Time-dependent degradation of sliding cohesion due to subcritical crack propagation and damage to rock bridge in rock slopes

The time-dependent properties of brittle rocks with discontinuities are important for long-term rock-slope stability. This study proposes a subcritical crack growth model considering damage (SCGMD) for the time-dependent degradation of rock joint cohesion under compression-shear stress. In this model, the rock joint cohesion was derived as a function of the damage degree and of the length of rock bridges along the joint surface; the former was determined by using a Weibull distribution for the rock cohesion elements and the Kachanov damage rate law. As demonstrated by two time-dependent degradation examples, e.g., a simple plane-sliding slope and a landslide with irregular sliding surfaces, the SCGMD can be used to predict the cohesion of rock bridges and the slope stability. The results indicate that the time-dependent cohesion decreased slowly at first and then abruptly after a certain time, and that the time of the slope failure as result of rock bridge damage was significantly shorter than that of the slope failure without rock bridge damage. In addition, the slope failure occurred earlier as the scale and shape parameters of the Weibull distribution increased. The results of this study show that the time-dependent stability prediction of slopes/landslides has a potential to provide timely and adequate warning to prevent catastrophic events.