2nd Lecture ,Lecture on site investigation for Handout ...engineering.mu.edu.iq/wp-content/uploads/2018/11/2nd-Lecture-Lecture-on-site...properties required for foundation design are

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.


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

12

Determination of the minimum depth of boring

Dr. Hussein M. Al.Khuzaie; [email protected]

Effective overburden pressure

q

DepthofBoring

13

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

17

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

21

Auger boring Power drills


Boringtools


Wash boring rig

23

Rotary Drilling rig


Boringtools


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.


34

SoilsInvestigation


Disturbed vsUndisturbed

(%) 100..

....2

22

´-

=DI

DIDOAR

35

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


CommonSamplingMethods


ROCKSAMPLING

• Rockcoresarenecessaryifthesoundnessoftherockistobeestablished.

• smallcorestendtobreakupinsidethedrillbarrel.

• Largercoresalsohaveatendencytobreakup(rotateinsidethebarrelanddegrade),especiallyiftherockissoftorfissured.


Rockcoring


ROCKSAMPLING- Definition


RockCoreDrilling

• Donewitheithertungstencarbideordiamondcorebits

• Useadoubleortripletubecorebarrelwhensamplingweatheredorfracturedrock

• UsedtodetermineRockQualityDesignation

41core barrelDr. Hussein M. Al.Khuzaie; [email protected]

RockQualityDesignation(RQD)


RockQualityDesignation

43

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


65

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



GPR


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 ...engineering.mu.edu.iq/wp-content/uploads/2018/11/2nd-Lecture-Lecture-on-site...properties required for foundation design are

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