Study On Shield Tunnel Support Based On Three-dimensional Bucket Soil Arch

The advantages of shield tunnel construction are outstanding,and it has become the preferred construction method for underground tunnel construction.When shield tunneling is widely used,it is often faced with the problem of tunnel face stability.With the construction of shield tunnels getting deeper and deeper,the stability of shield excavation faces is quite different from that of shallow tunnels.When a shallow shield tunnel is excavated,a continuous and complete sliding surface that penetrates to the ground will be generated above the tunnel.For deep-buried tunnels and complex soil layers,the shield itself and the outside world have a great influence,the soil arching effect is often unable to play a full role,and the sliding surface is not all vertical.The existence of soil arching effect has a significant influence on the horizontal limit supporting force of the excavation face of shield tunnel,and the stability of the excavation face should be fully considered.In this paper,the research background and status of horizontal support force and soil arching effect of shield tunneling face are firstly discussed.Then the vertical earth pressure of shield tunnel is calculated and the soil arching effect is fully considered in the calculation process.The vertical earth pressure considering soil arching effect is applied to the calculation of horizontal limit supporting force,and the active horizontal limit supporting force of excavation face is obtained.Finally,the numerical simulation of shield tunnel is carried out and verified with theoretical calculation.The main contents are as follows:(1)The traditional theory of loose soil pressure usually adopts the assumption of vertical sliding crack surface,but according to different soil parameters,tunnel buried depth diameter ratio and soil displacement in loose area,the sliding crack surface is not all vertical.In this paper,the failure surface of the loose zone is regarded as the inclined slip crack surface and the lateral earth pressure coefficient is obtained considering the soil arching effect.In the case of two-dimensional trapezoid soil arch and three-dimensional bucket soil arch,the analytical solution of vertical earth pressure in the loose zone of tunnel overburden is derived.(2)Soil arching effect can be divided into two states: full play and incomplete play.For the vertical earth pressure under the two-dimensional trapezoidal soil arching effect,the influences of the slope angle of the slip surface,the depth of the overlying soil layer on the excavation surface,the internal friction angle and the cohesion force on the vertical earth pressure are considered.For the three-dimensional bucket vertical earth pressure,in addition to the two-dimensional model influence factors,and the loose zone buried depth ratio,length and other factors are analyzed by numerical examples.(3)The local and global failure of the horizontal limit supporting force of the excavation face were solved,and the influence of soil arching effect was considered in the solution process.The loose earth pressure is the vertical earth pressure under the effect of three-dimensional bucket soil arch.The influencing factors of the horizontal limit supporting force under local and global failure are analyzed by numerical examples.(4)Numerical experiments are carried out on shield tunnels with complex terrain,and the numerical results are compared with the theoretical results of the horizontal limit support force of the excavation surface.During the simulation process,a progressive failure model of the excavation surface was obtained;Considering the effect of soil arching,the active and passive extreme values of horizontal limit supporting force are obtained;The soil arching effect caused by tunnel excavation is analyzed,and the deformation law of shield tunnel excavation surface is obtained.