Analysis And Control Method Research On Ground Deformation Of Tunnel Undercrossing Existing Highway Retaining Wall

Subway is an important component of urban three-dimensional transportation and an important user of urban underground space.With the improvement of Grade separation,it is more and more common to cross high-rise buildings and large facilities.How to reduce the impact of urban tunnel construction on adjacent buildings and ensure the safety of existing buildings and structures has become a prominent issue in urban tunnel construction.At present,there is a lot of research on buildings or building clusters under tunnels,but there is less research on the structure of deep backfill areas.This paper is based on the section project from Liujiatai station to Jiangbeicheng station of Chongqing Rail Transit Line 9 under the retaining wall of Huanghuayuan Bridge approach.The influence of different reinforcement measures and excavation methods on surrounding stratum,ground surface,Pile foundation of retaining wall and retaining wall structure is studied by combining finite element software numerical simulation with on-site monitoring.The main research contents and conclusions are as follows:(1)Based on previous research,summarize and analyze the deformation patterns of strata and the impact of different excavation methods on the deformation of surrounding rocks when underground tunnels pass through buildings(structures).(2)Combined with the characteristics of the supporting project located in the deep backfill area,the treatment measures of surface grouting and pipe shed grouting in the tunnel are proposed for the possible adverse settlement caused by the shallow buried tunnel passing through buildings and structures.MIDAS GTS NX is selected as the simulation tool to simulate the three-dimensional structure of the retaining wall and its cushion cap Pile foundation,and the full section method,the upper and lower bench method and the reserved core soil method are used for construction phase analysis.(3)The stiffness reduction method is used to analyze the grouting effect.After grouting reinforcement,the Factor of safety of the retaining wall is significantly increased by 23%.According to the results of finite element simulation,the settlement of Pile foundation of retaining wall decreases by 33%.After combining different excavation methods(full section,step method,and reserved core soil method)for grouting reinforcement,the settlement value of the retaining wall decreases by more than 50%,and the surface settlement value decreases by about 46%.(4)The use of pipe shed reinforcement alone has a significant effect on controlling deformation at the arch crown,but its control over the surface and retaining walls is limited,making it difficult to ensure that the settlement is stable within a safe range;By simultaneously reinforcing the pipe shed and surface grouting,it can significantly reduce the deformation of surrounding rock,surface and retaining wall settlement.(5)By comparing the simulation prediction results with on-site monitoring data,the MIDAS GTS NX prediction values are basically consistent with the monitoring values,further verifying the rationality of the model.Suggestion was proposed to use the reserved core soil method for construction.