Upper Bound Analysis Of Safety Factor For Shield Tunnel Face Subjected To Nonlinear Failure Criterion

With the acceleration of urbanization in China,a series of "urban diseases" such as traffic jams,construction land shortages and atmospheric pollution have become problems encountered in the sustainable development of major cities.Among the many solutions,Metro has become the first choice for relieving urban traffic congestion because of its advantages of speed,safety,high traffic volume,and lack of floor space.At present,the shield tunneling method is the main construction method for most subway tunnels.During the tunneling process of shield tunnels,the instability of the excavation surface will cause surface subsidence to threaten the safety of the ground construction and the tunnel itself.In view of the above situation,this paper uses the Hoek-Brown nonlinear failure criterion and the limit analysis upper bound theory to propose a calculation method for the safety factor of the shield tunnel excavation surface,which can be used to evaluate the stability of the excavation face of a shield tunnel in shallow crushing rock mass.Provide evidence.The main research content is as follows:(1)According to the characteristics of the collapse of the excavation face when the shield tunnel is excavated in the shallow crushing rock mass,the upper limit destruction mechanism of the excavation face of the shield tunnel is generated by the "point-to-point"method using the space discrete technology;(2)Based on the nonlinear mechanical characteristics of broken surrounding rock,the Hoek-Brown failure criterion is introduced into the energy calculation of the upper limit analysis.The shield tunnel excavation is constructed by calculating the external power and the internal energy dissipation power in the upper speed field.The upper limit objective function of the surface safety factor,using the nonlinear programming method to optimize the objective function,the upper limit solution of the safety factor and the excavation surface failure mode in the limit state are obtained;(3)Sensitivity analysis method is used to analyze the influence of different parameters on the safety factor of the excavation surface.By comparing the sensitivity factors of each parameter,the parameters that have the greatest influence on the safety factor of the excavation surface are obtained;(4)Numerical simulation technology was used to simulate the tunneling process of shield tunnel.The numerical solution of the safety factor of the excavation surface under the Hoek-Brown failure criterion was obtained.The upper limit solution of the safety factor under the same parameters was compared with the numerical solution.The correctness of theoretical calculations;(5)Taking the tunnel of a certain section of Changsha Metro Line 2 as the engineering background,the upper and the numerical solutions of the safety factor of the tunnel excavation face in the interval were calculated based on the measured tunnel pressure and the surrounding rock parameters of the shield tunnelling machine.The effectiveness of the method in this paper.