Fracture Criteria for Anisotropic Rocks

Abstract

Most rocks of sedimentary and regional metamorphic origin are characterized by some degree of strength anisotropy. On a large scale, systems of rocks usually contain joints, bedding-plane partings or faults which impart considerable anisotropy to strength and other properties. In the present paper, the general propesties of fracture criteria of anisotropic rocks or systems of rocks are discussed. A General fracture criterion of them can be approximated in the load space or in the principal stress space by the minimum composite surface constructed from all the possible surfaces, each of which is determined as if a single plane of weakness or a crack were contained in the materials or in the systems of materials. Several fracture criteria in two dimensions based on three types of model are critically reviewed. It is shown that they are best summarized in the Coulomb or the Mohr quadratic type criterion. Two types of fracture surface in the principal stress space are also discussed as a formal extensison of the Coulomb and Mohr type criteria. These criteria, both the two dimensional and the three dimensional, are in good agreement with experimental results. These criteria, thus, can be used to predict fracture of anisotropic rocks or systems of rocks which exhibit planar anisotropy.