The mechanical mechanisms of large-scale toppling failure for counter-inclined rock slopes

Toppling failure is a common instability mode for counter-inclined slopes, but the failure mechanisms involved present an ongoing engineering challenge in the geotechnical field. This study analyzes the instability failure mode of large-scale toppling failure at a counter-inclined slope on the southwestern stope of the Changshanhao open-pit gold mine. An instability failure is found here that mainly comes through two forms; one is the flexural-toppling and vertical fractures that form due to induced toppling failure at front-edge faults, the other one is bending-toppling failure and vertical fractures that form in trailing-edge steeply dipping faults. A simple mechanical mechanism for toppling failure is then established based on superimposed cantilever beam theory. By applying the maximum tensile stress strength criterion of brittle failure, a computational formula is derived for the depth to which vertical fractures extend in counter-inclined toppling failure, taking the effect of blasting vibration load into account. The relationship between the structural parameters of a cantilever beam slice and slope stability under blasting vibration are investigated. Geophysical evidence for the depth of fracturing and the related failure mechanism is then obtained using the transient surface wave method. The results of this geophysical prospecting indicate that it is feasible to simplify the rock formation as a cantilever beam slice and investigate the toppling failure of a counter-inclined rock slope under blasting vibration load using a quasi-static method. The applicability of the present research to this region is thus validated, indicating that this approach can also provide useful input for other similar engineering applications.