Soil Water Retention Behavior of Unsaturated Bentonite Polymer Composite Geosynthetic Clay Liners
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Abstract
When geosynthetic clay liners (GCLs) are placed in the subsoil to be used as hydraulic barriers in waste containment facilities such as landfills, the in-field hydration driven by differences in suction is an important component in the longstanding hydraulic performance of GCLs. Generally, the hydration process is generally not simple due to several factors, like soil properties, environmental and operating conditions of the landfill. As some liquids like water or leachates can migrate into the GCLs, and the moisture content can be variable increasing and decreasing along with changes in suction. In order to provide further insight into the quantification of water movement or distribution in unsaturated soil, analysis of soil water retention behavior of BPC-GCLs is essential. To simulate potential hydration and dehydration processes that GCLs go through in the field, moisture-suction relationships were examined along both wetting and drying paths. Five variable GCLs hydrated with three different solutions were analyzed. Two different suction measurement methods were carried out with the purpose of observing how and why the characteristics of each material influences water retention behavior. Both measurement methods were used to form wetting and drying paths in a range of suction between 50 and 300 MPa and are presented with their corresponding gravimetric water content. The obtained water retention curves of the different material tested showed significant variation for suction values below 20 MPa in the wetting path, while for the drying path the variation in suction occurs for values below 10 MPa. This difference indicates that the polymer loading has a significant influence on the swelling behavior of the GCLs. In addition, to relate soil water content and suction, individual moisture-suction relationship for wet and dry condition was analyzed mathematically using the sigmoidal van Genuchten (1980) and Lu (2016) functions. The fitting parameters, obtained based on the empirical data for the wetting and drying path, can offer insight into the soil water retention curve like the air entry, water entry, and air expulsion values, pore-size distribution, and residual suction.