Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem Water retention of geosynthetics clay liners: Dependence on void ratio and temperature Ali Ghavam-Nasiri a,∗ , Abbas El-Zein a , David Airey a , R. Kerry Rowe b a School of Civil Engineering, The University of Sydney, Australia b Canada Research Chair in Geotechnical and Geoenvironmental Engineering, GeoEngineering Centre at Queen's–RMC, Queen's Univ., Ellis Hall, Kingston, Canada ARTICLE INFO Keywords: Geosynthetics Void ratio and temperature-dependent SWCC GCL Composite lining systems ABSTRACT The dependence of the geosynthetic clay liners (GCLs) soil-water characteristic curve (SWCC) on temperature and overburden stress are characterised experimentally. It is shown that changes in void ratio and temperature alter the relationship between suction and moisture content and new forms of existing SWCC equations are developed. To cover a wide suction range, the SWCCs are measured using axis-translation and dew point methods. Based on the available experimental data, both proposed SWCCs are shown to perform well in pre- dicting the effects of void ratio on SWCC along the drying path when compared to the experimental results. It is found that the air-entry value increases as the net vertical stress increases for the experiments under the same temperature. In addition, elevation of temperature reduces retention capacity of the GCL. 1. Introduction Geosynthetic clay liners are widely used to protect the environment from contamination, especially groundwater (Rowe, 2012). GCLs, commonly comprised of a layer of sodium bentonite between two layers of geotextile and held together by needle-punching (Rowe et al., 2004), usually hydrate from the subgrade and operate under unsaturated conditions. In general, their initial gravimetric water content is very low (typically less than 10%), and they rarely reach full saturation even when properly hydrated by the subsoil. GCLs can undergo a notable increase in water content and achieve a relatively high void ratio under low stresses. This is important for their performance since, without hydration from the subsoil, GCLs would not achieve the swelling and associated low hydraulic conductivities required in liner designs. Un- derstanding hydration dynamics of GCLs and the effects of subsoil properties such as particle size and mineralogy are therefore critical (Bouazza et al., 2017). In addition, GCLs, used as part of composite bottom liners, are often exposed to significant temperature increases in applications such as landfills with maximum temperatures of 55–70 °C (Southen and Rowe, 2005; Yeşiller et al., 2005; Jafari et al., 2014), and brine ponds with maximum temperatures of 70–90 °C (Leblanc et al., 2011; Bouazza et al., 2014; Rowe and Shoaib, 2017). Hence, a thermo- hydro-mechanical (THM) theory for unsaturated porous media is re- quired to describe the complex behaviour of these lining systems. A key constitutive equation in unsaturated soil mechanics is the relationship between water content and suction, known as soil-water characteristic curve (SWCC). The SWCC of a GCL is important in de- termining its hydraulic behaviour, volume change, and strength. These factors are essential in evaluating the performance of GCLs as a hy- draulic barrier for two main reasons: 1) predicting the extent and rate of hydration from the subsoil and 2) assessing the risk of desiccation of GCLs under thermal gradients. It has been well-established that the SWCC of a porous media alters as a result of changes in volume (e.g. Khalili et al., 2008; Tarantino, 2009; Gallipoli, 2012; Russell, 2014; Huang et al., 2016) and changes in temperature (e.g. Romero et al., 2001; Ye et al., 2009; Zhou et al., 2014; Gao and Shao, 2015; Roshani and Sedano, 2016). Therefore, it is important to consider these effects on the SWCC of GCLs. 2. Background The range of suctions in a GCL is wide and this necessitates a number of different methods to measure or estimate the SWCCs of GCLs. Experiments on different soils show that soil suction can vary from zero at a fully saturated state to hundreds of MPa at an oven-dry state (105 °C) (Wang et al., 2016). Measuring SWCCs over the entire range of suctions in a GCL is a challenging task. The composite structure of the GCL and the possibility of capillary breakage because of the https://doi.org/10.1016/j.geotexmem.2018.12.014 Received 11 July 2018; Received in revised form 25 November 2018; Accepted 22 December 2018 ∗ Corresponding author. E-mail addresses: ali.ghavam-nasiri@sydney.edu.au (A. Ghavam-Nasiri), abbas.el-zein@sydney.edu.au (A. El-Zein), david.airey@sydney.edu.au (D. Airey), kerry.rowe@queensu.ca (R.K. Rowe). Geotextiles and Geomembranes 47 (2019) 255–268 0266-1144/ © 2019 Elsevier Ltd. All rights reserved. T