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Geotextiles and Geomembranes xxx (2015) 1e5

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Geotextiles and Geomembranes

journal homepage: www.elsevier .com/locate/geotexmem

Technical note

Electrical resistance method for assessing spatial variation of watercontent in geosynthetics clay liners at laboratory scale

Hossam M. Abuel-Naga a, *, Abdelmalek Bouazza b, 1

a Civil Engineering Discipline, La Trobe University, Melbourne, Vic. 3086, Australiab Department of Civil Engineering, 23 College Walk, Monash University, Melbourne, Vic. 3800, Australia

a r t i c l e i n f o

Article history:Received 20 September 2014Received in revised form22 June 2015Accepted 1 July 2015Available online xxx

Keywords:GCLLinerLandfillMoistureHomogeneityElectrical resistance

* Corresponding author. Tel.: þ61 394791181.E-mail addresses: h.naga@latrobe.edu.au (H.M. A

monash.edu (A. Bouazza).1 Tel.: þ61 3 9905 4956; fax: þ61 3 9905 4944.

http://dx.doi.org/10.1016/j.geotexmem.2015.07.0020266-1144/© 2015 Elsevier Ltd. All rights reserved.

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a b s t r a c t

Non-uniform moisture distribution throughout pre-hydrated geosynthetics clay liner (GCL) laboratorytesting specimens could significantly affect their liquid/gas permeability test results. For a reliablecomparison between different pre-hydrated GCL specimens, uniform moisture distribution conditionshould be ensured before testing their permeabilities. This study presents a simple non-destructiveelectrical probing approach to assess the moisture homogeneity of GCL specimens before their use inlaboratory tests. An experimental program was conducted to check the feasibility and the validity of theproposed method on GCLs hydrated at different moisture contents. The outcomes of the experimentalprogram prove the adequacy of the proposed method.

© 2015 Elsevier Ltd. All rights reserved.

1. Introduction

Geosynthetic clay liners (GCLs) aremost typically comprised of athin layer of bentonite contained between two layers of geotextilewith the components being held together by needle-punching orstitch bonding. They are widely used in lining systems of modernwaste containment facilities to minimise migration of contami-nants and gases (Bouazza, 2002; Rowe, 2012, 2014). In this respect,there is a wide body of work available on their hydraulic and/gasbarrier performance (Shackelford et al., 2000; Bouazza andVangpaisal, 2004, 2006, 2007; Benson et al., 2010; Gates andBouazza, 2010; Scalia and Benson, 2011; Bradshaw et al., 2013;Mazzieri et al., 2013; Rowe and Abdelatty, 2013; Abuel-Nagaet al., 2013, Abuel-Naga and Bouazza, 2014; Hosney and Rowe,2014a,b; Ashe et al., 2014, 2015; Bouazza and Gates, 2014; Liu et al.,2013, 2014, 2015; Rowe and Hosney, 2015; Take et al., 2015; Roufet al., 2015).

Several studies have shown the importance of GCL initial hy-dration with a non-chemically aggressive hydration fluid to

buel-Naga), malek.bouazza@

a, H.M., Bouazza, A., Electrica, Geotextiles and Geomembra

improve its chemical compatibility to leachates or other moreaggressive solutions (Vasko et al., 2001; Lee and Shackelford, 2005;Katsumi et al., 2008; Liu et al., 2015). In common practice, initialhydration of GCL could be achieved through a passive process inwhich water vapour is transferred from the subgrade to the GCL ifthere is no intimate contact (Rouf et al., 2014) or through an activeprocess where moisture can be taken from the subgrade in liquidform if there is an intimate contact between the subgrade and theGCL (Rayhani et al., 2011).

To assess the effect of the initial pre-hydration on the hydraulic/gas performance of GCL at the laboratory scale, GCL specimens areusually pre-hydrated to different moisture content targets (Vaskoet al., 2001; Vangpaisal and Bouazza, 2004; Katsumi et al., 2008).Furthermore, a homogenous moisture content distributionthroughout the GCL specimen must be achieved otherwise thehydraulic conductivity and/or gas permeability of heterogeneouslypre-hydrated GCLs to contaminant solutes and/or gas can becomeunreliable (Katsumi et al., 2008; Bouazza and Vangpaisal, 2003;Vangpaisal and Bouazza, 2004). This is due to the presence ofpreferential flow paths caused by a non-uniform distribution ofmoisture content in the GCL.

The usual practice of verifying the moisture content distributionin a GCL specimen is to conduct destructive tests (Bouazza andVangpaisal, 2003; Bouazza et al., 2014) which involves cutting the

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specimen in several slices and oven dry them for 24 h. This processis most often repeated if the target moisture content distribution isnot reached in laboratory experiments. This paper presents a sim-ple non-destructive technique to assess the homogeneity of themoisture content in a GCL specimen using an electrical resistancemethod.

Fig. 1. Electrical resistivity cell.

2. Proposed methodology

A non-destructive electrical resistance probing approach isproposed in this study to assess the moisture homogeneity of GCLspecimens. The electrical resistivity of porous media is mainlyfunction of moisture content and several other parameters such astemperature, soil structure, texture, mineralogy, and the salt con-tent of the water (Archie, 1942; Gupta and Hanks, 1972; Rhoadeset al., 1976; Gu�eguen and Palciauskas, 1992; Kalinski and Kelly,1993; Abu-Hassanein et al., 1996; McCarter and Desmazes, 1997;Revil et al., 1998; Seladji et al., 2010; Beck et al., 2011; Kibria andHossain, 2012). The general premise behind the use of electricalresistivity measurements for assessing the moisture homogeneityof a GCL specimen is based on the assumption that the bentonitelayer of GCL specimen has homogenous properties in terms ofdensity, structure, texture, mineralogy, and water salt content. Thisassumption could be supported by the fact that GCLs areman-madematerials that usually go through quality control (QC) and qualityassurance (QA) procedures to ensure the homogeneity condition ofthe materials. Therefore, the spatial variability of the electrical re-sistivity measurements could be directly linked to the moisturecontent distribution within the GCL specimen. However, it shouldbe mentioned that the validity of this method to assess the mois-ture homogeneity is limited by the fact that the rate of change ofelectrical resistivity for clays decreases as moisture content in-creases to become almost zero when the degree of saturation ex-ceeds 70% (McCarter, 1984). However, Rayhani et al. (2008) showedthat for different types of GCL the maximum degree of saturationdue to GCL hydration from subsoil could be in the range of 60%e80%. Therefore, the valid working range of the electrical resistancemethod proposed in this study fits with the purpose of verifying themoisture distribution of a pre-hydrated GCL laboratory testingspecimen.

In this study a modified oedometer cell (Fig. 1) was used toquantify the spatial variation of the electrical resistivity throughouta GCL specimen. The cell is made of PVC material and can accom-modate a GCL specimen having up to 100 mm diameter. TheWenner four-electrode method (Wenner, 1915; ASTM G57-06,2012) for measuring the electrical resistivity was incorporatedinto the top cap as shown in Fig. 1. The electrical resistivity of theGCL specimen can be measured at different radial sections byrotating the top cap in-plan. Therefore, this method enables radialscanning of the average moisture contents throughout the GCLspecimen.

The Wenner four-electrode method is usually used to measuresoil resistivity in the field. The method involves using four cooperelectrodes placed with equal separation, a (cm), in a straight line inthe surface. Avoltage is applied between the outer electrodeswherethe corresponding current, I, and the voltage drop between theinner electrodes, V, are measured. The resistivity, r (U cm), is then:

r ¼ 2p a ðV=IÞ (1)

It should be mentioned that the measured r by the Wennerfour-electrode method represents the average resistivity of ahemisphere of soil of a radius approximately proportional in ho-mogenous media to the electrode separation where the term (2pa)is a geometrical factor defined based on a semi-infinite boundary

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condition (half-space). However, this geometric boundary condi-tion is not applicable for the cell shown in Fig. 1. As the geometricboundary conditions of every radial section through the GCLspecimen are similar and the main purpose of the measurements isto assess the homogeneity throughout the specimen rather thanthe actual resistivity (r) of the GCL, the electrical resistance mea-surements, R ¼ V/I, can be used instead of r for this purpose.

In this study 10 DC voltages was impressed across the outerelectrodes where the current injection time duration and delaywere 10.0 s and 0.0 s, respectively. The voltage drop across the innerelectrodes and the current across the outer electrodes were recor-ded with resolution of 250 mV, and 10 nA, respectively.

3. Material and specimen preparation

Table 1 lists the properties of the GCLmaterial used in this study.A GCL sample was cut from a large GCL sheet, using a sharp utilityknife, to an A4 size. A circular stainless steel cutting ring with aninner diameter of 100 mm was used to cut the GCL specimen. TheGCL A4 size sample was placed between the cutting ring and aplywood plate, which was used as a cutting base. Thewhole set wasthen placed on the platen of a compression machine to cut the GCLspecimen to the required size.

The pre-hydration process of the GCL involved immersing thecutting ring with the GCL specimen still inside in de-ionized waterfor different time durations (30 s, 60 s) to obtain specimens withdifferent pre-hydrated moisture contents. Once the immersionprocess was completed, the GCL still in its cutting ring was stored ina double plastic bag for two-week curing under zero pressureconfinement. This could represent the case when the GCL beginshydrating before the placement of a soil cover. The average mois-ture content (wcavg) achieved was 49% and 113%, respectively, forimmersion times of 30 s and 60 s, respectively. After completion ofthe curing period, the GCL was carefully pushed from the cuttingring into the electrical resistivity cell.

l resistance method for assessing spatial variation of water content innes (2015), http://dx.doi.org/10.1016/j.geotexmem.2015.07.002

Table 1GCL properties.

GCL mass per unit area (kg/m2) 5.35As-received GCL thickness (mm) 8 to 9Mineral composition of bentonite 90% smectite, 4% cristobalite, 3% quartz,

and 3% Ca-albiteAtterberg limits LL ¼ 405%

PI ¼ 351%Bentonite form PowderBentonite mass per unit area (kg/m2) 4.7Cover geotextile type; mass per

unit area (kg/m2)Nonwoven geotextile; 0.27

Carrier geotextile; mass per unitarea (kg/m2)

Nonwoven geotextile reinforced by awoven geotextile; 0.38

Bonding method Needle-punched, thermally treatedSwelling pressure (kPa) 175

Fig. 3. Adsorbed water of the GCL specimen hydrated by vapour equilibriumtechnique.

H.M. Abuel-Naga, A. Bouazza / Geotextiles and Geomembranes xxx (2015) 1e5 3

Furthermore, one GCL specimen was pre-hydrated using thevapour equilibrium technique where it was placed in a desiccatorand was subjected to a humid air (relative humidity RH ¼ 100%)circulated through a pump for one year as shown in Fig. 2. Fig. 3shows the weight of the water adsorbed by the GCL specimenduring this period (i.e 1 year). The results indicate that the vapourequilibrium system relying on humid air circulation was able toraise the averagemoisture content of the GCL specimen fromz10%to only 18.6%. Similar behaviour was reported by Fu et al. (1990)and Vasko et al. (2001).

4. Validation of the proposed method

The moisture homogeneity test was conducted by rotating in-plan the top cap in increments of 5� over the range of 360� andmeasuring the electrical resistance, R, at each position, as shown inFig. 4a, where the normalized electrical resistance, RN, is expressedas follows:

RN ¼ R�Ravg (2)

where Ravg is the average electrical resistance value. A verticalstress of about 10 kPa was applied during the measurements of theelectrical resistance to achieve a good contact between the elec-trical pins and the GCL specimen. Three rotations were conductedto check the repeatability of the measured R values and satisfactoryresults were obtained as shown in Fig. 4a. The observed variabilityof the resistivity measurements between the three rotations, up to35%, could be attributed to the possible change in the contactcondition between ER points and GCL geotextile layer for eachrotation. The average electrical resistance distribution is shown inFig. 4b.

Fig. 2. Vapour equilibrium cell.Fig. 4. Electrical resistance and moisture content distribution of the GCL samplesubmerged in water for 60 s (wcavg ¼ 113%).

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Fig. 5. Cutting configuration of the GCL specimen to determine its water contentdistribution.

Fig. 7. Electrical resistance and moisture content distribution of the GCL sample hy-drated by Vapour equilibrium technique (RH ¼ 100%) for a year (wcavg ¼ 18.60%).

H.M. Abuel-Naga, A. Bouazza / Geotextiles and Geomembranes xxx (2015) 1e54

As the change in the electrical resistance measurementsthroughout the tested GCL specimen should bemainly attributed tomoisture content change, the inverse of the electrical resistancedistribution can be qualitatively used to express the moisturecontent distribution. To verify this point, the GCL specimenwas cutinto 6 equal slices at the end of the electrical resistivity test asshown in Fig. 5. Then, the moisture content, wc, of each slice wasmeasured and normalised to the average moisture content value,wcavg. The normalized moisture content, wcN, is expressed asfollows:

wcN ¼ wc�wcavg (3)

The average of RN values measuredwithin each slice was plottedin Fig. 4b, together with the normalized moisture content, wcN. Theresults shown in Fig. 4b indicate with a reasonable confidence thatthe RN distribution is the inverse of the wcN distribution. Similarbehaviour was also observed for the other two GCL specimens asshown in Figs. 6 and 7, respectively. Therefore, the validity of theelectrical resistivity approach, proposed in this study, to qualita-tively assess the moisture homogeneity of GCL samples isconfirmed.

Fig. 6. Electrical resistance and moisture content distribution GCL specimen sub-merged in water for 30 s (wcavg ¼ 49.30%).

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5. Conclusions

A simple nondestructive electrical resistivity method usingWenner four-electrode method was developed to verify the mois-ture content homogenity of GCL specimens where degree of satu-ration is less than 70%. The method makes use of the inverserelationship between the electrical resistivity andmoisture contentof porous media. Its validity was verified on several GCL specimenshydrated at different moisture contents. The electrical resistancedistributions obtained by this method were compared againstmoisture content distributions obtained by a destructive methodand a reasonable qualitative agreement was observed in terms ofmatching the overall expected trend. The method is easily repro-ducible and can be used to characterise the moisture content dis-tribution in GCL specimens used in the laboratory.

References

Abuel-Naga, H.M., Bouazza, A., Gates, W., 2013. Impact of bentonite form on thethermal evolution of the hydraulic conductivity of geosynthetics clay liners.Geotech. Lett. 3, 26e30.

Abuel-Naga, H., Bouazza, A., 2014. Numerical experiment-artificial intelligenceapproach to develop empirical equations for predicting leakage rates throughGM/GCL composite liners. Geotext. Geomembr. 42 (3), 236e245.

Abu-Hassanein, Z.S., Benson, C.H., Blotz, L.R., 1996. Electrical resistivity of com-pacted clays. J. Geotech. Eng. 122, 397e406.

Ashe, L., Rowe, R.K., Brachman, R.W.I., Take, W.A., 2014. Laboratory simulation ofbentonite erosion by downslope flow on a GCL. ASCE J. Geotech. Geoenviron.Eng. 140 (8) http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0001142,04014044e1 to 04014044-9.

Ashe, L., Rowe, R.K., Brachman, R.W.I., Take, W.A., 2015. Laboratory study of down-slope erosion for ten different GCLs. ASCE J. Geotech. Geoenviron. Eng. 141 (1)http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0001191, 04014079:1 e 8.

Archie, G.E., 1942. The electrical resistivity log as an aid in determining somereservoir characteristics. Trans. Am. Inst. Min. Metall., Pet. Eng. Inc. 146 (1),54e62.

ASTM G57-06, 2012. Standard Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-electrode Method. ASTM International, West Con-shohocken, PA, 2012. www.astm.org.

Beck, Y.L., Lopes, S.P., Ferber, V., Cote, P., 2011. Microstructural interpretation ofwater content and dry density influence on the DC-electrical resistivity of afine-grained soil. Geotech. Test. J. 34 (6), 1e14.

Benson, C.H., Oren, H., Gates, W.P., 2010. Hydraulic conductivity of two geosyntheticclay liners permeated with a hyperalkaline solution. Geotext. Geomembr. 28(2), 206e218.

Bouazza, A., 2002. Geosynthetic clay liners. Geotext. Geomembr. 20 (1), 1e17.Bouazza, A., Vangpaisal, T., 2003. An apparatus to measure gas permeability of

geosynthetic clay liners. Geotext. Geomembr. 21 (2), 85e101.Bouazza, A., Vangpaisal, T., 2004. Effect of straining on gas advective flow of a

needle punched GCL. Geosynth. Int. 11 (4), 287e295.Bouazza, A., Vangpaisal, T., 2006. Laboratory investigation of gas leakage rate

through a GM/GCL composite liner due to a circular defect in the geomembrane.Geotext. Geomembr. 24 (2), 110e115.

Bouazza, A., Vangpaisal, T., 2007. Gas permeability of GCLs: effect of poor distri-bution of needle punched fibres. Geosynth. Int. 14 (4), 248e252.

l resistance method for assessing spatial variation of water content innes (2015), http://dx.doi.org/10.1016/j.geotexmem.2015.07.002

H.M. Abuel-Naga, A. Bouazza / Geotextiles and Geomembranes xxx (2015) 1e5 5

Bouazza, A., Gates, W.P., 2014. Overview of performance compatibility issues ofGCLs with respect to leachates of extreme chemistry. Geosynth. Int. 21 (2),151e167.

Bouazza, A., Singh, R.M., Rowe, R.K., Gassner, F., 2014. Heat and moisture migrationin a geomembrane-GCL composite liner subjected to high temperatures andlow vertical stresses. Geotext. Geomembr. 42 (5), 555e563.

Bradshaw, S.L., Benson, C.H., Scalia, J., 2013. Hydration and cation exchange duringsubgrade hydration and effect on hydraulic conductivity of geosynthetic clayliners. J. Geotech. Geoenviron. Eng. 139 (4), 526e538.

Fu, M.H., Zhang, Z.Z., Low, P.F., 1990. Changes in the properties of a montmorillonite-water system during the adsorption and desorption of water-hysteresis. ClaysClay Miner. 38, 485e492.

Gates, W.P., Bouazza, A., 2010. Bentonite transformations in strongly alkaline so-lutions. Geotext. Geomembr. 28, 219e225.

Gu�eguen, Y., Palciauskas, V., 1992. Introduction �a la physique des roches. Hermann,�editeurs des sciences et des arts.

Gupta, S.C., Hanks, R.J., 1972. Influence of water content on electrical conductivity ofthe soil. Soil Sci. Soc. Am. Proc. 36 (6), 855e857.

Hosney, M.S., Rowe, R.K., 2014a. Performance of three GCLs used for covering goldmine tailings for 4 years under field and laboratory exposure conditions.Geosynth. Int. 21 (3), 197e212.

Hosney, M.S., Rowe, R.K., 2014b. Performance of GCL after 10 years service in theArctic. ASCE J. Geotech. Geoenviron. Eng. 140 (10) http://dx.doi.org/10.1061/10.1061/(ASCE)GT.1943-5606.0001160, 04014056: 1e12.

Kalinski, R.J., Kelly, W.E., 1993. Estimating water content of soils from electricalresistivity. Geotech. Test. J. 16 (3), 323e329.

Katsumi, T., Ishimori, H., Ogawa, A., Maruyama, S., Fukagawa, R., 2008. Effect ofwater content distribution on hydraulic conductivity of prehydrated GCLsagainst calcium chloride solutions. Soils Found. 48 (3), 407e417.

Kibria, G., Hossain, M., 2012. Investigation of geotechnical parameters affectingelectrical resistivity of compacted clays. J. Geotech. Geoenviron. Eng. 138 (12),1520e1529.

Lee, J.-M., Shackelford, C.D., 2005. Concentration dependency of the prehydrationeffect for a geosynthetic clay liner. Soils Found. 45 (4), 27e41.

Liu, Y., Gates, W.P., Bouazza, A., 2013. Acid induced degradation of thebentonite component used in geosynthetic clay liners. Geotext. Geomembr.36, 71e80.

Liu, Y., Gates, W.P., Bouazza, A., Rowe, R.K., 2014. Fluid loss as a quick method toevaluate the hydraulic conductivity of geosynthetic clay liners under acidicconditions. Can. Geotech. J. 51 (2), 158e163.

Liu, Y., Bouazza, A., Gates, W.P., Rowe, R.K., 2015. Hydraulic performance of geo-synthetic clay liners to sulfuric acid solutions. Geotext. Geomembr. 43 (1),14e23.

McCarter, W.J., 1984. The electrical resistivity characteristics of compacted clays,.Geotechnique 34 (2), 263e267.

McCarter, W.J., Desmazes, P., 1997. Soil characterization using electrical measure-ments. G�eotechnique 47 (1), 179e183.

Mazzieri, F., Di Emidio, G., Fratalocchi, E., Di Sante, M., Pasqualini, E., 2013.Permeation of two GCLs with an acidic metal-rich synthetic leachate. Geotext.Geomembr. 40, 1e40.

Please cite this article in press as: Abuel-Naga, H.M., Bouazza, A., Electricageosynthetics clay liners at laboratory scale, Geotextiles and Geomembra

Rayhani, M.H.T., Rowe, R.K., Brachman, R.W.I., Siemens, G., Take, W.A., 2008. Closed-system investigation of GCL hydration from subsoil. In: Proc., 61st CanadianGeotechnical Conf. Canadian Geotechnical Society, Edmonton, Alberta, Canada,pp. 324e328.

Rayhani, M.T., Rowe, R.K., Brachman, R.W.I., Take, W.A., Siemens, G., 2011. Factorsaffecting GCL hydration under isothermal conditions. Geotext. Geomembr. 29(6), 525e533.

Revil, A., Cathles, L.M., Losh, S., Nunn, J.A., 1998. Electrical conductivity in shalysands with geophysical applications. J. Geophys. Res. Solid Earth 103 (B10),23925e23936.

Rhoades, J.D., Raats, P.A.C., Prather, R.J., 1976. Effects of liquid-phase electricalconductivity, water content, and surface conductivity on bulk soil electricalconductivity. Soil Sci. Soc. Am. J. 40, 651e655.

Rouf, M.A., Singh, R.M., Bouazza, A., Gates, W.P., Rowe, R.K., 2014. Evaluation of ageosynthetic clay liner water retention curve using vapour equilibrium tech-nique. In: Proceedings 6th International Conference on Unsaturated Soils,Sydney, Australia, vol. 2, pp. 1003e1009.

Rouf, M.A., Singh, R.M., Bouazza, A., Rowe, R.K., Gates, W.P., 2015. Gas permeabilityof partially hydrated geosynthetic clay liner under two stress conditions.J. Environ. Geotech. http://dx.doi.org/10.1680/envgeo.14.00009.

Rowe, R.K., 2012. Design and construction of barrier systems to minimize environ-mental impacts due to municipal solid waste leachate and gas. 3rd IndianGeotechnical Society: Ferroco-Terzaghi Oration. IndianGeotech. J. 42 (4), 223e256.

Rowe, R.K., 2014. Performance of GCLs in liners for landfill and mining applications.Environ. Geotech. 1, 3e21.

Rowe, R.K., Abdelatty, K., 2013. Leakage and contaminant transport through a singlehole in the geomembrane component of a composite liner. ASCE J. Geotech.Geoenviron. Eng. 139 (3), 357e366.

Rowe, R.K., Hosney, M.S., 2015. Hydraulic conductivity and interface transmissivityof GCLs below poured concrete. Geosynth. Int. 22 (1), 48e69.

Scalia, J., Benson, C.H., 2011. Hydraulic conductivity of geosynthetic clay linersexhumed from landfill final covers with composite barriers. J. Geotech. Geo-environ. Eng. 137 (1), 1e13.

Seladji, S., Cosenza, P., Tabbagh, A., Ranger, J., Richard, G., 2010. The effect ofcompaction on soil electrical resistivity: a laboratory investigation. Eur. J. SoilSci. Br. Soc. Soil Sci. 61, 1043e1055.

Shackelford, C., Benson, C., Katsumi, T., Edil, T., Lin, L., 2000. Evaluating the hydraulicconductivity of GCLs permeated with nonstandard liquids. Geotext. Geomembr.18 (2e4), 133e162.

Take, W.A., Brachman, R.W.I., Rowe, R.K., 2015. Observations of bentonite erosionfrom solar-driven moisture migration in GCLs covered only by a black geo-membrane. Geosynth. Int. 22 (1), 78e92.

Vangpaisal, T., Bouazza, A., 2004. Gas permeability of partially hydrated geo-synthetic clay liners. J. Geotech. Geoenviron. Eng. 130 (1), 93e102.

Vasko, S., Jo, H., Benson, C., Edil, T., Katsumi, T., 2001. Hydraulic conductivity ofpartially prehydrated geosynthetic clay liners permeated with aqueous calciumchloride solutions. In: Proceedings of Geosynthetics 2001. Industrial FabricsAssociation International, St. Paul, Minnesota, USA, pp. 685e699.

Wenner, F., 1915. A method of measuring earth resistivity. US. Dept. Com. Bur. Stand.Sci. Paper 258.

l resistance method for assessing spatial variation of water content innes (2015), http://dx.doi.org/10.1016/j.geotexmem.2015.07.002