Subway Separation Of The Island Stations And Range Of Group-hole Effect

As the metro's fast development and underground space's utilization, the structure of metro station must come to the requirement of complicate underground environment at present. Consequently, a new type of metro station that we call it separated island metro station comes true. This new type station can be adopted in dispersive underground spaces. It can dodge piles of Overpass Bridge and reduce pile foundation underpinning. It also has much difficulties and challenges to the designers and builders because of its novelty and complexity. Based on Fenghuang Xincun metro station and interval tunnel project in Guangzhou city, the distribution of stratum deformation, stability of surrounding rock and safety of tunnel lining in construction process are analyzed in this dissertation. Numerical analysis is adopted as the main research method and field data are used conform the numerical calculation results. The main work and conclusion are as follows:(1) By establish 2D numerical calculation model, stratum deformation and tunnel lining inner force distribution are analyzed as net distances varied with relative location of two overlapped tunnels. The results show us: it is reasonable to build overlapped tunnels as the net distance between two tunnels is too narrow, and to build parallel tunnels as the net distance is greater than excavation width 1.5 times.(2) By establish 3D numerical calculation model, construction space effects of overlapped tunnels are analyzed. The results show us: the excavation of the tunnel under construction will obviously impact the tunnel constructed, and the adverse impact region locates in front of the working face. Temporary supporting system should be used in lower tunnel as low bench of upper tunnel is in construction. In order to improve the stability of disturbed stratum and working face, surrounding rock between overlapped tunnels should be strengthened by grouting.(3) The construction of connective passage will cause more disturbances after the main tunnel's excavation during construction process of the separated island metro station. The rational construction sequence between the main tunnel and connective passage is suggested in this dissertation. As for Fenghuang Xincun metro station, the best construction sequence is to excavate left line first, then connective passage, and right line finally.(4) The trumpet-like tunnel's construction mechanics behavior is researched, two typical construction instances was analyzed, and construction sequence is optimized in this dissertation. The results show us: it can distinctly reduce the stratum deformation and protect constructed lining better if we excavate small-section tunnels first and later the larger-section tunnels.(5) Two-stage analysis method is adopted to calculate additional inner force and settlement of Overpass Bridge pile foundation induced by adjacent tunnelling. The influence of distance between pile and tunnel is discussed, and the concept of critical distance between pile and tunnel is put forward. The results show us: the influence to the adjacent pile caused by tunnelling is proportionally increases by the ground loss ratio. As the distance between pile and tunnel increases, the settlement and maximum axial force of pile foundation decreased.