Research On Mechanical Behavior Of Adjacent Existing Tunnels In Urban Underground Tunnel Group Construction

With the rapid development of Chinese economy,the development of underground space has become one of the important ways to alleviate urban traffic congestion.However,with the continuous increase of urban underground traffic network,there are more and more cases in which the construction of new tunnel group is close to the existing tunnel project.Due to the complexity of underground environment,the construction of new tunnel group destroys the initial stress balance of the original surrounding rock.The propagation through the stratum will cause great disturbance to the existing tunnel and even affect the safe use of the existing tunnel.Therefore,it has become the most important control node in adjacent tunnel construction to reduce the disturbance of the existing tunnel and ensure the safe and efficient construction of the new tunnel group.In this paper,based on the existing tunnel project near the construction of a tunnel group in an underground city of Chongqing,using numerical simulation,theoretical analysis and field monitoring and other research methods,the mechanical behavior evolution law and related control technology of the support structure near the existing tunnel group construction were studied.The following important research results are obtained:(1)Through the full construction process of the tunnel group,a numerical simulation analysis of the surrounding rock surrounding rocks and support structures around the existing tunnel is obtained.The response of the tunnel group construction was significantly higher than that of the bottom part of the tunnel;through the law of support structure stress distribution,the disturbance caused by the construction of the tunnel group made the stress in the middle of the tunnel in the middle of the tunnel more concentrated,which had an impact on the safe use of the existing tunnel.(2)Through the Von Mises stress numerical analysis of the existing tunnel support structure in the process of tunnel group construction,it is concluded that the most vulnerable danger area of the existing tunnel is the side wall area in the middle part of the tunnel.Through analyzing the Von-Mises stress of the existing tunnel parallel through the main tunnel A and the main tunnel B,it is concluded that the Von-Mises stress and risk in the non-coincidence area can be reduced by parallel excavation above the overlapping tunnel area.(3)By studying the stress and displacement changes of the existing tunnel support structure under different construction sequence conditions,the reasonable excavation order of the tunnel group is obtained at the actual conditions: Jiabin Road Connection Tunnel → Graduate Jiabin Road Widening Connecting tunnels → Cathay Plaza connect to tunnel → main tunnel A → main tunnel B.(4)By studying the mechanical behavior analysis of the existing tunnel supporting structure caused by tunnel group construction under different supporting parameters,the optimal control measures for the mechanical behavior of the existing tunnel under the consideration of economic factors are obtained.At the same time,it is found that improving the grade of supporting material is more beneficial to the stability of the existing tunnel than increasing the supporting thickness.(5)By comparing the measured data with the numerical simulation results,the accuracy of the tunnel group surrounding rock deformation is verified.By comparing the actual monitoring data with the simulation results of optimal supporting parameters construction scheme,the effectiveness of the control technology is verified.