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 influence on drained strength unless it
supports a significant 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.