Geometrical aspects in the consideration of actual opposed surface along shearing direction in rock joints

Abstract

Shear behaviour of rock joints is strongly influenced by the roughness of its surface as the different failure mechanisms will be conditioned by the shape and distribution of the asperities and undulations in it. Currently, this surface can be digitalized using scanning methods directly in the field or in representative laboratory samples. After that, the surface is digitally reproduced using triangulation methods. This allows to analyse it using stablished parameters that do not depend on the arbitrariness of the technician. Despite the fact that 2D roughness parameters are still of great importance, these techniques are nowadays provoking a tendency to implement 3D measuring methods that allow to treat all the surface simultaneously and thus gathering valuable information of the rock joint as a whole. The vast majority of the 3D most powerful methods consider the area of the surface that is opposed against the shearing direction in order to determine the roughness, anisotropy and peak shear strength of the rock joint. However, not always the whole surface of each triangle that faces against shearing direction should be considered. In this work, a new methodology to consider the actual area of each triangular element that is involved in the shearing process is mathematically derived. Therefore, improving the accuracy of current methods, as well as the truthfulness of the mechanical characterization of rock joints.