Fissure Parameters in Stiff Clays under Compression

Abstract

Stiff clays and shales forming part of natural slopes and earth dams contain fissures in their structure. Very little is known about the effect that fissure parameters such as orientation, length, number of fissures, and their mode of arrangement have on the unconfined compressive strength of stiff clays and shales. This study reports laboratory investigations designed to understand the effect that such fissure parameters have on the unconfined compressive strength of stiff fissured clays. To this end, prismatic samples of brittle kaolinite clay with preexisting cracks are tested in the laboratory under uniaxial compressive stress conditions. It is found that the orientation, length, number, and arrangement of cracks in a clay sample has a marked influence on its unconfined compressive strength. The laboratory results indicate that: (1) There is a critical crack orientation in a sample at which the uniaxial compressive strength reaches a minimum value; (2) the longer the length of a crack or the larger the number of cracks in a sample, the lower is its confined compressive strength; and (3) samples with cracks arranged in a leftstepping manner are weaker in compression than samples containing right‐stepping cracks.