A general framework for the mechanical behaviour of clays

Abstract

It is suggested that the structure of clays may be distinguished simply as either ‘sedimentation’ or ‘post-sedimentation’, depending on whether gross yield in one-dimensional compression in void ratio-vertical effective stress plane occurs on the original sedimentation compression curve or to the right of this curve. A behavioural framework is proposed for clays having either of these structures, the magnitude of the strength sensitivity St when consolidated to the gross yield state (in compression) quantifying the effects of structure. The behaviour of natural clay consolidated to stress states pre-gross yield is related to the undisturbed clay sensitivity St; the gross yield curve is generally of arch shape, its size relative to that of the reconstituted clay depending on this sensitivity. Clays having St > 1 consolidated to stresses beyond gross yield exhibit post-gross yield behaviour in which values of sensitivity reduce with increasing post-yield strain. It is found that following normalization for composition (using the stress ratio at critical state M), volume (using p*e) and structure (using the sensitivity at gross yield St ), many different clays have the same gross yield curve. A basically frictional linear flow rule is found to operate from small or medium to large strains for both natural and reconstituted clays.