EFFECT OF WETTING AND DRYING CYCLES ON THE PERFORMANCE OF MODIFIED AND NON-MODIFIED GCLS USED IN COVER AND BASE SYSTEMS AND UNDER HIGH HYDRAULIC GRADIENT
GCLs , Wet and dry cycles , Hydraulic conductivity , Polymer enhanced bentonite
The effect of prolonged exposure to wet and dry cycles on the hydraulic performance of five different GCLs was studied. Three GCLs had polymer-modified bentonite and two GCLs had standard sodium bentonite. The GCLs were placed on a 3H:1V slope and subjected to three different modes of wet and dry cycles. The wetting cycles of the three modes lasted for eight hours, while the drying cycles varied between 16h for the W/D: 8h/16h mode, seven days for the W/D: 8h/7d mode, and 14d for the W/D: 8h/14d mode. Tap water was used for the wetting cycles and the drying cycles were conducted at room temperature. After one year of wet-dry aging, the hydraulic conductivity of the GCLs was examined by adopting conditions simulating the GCLs were used (i) alone or under a thin layer of cover soil and exposed to rainfall in cover systems, (ii) under a geomembrane’s wrinkle with a hole in a landfill base system. The k of the standard bentonite GCLs increased by one to two orders of magnitude and the polymer-modified bentonite GCLs increased by three to four orders of magnitude when permeated with tap water. When permeated with two strong synthetic leachates, the k was affected by the RMD of the permeant as the higher RMD of the solution, the lower k of the GCL. However, the GCLs directly under the GMB’s wrinkle had the poorer k. Four GCLs (two GCLs with polymer amended bentonite) were subjected to a high hydraulic gradient (i ~ 2000) of tap water infiltrating through the GCL for around one year. The k of the modified bentonite GCLs was lower than the standard bentonite GCLs when permeated with tap water, and higher than the standard bentonite GCLs when permeated with strong synthetic leachates. The effect of the number and the size of the needle punching bundles, the carrier geotextile type, the bundles’ thermal treatment, and the length of the drying cycles are discussed.