Study On Stability Of New Subway Tunnels Underpassing Existing Lines

During the development of urban subway construction,there are more and more crossovers of metro lines.Under the premise of safe construction,the problem of ensuring the safety of ground buildings and structures,underground trenches and underground metro lines is becoming more and more prominent.This paper takes the hidden digging section of the subway station of the University South Station of Guangzhou Metro Line 12,which is under the subway line 7project,as an example.The combination of theoretical calculation and numerical simulation is used to study the design choice.The research results are as follows:(1)Because the circular section is superior to the rectangular section in the excavation process,the design of the circular section has sufficient advantages when strictly controlling the vertical displacement.However,during the excavation process,the force of the face is not as good as that of the rectangular section.Therefore,in the aspect of controlling the axial displacement of the tunnel,the tunnel designed as a rectangular section is more reasonable.From the form of force in the excavation stage,the vertical displacement of the arch position and the longitudinal displacement direction of the face in the tunnel direction,the stress redistribution law of the excavation surrounding rock in different tunnel sections and the damage of the surrounding rock of the tunnel are analyzed.Form and destruction location.According to the actual engineering conditions,the design scheme of determining the triple arch mode of the undercut tunnel is selected,and the depth of the excavation and the excavation mode are determined.(2)Numerical simulation analysis was carried out on the factors affecting different grouting,and the grouting rules of small pipes were summarized:When the external insertion angle is set to about 10° during the grouting reinforcement process,grouting small pipe exerts obvious influence on the deformation control of the surrounding rock.The range of grouting small pipe is chosen to be as close as possible to 240°.For complex multi-arch sectional forms,the 240°small pipe layout in the form of a single arch should be guaranteed as much as possible.The reinforcement measures for the verification design are applicable to the tunneling of the triple-arch tunnel under the subsurface excavation.(3)The load structure method and the bottom structure method are used to analyze the force form of the subsurface excavation section and the lining structure of the subsurface excavation section and the reinforcement calculation is carried out,which is to verify that the second lining structure form and the calculated thickNess meet the design requirements.(4)Two kinds of dynamic analysis methods are used to verify that the subsurface excavation sectional structure form meets the safety standards met by the specification,so that the research sectional design scheme is feasible.