The Face Stability And Control Of The Large Section Tunnel In Soft Rock

A lot of large-section tunnels in weak surrounding rock has been encountered when urban subway and underwater tunnel were built in recent years. The stability of tunnel face is a key and valuableproblem to be solved.In this dissertation, some engineering such as Liuyanghe tunnel were chosen as background, theoretical analysis, numerical simulation model test and field monitor were adopt to carry research on the face stability and control of the large section tunnel in soft rock.The main work and relevantconclusion of the dissertation are described as follows:1. The stability of double line railway tunnel face was classified based on the surrouding rock grading standard of railway tunnel in china.The tunnel face behavior is stable, stable in short term and unstable when the extrusion of tunnel face is less than8mm, between8mm and45mm, larger than45mm, or when the average plastic shear strain of tunnel face is less than0.001, between0.001and0.006, larger than0.006respectively.2. The method by the principle of dichotomy was applied to back calculate the grout cohesive strength and grout friction angle based on a given pullout force of rock bolt, and the back calculated value was used to instead the real value in other relevant numerical analyses.3. The reinforcement density of bolt was determined by the balance principle of tunnel face; by using which, the extrusion of tunnel face can be control accurately; The reinforcement scope of bolt was determined by the comparison of extrusion in different reinforcement density; the depth of fracture plane was chosen as the reinforcement length; the optimal axial stiffness of bolt was defined by comparison of reinforcement effect of bolt with different axial stiffness.4. There is an optimal permeability coefficient of rock for the stability of tunnel face. The extrusion deformation of tunnel face will be the minimal value with the optimal permeability coefficient. Water pressure is unfavorable for the stability of tunnel face. The tunnel face will became unstable with large water pressure.5. The dynamic effect of earthquake is unfavorable for the stability of tunnel face. The influence of dynamic effect on tunnel face is different in different strata, tunnels in hard rock strata are less affected while tunnels in soft rock strata are major affected.Blasting load result in increasing of tunnel face extrusion, which will lead to unstable of tunnel face.6. The safety of tunnel has been verified by the analysis of numerical calculation, field monitoring and model test. Since the major extrusion of tunnel face emerged before the expose of tunnel face, incorrect measurement method will lead to serious small result.