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CHARACTERIATION ANDCONTROL MEASURES FOR
EXPANSIVE SOIL
Prof. P.V. SIVAPULLAIAH
Department of Civil Engineering
Indian Institute of Science, angalore ! "#$ $%&
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SOILS WITH SPECIAL PROPERTIESSOILS WITH SPECIAL PROPERTIES
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1.Expansive Sois ! Soils that swell and shrink with change in
moisture content
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Warped sidewalk due to
collapsing soils near Meeker,
Colorado.
Photo by Jon White
Hydrocompaction or collapsing soil
caused this driveway to drop inches.
Photo by J. White
". Coapsi#e Sois ! Soils that have
potential to collapse and possess
porous te"tures with high void ratios
and relatively low densities.
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$.La%e&i%i' Sois ! #hese soils are so$t, clay!rich hori%ons
showing marked iron segregation or mottling and also to gravelly
materials comprised mainly o$ iron o"ide concretions or pisoliths.
&ecause o$ the presence o$ a hardened crust near the sur$ace, thestrength o$ laterite may decrease with increasing depth. Possesses
a wide range o$ void ratios and pore si%es.. Many partially
saturated tropical residual soils are collapsible.
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(.Dispe&sive Sois ! 'ispersive soils contain a higher content o$
dissolved sodium (up to )*+ in their pore water than ordinary
soils. Serious piping damage to embankments and $ailures o$earth dams.
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).Sois o* A&i+ Re,ions ! #hese are e"tensive saline $lats that
are underlain by sand, silt or clay and o$ten are encrusted with
salt. -roundwater in coastal sabkhas is recharged directly $rom
the sea, $rom inland sources or by in$iltration o$ seawater blown inland by on!shore winds. Minerals that are precipitated
$rom groundwater in arid problems are increased permeability,
reduced density and settlement.
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-.Pea%!Soils containing partially decomposed and disintegrated
plant remains preserved under conditions o$ incomplete aeration
and high water content.
• #he void ratio o$ peat ranges between , $or dense amorphousgranular peat, up to */, $or $ibrous types.
• 0t usually tends to decrease with depth within a peat deposit.
• #he bulk density o$ peat is both low and variable.
• Peats $re1uently are not saturated and may be buoyant under
water due to the presence o$ gas.
• 2"cept at low water contents with high mineral contents, the
average bulk density o$ peats is slightly lower than water• #he dry density is in$luenced by the mineral content and higher
values than that 1uoted can be obtained when peats possess high
mineral residues.
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F&o/en Soi ! 3ound in regions where the winter temperatures
rarely rise above $ree%ing point and the summer temperatures
are only warm enough to cause thawing in the upper meter or
so.
• 3ro%en granular soils e"hibit a reasonable high compressive
strength only a $ew degrees below $ree%ing.
• 3ro%en soil undergoes appreciable de$ormation under
sustained loading.
• 4s the soil thaws downwards the upper layers become
saturated and, since water cannot drain through the $ro%en soil
beneath, it may su$$er a complete loss o$ strength. 4s ice melts,
settlement occurs.. 2"cess pore pressures develop when the rate
o$ ice melt is greater than the discharge capacity o$ the soil.
• Shrinkage presents another problem when soil is sub5ected to
$ree%ing.
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3ig. F&o/en Soi
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COMMON SOIL MINERALSCOMMON SOIL MINERALS
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CLA0 MINERALSCLA0 MINERALS
• #he clay minerals and soil organic matter are colloids.
• #he most important property o$ colloids is their small si%eand large sur$ace area. #he total colloidal area o$ soil colloids
may range $rom )6 m*7g to more than 66 m*7g depending the
e"ternal and internal sur$aces o$ the colloid.
• Soil colloids also carry negative or positive charges on theire"ternal and internal sur$aces.
• Soils colloids play a very important role in the chemical
reaction which take play in soil
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T0PE OF CLA0 MINERALST0PE OF CLA0 MINERALS
#here are $our ma5or types o$ clay minerals . ! layer silicates,
the metal o"ides and hydro"ides and o"y!o"ides, amorphous
and allophanes, and crystalline chain silicates
SILICATE CLA0SSILICATE CLA0S
• #he silicate clays are layers o$ tetrahedral and octahedral
sheets.
• #he basic building blocks o$ tetetrahedral and octahedral
sheets are the silica tetrahedron and the aluminum octahedra.
• #he Si89
cation occurs in $our$old and tetrahedralcoordination with o"ygen whilst the al:9 is generally $ound in
si" $old or octahedral coordination
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• ;ayer silicate minerals are sometimes de$ined on the basis o$
the number o$ certain positions occupied by cations. When
two!thirds o$ the octahedral positions are occupied , the
mineral is called dioctahedral (gibbsite or yellow sheet< Whenall : positions are occupied it is called trioctahedral (brucite or
blue sheet.
• When one octahedral sheet is bonded to one tetrahedral sheet
a )=) clay mineral results. Presence o$ sur$ace and broken !edge oh groups gives the kaolinite clay particles their electro!
negativity and their capacity to absorb cations.
• 0n *=) clay mineral an octahedral sheet is bonded to two
tetrahedral sheets. #he octahedral sheet is generallysandwiched between the two tetrahedral sheets.
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• #he *=) clays can be classi$ied into e"panding (smectites
and non!e"panding clays (illite and micas on the basis o$ thesheet where isomorphous susbstitution is taking
predominantly taking place.
• 0n the *=)=) lattice clays, a positively charge brucite sheet
sandwiched between layers restricts swelling, decreases
e$$ective sur$ace area, and decreases the e$$ective cec o$
mineral.
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CHARE DEVELOPMENT ON CLA0SCHARE DEVELOPMENT ON CLA0S
• #wo main sources o$ charge in clay minerals areisomorphous substitution and ph!dependent charges.
• Charge development o$ on silicate clays is mainly due to
iso2o&p3o4s s4#s%i%4%ion. #his is the substitution o$ one
element $or another in ionic crystals with out change o$ thestructure. 0t takes place during crystalli%ation and is not sub5ect
to change a$terwards.
• 0t takes places only between ions di$$ering by less than about
)6+ to )/+ in crystal radii.. 0n tetrahedral coordination, 4l:9 $or Si89 and in octahedral coordination Mg*9, 3e*9, 3e:9 $or 4l:9.
Charges developed as a result o$ isomorphous substitution are
permanent and not ph!dependent.
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• 0n allophanes, some silicate clays e.-. >aolinite, and the
metal o"ides the charges are termed ph !dependent charges
as they vary with the ph o$ the soil.
• pH depend charges may either be positive or negative
depending on the ph o$ the soil.
• 4cid soils tend to develop positive charges because o$ the protonation o$ the oh group on the o"ide sur$aces.
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SWELLIN ! INCREASE IN VOLUMESWELLIN ! INCREASE IN VOLUME
D4e %o Re+4'%ion in No&2a S%&ess
When a soil is sub5ect to a reduction in total normal stress the
scope $or volume increase is limited because particle
rearrangement due to a total stress increase is largely
irreversible.
D4e %o Wa%e& Con%en% In'&ease
?olume increase due to swelling does not always accompany
water content increase on rewetting o$ a soil. 4 dry soil can
take up water, with air in the voids being replaced by water,without a conse1uent increase in volume. #his occurs
typically $or sandy and silty soils.
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• Swelling o$ clay soils is usually an e$$ect associated with
particle hydration.
• #he adsorbed water surrounding clay mineral particles will
e"perience recoverable compression due to increase in
interparticle $orces, especially i$ there is $ace!to!$ace
orientation o$ the particles.
• When a decrease in total normal stress takes place in a soil
there will thus be a tendency $or the soil skeleton to e"pand
to a limited e"tent, especially in soils containing an
appreciable proportion o$ clay mineral particles.
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The hydration of particles is mainly due to :
C'arge on cla( particle surface, )'ic' is
responsi*le for interaction )it' )ater anddevelopment of electrical dou*le la(er .
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SWELLIN SOILSSWELLIN SOILS
• Mon%2o&ioni%e
• Ve&2i'4i%e an+
• So2e 2ixe+ a5e& 2ine&as i6e 2on%2o&ioni%e o&
#ei+ei%e7 in%e&a5e&e+ 8i%3 '3o&i%e o& 8i%3 a 2i'a
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MINEROLO0 OF EXPANSIVE SOILSMINEROLO0 OF EXPANSIVE SOILS
2"posed o"ygen
0somorphous substitution
;arge negative charges
@epulsion
S%&4'%4&e o* 2on%2o&ioni%e
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PHASES + S-ELLI/PHASES + S-ELLI/
Part of the sorbed water fills the pores and part is
oriented on the surface of the particles to produce theswelling.
Thus swelling occurs in two phases.
First the relatively faster swelling due to flow of water due
to release of water stresses in the partially saturated
voids of the soil.
Then the secondary slow swelling due to progressivehydration of active clay mineral within the soil.
Volume increase due to swelling does not always
accompany water content increase.
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STAES OF SWELLINSTAES OF SWELLIN
First stage is when the initial distance between the particles
is less than *nm. 'uring this stage, the swelling is opposed by
the electrostatic attraction between cations and negatively
charged layers.
Second stage is swelling beyond *nm and is possible
provided the hydration energy o$ cation is more than theenergy o$ attraction.
Swelling continues to the second stage i$ only monovalent
cations are present. #he distance between the neighbouring
sheets rises smoothly up to tens o$ nm.
0n third stage, the sheets are totally separated and $orm an
arrangement caused by edge to $ace and edge to edge $orces.
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S%a,es o* s8ein,
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S8e po%en%ia isS8e po%en%ia is
'e$ined as percentage o$ swell under a )!psi surcharge o$
laterally con$ined specimen compacted at AMC to M''
Correlated with activity o$ clay content, P0, S0 etc. (Seed et
al., @anganatham and Satyanarayana
Swelling and shrinkage are related.
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SWELL POTENTIAL OF CLA0S DEPENDS ONSWELL POTENTIAL OF CLA0S DEPENDS ON
4mount and type o$ clay minerals present,
#ype o$ e"changeable ions,
2lectrolyte content o$ the a1ueous solution,
Particle!si%e distribution,
?oid si%e and distribution,
Water content,
Superimposed load.
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PREDICTION OF AMOUNT OF SWELLINPREDICTION OF AMOUNT OF SWELLIN
Time versus percent swelling is similar to that of a
rectangular '(per*ola.
t/s = c m!t.
STA9ILI:ATIONSTA9ILI:ATION
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STA9ILI:ATIONSTA9ILI:ATION
•The alteration of properties of the e"isting soil
so as to create a new site material capable ofmeeting the specific engineering re#uirement is
called soil sta*ilisation.
•The properties of a soil may be altered in manyways$ among which included are c'emical,
t'ermal, mec'anical and ot'er means.
•%ecause of the great variability of soils$ no one
method is ever successful in more than a
limited number of soils.
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STA9ILI:ATION OF EXPANSIVE SOILSSTA9ILI:ATION OF EXPANSIVE SOILS
Treatment procedures that are available forstabili&ing e"pansive soils are:
√ C'emical additives√ Pre0)etting
√ Soil replacement )it' compaction control
√ Surc'arge loading
√ 1'ermal met'ods
SELECTION OF METHODSELECTION OF METHOD
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SELECTION OF METHODSELECTION OF METHOD
'eotechnical site investigations and testing
programs (ome factors of special interest are:
⇒ Potential for volume change⇒ )epth of active &one
⇒ )egree of fracturing⇒ *eterogeneity or uniformity of soil on site⇒ +ime reactivity of the soil⇒ Presence of undesirable chemical compounds
⇒ ,oisture variation within the soil mass⇒ (oil permeability⇒ (trength of the soil needed for the pro-ect
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STA9ILI:ATION 90 CHEMICAL ADDITIVESSTA9ILI:ATION 90 CHEMICAL ADDITIVES
Treatment of e"pansive soils is either to
a convert the soil to a rigid granular mass$ the
particles of which are sufficiently strongly bound
to resist the internal swelling pressure of the clayor
b retard moisture movement within the soil.
Provided the retardation is sufficient to overcomenormal seasonal changes 0 it is ade#uate for
practical purposes.
'on%in4e+
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•1mpervious membranes are available and useful$
unless they wholly isolate the area to be stabili&ed
their function will be merely to lengthen the pathand hence time of the moisture movement.
•2ther than loading to restrict swell$ there is no
good alternative to stabili&ation to overcome thedisruptive effects of moisture changes in an
e"pansive soil.
•)ensification is almost always a useful means for
upgrading the mechanical properties of a soil$
whatever additional stabili&ation systems are
employed.
'on%in4e+;
'on%in4e+;
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• 3hemical admi"ture eg. lime
stabili&ation has been e"tensively used in
both shallow and deep stabili&ation to
improve inherent properties of soil.
• 4n increment in strength a reduction incompressibility an improvement of the
swelling or s#uaring characteristics and
increasing durability of the soil are the main
aims of the admi"ture stabili&ation.
'on%in4e+;
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MECHANISM OF LIME STA9ILI:ATIONMECHANISM OF LIME STA9ILI:ATION
The ma-or strength gain of lime treated clay is
mainly derived from these reactions.
• De'(dration of soil• Ion e2c'ange and flocculation• Po33olanic reaction
3arbonation cause minor strength increase
(hort time reaction include hydration andflocculation$
+ong term reactions are cementation and
carbonation.
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H(dration reaction
3a2 *52 → 3a 2*5 *eat
3a2*5 → 3a5 52*6
578 calories/gm of 3a2
Ion E2c'ange reaction
3a 3lay → 3a 3lay 9a$
Po33olanic 4eaction
3a
5 2*6
(i 25 →
3(*3a 5 2*6 4l52; → 34*
Car*onation
3a 2*5 325 → 3a 32; *52
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actors controlling t'e c'aracteristics of Lime
1reated Cla(
1(pe of Lime
+ime 3ontent 6
+ime Fi"ation Point optimum lime content
3uring Time 6 Testing Procedures
1(pe of Soil 0
'rain (i&e )istribution$ 3lay mineral soil p*
3uring Temperature
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Effect of Dela(ed Compaction
• Time interval between wet mi"ing and
compaction of a soil6lime mi"es generally ta>es
place due to some unavoidable interruptions in
construction$ non 6 availability of rollers in propertime and lac> of proper supervision.
• )elay in compaction reduces the strength.
• The delay upto 5/? hours is not substantial.
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Appi'a%ion Me%3o+sAppi'a%ion Me%3o+s
,i"ed in Place and
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5i2ed in Place and 4ecompacted
,i" mechanically with either a disc harrow or asmall ripper. )ifficult to mi" deeper than ;88 mm.
Drill Hole Lime
1ntroduce #uic> or hydrated lime in slurry form
into holes.
*oles AB8 to ;88 mm in dia. are drilled throughthe pavement to depths of CB8 to A5B8 mm.
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Pressure0In6ected Lime
P1+ or +(P1 techni#ue was developed toproduce greater lime slurry penetration in the
drill6hole.
+ime slurry is pumped through hollow in-ectionrods at pressures of about ;88mm.
(lurry is in-ected until either the soil will not ta>e
additional slurry$ or until in-ection begin tofracture or distort the surface.
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Dr( 6et mi2ing met'od
Duic>lime is in-ected into deep ground through
a no&&le pipe with the aid of compresses air
and then the powder is mi"ed mechanically byrotary wings.
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-et 7et /routing mi2ing met'ods
(lurry is in-ected into the clay by a pressure of58 ,Pa from a rotating no&&le.
The diameter of improved column trends to vary
with depth according to the vartiations of thesubsoil shear strengths.
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LI5E PILES
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LI5E PILES
2ffers an effective and ine"pensive method of
compacting saturated soils.
+arge )ensity difference between o"ide ;.;
and hydro"ide 5.5 which gives rise to
e"pansion on hydration.
+ime piles can be installed in saturated soils by
means of a special tube with a closed tip$ holes
being driven to depths of B 6 7 m and spread at
A.B 6 5.Bm centres. Then the tube is withdrawnfrom the soil and the hole is filled with lumps of
#uic>lime. 3asing used is removes as the
#uic>lime is placed. The #uic>lime is pac>ed by
tamping.
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Procedure $or construction o$ ;ime Piles in slopes
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Lime Columns
+ime drains can be installed in6situ by means ofa tool reminiscent of a giant eggbeaterG. The
mast and the rotary table are usually mounted
on a front wheel6 loader. 4 container is attached
to the loader to store the unsla>ed lime. 1t ta>es
about A8 min to install a drain to a depth of A8m.
The tool is screwed into the soil to the re#uired
depth of the drain. The rotation then is reversedand unsla>ed lime is forced into the soil$ by
compressed air$ through openings placed -ust
above the blades of the mi"ing tool
Th t f li d i t t B
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The amount of lime used appro"imates to B 6
7 E of the dry weight of the soil.
Hhen the tool is e"tracted$ the retrieval rate is
about one tenth of the rate at which it is
screwed into the soil$ so that the lime can be
thoroughly mi"ed with the soil.
This is important since the rate of diffusion of
calcium ions in most cohesive soils is low.
These lime columns bring about drainage ofthe soil and compare favourably with sand
drains due to their large surface areaI they
have a diameter of about 8.B m.
+ime columns have been used instead of piles as
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p
foundations for light structures.
The bearing capacity of a 8.Bm diameter limecolumn varies normally between B8 and B88 >9
depending on the soil type and the amount of lime
added.
The columns reduce total and differential
settlements and may be placed in a s#uare
pattern with a concentration beneath the loaded
walls. The load of the structure can be distributedto the lime columns by way of a thin concrete slab
e.g. if the number of columns is large the slab
need only be about 78 mm thic>.
1n the case of light structures the amount of
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settlement which occurs usually is a more
significant factor than the shear strength of the
soil.
The final amount of settlement undergone by soil
treated with lime columns generally is calculated
by assuming that the stiffness of the foundationcorresponds to the sum of the stiffness of the lime
columns and of the unstabili&ed soil between the
columns.
1t therefore is further assumed that the
deformation of the lime columns will be the same
as that of the unstabili&ed soil between the
columns.
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The calculation of the time6settlement
relationships is usually based on the
assumption that the lime columns function asvertical drains in the soil and that drainage
ta>es place hori&ontally.
The ma"imum total settlement of a structuresupported by lime column is ta>en e#ual to the
sum of the local settlement of the reinforced
bloc> and the local settlement of the
unstabilised soil below the bloc>.
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[ ] ( ) &;CtoB;&HC* uugroup,ult ++=
+= l
b
*.6)C/./ avult
The ultimate bearing capacity of lime colmn
groups depends on both the shear strength
of the untreated soil between the columnsand on the shear strength of the column
material
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The ma"imum total settlement of a
structure supported on lime columns is
ta>en as to the sum of the local settlementof the reinforced bloc> and the local
settlement of the unstabilised sol below the
bloc>.
The applied is load is relatively low and the
creep of the column will not be e"ceeded.
1n the second case the applied load is
relatively high and the a"ial load in thecolumn will correspond to the creep limit
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soilcol
)Ma)(aM
1H
h −+=∆
The columns and the untreated soil between the
columns deform as a unit and that the a"ial
shortening of the columns corresponds to the
settlement of the surrounding soil.
The a"ial stress in the column is e"presses as:
Hhere # is the average contact pressure$ a is
the relative column area$ 9acol/ %+ is the ratio ofthe total area of the columns 94col$ and the
stabilised area %+$ ,soil and ,col are the
compression modului of the surrounding soil and
of the column.
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APPLICATIONSAPPLICATIONS• Su*grade and Su*0*ase Sta*ilisation
• Dr(ing Soil
• Sta*ilising Em*an8ments and Canal Lining
• oundation Improvement
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Su*grade and Su*0*ase Sta*ilisation
• (ubgrade stabilisation usually involves
stabilising the soil in place. 4fter the soil has
been brought to grade$ the roadway should be
scrarifid to full depth and width and then partlypulverised.
• The lime should be spread evenly using dry or
slurry methods.
• (ome idea of the amount of lime to be applied
to the soil can be obtained from figure.
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Dr(ing Soil
*eavy costs can be incurred whenconstruction e#uipment and transport
become bogged down on site due to heavy
rainfall turning clayey ground into mud.
4nhydrous granular #uic>lime dries soil
more #uic>ly.
Hater for sla>ing comes from the soil duringmi"ing. Duic>lime combines with up to one6
third of its weight of water when reacting.
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Sta*ilising Em*an8ments
and Canal LiningFor many >inds of Jmban>ment construction$
such as road and railway$ earth dams$ and
levees.
1n the case of construction of emban>ment
which carry roads and railways$ as well as
slopes$ both natural and in cuttings$ these are
treated when the shear strength of soil needsto be enhances.
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oundation Improvement
+ime stabilisation of e"pansive soils is used to
minimise the amount of shrin>age$ swellingand settlement. This reduces the number and
si&e of crac>s developed by buildings founded
on e"pansive soils.
For light structures$ lime stabilisation may be
applied immediately below strip footings.
Treatment is better as a layer beneath a raft tominimise differential settlements.
+(P1 is economical in situ for treating
e"pansive soils .
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T3an6 5o4T3an6 5o4