Study On The Stability Of The Excavation Face Of Tunnel Under The Upper-soft Lower-hard

How to maintain the stability of the excavation surface of the shield tunnel is an important aspect of ensuring the safety of the construction.When the shield machine through the upper-soft lower-hard complex formation,the pressure control of tunnel excavation face is unsuitable,and it is very easy to appear the instability of tunnel excavation surface,it poses a great threat to the safety of the construction.In view of the above situation,based on the background of a nuclear power plant drainage tunnel project,using a combination of numerical simulation and theory,the tunnel shield excavation face stability,soil deformation law,soil parameters sensitivity is studied,the main research results are as follows:(1)To maintain the stability of tunnel excavation is key to determine the reasonable supporting force,to determine shield tunnel excavation face limit supporting force under complex formation as the goal,the calculation model of pore water pressure after the correction,the theoretical calculation method of tunnel excavation face limit support force is improved and applied under the upper-soft lower-hard complex formation,and the numerical simulation technique is used to verify the above calculation results.(2)Using numerical simulation technology,the shield construction simulation was implemented under the upper-soft lower-hard complex formation.Failure form of tunnel excavation face and the relationship between the stress ratio of the tunnel excavation face and the displacement of the soil in front of the excavation face is studied,the relationship between the supporting stress ratio and the surface subsidence and the uplift in front of the excavation face is provided,which provides guarantee for the efficient construction of shield tunnel under complex geological conditions.(3)Considering the limitations of the geological survey,there is a big risk for rock soil physical and mechanical properties of accuracy,the sensitivities of the minimum supporting force of shield tunnel face is analyzed with the mechanical indexes of rock and soil,the variation of the deformation of the excavation face with the support stress ratio and the variation of the excavation support force with the cohesion and internal friction angle of the rock and soil are obtained.The relevant results can provide the basis for the determination of the maximum and minimum supporting force of shield tunnel excavation face and the safe construction for the complex geological conditions.