Sand–bentonite liners: predicting permeability from laboratory tests

Soil–bentonite mixes are frequently used as impervious blankets in waste disposal projects. Numerous results of laboratory permeability tests are presented for sands containing up to 33% bentonite. These results seem difficult to analyze because different testing methods have been used in which it is not easy to control certain parameters, such as hydration period, degree of saturation, and swelling under low confining pressure. Hydraulic conductivity, however, can be obtained by using empirical equations that take into account the bentonite content, porosity, and degree of saturation of the sand alone when tested at its optimum modified Proctor value in a permeameter. This preliminary evaluation helps to select the soil to be tested. Then, the laboratory test results can be used to predict the in situ hydraulic performance after due consideration of the variabilities in natural sand and bentonite content. Key words: liner, soil, bentonite, permeability, laboratory, field.