The strength of unsaturated bentonite-enhanced sand

A modification to Rowe's stress-dilatancy equation is presented that extend s its range of application to include unsaturated soil behaviour. The resul ts of a programme of constant water content triaxial tests on unsaturated b entonite-enhanced sand (BES) are reported, together with those of a program me of saturated drained triaxial tests on the sand. It is shown that the va riation in the rate of dilation at failure with the sand relative density i s similar for the two materials. It is proposed that the packing and fricti on angle of the sand particles and the degree of saturation control the she ar strength of unsaturated BES containing modest amounts of bentonite, and that the shear strength of the bentonite component can be ignored.