| During the operation of urban rail transit,the number of adjacent projects has been increasing day by day,which caused different degrees of additional internal force and displacement in the adjacent metro structure.Especially for the tunnel structure in soft soil area,with the increase of service life,lining structure diseases such as water leakage and lining cracks have emerged.Therefore,the complete near construction impact analysis should include the determination of the service status of tunnel structure before construction and the construction impact analysis on this basis.Based on the idea of two-stage method,this paper combines stratum structure method with state space method and structural nonlinear analysis respectively.Two new influence analysis methods of side excavation were proposed,which could provide important guidance for the health and safety management of tunnel structure during operation.The large-scale model based on the stratum structure method could effectively consider the complexity of geotechnical engineering environment.Especially for the irregular shape foundation pit,the spatial and temporal effects of foundation pit excavation were well considered.However,the consideration of the structure was relatively simple,and the tunnel was often equivalent to a homogeneous ring with reduced stiffness.The load structure analysis of the tunnel took into account the segment joint,and the structure was further refined.However,the linear elastic foundation spring of the model failed to fully consider the change of the surrounding environment.Therefore,the two-stage analysis methods were proposed in this paper.Firstly,the structure service status of typical interval tunnels was determined,and the deformation and internal force response of the adjacent metro structure under side excavation construction were obtained by stratum structure method.On this basis,considering the segment joint and structural nonlinearity,the displacement and internal force were superimposed as the external load of the structure to the foundation bed model for the second stage calculation.The research contents and conclusions of this paper are as follows :(1)According to the tunnel lining disease detection in the influence area of foundation pit excavation,the maximum convergence and structural diseases of single ring tunnel was counted.What’s more,the circumferential and longitudinal distribution of tunnel structure disease were obtained.Lastly the service status of the interval tunnel was evaluated to obtain the safety control index of the tunnel structure.(2)The three-dimensional numerical model of station-tunnel-foundation pit was established based on the stratum structure method,which considered the interaction between soil and structure and the space-time effect of foundation pit excavation.Combined with the safety control index of tunnel structure,the influence of excavation of adjacent foundation pits on the deformation of the metro structure was analyzed.The obtained tunnel displacement and internal force response results were used as the external loads for the subsequent second stage analysis.(3)Multi-parameter analysis was carried out for the influence of the excavation of the lateral foundation pit on the metro structure.The results show that the change of the distance between the pit and tunnel influences the station deformation and the longitudinal deformation of shallow and deep tunnels.What’s more,analyzed the restraint effect of the corners of the foundation pit retaining structure on the longitudinal displacement of the tunnel under different pit-tunnel distances and foundation pit excavation depths.(4)Based on the maximum convergence amount of tunnel and the tunnel displacement and the surrounding earth pressure calculation results by the stratum structure method,it was proposed to carry out stress superposition or displacement superposition on the single-ring lining bed model.The lateral deformation,internal force response and structural damage response of the tunnel structure were obtained through two-stage calculation and analysis.The results proved that the methods could not only take into account the large-scale modeling in the complex geotechnical environment,but also meet the needs of fine analysis of the lining structure. |
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