Numerical Simulation of Rock Bridge Failure Using Combined Finite-Discrete Element Method

ABSTRACT: The Bologna Interpretation of rock bridges by Elmo (2023) compared rock bridges to a spinning coin: you can only tell whether the coin is tail or head when it stops spinning. The spinning coin represents a stable rock mass, and rock bridges inside the rock mass can only be observed or measured when the rock mass has failed. Therefore, the rock bridge percentage approach to relating equivalent rock mass strength should not be used since the value of rock bridge percentage cannot be directly measured before the failure occurs. It has been discussed that rock bridge failure is a time-dependent brittle failure process, and the mode of failure is directly related to rock block and joint strengths. This paper presents the results of predictive analysis for investigating the mechanisms of rock bridge failure using Parus rock (скала́ Па́рус) as a case study. A numerical model implementing the combined Finite-Discrete Element Method (FDEM) is used to capture the process of rock bridge failure. The simulation results show that the tensile cracks initiate at the point where the joint terminates. The initiated cracks propagate across rock blocks and coalesce with other induced or natural fractures forming rock bridges. The rock fragments exposed to the free surface slide along well-coalesced fractures leading to potential catastrophic failure. This study concludes that 1) rock bridge failure is a time-dependent process which was not considered in the previously developed mathematical equations for calculating rock bridge strength, and 2) both rock block and joint strength affect the modes of rock bridge failure.