Karst caves are often encountered during tunnelling in China. When the caves are filled with groundwater with a high static head, drilling and blasting may induce failure or collapse in the cave wall, resulting in a water inrush or debris flow into the tunnel. The mechanism of damage to the cave wall must be elucidated in order to mitigate the hazards. A conceptual model was set up based on the Yuanliangshan Tunnel, where a cave wall collapse and debris flow were induced by drill-and-blast operations. Particle Flow Code was utilized to simulate the collapse of the cave wall and the evolution of the damage.