Three-Dimensional Refined Modeling and Mechanical Response Analysis of Tunnel Structure Safety in Karst Areas

Deep-buried tunnels in karst regions are prone to complex deformation and stress redistribution due to the heterogeneity of surrounding rock and the presence of cavities. This study establishes a three-dimensional finite element model to investigate the mechanical behavior of tunnel linings under varying karst distributions and distances. The model incorporates realistic geological parameters and boundary conditions to analyze stress evolution and radial displacement of the lining under coupled mechanical effects. The results indicate that karst cavities located near the tunnel, especially beneath it, significantly amplify radial deformation and induce asymmetric stress concentrations. As the distance between the karst and the tunnel increases, the influence on lining response rapidly decreases and becomes negligible beyond approximately 3 m. The introduction of a secondary lining effectively reduces both tensile and compressive stresses by more than 65% and mitigates local deformation. The study concludes that the spatial position of karst features is the dominant factor affecting lining performance, and the composite lining structure provides an efficient means of ensuring safety and stability in water-rich karst tunnels.