Shear band formation and propagation in clay slopes

Stiff clays in the ground are highly overconsolidated, with lateral pressures several times greater than the present overburden stress. When a cut is made in deposits of stiff clays, the resulting stress relief causes the clay near the cut faces to exhibit large lateral movements towards the face of the cut. Such movements lead to the concentration of stresses in regions close to the toe of the cut, resulting in the formation of what is referred to as "shear band" or "toe crack" at the base of the cut. The present study presents the results of laboratory and theoretical investigations designed to understand the mechanics of formation and propagation of a shear band in vertical cuts in clay Laboratory tests on simulated vertical slopes in clay containing a small shear band (crack) at their toe indicated that the shear band did not propagate in its own plane when subjected to a combination of normal and shear stresses. Instead, the shear band or toe crack propagated in the form of a secondary crack that developed an angle with respect to the plane of the shear band. This study also presents a way to obtain the critical height of a cut in clay considering a failure surface that is made of a shear band of small length at the base of the cut, a secondary crack at an angle with the plane of the small shear band, and a tensile crack at the top of the cut.