Advanced Support Effect And Parameter Optimization Analysis Of Pipe-Roof In Tunnel Construction Project Undercrossing Exisiting Metro In Water-rich And Sandy-cobble Stratum

Due to the complexity of the hydrogeogical conditions?small space of the palm surface,Subway crossing construction is considered as a difficult project with high risk.Because of the extremely high requirements for the existing line subsidence,crossing the existing project is a premium risk source in the system of subway risk management.In addition to crossing the existing line,in this paper,the construction is in rich water pebbles and fine sand layer.Under the tunnel existed a layer of pressure water and without any condition to dewatering,in tunnel struction,so the risk factor greatly increased.In order to control the deformation of the existing tunnels and the structure of the entrances as well as,the normal operation of the existing lines and the safety of the new construction,the method of pipe grouting combined with reinforcement is adopted to apply a good shoring,the supporting effect of the method,the selection of the pipe parameters and the optimization analysis,which is of great guidance to similar projects.Based on the results of field monitoring and the subway crossing construction,the reinforcement effect analysis and the numerical simulation is studied in this paper.The main contents are as follows:(1)According to the characteristics of the project,to a monitoring programs was conducted and executed,Based on site monitoring data,the impact of the existing tunnels and the extrance due to crossing construction was researched,which was under the comditions of the pipe grouting support.(2)According to the relative position relationship of the actual crossing project,the hydrogeological condition and the pipe grouting reinforcement method,the FLAC3D5.0 software was used to simulated the construction based on the actual process.The displacement and stress data of the existing shield tunnel and the entrance and of the station was analysised,which were compared with the results of pure grouting to verify the necessity of using pipe curtain support,and then compared the simulation data with the measured data to verify the applicability of numerical simulation.(3)The numerical simulation of the pipe curtain support scheme with different diameter and circumferential arrangement was carried out.Based on the vertical settlement and lateral displacement of the existing structure,the optimal pipe diameter and the pipe ring arrangement range were selected and the pipe parameters were optimized.