Variation in contact areas of rock joint surfaces as a function of scale

Abstract

Abstract Scale effects on the shear strength of rock joints have been recognised and investigated by many authors. The aim of this study is to explore the mechanisms underlying this phenomenon by taking into account the geometric and mechanical characteristics of the entire surface of the joint and by focusing in particular on the variation in the contact areas as a function of joint size. A special testing method has been developed to determine the contact areas on rock joint replicas subjected to direct shear tests. Test results were assessed through a mechanical model specially developed to simulate the contact between surfaces created through the application of self-affine fractal geometry. The comparisons performed on the initial results showed satisfactory agreement. The use of this mechanical model also made it possible to bring out the reduction in normal stiffness and in the ratio between contact areas and total area with increasing joint size.