The Nonlinear Energy Analysis Of Rock Mass Deformation Induced By Adjacent Pit Excavation For Shield Tunnels

In recent years,the rapid development of urban rail transit has made outstanding contributions to the improvement of urban public traffic conditions.As a form of rail transit,the subway has the advantages of not occupying space on the ground,high efficiency and safety,and it is also the first choice for solving the problem of urban traffic congestion.The central area of the city as a core business district is often a place where underground buildings are highly dense;in order to maximize the commercial value of the ground buildings in the central city,many newly-built high-rise buildings are often built next to existing subway tunnels.At present,there are more and more examples of engineering excavation in the vicinity of existing shield tunnels.The characteristics of deformation and failure of surrounding rock of adjacent existing tunnels caused by excavation of foundation pits are analyzed,and it is helpful to study how to reduce the influence of excavation on the safety of adjacent tunnels.Therefore,based on the Hoek-Brown nonlinear failure criterion and the upper bound theorem of limit analysis,this paper studies the failure modes and mechanism of the surrounding rock of adjacent existing shield tunnel induced by excavation.The main research content is as follows:(1)According to the deformation characteristics of surrounding rock excavation around the existing shield tunnel caused by excavation and excavation,the upper limit damage mechanism of surrounding rock deformation of adjacent shield tunnels caused by excavation and excavation is constructed using curves of arbitrary lines;(2)Combined with the Hoek-Brown failure criterion and the upper limit analysis theorem,the external force power and the internal energy dissipation power at the speed discontinuity surface in the destruction mechanism are calculated respectively.On this basis,the upper bound objective function including the failure surface equation is obtained,and then the analytical equation of the failure surface of the surrounding rock of the shield tunnel under the limit state is calculated by the variational method;(3)Using the calculated upper bound equation of the surrounding rock failure surface around the shield tunnel,the shape of the failure mode is plotted.Based on this,the single variable method is used to analyze the influence of different parameters on the failure mode;(4)Based on actual engineering cases,FLAC3D numerical software is used to build a three-dimensional model for excavation of foundation pits in the vicinity of existing shield tunnels.By simulating the excavation process of the foundation pit,a numerical solution of the collapse and failure shape of the surrounding rock surrounding the existing shield tunnel is obtained.Comparing the numerical solution of the collapsed surface with the theoretically deduced analytical solution of the failure surface,the correctness of the theoretical calculation is verified;(5)The method of sensitivity analysis was introduced to analyze the influence of different parameters on the collapse surface of the surrounding rock of the shield tunnel.According to the results of sensitivity analysis,the parameters that have the greatest impact on the deformation of the surrounding rock of the existing shield tunnel are obtained.