SHEAR AND COMPRESSIVE YIELD IN THE FILTRATION OF A BENTONITE SUSPENSION

A suspension of compressive yield stress P0 will not be filtered unless the differential filtration pressure P exceeds P0. Measurements showing this pressure threshold are reported for a bentonite clay suspension. The cumulative filtrate volume for the suspension is found to vary as P0.215-P-0(0.215), from which P0 is obtained. The shear yield stress tau0 of the suspension is obtained from analyses of conventional shear rheological data. A friction angle alpha for bentonite, given by arcsin(tau0/P0), is closely similar in magnitude to literature data for similar clays in plastic deformation. Interpreted as an elastic property, tau0/P0 gives a Poisson ratio for the floc network which is numerically close to that of an elastic polymeric network.