A New Approach to Characterise the Impact of Rock Bridges in Stability Analysis

Rock bridges have been the subject of considerable research since the 1970’s with a focus on developing methods to measure rock bridges and quantifying their role with respect to rock mass strength. In the literature, rock bridges are generally defined as a portion of intact rock separating discontinuity surfaces; however, whether a portion of intact rock resists failure and, therefore, represents a critical rock bridge depends on the failure mechanisms that may develop within the rock mass. The difficulty of defining what constitutes a rock bridge is associated with the challenge of measuring rock bridges in the field. This aspect is often ignored by engineers and practitioners, who fail to recognise that rock bridges could exist even within a rock mass characterised by fully continuous surfaces. Furthermore, field evidence of rock slope failure shows that rock bridges do not fail at the same time, and a simple definition of a rock bridge as the distance between existing discontinuities cannot account for progressive rock mass damage and changes in stresses within a rock mass. The authors suggest that the concept itself of rock bridges may be flawed, and more attention should be given to better understanding damage-related processes, including time-dependent damage in the context of engineered structures.