Calculation Model of Safety Distance between Shield Tunnels and Underground Cavities in Water-Rich Sandy Cobble Stratum

［Objective］In order to ensure the shield tunnel construction safety in water-rich sandy cobble stratum when passing through underground cavities, it is necessary to study the safe distance between the shield tunnels and the underground cavities. ［Method］Taking the tunnel project of Nanchang Metro Line 1 East Extension as an example, combining theoretical calculation and numerical simulation methods, a quantitative analysis is conducted on the safety distance between underground cavities and tunnels based on the catastrophe theory. The above-mentioned safety distance is calculated by combining the structural mechanics approximate analysis method, and a calculation model for the safety distance between the shield tunnels in water-rich sandy cobble stratum and the underground cavities is established. The rationality of the proposed calculation model is verified by the Abaqus software numerical simulation, taking whether the plastic zone of the rock-soil system between the underground cavity and the tunnel is connected as the criterion. ［Result & Conclusion］The proposed calculation model for the safety distance between the shield tunnels in water-rich sandy cobble stratum and the underground cavities has certain accuracy and rationality and can be applied in engineering practice. The above-mentioned safety distance increases as the span of the underlying cavity increases, decreases as its height-to-span ratio increases, and increases as the level of surrounding rock influence factors increases.