2nd Lecture ,Lecture on site investigation for Handout...
Transcript of 2nd Lecture ,Lecture on site investigation for Handout...
Dr. Hussein M. Al.Khuzaie; [email protected] 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
SITEINVESTIGATION
2Dr. Hussein M. Al.Khuzaie; [email protected]
Definition
Theprocessofdeterminingthelayersofnaturalsoildepositsthatwillunderlieaproposedstructureandtheirphysicalpropertiesisgenerallyreferredtoassiteinvestigation.
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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.
4Dr. Hussein M. Al.Khuzaie; [email protected]
EXPLORATIONPROGRAM
Thepurposeoftheexplorationprogramistodetermine,withinpracticallimits,thestratificationandengineeringpropertiesofthesoilsunderlyingthesite.Theprincipalpropertiesofinterestwillbethestrength,deformation,andhydrauliccharacteristics.Theprogramshouldbeplannedsothatthemaximumamountofinformationcanbeobtainedatminimumcost.
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Stepsofsubsurfaceexplorationprogram[Stage1]
1. Assemblyofallavailableinformationondimensions,columnspacing,typeanduseofthestructure,basementrequirements,andanyspecialarchitecturalconsiderationsoftheproposedbuilding.Foundationregulationsinthelocalbuildingcodeshouldbeconsultedforanyspecialrequirements.Forbridgesthesoilengineershouldhaveaccesstotypeandspanlengthsaswellaspierloadings.Thisinformationwillindicateanysettlementlimitations,andcanbeusedtoestimatefoundationloads.
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Stepsofsubsurfaceexplorationprogram[Stage2]
2.Reconnaissanceofthearea:Thismaybeintheformofafieldtriptothesitewhichcanrevealinformationonthetypeandbehaviorofadjacentstructuressuchascracks,noticeablesags,andpossiblystickingdoorsandwindows.Thetypeoflocalexistingstructuremayinfluence,toaconsiderableextent,theexplorationprogramandthebestfoundationtypefortheproposedadjacentstructure.
7Dr. Hussein M. Al.Khuzaie; [email protected]
Stepsofsubsurfaceexplorationprogram[Stage3]
3.Apreliminarysiteinvestigation:Inthisphaseafewboringsaremadeoratestpitisopenedtoestablishinageneralmannerthestratification,typesofsoiltobeexpected,andpossiblythelocationofthegroundwatertable.Oneormoreboringsshouldbetakentorock,orcompetentstrata,iftheinitialboringsindicatetheuppersoilislooseorhighlycompressible.Thisamountofexplorationisusuallytheextentofthesiteinvestigationforsmallstructures.
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Stepsofsubsurfaceexplorationprogram[Stage4]
4.Adetailedsiteinvestigation:Wherethepreliminarysiteinvestigationhasestablishedthefeasibilityoftheproject,amoredetailedexplorationprogramisundertaken.Thepreliminaryboringsanddataareusedasabasisforlocatingadditionalborings,whichshouldbeconfirmatoryinnature,anddeterminingtheadditionalsamplesrequired.
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DepthofBoring
Theapproximaterequiredminimumdepthoftheboringsshouldbepredetermined.Theestimateddepthscanbechangedduringthedrillingoperation,dependingonthesubsoilencountered.Todeterminetheapproximateminimumdepthofboring,engineersmayusethefollowingrule:
10Dr. Hussein M. Al.Khuzaie; [email protected]
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.
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DepthofBoring
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Determination of the minimum depth of boring
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Effective overburden pressure
q
DepthofBoringForhospitalsandofficebuildings,thefollowingrulecouldbeusedtodetermineboringdepth
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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.
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SpacingofBoring
Therearenohardandfastrulesforthespacingoftheboreholes.Thefollowingtablegivessomegeneralguidelinesforboreholespacing.Thesespacingcanbeincreasedordecreased,dependingonthesubsoilcondition.Ifvarioussoilstrataaremoreorlessuniformandpredictable,thenumberofboreholescanbereduced.
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SpacingofBoring
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Approximate Spacing of Boreholes
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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
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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.
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SOILBORING
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Boringtools
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Boringtools
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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
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Dr. Hussein M. Al.Khuzaie; [email protected] 28
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32Dr. Hussein M. Al.Khuzaie; [email protected]
SOILSAMPLINGTwotypesofsoilsamples canbeobtainedduringsamplingdisturbed and undisturbed.Themostimportantengineeringpropertiesrequiredforfoundationdesignarestrength,compressibility,andpermeability.Reasonablygoodestimatesofthesepropertiesforcohesive soilscanbemadebylaboratorytestson undisturbed sampleswhichcanbeobtainedwithmoderatedifficulty.Itisnearlyimpossibletoobtainatrulyundisturbedsampleofsoil;soingeneralusagetheterm"undisturbed"meansasamplewheresomeprecautionshavebeentakentominimizedisturbanceorremoldingeffects.Inthiscontext,thequalityofan"undisturbed"samplevarieswidelybetweensoillaboratories.
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Disturbed vsUndisturbed
(%) 100..
....2
22
´-
=DI
DIDOAR
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Good quality samples necessary.
AR<10%
sampling tube
soil
area ratio
Thicker the wall, greater the disturbance.Dr. Hussein M. Al.Khuzaie; [email protected]
Disturbed vsUndisturbed
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CommonSamplingMethods
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ROCKSAMPLING
• Rockcoresarenecessaryifthesoundnessoftherockistobeestablished.
• smallcorestendtobreakupinsidethedrillbarrel.
• Largercoresalsohaveatendencytobreakup(rotateinsidethebarrelanddegrade),especiallyiftherockissoftorfissured.
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Rockcoring
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ROCKSAMPLING- Definition
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RockCoreDrilling
• Donewitheithertungstencarbideordiamondcorebits
• Useadoubleortripletubecorebarrelwhensamplingweatheredorfracturedrock
• UsedtodetermineRockQualityDesignation
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RockQualityDesignation(RQD)
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RockQualityDesignation
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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.
Dr. Hussein M. Al.Khuzaie; [email protected]
ExampleonCoreRecovery&RQD
• Corerunof150cm• Totalcorerecovery=125cm
• Corerecoveryratio=125/150=83%
• Onmodifiedbasis,95cmarecountedRQD =95/150=63%
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GROUNDWATERTABLELEVEL
Groundwaterconditionsandthepotentialforgroundwaterseepagearefundamentalfactorsinvirtuallyallgeotechnicalanalysesanddesignstudies.Accordingly,theevaluationofgroundwaterconditionsisabasicelementofalmostallgeotechnicalinvestigationprograms.Groundwaterinvestigationsareoftwotypesasfollows:
• Determinationofgroundwaterlevelsandpressures.• Measurementofthepermeabilityofthesubsurfacematerials.
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FIELDSTRENGTHTESTSThefollowingarethemajorfieldtestsfordeterminingthesoilstrength:1. Vanesheartest(VST).2. StandardPenetrationTest(SPT).3. ConePenetrationTest(CPT).4. TheBoreholeShearTest(BST).5. TheFlatDilatometerTest(DMT).6. ThePressure-meterTest(PMT).7.ThePlateLoadTest(PLT).
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FIELDSTRENGTHTESTS
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StandardPenetrationTest(SPT)
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StandardPenetrationTest(SPT)
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StandardPenetrationTest(SPT)
CorrectionsarenormallyappliedtotheSPTblowcounttoaccountfordifferencesin:•energyimpartedduringthetest(60%hammerefficiency)
•thestresslevelatthetestdepthThefollowingequationisusedtocompensateforthetestingfactors(Skempton,1986):
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StandardPenetrationTest(SPT)
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StandardPenetrationTest(SPT)
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Cone PenetrationTest(CPT)
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Cone PenetrationTest(CPT)
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Cone PenetrationTest(CPT)
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Cone PenetrationTest(CPT)
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Cone PenetrationTest(CPT)
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ThePlateLoadTest(PLT)
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ThePlateLoadTest(PLT)
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ThePlateLoadTest(PLT)
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ThePlateLoadTest(PLT)ScaleEffectinFoundationDesign
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GeotechnicalDesignReports• Attheendofallsubsoilexplorationprograms,thesoiland/orrockspecimenscollectedfromthefieldaresubjectedtovisualobservationandappropriatelaboratorytesting.Afterthecompilationofalloftherequiredinformation,asoilexplorationreportispreparedfortheuseofthedesignofficeandforreferenceduringfutureconstructionwork.Althoughthedetailsandsequenceofinformationinthereportmayvarytosomedegreeisdependingonthestructureunderconsiderationandthepersoncompilingthereport.
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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
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SubsoilExplorationReport
Thefollowinggraphicalpresentationsshouldheattachedtothereport:
1.Asitelocationmap2.Aplanviewofthelocationoftheboringswithrespecttotheproposedstructuresandthosenearby
3.Boringlogs4.Laboratorytestresults5.Otherspecialgraphicalpresentations
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Example: Table of Contents for a Geotechnical Investigation (Data) Report
Dr. Hussein M. Al.Khuzaie; [email protected]
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GPR
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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
Dr. Hussein M. Al.Khuzaie; [email protected] 68
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