Uncertainty in geotechnical engineering is inherent and due diligence requires that the geological engineer use all of the avenues/tools available to them. While estimating the stability of rock slopes, numerical tools (e.g. discrete element modeling) are not always available to practicing engineers and therefore, practical recommendations regarding appropriate slope failure mechanisms based on these theoretically correct models are required, coupled with avenues for practical solutions. This paper presents the results of limit equilibrium and discrete element modeling of a dip slope with orthogonal jointing. Results show that the Sarma method of slices utilizing plasticity theory estimates a reasonable failure surface and mechanism suitable for practical solutions where the set back distance of structures is required behind a dip slope.


A dip slope is a natural or engineered/cut rock slope that has an inclination coincident with a prominent discontinuity or set of discontinuities. The prominent discontinuity provides a plane of weakness upon which, sliding may occur. Because the slope inclination is the same as the discontinuity inclination, the discontinuity does not ‘daylight’ in the slope and is precluded from a typical planar/wedge kinematic evaluation (e.g. Hoek & Bray 1974). In order for failure to occur, ‘toe-breakout’ is required and therefore, the key issue to understanding dip slope failures is to understand the toe-breakout mechanisms. This paper focuses on the failure mechanisms associated with dip slope failures, where slope parallel bedding planes are cross-cut by natural orthogonal joints. The application of different techniques for estimating their stability is investigated and practical recommendations for stability evaluation of dip slopes with similar geologic characteristics are provided. The paper provides a comparison of these different techniques utilizing a sensitivity analysis of a typical dip slope geometry, focusing on limit equilibrium (LEM) and discrete element (DEM) modeling.

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