Surface Subsidence Law And Control Techniques Of Ao-sen Regional Tunnel Excavated By Shallow Buried Covered Method

It is has important theoretical significance and practical engineering value that research the surface settlement law and control techniques of city tunnel excavated by shallow buried covered method. Choosing AO-SEN regional tunnel engineering of Olympic branch line in Beijing subway as the engineering background, surface settlement laws of shallowly buried and darkly excavated tunnel in the city are studied through theoretical analysis, FLAC numerical simulation and field monitoring. The main contents and conclusions as follows:(1)Influence factors and characteristics of surface settlement are studied which caused by shallow buried covered excavation of city tunnel. The main influential factors to surface settlement of shallowly buried and darkly excavated tunnel include: characteristics of stratum and soil mass, groundwater, buried depth, superimposed deformation caused by adjacent tunnels excavation, construction methods, excavation progress, construction speed, and the early forms of lining and so on. Surface settlement has a strong time-space effect.It can be divided two types: the total settlement pattern and arch-deposition pattern. Surface settlement has 4 deformation stages: advance uplift phase, rapid deformation stage, slow deformation stage and stable deformation stage.(2) Taking reservation core soil method and benching tunneling method as construction plan, the tunnel excavation and construction process of 2 construction plan mentioned above are simulated with plane FLAC. Reservation core soil method was determined as the construction scheme of shallowly buried and darkly excavated tunnel according to FLAC simulation results. The surface deformation law is predicted by using FLAC simulation results. It is proposed that joint construction method combined leading steel pipeline shed, ahead ductile grouting method and grid steel frame serve as control measures for surface settlement and deformation of AO-SEN regional tunnel.(3)Deformation monitoring program design and field monitoring work has been done for tunnel ground ang tunnel surrounding rock Monitoring datas show that the maximum value of monitoring projects, for example, clearance convergence, vault crown settlement, surface settlement and so on, are all less than monitoring standard in the left line of the tunnel. The field monitoring data are basically consistent with FLAC simulation results. It indicates that FLAC simulation results are reasonable. Tunnel excavation plan and control measures of surface settlement and deformation determined in this paper are feasible, safe and effective.