Research On Deformation Of Shield Nearby Undercrossing The Existing Underground Frame Structure

With the rapid development of major cities in China,the situation of road traffic congestion has become increasingly serious,and the construction of underground rail transit has become an important means to solve urban road traffic problems in the future.However,with the gradual increase in the utilization rate of underground space in cities,it becomes inevitable that new subway lines nearby undercrossing of existing underground frame structure.How to effectively control the impact of the construction of new subway tunnels on the surrounding environment,especially the impact on existing buildings and existing pipelines,so as to ensure the safety of the surrounding environment and existing structures,has become the key points and difficulties in the construction control of urban tunnels.Based on Wuhan rail transit line,a three-dimensional numerical model was established by ABAQUS to simulate the problem of shield nearby undercrossing of existing underground frame structure.Considering the influence of pre-construction(deep foundation excavation and underground frame construction)on the stress distribution in soil,this paper will conduct finite element simulation calculation for the whole construction process.The calculation process is divided into three stages: deep foundation excavation,underground frame structure construction,and shield dynamic excavation.Through stress balance which is carried out by importing the results of the previous stage,the purpose of stress transfer and eliminate the pre-construction displacement can be realized.The main contents and conclusions of this paper are as follows:(1)In the case of soil reinforcement and unreinforced,the numerical simulations of the shield nearby undercrossing of existing underground frame structure are conducted separately.In the calculation process,the lateral deformation of the retaining wall in the process of excavation of the deep foundation pit,the settlement of the ground surface outside the foundation pit,the additional deformation of the bottom plate when the shield nearby undercrossing,and the lining deformation are studied.The results show that the maximum lateral displacement of retaining wall,the maximum ground settlement outside the pit and the maximum additional deformation of the underground frame floor are too large when the soil is not reinforced,and there is even potential safety hazard.After the jet grouting reinforcement,all component deformation values are effectively controlled and can meet the design specification.(2)After comparison and analysis of the deformation values of each component in the above two cases,it can be seen that the deformation amplitude of the various components in the dynamic tunneling stage of the shield is reduced most significantly after the soil jet grouting reinforcement treatment.However,the deformation value of each member in the construction phase of the underground frame structure only slightly decreased.(3)Comparing and analyzing the construction site monitoring data with the finite element calculation results after soil rotary jet reinforcement,the results show that the finite element calculation results after reinforcement are basically consistent with the field monitoring results,which shows the reliability of the calculation results and verifies the correctness of the analysis method.