Stability Analysis Of Soil Pressure Balance Shield Tunneling Face In Sand Stratum

With the acceleration of urbanization in China and the increase of urban population,subway has become the first choice of transportation to alleviate traffic pressure and promote urban development in order to solve the traffic congestion problem.Shield tunneling is widely used in subway tunnel construction due to its advantages of small environmental impact and high degree of automation,in which soil pressure balance shield is more widely used because of its advantages such as small site influence,low cost and so on.Because of the poor stability of sand stratum,it is very important to maintain the stability of excavation surface in shield tunnel construction with balanced soil pressure.If the support force is not properly controlled,it is easy to cause the destruction of the soil in front of excavation,resulting in the collapse or uplift of the ground.In this paper,based on the displacement earth pressure theory,numerical simulation and theoretical analysis are used to study the deformation process,failure and instability mode,and the relationship between the support force of excavation surface and the displacement in front of soil pressure balance shield.The main work and research results are as follows:(1)Numerical simulation method is used to simulate the decrease and increase of supporting force of excavation surface under different working conditions.The failure development process and failure mode of soil in front of shield tunneling are analyzed,and the relation curve between supporting force and displacement of excavation surface is analyzed.The influence factors of the ultimate supporting force of the excavated face.(2)Based on the results of numerical simulation,according to the displacement earth pressure theory and the plastic limit equilibrium theory of soil mass,the formula of the relation between the active support force of shield excavation surface and the displacement of excavation surface is established.Considering the same excavation condition as the numerical simulation,the relation curve between the active support force of the excavation surface and the displacement of the excavation surface is obtained,and the influence of the buried depth ratio and the angle of internal friction on the support force is analyzed.(3)According to the displacement earth pressure theory and the plastic limit equilibrium theory of soil mass,the formula of the relation between the passive support force of shield excavation surface and the displacement of excavation surface under shallow overburden formation is derived.Considering the same excavation condition as the numerical simulation,the relation curve between the passive support force of the excavation face and the displacement of the excavation surface is obtained,and the influence of the internal friction angle on the support force is analyzed.(4)The numerical simulation results are compared with the theoretical analysis results of the derived formula.The results show that the theoretical analysis results are reasonable.The research results in this paper are of great significance for the selection of thrust and the stability control of excavation surface in soil pressure balance shield tunneling.