A study on the behavior of the compacted bentonite in the presence of salt solutions

Wastes that are generally disposed off in an engineered landfill disposal site produce leachates. These leachates, which are very toxic in nature, once come in contact with percolating rain water, move downwards and pollute the ground water source. In order to prevent the ground water being polluted from the leachate, a liner is provided below the landfill disposal site. Generally, a compacted layer of bentonite is used as a barrier material at the waste disposal site. Because of its high swelling capacity and lower hydraulic conductivity, bentonite is used as a liner material. However, when bentonite comes in contact with salts present in leachates, its swelling property and hence also its hydraulic conductivity change. In this study, the effects of two different salt solutions, i.e. NaCl and CaCl2 by varying concentrations on bentonite were experimentally investigated. Tests were carried out to study the swelling potential, swelling pressure, and hydraulic conductivity of compacted bentonite. In order to study the effect of initial water content, study was carried out on two compacted samples varying in initial water content. Results indicate that liquid limit, plasticity, swell potential, and swell pressure decrease and hydraulic conductivity increases with increase in salt concentration. Result also shows that initial water content has a marginal effect on swelling pressure. However, the samples compacted on the dry side of optimum moisture content (OMC) exhibited a higher swelling pressure in comparison to the samples compacted at OMC.