Abstract: Water and sand inrush in operational mountain tunnel in karst areas is common. Therefore, engineering analogy and theory analysis are employed to explore the groundwater runoff and sediment resource, revealing the sand inrush mechanism from tunnel drainage hole. A lining structure design principle, grouting sealing and limited discharge, is designed, and waterproof measures are enhanced. The research results reveal that: (1) Surrounding rocks should be effectively reinforced to form waterproof curtain, reduce the water pressure acted on lining, and guarantee the underground water environment protection and tunnel safety. (2) Drainage tunnels should be arranged when the water inflow is out of control, and the positions of the drainage tunnels can be determined based on the groundwater runoff direction, the positional relationship between drainage and operational tunnels, the lowest position of drainage tunnel, and the tunnel exit location. The gravity flow drainage method can be adopted.

Key words: karst area, mountain tunnel, fault, water and sand inrush, drainage tunnel