Study On Excavation Stability And Instability Characteristics Of Large Cross-Section Highway Tunnel In Karst Formation With Water-Rich

With the western development strategy of our country progresses and the growing density of traffic network planning, tunnel construction in karst region of Southwest China has become the norm, in recent years. As for the influence of high water pressure dissolved cavity, top collapse, surface subsidence, deformation of surrounding rock and even destruction disasters become incidental in karst area, therefore, research in tunnel excavation stability and the instability characteristics of surrounding rock as well as initial support in karst area get even more important.Basing on Chongqing Shuangbei Tunnel engineering, indoor similar model experiment and numerical simulation was applied to simulate the tunnel excavation in karst region, the research mainly focus on excavation stability and unstable failure process of large cross-section highway tunnel in karst formation with water-rich, the main contents and results are as follows:(1) By means of literature research, karst cave characteristics of distribution was statisticed, hydraulic calculation method is introduced, the evaluation methodology of excavation stability and surrounding rock collapse mechanism were analyzed.(2) By carrying out indoor similar model experiment, the effect of dissolved cavity in pressure with different locations on tunnel excavation stability was analyzed, in the premise of excavation stability, progressively increasing the dissolved cavity pressure until tunnel unstable failure, thereby, the convergence of tunnel inner perimeter, surrounding rock pressure and internal force variation of initial support under high water pressure were obtained.(3)The safe critical distance between the tunnel face and different pressurized cavity which locates in front of the working face has been studied in this paper by numerical simulation. On the basis of the result, scaled model test was carried out by increasing the cavity pressure progressively, in which, the working face displacement and surrounding rock pressure and the variation of primary-support internal force in the tunnel unstable failure process were researched.