Three-Dimensional Upper Bound Limit Analysis Of Face Stability Of Inclined Tunnel

Recently,many cities in China are accelerating the construction of urban rail transit to ease traffic congestion,it will inevitably involve numerous tunnel engineering.Shield method is used more widely in tunnel construction because of its fast excavation and high safety.In the construction of shield tunnel,it is crucial to ensure the stability of the tunnel face.Many researchers study the stability of tunnel face,but these studies often assumes that the tunnel is horizontal.In fact,the tunnel inclination angle generally exists during the excavation of most shield tunnels,Therefore,it is necessary to study the stability of tunnel face considering the influence of tunnel inclination.Based on the upper-bound limit analysis,an improved failure mechanism is proposed to study the face stability of inclined tunnel,the details are shown below:(1)Based on the linear Mohr-Coulomb failure criterion and upper-bound limit analysis,the three-dimensional active and passive failure mechanisms are given considering the tunnel inclination angle.The method to obtain limit support pressure is derived based on the energy equation of limit analysis.(2)The stability of inclined tunnel face is studied based on the Hoek-Brown nonlinear failure criterion and upper-bound limit analysis.Using the “tangent method”,based on the three-dimensional failure mechanism,the method to obtain limit support pressure considering the inclination angle is derived for collapse and blow-out case.(3)The excavation of inclined tunnel is simulated by the finite element software(FLAC3D)to obtain the seepage field of the tunnel face.The seepage field is interpolated on the three-dimensional failure model by using the linear interpolation method,and the method to obtain limit support pressure is derived considering the pore water pressure.(4)Based on the shield tunnel of Nantong and Hangzhou subway,the collapse and blow-out mechanisms considering the inclination angle are used to study the stability of the tunnel face in longitudinal slope section.