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Analysis ofAnalysis of
expansive soilsexpansive soils
7/24/2019 Analysis of Expansive Soils
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Archana M Aparna P
[email protected] [email protected]
B.Tech IInd year
Department of civil Engineering
GAYATHRI VIDYA PARIAD !"##EGE "$ E%GI%EERI%G
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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.
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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.
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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
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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.
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+rac# on roads +rac# in earth dam
2iagonal crac#
6ertical crac#
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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
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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.
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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
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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.
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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.
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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
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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
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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
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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.
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Thank youThank you