A preview of soil behavior

this is the presentation of Dr. P. K. Basudhar, Dept of Civil Engineering, IIT Kanpur. it is good material to have a basic sight about soil mechanics and foundation. FOUNDATIONS • WHAT ARE FOUNDATIONS? • TYPES OF FOUNDATIONS – SHALLOW FOUNDATIONS – DEEP FOUNDATIONS • MAIN PROBLEM IN THE DESIGN – TO PREVENT SETTLEMENT • TOTAL SETTLEMENT • DIFFERENTIAL SETTLEMENT

An Overview

of Soil Mechanics

Dr P K Basudhar Dept of Civil Engineering

IIT Kanpur

Soil Problems

&

Solutions

A Preview of Soil Behavior Pioneers in

Soil Mechanics

CIVIL ENGINEER SOIL

Classic case of bad foundation

•• FigFig showsgg shows thethe PalacioPalacio dede laslas

this partpart ofof thethe citycity isis 77 mm

•• (Photograph(Photograph complimentscompliments ofof

Raul

Raul Marsal)Marsal)

Example of Shallow foundations

•• Fig Fig shows shows the the MIT MIT students

students centre centre

•• Mat Mat foundation foundation

•• Floatation Floatation technique technique

•• Floatation Floatation technique technique

during construction gg construction to to prevent prevent cave pp cave ins ins of of soil? soil?

33 Would Would itit be be necessary necessary to to lower lower the the water water table table in in order

order to to excavate excavate and and construct construct the the foundation foundation and, and, ifif so so h t h t me ns me ns sho ld sho ld be be sed sed to to omplish omplish this this

ifif so, so, what what means means should should be be used used to to accomplish accomplish this this lowering

lowering of of the the ground ground water water (dewatering)? (dewatering)?

44 Was Was there there aa danger danger of of damage damage to to adjacent adjacent buildings? buildings?

44 Was Was t e e t e e aa da ge da ge oo da age da age to to adjace t adjace t b d gs? b d gs? 55 How How much much would would the the completed completed building building settle settle and and would

would itit settle settle uniformly? uniformly?

66 For For what what stresses stresses and and what what stress stress distribution distribution should should the

the mat mat of of the the building building be be designed? designed?

Example of Deep foundations

•• MITMIT materialmaterial centrecentre hashasdeep

deep pilepp pppile foundationfoundation

•• PointPoint bearingbearing pilepile

•• FrictionFriction pilepilepp

•• Augering

Main Factors

I What type of pile should be used?

Main Factors

I What type of pile should be used?

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 what spacing should the piles be driven?

4 How should the piles be driven?

5 How much variation from the vertical should be permitted in a pile?

6 What was the optimum sequence for driving piles?

7 Would the driving of piles have an influence on

adjacent structures?

Example of Embankment

on Soft Soil

•• 10 10 77 m m embankment embankment on

on aa 99 88m m layer layer of of on

on aa 99 88m m layer layer of of soft

soft soil soil

•• Preloading Preloading technique technique

•• Preloading Preloading technique technique

•• Shear Shear rupture rupture should should not

not occur occur

Main Factors

11 How How high high aa fill fill could could be be placed? placed?

Main Factors

11 How How high high aa fill fill could could be be placed? placed?

22 How How fast fast could could the the fill fill be be placed? placed?

33 Wh t Wh t rr th th m im m m im m l p l p f r f r th th fill? fill?

33 What What were were the the maximum maximum slopes slopes for for the the fill? fill?

44 Could Could the the fill fill be be placed placed without without employing employing special special

t h i tt t i d i d i th th ft ft f f d ti d ti techniques

techniques to to contain contain or or drain drain the the soft soft foundation foundation soil?

55 H H hh ld ld hh fill fill l ?

55 How How much much would would the the fill fill settle? settle?

66 How How long long should should the the fill fill be be left left in in place place in in order order

Example of Foundation Heave

•• Occurs Occurs when when foundation foundation soil soil expands expands when when the the confining

confining pressure pressure is is reduced reduced and and // or or the the water water content content confining

confining pressure pressure is is reduced reduced and and // or or the the water water content content of

of the the soil soil is is increased increased

•• Arid Arid regions regions gg

•• Presence Presence of of montmorillonite montmorillonite

•• The The pile pile should should be be long long enough enough to to extend extend below below

•• The The pile pile should should be be long long enough enough to to extend extend below below the

the depth depth of of the the soil soil that that would would expand expand

CONSTRUCTION MATERIAL

•• Select proper type of soil

•• Method of placement

•• Control of actual placement

•• Control of actual placement

•• Filling

Example of an Earth Dam

•• Two main zones

–– Clay coreClay coreyy

–– Rock toeRock toe

•• Gravel filter

•• Rock facing

•• Zoned earth dam & homogeneous earth dam

Main Factors

II WhatWhat shouldshould bebe thethe dimensionsdimensions ofof thethe damdam toto givegive thethe mostmost

Main 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 toto

33 HowHow thickthick aa layerlayer ofof gravelgravel andand rockrock facingfacing isis necessarynecessary totokeep

keep anyany swellingswelling ofof thethe clayclay corecore toto aa tolerabletolerable amount?amount?

44 WhatWhat moisturemoisture contentcontent andand compactioncompaction techniquetechnique shouldshould bebeemployed

employed toto placeplace thethe gravelgravel andand clayclay materials?materials?

employed

employed toto placeplace thethe gravelgravel andand clayclay materials?materials?

55 WhatWhat areare thethe strengthstrength andand permeabilitypermeability characteristicscharacteristics ofof thetheconstructed

constructed dam?dam?

66 HowHow wouldwould thethe strengthstrength andand permeabilitypermeability ofof thethe darndarn varyvary

66 HowHow wouldwould thethe strengthstrength andand permeabilitypermeability ofof thethe darndarn varyvarywith

with timetime andand depthdepth ofof waterwater inin thethe reservoir?reservoir?

77 HowHow muchmuch leakageleakage would,would, occuroccur underunder andand throughthrough thethe dam?dam?

Example of a Reclamation Structure Example of a Reclamation Structure

•• Non Non availability availability yy of good

good building building sites sites

•• Harbor Harbor and Harbor Harbor and and terminal and terminal terminal terminal facilities

•• Hydraulic Hydraulic filling filling

•• Hydraulic Hydraulic filling filling

Main Factors

II HowHow deepdeep shouldshould thethe sheetsheet pilepile wallwall penetratepenetrate thethe foundationfoundationsoil?

22 HowHow shouldshould thesethese pilespiles bebe bracedbraced laterally?laterally?

33 WhatWhat isis thethe mostmost desirabledesirable patternpattern ofof fillfill placementplacement ii ee ,, howhow

33 WhatWhat isis thethe mostmost desirabledesirable patternpattern ofof fillfill placementplacement ii ee ,, howhowshould

should thethe exitexit ofof thethe dredgedredge pipepipe bebe locatedlocated inin orderorder toto getgetthe

the firmerfirmer partpart ofof thethe fillfill atat thethe locationslocations wherewhere thethe maximummaximumfoundation

foundation loadsloads wouldwould bebe placed?placed?pp

44 WhatWhat designdesign strengthstrength andand compressibilitycompressibility ofof thethe hydraulichydraulic fillfillshould

should bebe usedused forfor selectingselecting foundationsfoundations forfor thethe tanks,tanks,buildings,

buildings, andg , and pumpingpumping facilitiespp p gp g facilities toto bebe placedplaced onpp on thethe island?island?55 WhereWhere diddid thethe soilsoil finesfines inin thethe dirtydirty effluenteffluent whichwhich wentwent outout ofofthe

the islandisland overover thethe spillwayspillway ultimatelyultimately settle?settle?

Example of Highway Pavement

•• Most common use of soil as constr ction material

•• Pavements

–– Rigid Rigid –– Flexible Flexible

Main Factors

11 How How How thick How t c thick should t c s o d should the s o d t e the various t e va o s various components va o s co po e ts components of co po e ts oo t e of the the t e pavement

pavement be be to to carry carry the the expected expected loads? loads?

22 What What is is the the optimum optimum mixture pp mixture of of additives additives for for stabilizing

stabilizing the the desert desert sand? sand?

33 Is Is the the desert desert sand sand acceptable acceptable for for the the construction construction of of the

the wearing wearing surface? surface?

44 What What grade grade and and weight weight of of available available asphalt asphalt make make

hh i l i f ii f f ? ? the

the most most economical, economical, satisfactory satisfactory wearing wearing surface? surface? 55 What What type type and and how how much much compaction compaction should should be be

sed?

used?

SLOPES AND EXCAVATIONS

(a) Natural Slope (b) Excavation for Building

(c) Excavation for Pipe (d) Canal

UNDERGROUND AND EARTH

–– Pipe shells Pipe shells

–– Basement walls of the building Basement walls of the building

–– Sheet pile wall Sheet pile wall

–– Tunnels Tunnels

–– Drainage structures Drainage structures

Example of Earth retaining structure

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?

Main 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 totoprevent

prevent 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 ll d?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 systemgg system shouldshould bebe employedemployed atat thetheonshore

onshore endend ofof thethe anchoranchor tie?tie? (One(One wayway toto anchoranchor thethe wallwall isis totouse

use aa largelarge massmass ofof concrete,concrete, ii ee ,, dead dead man man AnotherAnother wayway isis toto useuse

aa systemsystem ofof pilespiles ;;includingincluding somesome drivendriven atat aa slopeslope withwith thethevertical

vertical;; suchsuch aa slopingsloping pilepile isis termedtermed aa batter batter pile) pile)

vertical

vertical;; suchsuch aa slopingsloping pilepile isis termedtermed aa batter batter 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 diffdiff i li l ff dd l il i hh i idi id fflarge

large differentialdifferential waterwater pressurepressure fromfrom developingdeveloping onon thethe insideinside ofofthe

the wall?wall?

88 HowHow closeclose toto thethe wallwall shouldshould thethe loadedloaded cranecrane ((578578 kNkN whenwhen

f ll

f ll l d d)l d d) bb pp itt d?itt d?

fully

fully loaded)loaded) bebe permitted?permitted?

99 WhatWhat restrictions,restrictions, ifif any,any, areare necessarynecessary onon thethe storagestorage ofof cargocargo ononthe

the areaarea backback ofof thethe wall?wall?

Example of Buried Pipeline

•• Fl ibl dd Ri idRi id PipPip

•• FlexibleFlexible andand RigidRigid PipesPipes

•• Failures

–– FaultyFaulty constructionconstruction

–– FaultyFaulty constructionconstruction–– ExcessExcess constructionconstruction loadload–– SaggingSagging ofSaggingSagging ofof pipeof pipepipepipe

the installationinstallation

SPECIAL PROBLEMS SPECIAL PROBLEMS

Oil storage

Frost Heave

Composition of actual

soil masses

EXPERIENCE

ECONOMICS

Why Soil problems are UNIQUE?

11 Soil Soil does does not not possess possess aa linear linear or or unique unique stress stress strain strain

relationship

22 Soil Soil behavior behavior depends depends on on pressure, pressure, time, time, and and

environment

33 Th Th ilil tt ti ll l l ti ti ii diff diff t t

33 The The soil soil at at essentially essentially every every location location is is different different

44 In In nearly nearly all all cases cases the the mass mass of of soil soil involved involved is is under

An Overview

™ Particulate Nature of Soil

™ Nature of Soil Deformation

™ Role of Pore Phase

¾ Chemical Interaction

¾ Physical Interaction

¾

¾ Sharing the Load

™ A brief look at Consolidation

Particulate Nature of Soil f

• Soil is composed of microscopic or macroscopic discreteSoil is composed of microscopic or macroscopic discreteparticles, 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 thescience dealing with the stress-strain behavior of soils is referred

as Particulate Mechanics

Nature of Soil Deformation

applied forces

• Contact forces are resolved into

normal N and tangential T forces

• The usual types of deformation in

the vicinity of contact forces

• Contact area enlarges due tothe deformations and thus thecenter of the particles come

closer (Fig a)

• Plate like particles bend to

between adjacent particles

(Fig b)

( g )

• Interparticle sliding occurswhen the shear force at thecontact surface exceeds theshear resistance of soil particle

(Fig c)

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

deformation and interparticle sliding

deformation and interparticle sliding

• Relative sliding of soil particles result in rearrangement of soil

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

• Frictional and adhesion forces are also effective in producing

particle deformation

• There are 5 million contacts within 1 cm 3 of sand mass Hence,

defining stress-strain relation of soil at each of the contacts isimpossible, and thus one has to rely on experimental results

• If the box has rigid walls, andthe vertical load is increased

the vertical load is increased,the soil particles will nestlecloser and closer This is called

Volumetric Compression

• Sliding failure will occur atgindividual contacts, but the soil

overall shear failure

• Removal of the load will result

in Expansion or Swell of soil

mass through a reverse process

particles

• If the box has flexible walls,,the entire soil mass will

failure

• The load at which failure

occurs is called the Shear

Strength of Soil

• Shear strength is determined

by the resistance to sliding

laterally to each other

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

¾ Mineral Phase (Mineral Skeleton)

¾ Fl id Ph (P Fl id)

¾ 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