Strength, deformability and fluid flow properties of rock joints are to a great extent controlled by the surface roughness. The roughness parameters classically proposed in the literature, such as the JRC or the fractal dimension D, are usually estimated from the analysis of a single linear profile. Three-dimensional characterisation of the surface morphology would obviously yield more information. Next, the dependence of the shear strength on the direction of the motion was studied by shearing identical surfaces in different directions. A good correlation was found between the shear strength values obtained during laboratory tests, and the morphological parameters that were calculated from three-dimensional surface measurements. The experimental results confirmed that the shear strength of rock joints is direction-dependent, and show that the new surface parameters to can be used to estimate the anisotropy in the shear strength of a rock fracture.
The assessment and management of risks associated with natural hazards play a crucial role for the sustainable development of a liveable and safe environment. One of the major problems for efficient risk management is the current lack of a thorough understanding of the physical processes involved in most kinds of natural instabilities. Undoubtedly, among all factors that influence the behaviour and the stability of rock masses, fractures play a major role. Nevertheless, the contribution to shear strength provided by the roughness decreases with the increase of the normal stress magnitude (ling et al 1992). The geometry of roughness influences the size and distribution of contact areas during shearing. Consequently, it has to be considered the most important geometrical boundary condition for explaining this process under low normal load conditions. In addition, the size, shape, and spatial distribution of damaged areas depend on the shear direction, the degree and distribution of stress, and horizontal displacement (Gentier et al 2000). The common characteristic among all damaged areas is that they are without exception located in the steepest zones facing the shear direction (Dong et al 1993, Haberfield & Johnston 1994, Myshkin et al 1998, Yang & Chiang 2000). The shape of the damage zones also depends on the local geometry of the fracture surface, including the size and shape of the asperities, as well as on the mechanical parameters of the rock (Grasselli et al 2001). In order to estimate the position of the damaged areas that will occur during shearing, it is first necessary to know the shear direction. However, little attention has been paid to the variation of the shear strength respect to the shear direction (Huang & Doong 1990, Jing et al 1992, Kulatilake et al 1995). In this paper, four different rock-joint surfaces were analysed along all possible shear directions. The results are plotted on polar diagrams that illustrate the roughness anisotropy of the surface. Moreover, the adopted surface parameters are proved to be proportional to shear strength; hence, the diagrams provide formidable tools for the visualisation of the anisotropy of rock joint strength, and for its qualitative estimation.