Numerical Study on Dynamic Fracture and Energy Transformation Characteristics of Rock Unloading Failure under Identical Energy Stored Levels

Abstract

Rock bursts are aggressive dynamic failure processes that involve the rapid release of strain energy stored in a rock under unloading conditions. The dynamic fracture and strain energy transformation characteristics of rock unloading failure must be investigated to predict and control rock bursts. This study adopts the discretized virtual internal bond (DVIB) method to investigate this problem. The element partition method is performed in the DVIB method to investigate the effect of cracks on rock unloading failure. Three indicators, i.e., fracture area, the fractal dimension of the failure pattern, and energy release ratio (kinetic energy over strain energy), are adopted to evaluate the failure intensity. Simulation results show that a critical strain energy density (SED) for rock unloading failure exists. The unloading failure occurs only when the SED exceeds the critical value. Subsequently, under the same SED conditions, the effect of the lateral pressure coefficient (LPC), heterogeneity, and size on rock unloading failure is investigated. As the LPC increases, the failure intensity increases slowly and then decreases significantly. The critical LPC is approximately 0.5, indicating that the unloading failure is the most severe. The simulation results suggest that the crack can reduce the energy release capacity of the rock and then restrain rock unloading failure. When the precrack angle is 0° or 90°, the precrack barely affects the rock unloading failure, and the failure intensity is similar to that of the intact rock. When the precrack length or the density of random precracks is larger, the rock unloading failure is weaker.