Effect of discontinuity roughness and orientation on the parameters of the rock failure criterion under triaxial compressive stress

Discontinuity roughness is one of the most important parameters for understanding the mechanical characteristics of jointed rock under triaxial compressive stress. Discontinuity roughness can vary in a wide range and can play an important role in the failure mechanism of rock under triaxial stress, particularly with varying joint orientation angles and confining pressure. In this work, the effects of discontinuity roughness on rock strength under triaxial compressive stress were investigated. Different methods were applied to create cylindrical specimens with a wide range of discontinuity roughness and orientation angles. Fifteen groups of specimens with three different types of discontinuities roughness: tooth-shaped asperity (TSA), rough undulating (RU), and smooth and planar (SP) and five orientation angles (0, 30, 45 60, and 90 degrees) were tested, and in total 255 triaxial compression tests were carried out on jointed specimens. For specimens having different roughness and orientation angles of 45 and 60 degrees, failure took place in the direction of the discontinuity. Tooth-shaped asperities were interlocked and broken along the discontinuities, particularly under high confining pressures. For specimens having TSA discontinuity and an orientation angle of 60 degree, sliding occurred at one side of the teeth planes under uniaxial loading. Greater discontinuity interlocking and axial strength (A ) were observed with increasing roughness and confining pressure. The results show that the roughness and orientation angle of discontinuities have a major effect on the parameters of jointed rock failure criteria. New relationships between the failure criteria parameters, roughness, orientation angle, and uniaxial compressive strength of jointed specimens have been derived.