Rock strength properties and their measurement

This chapter discusses the shear strength properties of discontinuity surfaces and describes methods of measuring the friction angle in the laboratory. In analyzing the stability of a rock slope, the most important factor to be considered is the geometry of the rock mass behind the face. The sliding surface in a slope may consist of a single plane continuous over the full area of the surface, or a complex surface made up of both discontinuities and fractures through intact rock. The actual shear performance of discontinuity surfaces in rock slopes depends on the combined effects of the surface roughness, the rock strength at the surface, the applied normal stress and the amount of shear displacement. The presence of infillings along discontinuity surfaces can have a significant effect on stability. The most important influence of water in a discontinuity is the diminished shear strength resulting from the reduction of the effective normal shear stress acting on the surface.