeefficiencyofthevariousboringmethods
insuchmaterials
▪Theavailablefacilityandaccuracywithwhichchangesinthesoilandgroundwater
conditionscanbedetermined
▪Possibledisturbanceofthematerialtobesampled

46. Methods of Boring
Thedifferenttypesofboringmethodsare:
1.Augerboring
2.Continuoussampling
3.Washboring
4.Rotarydrilling
5.Percussiondrilling

47. Boreholes
Therightchoiceofmethoddependson:
▪Groundcondition:presenceofhardclay,gravel,rock.
▪Ground-watercondition:presenceofhighground-watertable(GWT).
▪Depthofinvestigation
▪Siteaccess

48. Auger boring
▪It'samethodofsubsurfaceexplorationthatusesarotatingscrew-liketool(auger)to
excavatesoilandrocks,thuscollectingsamplesandinformationaboutthesubsurface.
▪Handoperatedorpowerdrivenaugersmaybeused.
▪SuitableinallsoilsaboveGWTbutonlyincohesivesoilbelowGWT.

49. Auger boring

50. Wash Boring
▪Itisapopularmethodduetotheuseoflimitedequipment.
▪Theadvantageofthismethodistheuseofinexpensiveandeasilyportablehandlingand
drillingequipment.
▪Amethodofsubsurfaceexplorationthatusesarotatingdrillbitandahigh-pressurejetof
watertoexcavateandremovesoilandrocks,collectingsamplesandinformationaboutthe
subsurfaceconditions.
▪Applications:Usefulinsoft,unconsolidatedsoils,especiallywheredeeppenetrationis
needed.

51. Wash Boring

52. Rotary Drilling
▪Rotarydrillingisamethodusedforboringholesintothegroundbyrotatingadrillingbit
thatcutsandgrindsthesubsurfacematerials.Itiscommonlyusedfordeepboreholesinsoil,
softrock,andhardrockformations.
▪Arotatingbitisattachedtothedrillpipeandcontinuouslyrotatestocut,grind,orcrush
thesoilorrock.
▪Acirculatingdrillingfluid(mudorwater)ispumpeddownthedrillpipeto:
oCoolandlubricatethebit.
oCarrycuttingstothesurface.
oStabilizetheboreholewalls.
▪Themudwithdrilledfragments(cuttings)returnstothesurfacethroughtheannularspace
betweenthedrillpipeandboreholewalls.
▪Rotarydrillingisusedtocollectsoilandrockstratasamples,ortoformdeepobservation
boreholesaspartofGeotechnicalandEnvironmentalSiteinvestigations.
▪Rotarydrillingisafastdrillingtechniquethatadvancesaboreholeusingimpactenergyplus
rotation.

53. Rotary Drilling

54. Percussion Drilling
●Percussiondrillingisemployedwhenaugerorwashboringisnotpossibleinverystiffsoil
orrock.Italsocanbeusedinmostsoiltypes.
●Heretheadvancementofaholeisachievedbyalternativelyliftinganddroppingaheavy
cuttingorhammeringbitthatisattachedtoaropeorcablethatisloweredintoanopenhole
orinsideatemporarycasing(casingsarehollowcylindricalpipesusedforboreholestability
andtopreventthelossofdrillingfluidthroughtheboreholes).
●Percussiondrillinginvolvesrepeatedlyraisinganddroppingaheavydrillingbittobreakup
soilandrockformations.Thecrushedmaterialmixeswithwatertoformaslurry,whichis
thenremovedfromtheboreholetoallowfurtherprogress.

55. Percussion Drilling

56. Soil Sampling
NeedforSoilSampling
▪Asatisfactorydesignofafoundationdependsupontheaccuracywithwhichthevarioussoil
parametersrequiredforthedesignareobtained.
▪Theaccuracyofthesoilparametersdependsupontheaccuracywithwhichrepresentative
soilsamplesareobtainedfromthefield.
▪Samplingiscarriedoutinorderthatsoilandrockdescription,andlaboratorytestingcanbe
carriedout.
▪Laboratoryteststypicallyconsistof:
oIndextests(forexample,specificgravity,watercontent,etc.)
oClassificationtests(forexample,Atterberg’slimittestsonclayeysoil)
oTeststodetermineengineeringdesignparameters(forexamplestrength,
compressibility,andpermeability).

57. Soil Sampling
Factorstobeconsideredwhilesamplingsoil
▪Samplesshouldberepresentativeofthegroundfromwhichtheyaretaken.
▪Theyshouldbelargeenoughtocontainrepresentativeparticlessizes,fabric,andfissuring
andfracturing.
▪Theyshouldbetakeninsuchawaythattheyhavenotlostfractionsoftheinsitusoil(for
example,coarseorfineparticles).
▪Wherestrengthandcompressibilitytestsareplanned,theyshouldbesubjecttoaslittle
disturbanceaspossible.

58. Soil Sampling
Non-RepresentativeSoilSamples
▪Non-representativesoilsamplesarethoseinwhichneitherthein-situsoilstructure,moisture
contentnorthesoilparticlesarepreserved.
▪Theycannotbeusedforanytestsasthesoilparticleseithergetsmixeduporsomeparticles
maybelost.
▪Samplesthatareobtainedthroughwashboringorpercussiondrillingareexamplesofnon-
representativesamples

59. Soil Sampling
Representative Soil Samples
There are two types of samples:
▪Disturbed Soil Samples
▪Undisturbed Soil Samples

60. Disturbed Soil Samples
Disturbedsoilsamplesarethoseinwhichthein-situsoilstructureandmoisturecontentarelost,
butthesoilparticlesareintact.
▪Theyarerepresentative.
▪Theycanbeusedforthefollowingtypesoflaboratorysoiltests:
○grainsizeanalysis
○atterberglimits
○specificgravity
○compactiontests
○moisturecontent
○organiccontentdetermination
▪ThemajorequipmentusedtoobtaindisturbedsamplesisSplitSpoon

61. Disturbed Soil Samples
▪ThemajorequipmentusedtoobtaindisturbedsamplesisSplitSpoon

62. Undisturbed Soil Samples
Undisturbedsoilsamplesarethoseinwhichthein-situsoilstructureandmoisturecontentare
preserved.
▪Theyarerepresentativeandalsointact.
▪Theseareusedforthefollowingtypesoflaboratorysoiltests:
oConsolidationtests.
oHydraulicConductivitytests.
oShearStrengthtests.
▪Thesesamplesaremorecomplexandexpensive,andtheyaresuitableforclays,howeverin
sand,itisverydifficulttoobtainundisturbedsamples.
▪ThemajorequipmentusedtoobtainundisturbedsampleisShelbytube(thin-walledtube)
andpistonsampler.

63. Undisturbed Soil Samples

64. Degree of Disturbance
Ifwewanttoobtainasoilsamplefromanysite,thedegreeofdisturbanceforasoilsampleis
usuallyexpressedas:
D
o=outsidediameterofthesamplingtube.
D
i=insidediameterofthesamplingtube.
If(A
R)≤10%→thesampleisundisturbed
If(A
R)>10%→thesampleisdisturbed

65. GROUNDWATER

66. IN-SITU TESTS
●The ground is tested in-placeby instruments that are inserted in or penetrate the ground.
●In-situ tests are normally associated with tests for which a borehole either is unnecessary or
is only an incidental part of the overall test procedure, required only to permit insertion of
the testing tool or equipment.
●Improvements in apparatus, instrumentation, and technique of deployment, data acquisition
and analysis procedure have been significant.

67. IN-SITU TESTS
▪Standardpenetrationtest-SPTforbearingstrengthprediction
▪DynamicconepenetrationLighttest(DPL)-forstrengthprediction
▪Dynamicconepenetrationtest(DCP)-forCBRpredictionsandlayerthickness
▪Plateloadtest-usedtodeterminethebearingcapacityandsettlementofsoilsunderagiven
load.
▪TheConePenetrationTest(CPT)-providesvaluableinformationonseveralsoilproperties,
includingundrainedshearstrength,soilsensitivity,relativedensity,stiffness,andelastic
modulus.ThesepropertiesarederivedusingempiricalcorrelationsbasedonmeasuredCPT
parameterssuchastipresistance(qₜ),sleevefriction(fₛ),andporewaterpressure(u).
▪Shearvanetest-forshearstrengthprediction
▪FlatDilatometerTest(DMT)-usedtoassesssoilstiffness,lateralstress,andstrength.
▪PressuremeterTest(PMT)-usedtomeasurein-situstress-strainbehaviorofsoilsandrocks.

68. IN-SITU TESTS

69. IN-SITU TESTS
Advantages
▪Testsarecarriedoutinplaceinthenaturalenvironmentwithoutsamplingdisturbance,
whichcancausedetrimentaleffectsandmodificationstostresses,strains,drainage,fabric
andparticlearrangement.
▪Continuousprofilesofstratigraphyandengineeringproperties/characteristicscanbe
obtained.
▪Detectionofplanesofweaknessanddefectsaremorelikelyandpractical.
▪Methodsareusuallyfast,repeatable,producelargeamountsofinformationandarecost
effective.
▪Testscanbecarriedoutinsoilsthatareeitherimpossibleordifficulttosamplewithoutthe
useofexpensivespecializedmethods.
▪Alargevolumeofsoilmaybetestedthanisnormallypracticableforlaboratorytesting.This
maybemorerepresentativeofthesoilmass.

70. IN-SITU TESTS
Disadvantages
▪Samplesarenotobtained;thesoiltestedcannotbepositivelyidentified.Theexceptionto
thisistheSPTinwhichasample,althoughdisturbed,isobtained.
▪Thefundamentalbehaviorofsoilsduringtestingisnotwellunderstood.
▪Drainageconditionsduringtestingarenotknown.
▪Consistent,rationalinterpretationisoftendifficultanduncertain.
▪Thestresspathimposedduringtestingmaybearnoresemblancetothestresspathinduced
byfull-scaleengineeringstructure.
▪Mostpush-indevicesarenotsuitableforawiderangeofgroundconditions.
▪Somedisturbanceisimpartedtothegroundbytheinsertionorinstallationoftheinstrument.
▪Thereisusuallynodirectmeasurementofengineeringproperties.Empiricalcorrelations
usuallyhavetobeappliedtointerpretandobtainengineeringpropertiesanddesigns

71. STANDARD PENETRATION TEST (SPT)
Definition
▪Thisempiricaltestconsistsofdrivingasplit
spoonsampler,withanoutsidediameterof50
mm,intothesoilatthebaseofaborehole.
▪Drivageisaccomplishedbyatriphammer,
weighingis622.72N(63.5kg),fallingfreely
throughadistanceof76.2cmontothedrivehead,
whichisfittedatthetopoftherods.
▪Thesplit-spoonisdriventhreetimesfora
distanceof15cmintothesoilatthebottomof
theborehole.
▪Thenumberofblowsrequiredtodrive(only)the
lasttwo15cmarerecorded.Theblowcountis
referredtoastheSPTNumber,SPT-N“N”.

72. STANDARD PENETRATION TEST (SPT)

73. STANDARD PENETRATION TEST (SPT)

74. SPT (CORRECTION TO N VALUE)
▪There are several factors contribute to the variation of the standard penetration number (N)
at a given depth for similar profiles. Among these factors are the SPT hammer efficiency,
borehole diameter, sampling method, and rod length.
▪In the field, the magnitude of hammer efficiency can vary from 30 to 90%, the standard
practice now is to express the N-value to an average energy ratio of 60% (N60), so
correcting for field procedures is required as following:
N=measured penetration number.
N
60=standard penetration number, corrected for the field conditions.
η
H=hammer efficiency (%).
η
B=correction for borehole diameter.
η
S=sampler correction.
η
R=correction for rod length.

75. SPT (CORRECTION TO N VALUE)

76. Correction for Effective Overburden Pressure

77. SPT (N
60CORRELATIONS)
N
60can be used for calculating some important parameters such as:
Cohesive soils
oConsistency Index (CI)
oUndrained shear strength (Cu)
oOverconsolidationratio (OCR)

78. SPT (N
60CORRELATIONS)

79. SPT (N
60CORRELATIONS)

80. SPT (N
60CORRELATIONS)

81. SPT (N
60CORRELATIONS)

82. SPT (N
60CORRELATIONS)
N
60can be used for calculating some important parameters such as:
Granular soils
○Relative Density (D
r)
○Angle of internal friction (??????)

83. SPT (N
60CORRELATIONS)

84. SPT (N
60CORRELATIONS)

85. SPT (N
60CORRELATIONS)

86. SPT (N
60CORRELATIONS)

87. VANE SHEAR TEST (VST)
Vanesheartestisusedtoevaluatethein-situundrainedshearstrength(c
u)ofsofttostiffclays
andsilts.Bothpeakandremoldedstrengthscanbemeasuredandtheirratioistermedsoil
sensitivity.
•A four-bladed vane is inserted into the soil and rotated at a slow, constant speed.
•The torque required to shear the soil is measured and used to calculate undrained shear
strength.
•It is useful for assessing soil stability in foundation design, embankments, and slopes.
AdvantagesofVST:
oSimpletestandequipment
oLonghistoryofuseinpractice
DisadvantagesofVST:
oLimitedapplicationtosofttostiffclaysandsilts
oSlowandtime-consuming
oRawc
uvaluesneed(empirical)correction

88. VANE SHEAR TEST (VST)
VSTconsistsofinsertingasimplefour-bladedvaneintoeitherclayorsiltandrotatingthe
deviceaboutaverticalaxisandmeasuringthetorque.
Limitequilibriumisusedtorelatethemeasuredtorquetotheundrainedshearstrength
mobilized.Bothpeakandremoldedstrengthscanbemeasured.

89. VANE SHEAR TEST (VST)

90. Cone Penetration Test (CPT)
TheConePenetrationTest(CPT)isanin-situgeotechnicaltestingmethodusedtodetermine
soilproperties,stratigraphy,andengineeringparameters.Itprovidesacontinuousprofileofsoil
resistanceandiswidelyusedforfoundationdesign,soilclassification,andliquefaction
assessment.

91. PRESSUREMETER TEST (PMT)
●Thepressuremetertestcanbeusedtoevaluatethestress-strainresponseofawiderangeof
soilsandrock.

92. Rock Sampling (Coring)
▪Rocksamplesarecalled“rockcores”,
andtheyarenecessaryifthesoundness
oftherockistobeestablished.
▪Smallcorestendtobreakupinsidethe
drillbarrel.
▪Largercoresalsohaveatendencyto
breakup(rotateinsidethebarreland
degrade),especiallyiftherockissoftor
fissured.

93. Rock Sampling (Coring)
▪Coringisdonewitheithertungsten
carbideordiamondcorebits.
▪Rocksampleriscalled“corebarrel”
whichusuallyhasasingletube.
▪Doubleortripletubecorebarrelisused
whensamplingofweatheredorfractured
rock.

94. Rock Sampling (Coring)

95. Rock Sampling (Coring)
▪Corestendtobreakupinsidethedrill
barrel,especiallyiftherockissoftor
fissured.
▪Corerecoveryparametersareusedto
describethequalityofcore.
▪Lengthofpiecesofcoreareusedto
determine:
oCoreRecoveryRatio(Rr)
oRockQualityDesignation(RQD)

96. Rock Sampling (Coring)
▪RQD(RockQualityDesignation)isa
measureofthequalityofrockcore
samplesobtainedfromdrilling.
▪Itiscommonlyusedingeotechnicaland
miningengineeringtoassessrockmass
integrityandsuitabilityforconstruction
orexcavationprojects.

97. Rock Sampling (Coring)

98. Rock Sampling (Coring)

99. Example on Core recovery & RQD

100. BORING LOGS

101. BORING LOGS

102. GEOTECHNICAL REPORT
▪Uponcompletionofthegeotechnicalinvestigationandanalysis,theinformationand
findingsmustbecompiledinastandardreportformat.
▪Thereportservesasthepermanentrecordofallgeotechnicaldataknowntobepertinentto
theprojectandisreferredtothroughoutthedesign,construction,andservicelifeofthe
project.
▪ThedataandrecommendationsaretypicallycompiledinaGeotechnicalReport.Theintent
oftheGeotechnicalReportistopresentthedatacollectedinaclearmanner,todraw
conclusionsfromthedata,andtomakerecommendationsforthegeotechnicalaspectsofthe
project.
▪Theprimaryclientsthatusethereportareroadwaydesigners,BridgeEngineers,
constructionpersonnel,andcontractors.

103. Geophysical Exploration
▪Geophysical exploration uses physical methods (seismic, gravitational, magnetic, electrical,
and electromagnetic) to measure the Earth's subsurface properties, helping to detect and
locate geological features and resources like ore deposits, hydrocarbons, and groundwater.
▪Although boring and test pits provide definite results but they are time consuming and
expensive.
▪Subsurface conditions are known only at the bore or test pit location.
▪The subsurface conditions between the boring need to be interpolated or estimated.
▪Geophysical methods are more quick and cheaper.
▪They provide thorough coverage of the entire area.
▪The results of Geophysical testing however are less definitive and require subjective
interpretation.
▪Therefore, both methods are important. In case geophysical testing is major in scope, few
borings and sampling will be required for accurate determination of soil properties.
▪If boring is major in scope, then few geophysical lines will be required to know the
conditions in-between the borings.

104. Geophysical Exploration

105. Geophysical Exploration

106. Geophysical Test Methods

107. Subsoil Exploration Report