Kinematical Analysis Of The Face Stability For A Shield-driven Tunnel

Abstract:It is important to ensure the stability of the soils before the tunnel face when a shield machine is tunnelling. The soils before the tunnel face will collapse due to a lack of sufficient supporting pressure acting by the shield machine, which would result in excessive surface depressions. Such a failure is called the active failure. On the basis of upper theorem, the active failure mechanism as well as the supporting pressure is investigated in this paper.1. Simplifying tunnels into plane strain condition in the longitudinal direction and using failure mechanism of two-dimensional double logarithmic spiral lines, the active soil failure mechanism in front of the tunnel face is studied based on upper bound theorem of limit analysis. The upper solutions of supporting forces are obtained by taking the supporting forces acting on the face by shield machine as uniformly distributed loads. A Fortran program is established to obtain the optimal solution of the upper bound solution. The influences of the various parameters on both the value of the supporting forces and the shape of the failure mechanism are discussed.2. On the basis of the related research in the previoue chapter, the stability of the face is further studied in soils with the spatial variing internal friction angle and cohesion with the help of a spatial discretization method which is employed to construct the active failure mechanism. The spatial discretization method is validated in a comparision with the analytical method dissicued in the former chapter. Then, the influence of the anisotropy and the non-uniformity of cohesion of cohesion, the non-uniformity of internal friction angle on optimal solutions and failure mechanism are studied.3. Relying on a subway engineering, the finite difference software FLAC3D is applyied to conduct a numerical simulation, which prove that the analytical calculation is valid.