Anisotropic Rock Strength Function

Abstract

In rock engineering, anisotropic rock masses are often encountered and cannot be simplified as an isotropic problem in numerical models. Hence an anisotropic function in the numerical model is required.

Rock anisotropy includes strength anisotropy and modulus anisotropy. Developing the anisotropic function in FRACOD requires significantly different complexity for strength anisotropy and modulus anisotropy. The strength anisotropy function alone does not require any alteration in the way FRACOD calculates the rock stress and displacement, and therefore it is relatively straightforward. The modulus anisotropy function, on the other hand, will require the modification of the fundamental equations of stress and displacement, and hence will be much more complex and difficult. In actual rock engineering, the strength anisotropy is often considered to be much more pronounced and important than the modulus anisotropy, and it dominates the stability and failure pattern of the rock mass.

This chapter discusses work related to the development of the strength anisotropy in FRACOD. This function has been developed for modelling the rock fracturing behaviours at the Finnish URL for high-level radioactive waste disposal where the host rock of gneiss is highly foliated and anisotropic.