Fractal analysis of the progressive failure of shales and stiff clays under shear

Abstract

Shales and stiff clays when deformed under direct shear stress conditions develop narrow shear zones within which different sets of discontinuities or cracks are present. These cracks form in the shear zone in a progressive manner. In the first stage of deformation, a small set of unconnected cracks called Riedel shears form. In the second stage of deformation, a series of cracks called Thrust shears form. They connect with the Riedel shears. In the third stage of deformation, The Riedel and Thrust discontinuities interact, forming an undulating and rough failure surface. In this study, the fractal dimension concept from fractal theory is used to evaluate the progressive degree of cracking in the shear zone that causes the failure of shales and stiff clays forming part of natural slopes and earth dams. It was established that the intensity of cracking in the samples was reflected in the fractal dimension values. High levels of cracking were associated with high values of the fractal dimension.