Study On Upper Limit Of Failure Mode Of Shield Tunnel Excavation Based On Hoek-Brown Failure Criterion

With the acceleration of urbanization in our country and the increase of the proportion of urban population,traffic congestion and urban construction land tension and other " urban diseases" become the primary problem of restricting urban sustainable development.As a form of rail transit,the underground railway does not take up the surface space,but also has a fast,safe,punctuality and other advantages,to solve China's major cities in the first choice of traffic problems.At present,the vast majority of subway tunnel construction method is used in the shield tunneling process,prone to earth pressure cabin set improperly caused by the excavation surface collapse or extrusion damage,and thus to the safety of the ground create a threat.Therefore,this article bases on the Hoek-Brown nonlinear failure criterion and the limit analysis theory,to study the failure mode and the mechanism of the tunnel excavation.The main research content is as follows:(1)According to the failure characteristics of excavation surface of shield tunnel under different supporting forces,built two kinds of failure mechanisms of excavation surface slumping and extrusion;(2)Based on the Hoek-Brown failure criterion and the upper limit method,calculate the cave and squeeze out two kinds of failure mechanism of external power and internal energy dissipation power;(3)Using the upper limit equation of the failure surface of the tunnel excavation surface to draw out of the cave and extrusion damage surface shape under two kinds of failure mode,and analyzes the influence of different parameters on the excavation surface;(4)Using the numerical simulation software FLAC3D,by simulating the tunneling process of the shield tunnel,the numerical solution of the excavation surface of the shield tunnel is obtained,the correctness of the theoretical calculation is verified by comparing the numerical solution of the failure surface with the upper limit solution;(5)Combined with the tunnel of Changsha subway line 2,calculated the numerical solution and upper limit solution of tunnel failure surface under extrusion failure mode by using this method,and then,compared the numerical solution and the upper limit solution,the correctness of the method can be verified again...