| The construction of urban tunnels has always been an important part of China’s transportation industry.With the increasingly obvious trend of urbanization development in China,urban tunnel construction will also further develop,and the utilization rate of urban underground space will become higher and higher.The routes will also overlap and tend to be networked.Urban intersecting tunnels,as a structural form that efficiently utilizes underground space,are becoming increasingly common in urban construction.How to choose a reasonable construction sequence to excavate the intersection section,and how to support the intersection section with reasonable support parameters,plays an important role in ensuring the safety of tunnel construction and reducing the impact on surface buildings.This thesis relies on Monument to the people’s Liberation Underground Parking Lot and Connecting Passage Phase III Project in Chongqing to select the intersecting section between the connecting road(double-arch tunnel)and the main channel(single tunnel).Numerical simulation is conducted using ANSYS finite element software,and combined with on-site monitoring measurement data,the excavation sequence and support parameters optimization of the tunnel intersecting section are studied.The main research content and conclusions are as follows:1)Analyzed the deformation and failure mechanism of tunnel surrounding rock,elucidated the destructive effects of factors such as stress release,unloading rebound,complete plastic zone failure,expansion and deflection,flow deformation,and plastic wedge on the surrounding rock;Based on the empirical formula method and random medium theory,a prediction formula for surface settlement and deformation at the intersection of tunnels has been derived.2)Studied the construction sequence of the intersecting section between the connecting road and the main tunnel,and determined the optimal construction sequence.Based on the research of the construction sequence at the intersection of a connecting road and the main channel in Monument to the people’s Liberation Underground Parking Lot and Connecting Passage Phase III Project in Chongqing,three construction sequences were analyzed.Through the finite element numerical simulation software ANSYS,three-dimensional numerical simulations were conducted on the three construction sequences,comparing the three quantitative indicators of surface settlement,arch settlement,and surrounding rock stress after tunnel excavation.3)The optimal support parameters for the intersecting section of the tunnel were established through numerical simulation.The numerical simulation result showed that the displacement cloud map of the rock and soil mass and the displacement cloud map of the lining are the largest at the intersecting section.It is necessary to optimize the support parameters at the intersecting section.Started from three factors: the thickness of sprayed concrete at the intersection section,the spacing of steel arch frames,and the support range of the intersecting section,analysis is conducted on three indicators:surface settlement,arch crown settlement,and arch waist convergence.4)The on-site monitoring and measurement plan was designed.Through on-site monitoring and measurement,the measurement data was analyzed and compared with numerical simulation results and theoretical calculation results to verify the reliability of numerical simulation and the correctness of theoretical formulas.At the same time,the horizontal convergence of tunnel intersection clearance,the characteristics and laws of arch settlement and surface settlement were analyzed.5)Studied the use of the load structure method to calculate the internal force of the lining at the intersection of shallow buried Grade IV surrounding rock tunnel,and determined the correction coefficient for the load.The value range of the correction coefficient is between 1.15 and 1.20. |
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