Effect of discontinuity orientation and confinement on the strength of jointed anisotropic rocks

We have investigated the effects of discontinuity dip and dip direction difference on rock mass strength, together with an assessment of how the degree of anisotropy varies with changes of the confining pressures. This assessment was made possible through introduction of a dimensionless “Anisotropy Effect” parameter. Numerous studies have been conducted on the effect of dip variation so far, but none of them have paid attention to the dip direction difference of joints on the strength response of the rocks. To begin with, we investigate the behavior of anisotropic specimens with regard to confining pressure and the jointing inclinations in order to assess the failure mechanism. Then, we proceed to study the effects of discontinuities dip direction difference on the rock mass strength through testing artificial (plaster) specimens. The samples were tested under triaxial conditions, subjected to different confining pressures. We present the details of the investigations, tables of the evaluated test results, and the empirical equation deduced during the course of this research.

► Effect of joints dip and dip direction difference on rock strength was studied.
► Degree of anisotropy varying with changes of the confining pressures was assessed.
► A dimensionless parameter termed as “Anisotropy Effect (Ae)” was introduced.