Stabilization Research Of Shallow Tunnel Face In Horizontal Layered Soil Conditions

The soil layers of shallow tunnel face are tend to be more complex,because the shallow tunnel has the large excavation face and the shallow depth.Different types of soil have important influence on the safety of tunnel face,which is a main factor of the safety of the tunnel construction.The key of tunnel face safety is an appropriate limit support pressure.This thesis studies the limit support pressure of shallow tunnel face in horizontal layered soil conditions.Firstly,the stability of tunnel face is studied to determine the failure mode.Most existing failure mode of tunnel face is based on the homogeneous soil layer.According to the assumption of logarithmic spiral arcs in Murayama formula and cave mode of layering slope,the limit rotation destruction mechanism in nonhomogeneous advanced core soil is established,with the common center of rotation,and present the failure mode of tunnel face in soil layer condition.Secondly,Tunnel cladding cave is similar to the wedge cave,according to previous experimental study.The mechanism of the influence of covering soil layers on the tunnel face is simplified based on the wedge failure mode.Then the external load power is calculated,including advanced core soil in covering soil layer and surface pressure.Meanwhile,the internal energy dissipation is obtained including dissipation power in advanced core soil slip plane and cladding cave slip.Lastly,the equilibrium equation is employed,with support pressure to derive the minimum support pressure formula for tunnel face.In order to verify the accuracy of the formula,the minimum support pressure of tunnel face was simulated by finite difference software FlAC3 D.In the end,the theoretical analysis results are compared with the numerical simulation results to demonstrate the accuracy of the above theory.This study show that stability of tunnel face in the horizontal layered soil is related to many factors,including the soil type,excavation diameter,cladding thickness.This research provides theoretical guidance for the supporting security of shallow tunnel face in horizontal layered soil conditions.