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Received 9 February 2012; received in revised form 15 May 2013; accepted 10 June 2013

Keywords: Expansive soil; Wetting and drying; Distilled water; Saline water; Acidic water

The Japanese

www.scjournal homepage: w

Soils an

nCorresponding author. Tel.: 98 26 32241119; fax: 98 26 32226181

A.A.Javadi@exeter.ac.uk (A.A. Javadi).

Soils and Foundations 2013;53(5):617627expansive soils under cycles of wetting and drying has beenthe subject of intensive investigation during recent years.A number of researchers, such as Rao and Satyadas (1987)and Chen (1988), have subjected remoulded clay samples to

0038-0806 & 2013 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.sandf.2013.08.001magnitude of the surcharge pressure and the amount of non-expansive material. In general, the swelling potential increases

E-mail addresses: raeesi@ut.ac.ir (A.R. Estabragh),M.Moghadas@ut.ac.ir (M. Moghadas),2Tel.: 44 1392 723 640; fax: 44 1392 217 965.Peer review under responsibility of The Japanese Geotechnical Society.as the dry density increases and the water content decreases(Hanafy, 1991; Fredlund and Rahardjo, 1993; Marinho andStuermer, 2000; Ferber et al., 2009). The behaviour of

1Tel.: 98 26 32241119; fax: 98 26 32226181.1. Introduction

Expansive soils are a worldwide problem as they causeextensive damage to Civil Engineering structures. The averagecost of this damage to buildings, roads, airports and pipelinesis about $9 billion per annum in the USA. This is more thantwice the combined average annual damage due to all earthquakes,

oods, tornados and hurricanes in the USA (Jones and Jones,1987). As a result, a clear understanding of the behaviour ofexpansive soils is required for the effective design of structuresand infrastructures on these soils.There are many factors that govern the expansive behaviour

of soils. The initial factors are the availability of moisture andthe amount of clay particles in the soil. Other factors affectingthe expansive behaviour include the type of soil, the conditionof the soil in terms of dry density and the moisture content, theAbstract

This paper presents the results of an experimental investigation into the mechanical behaviour of an expansive soil during wetting and dryingcycles. The experimental tests were conducted in a modied oedometer under two different surcharge pressures (10 and 20 kPa). During the tests,the samples were inundated with different types of wetting uids (distilled water, saline water and acidic water). The volumetric deformation,void ratio and water content of the samples were determined during cycles of wetting and drying. The results show that the swelling potentialincreases with an increasing number of wetting and drying cycles. The effect of the distilled water on the swelling potential is not the same as thatof the saline water or the acidic water, particularly for different surcharge pressures. The variations in void ratio and water content show that, atthe equilibrium condition, the wetting and drying paths converge to nearly an S-shaped curve. This curve consists of a linear portion and twocurved portions, and the majority of the deformation is located between the saturation curves of 90% and 40%.& 2013 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.Available online 24 September 2013Effect of different types of wof expansive soil dur

A.R. Estabragha,n, M. MaFaculty of Soil and Water Engineering, Universit

bComputational Geomechanics Group, College of Engineering, Mathetting uids on the behaviourg wetting and drying

hadasa,1, A.A. Javadib,2

Tehran, PO Box 4411, Karaj 31587-77871, Irancs and Physical Sciences, University of Exeter, Devon EX4 4QF, UK

Geotechnical Society

iencedirect.comww.elsevier.com/locate/sandf

d Foundations

as Cui et al. (2002), Lloret et al. (2003), Cekerevac and Laloui

in the standard compaction test was 18% and the maximum dryunit weight was 16.0 kN/m3.

2.2. Sample preparation

Several mixtures were prepared using kaolin and bentonitewith preselected quantities of different types of wetting uids(distilled water, saline water or acidic water). The mixtureswere kept in closed plastic bags and allowed to cure for 24 h.This allowed the moisture in the soil to distribute evenlythroughout the mass of soil. In order to obtain uniform andrepeatable samples, a mould was designed and made fromstainless steel. The mould was a split compaction mould whichconsisted of three sections: a top collar, a middle section and abottom collar. The dimensions of the middle section wereexactly the same as those of the ring of the oedometer. Themould was also provided with a piston that was used tocompress the sample inside the mould. Silicon grease was usedon the inner surface of the mould, before compaction, toreduce the friction during compaction. Samples were preparedin three layers, by static compaction of the moist soil in the

Chemical component Amount

Na (meq/L) 73.5K (meq/L) 0.04Ca2 (meq/L) 8.4Mg2 (meq/L) 4.9Cl (meq/L) 35.6CO23 (meq/L) 0.1

SO24 (meq/L) 50.8HCO3 (meq/L) 31.1pH 8.2Electrical conductivity (S/cm) 7610

d F(2004), Cuisinier and Masrouri (2005), Tang et al. (2008),Wang et al. (2013). They concluded that heating has a signi-cant effect on the mechanical behaviour of expansive soils.However, to the authors knowledge, no research studies haveever been reported in literature on the effect of different typesof wetting uids on the behaviour of clay soil during cycles ofwetting and drying. The main objective of this study, therefore,is to investigate the effect of different types of wetting uidson the wetting and drying behaviour of clay soil. The results ofthis experimental study will be presented in terms of thevolumetric deformation and the void ratio-water contentrelationship. The effect of surcharge pressure on the swellingbehaviour will also be studied. It will be shown that it ispossible to minimize the effects of volume changes duringwetting and drying by conducting appropriate tests to char-acterize the potential of the swelling and shrinkage ofexpansive soils, taking the necessary precautions and design-ing a suitable foundation system.

2. Experimental work

2.1. Material

The soil used in the testing program was highly expansive clay(according to the classication by McKeen (1992)). The soil wasprepared by mixing bentonite with low-plasticity kaolin. A widerange of soil mixtures was investigated to identify a mixture withthe desired wetting and drying properties (a high potential forswelling and shrinkage). Finally, the soil chosen comprised amixture of 20% bentonite and 80% kaolin. The physical andchemical properties of the soil are shown in Tables 1 and 2,respectively. According to the Unied Soil Classication System(USCS), the soil can be classied as clay with high plasticity(CH). The soil had a swelling pressure of 120 kPa and it wasdetermined according to the ASTM D4546 (2008) standard.Drinking water, with a pH value of 7.76, a Cl1 content offull swelling and then allowed them to dry to their initial watercontent. By repeating this procedure, the soil showed signs ofirreversible deformation after each cycle of wetting and drying.Dif and Blumel (1991) found almost no volume change inremoulded clay after at least three or four drying and wettingcycles. Many researchers, such as Wheeler et al. (2003),Alonso et al. (2005), Nowamooz and Masrouri (2008), havestudied the behaviour of expansive soils during wetting anddrying cycles by controlling the suction. Tripathy et al. (2002)studied the wetting and drying behaviour in terms of the voidratio and the water content. Several investigations have shownthe behaviour of expansive soils under chemical inuence(Alawaji, 1999; Musso et al., 2003; Di Maio et al., 2004; Raoand Shivananda, 2005; Rao and Thyagaraj, 2007a, 2007b;Casttellanos et al., 2008; Siddiqua et al., 2011). The hydro-mechanical behaviour of compacted swelling soils at ambienttemperature has been studied by a number of researchers, such

A.R. Estabragh et al. / Soils an6181.7 meq/L and a Ca2Mg2 content of 9.1 meq/L, was usedto compact and prepare the samples. The optimum water contentTable 2Chemical composition of soil.Table 1Physical and mechanical properties of soil.

Soil properties Values

Specic gravity 2.75Consistency limitsLiquid limit (LL) 70%Plastic limit (PL) 23%Plastic index (PI) 47%Shrinkage limit (SL) 13%USCS classication CH

Swelling pressure 120 kPaCompaction studyOptimum water content 18%Maximum dry density 1.6 Mg/m3

Grain size analysisSand 27%Silt 33%Clay 40%

oundations 53 (2013) 617627mould, to a given dry unit weight of 15.7 kN/m3 and a watercontent of 13.5% (4.5% less than the optimum water content

ut o

d Ffrom standard Proctor compaction tests). Each layer wascompacted to a vertical stress of 860 kPa in a compressionframe at a displacement rate of 1.5 mm per minute. Beforeplacing the next layer, the surface of the compacted layer wasscaried so that there was a good bond between the adjacentlayers of soil. All samples were compacted in an identicalfashion in order to provide the same initial fabric in the samples.

2.3. Apparatus

A conventional oedometer was modied to allow tests to beconducted under a controlled temperature and surchargepressure. The apparatus consisted of a xed ring with amodication to allow the shrinkage and the swelling of thesamples under the controlled surcharge pressure and tempera-ture, as shown in Fig. 1. Before starting the main tests, anumber of free swelling tests, hereafter referred to as thepreliminary tests, were carried out on the samples, according toASTM D4546 (2008), to nd the time required for theequalization of each test path. This was found to be about 5days for the rst wetting path. After the swelling tests, thesample was moved to an oven set at a temperature of 45 1C.The dimensions and the water content of the sample weremeasured in different time intervals until they reached aconstant value after about 7 days. Based on these preliminary

Fig. 1. Layo

A.R. Estabragh et al. / Soils antests, the duration of each cycle was found to be about 12 days.In order to reduce the length of the drying samples, Umezakiand Kawamura (2013) proposed the vacuum evaporationmethod. The calibration of the temperature was done with athermometer. The sample was placed in the ring between twoporous stones with a loading plate resting on the upper porousstone. The sample was loaded to a prescribed surchargepressure and the pressure was maintained until full settlementwas achieved. The sample was then inundated with water andallowed to swell under the applied surcharge pressure. Afterthe completion of swelling, a drying stage was implemented.The vertical deformations of the samples were measuredduring wetting and drying using a dial gauge. The variationin water content with void ratio during the wetting and dryingcycles was determined with the information from the dupli-cated samples. After the completion of swelling, a drying stagewas implemented. The drainage valve was opened so the watercould ow out from the cell and the temperature controller wasxed at 45 1C. During the heating process, the water wasgradually expelled from the sample and the volume decreased.The vertical deformation was recorded from the dial gaugereadings. The duration of this stage was nearly 7 days. Theduplicated samples were placed in the oven under the samesurcharge pressure at 45 1C and their water contents weremeasured at certain time intervals in order to determine thevariation in water content and void ratio during the dryingstage. Liu et al. (2012) recently proposed a modied controlapparatus that measures the volume change of the sampleduring the wetting and drying cycles. When using thisapparatus, there is no need to duplicate the samples. Thecombination of one swelling and the subsequent shrinkage stepsis designated as one swell-shrink cycle.During drying, the shrinkage of the soil sample caused the

sample to decrease in diameter and height. Therefore, exceptfor the rst swelling cycle, the volume change of the sampleduring the subsequent swelling cycles in this case was threedimensional. In order to plot the wetting path within eachcycle, at least six or seven samples were tested. Similarly, inorder to plot the drying path, at least ve samples were tested.The duplicated samples were dismantled and their height anddiameter were measured. The diameter was measured for atleast three points and then the mean of the measurements was

f apparatus.

oundations 53 (2013) 617627 619considered. It is generally known that clay soils can crackduring drying. Cracks occur when the tensile stress developingin the soil, due to the drying, exceeds the tensile strength of thesoil. Tensile stress develops only when the soil is restrained insome way against shrinkage (Kodikara et al., 2000). Theformation of cracks is enhanced by the availability of the clay(Mitchell, 1993). In high plasticity soils, the self-healing mayresult in the close-up of cracks during wetting. The determina-tion of the crack dimensions (width, length and depth), thespatial distribution and the connectivity controls the rate andvelocity at which the solutes are transported in the soil (Horganand Young, 2000). Most importantly, the soil hydraulic proper-ties are directly controlled by the desiccation crack networks(Chertkov, 2000). Albrecht and Benson (2001) indicated that thehydraulic conductivity of cracked soil is several orders ofmagnitude greater than that of intact soil. There is no standardmethod for measuring the crack dimensions at the end of drying.

cracet awid

behrep

for pore water extraction for the soluble salt determination ASTMD4542 (1995), EC and pH.

2.6. Soilwater characteristic curve

The soilwater characteristic curve is the relationshipbetween the water content (either volumetric or gravimetric)or the degree of saturation and soil suction. The lter paper testwas used, according to ASTM D5298 (2010), to determine thesoilwater characteristic curve.

3. Results

d Foundations 53 (2013) 617627equilibrium condition. Subba Rao et al. (2000) and Tripathyet al. (2002) used mercury displacement to measure thedimensions of the soil sample, but there is a possibility thatmercury lls the cracks and reduces the accuracy. Punthauaechaet al. (2006), Pron et al. (2006), Tang et al. (2008) used themethod of measuring the dimensions of a sample to calculatethe volumetric deformation of the sample. In this work, themethod of measuring dimensions was used to calculate thevolume of the duplicated samples. Void ratio and water contentwere calculated without considering the effect of cracks; thisresulted in a reduction in accuracy.

2.4. Water

For inundating the samples during wetting cycles, threekinds of water were used:

(1) Distilled water with a pH of 7.2 and an electric conductiv-ity (EC) equal to 14 S/cm.

(2) Saline water with a pH and an EC of 8.0 and 900 S/cm,respectively. This water was prepared by adding sodiumchloride into distilled water (2.5g sodium chloride wasmixed with 1000 ml of distilled water).

(3) Acidic water with a pH of 5.5 and an EC of 19 S/cm. Forpreparing the acidic water in the laboratory, 10 ml ofsulphuric acid with normality equal to 0.01 was mixedwith 990 ml of distilled water.

2.5. Chemical tests

At the end of the swelling stage in each test, a 10-ml sampleof water was extracted from the oedometer reservoir and usedto determine the electric conductivity (EC) and the pH of thewater. The inundated samples (identical samples were preparedof wcracwithwetting and drying cycles on clay soil samples to nd the effectetting and drying on the initiation and the evolution ofks. They found that after three cycles the cracks attained theWahwet00), Tripathy et al. (2002), who have worked on studying theaviour of soils in cycles of wetting and drying, have notorted the existence of any cracks in the drying stage. Alab and El-Kedrah (1995) and Tang et al. (2011) conductedBas(20k area have been suggested by Peng et al. (2006). Rayhanil. (2008) used a digital calliper to measure the length and theth of cracks. Researchers such as Al-Homoud et al. (1995),ma et al. (1996), Dif and Blumel (1991), Subba Rao et al.Kleppe and Olson (1985) developed a scale in the range of 04to describe the severity of cracking, but Miller et al. (1998) usedthe crack intensity factor (CIF) to explain the cracking. CIF isdened as the ratio of the crack area (Ac) to the total area (At) ofa drying soil mass during drying. It is used as a descriptor of theextent of the surcial cracking and quanties the cracks. Tanget al. (2011) used image processing to determine the behaviourof cracks. Using photographs of soil samples and recording the

A.R. Estabragh et al. / Soils an620similar initial conditions as the main samples and subjected toting and drying) were dismantled using the ASTM procedureIn this work, compacted soil samples were subjected towetting and drying cycles with different types of wetting uidsunder constant surcharge pressure. The samples were rstwetted so that they experienced an increase in volume due tothe decrease in suction (increase in water content); theyexperienced shrinkage in the subsequent drying stage.The vertical deformation of the samples is expressed as the

change in the height (H) of the sample during either swellingor shrinkage as a percentage of the initial height of the sampleat the beginning of the rst swell-shrink cycle. The volumetricstrain for each cycle was calculated by combining the verticaland radial strain (obtained from duplicated samples). Byplotting the volumetric deformation of a sample for severalswell-shrink cycles, the trend of the variation in the change involume of the sample during wetting and drying cycles wasobserved. The volumetric deformations in the cycles of wettingand drying, for the samples tested with an initial water contentof 13.5% and a surcharge pressure of 10 kPa, inundated withdistilled water, acidic water and saline water, are shown inFig. 2. In the rst cycle, the deformations of the sampleinundated with distilled water are 9.75% and 21.17% duringwetting and drying, respectively. In the second cycle, thedeformations are 25.52% and 26.1% in the wetting and dryingpaths, respectively, showing an increase in deformationcompared with the rst cycle. It is obvious that by increasingthe cycles, the deformations are increased and the equilibriumcondition is nally reached in the fth cycle with a 29.9%deformation. This nal (and nearly reversible) deformationshows an increase of more than 100% in swelling potentialFig. 2. Wetting and drying cycles for different types of wetting uids undersurcharge pressure of 10 kPa.

compared with the rst cycle. In the case of samples inundatedwith acidic water, the volumetric strains during the rst cycleare 6.85% and 16.95% for the wetting and drying paths,respectively, indicating that the shrinkage potential is morethan the swelling potential in this cycle. The volumetric strainsin the second cycle are 22.6% and 24.5% for wetting anddrying, respectively, and they are increased by increasing thenumber of cycles. At the equilibrium condition, the volumetricstrain reached 39.0%. The results for the samples inundatedwith saline water (Fig. 2) show that in the rst cycle, thevolumetric strains are 6.85% and 18.85%, indicating thatthe potential for swelling is less than the potential forshrinkage. In the second cycle, they increase to 21.6% and23.9%. By increasing the number of cycles, these values

gradually increase. The equilibrium condition is achieved inabout the fth cycle with a volumetric strain of 38.15%.Fig. 3 shows the volumetric strain of the samples inundated

with distilled water, acidic water and saline water under asurcharge pressure of 20 kPa. The volumetric strains in the rstcycle for the sample inundated with distilled water are 2.15%and 10.65% during wetting and drying, respectively; thus, theamount of shrinkage during drying is more than the amount ofswelling during wetting. In the second cycle, they reach 14.3%and 14.9%, respectively, indicating an increase in the potentialfor swelling and shrinkage. The equilibrium condition isachieved in the fourth cycle with deformations of about18.4% and 18.5% for wetting and drying, respectively. Theresults for the sample inundated with acidic water (Fig. 3)show that the deformations in the rst cycle are 3.15% and13.45%, respectively. In other words, the amount of shrinkageduring drying is about 4 times the amount of swelling due towetting. In subsequent cycles, the swelling and shrinkagepotentials increase until the equilibrium condition is reached inthe fourth cycle with a deformation of 19.1% with the majorityof the deformation being compressive. For the samplesinundated with saline water, the volumetric strains during therst cycle of wetting and drying are 3.15% and 18.15%,respectively. In other words, the amount of shrinkage duringdrying is about 6 times the amount of swelling due to wetting

Fig. 3. Wetting and drying cycles for different types of wetting uids undersurcharge pressure of 20 kPa.

A.R. Estabragh et al. / Soils and Foundations 53 (2013) 617627 621Fig. 4. Water contentvoid ratio paths for acidic water under surcharge preand the amount increases in subsequent cycles. During thethird and subsequent cycles, the deformations are compressiveand the difference between swelling and shrinkage deforma-tions is reduced by increasing the number of cycles until theyssure of 10 kPa in (a) cycle 1, (b) cycle 2, (c) cycle 3 and (d) cycle 4.

reach equilibrium (deformation of about 21%) in the sixthcycle. In the tests conducted under a surcharge pressure of20 kPa, except for the rst cycle, the majority of the deforma-tion in the other cycles is located in the region of compression.From the results, the values for the void ratio and the water

content were determined for the different tests. Typical resultsfor void ratio versus water content for the sample tested withacidic water under a surcharge pressure of 10 kPa, along withvarious constant saturation lines, are shown in Fig. 4(a)(d).In these gures, the changes in void ratio with the watercontent are shown from the initial (compacted) condition to thefourth cycle of wetting and drying. In Fig. 4, points 1, 2, 3 and4 show the positions of the samples at the end of the shrinkage(drying) stages in different cycles; points B, C, D and E indi-cate the positions of the samples at the end of the swelling(wetting) stages. Point A in Fig. 4(a) shows the initial, or com-pacted, void ratio (e0) and the water content (w0) of the sample.The procedure followed in the wetting and drying cycles isshown in Fig. 4. In the rst cycle, swelling occurred frompoint A to point B followed by shrinkage from point B to 1

(see Fig. 4(a)). It is seen from Fig. 4 that the soil samplereached nearly full saturation in all stages of wetting and thatall the wetting and drying curves were S shaped. The tendencyto converge to the same S-shaped curve was evolved byrepeating the cycles of wetting and drying.The results of chemical tests on the pore water extracted

from the soil sample and the reservoir water of the consolida-tion cell after each cycle are shown in Tables 35 for distilled,saline and acidic water, respectively. These results show thatthe initial EC of the reservoir water increased and that thevalues of Na1,Ca2Mg2 and pH of the extracted porewater decreased.The soilwater characteristic curve was determined using

the lter paper test; the results are shown in Fig. 5. Thefollowing empirical relationship was obtained for the waterretention curve of the soil:

w 87:1438:21 Lns 1where w and s are the water content in % and the suction in kPa,respectively. This relationship is similar to the relationship that

Table 3Chemical composition of extractor pore water and reservoir water at the end of each cycle of sample inundated with distilled water.

Condition Chemical composition of extracted pore water Chemical composition of reservoir water

Cycle EC (mS/cm) pH Ca2Mg2 (meq/L) Na (meq/L) pH ECa (mS/cm)

1 14.64 7.62 0.256 9.15 7.55 0.6552 14.35 7.51 0.21 8.17 7.51 0.5503 14.15 7.42 0.165 7.19 7.40 0.5524 13.87 7.32 0.145 6.67 7.33 0.524

aElectrical conductivity.

f ea

f ea

A.R. Estabragh et al. / Soils and Foundations 53 (2013) 617627622Table 5Chemical composition of extractor pore water and reservoir water at the end o

Condition Chemical composition of extracted pore water

Cycle EC (mS/cm) pH Ca2Mg2 (meq/L)

1 14.79 7.72 0.252 14.50 7.33 0.223 14.19 7.39 0.18

Table 4Chemical composition of extractor pore water and reservoir water at the end o

Condition Chemical composition of extracted pore water

Cycle EC (mS/cm) pH Ca2Mg2 (meq/L)

1 14.89 7.03 0.202 14.75 7.72 0.163 14.58 7.54 0.134 14.39 7.45 0.12

aElectrical conductivity.4 13.94 7.33 0.15

aElectrical conductivity.ch cycle of sample inundated with acidic water.

Chemical composition of reservoir water

Na (meq/L) pH ECa (mS/cm)

10.28 5.93 0.6819.88 5.83 0.6539.54 5.74 0.642

ch cycle of sample inundated with saline water.

Chemical composition of reservoir water

Na (meq/L) pH ECa (mS/cm)

29.85 8.4 1.60927.87 8.24 1.58527.13 8.21 1.50226.70 8.15 1.4739.35 5.7 0.638

brium condition are expansive during wetting and drying,while the deformations of the samples inundated with saline

d Fand acidic water are contractive. This difference can beattributed to the reactions of the clay soil and the water usedwas presented by Villar (1995) for bentonite and was also usedsuccessfully by Alonso et al. (2005) to interpret their results.

4. Discussion

Over a full cycle of wetting and drying, there is a net changein the volume of the sample, indicating that the soil response iselasto-plastic. Therefore, the deformations consist of elasticand plastic strains. This phenomenon can be explained by theLC (LoadingCollapse) yield curve. As the tests began with aninitial wetting, the LC yield curve shrank from its initialposition and softening occurred in the sample. However, if thetests had been started with drying, the LC yield curve wouldhave expanded from its initial condition and hardening wouldhave occurred in the sample. Such behaviour was reported byAlonso et al. (2005) who conducted tests of drying and wettingcycles (drying rst) on mixtures of bentonite-sand. In thiswork, however, the rst cycle was started with wetting.It can be seen from Fig. 2 that in the case of the sample

inundated with distilled water, the deformations in the equili-

Fig. 5. Soilwater characteristic curve.

A.R. Estabragh et al. / Soils anfor inundating the samples during wetting.The surfaces of most clay particles (under dry or wet

conditions) carry an unbalanced negative charge, whichattracts cations. These positive ions become strongly attractedto a dry clay surface. The diffuse double layer can bedeveloped for individual layers or clay platelets. The interac-tion of the diffuse double layers of neighbouring unit layersresults in a net repulsive force between them. However,attractive forces develop between the two double layersapproaching extremely close to each other. The long-rangeattractive force is primarily due to the London vander waalesforces (vander waales forces are the sum of the attractive orrepulsive forces between molecules, atoms and surface). Thisforce was named the London dispersion force (London, 1937).The long-range repulsive force develops as a result of theelectrostatic repulsion between two adjacent clay particles(Barbour and Fredlund, 1989).Before saturation, the soil samples are in an unsaturatedstate. They have two suction components, namely, matricsuction (s) that arises from the capillary phenomenon inunsaturated voids and osmotic suction () that arises fromthe presence of salt in the soil water (Fredlund and Rahardjo,1993). When the soil sample is placed in the apparatus, it is inan unsaturated condition. By inundating the sample withdifferent types of wetting uids (distilled water, saline wateror acidic water), the water ow from the reservoir to the soilsample will continue until the matric suction has dissipated andthe sample has become saturated. In the case of inundating thesoil sample with distilled water, osmotic suction appears in thesample after saturation, the water ows to the sample (due tothe gradient between the soil water and the reservoir water)and the pore water pressure increases. The variation in porewater pressure (uw) during the osmotic ow can be expressedby the following equation:

s suw 2

where s is the external load (surcharge pressure) that isconstant during the test and s is the effective stress. uw isthe pore water pressure and its variations are due to theosmotic ow to the sample. By increasing the osmotic ow,therefore, the value of s is decreased by increasing uw and thisresults in a change in the ion concentration in the doublediffused layer. It is concluded in the case of the distilled waterthat there is a high chemical gradient between the pore water ofthe sample and the water in the reservoir. Thus, more waterenters the pores of the sample which, in turn, causes a greaterincrease in uw and a decrease in s in comparison with theothers soaked with saline water or acidic water. As a result, theswelling in the samples with the distilled water is greater thanthe swelling with either saline or acidic water.After the osmotic suction appears in the sample, migration

of the salt from the sample to the reservoir occurs due todiffusion. The results of the chemical analysis of the tests showthat for the sample inundated with distilled water, the initial pH(7.2) and the EC (14 S/cm) were increased to 7.55 and655 S/cm, respectively. However, the amounts of Na1 andCa2Mg2 of the extracted pore water from the samplewere 9.15 and 0.256 meq/lit, respectively. The increase in ECof the reservoir water indicates an increase in the concentrationof salt in the reservoir. The results also show that the value forEC decreases with an increase in the number of cycles ofwetting and drying and its variation is moderately slow whenthe equilibrium condition is attained. By comparing the resultsof the chemical analysis of the extracted pore water from thesample (Tables 35) with those of the original soil sample(Table 2) and considering the increase in the EC of thereservoir water, it can be concluded that the migration of salt tothe reservoir has occurred. Similar observations and resultswere obtained for the samples inundated with saline and acidicwater (Tables 4 and 5). However, the sample prepared withsaline water had the greatest amount of salt diffusion among

oundations 53 (2013) 617627 623the three and the distilled water had the least effect on themigration of salt.

the number of cycles; therefore, the total applied load on thesample is decreased by increasing the number of cycles.Figs. 7 and 8 show the results of the nal stage of wetting

and drying (the equilibrium condition) under surcharge pres-sures of 10 and 20 kPa, respectively, for the samples inundatedwith distilled, saline and acidic water. The results show that thepaths from the end of swelling to the end of shrinkage consist

Fig. 6. Variations in osmotic suction during wetting and drying cycles fordifferent types of wetting uids.

Fig. 7. Equilibrium condition of swell-shrink paths for different types ofwetting uids under surcharge pressure of 10 kPa.

Fig. 8. Equilibrium condition of swell-shrink paths for different types ofwetting uids under surcharge pressure of 20 kPa.

d FThe results show that under both surcharge pressures, thepotential for swelling and shrinkage increases with an increas-ing number of cycles. These results are not consistent with thendings of researchers such as Al-Homoud et al. (1995),Basma et al. (1996), Dif and Blumel (1991), Tripathy et al.(2002). They suggested that the swelling potential decreaseswhen expansive soil is repeatedly subjected to wetting anddrying cycles. However, the results are in agreement withthose presented by some other researchers, such as Osipovet al. (1987) and Day (1994), who showed that the potential forswelling increases after the rst cycle when the samples ofexpansive soil are allowed to fully desiccate. By comparing theresults of Figs. 2 and 3, it is seen that the deformation of thesoil sample inundated with distilled water under 20 kPa is lessthan the deformation under 10 kPa (at equilibrium, the defor-mations are 29.9% and 18.5% for surcharge pressures of 10and 20 kPa, respectively). It can be said that the swellingpotential of the soil sample is controlled by the surchargepressure and the different types of wetting uids. In the case ofdistilled water, the expansion of the soil due to the swellingpotential is greater than its contraction due to the surchargepressure; and hence, the net deformation is expansive (Fig. 2).In the case of the acidic water, and particularly the salinewater, however, the swelling potential is less than the effect ofthe surcharge pressure.The results for the samples that were inundated with acidic

and saline water show compressive deformations at equili-brium which are different from those for the sample tested withdistilled water. For the sample inundated with acidic water, thedeformations in the sixth cycle (at equilibrium) are 39.0% and19.1% under surcharge pressures of 10 and 20 kPa, respec-tively, and the corresponding deformations for the sampletested with saline water are 38.15 and 21.0, respectively. Thesendings are in agreement with the results presented byTripathy et al. (2002) and Rao and Thyagaraj (2007a).The concept of osmotic suction can be used to explain these

conditions. Since the values of EC for the pore uid of thesample and the reservoir were measured at the end of eachcycle, the osmotic suction can be estimated at the end of eachcycle. The osmotic suction was determined from the USDA(1950) calibration curve (Fredlund and Rahardjo, 1993). TheUSDA (1950) calibration curve relates the osmotic suction tothe EC according to the following equation (Rao andThyagaraj (2007a)):

31:92EC1:08 3

where is the osmotic suction in kPa and EC is the differencebetween the electrical conductivities of the water extracted fromthe sample and that extracted from the reservoir in mS/cm(Tables 35). Fig. 6 shows the variations in osmotic suctions forthe different types of wetting uids at the end of four cycles ofwetting and drying. It is observed from the gure that theosmotic suction decreases when the number of cycles isincreased. Osmotic suction acts as an additional stress that is

A.R. Estabragh et al. / Soils an624experienced by the soil sample. The value of this load isdecreased due to the reduction in osmotic suction by increasingoundations 53 (2013) 617627of nearly two curved portions and a linear portion. At the topand bottom (curved) portions of the S-shaped curves, the

change in void ratio due to the changes in water content isinsignicant. The linear portions of the swelling and shrinkagepaths are nearly parallel to the full saturation line for samplesunder a surcharge pressure of 10 kPa. During successive cyclesof wetting and drying, the shrinkage curve gradually movesaway from the full saturation line and the samples becomemore unsaturated, resulting in very small changes in the voidratio for a decrease in the water content. This ends at a watercontent corresponding to a degree of saturation of less than40%. It is seen from Figs. 7 and 8 that the distance between thesaturation line and the S-shaped curve depends on the qualityof the water; this distance is the greatest for the soil inundatedwith distilled water and is the smallest for the soil tested with

hysteresis in wetting and drying paths was seen for the rst to

The purpose of this work was to investigate the effect ofdifferent types of wetting uids on the swelling potential of anexpansive clay soil during wetting and drying cycles. Theresults of the laboratory experiments highlighted the effect ofacidic water and saline water in reducing the swelling potentialof expansive soils. The following conclusions can be drawnfrom this study:

Osmotic suction and diffusion cause a growth in theswelling potential and its magnitude depends on thedifferent types of wetting uids.

The results show that the diffusion of salts from the soilwater to the reservoir will enhance the swelling potential ofcompacted soil due to the reduction in salt concentration.

A.R. Estabragh et al. / Soils and Fsaline water. As is shown in the gures, most of the variationin void ratio is between the curves of saturation degrees of40% and 90%. The results shown Figs. 7 and 8 are similar tothose presented by Tripathy et al. (2002) for differentsurcharge pressures. It is seen that during wetting and dryingat the equilibrium condition, the samples under differentsurcharge pressures have an S-shaped curve in the spaces ofw (water content) and e (void ratio). This curve shifts to theright and downward as the surcharge pressure is increased.The soilwater characteristic curve is hysteric; that is, for a

given suction, the water content is always higher during thedrying path than during the wetting path. Although the hysteresisis usually described through the soilwater characteristic curveduring wetting and drying, the irreversibility of the void ratio canalso be linked to the hysteresis (Sharma, 1998).It is possible to relate the void ratio to suction by using a

combination of the soilwater characteristic curve (or Eq. (1))and the void ratio-water content relationship (Figs. 7 and 8).Typical results for the variation in suction during wetting anddrying cycles for the sample tested with distilled water under asurcharge pressure of 10 kPa are shown in Figs. 9 and 10.These gures show the variations in void ratio with suction forcycles 1 and 5 of the sample. During wetting and drying, thevoid ratio is not the same for the rst cycle (Fig. 9); this can beattributed to the irreversible deformation that was observedduring wetting and drying. The difference between void ratiosis decreased by increasing the number of cycles of wetting anddrying until all deformations become almost reversible, asFig. 9. Variation in void ratio with suction in cycle 1 for sample undersurcharge pressure of 10 kPa and inundated with distilled water.fourth cycles. This is repeated until the fourth cycle (theequilibrium condition), after which the paths of swelling andshrinkage are found to be the same and the hysteresis iseliminated. This phenomenon can be attributed to the contin-uous rearrangement of the soil particles during drying andwetting which leads to a more intensive destruction of theinternal clay structure.There are many methods for treating expansive soils for

construction works. These include the use of lime, cement andy ash agents, among others. The method of cyclic wetting anddrying can be also considered as another method for improvingthe mechanical behaviour of this kind of soil. In this experimentalwork, three different types of wetting uids were used toinvestigate the swelling potential of an expansive soil. The resultsshowed that the potential for swelling is reduced by inundatingthe sample with acidic water, and particularly, saline water.Acidic and saline water can, therefore, be used as stabilizingagents to improve the mechanical behaviour of expansive soils inthe eld. Detailed laboratory tests should be conducted to identifythe appropriate type of water for different expansive soils.

5. Conclusionshown in Fig. 10. In this experimental work, however, the

Fig. 10. Variation in void ratio with suction in cycle 5 for sample undersurcharge pressure of 10 kPa and inundated with distilled water.oundations 53 (2013) 617627 625The effect of acidic water and saline water in controlling theswelling potential in compacted soil is similar to the effect

mechanical behaviour of a clay. International Journal for Numerical and

Cu

Di

Dif

d FMaio, C., Santoli, L., Schiavine, P., 2004. Volume change behaviour ofclays: the inuence of mineral composition, pore uid composition andstress state. Mechanics of Materials 36 (56), 435451.Day233250.isinier, O., Masrouri, F., 2005. Hydromechanical behaviour of a compactedswelling soil over a wide suction range. Engineering Geology 81, 204212., R.W., 1994. Swell-shrink behaviour of expansive compacted clay.Journal of Geotechnical Engineering 120 (3), 618623.Analytical Methods in Geomechanics 28 (3), 209228.Chen, F.H., 1988. Foundation on Expansive Soils, 2nd ed. Elsevier Science

Publishing Co., New York, USA.Chertkov, V.Y., 2000. Using surface cracks spacing to predict crack network

geometry in swelling soils. Soil Science Society of American Journal 64,19181921.

Cui, Y.J., Yahia-Aissa, M., Delage, P., 2002. A method for the volume changebehaviour of heavily compacted swelling clays. Engineering Geology 64,of increasing the surcharge pressure on soil inundated withnatural water (Tripathy et al., 2002).

The variations in void ratio with water content at theequilibrium condition are represented by an S-shaped curve,and the majority of the deformation occurs between thedegrees of saturation of 40% and 90%.

Additional studies are needed to investigate the effect ofdifferent types of wetting uids on different expansive soilsbecause different clays have different levels of suscept-ibility to wetting and drying.

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Effect of different types of wetting fluids on the behaviour of expansive soil during wetting and dryingIntroductionExperimental workMaterialSample preparationApparatusWaterChemical testsSoilwater characteristic curve

ResultsDiscussionConclusionReferences