Rock fracture mechanism of buffer blasting with cushion layer at the borehole bottom

This study primarily investigates the rock fracture mechanism of bottom cushion layer blasting and explores the effects of the bottom cushion layer on rock fragmentation. It involves analysis of the evolution patterns of blasting stress, characteristics of crack distribution, and rock fracture features in the specimens. First, blasting model experiments are carried out using the dynamic caustics principle to investigate the influence of bottom cushion layers and initiation methods on the integrity of the bottom rock mass. The experimental results indicate that the combined use of bottom cushion layers and inverse initiation effectively protects the integrity of the bottom rock mass. Subsequently, the process of stress wave propagation and dynamic crack propagation in rocks was simulated using the Continuous-Discontinuous Element Method (CDEM) and the Landau explosion source model, with varying thicknesses of bottom cushion layers. The numerical simulation results indicate that with increasing cushion thickness, the absorption of energy generated by the explosion becomes more pronounced, resulting in fewer cracks in the bottom rock mass. This illustrates the positive role of the cushion layer in protecting the integrity of the bottom rock mass.