Mitigation of Karst Tunnel Water Inrush during Operation in Seasonal Variation Zone: Case Study in Nanshibi Tunnel

A discrimination method with drainage or plugging that mitigates the karst tunnel water inrush during operation in a seasonal variation zone is proposed to cope with repeated water inrush disasters. This method identifies the critical-water-pressure working state of the tunnel lining by analyzing the water inrush mechanism during the karst operation period. Based on the working state of the tunnel's critical water pressure, a more accurate method for calculating the equivalent permeability coefficient of the surrounding rock in the karst tunnel is proposed, and then the treatment principles of plugging and drainage can be distinguished theoretically. By taking the Nanshibi operating tunnel as an example, a field test of water inrush disaster treatment was carried out to testify the effectiveness of the proposed approach. Results indicate that: (1) the discrimination method of drainage or plugging can effectively guide the management of water inrush disasters in operating tunnels, and (2) the grouting plugging plan and grouting treatment effect inspection method proposed for operating tunnels have high applicability.