The City Subway Tunnel Shield Method With Shallow Tunnel Excavation Method Closing Construction Scheme Optimization

Construction process of underground tunnel construction is full of risk, and little distance tunnel construction has greatly increased the risk of construction. Once in the process of construction, the construction load reaches a critical state, or unable to bear the load of surrounding soils, may cause great potential security risk to the construction personnel. So necessary analysis was carried out on the construction and excavation process.At So it is important to determine the appropriate construction order at design stage, take corresponding reinforcement measures in construction stage to ensure construction safety.In this paper,We take the subway construction of nanning rail transit line 1 as the background, with the tunnel shield method and shallow tunnel construction method paralleling and crossing litle distance tunnel construction were studied. In comprehensive research results on the basis of past scholars, using MIDAS GTS respectively set up three numerical model of parallel tunnel and cross tunnel, selected a proper constitutive equation and model parameters to simulate excavation and support process. Parallel and cross section of tunnel shield tunnel leading or shallow tunnel leading the construction of two different schemes in the displacement nephogram, the maximum stress and maximum shear stress of surrounding rock, bending moment and axial force were analyzed. Besides under the condition of same construction steps take different reinforcement measures to analysis the surrounding rock displacement and settlement curve, and finally determine the optimum construction scheme. In this paper, the conclusion as follows:(1) In parallel tunnel section,shield tunnel, in the maximum internal force of tunnel structure, bending moment, subsidence displacement is less than the shallow depth excavation tunnel on the first.Through the grouting reinforcement and grouting and wall reinforcement and no reinforcement three kinds of scheme comparison, concludes that grouting and wall reinforcement is helpful to control the settlement and reduce the mutual influence between the tunnel.(2) Cross section in the tunnel, the shield tunnel excavation in advance, the maximum internal force of tunnel, the bending moment is less than the shallow depth excavation tunnel in advance. By grouting reinforcement and no strengthening two scheme comparison, it is concluded that the grouting reinforcement is helpful to control the surface settlement and the mutual influence between the tunnel. Shield tunnel leading and grouting should be taken.(3) Of shield tunnel and the shallow tunnel after tunnel excavation, the tunnel vault subsidence, arch bottom uplift, maximum subsidence and uplift in the bottom of the vault and arch, after excavation subsidence change is bigger, then gradually convergence. Due to the shallow depth excavation tunnel hole diameter is larger, vault subsidence and the vault uplift value is greater than the shield tunnel.