The Research Of Proximal Influence And Control Technology Of Subway Shield Tunnel Underacross Existing Access Line Tunnel

The left-line running tunnel from Guangdu station to Wugensong station of Chengdu Metro line 1,under-cross the access line of Dongsi depot.A full face shield was drived in complex geological conditions with pebble soil and composite strata.Tunneling under the existing Metro line,the protection level is very high,which requires strict control of the tunnel structure,the traffic track settlement and deformation.When shield tunnel excavate in mudstone formations,driving speed,residue improve,synchronous grouting will cause excessive perturbation of the upper soil stratum,result in gushing,super excavation and more excavations.‘muck cake'would be easy formed in cutter and chamber,and make the tool lose the capacity of excavation,furthermore,disturbed strata and super excavation will eventually lead to the ground collapse.Aiming to the risk of the running tunnel under-crossing the access line of Dongsi depot,a numerical simulation was adopted to analyze the impact on the access line by shielding driving in different reinforcement measures.In accordance with the numerical calculation results and the actual conditions of the field,pre-strengthening measures are used for the crossing section of the tunnel.In the process of shield tunneling under the access line,parameter control and adjustment are strengthened,and the influence of shield tunneling on existing structure is mastered in real time through automatic monitoring system.According to the actual situation of the section,the earth pressure balance shield was selected for tunnel construction.According to the stratum,surrounding environment and the characteristics of lines,the shield machine is specially designed to pass the special section safely and smoothly.The relationship between advance speed,total thrust,pressure of the soil chamber,horizontal and vertical deviation,grouting capacity and time was analyzed.And we obtained the tunneling parameters that effectively control the formation deformation under this formation condition,which provided a basis for the follow-up project.According to the numerical analysis and monitoring results,the shield tunnel had less influence on the access line due to the under-penetrating conditions reserved,and the displacement values are far less than the control standards of tunnel structure and orbitdeformation,ensuring the normal operation of existing lines and shield safety,continuous,smooth through.