The hydraulic conductivity, k, of model sand-bentonite backfills containing HYPER clay (Na bentonite treated with carboxymethyl cellulose [CMC]) was investigated in this study. Flexible-wall tests were performed on backfill specimens composed of clean, fine sand and 2.7-5.6 % HYPER clay containing either 2 % CMC (HC2) or 8 % CMC (HC8). The geometric mean k to water (k_w) for HC8 specimens decreased by nearly two orders of magnitude (from ～3×10~(-9) m/s to ～3×10~(-11) m/s) with increasing HC8 content from 2.7 to 5.6 %. The geometric mean k_w of 3×10~(-11) m/s for the 5.6 % HC8 backfill was nearly an order of magnitude lower than k_w reported previously for similar backfill specimens containing 5.7 % Na bentonite (Naturalgel~® [NG]) or 5.6 % multiswellable bentonite (MSB) due to the greater water absorption and swell capacity of HC8 relative to the NG and MSB. The 5.6 % HC2 specimens exhibited slightly lower k_w relative to specimens containing 5.7 % NG or 5.6 % MSB. Also, whereas the NG and MSB specimens exhibited increases in k when the permeant liquid was changed to a 10-mM CaCl_2 solution, no increases were observed for 5.6 % HC2. Although further testing is needed, the results illustrate the potential for HYPER clay to enhance the hydraulic performance of soil-bentonite vertical barriers.
展开▼
