The ultimate shear strength of a bentonite±sand
mixture depends primarily on the relative density
and critical-state friction angle of the sand within
the mixture. Over the range of bentonite contents
used for environmental barriers, the bentonite has
very little in¯uence on drained strength unless it
supports a signi®cant proportion of the stress (indicated
by a low clay void ratio). However, at very
high bentonite contents (and consequently high
sand void ratios) the strength of the mixture will
tend towards the strength of the clay.