Stability analysis of karst tunnel surrounding rock considering initial damage and filling load.

The presence of karst will not only reduces the integrity of the surrounding rock of underground engineering, but also erode the surrounding rock mass for a long time due to its internal filler, leading to initial damage on different degrees of the surrounding rock. Taking the Taojia Tunnel in Chongqing as the research object, the main causes of the sand surge accident were analyzed and the stability analysis of the surrounding rock of the karst tunnel under the influence of initial damage and filling load was carried out with the help of the limited difference software FLAC^3D 6.0. The main conclusions are as follow. The unloading of rock mass caused by tunnel excavation and the gravity action of the filling material inside the karst cave are the main causes of sand and mud flooding accidents. The influence of initial damage of rock mass on the vertical displacement and stability of the surrounding rock of the tunnel arch roof cannot be ignored. It is suggested that the initial damage coefficient should be 0.4-0.5. The filling load has a great influence on the stability of surrounding rock. When the load value is greater than 75 t/m², the vertical displacement of surrounding rock increases obviously, and the stability decreases sharply The greater the filling load and initial damage coefficient are, the greater the influence of intermediate principal stress (σ₂) on the stability of tunnel surrounding rock is. [ABSTRACT FROM AUTHOR]