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The problem of the stability of a rock slope containing a three-dimensional wedge resting on two intersecting discontinuities is analyzed by means of engineering graphics, using spherical projections and analytically. The effects of an obliquely inclined upper slope surface, a tension crack behind the slope face, water within the tension crack and on the sliding surfaces and an external force, due for example to a cable anchor, are included in the analysis. Resistance to sliding results from both friction and cohesion on the sliding surfaces.A worked example, using all three methods, is given. ProblemThe face of a slope has a dip of 65 ~ and a dip direction* of 185 ~ The upper surface of *The term dip direction is used throughout this analysis in preference to the more common term strike (strike = dip direction-90 ~ in order to avoid the ambiguity which can be associated with the use of strike. E. Hoek, Professor of Rock Mechanics.

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Rock wedges in the roofs of underground excavations may be wholly or partly self-supporting due to the mobilization of shear resistance on discontinuities bounding such wedges. The extent of the mobilization, which occurs as the wedge deforms, is markedly influenced by the magnitude of the stress field tangential to the opening and the relative stiffness of the intact rock and the shear and normal stiffnesses of the discontinuities. Analytical and numerical models are described for determining the upper and lower bounds of the failure loads for two-dimensional asymmetric and symmetric rock wedges. Experiments conducted on physical models indicate that the stability of rock wedges may be substantially reduced by loosening and that the analytical solutions may overestimate the load necessary to cause failure. Keywords: rock wedge stability, in situ stresses, joint stiffness.