Updating the probability of failure of rock wedges

Abstract

In hard rock masses, discontinuities control the slope stability, rather than block matrix breakage. The relative position and orientation of joints and slope face define the most likely mechanisms of failure. Among these mechanisms, the wedge failure is one of the most common modes of failure in which joint sets dip and dip direction, slope geometry and direction, external forces (including water pressure and earthquake) and rock and joints mechanical properties control the stability. The determination of these input parameters is not straightforward, mainly due to their variability and the limited amount of information available. Besides, in most projects, input parameters come from different sources (e.g., expert opinion, back-calculation, laboratory tests, field test or different project stages). Therefore, this limited information from different sources should be appropriately incorporated into the stability analysis to assist the design and decision-making process. In this context, random sets arise as a powerful tool to combine different sources of information and to perform a reliability assessment under limited information. This feature makes it possible to update the probability of failure as new evidence is available. With this framework, this paper presents a reliability assessment of wedge stability in a rock slope of a sandstone quarry, located in Une Cundinamarca, where information on mechanical and geometrical parameters has been collected for 20 years. This approach allowed to update the probability of failure. As a result, an updated probability of failure raging between 0.04 and 0.25 was calculated.