an overview of soil mechanics

8/3/2019 An Overview of Soil Mechanics

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An Overviewn Overviewn Overviewn OverviewoffffSoil Mechanicsoil Mechanicsoil Mechanicsoil Mechanics

Dr. P. K. Basudharr. P. K. BasudharDept of Civil Engineering

IIT Kanpur


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Soil Problemsoil Problemsoil Problemsoil Problems&Solutionsolutions

A Preview ofPreview ofSoil Behavioroil BehaviorPioneers inioneers inSoil Mechanicsoil Mechanicsoil Mechanicsoil Mechanics


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WHERE ?

SOIL AS A

FOUNDATION

SOIL RETAINING


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TYPES OF FOUNDATIONS

DEEP FOUNDATIONS MAIN PROBLEM IN THE DESIGN

TO PREVENT SETTLEMENT

TOTAL SETTLEMENT

DIFFERENTIAL SETTLEMENT


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StructuralStructural loadsloads arearecarriedcarried byby thethe soilsoil

directlydirectly underunder thethestructurestructure


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UsedUsed toto carrcarr thetheloadsloads toto firmfirm soilsoil atat

somesome de thde th


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FigFig.. showsshows thethe PalacioPalacio dede laslas

BellasBellas Artes,Artes, MexicoMexico CityCity The The 22 mm differentialdifferential

andand thethe buildingbuilding onon thethe rightright

necessitatednecessitated thethe stepssteps whichwhich

occurredoccurred

The The generalgeneral subsidencesubsidence ofof

(Photograph(Photograph complimentscompliments ofofRaulRaul Marsal)Marsal)


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FigFig showsshows thethe MITMIT

studentsstudents centrecentre

MatMat foundationfoundation

uu


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Main FactorsMain Factors11.. JustJust howhow deepdeep intointo thethe soilsoil shouldshould thethe buildingbuilding bebe

22.. WouldWould thethe excavationexcavation havehave toto bebe enclosedenclosed byby aa wallwalldurindurin constructionconstruction toto reventrevent cavecave--insins ofof soil?soil?

33.. WouldWould itit bebe necessarynecessary toto lowerlower thethe waterwater tabletable inin

orderorder toto excavateexcavate andand constructconstruct thethe foundationfoundation and,and,so,so, w aw a meansmeans s ous ou ee useuse oo accomp saccomp s ssloweringlowering ofof thethe groundground waterwater (dewatering)?(dewatering)?

44.. WasWas therethere aa dan erdan er ofof dama edama e toto ad acentad acent buildin s?buildin s?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?


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MITMIT materialmaterial centrecentre hashas

deedee ileile foundationfoundation

ReasonsReasons Basement space notBasement space not

desirabledesirable

No sand and gravel atNo sand and gravel att e s tet e s te

Not to disturbNot to disturbunder round utilitiesunder round utilities

PointPoint bearingbearing pilepile

FrictionFriction ileile

AugeringAugering


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..

2. What was the maximum allowable load for a pile?2. What was the maximum allowable load for a pile?

. w a spac ng s ou e p es e r ven. w a spac ng s ou e p es e r ven

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?


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Example of EmbankmentExample of Embankment

on Soft Soilon Soft Soil

1010..77 mm embankmentembankment..

softsoft soilsoil

ShearShear rupturerupture shouldshould

notnot occuroccur


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..

22.. HowHow fastfast couldcould thethe fillfill bebe placed?placed?

.. aa were were ee max mummax mum s opess opes oror ee

44.. CouldCould thethe fillfill bebe placedplaced withoutwithout employingemploying specialspecialec n quesec n ques oo con a ncon a n oror ra nra n ee soso oun a onoun a onsoil?soil?

.. owow mucmuc wou wou t et e sett esett e66.. HowHow longlong shouldshould thethe fillfill bebe leftleft inin placeplace inin orderorder

t att at t et e oun at onoun at on ee compressecompresse enougenoug toto

permitpermit constructionconstruction andand useuse ofof thethe tank?tank?


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Example of Foundation HeaveExample of Foundation Heave

OccursOccurs when when foundationfoundation soilsoil expandsexpands when when thethe

ofof thethe soilsoil isis increasedincreased

AridArid re ionsre ions

PresencePresence ofof montmorillonitemontmorillonite


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, ,, ,

pilespiles

uu uu xx ww

thethe depthdepth ofof thethe soilsoil thatthat wouldwould expandexpand ee eptept se ectese ecte nn sucsuc aa wayway t att at t et e

confiningconfining pressurepressure fromfrom thethe soilsoil overburdenoverburden

p usp us m n mumm n mum oaoa ss su c entsu c ent toto preventpreventexpansionexpansion


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Select proper type of soilSelect proper type of soil

Method of placementMethod of placement

uu

FillinFillin


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Example of an Earth DamExample of an Earth Dam

Two main zonesTwo main zones

Cla coreCla core

Rock toeRock toe

Gravel filterGravel filter

Rock facingRock facing

Zoned earth dam & homogeneous earth damZoned earth dam & homogeneous earth dam


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NonNon--availabilitavailabilit ofofgoodgood buildingbuilding sitessites

facilitiesfacilities


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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 atternattern ofof fillfill lacementlacement ii..ee.. howhow

shouldshould thethe exitexit ofof thethe dredgedredge pipepipe bebe locatedlocated inin orderorder toto getgetthethe firmerfirmer partpart ofof thethe fillfill atat thethe locationslocations wherewhere thethe maximummaximumfoundationfoundation loadsloads wouldwould bebe laced?laced?

44.. WhatWhat designdesign strengthstrength andand compressibilitycompressibility ofof thethe hydraulichydraulic fillfillshouldshould bebe usedused forfor selectingselecting foundationsfoundations forfor thethe tanks,tanks,buildin s,buildin s, andand um inum in facilitiesfacilities toto bebe lacedlaced onon thethe island?island?

55.. WhereWhere diddid thethe soilsoil finesfines inin thethe dirtydirty effluenteffluent whichwhich wentwent outout ofofthethe islandisland overover thethe spillwayspillway ultimatelyultimately settle?settle?


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Most common use of soil asMost common use of soil as

uu PavementsPavements

RigidRigid

FlexibleFlexible


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11.. HowHow thickthick shouldshould thethe variousvarious com onentscom onents ofof thethe

pavementpavement bebe toto carrycarry thethe expectedexpected loads?loads?22.. What What isis thethe o timumo timum mixturemixture ofof additivesadditives forfor

stabilizingstabilizing thethe desertdesert sand?sand?

33.. IsIs thethe desertdesert sandsand acceptableacceptable forfor thethe constructionconstruction ofofthethe wearingwearing surface?surface?

44.. WhatWhat gradegrade andand weightweight ofof availableavailable asphaltasphalt makemake

t et e mostmost econom ca ,econom ca , sat s actorysat s actory wear ngwear ng sur acesur ace55.. WhatWhat typetype andand howhow muchmuch compactioncompaction shouldshould bebe

useuse


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(a) Natural Slope (b) Excavation for Building

(c) Excavation for Pipe (d) Canal


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UNDERGROUND AND EARTHUNDERGROUND AND EARTH

--

RETAINING STRUCTURESRETAINING STRUCTURES

ExamplesExamples

P pe s e sP pe s e s

Basement walls of the buildingBasement walls of the building Sheet pile wallSheet pile wall

Drainage structuresDrainage structures


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Take care of lateralTake care of laterals ressess resses

Stability against shearStability against shear

rupturerupture


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Main FactorsMain Factors.. aa ypeype oo wawa ma er ama er a anan crosscross sec onsec on s ous ou ee useuse

22.. HowHow deepdeep mustmust thethe wallwall penetratepenetrate thethe foundationfoundation soilsoil inin orderorder totopreventprevent thethe wallwall fromfrom kickingkicking outout toto thethe leftleft atat itsits base?base?

.. tt w atw at e g te g t onon t et e wawa s ous ou t et e anc oranc or t et e ee ocateocate

44.. HowHow farfar fromfrom thethe wallwall shouldshould thethe anchoranchor tietie extend?extend?55.. What What typetype ofof anchoringanchoring systemsystem shouldshould bebe employedemployed atat thethe

onshoreonshore endend ofof thethe anchoranchor tie?tie? (One(One wayway toto anchoranchor thethe wallwall isis totouseuse 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 ver caver ca ;; sucsuc aa s op ngs op ng p ep e ss ermeerme aa66.. WhatWhat waswas thethe distributiondistribution ofof stressesstresses actingacting onon thethe wall?wall?77.. WhatWhat typetype ofof (drainage(drainage systemsystem shouldshould bebe installedinstalled toto preventprevent aa

argearge erent aerent a waterwater pressurepressure romrom eve op ngeve op ng onon t et e ns ens e oothethe wall?wall?88.. HowHow closeclose toto thethe wallwall shouldshould thethe loadedloaded cranecrane ((578578 kNkN whenwhen

u yu y oa eoa e ee perm eperm e99.. WhatWhat restrictions,restrictions, ifif any,any, areare necessarynecessary onon thethe storagestorage ofof cargocargo onon

thethe areaarea backback ofof thethe wall?wall?


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ex eex e anan gg pespes

FailuresFailures

ExcessExcess constructionconstruction loadload

Sa inSa in of of i ei e

SelectSelect

ProperProper thicknessthickness ofof thethe

pipepipe wallwall Workout Workout andand supervisesupervise

t et e nsta at onnsta at on


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Explosions and earthquakesExplosions and earthquakes

Storage o n ustr a u s n eart reservo rsStorage o n ustr a u s n eart reservo rs

FrostFrost Regional subsidenceRegional subsidence


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SOLUTIONSSOLUTIONS

SOIL MECHANICS

Stress-strain

ro erties Theoretical

analyses forsoil masses

GEOLOGY,

EXPLORATION

ENGINEERING

JUDGEMENTsoil masses


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Why Soil problems are UNIQUE?Why Soil problems are UNIQUE?

11.. SoilSoil doesdoes notnot possesspossess aa linearlinear oror uniqueunique stressstress--strainstrainrelationshiprelationship

22.. SoilSoil behaviorbehavior dependsdepends onon pressure,pressure, time,time, andandenvironmentenvironment.. ee soso aa essen a yessen a y everyevery oca onoca on ss ereneren

44.. InIn nearlynearly allall casescases thethe massmass ofof soilsoil involvedinvolved isis underunder--

evaluatedevaluated onon thethe basisbasis ofof smallsmall samplessamples obtainedobtainedfromfrom isolatedisolated locationslocations

.. ostost so sso s areare veryvery sens t vesens t ve toto stur ancestur ance romromsampling,sampling, andand thusthus thethe behaviorbehavior measuredmeasured byby aalaboratorlaborator testtest mama bebe unlikeunlike thatthat ofof thethe inin situsitusoilsoil


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An OverviewParticulate Nature of Soil

Nature of Soil Deformation

Role of Pore Phase

Physical Interaction

Sharing the Load

A brief look at Consolidation


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Particulate Nature of Soil

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 articles

Particulate s stem ertains to a s stem of articles and the

science dealing with the stress-strain behavior of soils is referred

as Particulate Mechanics


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Nature of Soil Deformation Contact forces develop due to

applied forces

Contact forces are resolved into

normal Nand tangential Tforces

The usual types of deformation in

the vicinity of contact forces

Elastic strain

Plastic strain

Particle crushing under high stress


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Contact area enlarges due to

,center of the particles come

closer (Fig. a)

Plate like particles bend to

allow relative movement

between adjacent particles

Fi . b

Interparticle sliding occurs

when the shear force at thecontact surface exceeds the

(Fig. c)


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Overall strain of a soil mass is the combined effect of particle

e orma on an n erpar c e s ng.

particles , which is a nonlinear and irreversible phenomena, thusresulting in a non-linear and irreversible stress-strain behavior of

soils.

r c ona an a es on orces are a so e ect ve n pro uc ng

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


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If the box has rigid walls, and

,the soil particles will nestlecloser and closer. This is called

Slidin failure will occur atindividual contacts, but the soilmass will not undergo an

v

Removal of the load will result

in Expansion or Swellof soilmass through a reverse processdue to rearrangement ofparticles


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If the box has flexible walls

the entire soil mass will

undergo an overall shear

a ure

The load at which failure

occurs is called the Shear

Shear strength is determinedby the resistance to sliding

laterally to each other


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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)

u ase ore u

Pore fluid influences the magnitude of the shear

resistance existing between two particles byintroducing chemical matter to the surface of

contact

Pore fluid intrudes particle spaces and acts in

transmission of normal and tangential forces


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Role of Pore Phase : Physical Interactionole of Po e Phase : Physical Inte action H drostatic condition of water

pressure

The pressure in the pore water

at any point is equal to the unit

depth of the point below the

water surface

In this case, there is no flow of

water


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a er pressure a e ase obox is increased, while

overflows hold the water

surface constant

Upward flow of water takes

place, the amount of which is

at base and Permeability of the

soil mass

The more the permeable a soil,

given excess pore pressure


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e excess wa er pressure athe 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

The soil will occu reater

volume than initial state, andhas less shear strength than


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l f h h i h dole of Pore Phase : Sharing the Load As soil is a multiphase system, the load applied to a soil

mass 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

Modelfor load sharing and consolidation.


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Fig (a) shows a cylinder of

saturated soil

The porous piston permits load

and yet permits escape of the

fluid from the pores of the soil


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g s ows ahydromechanical analog in

which the properties has been

lumped

The resistance of the mineral

skeleton to compression is

The resistance to the flow of

water through the soil isrepresented by a a valve in an


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Fig (c) represents a load applied to

e p s on o e y romec an caanalog but the valve is kept closed

The piston load is apportioned by thewater and the spring

The piston will be moved very little

as t e water s near y ncompress e.

The spring shortens very slightly as it

carries a ver little load

Essentially all of the applied load is

resisted by an increase in the fluid

pressure within the chamber


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Fig (d) shows the valve to be

opened

As water escapes, the spring

shortens and begins to carry a

applied

There is a corresponding decreasein pressure in the chamber fluid


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Fi e shows a condition in

which all the applied load is

carried by the spring

The pressure in the water has

hydrostatic condition

Now, there is no further flowof water


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any interval of time

The process of transferring load from water to the spring is agradual process, which is shown in Fig (f)


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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

related to the applied load and also to the amount of stress

transmitted at the particle contacts i.e. to the difference

etween t e app e stress an t e pore pressure. s

difference gives the concept ofEffective Stress


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the delayed settlement of structures


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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

,

skeleton, and the volume of the soil

e t me s ou e nverse y proport ona to ow ast t e 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

propor ona o e u pressure os w n e so v e y e

distance of the flow path of the fluid.


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mt

where,

t = The time required to complete some percentage ofconsolidation process

= The change in the applied stress

m = e compress ty o t e m nera s e eton

H= The thickness of the soil mass (per drainage surface)

=

The time required to reach a specified stage in the


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The time required to reach a specified stage in the

mHt

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

Coarse granular soils consolidates very quickly, in a matter

of minutes


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f lonsequences of Particulate Natureof Soilsf Soils


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1st ConsequenceThe deformation of a mass of soil is controlled by

interactions between individual particles, especiallyby sliding between particles


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2nd Consequence,

the pore phase will influence the nature of the

mineral surfaces and hence affect the processes of

force transmission at the particle contacts


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3rd Consequence

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


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4th ConsequenceWhen the load applied to a soil is suddenly changed,

the change is carried by jointly by the pore fluid and

pressure will cause water to move through the soil,

ence e proper es o e so w c ange w

time

Consolidation Theory


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Construction

o er am ana ysis

Landslide MechanismsFamous Book

rom eory oPractice in Soil

K ARL VON TERZAGHI(1883 - 1963)

Father o f So i l Mechanic s

Fundamentals of soilmechanics


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mechanics.

Consolidation

S ear strengt o

cohesive soils

Stability of earth

slo es Famous Book

DONALD WOOD TAYLORSoil Mechanics

DONALD WOOD TAYLOR1900 - 1955


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Seepage through

eart structures

Shear Stren th

Best Teacher in TheHarvard Universit

ARTHUR CASAGRANDEC S G(1902 - 1981)

Application of soilmechanics to design


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mechanics to design

and construction

presentation of theresults o research inform suitable for

read use b thepracticing engineerFamous Book

Soil Mechanics in

RALPH BRAZELTON PECK(1912 - )

Fundamentals ofeffective stress


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effective stress

Pore pressures in

Bearing capacity

Slope stability

Best Teacher in The

Imperial College in The

ALEC WESTLEY SK EMPTONUniversity of LondonC S S O(1914 2001)

Fundamentals of shearstrength


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strength

Sensitivity of clays

Sta i ity o natura

slopes

Best Teacher and theFirst Director in The

Norwegian Geotechnical

LAURITS BJ ERRUMInstitute(1918 1973)


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Active and PassiveEarth Pressure theories

Pioneer with a

WILLIAM J OHN MAQUORN RANK INEeterm nat on(1820 - 1872)


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Stability Analysis

Geotechnical professor

emeritus at theNorwegian Technical

University, Trondheim,

NILMAR J ANBUNorway(1920 - )


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1. Engineer of the Year (Georgia Society ofProfessional Engineers), 1973

2. The Herschel Prize (The Boston Society of


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,

3. The ASCE Middlebrooks Award, 1977

4. The Terzaghi Lecture, 1979

. e ar n a ec ure n ew or ,1985

6. The Brooks Award, 1990

.Engineering, 1994

8. The ASCE Middlebrooks Award, 1994

9. ASCE Forensic En ineer of the Year Award,1994

10. The ASCE Terzaghi Award, 1995

Heck of an En ineer &

GEORGE F SOWERSA Master of Anecdotes

GEORGE F. SOWERS(1921 - 1996)

Mechanics of PileFoundations and Soil-Pile


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Soil Compaction

Analytical Methods in

Pavement Design

Analytical and experimentaltechniques of earthquake

Father of Geotechnical

HARRY BOLTON SEEDEarthquake EngineeringAugust 19, 1922 April 23, 1989

Appropriate methods of calculationfor Seismic Design of Foundations


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determine the dynamical properties ofsoil

esonance per o o e su so

Coastal Engineering and DewateringSystem

Highly compressible soils

kamous BookFoundation En ineerin

for Difficult SubsoilConditions

LEONARDO ZEEVAERT WIECHERS


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an overview of soil mechanics

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