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DrPVS Expansive Soil

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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


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