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A modi®cation to Rowe's stress-dilatancy equation is presented that extends its range of application to include unsaturated soil behaviour. The results of a programme of constant water content triaxial tests on unsaturated bentonite-enhanced sand (BES) are reported, together with those of a programme of saturated drained triaxial tests on the sand. It is shown that the variation in the rate of dilation at failure with the sand relative density is similar for the two materials. It is proposed that the packing and friction angle of the sand particles and the degree of saturation control the shear strength of unsaturated BES containing modest amounts of bentonite, and that the shear strength of the bentonite component can be ignored.

This paper considers the engineering properties of bentonite-enhanced sand (BES) mixtures in relation to their performance as landfill liners. Data on the swelling, hydraulic conductivity, strength and desiccation of such mixtures are presented. The hydraulic conductivity depends on the proportions of sand and clay, the confining stress and the permeating fluid. The drained strength of mixtures typically used as landfill liners depends primarily on the relative density and critical state friction angle of the sand component. The susceptibility to desiccation cracking is a function of the moisture content and the proportion of bentonite used in the mixture. A model for BES mixtures is proposed that can be used to predict their swelling and hydraulic conductivity in water and salt solutions. The model requires the swelling behaviour and hydraulic conductivity of the bentonite in the relevant solution, and the compressibility, porosity and tortuosity of the sand component as input parameters. Sand tortuosity is estimated. The strength can be predicted using the void ratio of the sand component calculated from the proposed model.

A modi®cation to Rowe's stress-dilatancy equation is presented that extends its range of application to include unsaturated soil behaviour. The results of a programme of constant water content triaxial tests on unsaturated bentonite-enhanced sand (BES) are reported, together with those of a programme of saturated drained triaxial tests on the sand. It is shown that the variation in the rate of dilation at failure with the sand relative density is similar for the two materials. It is proposed that the packing and friction angle of the sand particles and the degree of saturation control the shear strength of unsaturated BES containing modest amounts of bentonite, and that the shear strength of the bentonite component can be ignored.

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