Analysis of Expansive Soils

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Analysis ofAnalysis of

expansive soilsexpansive soils



Archana M Aparna P

[email protected] [email protected]

B.Tech IInd year

Department of civil Engineering

GAYATHRI VIDYA PARIAD !"##EGE "$ E%GI%EERI%G



ABSTRACT

Analysis and assessment of expansive soils is of utmost

importance while founding the structures, as these soils undergo largevolumetric changes even due to small fluctuations in water content. The

volumetric changes are very large in magnitude and they are responsible

for distress of structures. The amount of damage caused by expansive

soils is alarming. Estimated average annual loss in the world, attributed

to expansive soil movement is approximately 1, 50,!! millions ofrupees, which exceeds the combined average of annual damages from

floods, hurricanes, earth"ua#es and tornados. $n this paper various types

of damages caused by expansive soils are given. Through understanding

of engineering properties of soils are essential not only for using current

methods in the design of earth structures, but also to provide a #ey tofurther progress in the field of geotechnical engineering. This paper

contains the essential data of properties in the form of tables. According

to the characteristics and properties of swelling soils, various important

techni"ues, that has to be adopted, while constructing a foundation on

expansive soils is discussed in the present paper.



INTRODUCTION

%oil engineers did not recogni&e the problem of expansive

soils until 1'0.The increasingly extensive use of concrete slabs on

ground construction after 1(0 has further increased the damage to the

structure caused by expansive soils. )otentially expansive soils can be

found almost anywhere in the world. The countries in which expansive

soils have been reported as follows*

Argentina +uba $ndia %pain

Australia Ethiopia hana %outh Africa

-urma $srael exico Tur#ey

+anada $ran /hodesia %A

$n $ndia the expansive soil is called the blac# cotton soil

which covers ', 00,000 es". widely.



BEHAVIOUR OF EXPANSIVE SOILS

Expansive soils having inherent property of shrin#ing when it is dried and

swelling when water is absorbed. hen water is absorbed the clayey soilwhich had shrin# by the evaporation of pore water, the compression

forces between soil particles reduces considerably and elastic expansion

occurs and this causes swelling.

%hrin#ing

%welling



DAMAGES CAUSED BY EXPANSIVE SOILSDAMAGES CAUSED BY EXPANSIVE SOILS

2AAE% $3 EA/T4E3 2A% The hearting of the earthen dam made of clay core exhibits even small

swelling pressure, due to change in water content initiate sheer crac#s and thesemay cause instability to earthen .

2AAE% $3 -$2$3%4ori&ontal crac#s in interior corner of main walls due to shrin#ing of

foundation. 2iagonal crac#s in exterior arched walls supported by piers and from

footings because of swelling and shrin#age. 6ertical crac#s in the wall bottoms

occur due to lateral moments.

2AAE T7 +A3A%hen the side slopes at the canal are sub8ected to change in water

content these slopes are li&ely to get damaged if they are made 'p of the e(pan)ive

)oil).

.

2AAE T7 /7A2% The roads that pass through expansive sub grade are sub8ected to heaving

and settlement of treacherous soils. 3o full proof solution yet obtained and a ma8or

research effort $ndia has been directed to find a solution to the roads passing through

blac# cotton soil areas.



+rac# on roads +rac# in earth dam

2iagonal crac#

6ertical crac#





METHODS OF FOUNDATION PRACTICESMETHODS OF FOUNDATION PRACTICES

The following are the important methods to adopt, whileThe following are the important methods to adopt, whileconstructing foundations on expansive soils.constructing foundations on expansive soils.

9ootings with special cushions9ootings with special cushions %trip footing %trip footing +3%:% technology +3%:% technology +hemical stabili&ation+hemical stabili&ation oisture control oisture control ranular pile anchor ranular pile anchor %tiffened mat foundation%tiffened mat foundation



FOOTINGS WITH SPECIAL CUSHIONS:FOOTINGS WITH SPECIAL CUSHIONS:

$n this method the excavation is$n this method the excavation iscarried out up to the depth ofcarried out up to the depth ofgreater than depth of foundationgreater than depth of foundationand freely draining soil such as aand freely draining soil such as amixture of sand and gravel, ismixture of sand and gravel, isfilled up and compacted up tofilled up and compacted up to

base level of the foundation.base level of the foundation./einforced concrete footing is/einforced concrete footing isconstructed at this level and overconstructed at this level and overthis bric# wall may bethis bric# wall may beconstructed. ixture of sand andconstructed. ixture of sand andgravel is filled up loosely over thegravel is filled up loosely over the

footing. A cushion of granular soilfooting. A cushion of granular soilbelow the foundation absorbs thebelow the foundation absorbs theeffect of swelling and so theireffect of swelling and so theireffects on foundation willeffects on foundation willconsiderably reduce.considerably reduce.



STRIP FOOTINGSTRIP FOOTING

The design procedure used atThe design procedure used at

present for strip footings does not present for strip footings does notconsider the distortion mode ofconsider the distortion mode ofhogging when perimeter shrin#agehogging when perimeter shrin#agecauses corner down subsidence. $tcauses corner down subsidence. $twas reali&ed that conventional stripwas reali&ed that conventional stripfoundations with sand cushionsfoundations with sand cushions

were inade"uate reinforcing thewere inade"uate reinforcing theshallow strip footings was thenshallow strip footings was thentried and inverted ;T< foundations istried and inverted ;T< foundations isnow commonly used.now commonly used.

The common types of strip footingsThe common types of strip footings

that have been used for lightthat have been used for lightbuildings are*buildings are* i= nreinforced with plinth band i= nreinforced with plinth band ii= 3ominally reinforced with plinthii= 3ominally reinforced with plinth

band band

iii= 3ominally reinforced inverted T iii= 3ominally reinforced inverted T



CNS-MSM Technolo!

$n this technology we intercept cohesive non swelling soil layer below the

shallow foundations on expansive soils. The +3% concept is based on self

e"uilibrating phenomenon with a difference that clay minerals present in +3% are

non expanding such as #ainite, chlorine etc. The thic#ness of +3% needed to prevent transmission of swelling pressure and heave to the foundation. Thic#ness

depends upon swelling pressure, heave, index properties, density and compression

index of under laying expansive soil and also on the index properties, density and

compression index of +3% material. +3% can be obtained as a natural material or

can be produced by blending two or more materials.

MSM Technology

$n this technology we

intercept the layer of mechanically

stabili&ed mix over +3% intercepting

layer, to improve the bearing capacityof the system. 3ormally %

consists of graded aggregate, sand

and fines with more plasticity, similar

to that allowed in water bond

macadam mix $f possible better

compaction may be adopted.



CHEMICAL STABILISATIONCHEMICAL STABILISATION

%oils treated with calcium carbide do not easily pic#%oils treated with calcium carbide do not easily pic#up water, as it is deli"uescent and hygroscopic up water, as it is deli"uescent and hygroscopic

hen sodium chloride is added to the soil,hen sodium chloride is added to the soil,crystalli&ation occurs in the pores of the soil and itcrystalli&ation occurs in the pores of the soil and it

forms a dense hard mat. %o absorption of moisture isforms a dense hard mat. %o absorption of moisture is prevented. prevented.

)hosphoric acid combined with wetting agent can be)hosphoric acid combined with wetting agent can beused for stabili&ation of expansive soils as it reactsused for stabili&ation of expansive soils as it reactswith clay minerals and forms insoluble aluminumwith clay minerals and forms insoluble aluminum

phosphate, which serves as moisture proof. phosphate, which serves as moisture proof. %ome agents such as sodium silicate, al#yl chloro%ome agents such as sodium silicate, al#yl chloro

silanes, siliconate amines, and chrome lingning cansilanes, siliconate amines, and chrome lingning canbe used for the water proofing of the soils.be used for the water proofing of the soils.



MOISTURE CONTROLMOISTURE CONTROL

$f the water is$f the water is prevented from prevented frommoving into the soil,moving into the soil,under and near theunder and near thebuilding postbuilding post

construction, swellconstruction, swelland shrin#age isand shrin#age isreduced. 9or thatreduced. 9or thatmoisture barriers aremoisture barriers are placed around the placed around the

perimeter of the perimeter of thebuilding. Theybuilding. Theyefficiently reduce theefficiently reduce thevariations in watervariations in watercontent andcontent anddifferentialdifferential



GRANULAR PILE ANCHOR METHODGRANULAR PILE ANCHOR METHOD

ranular anchor pile is one, which the

foundation is anchored at the bottom of the

granular pipe, to the mild steel plate through a

central mild steel rod. This serves to hold the

particulate granular medium and prevents thegranular pile from being seared away by the

swelling soil and thus instrumental in mobili&ing

frictional resistance to uplift force on the

foundation. %o the uplift force caused on thefoundation is resisted by *

a= weight of the granular anchor pile

b= frictional resistance along the pile



STIFFEND MAT FOUNDATIONSTIFFEND MAT FOUNDATION::

The commonThe commonmethod of stiffeningmethod of stiffeningconsists of a slabconsists of a slabcast beams '>( mtscast beams '>( mtsapart bothapart both

longitudinally ?longitudinally ?laterally. The rigiditylaterally. The rigidityof mat minimi&eof mat minimi&edistortion of thedistortion of thesuper structure fromsuper structure from

both hori&ontal andboth hori&ontal andvertical movementsvertical movementsof foundation soil.of foundation soil.2ifferential heave2ifferential heavealso reduced whenalso reduced whenstiffens of slab andstiffens of slab and

super structure issuper structure is



CONCLUSONS!CONCLUSONS!

Deeper fo'ndation) are m'ch )afer than )hallo*Deeper fo'ndation) are m'ch )afer than )hallo*fo'ndation) a) they offer more frictional re)i)tance.fo'ndation) a) they offer more frictional re)i)tance.

Providing c')hion) 'nder the fo'ndation the effect ofProviding c')hion) 'nder the fo'ndation the effect of)*elling potential on fo'ndation.)*elling potential on fo'ndation.

Gran'lar Pile concept i) a ne* concept+ *hich i) moreGran'lar Pile concept i) a ne* concept+ *hich i) moreeffective and economically via,le than the e(i)tingeffective and economically via,le than the e(i)tingfo'ndation particle)+ partic'larly 'nder light )tr'ct're).fo'ndation particle)+ partic'larly 'nder light )tr'ct're).

A) moi)t're change) are re)pon)i,le for )*elling of A) moi)t're change) are re)pon)i,le for )*elling ofe(pan)ive )oil)+ it i) ,etter to provide moi)t're ,arrier)e(pan)ive )oil)+ it i) ,etter to provide moi)t're ,arrier)aro'nd the ,'ilding area to prevent the percolation ofaro'nd the ,'ilding area to prevent the percolation ofmoi)t're.moi)t're.

ome chemical) form *ater-proofing agent)+ *hen theyome chemical) form *ater-proofing agent)+ *hen theyare mi(ed *ith the )oil and prevent) the acce)) of theare mi(ed *ith the )oil and prevent) the acce)) of themoi)t're.moi)t're.



Thank youThank you



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Analysis of Expansive Soils

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