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.
Approximately one-quarter of the total land area of China is underlain by carbonate rocks. The carbonate rocks occur mainly in Guizhou, Yunnan, Guangxi, Guangdong, Sichuan, Hunan, and Hubei provinces, and in Chongqing municipality. The total area of the carbonate rocks, including sections covered by later formations, accounts for over 70% of the land area of China. The carbonate layers are generally 200 m to 300 m in thickness; the thickest layer is 1900 m (Lu, 1986). Water inrushes, mudbursts, tunnel collapses, loss of surface water and groundwater, and surface subsidence are typical geohazards resulting from tunnel construction in the deep karst zones and often result in the evolution of geohazard chains (Han, Wu, and Wang, 2007). Karst caves are often encountered during tunnelling. Occasionally the caves are filled with mud and groundwater with a high static head. As the surrounding rock is excavated, the cave wall becomes thinner and may collapse, inducing water inrushes and mudbursts, which can further decrease the stability of the surrounding rocks and result in tunnel collapses. The dewatering cone of tunnel drainage and excessive water inrushes can deplete the surface and upper groundwater systems, and this may be followed by extensive subsidence of the surface.