Hydraulic conductivity of compacted clay liners permeated with inorganic salt solutions

Transcription

1 Los Angeles, London, New Delhi and Singapore Copyright ISWA 2008 ISSN X Waste Management & Research 2008: 26: DOI: / X Hydraulic conductivity of compacted clay liners permeated with inorganic salt solutions Gonca Yılmaz, Temel Yetimoglu, Seracettin Arasan Department of Civil Engineering, Atatürk University, Erzurum, Turkey Due to their low permeability, geosynthetic clay liners (GCLs) and compacted clay liners (CCLs) are the main materials used in waste disposal landfills. The hydraulic conductivity of GCLs and CCLs is closely related to the chemistry of the permeant fluid. In this study, the effect on the hydraulic conductivity of clays of five different inorganic salt solutions as permeant fluid was experimentally investigated. For this purpose, NaCl, NH 4 Cl, KCl, CaCl 2, and FeCl 3 inorganic salt solutions were used at concentrations of 0.01, 0.10, 0.25, 0.50, 0.75 and 1 M. Laboratory hydraulic conductivity tests were conducted on low plasticity (CL) and high plasticity (CH) compacted raw clays. The change in electrical conductivity and ph values of the clay samples with inorganic salt solutions were also determined. The experimental test results indicated that the effect of inorganic salt solutions on CL clay was different from that on CH clay. The hydraulic conductivity was found to increase for CH clay when the salt concentrations increased whereas when the salt concentrations were increased, the hydraulic conductivity decreased for the CL clay. Keywords: Clay liners, electrical conductivity, hydraulic conductivity, inorganic salts, ph, wmr Introduction Because of their low permeability, geosynthetic clay liners (GCL) and compacted clay liners (CCLs) are the main materials used in waste disposal landfills. The clays are exposed to various chemical, biological and physical events, and they are affected by the resulting leachate in waste disposal landfills. Therefore, when attempting to define the geotechnical characteristics of clays, the use of distilled water or tap water is far from being representative of the in-situ conditions. It is well known that the mechanical and hydraulic behaviour of clay soils can be strongly affected by the clay fluid system interaction (Mitchell 1993). For this reason, to properly use the compacted raw clays as impermeable liners, more theoretical and experimental study is needed to investigate the variation of hydraulic conductivity with chemicals. A great number of experimental studies dealing with the effects of chemicals on hydraulic conductivity of GCLs and clays are available in the literature. Some of these studies focused on inorganic liquids (Petrov & Rowe 1997, Shackelford et al. 2000, Jo et al. 2001, 2004, 2005, Kolstad et al. 2004a, Lee et al. 2005, Lee & Shackelford 2005, Mishra et al. 2005). The other studies focused on organic liquids (Anderson et al. 1985, Foreman & Daniel 1986, Bowders & Daniel 1987, Fernandez & Quigley 1989, Kaya & Fang 2000, Anandarajah 2003, Park et al. 2006), and leachate components (Ruhl & Daniel 1997, Kayabalı & Mollamahmutoglu 2000, Shan & Lai 2002, Kolstad et al. 2004b). Most of the researchers pointed out that the hydraulic conductivity increased when the concentration of chemical solutions was increased. Some researchers have compared the quality of clays on interaction with chemicals. Gleason et al. (1997) investigated some geotechnical properties of Ca and Na-bentonite with different concentrations of CaCl 2 (varying between 0.01 and M), NaCl (varying between 0.01 and 0.1 M), and methanol (pure methanol and 50% methanol in distilled water), and gasoline. They reported that calcium bentonite would be more resistant than sodium bentonite to chemical constituents in the permeating fluids. It was also concluded that permeation with a strong calcium chloride solution would cause large increases in the hydraulic conductivity of sodium bentonite. Similarly, Stern & Shackelford (1998) investigated the substitution of attapulgite clay for bentonite in a sand bentonite mixture on interaction with CaCl 2 solutions. They Corresponding author: Seracettin Arasan, Department of Civil Engineering, Atatürk University, Erzurum, Turkey. Tel.: ; fax: ; arasan@atauni.edu.tr Received 19 December 2007; accepted in revised form 13 March

2 Hydraulic conductivity of inorganic salt-permeated compacted clay liners Table 1: Index properties of clays. CL clay CH clay Clay content < mm (%) Finer content < mm (%) Specific gravity G S Liquid limit w L (%) Plastic limit w P (%) Plasticity index I P (%) Optimum moisture content OMC (%) Maximum dry unit weight γ dmax (kn m 3 ) Hydraulic conductivity k (cm s 1 ) Electrical conductivity EC (µs cm 1 ) ph reported that for mixtures with the same clay soil content, complete substitution of attapulgite clay for bentonite significantly decreased the change in hydraulic conductivity relative to that observed for the sand bentonite mixtures upon permeation with a 0.5 M CaCl 2 solution. Another similar study was conducted by Lee & Shackelford (2005). These authors studied the impact of bentonite quality on the hydraulic conductivity of geosynthetic clay liners. They observed that the hydraulic conductivity for high-quality bentonite (k H ) was lower than the hydraulic conductivity for low-quality bentonite (k L ), when specimens were permeated with water. However, the value of k H was always higher than that for k L when the specimens were permeated with the CaCl 2 solutions. Thus, the GCL with the higher-quality bentonite was more susceptible to chemical attack than the GCL with lower-quality bentonite. In comparison with high plasticity clays, there are a limited number of studies in the literature on the effects of chemical solutions on the hydraulic conductivity of low plasticity clays. Park et al. (2006) studied the effects of surfactants (octylphenol polyoxyethylene, biosurfactant, and sodium dodecyl sulfate) and electrolyte solutions (NaPO 3, and CaCl 2 ) on some properties of two soil samples (100% kaolinite clay soil, and 30% kaolinite + 70% sand). They found that chemical solutions did not significantly affect the hydraulic conductivity. Arasan & Yetimoglu (2006, 2008) studied the effect of inorganic salt solutions on the consistency limits of CL and CH class clays. It was indicated that both the liquid limit and the plastic limit somewhat increased when the concentration of salt solutions was increased for CL class clay, whereas both the liquid limit and the plastic limit decreased when the concentration of salt solutions was increased for CH class clay. They also reported that CL and CH class clays transformed into low plasticity silt (ML) and high plasticity silt (MH) class soils respectively, according to the Unified Soil Classification System (USCS). The present study was undertaken to investigate the effect of some inorganic salt solutions on the hydraulic conductivity, electrical conductivity (EC), and ph values of compacted raw clays. The tests were carried out on two different commercial clays (i.e., low plasticity CL-class and high plasticity CH-class clays). Five different inorganic salt solutions (i.e., sodium chloride (NaCl), ammonium chloride (NH 4 Cl), potassium chloride (KCl), calcium dichloride (CaCl 2 ) and iron trichloride (FeCl 3 ) solutions) were chosen as the permeants for the tests. The tests were repeated at six different values of salt solution concentration (i.e., 0.01, 0.1, 0.25, 0.5, 0.75, and 1 M). Some of the tests were repeated as many as three times to ensure the repeatability of the results. Test results were compared with those in the literature and discussed. Materials and methods Clays Two different classes of commercial clay soils were used in the tests. According to the USCS, the class of one soil was low plasticity clay (i.e., CL) and the class of the other was high plasticity clay (i.e., CH). Some properties of clays are given in Table 1 and the grain-size distributions of the clays are shown in Figure 1. Fig. 1: Grain-size distribution of the clays. 465

3 G. Yılmaz, T. Yetimoglu, S. Arasan Table 2: Some properties of the salts used in the tests. Chemicals Molecular weight (g) Solubility [g/100 g H 2 O ( C)] NaCl (20) NH 4 Cl (20) KCl (20) CaCl 2.2H 2 O (40) FeCl 3.6H 2 O (20) Salt solutions When evaluating compacted raw clays in their application as impervious liners in landfills, it is necessary to study the properties of the clays not only with distilled water but also with chemical solutions. The solutions used in this study were selected in order to cover as many types of leachate components as possible. A large body of work on the chemical composition of landfill leachate can be found in Ehrig (1988), Tchobanoglous et al. (1993), Vadillo et al. (1999), Kjeldsen et al. (2002), and Jorstad et al. (2004). The salt solutions used in this study consisted of sodium chloride (NaCl), ammonium chloride (NH 4 Cl), potassium chloride (KCl), calcium dichloride (CaCl 2 ) and iron trichloride (FeCl 3 ). These solutions were selected to investigate the effects of cation valance (i.e., monovalent, divalent, and trivalent) and type of inorganic salt solution. Distilled (DI) water was used as the reference solution. Inorganic salt solutions for the tests were prepared at six different concentrations (i.e., 0.01, 0.1, 0.25, 0.5, 0.75 and 1 M) by dissolving powdered salts in distilled water at solubility temperature. When selecting the concentration range used in the present study, the concentration values used widely in the literature were taken into account. Some properties of the inorganic salt solutions are shown in Table 2. Hydraulic conductivity tests The hydraulic conductivity tests were conducted using the rigid-wall compaction mould permeameter in according with the procedure described in ASTM D5856. The equipment used in the experiments was mainly a permeameter with a diameter of 100 mm and a length of 115 mm (Fig. 2). The test apparatus consisted of a mould with lids (i.e., solution ports) and standpipe (i.e., a burette) 10 mm in diameter and 100 mm in length. Assuming that Darcy s law was valid, the hydraulic conductivity values (k) were calculated as follows: k al h = ln ---- At h 2 where a is the cross-sectional area of the burette (cm 2 ); L is the length of the sample (cm); A is thecross-sectional area of the sample (cm 2 ); t is the elapsed time between determination of h 1 and h 2 (s); h 1 is the head lost across the sample, at time t 1 (cm); and h 2 is the head lost across the sample, at time t 2 (cm). (1) Fig. 2: The apparatus used for the hydraulic conductivity tests. All the test samples were compacted at optimum water content using distilled water inside the compaction mould. The compaction was carried out following the procedure of the Standard Proctor Test in ASTM D698. The compacted samples were then placed in the test set-up as seen in Figure 2. After that, the standpipe was filled with the permeant salt solution (i.e., influent solution). To achieve saturation, the samples were kept under these conditions for at least 72 h. The head losses across the test samples were measured and recorded periodically for approximately 2 8 weeks. The tests were continued until at least four values of hydraulic conductivity were obtained over an interval of time in which the hydraulic conductivity was steady. Some of the tests were repeated as many as three times to ensure the repeatability of the results. The average of the test results is given in this paper but the whole test data can be found in Yılmaz (2007). 466

4 Hydraulic conductivity of inorganic salt-permeated compacted clay liners Electrical conductivity and ph tests The clay samples permeated by chemical solutions during hydraulic conductivity test were taken out of the compaction mould after the hydraulic conductivity tests. For the EC and ph tests, some of the permeated clay samples were cut and then dried in an oven at approximately 105 C. The EC values of the samples were determined using a method which involved mixing the dried samples with distilled water in a ratio of 1 (solid)/100 (water), shaking this suspension periodically for 1 h, and then measuring the EC of the suspension with a conductivity cell. Furthermore, the ph value of the same suspensions was determined with a ph meter. The EC and ph values of the influent solutions were also determined with the same conductivity cell and ph meter. Results In the following, the effects of inorganic salt solutions at varying concentrations on the hydraulic conductivity, EC and ph for CL and CH clays are presented. Effect of NaCl concentrations The variation of the hydraulic conductivity with the concentration of NaCl solution for both CL and CH clays obtained from the tests is shown in Figure 3a. For CL clay, it is seen that none of the NaCl concentrations used in the tests significantly affected the hydraulic conductivity. The hydraulic conductivity of CL clay for all NaCl concentrations was slightly lower than that for distilled water (D.W.). However, increases in the permeant NaCl concentration caused significant increases in the hydraulic conductivity of CH clay. For NaCl concentrations, the value of hydraulic conductivity could be up to 25 times greater than that for distilled water. The effects of NaCl salt solutions on the EC and ph of CL and CH clays are given in Figure 3b and c, respectively. The EC and ph values of the influent solutions were also determined and are shown on the same figures. The EC values of influent solutions and clay samples permeated by salt solutions during the hydraulic conductivity tests are given in the units ms cm 1 and µscm 1, respectively. For influent solutions, the EC values increased with increasing NaCl salt concentration (Fig. 3b). Similarly, the EC values of both CL and CH clay samples increased when the concentration increased. The gradient of the increase was more pronounced for CL clay samples. The ph of influent solutions (i.e., NaCl concentrations) increased to approximately 7 at 0.01 M. Beyond that (i.e., greater than 0.01 M), the ph slightly decreased when the concentration of NaCl was increased In comparison with that of the influent solution, a similar relationship between the ph of CL clay samples and the concentration was obtained. In other words, at 0.01 M NaCl concentration the ph increased, and at concentrations greater than 0.01 M the ph slightly decreased when the concentration for CL clay samples was increased. However, the ph of CH clay samples decreased at all NaCl concentrations. The decrease was more pronounced at 0.01 M concentration, beyond which the rate of decrease in the ph was less significant. Fig. 3: Effect of NaCl concentrations on the (a) hydraulic conductivity (test results by Yilmaz et al. 2008); (b), EC and (c) ph of samples. Effect of NH 4 Cl concentrations Figure 4a shows the variation of the hydraulic conductivity of CL and CH clays with the concentration of NH 4 Cl. It could be seen that the hydraulic conductivity drastically decreased as the NH 4 Cl concentrations increased, up to around 0.1 M for CL clay. For concentrations greater than 0.1 M, the 467

5 G. Yılmaz, T. Yetimoglu, S. Arasan Fig. 4: Effect of NH 4 Cl concentrations on the (a) hydraulic conductivity; (b), EC and (c) ph of samples. Fig. 5: Effect of KCl concentrations on the (a) hydraulic conductivity; (b), EC and (c) ph of samples. hydraulic conductivity increased. For CH clay, the hydraulic conductivity increased up to 0.1 M, then decreased up to 0.5 M, and beyond that concentration the hydraulic conductivity significantly increased with increasing NH 4 Cl concentration. The variation of EC and ph values with NH 4 Cl concentration for CL and CH clays are presented in Figure 4b and c, respectively. It can be seen from Figure 4b that the EC values of the influent solution increased when the NH 4 Cl concentration was increased, similar to that of NaCl salt. It can be also seen from Figures 5b, 6b and 7b that the EC values of influent solutions increased when the concentrations of all of the salt solutions used in this study (i.e., NaCl, NH 4 Cl, KCl, CaCl 2, and FeCl 3 ) were increased. Similar to the results obtained for 468

6 Hydraulic conductivity of inorganic salt-permeated compacted clay liners Fig. 6: Effect of CaCl 2 concentrations on the (a) hydraulic conductivity; (b), EC and (c) ph of samples. Fig. 7: Effect of FeCl 3 concentrations on the (a) hydraulic conductivity; (b), EC and (c) ph of samples. NaCl salt solutions, the EC values of CL clay samples increased when the NH 4 Cl concentration increased. However, the CH clay samples behaved differently from CL clay samples. In other words, the EC values of the CH clay samples decreased as the concentration increased. Figure 4c shows that there was a similar relationship between ph and concentration for CL, CH clay samples and influent solutions to those observed at Figure 3c (i.e., the effect of NaCl concentrations on the ph of clay samples). The ph of the CL clay samples initially increased at a concentration of 0.01 M, beyond which the ph decreased as the concentration was increased, but the decrease was less significant. However, the ph of CH clay samples decreased at all NH 4 Cl concentrations. The decrease was more pronounced at a con- 469

7 G. Yılmaz, T. Yetimoglu, S. Arasan centration of 0.01 M, beyond which the rate of decrease in the ph was less significant. Effect of KCl concentrations The effect of KCl concentrations on the hydraulic conductivity, EC, and ph of clay samples is shown in Figure 5a, b, and c, respectively. For all KCl concentrations, the hydraulic conductivity of CH clay samples slightly increased when the concentration was increased. On the other hand, the test results indicated that the hydraulic conductivity of CL clay samples initially decreased at 0.01 M and then increased as the KCl concentration increased. However, the hydraulic conductivity of the CL clay sample at the highest KCl concentration (i.e., at 1 M) remained lower than the hydraulic conductivity of CL clay tested with distilled water. Similar to the results for the NaCl salt solution, the EC values of CL and CH clay samples increased when the concentration increased for tests conducted with KCl salt solution (Fig. 5b). The EC value increased from 203 µs cm 1 for CH clay samples tested with distilled water to 241 µs cm 1 for CH clay sample tested with 1 M concentration of KCl salt solution. The EC value increased from 49 to 159 µscm 1 for CL clay samples tested with distilled water and 1 M concentration of KCl salt solution, respectively. Briefly, it could be concluded that the rate of increase was more pronounced for CL clay samples. The variation of ph obtained with KCl solutions was similar to those of the other salt solutions (i.e., NaCl and NH 4 Cl) for CL clay samples. However, the ph remained almost constant at all KCl concentrations for CH clay samples. Effect of CaCl 2 concentrations The hydraulic conductivity, EC, and ph of the CL and CH clay samples are shown in Figure 6a, b and c, respectively as a function of the concentration of CaCl 2 solution. It is seen that the change in the hydraulic conductivity was less significant for CH clay samples. However, the hydraulic conductivity of CL clay samples decreased when the CaCl 2 concentration increased. Additionally, the variation of EC and ph with CaCl 2 salt solutions for CL and CH clay samples was found to be similar to those of NaCl and KCl salt solutions. Effect of FeCl 3 concentrations The results of the hydraulic conductivity, EC, and ph tests for CL and CH clay samples permeated with FeCl 3 salt solutions are shown in Figure 7a, b and c, respectively. It can be seen that the variation of hydraulic conductivity with FeCl 3 salt solutions was similar to those of the other salt solutions (i.e., NaCl, NH 4 Cl, KCl, and CaCl 2 ). When the FeCl 3 concentration increased, the hydraulic conductivity decreased for CL clay samples but the hydraulic conductivity increased for CH clay samples. As can be seen from Figure 7b, the EC values of CL clay samples sharply increased with increasing FeCl 3 concentration, whereas the EC values of CH clay samples slightly decreased with increasing FeCl 3 concentration. The ph test results were found to be similar to those of the other salt solutions for both CL and CH clay samples; however, the ph values decreased from 6.2 for distilled water to 0.4 at 1 M concentration of FeCl 3 for the influent solution. Discussion In the following, the findings from the experimental tests are compared with those from other studies in the literature and discussed. Effect of inorganic salts on the hydraulic conductivity of clays The hydraulic conductivity of CH clay samples increased with increasing concentration of all salt solutions as stated in detail in the previous section. Similar to the findings of the present study, most other researchers have also indicated that the hydraulic conductivity increased when the concentration of inorganic salt solutions increased (Petrov & Rowe 1997, Shackelford et al. 2000, Jo et al. 2001, 2004, 2005, Kolstad et al. 2004a, Lee et al. 2005, Lee & Shackelford 2005, Mishra et al. 2005). In this study, the increase in hydraulic conductivity when the concentration of the salt solutions was increased is attributed to the decrease in the thickness of DDL, resulting in flocculation of the clay particles. Quigley (1993) indicated that clay minerals might undergo large interlayer shrinkage in contact with certain chemicals. This is accompanied by enormous loss in diffuse double layer (DDL) thickness, potential cracking, and increase in hydraulic conductivity values. The thickness of the DDLs is an important controlling factor for the structural development, hydraulic conductivity, and other physico-chemical and mechanical properties of soils (Mitchell 1993, Fukue et al. 1999). Furthermore, the thickness of DDLs around clay particles is governed by the concentration of salt and type of cation(s) in the soil water (van Olphen 1963). As indicated by the Gouy Chapman theory, the thickness of the DDL decreases as the ion concentration increases, resulting in flocculation of the clay particles and larger pore channels through which flow can occur (Mitchell 1993, Gleason et al. 1997). Furthermore, Bowders & Daniel (1987) advocated that the many chemicals tended to reduce the thickness of the DDL, causing the soil skeleton to shrink and causing a decrease in repulsive forces, thus promoting flocculation of clay particles, and dehydration of the interlayer zones of expandable clays, which subsequently became gritty or granular. Kaya & Fang (2000) also indicated that as repulsive forces decreased, the soil particles tended to flocculate and form aggregates due to attractive forces among particles, leading to a net increase in the effective flow area, resulting in increased hydraulic conductivity of the soil-pore fluid. In contrast with those for CH clay, test results indicated that for CL clay, the decrease in hydraulic conductivity with increasing concentration of all salt solutions was insignificant. Similarly, some experimental tests on kaolinite clay showed that hydraulic conductivity decreased when clay samples were permeated with chemical solutions such as acetone, benzene, diethylene glycol, nitrobenzene, phenol (Dragun 1988). Based on their experimental study with marine clay, Rao & 470

8 Hydraulic conductivity of inorganic salt-permeated compacted clay liners Mathew (1995) indicated that the reduction in hydraulic conductivity was related to the dispersion and deflocculation of clay. Furthermore, Park et al. (2006), after conducting an experimental study on low plasticity kaolinite clay, reported that the hydraulic conductivity was not significantly affected, but slightly decreased due to pore clogging and the high viscosity of the solutions. Similarly, Petrov et al. (1997) determined that for ethanol concentrations less than 50%, the hydraulic conductivity of the GCL decreased due to the increase in viscosity. Hence, the decrease in hydraulic conductivity could be attributed to dispersion of the clay particles when CL clay was permeated with inorganic salts. It could be also said that the decrease in hydraulic conductivity was due to formation of new swelling type of compounds as well (Sivapullaiah & Manju, 2005). It should also be pointed out that the hydraulic conductivity of clays permeated with chemical solutions depends on several other possible parameters. Cation valence is a parameter which affects the hydraulic conductivity of GCL and very high plasticity clays such as bentonite. In this sense, Shackelford et al. (2000), Jo et al. (2001), and Kolstad et al. (2004b) reported that the effects of the divalent and trivalent cations on the bentonite were different from those of monovalent cations. However, the results of this study indicated that the hydraulic conductivity of CH clay was not significantly affected by the cation valence of salt solutions. The difference between the findings of this study and the findings in the literature could be attributed to the differences in the type of the permeameter and the plasticity of clays. Shackelford et al. (2000), Jo et al. (2001), and Kolstad et al. (2004b) used flexible-wall permeameters in their experimental study, following the procedures described in ASTM D5084. But this study was conducted with rigid-wall permeameters, following the procedures described in ASTM D5856. Foreman & Daniel (1986) indicated that the type of the permeameter had little effect when the soils were permeated with water. They also indicated that the type of the permeameter affected the hydraulic conductivity values when the soils were permeated with organic compounds. Furthermore, Shackelford et al. (2000) and Kolstad et al. (2004b) used GCLs whereas Jo et al. (2001) used bentonite which had a liquid limit of 746%. However, the CL and CH clays used in this study had liquid limits of 40 and 113%, respectively. The clay mineralogy and liquid limit are seen to be among the most influential parameters for CL clay (Arasan & Yetimoglu 2006). Effect of inorganic salts on the EC of clays It should be noted that the experimental test results show that the EC values of clay samples were particularly sensitive to changes in the concentration of the salt solutions. It could be said that the EC values of the CL clay samples increased when the concentration for all salt solutions was increased. However, the EC values of CH clay samples increased for some salt solutions (i.e., NaCl, KCl, and CaCl 2 ), but decreased for other salt solutions (i.e., NH 4 Cl and FeCl 3 ) when the concentration was increased. Kaya & Fang (1997) reported that the EC of the clay-fluid system was not only a function of soil and pore fluid, but also of the chemical composition, grain size, and shape of the particles. Kaya (2001) reported that the electrical conductivity of kaolin and bentonite increased when the ion concentration of NaCl solution in the clay water mixture was increased. Furthermore, Shang & Rowe (2003) using synthetic leachate and CaCl 2 solutions reported that EC values increased when the ion concentration was increased. Effect of inorganic salts on the ph of clays The experimental study showed that the variation of ph with concentration was similar for all salt solutions when CL and CH clay samples were permeated with NaCl, NH 4 Cl, KCl, CaCl 2, and FeCl 3. Furthermore, the change in ph was found to be less significant for clay samples in all tests. The ph of CH clay samples slightly decreased when the concentration was increased. Similarly, Ouhadi et al. (2006) indicated that the ph of bentonite-pore fluid decreased when the heavy metal (i.e., Pb 2+, Zn 2+ ) concentrations were increased. The ph values of the clay samples were high (i.e., ph > 8), so the clay solution mixtures were alkaline. Kaya et al. (2006) reported that kaolinite clay settled as a flocculated form in acidic environments and as a dispersed form in alkaline environments. Furthermore, Abdullah et al. (1999) mentioned that a high ph was a condition conducive to a dispersed or oriented structure. It might be said that due to the high ph values of CL clay samples, the clay particles were dispersed and the hydraulic conductivity decreased in this experimental study. Conclusions A study was undertaken to investigate the effect of five different inorganic salt solutions (as permeant liquid) on the hydraulic conductivity, electrical conductivity, and ph of compacted clay samples. The five different inorganic salt solutions were: sodium chloride (NaCl), ammonium chloride (NH 4 Cl), potassium chloride (KCl), calcium dichloride (CaCl 2 ), and iron trichloride (FeCl 3 ). Tests were conducted on low plasticity (CL class) and high plasticity (CH class) commercial clays. In the tests, distilled water was used as the reference liquid and salt solutions (at six different concentrations varying between 0.01 and 1 M) were used as permeant liquid. The following conclusions are drawn, based on the test results and on the discussion presented in this study. 1. For CH clay, the hydraulic conductivity increased when the concentration of the salt solution was increased. This was observed for all of the salt solutions. 2. For CL clay, the hydraulic conductivity decreased when the concentration of the salt solution was increased. This was observed for all of the salt solutions. 3. When concentration increased, the EC values of CL and CH clays samples increased except for CH clay samples tested with NH 4 Cl and FeCl 3 salt solutions. 471

9 G. Yılmaz, T. Yetimoglu, S. Arasan 4. The ph values for the CL and CH clays samples were not significantly affected by any of the salt solutions used in the tests. It should also be pointed out that further studies on the geotechnical properties of CL and CH clays (such as stress strain, compressibility, swelling, and consistency limits) permeated with chemicals are needed to make more reasonable judgments concerning their use for waste disposal landfill design. Data on the electrokinetic properties of clays with salt solutions (e.g., cation exchange capacity, zeta potential, adsorption characteristics) are also needed to check the ability of the Gouy Chapman theory. Acknowledgements The authors wish to thank Professor Dr Recep Boncukcuoglu, and Asst. A. Erdem Yılmaz, from Ataturk University in Erzurum, Turkey, for their help during the experimental tests. References Abdullah, W.S., Alshibli, K.A. & Al-Zou bi, M.S. 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