A laboratory study of post-rupture strength

Abstract

Stiff intact clays exhibit rapid loss of strength after failure, with the formation of slip surfaces and the development of a well-defined ‘post-rupture’ strength envelope. This paper describes an experimental study of the influence of a number of factors on the post-rupture strength of initially intact samples of Vallericca Clay. These include changes in confining pressure after the formation of a slip surface, the magnitude of the relative displacement across the surface, comparison between the post-rupture strength envelopes in triaxial compression and extension, and the influence of existing slip surfaces on the formation and strength of subsequent rupture planes formed by rotation of the principal stresses. The results show that the post-rupture strength envelope is well defined, repeatable, and not very sensitive to stress history or the rotation of the principal stresses. Little reduction in shearing resistance takes place for relative displacements up to about 10 mm. The results are believed to be of significance in understanding the formation of fissures in stiff clays, and in evaluating their operational strength.