The safe thickness of water-barrier rock wall during excavation of karst tunnel

The rock mass between karst cave and tunnel heading is a natural barrier to avoid water-bursting hazard during karst tunnel excavation. On the basis of shear failure mechanism of the water-barrier rock wall, a simplified formula is induced to calculate the safe thickness of the wall. On the other hand, the finite element simulation is also adopted to calculate the safe thickness of the water-barrier rock wall in different conditions. The simulation results show that the water pressure, rock mass strength and in-situ stress have significant influence on the safe thickness of the water-barrier rock wall. A regression formula is proposed based on the numerical simulation results. Engineering examples demonstrate the practicability of the simplified formula and regression formula. And the formulas have reference value for construction of karst tunnels.