Compressibility and Hydraulic Conductivity of Sand/Clay-Bentonite Backfills

Soil-bentonite (S-B) vertical cutoff walls are effective and economical as engineering barriers for contaminant containment. Water content higher than liquid limit (w_L)is needed for S-B backfills to achieve a target slump, ranging from 100 to 150 mm, for the purpose of improving constructability. A series of one-dimensional consolidation tests was performed to evaluate the compressibility and hydraulic conductivity of S-B backfills. Kaolin and sand were selected to simulate in-situ soils. The results indicate that BC critically controls the compressibility and hydraulic conductivity (k) of S-B backfills. The effect of grain size of sand on compression index (C_c) and k is insignificant. C_c increases with an increase in initial water content (w₀). However, the effect of w₀ on the compressibility can be eliminated by using compression ratio (CR). In addition, values of k are further discussed based on Nagaraj's generalized state parameters (e/e_L) and an empirical method for predicting k using void ratio (e) and w_L.