Thermally-Induced Wedging–Ratcheting Failure Mechanism in Rock Slopes

Abstract

A thermally induced wedging–ratcheting mechanism for slope stability is investigated using a large-scale physical model and using a three-dimensional version of the numerical Distinct Element Method (3DEC). The studied mechanism consists of a discrete block that is separated from the rock mass by a tension crack filled with a wedge block or rock fragments. Irreversible block sliding is assumed to develop down a gently dipping sliding plane in response to climatic thermal fluctuations and consequent contraction and expansion of the sliding and wedge block materials. A concrete block assembly representing the rock mass is placed in a specially designed climate controlled room. An integrated measurement system tracks the block displacement and temperature evolution over time. Results of the numerical 3DEC model and an existing analytical solution are compared with the experimental results and the sensitivity of the numerical and analytical solutions to the input thermo-mechanical parameters is explored. To test the applicability of our physical and numerical models to the field scale, we compare our numerical simulations with monitored displacements of a slender block that was mapped in the East slope of Mount Masada, as up until recently the governing mechanism for this block displacement has been assumed to be seismically driven. By application of our numerical approach to the physical dimensions of the block in the field we find that, in fact, thermal loading alone can explain the mapped accumulated displacement that has surpassed by now 200 mm. We believe this new, thermally-induced, failure mechanism may play a significant role in slope stability problems due to the cumulative and repetitive nature of the displacement, particularly in rock slopes in fractured rock masses that are exposed to high temperature oscillations.