The surface topography of discontinuities in rock masses is generally consisted of a set of ridges and throughs in view of their genesis. The axis of these ridges and throughs is generally perpendicular to the direction of crack propagation or flow of magma or sediments. As a result, their surface morphology parameters become anisotropic, and the authors propose a procedure how to evaluate the anisotropy of the parameters utilising measurements along their eigen directions. Since surface morphology characteristics are anisotropic, their shear strength parameters consequently become anisotropic. The authors also propose some theoretical and approximate models to evaluate the anisotropy of the shear strength of rock discontinuities and check their validity through their own tests on model and natural discontinuities and some published experimental data reported in literature.
Rock discontinuities in the form of cracks, joints, bedding planes, schistosity planes etc. are commonly found in rock masses in the upper part of the earth crust. Discontinuities in rock masses influence the stability of rock engineering structures as well as thermo-hydrological characteristics of rock masses, which have become a field of interest in relation to radioactive waste disposal projects. There have been numerous experimental and numerical studies for the characterization of the surface morphology of discontinuities and for relating the surface morphology parameters to their thermo-hydro-mechanical properties in recent years. Most of the studies regard the surface morphology, deformability and strength parameters of rock discontinuities as isotropic. The surface topography of discontinuities in rock masses is generally consisted of a set of ridges and throughs in view of their genesis. The axis of these ridges and throughs is generally perpendicular to the direction of crack propagation or flow of magma or sediments (Figure 1). As a result, these parameters are likely to be anisotropic even though the discontinuity wall rock may be isotropic. The applications of the proposed procedure to natural discontinuities are described and its validity is checked. In the second part of the paper, it is experimentally shown that the shear strength parameters are also anisotropic when surface morphology characteristics are anisotropic. Then theoretical and approximate models are proposed to evaluate the anisotropy of the shear strength of rock discontinuities and their validity are checked through tests on model and natural discontinuties.
The characterization of the surface morphology of rock discontinuities is merely a geometrical procedure. In other words, it is an identification procedure of the topography of the discontinuity surfaces, which specifically involves; height, shape, and periodicity of protrusions, and the ratio of surface area over the base area. It will be appropriate if a function, which can represent the topography of discontinuity surfaces, can be found. This is extremely difficult not only because of finding an appropriate function but also because of the enormous efforts required in measuring and processing data. As a result of this, most of available techniques are based on linear profiles and various characterization parameters are proposed (Myers 1962, Sayles and Thomas 1977.