Upper limit analysis of stability of the water-resistant rock mass of a Karst tunnel face considering the seepage force

Based on the upper limit theorem of limit analysis and the Hoek-Brown failure criterion and considering the adverse influence of the seepage force, we established a stability analysis method of analyzing the water-resistant rock mass of a karst tunnel face, developed a critical safety thickness criterion for water inrush caused by the instability of the tunnel face, and conducted a sensitivity analysis of the main influencing parameters. We defined the safety coefficient (k) of the tunnel face's resistance to water-inrush instability during the tunnel excavation process and analyzed the dynamic evolution characteristics of the tunnel face's stability during the tunnel construction according to the safety coefficient. We used the method introduced in this paper to calculate the safe thickness of the water-resistant rock mass of the Xiema tunnel face in the first horizontal line of the Chongqing Expressway where it is adjacent to karst cavity 268. We compared these results with the calculation results of a method that did not consider the adverse influence of the karst water seepage force. The results showed that the safety thickness of the water-resistant rock mass calculated using the method proposed in this paper more accurately conformed to the actual situation of the project, which can more effectively ensure the construction safety of the tunnel segment adjacent to the anterior, concealed, high-pressure, water-rich karst cavity. The results of this study hold great significance for improving the predictability and targeted prevention of water-inrush disasters in karst tunnels.