FOUNDATION ENGINEERING FORDIFFICULT SUBSOILCONDITIONS FOUNDATION ENGINEERING FORDIFFICULT SUBSOILCONDITIONS LeonardoZeevaert SecondEdition Inii5IVANNOSTRANDREINHOLDCOMPANY ~New YorkCincinnatiTorontoLondonMelbourne Copyright 1983 by Van Nostrand Reinhold Company Inc. Libraryof Congress Catalog Card Number:82-1877 ISBN:0-442-20169-9 All rights reserved.Certain portions of this workcopyright 1972 by Van Nostrand Reinhold Company Inc.Nopart of this work covered by the copyright hereon may be reproduced or used in any formor by any means-graphic, electronic, or mechanical, including photocopying, recording,taping, or information storage and retrieval systems-without permission of the publisher. Manufactured in the United States of America Published by VanNostrand Reinhold Company Inc. 135West50th Street, New York,N.Y.10020 Van NostrandReinhold Publishing 1410 Birchmount Road Scarborough, Ontario MIP2E7, Canada Van Nostrand Reinhold Australia Pty.Ltd. 17Queen Street Mitcham, Victoria3132, Australia VanNostrand Reinhold Company Limited MollyMillarsLane Wokingham,Berkshire, England 15141312II1098765432I Library of Congress Cataolging in Publication Data Zeevaert, Leonardo,1914-Foundation engineering fordifficult subsoil conditions. Includes bibliographies and index. IFoundations.2.Soilmechanics.1.Title. TA775.z451982624.1'582-1877 ISBN0-442-20169-9AACR2 PREFACETOFIRSTEDITION Throughoutthirtyyearsof professional practice in suchdifficult subsoilconditions asthoseencounteredintheseismicareaof MexicoCity,theauthorhashadthe benefitof observinganddesigningmanylargefoundations.Thenew concepts and workinghypothesesgiveninthisbookarebasedonthisexperience,inorderto achievebetterdesignsonarationalbasis,reducingpracticalrulesthatinthepast haveresultedinpoorperformanceof buildingfoundations.Intheengineering professionitisnecessarytoinvestigatecontinuouslythephysicallawsof soilbe-havior and soilmasses, to be ableto eliminatethe guessworksupported by empirical generalizations.Statistics,however,isavaluableresearchtoolininvestigatingthe generaltrendofthephenomenaandanaidtoestablishtheoriesandworkinghy-potheseswhendeviationsfromthestatisticallawsestablishedareunderstoodand carefullyobserved. Severalgoodbooksonsoilmechanics,foundationsand engineering geology have beenwritten,inwhichthefoundationengineercanstudythegeneralaspectsof designandconstructioninfoundationengineering.Thescopeof thisbookisto supplementthis literature with basic technical fundamentals,pointing out theprob-lemsthatmaybeencounteredinpracticewhenthefoundationisinvolvedwith difficultsubsoilconditions.Therefore,thewriter assumesthereader isacquainted with the current literatureonthis subject. Foundationengineeringisnotanexact science.Nevertheless, sufficient precision isrequiredtoassureasuccessfulfoundationdesignandconstruction.Thisgoalis achievedwhenthebehaviorin the fieldcomplies within thepredictions andfactors of safetyused,thusobtainingasatisfactoryperformancewithoutsacrificing econ-omy.Difficultsubsoilconditionsmaybedefinedasthoseencounteredinsoil sedimentsof mediumtoveryhighcompressibilityandmediumtoverylowshear strengthextendingto great depth, and inthose wherethe hydraulic conditions play v viPREFACETOFIRSTEDITIOhl animportantrole,aswellaswhenthesoildeposits arefoundinareassubjected to stronggroundmotionsinducedbyearthquakes.Underthese environmental condi-tions,thefoundationengineer iscompelled to usealltheknowledgeand experience hehasgainedinsoilandfoundation engineering, sampling and testing of materials. Theaspectsof engineeringgeologyinrecognizing the engineering characteristics of thesubsoilusedforfoundationsareof primaryimportance,sinceitisrecognized that the behavior of a small soil sampleisnot representativeof that of the entire de-positor strata encountered.It shouldbekept in mindthatthefoundationengineer hastoworkwithsoildepositsthatarefarfrombeing isotropic andhomogeneous. Therefore,hisunderstandingof thebehaviorof thesubsoilcanonlybecomplete afterconsideringtherealconditionsthatmaybeexpectedfroma geologicalpoint of view. Allowanceshouldbegiveninallengineeringdesigns,usingafactorof safetyto cover thedeviationsof thetheories and working hypotheses, the mechanicalproper-tiesof thematerial,andconstructionproceduresthat mayalsodeviateto a certain degreefromdesignconsiderations.Theselectionof afactorof safetyshouldbe basedontheknowledgethefoundationengineerhasobtainedfromtheenviron-mentalconditionsandforcesinvolved,namely,thegeologicalandphysiographical conditions,hydraulicandmechanicalpropertiesofthesediments,aswellasthe functional requirements of the project forwhichthe foundations should bedesigned. Alltheseelementsshouldbemadecompatiblewiththeeconomyof thedesign; therefore,theprecisionrequiredinthe calculations is summarized bythe ability of thefoundationengineertomanipulatethelaws,theoriesandworkinghypotheses thatmaybeavailableinsoilsandfoundationengineeringtoadegreetowhichhe hasgainedconfidencefromexperience.Thisbookspeciallyemphasizesthisap-proachasstrictlynecessarytobeabletoperformarationaland successfuldesign. Inordertoavoidmentioning"approximatemethod"throughoutthisbook,the authorwishestopointoutthatactuallyincivilengineeringand mostly in founda-tionengineering,thereisnotsucha thing asan"exact method or theory."Allthe methodsproposedinthisbookhaveadegreeof accuracy,orshallwesay,anun-certaintyacceptablefromthepracticalengineeringpointof view.Nevertheless, it istruethatsomemethodsaremorereliablethanothersfortheproblemsencoun-teredinpractice.Theuncertaintyof aparticularmethodiscoveredbythecorre-spondingfactorof safety,whichasmentionedbefore,shouldalsocovernotonly theso-calledtheory,butalsothedeviationsofanyotherenvironmentalforces foundunderfieldconditions.Therefore,foundationengineeringrequiresexperi-enceoffieldbehaviorandof thedeviationsobtainedfromthetheoreticaldesign calculations.Moreover,oneshouldnotforgetthat theories and methods of design incivilengineeringaresubjectedtofurtherinvestigations,asmoreexperienceis gainedwithtime.Therefore,theorieshavetobeestablishedundersimplifiedas-sumptionscovering,inthebest possible manner, the mechanics expected under real conditions.Often, because of the nonuniform characteristics encountered, it would beawasteof time-orratheranillusion-totrytoapproximatethesolutionof a problemtoanunrealaccuracy.Thedecision depends on the abilityof thefounda-tionengineertovisualizetheproblemandmakeagoodestimatethatwillenable PREFACETOFIRSTEDITIONvii himtoobtainsufficientprecisionandeconomyinthedesign.Nevertheless,it shouldbekeptinmindtilatduringconstructionthedesignexpectationmaybe somewhataltered.Constructionmethodsshouldgotogetherwiththeoreticalde-sign, andthefactorof safety selected accordingly. ChapterIIhasbeenpreparedasa reviewof the mechanicalproperties of difficult soils,advancingsomeconceptsof approach,mainlyinthefieldof finesediments exhibitingintergranularviscosity.Themethodsexposedhavebeenusedbythe authorsatisfactorilyforseveralyears.Theyhavesufferedtheoreticaladjustments sincefirstpublishedtoobtainbettercorrelationswithbehaviorobservedinthe field. Indeformationproblems,thesoilshouldbeconsideredatwo-phasematerial. Thesolidphaserepresentedbytheskeletonstructureandtheliquidphaserepre-sentedbythewatershouldbestudiedseparately.Thisimpliesknowledgeof the stress-strain-timepropertiesof thematerialsandof the stressdissipation inthesoil massduetoloadapplication, aswell asof the stateof hydraulicpressures and their changesimposedduringconstructionorotherenvironmentalconditions.Chapters IIandIIIhavebeenpreparedtoreviewtheseconcepts,providingthepracticing foundationengineer,inChapterIII,withstressnetsto facilitateestimates of stress changes.Thetheoreticalbackgroundtotraceflownetsindifferentfoundation problemsisalsoreviewed.Theuseofwellsystemstodewaterexcavationsis treated.Attheend of Chapter III,theproblem on stability and bearing capacity is discussed.Bearing capacity factorsfor deepfoundations aregiven based on current theoreticalconsiderations; theresult given, however, isnot morethan another theo-reticalessayonbearingcapacity complying withthe experience of the author. InChaptersIV,VIandVIIanattempt ismadeto introduce the foundation engi-neertothecomplexfieldof sub gradereactions.This may beconsidered wherethe foundationandstructuralengineersmeet.Furthermore,theauthor believes,from hisexperience,that soil mechanics andfoundations cannot bedivorcedfromdesign of thefoundation structure, since there must existcompatibility between thesetwo branchesof civilengineering.The unit foundationmodulus, alsocalledthe "coeffi-cientofsubgradereaction,"isavariablefunctionof thegeometryof theloaded area,thesubgradereactiondistribution,andthemechanicalpropertiesof the sub-soilforthestresslevelapplied.Thefoundationstructuralproblembecomesvery complicatedwhenthefoundationstructureisinitselfastaticallyindeterminate structure.Theonlymeanstosolvethesecomplicatedproblemsinapractical manneris by means of simplified working assumptions,reducingtheunknowns to a numberthatmaybehandledbycurrentmethods.The methods giveninthe book maybeusedbytheexperiencedfoundationengineer.Nevertheless,sinceallof themgiveonlyparticularsolutions,theywillonlyserveasa guidetoestablisha schoolof thOUght.Thefinalassumptions and methods of calculation, however, call fortheskillandexperienceof thefoundationandstructuralengineersinvolved in thesolutionof theparticularproblem, toestablish the best and most practical pro-cedures.Computerprogramsmaybewrittentofacilitateandspeedupthe calculations. Thegroundsurfacesubsidenceoccurringindifficultsubsoilconditionsandthe viiiPREFACETOFIRSTEDITION implicationsof thisphenomenonincivilengineeringworkscannotbevv..:rlooked, sinceinmostoccasions,difficultandcomplex problems may beencountered.The illustrationanddeductionof workinghypothesestoevaluatetheseproblemsand theireffectsinfoundationengineeringmaybeexplained more simply by means of a casehistory, asused by the author in Chapter V. Thebehaviorof frictionpilesisanimportantiteminfoundationengineering, mainlyinthoseproblemsrelatedwithnegativeskinfrictioninpilesandpiers. ChapterVIn hasbeendevotedtoexplainthemechanicsanduseof frictionpiles, basedonanultimateskinfrictiontheory.Themethodsofcalculationarealso given;theirapplicationsare studied in Chapter IXforthefrictionpilecompensated foundation,andinChapterXfornegativefrictionon point bearing piles andpiers. Thesemethodsof calculationhavebeenusedextensivelybytheauthor with satis factoryresults,andarepublished forthefirsttimeto their fullextent in this book. Theprocessofperformingexcavationsisanimportantfactorinthefuturebe haviorof foundationsrequiringdeep excavations.The water flowinduced bydeep pumpingproduceschangesintheeffectivestressesinthesoilmass,affectingthe stabilityanddeformationduringexcavation.Theapproachtotheseproblemsis treatedinChapter XI; however,thereader shouldbeacquainted firstwith Chapters IIIand VII. Therearemanyplacesintheworldwith difficult subsoil conditions subjectedto destructiveearthquakes,whereit isnecessaryto investigatethe behavior of founda-tionsto be abletoperform a rational andsafedesign.For thispurpose, thefounda-tionengineershouldinvestigatetheprobablebehaviorofthesubsoilmassunder stronggroundmotions.ChapterXIIwasprepared with the aimof introducing the foundationengineertoseismicfoundationengineering.Withthisinmind,the authorhastaken thecase history of Mexico City, wherefieldinformation onstrong earthquakesisavailable.Thecontentsof sections3,4, 5 and6 of Chapter XIIare givenforthefirsttimeinthisbook.Theymaybetakenasanadvance andguidance frominvestigations carried onin this subject. Althoughthefoundationengineeriscompelledtogeneralizethesubsoilcondi-tionstobeabletoproduceworkableandpracticalmethodsof computation,this generalizationshouldbemadeonasoundandrationalbasisusing allthepower of soilmechanicshehasathisdisposal,considering,moreover,that innaturethere is nosuchthingasanisotropicsubsoilcondition.Themechanicalproperties of soils aremorecomplexthananyotherengineeringmaterial.Therefore, theonly means istousetheclosestrepresentativetheoriesandworkinghypothesesthatmaybe compatiblewiththebehaviorobservedinthefield,andfromthereestablishthe mostsimplecorrelationsatisfyingthestaticsof theproblem.Thedevelopment of theoriesisnecessarytoestablishthebasisof comparisonwithrealbehaviorinthe field,andaccordingly,screenoutinconsistencieswiththeaimof obtainingmore reliable andtechnical methods of approach. Thebibliographyinsoilmechanicsisveryextensiveatpresent,andhasgrown considerablyineachcountrywherebasicresearchiscarriedon.Theobtention of publishedmaterialandthethoroughstudyandselectionof itscontents,withthe PREFACETOFIRSTEDITIONix barrierof languages,isbecomingagigantictaskbeyondthepossibilitiesof anin-dividual.Therefore,theauthorwishestoapologize if someimportant publications onthe subjecttreated in this book haveescaped hisattention.The selected bibliog-raphygiventoeachchapterisintendedonlyto contribute inthe understanding of thecorresponding chapter. Themaincontentof thisbookisthecompilation of thework of theauthordur-inghisprofessionalpractice,whichhasbeengraduallyaddedtobyexperienced colleaguesinthefieldtowhomtheauthorisgreatlyindebted,mainlyonthe intergranular viscosityof soils, the critical stress inpreconsolidated soils and harden-ing,theplastictheory to estimate frictioninpiles,the dewatering of excavations to reduceheave,theinjectionof water outside excavations to reduce settlements, and thedriftingforcesonundergroundelements,motivatedbystrongground motions duetoearthquakes.Theauthorishighlyindebtedtohisnephew,Mr.AdolfoE. Zeevaert,C.E.,M.Sc.,forhisgreathelpandinterest during thepreparationof the manuscript,inthecalculation of graphs andtables,checking formulasandpractical illustrativeexamplesusedinthetext,andintheAppendices.Theauthorwishes ~ l s otoextendhisappreciationtohissecretary,Mrs.DianaA.deBalseca,forthe arduoustaskshehastakenintypingthemanuscript,andfinally,totheeditor, whoseinterestinthisbookcontributedinapresentationbeyondtheaimof the author. Mexico,D.F.Leonardo Zeevaert, Ph.D.,C.E. Professor of Soil Mechanics andFoundations atthe Faculty of Engineering,U.N.A.M. Consulting CivilEngineer. PREFACETOSECONDEDITION Intheeightyearssincetheappearanceof firstedition,and through its use inthe courses givenbytheauthor at the Graduate Schoolof Engineering of the V.N.A.M., theauthor hasimprovedthecontent of several chapters.Theseimprovements have beenincludedinthesecondeditiontomakeitmoreexplicitandpracticalfor graduate courses andfoundationengineering practice. Allthe chapters, however, havebeenrevised.In Chapter II,newand moreprecise formulasaregiventoestimate verticaldisplacement dueto the intergranular viscos-ityphenomenon.Thebasicprinciples,however,havebeenretaineduntilfuture investigations may showa moreaccurate and practical method to be used. ChapterIIIhasbeen extended to include, in the solid phase, formulasto calculate groundstressesforsurfacerectangularloadedareasandfordifferentvaluesof Frohlich'sconcentration factor.Also,theoretical methods of calculating the reduc-tion of piezometric water levelsinstratified subsoils and of estimating the depressed water table in wellgroups forexcavation purposes havebeen added. A completelynewChapterVIhasbeenwrittentoincludethemost recent prac-ticalmethodsdevelopedbytheauthorregardingsoil-structurefoundationinter-actionconsideringtheimportanceof knowingtheapproximatevalueof thesub-gradereactions in foundation structuraldesign.(SeeL.Zeevaert,1980, ISE.) ChaptersIV,VandVIIto XIhavebeenrevised,and moreon soil-structure inter-action hasbeen added to Chapter X. ChapterXIIhasbeenenlargedtoincludeapracticalandrationalmethodof estimatingthelossofbearingcapacityinloosecohesionlesssoilsduringstrong groundmotionsinducedbyearthquakes.A method isincluded for computing the seismicrockingphenomenonof boxtypefoundationsfortallbuildingssupported on stratified subsoilconditions.At the end of the chapter, a general method isgiven xi xiiPREFACETOSECONDEDITION forestimating the seismicsoil-pileinteraction behavior,including illustrativenumer-icalexamples. Finally,inAppendixE,newnumericalexamplesforChaptersVIandVIIare presentedwiththepurposeof illustratingthemethodsof computationforsoil-structure interaction given in Chapter VI. Theauthorhasconsideredthatnowadaysthepracticingfoundationengineeris gettingmoreandmoreinvolvedinmatrixalgebra calculations he can perform with hisdeskcomputer,thereforemorematrixalgebra has been used in the book.With thisinmindtheauthor hasgivenready to usealgorithmsand methods of computa-tionthatwillpermitthepracticingfoundationengineerto write hisown programs toexpeditehiscalculationswithanapproximationcompatiblewiththepractical problemsinvolved.Especiallyinterestingalongthisline,arethecalculationsto estimate the ultimate skin frictionin piles, subsoil seismic behavior, the soil-structure interactionof compensatedmatfoundations,theseismicrocking phenomenon and thebehavior of piles, piersor vertical shafts subjected to strong ground motions. Inthesoil-structureinteractionproblems,thefoundationengineershouldcare-fullyselectthesecantstress-strainparametersforthe increment of stressand stress levels involved,asdescribed in Chapters IIand VII. TheauthorisindebtedtoMissEloisaE.Rey,C.E.,M.I.,forhergreat helpand interestinassistingtheauthortorevisethenewadditions,formulasand examples forthesecondedition,andtotheeditor for hisinterest that this book should con-tinuetobeup-to-date,andservetheadvancedstudentandprofessionalpracticing foundation engineer forconsultation in hiseverydaywork. Mexico, D.F. Leonardo Zeevaert Professor of SoilMechanics and Foundation Engineering Faculty of Engineering, U.N .A.M. CONTENTS Prefacev INTRODUCTION1 1.1TypicalFoundations1 1.1IsolatedFootings2 1.2Continuous Footings4 1.3RaftFoundation6 1.4CompensatedFoundations7 1.5Compensated Foundations with Friction Piles8 1.6 PointBearing Pile Foundations9 1.7Pier Foundations12 1.8SandPier Foundations13 1.2SubsoilSediments15 2.1Residual Soils15 2.2EolianDeposits16 2.3Alluvial Deposits17 2.4Lacustrine andMarineSediments17 2.5Piemont Deposits17 2.6Recent Volcanic Deposits17 2.7Glacial Deposits18 1.3Total andDifferentialAllowable Settlements18 1.4Summary23 Bibliography25 IIMECHANICAL PROPERTiES OF SOIL26 11.1Introduction26 112Permeability28 11.3Stress-Strain-TimeRelationships32 3.1General Concepts32 3.2The Elastic Unit37 xiii xivCONTENTS 3.3The Plastic Unit38 3.4The Elasto-Plastic Unit39 3.5The Strain Modulus42 3.6The Compressibility of Fine Sediments47 3.6aNormallyLoaded andPreconsolidated-Type Sediments52 3.6bExpansive or SwellingSoils56 3.6c Soils57 3.6dCompaction andDesiccation61 3.7Linear Strain Modulus,Function of ConfiningStress62 3.8Linear Strain Modulus, Function of Time70 3.9The Theory of Consolidation72 3.10Viscous Unitof Linear Fluidity78 3.11The Kelvin-Terzaghi Relationships81 3.12Theory of Consolidation WhenLoadIncreases Linearly with Time82 3.13The Intergranular Viscosity inSaturatedSoil Sediments85 3.13aThe Z-Unit90 3.13bThe Strain-Time Behavior forRapidLoad Application95 3.13cStrain-Time Behavior forLinearLoadApplication96 3.14Intergranular Viscosity in Saturated Soilswith Cavities102 3.15Intergranular Viscosity in NonsaturatedSoils104 3.16The Useof Kv-ValueinSoils Exhibiting Intergranular Viscosity105 3.17Parameter Determination:Fitting Methods106 11.4ShearStrength114 4.1Basic Concepts114 4.2Coulomb-Terzaghi's Equation115 4.3Coulomb-Mom's Failure Concept118 4.3aThe DrainedShear Strength121 4.3bThe Consolidated-UndrainedShear Strength121 4.3cThe UndrainedShear Strength123 4.4Determination of the AverageShear Parameters c andI/>125 4.5Coulomb-Mohr's Plasticity Condition 125 4.6Rheological Considerations 127 4.7Shear Strength Applications134 4.8Conclusions139 Bibliography141 IIISOLIDANDLIQUIDPHASESOFSOIL144 111.1BasicConcepts 144 111.2SolidPhase 145 2.1Effective Stresses 145 2.2Stress Distribution inSoil Mass 149 2.3The Stress Nets 160 2.4StratifiedSoil Masses 168 2.5Vertical Displacements of RigidFootings 173 111.3Hydraulic Pressures:LiquidPhase 3.1Water FlowComponents 3.1 aDownwardFlow 3.1bUpwardFlow 3.2The FlowNet 3.2aIsotropic SoilMass 3.2bStratifiedSoil Mass 3.3Average Coefficients of Permeability 3.4Vertical Flow in Stratified Soil Deposits 3.5Dewatering by Wells 3.5aStudy of a Single Well 3.5bStudy of WellGroups 3.6Ratio of the Discharge in One Welland in a System of Wells 111.4Shear StrengthBehaviorinSoilMass 4.1Basic Considerations 4.2Bearing Capacity 4.2aShallowFootings 4.2bDeep Footings Bibliography IVSUBGRADEREACTION IV.1GeneralConsiderations IV.2FoundationModulus IV.3RigidFoundations IV.4BendingMoments andShearsinRigidFoundation 4.1ShearCorrection 4.2MomentCorrection IV.5Recommended k-Values Bibliography VGROUND SURFACE SUBSIDENCE V.1Introduction V.2Mechanics of GroundSurfaceSubsidence V.3GroundSurfaceSubsidenceinMexico City 3.1General andHistorical Considerations 3.2Subsoil Conditions 3.3General Soil Properties 3.4Piezometric Pressure andSurface Subsidence Measurements 3.5Foundation Problems 3.5aGeneral Considerations 3.5bCaseI:Water Wells 3.5cCaseII:Shrinkage Problem 3.5dCaseIII:Buildings on Surface Foundations 3.5eCaseIV:Buildingson Piles Bibliography CONTENTSxv 176 176 179 180 181 183 186 187 189 193 194 197 205 206 206 207 207 209 214 216 216 217 217 229 229 231 232 234 237 237 238 248 248 250 255 260 263 263 264 264 267 269 273 xvi CONTENTS VISOILFOUNDATIONSTRUCTUREINTERACTION 275 VL1Introduction 275 VL2Soil-Structure Interaction 278 VL3Soil-StructureInteraction Matrix Equation 285 Bibliography 288 VIICOMPENSATEDFOUNDATIONS 290 VIL1BasicConcepts 290 VIL2Shear Strength 294 VIL3CompressibilityandCriticalStress 295 VilAPlasticFlow 299 VIL5Elastic Heave andSubsequent Settlement 300 VII.6LateralContractionandSettlementOutsidetheExcavation 310 VIL7Methods to ReduceHeave 314 VIL8Overturning Moment andBaseShear317 8.1Introduction317 8.2ElasticResponse317 8.3Permanent Tilt324 8.4BaseShear326 VII.9Bending Moments andShearsintheFoundationStructure326 VII.10PracticalConsiderations331 Bibliography332 VIIIULTIMATELOAD CAPACITY OF PILESAND PIERS333 VII 1.1Introduction333 VII 102Point BearingCapacity339 2.1Theory Review339 2.2PileGroups341 2.3Point Vertical Displacements347 2.4Pile GroupBearing Capacity 349 VII 1.3NegativeFriction351 3.1BasicConcepts 351 3.2Effective Tributary Area361 3.3Useof Influence Charts 367 3.4Confining Stress at the Pile Point Elevation 370 3.5Allowable PointBearing Load 371 VII 104PositiveFriction onPiles 372 4.1Basic Concepts 372 4.2SkinFriction Considerations 374 4.3PileGroupasa SingleUnit 377 VII 1.5Behavior of PileFields BasedonMechanicalModels 381 5.1BasicConsiderations 381 5.2CASEI:PositiveFriction, NoPointResistance 383 5.3CASEII:PositiveFriction andPointResistance 385 5.4CASEIII:NegativeFriction 386 5.5CASEIV:NegativeFriction Usedfor Building Support 387 5.6CASEV:Restriction of StressRelief inSoilMass 389 5.7CASEVI:Friction toReduce Consolidation of Soil Mass 391 CONTENTSxvii 5.8CASE VII:Friction Piles in Consolidating Mass393 Conclusions395 VIII.6FieldLoadingTestsonPilesandTheirLimitations395 6.1Basic Concepts395 6.2Friction Pik in Cohesive Soil398 6.3Point Bearing Piles in Sand401 6.4VerticalDisplacement of SinglePile Tests, and Pile Groups404 VII1.7ReviewonPileSelectionandDriving406 7.1ProjectReq uiremen ts406 7.2StructuralLoads-Subsoil Exploration408 7.3PileFoundation-Selection of Pile Type409 7.4Pile Types MostCommonly Used413 7.5PileDriving and Control416 Bibliography420 IXDESIGNOFCOMPENSATEDFRICTION PILEFOUNDATIONS422 IX.1GeneralConsiderations422 IX.2FrictionPileRaftFoundations424 IX.3CompensatedFoundationsWithFrictionPiles431 3.1General Considerations431 3.2HeaveProblem431 3.3LoadReapplication435 3.4Importance of Point Resistance438 IX.4Overturning Moments439 IX.5BendingMomentsandShears439 Bibliography440 XDESIGNOFPOINT BEARING PILES AND PIERFOUNDATIONS441 X.1GeneralConsiderations441 X.2PointBearingPileFoundations444 2.1Typical Cases of Point Bearing Piles444 2.2CaseI444 2.3CaseII446 2.4CaseIII448 X.3PierFoundations452 X.4Overturning Moments andBaseShear455 4.1Tiltingof Foundation455 4.2Tilting Control for PileFoundations456 X.5ShearsandBendingMoments458 Bibliography460 XISTABILITY OFDEEPEXCAVATIONSFORFOUNDATIONS461 XI.1GeneralConsiderations461 XI.2Sheet-Pile Wall467 2.1Lateral Support467 2.2Timber468 2.3Concrete469 2.4Steel470 XI.3PressuresontheSheet-PileWall470 XI.4Dewatering ofExcavations475 xviiiCONTENTS XI.5Stability of theBottomof theExcavation Bibliography XIIINTRODUCTION TO EARTHQUAKE PROBLEMSIN BUILDINGFOUNDATIONS XI1.1GeneralConsiderations XI1.2EarthquakeEngineering Characteristics 2.1Introduction to SeismicWaves 2.2Magnitude 2.3Intensity 2.4EarthquakeRecording 2.5Response Spectrum XI1.3SubsoilBehavior 3.1Basic Concepts 3.2Resonant Periods of Vibration in Stratified Subsoil 3.3Contribution of Vibration Modes in the GroundMotion 3.4Problems Induced by Longitudinal Waves 3.5Reduction of the Bearing Capacity Because of Seismic Action XII.4ShearModulus of Elasticity 4.1BasicConcepts 4.2The Free TorsionPendulum 4.3Results XII.5SeismicBehavior of BuildingFoundations 5.1Introduction 5.2Foundation Response 5.3SeismicBaseShear XI1.6SeismicBehavior of UndergroundStructures 6.1General Considerations 6.2VerticalShafts, Pilesand Piers 6.3Underground Pipes and Tunnels Bibliography APPENDIX ALIST OF SYMBOLS APPENDIXBINFLUENCE STRESSNETS AND CHARTS APPENDIX CINTEGRATIONFORMULASFOR SKINFRICTION PROBLEMSIN PILEFIELDS APPENDIXDCONVERSIONTABLESFROM METRIC (CGS)TO THE ENGLISH SYSTEM APPENDIXENUMERICAL EXAMPLES TO CHAPTERS IV, VII, AND VIII ExampleA.IV ExampleB.IV ExampleA.VII ExampleB.VII ExampleVIII INDEX Calculationof a SemiflexibleFoundation RigidBoxTypeFoundation PontoonStripFoundation CaseHistoryof HeaveforDeep, Overcompensated Foundation Calculationof FrictionPiles 484 486 489 489 492 492 496 497 501 501 510 510 514 521 523 529 540 540 543 551 554 554 555 564 567 567 567 587 593 596 601 611 615 618 618 630 632 640 645 655 FOUNDATION ENGINEERING FORDIFFICULT SUBSOILCONDITIONS ~ I ~INTRODUCTION 1.1TYPICALFOUNDATIONS Theartof designingthebest and most economical foundationsfora project greatly dependsonacarefulinvestigationbythefoundationengineer.A studyshouldbe madeof theenvironmentalfactorsandthecompatibility of thesubsoil engineering conditionswiththetypeof foundationstructureonwhichtheloadingsaretobe supported.Hence,asafirstapproximation,thefoundationengineershouldcon-siderthequalitativeindexandmechanicalcharacteristicsof thesubsoilatthesite atwhichtheprojectwillbeconstructed.Thispreliminaryknowledgewillpermit himto judgethebehavior of thesubsoil under applied load, and after analyzing the probablebehaviorofdifferenttypesof foundationstructuralsystemsinconjunc-tionwiththeprojectrequirements,hewillbeinthepositiontoselecttheproper foundation. Thepurposeof this chapter isto visualizetheselection of thetypeof foundation, reviewingthetypicalfoundationstructuresthatmaybeusedinconjunctionwith thesubsoilconditionstobeencountered,tofulfilltherequirementsof totaland differentialsettlements.It mustbeborneinmind, however,that inthedesignof a foundationtherearetwoimportantmechanicalitemstobeconsidered:first,the bearingcapacityof thesoilfortheapplied load; and second, whether thetotaland differentialsettlementsarecompatible withthefoundation structure selected,type of superstructureandarchitecturaldemandsof theproject.Asanexampleof total anddifferentialsettlements,thecaseof widelyspacedfootingsusedforlight flex-ibleroofsmaybementioned,whereonemayallowlargedifferentialsettlements, incontrastwithotherproblems likeinstallation of machinery or equipment, where thedifferentialsettlemenfsareoften restricted to verysmall values.Therefore, the foundationengineershouldinvestigatethedifferential settlements that maybeper-2INTRODUCTION mittedfordifferentproblemsof buildingdesign,andalsothemagnitudeof theto-talsettlement not damaging adjacent construction. Thespecificationof totalanddifferential settlements isstudied carefullyforeach probleminquestion,astheallowancescanvarya great deal,depending ontheme-chanicallimitationsof theprojectinquestion,aswellason adjacentbuildings and publicutilities.Inotherwords, onecould saythat fora certain specificbuilding, a totalsettlementof30cmmaybeallowed,providedthatthereisnodamageand differentialsettlementsforcertainpredeterminedspansbetweencolumnsdonot exceed~cm.Thisspecificationappearsto bebold, sinceonecould sayalsothat a totalsettlementof 30 cmislarge, evenif no damagetakes place.If thetotal settle-ment,however,couldbeforecastandthebuildingisisolated inanarea awayfrom otherbuildingsandnodamageof any property isexpected,thenthereisno reason toallowlargesettlementsinthedesign,provided alsothat theconnections of pub-licutilitiesgoingintothebuildingaretakencareproperly,andthefoundation structureisdesignedinsuchawaythat differential settlements inthebuilding will notproducedamageto theconstruction.If such isthecase,thefunctionalrequire-mentsoftheprojectarefulfilledandthefoundationmaybeconsideredtowork undersatisfactoryconditions. Thefoundationengineerexperiencedinsoilmechanicsandengineeringgeology, aswellaswiththebehaviorof foundationstructures andbuildingdesign,isableto visualize,asafirststep,whichfoundationtoselectfortheprobleminquestion. Oncehehasselectedtheoptimumtypeof foundationtobeused,then hemay in-vestigatequantitativelyitsbehavior.Theselectionshouldalwaysbethemost eco-nomicaltypeof foundationthatcanbeused,fulfillingtherequirementsof allow-abletotalanddifferentialsettlementsinconjunctionwiththesubsoilcondition encountered. Inordertogivethefoundationengineerthefirstapproachinthephilosophyof selectingafoundation,theprincipaltypesof foundationswillbediscussed,andthe relationtheyhavewithdifferent subsoildeposits fromwhichtheprobablebehavior maybeforecast.Inthisapproach,thefoundationengineerisassumedtobeac-quaintedwiththeindexandgeneralmechanicalpropertiesofsoilsandwiththe generalbehavior of differenttypesof foundationstructures. 1.1I solatedFootings Footingsareunderstoodformedbyarigidrectangular baseof stoneor concreteof dimensions:width Bandlength L, inwhichtheratioof LIB willnot exceed1.5. Thefoundationstructurewillsupportthecolumnload.Thebearingcapacityof thefootingmaybeestimated,anditsdimensions selected; thereafter, a forecastof thesettlement ismade. Toillustratethecaseof footingfoundations,considerabuildingwithninecol-umns(Fig.loLl)supportedonisolatedfootings.Inthiscase,thefootingswill workindependentlyofeachother.Therefore,itisrequiredthatthedifferential settlementsbetweenfootingswillnotexceedtheallowabletotalanddifferential settlementrequirements.Thedifferentialsettlementsmaybereducedselecting 1.1TYPICALFOUNDATIONS3 L~1.5B L Fig.1-1.1Single footings. properlytheareaof thefootings,and attimes, usingthestiffness of the superstruc-ture.Fromthestructural point of view,however,thesuperstructureshould not be allowedtotakehighsecondarystressesinducedbythedifferentialsettlementsof thefootings,exceptinveryspecialcases.Singlefootingfoundations,ingeneral, willbeusedonlyinsoilsof lowcompressibilityand in structures wherethediffer-entialsettlementsbetweencolumnsmaybecontrolledbythesuperstructureflexi-bility,orincludinginthedesignof thebuilding jointsorhingesthatwilltakethe differentialsettlementsand/orrotations,respectively,withoutdamagingthe construction. 4INTRODUCTION 1.2.ContinuousFootings Whenitisnecessarytocontrolwithincertainlimitsthemagnitudeof differential settlementsbetweencolumnssupportedonfootings,and whensoildeposits of me-diumorlowcompressibilityareencountered, it isrecommendedto usecontinuous footings.Theymaybedefinedasresistingelements joiningcolumnstogetherby foundationbeams. Continuousfootingsarearrangedbyjoiningtwoor morecolumnstogether with beams.Theverticaldifferentialdisplacements may becontrolled viabeamstiffness (Fig.2-1.1).Theselectionof thefoundationbeams, either running inonedirection ortheother along columnrows,depends largelyonthelayout of thecolumn loads, Elevation Crosssection (a) 3 A B (b) c Fig. 2-1.1Continuous footings. 1.1TYPICALFOUNDATIONS5 3 } }