This paper reviews and critiques several approaches for estimating the hydraulic conductivity of compacted bentonite-sand mixtures. It then discusses the design of a modified version of a minicompaction cell (as presented by Kenney et al., 1992); which purports to account for many of the natural field conditions associated with compacted bentonite-sand liners. An equation that predicts the hydraulic conductivity of an ideal bentonite-sand mixture is presented and results from the minicompaction tests are related to this equation. A water content that yields the lowest hydraulic conductivity is identified as being associated with an ideal bentonite-sand mixture.
A compacted mixture of bentonite and sand is often used to form a seepage barrier (Haug et al., 1988, Haug and Wong 1992, Chapuis et al., 1992, and Kuroda et al., 1993). Bentonite-sand mixtures consist of two quite different soils with respect to grain size, permeability, chemical activity, and strength. He stated that the experimental results were hard to interpret because different testing methods made it difficult to control certain parameters (such as the hydration period, the degree of saturation, and the swelling under low confining pressure). Kenney et al., (1992) measured the hydraulic conductivity of compacted bentonite-sand mixtures and demonstrated the influence on hydraulic conductivity of the bentonite-sand ratio and the compaction water content. It allowed the samples to be dynamically compacted in permeameter cells using a miniature compaction rammer and a compaction energy per volume equal to that of the Standard AASHO compaction test. The specimens were consolidated and between consolidation steps, falling-head permeability tests were conducted with an initial hydraulic gradient of 15. Back pressure in the apparatus was 500 kPa with a vertical effective stress equal to 60 kPa. This equipment allowed measurement of the hydraulic conductivity of a sample with different void ratios.