Effects of Karst Cave Shape on the Stability and Minimum Safety Thickness of Tunnel Surrounding Rock

Abstract

Karst caves are often encountered during karst tunnel excavation, and the shape of the karst cave has an impact on the stability of the tunnel surrounding rock. This paper focused on the effects of karst cave shape on the stability and minimum safety thickness of tunnel surrounding rock. First, the 3D water-filled karst cave and tunnel models were established, and the tunnel excavation simulation under the different height–span ratios of the karst cave was carried out. Second, the stress and displacement fields of the surrounding rock were analyzed, and the change laws of stress and displacement with tunnel excavation were revealed. Third, on the basis of simulation results, the formulas for the minimum safety thickness of surrounding rock resisting water inrush were derived based on the catastrophe theory and strength theory. Finally, the numerical simulation and theoretical formulas were verified by contrastive analysis of the specific engineering project. The results showed that (1) as the height–span ratio of the top karst cave increases, the principal stress of the surrounding rock increases gradually, as well as the Y-displacement of tunnel vault and bottom; (2) the influence of height–span ratios of the top karst cave on the maximum principal stress and displacement of the tunnel vault is the largest; and (3) the formula for the minimum safety thickness of rock resisting water inrush is obtained based on the catastrophe theory. The research results have certain reference significance and engineering application value for the prevention and control of water inrush disasters in karst tunnels and other similar underground engineering construction.