A preview of soil behavior
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This document provides an overview of soil mechanics and discusses various soil problems and their solutions. It addresses issues civil engineers may encounter with soil, including using soil for foundations and construction materials. It also discusses specific examples to illustrate different soil-related challenges: shallow and deep foundations, embankments, foundation heave, using soil as a construction material in earth dams, and retaining walls. The document outlines key factors engineers must consider for different soil-related projects, such as foundation type and placement, filling techniques, and controlling settlement and drainage.
A preview of soil behavior
- 1. An OverviewAn OverviewAn OverviewAn Overview ofofofof Soil MechanicsSoil MechanicsSoil MechanicsSoil Mechanics Dr. P. K. BasudharDr. P. K. Basudhar Dept of Civil Engineering IIT Kanpur
- 2. Soil ProblemsSoil ProblemsSoil ProblemsSoil Problems && SolutionsSolutions A Preview ofA Preview of Soil BehaviorSoil Behavior Pioneers inPioneers in Soil MechanicsSoil MechanicsSoil MechanicsSoil Mechanics
- 3. CIVIL ENGINEER SOILCIVIL ENGINEER SOILENCOUNTERS WHERE ? CIVIL ENGINEER SOILCIVIL ENGINEER SOIL • SOIL AS A ENCOUNTERS – FOUNDATION – CONSTRUCTION MATERIALCONSTRUCTION MATERIAL • SOIL RETAINING SPECIAL PROBLEMS• SPECIAL PROBLEMS
- 4. FOUNDATIONSFOUNDATIONSFOUNDATIONSFOUNDATIONS • WHAT ARE FOUNDATIONS?WHAT ARE FOUNDATIONS? • TYPES OF FOUNDATIONS SHALLOW FOUNDATIONS– SHALLOW FOUNDATIONS – DEEP FOUNDATIONS • MAIN PROBLEM IN THE DESIGN – TO PREVENT SETTLEMENT • TOTAL SETTLEMENT • DIFFERENTIAL SETTLEMENT
- 5. SHALLOW FOUNDATIONSSHALLOW FOUNDATIONSSHALLOW FOUNDATIONSSHALLOW FOUNDATIONS •• StructuralStructural loadsloads areare carriedcarried byby thethe soilsoil directlydirectly underunder thethe structurestructure
- 6. DEEP FOUNDATIONSDEEP FOUNDATIONSDEEP FOUNDATIONSDEEP FOUNDATIONS •• UsedUsed toto carrycarry thetheUsedUsed toto ca yca y t et e loadsloads toto firmfirm soilsoil atat somesome depthdepthpp
- 7. Classic case of bad foundationClassic case of bad foundationClassic case of bad foundationClassic case of bad foundation •• FigFig.. showsshows thethe PalacioPalacio dede laslasgg BellasBellas Artes,Artes, MexicoMexico CityCity •• TheThe 22 mm differentialdifferential settlementsettlement betweenbetween thethe streetstreetsettlementsettlement betweenbetween thethe streetstreet andand thethe buildingbuilding onon thethe rightright necessitatednecessitated thethe stepssteps whichwhich werewere addedadded asas thethe settlementsettlementwerewere addedadded asas thethe settlementsettlement occurredoccurred •• TheThe generalgeneral subsidencesubsidence ofof thisthis partpart ofof thethe citycity isis 77 mmthisthis partpart ofof thethe citycity isis 77 mm •• (Photograph(Photograph complimentscompliments ofof RaulRaul Marsal)Marsal)
- 8. Example of Shallow foundationsExample of Shallow foundationsExample of Shallow foundationsExample of Shallow foundations •• FigFig showsshows thethe MITMIT studentsstudents centrecentre •• MatMat foundationfoundation •• FloatationFloatation techniquetechnique•• FloatationFloatation techniquetechnique
- 9. Main FactorsMain Factors 11.. JustJust howhow deepdeep intointo thethe soilsoil shouldshould thethe buildingbuilding bebe placed?placed?placed?placed? 22.. WouldWould thethe excavationexcavation havehave toto bebe enclosedenclosed byby aa wallwall duringduring constructionconstruction toto preventprevent cavecave--insins ofof soil?soil?gg pp 33.. WouldWould itit bebe necessarynecessary toto lowerlower thethe waterwater tabletable inin orderorder toto excavateexcavate andand constructconstruct thethe foundationfoundation and,and, ifif soso h th t me nsme ns sho ldsho ld bebe sedsed toto omplishomplish thisthisifif so,so, whatwhat meansmeans shouldshould bebe usedused toto accomplishaccomplish thisthis loweringlowering ofof thethe groundground waterwater (dewatering)?(dewatering)? 44.. WasWas therethere aa dangerdanger ofof damagedamage toto adjacentadjacent buildings?buildings?44.. WasWas t e et e e aa da geda ge oo da ageda age toto adjace tadjace t b d gs?b d gs? 55.. HowHow muchmuch wouldwould thethe completedcompleted buildingbuilding settlesettle andand wouldwould itit settlesettle uniformly?uniformly? 66.. ForFor whatwhat stressesstresses andand whatwhat stressstress distributiondistribution shouldshould thethe matmat ofof thethe buildingbuilding bebe designed?designed?
- 10. Example of Deep foundationsExample of Deep foundationsExample of Deep foundationsExample of Deep foundations •• MITMIT materialmaterial centrecentre hashas deepdeep pilepile foundationfoundationpp pp •• ReasonsReasons –– Basement space notBasement space not desirabledesirable –– No sand and gravel atNo sand and gravel at h ih ithe sitethe site –– Not to disturbNot to disturb underground utilitiesunderground utilitiesunderground utilitiesunderground utilities •• PointPoint bearingbearing pilepile •• FrictionFriction pilepilepp •• AugeringAugering
- 11. Main FactorsMain Factors I What type of pile should be used?I What type of pile should be used? Main FactorsMain Factors I. What type of pile should be used?I. What type of pile should be used? 2. What was the maximum allowable load for a pile?2. What was the maximum allowable load for a pile? 3 At h t p in h ld th pil b dri n?3 At h t p in h ld th pil b dri n?3. At what spacing should the piles be driven?3. At what spacing should the piles be driven? 4. How should the piles be driven?4. How should the piles be driven? 5. How much variation from the vertical should be5. How much variation from the vertical should be permitted in a pile?permitted in a pile? 6. What was the optimum sequence for driving piles?6. What was the optimum sequence for driving piles? 7. Would the driving of piles have an influence on7. Would the driving of piles have an influence on adjacent structures?adjacent structures?
- 12. Example of EmbankmentExample of Embankment on Soft Soilon Soft Soil •• 1010..77 mm embankmentembankment onon aa 99..88mm layerlayer ofofonon aa 99..88mm layerlayer ofof softsoft soilsoil •• PreloadingPreloading techniquetechnique•• PreloadingPreloading techniquetechnique •• ShearShear rupturerupture shouldshould notnot occuroccur
- 13. Main FactorsMain Factors 11 HowHow highhigh aa fillfill couldcould bebe placed?placed? Main FactorsMain Factors 11.. HowHow highhigh aa fillfill couldcould bebe placed?placed? 22.. HowHow fastfast couldcould thethe fillfill bebe placed?placed? 33 Wh tWh t rr thth m im mm im m l pl p f rf r thth fill?fill?33.. WhatWhat werewere thethe maximummaximum slopesslopes forfor thethe fill?fill? 44.. CouldCould thethe fillfill bebe placedplaced withoutwithout employingemploying specialspecial t h it h i tt t it i d id i thth ftft f d tif d titechniquestechniques toto containcontain oror draindrain thethe softsoft foundationfoundation soil?soil? 55 HH hh ldld hh fillfill l ?l ?55.. HowHow muchmuch wouldwould thethe fillfill settle?settle? 66.. HowHow longlong shouldshould thethe fillfill bebe leftleft inin placeplace inin orderorder hh hh f d if d i bb dd hhthatthat thethe foundationfoundation bebe compressedcompressed enoughenough toto permitpermit constructionconstruction andand useuse ofof thethe tank?tank?
- 14. Example of Foundation HeaveExample of Foundation Heave •• OccursOccurs whenwhen foundationfoundation soilsoil expandsexpands whenwhen thethe confiningconfining pressurepressure isis reducedreduced andand // oror thethe waterwater contentcontentconfiningconfining pressurepressure isis reducedreduced andand // oror thethe waterwater contentcontent ofof thethe soilsoil isis increasedincreased •• AridArid regionsregionsgg •• PresencePresence ofof montmorillonitemontmorillonite
- 15. Main FactorsMain Factors •• ProperProper sizesize capacitycapacity lengthlength andand spacingspacing ofof thethe Main FactorsMain Factors ProperProper sizesize ,capacity,,capacity, lengthlength andand spacingspacing ofof thethe pilespiles •• TheThe pilepile shouldshould bebe longlong enoughenough toto extendextend belowbelow•• TheThe pilepile shouldshould bebe longlong enoughenough toto extendextend belowbelow thethe depthdepth ofof thethe soilsoil thatthat wouldwould expandexpand ThTh d hd h l dl d ii hh hh hh•• TheThe depthdepth selectedselected inin suchsuch aa wayway thatthat thethe confiningconfining pressurepressure fromfrom thethe soilsoil overburdenoverburden ll i ii i l dl d ii ffi iffi iplusplus minimumminimum loadload isis sufficientsufficient toto preventprevent expansionexpansion
- 16. CONSTRUCTION MATERIALCONSTRUCTION MATERIALCONSTRUCTION MATERIALCONSTRUCTION MATERIAL •• Select proper type of soilSelect proper type of soil •• Method of placementMethod of placement •• Control of actual placementControl of actual placement•• Control of actual placementControl of actual placement •• FillingFillinggg
- 17. Example of an Earth DamExample of an Earth Dam •• Two main zonesTwo main zones –– Clay coreClay coreyy –– Rock toeRock toe •• Gravel filterGravel filter •• Rock facingRock facing •• Zoned earth dam & homogeneous earth damZoned earth dam & homogeneous earth dam
- 18. Main FactorsMain Factors II.. WhatWhat shouldshould bebe thethe dimensionsdimensions ofof thethe damdam toto givegive thethe mostmost Main FactorsMain Factors economical,economical, safesafe structure?structure? 22.. WhatWhat isis thethe minimumminimum safesafe thicknessthickness forfor thethe gravelgravel layers?layers? 33.. HowHow thickthick aa layerlayer ofof gravelgravel andand rockrock facingfacing isis necessarynecessary toto33.. HowHow thickthick aa layerlayer ofof gravelgravel andand rockrock facingfacing isis necessarynecessary toto keepkeep anyany swellingswelling ofof thethe clayclay corecore toto aa tolerabletolerable amount?amount? 44.. WhatWhat moisturemoisture contentcontent andand compactioncompaction techniquetechnique shouldshould bebe employedemployed toto placeplace thethe gravelgravel andand clayclay materials?materials?employedemployed toto placeplace thethe gravelgravel andand clayclay materials?materials? 55.. WhatWhat areare thethe strengthstrength andand permeabilitypermeability characteristicscharacteristics ofof thethe constructedconstructed dam?dam? 66 HowHow wouldwould thethe strengthstrength andand permeabilitypermeability ofof thethe darndarn varyvary66.. HowHow wouldwould thethe strengthstrength andand permeabilitypermeability ofof thethe darndarn varyvary withwith timetime andand depthdepth ofof waterwater inin thethe reservoir?reservoir? 77.. HowHow muchmuch leakageleakage would,would, occuroccur underunder andand throughthrough thethe dam?dam? 88 WhWh ifif i li l i ii i hh ii ff hh88.. What,What, ifif any,any, specialspecial restrictionsrestrictions onon thethe operationoperation ofof thethe reservoirreservoir areare necessary?necessary?
- 19. Example of a Reclamation StructureExample of a Reclamation StructureExample of a Reclamation StructureExample of a Reclamation Structure •• NonNon--availabilityavailability ofofyy goodgood buildingbuilding sitessites •• HarborHarbor andand terminalterminalHarborHarbor andand terminalterminal facilitiesfacilities •• HydraulicHydraulic fillingfilling•• HydraulicHydraulic fillingfilling
- 20. Main FactorsMain FactorsMain FactorsMain Factors II.. HowHow deepdeep shouldshould thethe sheetsheet pilepile wallwall penetratepenetrate thethe foundationfoundation soil?soil? 22.. HowHow shouldshould thesethese pilespiles bebe bracedbraced laterally?laterally? 33.. WhatWhat isis thethe mostmost desirabledesirable patternpattern ofof fillfill placementplacement ii..ee..,, howhow33.. WhatWhat isis thethe mostmost desirabledesirable patternpattern ofof fillfill placementplacement ii..ee..,, howhow shouldshould thethe exitexit ofof thethe dredgedredge pipepipe bebe locatedlocated inin orderorder toto getget thethe firmerfirmer partpart ofof thethe fillfill atat thethe locationslocations wherewhere thethe maximummaximum foundationfoundation loadsloads wouldwould bebe placed?placed?pp 44.. WhatWhat designdesign strengthstrength andand compressibilitycompressibility ofof thethe hydraulichydraulic fillfill shouldshould bebe usedused forfor selectingselecting foundationsfoundations forfor thethe tanks,tanks, buildings,buildings, andand pumpingpumping facilitiesfacilities toto bebe placedplaced onon thethe island?island?g ,g , p p gp p g pp 55.. WhereWhere diddid thethe soilsoil finesfines inin thethe dirtydirty effluenteffluent whichwhich wentwent outout ofof thethe islandisland overover thethe spillwayspillway ultimatelyultimately settle?settle?
- 21. Example of Highway PavementExample of Highway PavementExample of Highway PavementExample of Highway Pavement •• Most common use of soil asMost common use of soil as constr ction materialconstr ction materialconstruction materialconstruction material •• PavementsPavements –– RigidRigid –– FlexibleFlexible
- 22. Main FactorsMain FactorsMain FactorsMain Factors 11.. HowHow thickthick shouldshould thethe variousvarious componentscomponents ofof thethe.. HowHow t ct c s o ds o d t et e va o sva o s co po e tsco po e ts oo t et e pavementpavement bebe toto carrycarry thethe expectedexpected loads?loads? 22.. WhatWhat isis thethe optimumoptimum mixturemixture ofof additivesadditives forforpp stabilizingstabilizing thethe desertdesert sand?sand? 33.. IsIs thethe desertdesert sandsand acceptableacceptable forfor thethe constructionconstruction ofof thethe wearingwearing surface?surface? 44.. WhatWhat gradegrade andand weightweight ofof availableavailable asphaltasphalt makemake hh i li l i fi f ii f ?f ?thethe mostmost economical,economical, satisfactorysatisfactory wearingwearing surface?surface? 55.. WhatWhat typetype andand howhow muchmuch compactioncompaction shouldshould bebe sed?sed?used?used?
- 23. SLOPES AND EXCAVATIONSSLOPES AND EXCAVATIONSSLOPES AND EXCAVATIONSSLOPES AND EXCAVATIONS (a) Natural Slope (b) Excavation for Building (c) Excavation for Pipe (d) Canal
- 24. UNDERGROUND AND EARTHUNDERGROUND AND EARTH T T TT T T •• SoilSoil--structure interactionstructure interaction RETAINING STRUCTURESRETAINING STRUCTURES SoilSoil structure interactionstructure interaction •• ExamplesExamples Pi h llPi h ll–– Pipe shellsPipe shells –– Basement walls of the buildingBasement walls of the building –– Sheet pile wallSheet pile wall –– TunnelsTunnelsTunnelsTunnels –– Drainage structuresDrainage structures
- 25. Example of Earth retaining structureExample of Earth retaining structureExample of Earth retaining structureExample of Earth retaining structure •• Anchored bulkheadAnchored bulkheadAnchored bulkheadAnchored bulkhead •• Take care of lateralTake care of lateral trtrstressesstresses •• Stability against shearStability against shear rupturerupture
- 26. 11 Wh tWh t t pt p ff llll (m t ri l(m t ri l ndnd rr ti n)ti n) h ldh ld bb d?d? Main FactorsMain Factors 11.. WhatWhat typetype ofof wallwall (material(material andand crosscross section)section) shouldshould bebe used?used? 22.. HowHow deepdeep mustmust thethe wallwall penetratepenetrate thethe foundationfoundation soilsoil inin orderorder toto preventprevent thethe wallwall fromfrom kickingkicking outout toto thethe leftleft atat itsits base?base? 33 AA hh h i hh i h hh llll h ldh ld hh hh ii bb l d?l d?33.. AtAt whatwhat heightheight onon thethe wallwall shouldshould thethe anchoranchor tietie bebe located?located? 44.. HowHow farfar fromfrom thethe wallwall shouldshould thethe anchoranchor tietie extend?extend? 55.. WhatWhat typetype ofof anchoringanchoring systemsystem shouldshould bebe employedemployed atat thethegg onshoreonshore endend ofof thethe anchoranchor tie?tie? (One(One wayway toto anchoranchor thethe wallwall isis toto useuse aa largelarge massmass ofof concrete,concrete, ii..ee..,, deaddead manman.. AnotherAnother wayway isis toto useuse aa systemsystem ofof pilespiles ;;includingincluding somesome drivendriven atat aa slopeslope withwith thethe verticalvertical;; suchsuch aa slopingsloping pilepile isis termedtermed aa batterbatter pile)pile)verticalvertical;; suchsuch aa slopingsloping pilepile isis termedtermed aa batterbatter pile)pile) 66.. WhatWhat waswas thethe distributiondistribution ofof stressesstresses actingacting onon thethe wall?wall? 77.. WhatWhat typetype ofof (drainage(drainage systemsystem shouldshould bebe installedinstalled toto preventprevent aa ll diff i ldiff i l ff d l id l i hh i idi id fflargelarge differentialdifferential waterwater pressurepressure fromfrom developingdeveloping onon thethe insideinside ofof thethe wall?wall? 88.. HowHow closeclose toto thethe wallwall shouldshould thethe loadedloaded cranecrane ((578578 kNkN whenwhen f llf ll l d d)l d d) bb p itt d?p itt d?fullyfully loaded)loaded) bebe permitted?permitted? 99.. WhatWhat restrictions,restrictions, ifif any,any, areare necessarynecessary onon thethe storagestorage ofof cargocargo onon thethe areaarea backback ofof thethe wall?wall?
- 27. Example of Buried PipelineExample of Buried PipelineExample of Buried PipelineExample of Buried Pipeline •• Fl iblFl ibl dd Ri idRi id PipPip•• FlexibleFlexible andand RigidRigid PipesPipes •• FailuresFailures –– FaultyFaulty constructionconstruction–– FaultyFaulty constructionconstruction –– ExcessExcess constructionconstruction loadload –– SaggingSagging ofof pipepipeSaggingSagging ofof pipepipe •• SelectSelect –– ProperProper thicknessthickness ofof thethepp pipepipe wallwall –– WorkoutWorkout andand supervisesupervise hh i ll ii ll ithethe installationinstallation
- 28. SPECIAL PROBLEMSSPECIAL PROBLEMSSPECIAL PROBLEMSSPECIAL PROBLEMS •• VibrationsVibrationsVibrationsVibrations •• Explosions and earthquakesExplosions and earthquakes S f i d i l fl id i h iS f i d i l fl id i h i•• Storage of industrial fluids in earth reservoirsStorage of industrial fluids in earth reservoirs •• FrostFrost •• Regional subsidenceRegional subsidence
- 29. Oil storageOil storageOil storageOil storage
- 30. Frost HeaveFrost HeaveFrost HeaveFrost Heave
- 31. SOLUTIONSSOLUTIONS SOIL MECHANICS Stress-strain properties Theoreticalproperties Theoretical analyses for soil masses GEOLOGY, EXPLORATION Composition of actual ENGINEERING JUDGEMENT Composition of actual soil masses EXPERIENCEEXPERIENCE ECONOMICSECONOMICS
- 32. Why Soil problems are UNIQUE?Why Soil problems are UNIQUE? 11.. SoilSoil doesdoes notnot possesspossess aa linearlinear oror uniqueunique stressstress--strainstrain relationshiprelationship 22.. SoilSoil behaviorbehavior dependsdepends onon pressure,pressure, time,time, andand environmentenvironment 33 ThTh ilil tt ti llti ll l til ti ii diff tdiff t33.. TheThe soilsoil atat essentiallyessentially everyevery locationlocation isis differentdifferent 44.. InIn nearlynearly allall casescases thethe massmass ofof soilsoil involvedinvolved isis underunder-- groundground andand cannotcannot bebe seenseen inin itsits entiretyentirety butbut mustmust bebegroundground andand cannotcannot bebe seenseen inin itsits entiretyentirety butbut mustmust bebe evaluatedevaluated onon thethe basisbasis ofof smallsmall samplessamples obtainedobtained fromfrom isolatedisolated locationslocations 55 MM ilil i ii i di bdi b ff55.. MostMost soilssoils areare veryvery sensitivesensitive toto disturbancedisturbance fromfrom sampling,sampling, andand thusthus thethe behaviorbehavior measuredmeasured byby aa laboratorylaboratory testtest maymay bebe unlikeunlike thatthat ofof thethe inin situsitu soilsoilyy yy
- 33. An Overview Particulate Nature of Soil Nature of Soil Deformation Role of Pore Phase Chemical InteractionChemical Interaction Physical Interaction Sharing the Load A brief look at Consolidation
- 34. Particulate Nature of Soilf • Soil is composed of microscopic or macroscopic discreteSoil is composed of microscopic or macroscopic discrete particles, which are not strongly bonded together as crystals • Soil particles are relatively free to move with respect to another, less fluent than the movement of fluid particlesp • Particulate system pertains to a system of particles, and theParticulate system pertains to a system of particles, and the science dealing with the stress-strain behavior of soils is referred as Particulate Mechanics
- 35. Nature of Soil Deformation • Contact forces develop due to applied forces • Contact forces are resolved into normal N and tangential T forces • The usual types of deformation in the vicinity of contact forces Elastic strain Plastic strain P i l hi d hi hParticle crushing under high stress
- 36. • Contact area enlarges due to the deformations and thus thethe deformations, and thus the center of the particles come closer (Fig. a) • Plate like particles bend to ll l iallow relative movement between adjacent particles (Fig. b)( g ) • Interparticle sliding occurs when the shear force at the contact surface exceeds the shear resistance of soil particleshear resistance of soil particle (Fig. c)
- 37. • Overall strain of a soil mass is the combined effect of particle deformation and interparticle slidingdeformation and interparticle sliding. • Relative sliding of soil particles result in rearrangement of soil• Relative sliding of soil particles result in rearrangement of soil particles , which is a nonlinear and irreversible phenomena, thus resulting in a non-linear and irreversible stress-strain behavior of soils. F i ti l d dh i f l ff ti i d i• Frictional and adhesion forces are also effective in producing particle deformation • There are 5 million contacts within 1 cm3 of sand mass. Hence, defining stress-strain relation of soil at each of the contacts is impossible, and thus one has to rely on experimental results
- 38. • If the box has rigid walls, and the vertical load is increasedthe vertical load is increased, the soil particles will nestle closer and closer. This is called Volumetric CompressionVolumetric Compression • Sliding failure will occur atg individual contacts, but the soil mass will not undergo an overall shear failureoverall shear failure • Removal of the load will result i f ilin Expansion or Swell of soil mass through a reverse process due to rearrangement of particles
- 39. • If the box has flexible walls,, the entire soil mass will undergo an overall shear failurefailure • The load at which failure occurs is called the Shear Strength of SoilStrength of Soil • Shear strength is determined by the resistance to sliding between particles movingbetween particles moving laterally to each other
- 40. Role of Pore Phase : Chemical Interaction • The spaces among the soil particles are called Pore Spaces • The spaces are usually filled with air and/or water (with or without dissolved matter) • Soil is a Multiphase system Mineral Phase (Mineral Skeleton) Fl id Ph (P Fl id)Fluid Phase (Pore Fluid) • Pore fluid influences the magnitude of the shear resistance existing between two particles by introducing chemical matter to the surface of contact • Pore fluid intrudes particle spaces and acts in transmission of normal and tangential forces
- 41. Role of Pore Phase : Physical InteractionRole of Po e Phase : Physical Inte action • Hydrostatic condition of watery pressure • The pressure in the pore water at any point is equal to the unit weight of water times theweight of water times the depth of the point below the water surface • In this case, there is no flow of water
- 42. • Water pressure at the base of• Water pressure at the base of box is increased, while overflows hold the water surface constant • Upward flow of water takes place, the amount of which is controlled by excess pressurecontrolled by excess pressure at base and Permeability of the soil mass • The more the permeable a soil, the more water will flow for athe more water will flow for a given excess pore pressure
- 43. • If the excess water pressure at• If the excess water pressure at the base is increased, a pressure will be reached where the sand will start to flow upwards along with the upward flowing water • It is called Quicksand condition or Sand Boilingcondition or Sand Boiling • The soil will occupy greaterpy g volume than initial state, and has less shear strength than normal conditionnormal condition
- 44. • Changes in volume and shear• Changes in volume and shear strength come about due to the changes in contact pressure between the particles • Contact forces are related to the difference between thethe difference between the stress pressing downward (Total Stress) and the Pore PPressure • This difference is defined as• This difference is defined as the Effective Stress
- 45. l f h h i h dRole of Pore Phase : Sharing the Load • As soil is a multiphase system, the load applied to a soil ld b i d i b h i l k l dmass would be carried in a part by the mineral skeleton and partly by the pore fluid • The sharing of the load is analogous to the partial pressure in gases, and is well simulated by the Hydromechanical Model for load sharing and consolidation.
- 46. • Fig (a) shows a cylinder of saturated soil • The porous piston permits load to be applied to saturated soilto be applied to saturated soil and yet permits escape of the fluid from the pores of the soil
- 47. • Fig (b) shows a• Fig (b) shows a hydromechanical analog in which the properties has been lumped • The resistance of the mineral skeleton to compression is represented by a springrepresented by a spring • The resistance to the flow of water through the soil is represented by a a valve in an otherwise impermeable pistonotherwise impermeable piston
- 48. • Fig (c) represents a load applied to the piston of the hydromechanicalthe piston of the hydromechanical analog but the valve is kept closed • The piston load is apportioned by the water and the spring • The piston will be moved very little th t i l i blas the water is nearly incompressble. The spring shortens very slightly as it carries a very little loady • Essentially all of the applied load is resisted by an increase in the fluid pressure within the chamber
- 49. • Fig (d) shows the valve to be opened • As water escapes, the spring shortens and begins to carry a significant fraction of the loadsignificant fraction of the load applied • There is a corresponding decrease in pressure in the chamber fluid
- 50. • Fig (e) shows a condition ing ( ) which all the applied load is carried by the spring • The pressure in the water has returned to the originalreturned to the original hydrostatic condition • Now, there is no further flow of water
- 51. • A limited amount of water can flow out through the valve at• A limited amount of water can flow out through the valve at any interval of time • The process of transferring load from water to the spring is a gradual process, which is shown in Fig (f)
- 52. • This process of gradual squeezing out of water from the pore spaces of soil mass is call Consolidation • The time interval involved in the above mentioned phenomena is called Hydrodynamic Time Lagphenomena is called Hydrodynamic Time Lag • The amount of compression that has occurred at any time isThe amount of compression that has occurred at any time is related to the applied load and also to the amount of stress transmitted at the particle contacts i.e. to the difference b t th li d t d th Thibetween the applied stress and the pore pressure. This difference gives the concept of Effective Stress
- 53. • The most important effect of Hydrodynamic Time Lag is• The most important effect of Hydrodynamic Time Lag is the delayed settlement of structures
- 54. Consolidation • The time required for consolidation process is related to :: The time should be directly proportional to the volume of water squeezed out of the soil. The volume of water is related to the product of stress change the compressibility of the mineralproduct of stress change, the compressibility of the mineral skeleton, and the volume of the soil Th i h ld b i l i l h f hThe time should be inversely proportional to how fast the water can flow through the soil. The velocity of flow is related to the product of the permeability and the hydraulic gradient. The gradient is ti l t th fl id l t ithi th il di id d b thproportional to the fluid pressure lost within the soil divided by the distance of the flow path of the fluid.
- 55. ( )( )( )HΔ( )( )( ) ( )( )Hk Hm t / σ Δ Δ ∝ ( )( )Hk /σΔ where, • t = The time required to complete some percentage of consolidation process • Δσ = The change in the applied stress Th ibilit f th i l k l t• m = The compressibility of the mineral skeleton • H = The thickness of the soil mass (per drainage surface) • k = The permeability of the soil• k = The permeability of the soil
- 56. The time required to reach a specified stage in the consolidation process is given by ::consolidation process is given by :: mH t 2 ∝ The above relation suggests that the consolidation time : k Increases with increasing compressibility Decreases with increasing permeability Increases rapidly with increasing size of soil mass Is independent of the magnitude of the stress change Soils with significant clay content requires long time for consolidation – from one year to many hundreds of yearsconsolidation from one year to many hundreds of years Coarse granular soils consolidates very quickly, in a matter of minutes
- 57. f lConsequences of Particulate Nature of Soilsof Soils
- 58. 1st Consequence Th d f i f f il i ll d bThe deformation of a mass of soil is controlled by interactions between individual particles, especially by sliding between particles
- 59. 2nd Consequence Soil is inherently multiphase and the constituents ofSoil is inherently multiphase, and the constituents of the pore phase will influence the nature of the mineral surfaces and hence affect the processes of force transmission at the particle contacts
- 60. 3rd Consequence Water can flow through the soil and thus interactWater can flow through the soil and thus interact with the mineral skeleton, altering the magnitude of the forces at the contacts between particles and influencing the compression and shear resistance of the soil
- 61. 4th Consequence When the load applied to a soil is suddenly changed, the change is carried by jointly by the pore fluid and by the mineral skeleton. The change in poreby the mineral skeleton. The change in pore pressure will cause water to move through the soil, h th ti f th il ill h ithhence the properties of the soil will change with time
- 62. Consolidation Theory Foundation Design andFoundation Design and Construction C ff d l iCofferdam analysis Landslide MechanismsL M m Famous Book F Th tFrom Theory to Practice in Soil Mechanics KARL VON TERZAGHI Mechanics (1883 - 1963) Father of Soil Mechanics
- 63. Fundamentals of soil mechanics. Consolidation h h fShear strength of cohesive soils Stability of earth slopesp Famous Book Fundamentals of DONALD WOOD TAYLOR Fundamentals of Soil Mechanics DONALD WOOD TAYLOR (1900 - 1955)
- 64. Soil ClassificationSoil Classification Seepage through hearth structures Shear Strengthg Best Teacher in The Harvard University ARTHUR CASAGRANDE y U C S G (1902 - 1981)
- 65. Application of soil mechanics to design and construction Evaluation andEvaluation and presentation of the results of research inf form suitable for ready use by they y practicing engineer Famous Book Soil Mechanics in Engineering Practice RALPH BRAZELTON PECK (1912 - ) Engineering Practice
- 66. Fundamentals of effective stress Pore pressures in claysclays Bearing capacity Slope stability Best Teacher in The Imperial College in The ALEC WESTLEY SKEMPTON g University of London C S S O (1914 – 2001)
- 67. Fundamentals of shear strength Sensitivity of clays bili f lStability of natural slopes Best Teacher and the First Director in The Norwegian Geotechnical LAURITS BJERRUM Institute (1918 – 1973)
- 68. Concepts of Active and Passive Earth Pressure Concept of Friction C i d hCoined the term “Cohesion” Add d h A d fAddressed the Academy of Science (Paris, 1773) presenting a modest "essay on the application of the rules of maxima and minima to certain statics problems relevant to CHARLES AUGUSTIN DE COULOMB architecture (1736 - 1806) Grandfather of Soil Mechanics
- 69. Active and Passive Earth Pressure theoriesE Pioneer with a d t i ti WILLIAM JOHN MAQUORN RANKINE determination (1820 - 1872)
- 70. Concepts in SlopeConcepts in Slope Stability Analysis Geotechnical professor emeritus at the Norwegian Technical University, Trondheim, NILMAR JANBU Norway (1920 - )
- 71. PIONEERING CONTRIBUTIONS on Strength and compressibility of compacted clay soilscompacted clay soils Strength and consolidation of natural deposits of soft clay Cracking of earth dams Frost action Flexible and rigid pavement designFlexible and rigid pavement design Analysis of buried conduits Pile foundations, stability of slopes, y p and embankments on soft clays Stress-deformation and liquefaction of sand, and methodologies for GERALD A. LEONARDS of sand, and methodologies for investigating failures (1921 – 1997)
- 72. 1. Engineer of the Year (Georgia Society of Professional Engineers), 1973 2. The Herschel Prize (The Boston Society of Civil Engineers) 1976Civil Engineers), 1976 3. The ASCE Middlebrooks Award, 1977 4. The Terzaghi Lecture, 1979 5 The ASCE Martin Kapp Lecture in New Y rk5. The ASCE Martin Kapp Lecture in New York, 1985 6. The Brooks Award, 1990 7 Elected to The National Academy of7. Elected to The National Academy of Engineering, 1994 8. The ASCE Middlebrooks Award, 1994 9. ASCE Forensic Engineer of the Year Award,g 1994 10. The ASCE Terzaghi Award, 1995 Heck of an Engineer & GEORGE F SOWERS g A Master of Anecdotes GEORGE F. SOWERS (1921 - 1996)
- 73. Mechanics of Pile Foundations and Soil-Pile Interaction AnalysisInteraction Analysis Soil Compaction Analytical Methods in Pavement Design Analytical and experimental techniques of earthquake engineeringengineering Father of Geotechnical HARRY BOLTON SEED Earthquake Engineering August 19, 1922 — April 23, 1989
- 74. Appropriate methods of calculation for Seismic Design of Foundations free Torsion Vibrating Pendulum tofree Torsion Vibrating Pendulum to determine the dynamical properties of soil R i d f th b ilResonance period of the subsoil Coastal Engineering and Dewatering Systemy Highly compressible soils kFamous Book Foundation Engineeringou dat o g ee g for Difficult Subsoil Conditions LEONARDO ZEEVAERT WIECHERS