Study On Tunnel Face Stability In Water-Rich Weak Strata By Discrete Element Method

Taking the "The Belt and Road" strategy as an opportunity, long and deep tunnels and crossing rivers and seas tunnels will usher in a new climax, and complex geological problems gradually become the bottleneck of its development. Engineering practice showed that, tunnel through debris flow strata and saturated sandy strata will encounter severe safety problems. In this paper, focusing on the tunnel debris flow disaster and saturated sandy strata, and around the tunnel face stability problem, the three dimensional particle discrete element fluid-solid coupling method has been used to study mechanical behavior of tunnel face in the microscopic view. Then through theoretical analysis the calculation method of tunnel face stability has been established. The research results laid the foundation for the tunnle face stability control in the debris flow strata and the saturated sandy strata. Main research contents of this thesis are as follows:1. According to the regional geological characteristics of tunnel debris flow disaster, using the three dimensional particle discrete element method of liquid-solid coupling, the tunnel debris flow disaster numerical analysis model has been established, and the debris flow disaster of tunnel face catastrophic instability behavior has been studied. The evolution process of the debris flow disaster in the tunnel has been reconstructed. A method to identify the debris flow disaster in the tunnel has been proposed. The main influencing factors of debris flow disaster in the tunnel has been analyzed. The failure mechanism of the debris flow disaster has been proved.2. Based on the research result of the debris flow disaster of tunnel face catastrophic instability behavior, the plate rocks critical safety thickness calculation method of the tunnel debris flow disaster by means of empirical method, theoretical methods and numerical methods has been put forward. And the physical states of the surrounding rock changing from stability to collapsing has been realized.3. According to the physical and mechanical properties of saturated sandy strata using the three dimensional particle discrete element method of liquid-solid coupling, the numerical analysis model of the tunnel face stability in the saturated sandy strata has been established. The saturated sandy trata tunnel face failure rules on the condition of seepage and the limit support face pressure of the tunnel face has been researched. On this basis, the 3D wedge theory calculation model that has considered seepage was modified from the failure modes of tunnel face. The calculation method of the limit support pressure for tunnel face in saturated sandy strata under seepage condition is established.