Considerations of failure mechanisms associated with rock slope instability and consequences for stability analysis

The results of a series of physical model studies of the stability of jointed rock slopes carried out some years ago are described. These models were tested under centrifugal loading. Four 'geological' structures were tested; all had the same joint orientations and strengths, but the relative spacing of the joints was different. The results showed that the mechanisms of failure of the slopes varied for the different models, and the gravitational loads at which failure developed also varied. The following conclusions are drawn from the results of the physical model tests: the mechanism of slope failure is by progressive deformations throughout the slope the ratio of the spacings between the different sets of discontinuities exerts considerable influence on the slope failure in the models tested, the intact material strength had no noticeable influence on the stability of the jointed rock slopes (note that for hard rock, similitude conditions indicate a prototype slope height of 300 to 400 m, and therefore intact rock failure might not be expected under simple gravity conditions, i.e. no tectonic stresses) rock slope failures are three-dimensional and in general are not amenable to two-dimensional simplification knowledge of the orientations of discontinuities in the slopes does not allow prediction of a unique failure surface, nor of a volume of failure. The volume of failure is determined to a large extent by the plan configuration of the slope.