Stabilisation and treatI IIent ofclay soils with liI IiePart 1 — Basic principlesby F.G. BELL", MSc, PhD, CEng, MIMinE, MIMM, FGS

AbstractCLAY SOIL CAN BE STABILISED by theaddition of a small percentage, by weight, oflime; that is, it enhances many of theengineering properties of the soil. Thisproduces an improved construction material.Generally the amount of lime needed tomodify a clay soil varies from 1 to 3 per cent,whilst that required for cementation variesfrom 2 to 8 per cent. Montmorillonitic claysoils respond more rapidly to lime treatmentthan do those in which kaolinite is thedominant clay mineral.

When lime is added to clay soils, calciumions are combined initially with or adsorbedby clay minerals which leads to animprovement in soil workability, that is, to anincrease in the plastic limit of the clay andgenerally to a decrease in its liquid limit. Theoptimum lime additive for maximumincrease of the plastic limit of the soil isreferred to as the lime fixation point. Limeadded in excess of the fixation point isutilised in the cementation process and givesrise to an increase in soil strength. The initialincrease in strength has been attributed tothe formation of poorly ordered reactionproducts which surround the clay materials.However, the development of long-termstrength appears to be due to the gradualcrystallisation of structurally-ordered newminerals from the initial disordered reactionproducts.

The principle uses of the addition of lime toclay soils is for, firstly, stabilisation of sub-bases and subgrades in pavementconstruction and, secondly, to dry out wetsoils. Lime treatment also has been used tostabilise embankments and canal linings,and to improve foundation soils. In the latterinstance soil is stabilised beneath strip or raftfoundations, or lime piles or columns areformed.

1. IntroductionLime stabilisation refers to the stabilisation

of soil by the addition of burned limestoneproducts, either calcium oxide, Ca 0, orcalcium hydroxide, Ca (OH),. Quicklime is themost frequently used lime product for limestabilisation in Europe. On the other hand,hydrated lime is used more often thanquicklime in the United States, although useof quicklime is increasing. Generallyspeaking quicklime seems to be a moreeffective stabiliser of soil than hydrated lime.Furthermore, when quicklime, in slurry form,is added to a soil, a higher strength isdeveloped than when it is added in powderform.

Treatment with lime serves no usefulpurpose in those soils which are more or lessdevoid of clay. It also has little effect onhighly organic soils. On the other hand, limeusually reacts with most soils with a plasticity

'epartment of Civil and Structural Engtneering, TeessidePolytechnic, Ntiddlesbrough

index ranging from 10 to 50 per cent. Thosesoils with a plasticity index of less than 10per cent require a pozzolan for the necessaryreaction with lime to take place, fly-ash beingcommonly used. Other pozzolans used forthe enhancement of lime stabilisationinclude blast furnace slag and expandedshale. Lime is particularly suited to thestabilisation of heavy clays producing a morefriable structure than does admixture withcement, which is easier to work and compact,although a lower maximum density isobtainable.

All clay minerals are attacked by lime,those having the highest available silicanormally reacting most strongly. In otherwords three-layer clay minerals, whoselamellae expose silica faces on both sides,are more reactive than two-layer clayminerals whose lamellae expose silica at oneface only. For example, the reaction of limewith montmorillonitic clays is quicker thanwith kaolinitic clays; in fact the differencemay amount to a few weeks. A silica surface,however, should not be considered"available" if it is bound to a similar surfaceby ions which are not readily exchangeable.Accordingly, illite and chlorite, althoughattacked, are much less reactive thanmontmorillonite.

When lime is used to stabilise clay soil itforms a calcium silicate gel which coats andbinds lumps of clay together and occupiesthe pores in the soil. The gel then crystallisesto form an interlocking structure. The clayforms an integral component of the bondedmass in its degraded form, and not merely aninert filler as it is in cement stabilisation.Reaction only proceeds while water ispresent and able to carry calcium andhydroxyl ions to the surface of the clayminerals (that is, whilst the pH value is stillhigh). Consequently, reaction ceases ondrying and very dry soils do not react withlime. In fact, if quicklime is used, then extrawater may be necessary in soils with lessthan 50 per cent moisture content to allowfor the very rapid hydration process.

2. Lime stabilisation and itseffects

Lime stabilisation is characterised by anextremely rapid reaction, at exposed surfacesof clay clods, which converts even heavyclays into friable soils immediately uponmixing. In addition lime stabilisationimmediately transforms a clay soil whichwould otherwise soften, collapse, anddisperse in water, into a firm water-resistant material. The speed of the reactionmakes it particularly suited for stiffening softsoils. Lime stabilisation also increases thestrength of all clayey soils, increases theirpermeability, increases their erosionresistance, and markedly increases theirvolume stability against swelling andshrinkage. However, in most cases clays

stabilised with lime do not develop as muchstiffness as when mixed with cement. All thesame, as with cement, the mode of failure ofthe soil is changed from plastic to brittle afterlime treatment and compaction at optimummoisture content.

A number of explanations have beenproposed as mechanisms responsible for thechanges which occur in the engineeringproperties of a soil when it is mixed with lime.They include cation exchange, flocculation ofthe clay, carbonation and pozzolanicreactions. The first two reactions take placerapidly and produce immediate changes inplasticity, workability, and swell properties,as well as the immediate uncured strengthand load deformation properties (seeThompson, 1968). Plasticity and swell arereduced and workability is substantiallyimproved as a result of the low plasticity andfriable character developed by the lime-soilmixture. The third reaction is undesirablebecause it gives rise to weak cementingagents. The fourth reaction is timedependent, in other words strengthdevelopment is gradual but continues for along period.

When lime is added to a soil, it must firstsatisfy the affinity of the soil for lime. In otherwords ions are adsorbed by clay minerals andare not available for pozzolanic reactionsuntil this affinity is satisfied. Because thislime is fixed in the soil and is not available forother reactions, the process has beenreferred to as lime fixation (see Hilt andDavidson, 1960). Hence the amount of limerequired to bring about lime fixation isrelated to the proportion of clay mineralspresent in a soil and is independent ofcarbonate content, that is, it is related to thecation exchange capacity of a soil.

The quantity of lime to be added ideallyshould be related to the clay mineral contentof the soil, as the latter is needed for reaction.As illustration, Ingles and Metcalf (1972)suggested that the addition of up to 3 percent of lime would modify silty clays, heavyclays and very heavy clays, whilst 2 to 4 percent was required for the stabilisation of siltyclay, and 3 to 8 per cent was proposed forstabilisation of heavy and very heavy clays. Agood rule of thumb in practise is to allow 1per cent by weight of lime for each 10 percent of clay (minus 2 micron fraction) in thesoil. Exact prescriptions can usually be madeafter tests at and slightly each side of thisvalue.

Mixing is important, but perhaps not socritical as for cement. Nonetheless, if mixingis delayed after the lime has been exposed toair, then carbonation of the lime will reduceits effectiveness. It is desirable therefore thatmixing be effected as soon as possible andcertainly within 24 hours of exposure to air.

Because the lime-soil reaction involvesexsolution, it is inhibited if the water contentof the soil falls too low. Hence moist curingalways is desirable.

10 Ground Engineering

TABLE 1: CONSISTENCY LIMITS IN RELATION TO TYPE AND AMOUNT OF LIME ADDED TO A MONTMORILLONITIC CLAY

Type ofLime

Amountadded

(%)

PlasticLimit(%)

LiquidLimit

(%)

a) Plastic limit, liquid limit and plasticity index

PlasticityIndex

b) Shrinkagef

Type of Lime

None

Amount added Shrinkage Limit Shrinkage Ratio(%) (%)

0None

Calciumhydrated

lime

Dolomiticmono-hydrate

lime

Dolomiticdehydrate

lime

01

23468

1

23468

1

23468

24

344347484746

253543444444

273744444444

24

686560575655

706563605755

676563595452

67

342213999

50302016119

50281915108

Calciumhydrated lime

Dolomiticmonohydrate

lime

Dolomiticdehydrate

lime

Fig. 2 (right).Influence of theaddition of lime onthe plastic and liquidlimits of kaolinite,montmorilloni te andquartz

28

28

2537

1442

1439

1.51.31.91.2

1.91.2

3. Lime stabilisation andconsistency limits

In most cases the effect of lime on theplasticity of clay is more or lessinstantaneous. As explained by Davidson andHandy (1960), calcium ions from the limecause a reduction in the plasticity of cohesivesoils, so they become more friable and moreeasily worked. Very small quantities of limeare required to bring about these changes in

plasticity (Fig. 1). Generally the amountneeded varies from 1 to 3 per cent dependingon the amount and type of clay mineralspresent in the soil. As an example, testscarried out by the US Bureau of Reclamationindicated that the addition of 4 per cent limereduced the plasticity index of a clay from 47to 12 per cent (see Anon, 1975), It must beadded, however, that in kaolinitic soils limetreatment will sometimes increase theplasticity index.

I I ~ T I I I 1O) 1 E H V- K E T B

LZMS CONTRNT ( %C )Fig. 1. Influence of the addition of lime on theplastic limit, liquid limit and plasticity ofclay ofhigh plasticity

The addition of lime to a clay soil causes animmediate increase in its plastic limit. Forexample, Sherwood (1967) showed thatwhen 2 per cent lime was added to a clay witha moisture content of 35 per cent and aplastic limit of 25 per cent, this increased theplastic limit to about 40 per cent. Indeed theaddition of lime to plastic soils causes anincrease varying directly with the amount oflime added, up to a limited content ofadditive (the point of lime fixation referred toabove). Further increments of lime usuallybring little or no additional increase (Table 1).The largest increases in plastic limitattributable to lime treatment have beenobtained in those soils in whichmontmorillonite is the principal clay mineral.Mateous (1964) showed that the minimumamount of hydrated lime required to beadded to montmorillinitic clays for maximumincrease in plastic limit (PL;) was:

% 2 micron clayPL;= 35 + 1.25

Increases in the plastic limit of illitic-chloritic soils, although less than in

montmorillinitic soils with comparable claycontent, nonetheless may be appreciable.The smallest increases in plastic limit havebeen noted in kaolinitic clay soils (Fig. 2).

The liquid limit of clay soils is lowered bythe addition of lime. In fact Brandl (1981)found that the liquid limit underwent a moresignificant decrease after lime treatment, thehigher the amount of colloidal clay present in

a soil. Nevertheless the liquid limit ofkaolinite clays may remain unchanged afterlime treatment or even increase.

The shrinkage characteristics of clayeysoils are improved significantly by theaddition of lime (Fig. 3). In the example of theclay tested by the US Bureau of Reclamationquoted above the shrinkage limit increasedfrom 7 to 26 per cent (see Anon, 1975).Withsmall additions, high calcium hydrated limeis more effective than other hydrated limes orcement, but with about 8 per cent addition alllimes cause a similar increase in shrinkagelimit (Table 1).Quicklimes appear to be moreeffective than hydrated limes as far as theimprovement of the shrinkage character-

LZOIJXOLZMZTS

I"'R

0 MO+ nU

PLIIIISTZCLZMXTS

I-"R~ Iln'C, n>I I

O 1. ' V-

LZMIS CONTENT ( SC )

HRI+IUY CLIIII'.

Xf".ITTXRL I'lnIX:=.TUR ECoot-ITEI "IT EE

4 @ DRY'—+ ~ ORY.:

SXI TY CLRYZl 'IT

TWIRL

r II IX ~ 'TI IREc OI.)TEI 4T 1

l:.I C)R i ''=')RY '=~ I I I T I T 1

4-LZMR CONTSNT ( SII )

Fig. 3. Influence of lime on the linear shrinkageof heavy and silty clay

12 Ground Engineering

istics of a soil are concerned.The addition of lime to clayey soils also

reduces, or indeed removes, their potentialfor swelling. The reduction in swelling alsomeans that there is a decrease in moistureabsorption in lime treated soils (see Bhasin etal, 1978).

4. Lime stabiiisation andcompaction

Compaction of lime stabilised soils is moretolerant than those stabilised with cement.Not only is delay less critical, so also iscompaction moisture content. In otherwords, lime treatment flattens thecompaction curve, thereby ensuring that agiven percentage of the prescribed densitycan be achieved over a much wider range ofmoisture contents, so that relaxed moisturecontrol specifications are possible. Indeedquality is better ensured by moisture contentcontrol than by dry density specification.Also the optimum moisture content is movedtowards higher values, enabling soils in

wetter than original condition to becompacted satisfactorily.

The addition of lime to all clays increasesthe optimum moisture content and reducesthe maximum dry density for the samecompactive effort (Fig. 4). Accordingly, thedesign of lime stabilised soil must have dueregard for these changes in compactionoptima, which in fact are proportional to theamount of lime added (more lime, lowermaximum dry density and higher optimummoisture content). However, the strengthgain in the soil normally will more thancompensate for the changes in compactionoptima, and they should not be regarded asdisadvantageous.

Andrews and O'Flaherty (1968)maintained that the decrease in density wasdependent not only upon the limepercentage, but also on the amount of clayminerals present. For example, the optimummoisture content increases with increasingclay fraction and the maximum dry density isreduced. Lees et al (1 982) showed that at 30

+ I IIVTRERTED '=;DZLD 4S LZME DDMPRDTED

.ZMI"1EDZRTEL r4'Sl LXME C Dl 1PRD TED—4 ¹IIJR'FT ERMr. «:ONE

1EEQ)

C~e Lb'

EQ)P

14C3C~3

1~QQl

1DDT

E] 4 l WEE=I".~Q) ~ 1 14EE.H:

+ Tr-ie>EDXR TE7 1 l~T~'

B 1 ze sa 4 B B T ElI XMat CONTENT ( %4 )

Fig. 5. Influence of lime on the unconfinedcompressive strength of clay ofhigh plasticity

and 50 per cent clay content, the addition oflime results in a drop of approximately 5 percent in the values of maximum dry density.Furthermore at higher water contents, lime-soil mixtures tend to show a greatercompactability than untreated soil.

Croft (1964) found that highercompaction densities were obtained in limetreated kaolinitic clays than in soils in whichclay minerals with expandable latticespredominated. In soils with a high content ofmontmorillonite, the addition of lime may sodistort the shape of the optimum moisturecontent-dry density compaction curve that awell defined maximum density is not shown.The optimum moisture content forcompaction in such clay soils should be onethat produces the maximum strength.

A pronounced decrease occurs withincreasing time intervals between mixing andcompaction, and so maximum density occursat somewhat higher optimum moisturecontents. Moreover if a lime-soil mixtureremains uncompacted it undergoescarbonation, the cemented particles thenbehave like sand grains and any subsequentcompaction is not as easy.

5. Lime stabiiisation and strengthClays generally show a significant increase

in strength when lime is used forstabilisation. In many cases only a smallamount of clay is needed in a soil for reactionwith lime (Fig. 5).This view was supported byThompson and Harty (1973),who from limereactivity studies (this term refers to thedifference between the maximum strength ofthe lime-soil mixture at the optimum limecontent after 28 curing days at 20'C and thestrength of the untreated soil) concluded thatclay content was not correlated with the limereactivity of a soil. Hence it would appear thatthe absolute amount of silica or aluminarequired to sustain pozzolanic reaction in

soils is relatively small.The strength of lime-soil mixtures is

influenced by several factors such as soiltype, type of lime and amount added, curingtime and method (temperature and wateravailability), moisture content, unit weight,and time elapsed between mixing andcompaction. This has been illustrated byIngles and Metcalf (1972) who noted thatmontmorillonitic clays give lower strengthswith dolomitic limes than with high calciumor semi-hydraulic limes. Kaolinitic clays onthe other hand yield the highest strengthswhen mixed with semi-hydraulic limes andthe lowest strengths are obtained with highcalcium limes.

Montmorillonite and kaolinite give higherstrengths with lime than illite, chlorite orhalloysite (Table 2). Expansive clays respondmore quickly to strength increase, althoughthe final strength achieved is greater inkaolinitic clays. The position is complicatedfurther by the fact that Lees et al (1982)showed that at 8 per cent lime content, the28 day strength of specimens of kaoliniticsoils decreased progressively as the claycontent increased whereas the converseoccurred with specimens of montmorilloniticsoils.

Soil mixed with low lime content attainsmaximum strength in less time than that towhich a higher content of lime has beenadded. Strength does not increase linearlywith lime content, and in fact excessiveaddition of lime reduces strength (Fig. 6). Forinstance, beyond an optimum lime contentthe unconfined compressive strength candecline significantly and at times thedecrease may exceed 30 per cent (see Al-Rawi, 1981). The optimum lime contenttends to range from 4.5 per cent to 8 percent, higher values occurring in soils withhigher clay fractions. This decrease isbecause lime itself has neither appreciablefriction nor cohesion.

Curing is one of the major variablesaffecting the strength of lime stabilised soil

TABLE 2: SOME EXAMPLES OF UNCONFINED COMPRESSIVE STRENGTHS OF DIFFERENTTYPES OF LIME STABILISED SOILS

Type of Lime

1 748

Typeof

Soil

Curingtime

(daysj OptimumLime

content (%j

Strength(kNlm'I

Calcitic hydrated Dolomitic monohydrate

Optimum StrengthLime (kN/m'j

content (96j

T T i i r T 118 12: 14- 16 16 c'8 =2 4MOXSTURE CONTENT ( %C )

Montmorilloniticand Kaolinite 7

rich 28

lllite and 7chlorite rich 28

2-82-8

3-54-6

420-840850-1750

350-700910-1190

8-128-144-64-8

700-14001 750-2800

700-10501400-1750

Fig. 4. Influence of the addition of lime on thecompaction curves of clay soil

Halloysiterich

728

4-84-8

350-700525-875

4-86-14

350-7001050-1400

January 1988 13

QI QI

BBQIQI

BV-Q)Q

BQ)QIQI

B6Q)Q)

BQ)(RIB

1.BQ)B

1V-BQI

1BQIQ)

1 IZ)Q)QI

BQQ)

4-Q)QI

BQIQI

QI 1. B B 4- B 6 T BLZMR CONTRNT C %C )

Fig. 6. Effect of the addition of lime, in slurryand powder form, on the strength of silty clay

(Fig. 7). Its effect on strength is a function oftime, temperature and relative humidity. Forinstance, Laguros etal(1956) found that thestrength increases rapidly at first, notablyduring the first seven days of curing, thenincreases more slowly at a more or lessconstant rate for about 15 weeks. Thissupports the view that cementitiousproducts due to lime-clay reaction form at anearly stage, that is, as soon as flocculation is

$ 1BQIQI

1.6QIQI

1BRIG

1 lcd

p

~ 1 )Cr

ca Lp

I+ICRR — WRRKRC I C)O DPI R )

Fig. 7. Influence of curing time on theunconfined compressive strength ofclay soi Iofhigh plasticity treated with different amountsof lime

completed (see Lees et al, 1982). Indeed asteady, slow gain in strength over months ischaracteristic of lime-stabilised soil. Brandl(1981) observed that the increase instrength tailed off within one or two yearsand that no changes took place, even inactive clays, after seven years. He furthermaintained that the time dependent increasein strength is approximately linear with thelogarithm of time. This steady slow gain instrength provides a considerable factor ofsafety for designs based on 7-, 14-, or 28-day strengths.

Laguros et al (1956) also reported thathigher temperatures accelerated curing,resulting in a higher strength. This wassubsequently confirmed by Mateous (1964)and Marks and Haliburton (1972). Forexample, Mateous found that specimenscured at 35'C developed twice the strengthor more of those specimens cured at 25'C.Laguros et al also found that 90 per centrelative humidity gave the greatest ultimatestrength gain when comparing differentcuring conditions.

According to Thompson (1968) attemperatures less than approximately 4'Cthe lime-soil pozzolanic reaction is retardedand may cease. If a lime-soil mixture is to bedeveloped in a position where substantialstrength is necessary, it is therefore essentialto ensure proper field curing time underfavourable temperature conditions. Becausestrength development more or less ceaseswith the onset of cold weather, strength lossbecause of cyclic freezing and thawing iscumulative throughout the winter. Residualstrength at the end of the freeze-thaw periodconsequently must be sufficient to guaranteethe integrity and stability of the lime-soillayer. However, the lime-soil pozzolanicreaction continues after the winter periodand goes on as long as free lime remains inthe system and temperatures are favourable.

The strength of lime stabilised soils is alsoproportional to the reduction in the pH valueof the soil which occurs during curing. ThepH value is also an important factorcontrolling the rate of gain in strength.

The shear strength of lime stabilised claysalso is related to their natural moisturecontents (Fig. 8), decreasing with increasingmoisture content (see Holm, 1979). Eventhree months after lime stabilisation theshear strengths of clays with high moisturecontent remain low.

Saturation of soil specimens with waterbefore testing for unconfined compressivestrength simulates some of the worstconditions to which a stabilised soil may besubjected. It results in a reduction ofstrength. The amount of loss in strengthvaries, but Al-Rawi (1981)reported a loss ofover 50 per cent due to saturation.

However, results reported by Thompson(1970) showed that prolonged exposure towater produced only slight detrimentaleffects and that the ratio of soaked tounsoaked strength was high atapproximately 0.7 to 0.85. Increased curingtemperature results in a significant reductionin the loss in strength due to soaking.

On the other hand, lime-soil mixturescompacted at moisture contents aboveoptimum attain, after brief periods of curing,higher strengths than those compacted withmoisture contents less than optimum.According to Sabry and Parcher (1979) thisis probably because the lime is moreuniformly diffused and occurs in a morehomogeneous curing environment.Nevertheless, the strength of soilscompacted at or below optimum moisture

1 GC>ZIPEF XCID AFTER

':S FABZL XZCATXDI.I1 DA''

P G WEEFCB

6 -——rV.QI 6QI BCI 1GQI 1ZQI 1+QIMDXRTIJIRR DC)NTRNT C %4 )

Fig. 8. Influence of addition of4 per cent limeon the shear strength ofclay soil with differentmoisture contents

content generally can be enhanced by furtheraddition of water after compaction.

The compactive effect influences strengthsignificantly. For instance, Mateous (1964)showed that when the compactive effort wasincreased from standard to modifiedAASHO, the compressive strength of lime-soil mixtures increased by 50 per cent to 250per cent for both 7 and 28 day curingperiods. This increase in strength wasobtained by an accompanying increase inmaximum dry density of about 10per cent. Inthis context, Mitchell and Hooper (1961)reported that samples of clay compactedwithin one hour of mixing attained a higher

Fig. 9. Influence of the additi on of lime on theCBR of silty clay

V-6 I

I

A

/ /II II I

5 Ig,I

66 DA Y DLIRXI-IG TXI.1Egg 66 DAY C AEMDIJL DED )~ P DAY DLIRXI'-IG TXI 1E

DA Y DuAXI.-"IG TXI <E

II 1 6::. V- 6 6 . 6LXMR CDNTRNT C )II )

14 Ground Engineering

1, rnQI

Fig. 10. Influence of the addition of lime andcuring time on the Young s modulus of (a, /eftJkaolinite and (b, right) montmorillonite

BQI

I

l.e Qt

~e

Ql

1.QIf

~ EB DA'r"'osi IRZNra n Zr<E

T—~~B

LZME CONTENT C Se 1

strength than those which were compactedafter 24 hours had elapsed (Fig. 4).

6. Lime stabiiisation and otherproperties

The California Bearing Ratio (CBR) ofclayey soils is improved by the addition oflime (Fig. 9). Indeed the CBR increasesimmediately after the addition of lime andcontinues to increase with time if there islime in excess of the lime fixation point (seeMateous, 1964).

In tests carried out by Holm (1979), limestabilisation of soil was found to increase thevalue of Young's modulus by some 15 timesafter three weeks from treatment and around

35 times after 16 months. The Young'smodulus of the untreated soil was

300kN/m'nd,

with the addition of lime after theperiods mentioned, increased to

4.4MN/m'nd

10.8MN/m'espectively. Furthermorethe increase in Young's modulus increasesconsiderably with increase in curingtemperature (see AI-Rawi, 1981).Accordingto Brandl (1981)only a small addition of limeis required to make a soil behave in a "brittle"manner. Montmorillonite underwent aninitial increase in Young's modulus with only2 per cent addition of lime, the optimumamount occurring between 2 and 3 per cent.Bell and Tyrer (1987) noted that kaoliniteshowed a rapid increase in Young's moduluswith small increments of lime, namely,between 2 and 4 per cent, after which theincrease in value tailed off or may evendecline with extra amounts of lime added(Fig. 10.)

Al-Rawi and Awad (1981) indicated thatthe permeability of a clayey soil is increasedwhen treated with lime as the latter causesflocculation of the soil. The higher the clayfraction, the more the permeability of a lime-soil mixture increases. They found that thosesoils compacted on the dry side of optimummoisture content developed a higherpermeability than those compacted wet ofoptimum. What is more they identifiedparticular moulding moisture contents whichgave minimum permeability for all lime-soilmixtures irrespective of the amount of limeadded. In addition, with increased age ofcuring the permeability declined with allmoulding water contents. As Brandl (1981)explained, this presumably is due to theincreased production of gelatinouscementing agents with time, which occupyan increasing amount of void space and

~rn

DA r'

. DA".+ T DAYuk 1ci- DA'r''~ EB DAY

QII I I

IZI 1.

.URZr"IR TZI"IEri IRZI"4G TZt"IECUR ZNrm TZMEDURZNG TZI"IEDURzr~cg Tzr-IE

I I I I I

ct- B B T BLZME DDNTENT C PS )

eventually harden. It also should be borne inmind that the stabilised particles of soil aresurrounded by wider films of bound waterwhich further reduces the void space.

The resistance to frost action of limetreated clay soils increases rapidly withcuring time and for amounts over 2 per centlime. It is sufficiently high after 3 months toresist frost heave (see Brandl, 1981).Furthermore the rate and depth of frostpenetration is reduced by lime treatmentbecause flocculation increases the void ratiowhich, in turn, causes a poorer heatconductivity. The suction forces of clay soilsduring freezing also are reducedconsiderably by mixing with lime.

(Part II of this article will deal with the usesof lime stabilisation. It will end with a list of allthe references).

~ gfn I f gn tq ( I gn I gngn t,l„tf ~ ~ fsi ~ ~

ii l IL.ilL It Iii I Li.i I"I

~ L L I ~ ehiHexagonal or Square, Ihe Herk ales Piling System, which

s been developed by continuous research and long experience,ffers you the best advanced system of precast concrete segmentaling available today.

The adaptability of the Herkules Piling Systemaccepted and used byovemment departments, all

sectors of public and privatedustry and consultinggineers. It provides anonomical and sound solutionmany piling problems.

There are few occasionswhere the Herkules pile

nnot be used.

~ worth, Surrey KT6 7DQ.Telephone: 01-3907977 Telex: 946398 TCPLON G~~~~g g g ~+ Telefax: 01-3902263Ahed House, Dewsbury Road, Ossett, West Yorkshire WFS 9ND.Telephone: 0924 278181 Telex: 556450 AHCOMP G Telefax: 0924262958

P Balmore, Torrance, Glasgow G64 4AB.Telephone: 0360 22882 Telex: 77311 HERKUL GTelefaxi 0360 22214 Member of The Nordstlernon Group.

January 1988 15