Soils and Foundations 2013;53(5):617–627The Japanese Geotechnical Society Soils and Foundations www.sciencedirect.com journal homepage: www.elsevier.com/locate/sandf Effect of different types of wetting fluids on the behaviour of expansive soil during wetting and drying A.R. Estabragha,n, M. Moghadasa,1, A.A. Javadib,2 b a Faculty of Soil and Water Engineering, University of Tehran, PO Box 4411, Karaj 31587-77871, Iran Computational Geomechanics Group, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Devon EX4 4QF, UK Received 9 February 2012; received in revised form 15 May 2013; accepted 10 June 2013 Available online 24 September 2013 Abstract This paper presents the results of an experimental investigation into the mechanical behaviour of an expansive soil during wetting and drying cycles. The experimental tests were conducted in a modified oedometer under two different surcharge pressures (10 and 20 kPa). During the tests, the samples were inundated with different types of wetting fluids (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 potential increases with an increasing number of wetting and drying cycles. The effect of the distilled water on the swelling potential is not the same as that of the saline water or the acidic water, particularly for different surcharge pressures. The variations in void ratio and water content show that, at the equilibrium condition, the wetting and drying paths converge to nearly an S-shaped curve. This curve consists of a linear portion and two curved 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. Keywords: Expansive soil; Wetting and drying; Distilled water; Saline water; Acidic water 1. Introduction Expansive soils are a worldwide problem as they cause extensive damage to Civil Engineering structures. The average cost of this damage to buildings, roads, airports and pipelines is about $9 billion per annum in the USA. This is more than twice the combined average annual damage due to all earthquakes, n Corresponding author. Tel.: þ98 26 32241119; fax: þ 98 26 32226181 E-mail addresses:
[email protected] (A.R. Estabragh),
[email protected] (M. Moghadas),
[email protected] (A.A. Javadi). 1 Tel.: þ98 26 32241119; fax: þ98 26 32226181. 2 Tel.: þ44 1392 723 640; fax: þ44 1392 217 965. Peer review under responsibility of The Japanese Geotechnical Society. floods, tornados and hurricanes in the USA (Jones and Jones, 1987). As a result, a clear understanding of the behaviour of expansive soils is required for the effective design of structures and infrastructures on these soils. There are many factors that govern the expansive behaviour of soils. The initial factors are the availability of moisture and the amount of clay particles in the soil. Other factors affecting the expansive behaviour include the type of soil, the condition of the soil in terms of dry density and the moisture content, the magnitude of the surcharge pressure and the amount of nonexpansive material. In general, the swelling potential increases as the dry density increases and the water content decreases (Hanafy, 1991; Fredlund and Rahardjo, 1993; Marinho and Stuermer, 2000; Ferber et al., 2009). The behaviour of expansive soils under cycles of wetting and drying has been the 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.2013.08.001 It will be shown that it is possible to minimize the effects of volume changes during wetting and drying by conducting appropriate tests to characterize the potential of the swelling and shrinkage of expansive soils.4 4. The optimum water content Several mixtures were prepared using kaolin and bentonite with preselected quantities of different types of wetting fluids (distilled water.1 50. Alonso et al. a mould was designed and made from stainless steel.6 0. Drinking water. The effect of surcharge pressure on the swelling behaviour will also be studied.2 7610 in the standard compaction test was 18% and the maximum dry unit weight was 16. A wide range of soil mixtures was investigated to identify a mixture with the desired wetting and drying properties (a high potential for swelling and shrinkage). Material The soil used in the testing program was highly expansive clay (according to the classification by McKeen (1992)). The main objective of this study.5% less than the optimum water content . Wang et al. Lloret et al. 2005. By repeating this procedure. (2013).0 kN/m3. Cuisinier and Masrouri (2005). to the authors’ knowledge. with a pH value of 7.76. a Cl 1 content of 1. to a given dry unit weight of 15. 1999.8 31.04 8. (2002) studied the wetting and drying behaviour in terms of the void ratio and the water content.. (2003). The results of this experimental study will be presented in terms of the volumetric deformation and the void ratio-water content relationship.1 meq/L. Rao and Thyagaraj. Tang et al. (2008). The soil was prepared by mixing bentonite with low-plasticity kaolin. The dimensions of the middle section were exactly the same as those of the ring of the oedometer.7 meq/L and a Ca þ 2 þ Mg þ 2 content of 9. Estabragh et al.. / Soils and Foundations 53 (2013) 617–627 full swelling and then allowed them to dry to their initial water content.7 kN/m3 and a water content of 13. The mould was also provided with a piston that was used to compress the sample inside the mould. 2008. before compaction. Siddiqua et al. such as Wheeler et al.. 2007b. Cekerevac and Laloui (2004). Finally.. is to investigate the effect of different types of wetting fluids on the wetting and drying behaviour of clay soil. 2. Table 1 Physical and mechanical properties of soil. Dif and Blumel (1991) found almost no volume change in remoulded clay after at least three or four drying and wetting cycles. 2004.6 Mg/m3 27% 33% 40% Table 2 Chemical composition of soil. The mixtures were kept in closed plastic bags and allowed to cure for 24 h. Di Maio et al. taking the necessary precautions and designing a suitable foundation system. Musso et al. Several investigations have shown the behaviour of expansive soils under chemical influence (Alawaji. 2011). The mould was a split compaction mould which consisted of three sections: a top collar. Samples were prepared in three layers.1 8. The physical and chemical properties of the soil are shown in Tables 1 and 2.1.75 70% 23% 47% 13% CH 120 kPa 18% 1. the soil showed signs of irreversible deformation after each cycle of wetting and drying. Casttellanos et al. Soil properties Values Specific gravity Consistency limits Liquid limit (LL) Plastic limit (PL) Plastic index (PI) Shrinkage limit (SL) USCS classification Swelling pressure Compaction study Optimum water content Maximum dry density Grain size analysis Sand Silt Clay 2. Rao and Shivananda. The soil had a swelling pressure of 120 kPa and it was determined according to the ASTM D4546 (2008) standard.5% (4. Nowamooz and Masrouri (2008). was used to compact and prepare the samples. the soil can be classified as clay with high plasticity (CH). such as Cui et al. the soil chosen comprised a mixture of 20% bentonite and 80% kaolin. therefore. According to the Unified Soil Classification System (USCS). 2003. no research studies have ever been reported in literature on the effect of different types of wetting fluids on the behaviour of clay soil during cycles of wetting and drying. This allowed the moisture in the soil to distribute evenly throughout the mass of soil. However. (2003). (2005). In order to obtain uniform and repeatable samples. by static compaction of the moist soil in the mould. a middle section and a bottom collar. (2002). Sample preparation 2. 2007a.618 A. Chemical component Amount Na þ (meq/L) K þ (meq/L) Ca2 þ (meq/L) Mg2 þ (meq/L) Cl (meq/L) CO2 3 (meq/L) SO2 4 (meq/L) HCO 3 (meq/L) pH Electrical conductivity (μS/cm) 73. to reduce the friction during compaction. They concluded that heating has a significant effect on the mechanical behaviour of expansive soils. saline water or acidic water). respectively.R. The hydromechanical behaviour of compacted swelling soils at ambient temperature has been studied by a number of researchers.5 0.2. Many researchers. Silicon grease was used on the inner surface of the mould. Experimental work 2.9 35. Tripathy et al. have studied the behaviour of expansive soils during wetting and drying cycles by controlling the suction. the self-healing may result in the close-up of cracks during wetting. . Based on these preliminary tests. During the heating process. Tensile stress develops only when the soil is restrained in some way against shrinkage (Kodikara et al. Apparatus A conventional oedometer was modified to allow tests to be conducted under a controlled temperature and surcharge pressure. The sample was placed in the ring between two porous stones with a loading plate resting on the upper porous stone. When using this apparatus. The vertical deformation was recorded from the dial gauge readings. 1.A. All samples were compacted in an identical fashion in order to provide the same initial fabric in the samples. the volume change of the sample during the subsequent swelling cycles in this case was three dimensional. 2000). In order to reduce the length of the drying samples. The duplicated samples were dismantled and their height and diameter were measured. In high plasticity soils.5 mm per minute. Liu et al. The diameter was measured for at least three points and then the mean of the measurements was considered. at least six or seven samples were tested. Estabragh et al. 2000). In order to plot the wetting path within each cycle. the spatial distribution and the connectivity controls the rate and velocity at which the solutes are transported in the soil (Horgan and Young. were carried out on the samples. Cracks occur when the tensile stress developing in the soil. The determination of the crack dimensions (width. as shown in Fig. During drying. a number of free swelling tests. the sample was moved to an oven set at a temperature of 45 1C. Umezaki and Kawamura (2013) proposed the vacuum evaporation method. hereafter referred to as the preliminary tests. except for the first swelling cycle. exceeds the tensile strength of the soil. The vertical deformations of the samples were measured during wetting and drying using a dial gauge. After the swelling tests. the duration of each cycle was found to be about 12 days. a drying stage was implemented. The sample was then inundated with water and allowed to swell under the applied surcharge pressure. the water was gradually expelled from the sample and the volume decreased. 2000). The duplicated samples were placed in the oven under the same surcharge pressure at 45 1C and their water contents were measured at certain time intervals in order to determine the variation in water content and void ratio during the drying stage. the surface of the compacted layer was scarified so that there was a good bond between the adjacent layers of soil. due to the drying. The dimensions and the water content of the sample were measured in different time intervals until they reached a constant value after about 7 days. to find the time required for the equalization of each test path. This was found to be about 5 days for the first wetting path. It is generally known that clay soils can crack during drying. After the completion of swelling. The combination of one swelling and the subsequent shrinkage steps is designated as one swell-shrink cycle. (2012) recently proposed a modified control apparatus that measures the volume change of the sample during the wetting and drying cycles. there is no need to duplicate the samples. length and depth). at least five samples were tested. 2. The drainage valve was opened so the water could flow out from the cell and the temperature controller was fixed at 45 1C. the soil hydraulic properties are directly controlled by the desiccation crack networks (Chertkov. The calibration of the temperature was done with a thermometer. 1993). 1. Layout of apparatus. in order to plot the drying path.. Therefore. Before placing the next layer. Most importantly. Albrecht and Benson (2001) indicated that the hydraulic conductivity of cracked soil is several orders of magnitude greater than that of intact soil.3. from standard Proctor compaction tests).R. a drying stage was implemented. After the completion of swelling. Similarly. The sample was loaded to a prescribed surcharge pressure and the pressure was maintained until full settlement was achieved. The duration of this stage was nearly 7 days. according to ASTM D4546 (2008). Before starting the main tests. / Soils and Foundations 53 (2013) 617–627 619 Fig. There is no standard method for measuring the crack dimensions at the end of drying. The variation in water content with void ratio during the wetting and drying cycles was determined with the information from the duplicated samples. the shrinkage of the soil sample caused the sample to decrease in diameter and height. Each layer was compacted to a vertical stress of 860 kPa in a compression frame at a displacement rate of 1. The formation of cracks is enhanced by the availability of the clay (Mitchell. The apparatus consisted of a fixed ring with a modification to allow the shrinkage and the swelling of the samples under the controlled surcharge pressure and temperature. (2002) used mercury displacement to measure the dimensions of the soil sample.6. The volumetric deformations in the cycles of wetting and drying. compacted soil samples were subjected to wetting and drying cycles with different types of wetting fluids under constant surcharge pressure. respectively. (1995).17% during wetting and drying. the deformations are increased and the equilibrium condition is finally reached in the fifth cycle with a 29. 2. Rayhani et al. (2002). Al Wahab and El-Kedrah (1995) and Tang et al. who have worked on studying the behaviour of soils in cycles of wetting and drying. (3) Acidic water with a pH of 5. Tang et al. 2. Researchers such as Al-Homoud et al.9% deformation. respectively. (2000). (2) Saline water with a pH and an EC of 8. (2006). Void ratio and water content were calculated without considering the effect of cracks. Tang et al. 3. In the second cycle. but Miller et al. 10 ml of sulphuric acid with normality equal to 0. Dif and Blumel (1991). the deformations are 25. / Soils and Foundations 53 (2013) 617–627 Kleppe and Olson (1985) developed a scale in the range of 0–4 to describe the severity of cracking. It is obvious that by increasing the cycles. EC and pH. but there is a possibility that mercury fills the cracks and reduces the accuracy.5g sodium chloride was mixed with 1000 ml of distilled water). (1998) used the crack intensity factor (CIF) to explain the cracking. they experienced shrinkage in the subsequent drying stage.2 and an electric conductivity (EC) equal to 14 μS/cm. Péron et al. 2. Chemical tests At the end of the swelling stage in each test. CIF is defined as the ratio of the crack area (Ac) to the total area (At) of a drying soil mass during drying. The vertical deformation of the samples is expressed as the change in the height (ΔH) of the sample during either swelling or shrinkage as a percentage of the initial height of the sample at the beginning of the first swell-shrink cycle. Wetting and drying cycles for different types of wetting fluids under surcharge pressure of 10 kPa.0 and 900 μS/cm. showing an increase in deformation compared with the first cycle. . (2008) used a digital calliper to measure the length and the width of cracks. They found that after three cycles the cracks attained the equilibrium condition. (2011) used image processing to determine the behaviour of cracks.5. a 10-ml sample of water was extracted from the oedometer reservoir and used to determine the electric conductivity (EC) and the pH of the water. 2. Punthauaecha et al.R.620 A. The samples were first wetted so that they experienced an increase in volume due to the decrease in suction (increase in water content). In the first cycle. according to ASTM D5298 (2010). Using photographs of soil samples and recording the crack area have been suggested by Peng et al. are shown in Fig. this resulted in a reduction in accuracy. respectively. It is used as a descriptor of the extent of the surficial cracking and quantifies the cracks.75% and 21. Subba Rao et al. Tripathy et al. For preparing the acidic water in the laboratory. This final (and nearly reversible) deformation shows an increase of more than 100% in swelling potential 2. three kinds of water were used: (1) Distilled water with a pH of 7. Estabragh et al.4.5% and a surcharge pressure of 10 kPa. Subba Rao et al.52% and 26. (1996). Water For inundating the samples during wetting cycles. (2006). This water was prepared by adding sodium chloride into distilled water (2. Basma et al. Soil–water characteristic curve The soil–water characteristic curve is the relationship between the water content (either volumetric or gravimetric) or the degree of saturation and soil suction. (2011) conducted wetting and drying cycles on clay soil samples to find the effect of wetting and drying on the initiation and the evolution of cracks. inundated with distilled water. the trend of the variation in the change in volume of the sample during wetting and drying cycles was observed. By plotting the volumetric deformation of a sample for several swell-shrink cycles. Results In this work. for the samples tested with an initial water content of 13. for pore water extraction for the soluble salt determination ASTM D4542 (1995). (2000) and Tripathy et al.1% in the wetting and drying paths.5 and an EC of 19 μS/cm. have not reported the existence of any cracks in the drying stage. The inundated samples (identical samples were prepared with similar initial conditions as the main samples and subjected to wetting and drying) were dismantled using the ASTM procedure Fig. acidic water and saline water. the deformations of the sample inundated with distilled water are 9. The volumetric strain for each cycle was calculated by combining the vertical and radial strain (obtained from duplicated samples). In this work.01 was mixed with 990 ml of distilled water. (2008) used the method of measuring the dimensions of a sample to calculate the volumetric deformation of the sample. (2006). The filter paper test was used. to determine the soil–water characteristic curve. the method of measuring dimensions was used to calculate the volume of the duplicated samples. In the second cycle.9%. (b) cycle 2.15%. respectively.5% for wetting and drying.0%.6% and 24. the amount of shrinkage during drying is more than the amount of swelling during wetting. 4.6% and 23. During the third and subsequent cycles.3% and 14. In subsequent cycles. respectively. acidic water and saline water under a surcharge pressure of 20 kPa. The results for the samples inundated with saline water (Fig. In the case of samples inundated with acidic water.65% during wetting and drying.85% and 18.85%. indicating that the shrinkage potential is more than the swelling potential in this cycle. the amount of shrinkage during drying is about 6 times the amount of swelling due to wetting and the amount increases in subsequent cycles. they increase to 21.R. thus. The results for the sample inundated with acidic water (Fig. and they are increased by increasing the number of cycles. they reach 14. In the second cycle. indicating that the potential for swelling is less than the potential for shrinkage. The equilibrium condition is achieved in the fourth cycle with deformations of about 18. the volumetric strains during the first cycle are 6. The volumetric strains in the first cycle for the sample inundated with distilled water are 2. Fig.A. In other words. respectively. The equilibrium condition is achieved in about the fifth cycle with a volumetric strain of 38. 3. By increasing the number of cycles. 621 gradually increase. respectively. (c) cycle 3 and (d) cycle 4. 3 shows the volumetric strain of the samples inundated with distilled water.15% and 18.9%. indicating an increase in the potential for swelling and shrinkage. For the samples inundated with saline water.4% and 18. the volumetric strains during the first cycle of wetting and drying are 3. the swelling and shrinkage potentials increase until the equilibrium condition is reached in the fourth cycle with a deformation of 19. The volumetric strains in the second cycle are 22. Wetting and drying cycles for different types of wetting fluids under surcharge pressure of 20 kPa. respectively. the volumetric strains are 6. In other words. At the equilibrium condition. these values Fig. / Soils and Foundations 53 (2013) 617–627 compared with the first cycle.15%. Water content–void ratio paths for acidic water under surcharge pressure of 10 kPa in (a) cycle 1. the deformations are compressive and the difference between swelling and shrinkage deformations is reduced by increasing the number of cycles until they Fig. . the amount of shrinkage during drying is about 4 times the amount of swelling due to wetting. 2) show that in the first cycle. Estabragh et al. respectively.85% and 16.1% with the majority of the deformation being compressive.15% and 13. the volumetric strain reached 39. 3) show that the deformations in the first cycle are 3.5% for wetting and drying.15% and 10. respectively.45%.95% for the wetting and drying paths. 3 and 4 show the positions of the samples at the end of the shrinkage (drying) stages in different cycles. These results show that the initial EC of the reservoir water increased and that the values of Na þ 1.87 27.93 5.552 0.19 13.653 0. points B.70 8. Estabragh et al.256 0. The procedure followed in the wetting and drying cycles is shown in Fig.473 Electrical conductivity. The results of chemical tests on the pore water extracted from the soil sample and the reservoir water of the consolidation cell after each cycle are shown in Tables 3–5 for distilled. þMg Chemical composition of reservoir water 2þ (meq/L) þ Na (meq/L) pH ECa (mS/cm) 10.87 7.50 14.20 0.35 14. Condition Chemical composition of extracted pore water Cycle EC (mS/cm) pH Ca2 þ þMg2 þ (meq/L) Na þ (meq/L) pH ECa (mS/cm) 1 2 3 4 14.28 9.39 7. 2.21 8.62 7.24 8.42 7.7 0. The tendency to converge to the same S-shaped curve was evolved by repeating the cycles of wetting and drying.33 0. Point A in Fig. C.609 1. the changes in void ratio with the water content are shown from the initial (compacted) condition to the fourth cycle of wetting and drying.4 8.39 7. In these figures.25 0. saline and acidic water. points 1.15 a Electrical conductivity. 4 that the soil sample reached nearly full saturation in all stages of wetting and that all the wetting and drying curves were S shaped. the values for the void ratio and the water content were determined for the different tests.681 0.655 0.45 0.67 7. In Fig. / Soils and Foundations 53 (2013) 617–627 reach equilibrium (deformation of about 21%) in the sixth cycle. or compacted.72 7. Condition Chemical composition of extracted pore water 2þ Cycle EC (mS/cm) pH Ca 1 2 3 4 14. Table 5 Chemical composition of extractor pore water and reservoir water at the end of each cycle of sample inundated with acidic water. respectively. along with various constant saturation lines.19 6.35 5.03 7.165 0. respectively.40 7.12 a þMg Chemical composition of reservoir water 2þ (meq/L) þ Na (meq/L) pH ECa (mS/cm) 29. 5. are shown in Fig. the majority of the deformation in the other cycles is located in the region of compression.94 7.64 14.585 1. Condition Chemical composition of extracted pore water 2þ Cycle EC (mS/cm) pH Ca 1 2 3 4 14. From the results.75 14. 4(a) shows the initial.17 7. void ratio (e0) and the water content (w0) of the sample.58 14. Table 4 Chemical composition of extractor pore water and reservoir water at the end of each cycle of sample inundated with saline water. In the tests conducted under a surcharge pressure of 20 kPa.15 8. The following empirical relationship was obtained for the water retention curve of the soil: w ¼ 87:1438:21 LnðsÞ ð1Þ where w and s are the water content in % and the suction in kPa.33 0.18 0.13 0.638 .15 1.54 9.32 0. In the first cycle. 4(a)–(d).145 9.85 27. Typical results for void ratio versus water content for the sample tested with acidic water under a surcharge pressure of 10 kPa.88 9.51 7.21 0.Ca þ 2 þ Mg þ 2 and pH of the extracted pore water decreased.R. It is seen from Fig. 4. 4(a)).642 0.89 14.79 14.550 0.502 1.22 0. except for the first cycle.622 A.15 13.33 7.74 5. This relationship is similar to the relationship that Table 3 Chemical composition of extractor pore water and reservoir water at the end of each cycle of sample inundated with distilled water.51 7.13 26. 4. the results are shown in Fig.72 7.54 7.524 a Chemical composition of reservoir water Electrical conductivity. The soil–water characteristic curve was determined using the filter paper test.83 5. D and E indicate the positions of the samples at the end of the swelling (wetting) stages. swelling occurred from point A to point B followed by shrinkage from point B to 1 (see Fig.16 0.55 7. the value of s′ is decreased by increasing uw and this results in a change in the ion concentration in the double diffused layer. The results of the chemical analysis of the tests show that for the sample inundated with distilled water. therefore. This difference can be attributed to the reactions of the clay soil and the water used for inundating the samples during wetting. / Soils and Foundations 53 (2013) 617–627 Fig. The long-range repulsive force develops as a result of the electrostatic repulsion between two adjacent clay particles (Barbour and Fredlund. in turn. matric suction (s) that arises from the capillary phenomenon in unsaturated voids and osmotic suction (π) that arises from the presence of salt in the soil water (Fredlund and Rahardjo. Before saturation. 1993). the first cycle was started with wetting. In this work. By comparing the results of the chemical analysis of the extracted pore water from the sample (Tables 3–5) with those of the original soil sample (Table 2) and considering the increase in the EC of the reservoir water. there is a net change in the volume of the sample. respectively. if the tests had been started with drying. the soil samples are in an unsaturated state. the water flows to the sample (due to the gradient between the soil water and the reservoir water) and the pore water pressure increases. 1937). Soil–water characteristic curve. osmotic suction appears in the sample after saturation. The results also show that the value for EC decreases with an increase in the number of cycles of wetting and drying and its variation is moderately slow when the equilibrium condition is attained. the LC yield curve would have expanded from its initial condition and hardening would have occurred in the sample. Thus. 623 ð2Þ where s is the external load (surcharge pressure) that is constant during the test and s′ is the effective stress. Similar observations and results were obtained for the samples inundated with saline and acidic water (Tables 4 and 5). causes a greater increase in uw and a decrease in s′ in comparison with the others soaked with saline water or acidic water. The diffuse double layer can be developed for individual layers or clay platelets. indicating that the soil response is elasto-plastic. respectively. it can be concluded that the migration of salt to the reservoir has occurred. By increasing the osmotic flow. namely. However. Therefore.R. However. They have two suction components. (2005) to interpret their results. However. As a result. however. The variation in pore water pressure (uw ) during the osmotic flow can be expressed by the following equation: s′ ¼ suw 4.55 and 655 μS/cm. When the soil sample is placed in the apparatus. the water flow from the reservoir to the soil sample will continue until the matric suction has dissipated and the sample has become saturated. the swelling in the samples with the distilled water is greater than the swelling with either saline or acidic water.A. atoms and surface). it is in an unsaturated condition. the initial pH (7. Such behaviour was reported by Alonso et al. which attracts cations.2) and the EC (14 μS/cm) were increased to 7. the amounts of Na þ 1 and Ca þ 2 þ Mg þ 2 of the extracted pore water from the sample were 9. The long-range attractive force is primarily due to the London vander waales forces (vander waales forces are the sum of the attractive or repulsive forces between molecules. As the tests began with an initial wetting. the LC yield curve shrank from its initial position and softening occurred in the sample. migration of the salt from the sample to the reservoir occurs due to diffusion. the deformations consist of elastic and plastic strains. 2 that in the case of the sample inundated with distilled water. was presented by Villar (1995) for bentonite and was also used successfully by Alonso et al. It can be seen from Fig. The increase in EC of the reservoir water indicates an increase in the concentration of salt in the reservoir. Estabragh et al. . uw is the pore water pressure and its variations are due to the osmotic flow to the sample. saline water or acidic water). The interaction of the diffuse double layers of neighbouring unit layers results in a net repulsive force between them. 1989). Discussion Over a full cycle of wetting and drying. These positive ions become strongly attracted to a dry clay surface. the sample prepared with saline water had the greatest amount of salt diffusion among the three and the distilled water had the least effect on the migration of salt.15 and 0. more water enters the pores of the sample which.256 meq/lit. This phenomenon can be explained by the LC (Loading–Collapse) yield curve. In the case of inundating the soil sample with distilled water. while the deformations of the samples inundated with saline and acidic water are contractive. attractive forces develop between the two double layers approaching extremely close to each other. By inundating the sample with different types of wetting fluids (distilled water. The surfaces of most clay particles (under dry or wet conditions) carry an unbalanced negative charge. It is concluded in the case of the distilled water that there is a high chemical gradient between the pore water of the sample and the water in the reservoir. the deformations in the equilibrium condition are expansive during wetting and drying. (2005) who conducted tests of drying and wetting cycles (drying first) on mixtures of bentonite-sand. After the osmotic suction appears in the sample. This force was named the London dispersion force (London. 5. However. 5% for surcharge pressures of 10 and 20 kPa. Fig. By comparing the results of Figs. In the case of distilled water. (2002). Variations in osmotic suction during wetting and drying cycles for different types of wetting fluids. In the case of the acidic water. The value of this load is decreased due to the reduction in osmotic suction by increasing Fig.1% under surcharge pressures of 10 and 20 kPa. Fig. The results show that the paths from the end of swelling to the end of shrinkage consist of nearly two curved portions and a linear portion. the potential for swelling and shrinkage increases with an increasing number of cycles. These results are not consistent with the findings of researchers such as Al-Homoud et al. such as Osipov et al. respectively. Dif and Blumel (1991). They suggested that the swelling potential decreases when expansive soil is repeatedly subjected to wetting and drying cycles. It can be said that the swelling potential of the soil sample is controlled by the surcharge pressure and the different types of wetting fluids. The osmotic suction was determined from the USDA (1950) calibration curve (Fredlund and Rahardjo. and the corresponding deformations for the sample tested with saline water are 38. (1987) and Day (1994). It is observed from the figure that the osmotic suction decreases when the number of cycles is increased. At the top and bottom (curved) portions of the S-shaped curves. Osmotic suction acts as an additional stress that is experienced by the soil sample. the net deformation is expansive (Fig. Equilibrium condition of swell-shrink paths for different types of wetting fluids under surcharge pressure of 20 kPa. These findings are in agreement with the results presented by Tripathy et al. and hence. Tripathy et al. the number of cycles. Basma et al. (2002) and Rao and Thyagaraj (2007a).624 A. 6 shows the variations in osmotic suctions for the different types of wetting fluids at the end of four cycles of wetting and drying. for the samples inundated with distilled. Estabragh et al. the total applied load on the sample is decreased by increasing the number of cycles. However.0% and 19. Since the values of EC for the pore fluid of the sample and the reservoir were measured at the end of each cycle. the . The USDA (1950) calibration curve relates the osmotic suction to the EC according to the following equation (Rao and Thyagaraj (2007a)): π ¼ 31:92EC1:08 ð3Þ where π is the osmotic suction in kPa and EC is the difference between the electrical conductivities of the water extracted from the sample and that extracted from the reservoir in mS/cm (Tables 3–5). / Soils and Foundations 53 (2013) 617–627 The results show that under both surcharge pressures. respectively. who showed that the potential for swelling increases after the first cycle when the samples of expansive soil are allowed to fully desiccate. saline and acidic water. Figs. however. the deformations are 29. 2 and 3. therefore. the osmotic suction can be estimated at the end of each cycle. For the sample inundated with acidic water. The concept of osmotic suction can be used to explain these conditions. the deformations in the sixth cycle (at equilibrium) are 39. 8. (1996). respectively. the swelling potential is less than the effect of the surcharge pressure. 6. 7 and 8 show the results of the final stage of wetting and drying (the equilibrium condition) under surcharge pressures of 10 and 20 kPa. Equilibrium condition of swell-shrink paths for different types of wetting fluids under surcharge pressure of 10 kPa. and particularly the saline water. 7. the results are in agreement with those presented by some other researchers. it is seen that the deformation of the soil sample inundated with distilled water under 20 kPa is less than the deformation under 10 kPa (at equilibrium. 1993).R. 2).9% and 18.15 and 21. (1995). the expansion of the soil due to the swelling potential is greater than its contraction due to the surcharge pressure.0. The results for the samples that were inundated with acidic and saline water show compressive deformations at equilibrium which are different from those for the sample tested with distilled water. Fig. respectively). Estabragh et al. the shrinkage curve gradually moves away from the full saturation line and the samples become more unsaturated. There are many methods for treating expansive soils for construction works. It is possible to relate the void ratio to suction by using a combination of the soil–water characteristic curve (or Eq. – The results show that the diffusion of salts from the soil water to the reservoir will enhance the swelling potential of compacted soil due to the reduction in salt concentration. / Soils and Foundations 53 (2013) 617–627 change in void ratio due to the changes in water content is insignificant. the void ratio is not the same for the first cycle (Fig. These figures show the variations in void ratio with suction for cycles 1 and 5 of the sample. that is. 9). The soil–water characteristic curve is hysteric. the hysteresis in wetting and drying paths was seen for the first to fourth cycles. however. three different types of wetting fluids were used to investigate the swelling potential of an expansive soil. 7 and 8). These include the use of lime. cement and fly ash agents. In this experimental work. 9. shown in Fig. The difference between void ratios is decreased by increasing the number of cycles of wetting and drying until all deformations become almost reversible. The linear portions of the swelling and shrinkage paths are nearly parallel to the full saturation line for samples under a surcharge pressure of 10 kPa. this distance is the greatest for the soil inundated with distilled water and is the smallest for the soil tested with saline water. Acidic and saline water can. The results showed that the potential for swelling is reduced by inundating the sample with acidic water. for a given suction. (2002) for different surcharge pressures. The method of cyclic wetting and drying can be also considered as another method for improving the mechanical behaviour of this kind of soil. 10. and particularly. resulting in very small changes in the void ratio for a decrease in the water content. this can be attributed to the irreversible deformation that was observed during wetting and drying. As is shown in the figures. 9 and 10. The results shown Figs. Although the hysteresis is usually described through the soil–water characteristic curve during wetting and drying. This is repeated until the fourth cycle (the equilibrium condition). This ends at a water content corresponding to a degree of saturation of less than 40%. – The effect of acidic water and saline water in controlling the swelling potential in compacted soil is similar to the effect . 7 and 8 are similar to those presented by Tripathy et al. Detailed laboratory tests should be conducted to identify the appropriate type of water for different expansive soils. Variation in void ratio with suction in cycle 5 for sample under surcharge pressure of 10 kPa and inundated with distilled water. During wetting and drying. In this experimental work. Conclusion The purpose of this work was to investigate the effect of different types of wetting fluids on the swelling potential of an expansive clay soil during wetting and drying cycles. This phenomenon can be attributed to the continuous rearrangement of the soil particles during drying and wetting which leads to a more intensive destruction of the internal clay structure. 7 and 8 that the distance between the saturation line and the S-shaped curve depends on the quality of the water. most of the variation in void ratio is between the curves of saturation degrees of 40% and 90%. Variation in void ratio with suction in cycle 1 for sample under surcharge pressure of 10 kPa and inundated with distilled water. 10. be used as stabilizing agents to improve the mechanical behaviour of expansive soils in the field. It is seen that during wetting and drying at the equilibrium condition. – Osmotic suction and diffusion cause a growth in the swelling potential and its magnitude depends on the different types of wetting fluids. the samples under different surcharge pressures have an S-shaped curve in the spaces of w (water content) and e (void ratio). as 625 Fig. among others. 1998). During successive cycles of wetting and drying. The following conclusions can be drawn from this study: Fig.R. It is seen from Figs. This curve shifts to the right and downward as the surcharge pressure is increased. Typical results for the variation in suction during wetting and drying cycles for the sample tested with distilled water under a surcharge pressure of 10 kPa are shown in Figs. therefore. 5. the irreversibility of the void ratio can also be linked to the hysteresis (Sharma.A. The results of the laboratory experiments highlighted the effect of acidic water and saline water in reducing the swelling potential of expansive soils. after which the paths of swelling and shrinkage are found to be the same and the hysteresis is eliminated. the water content is always higher during the drying path than during the wetting path. saline water. (1)) and the void ratio-water content relationship (Figs. .P.G. Santoli. H. 1992. 229–237.. El-Kedrah.F. M. Rumjantseva.. Estabragh et al. Experimental study of desiccation of soil..K.H. Auriol. USA. Basma.. Hanafy. Quantification of soil shrinkage in 2D by digital image processing of soil surface.G. ASCE.. A. E. Applied Clay Science 2 (7). 1996. Villar. 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