Analytical Methods for Rock Slope Analysis
Although a rock slope is not normally thought of as an engineering structure in the conventional meaning of the word — probably because it is either a natural slope or, if man-made, a kind of negative structure built by taking material away rather than by
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* All figures quoted in the text are at the end of the lecture. L. Müller (ed.), Rock Mechanics © Springer-Verlag Wien 1972
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H. K. Kutter
Introduction Although a rock slope is not normally thought of as an engineering structure in the conventional meaning of the word - probably because it is either a natural slope or, if man-made, a kind of negative structure built by taking material away rather than by assembling it together - its design follows basically the same principles and requirements as that of any other structure. The solution of any structural problem requires first the definition, knowledge or assumption of five essential factors: 1) The geometry of the entire structure i.e. its external boundaries and its internal discontinuities (e.g. geological boundaries). 2) The external loads and body forces (static and dynamic) and force histories to which the structure is exposed. 3) The relevant mechanical properties of the materials which constitute the structure. 4) A definition and mechanism of failure and a criterion for its initiation or progression, which all are highly dependent on the type of structure and the purpose which the structure has to serve. S) The factor of safety or the acceptable probability of failure based on past design experience and in effect a factor of overdesign necessary because of insufficient knowledge of any of the four previous factors. Before going into a discussion of the techniques available for the analytical solution of slope stability problems, a few comments and clarifications on the above listed design factors are first needed. Rock is in the rarest of cases a continuous uniform material. It is full of discontinuities and weak structural features which greatly control the strength of the entire rock mass and consequently also the failure surfaces. The geometry of the potential sliding mass of an unstable rock slope is therefore determined by the location and orientation of the discontinuities. Only in the rare case of randomly oriented and relatively narrow-spaced joints will the rock mass behave similarly to a soil where the failure surface is curved and determined by the minimum energy principle. In the more normal case, however, the potential failure surfaces are dictated by the structural weaknesses, such as fault zones. joints, bedding and foliation planes. A thorough site investigation and a careful mapping of the discontinuities are therefore the first and most important step in a slope stability analysis. Dependent on the orientation, spacing and distribution of discontinuities the types of rock slope failures due to sliding can be categorized as illustrated in Figure 1. The complexity of the slide geometry
Analytical Methods for Rock Slope Analysis
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generally increases with the volume of the sliding mass and the initial or triggering failure may be of a very different kind than the final one. In any stability analysis ;J number of likely failure geometries should therefore be investigated. The static loads and the body forces acting on the sliding
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