Construction Mechanics Effect Of Pile-Beam-Arch Tunneling Method In Metro Construction

With the rapid urbanization and urban population's gathering, ground traffic of the city became increasingly crowd. For effective improvement of urban traffic system, A new development opportunity of subway occured due to its convenience, rapidness, friendly environment, high efficiency, safety and timeliness. The construction methods of underground structure were innovated continuously. Pile-beam-arch(PBA)tunneling method of underground excavation in shallow-burial tunnel was one of the new construction methods in recent years. It absorbed the achievement of shallow buried tunnel and top-down construction method. With the combination of small section pilot tunnel, supporting arch and pile, a new excavation and support of shallow buried tunnel-PBA tunneling method was developed. This construction method could effectively decrease the settlement deduced by underground excavation in districts with soft stratum and lessen the disturbance to urban center with high population density, heavy traffic and complex underground utilities. With the successful application of PBA in Beijing subway, remarkable economic benefits and social benefits were gained. However, current research on PBA mainly concentrated on construction process, few involved theoretical issue.This dissertation was founded by the State Natural Sciences Foundation project'the tunnel and the underground structure stability and the reliability'. Takes the North Gongti Road station of Beijing subway line 10 as example, systematical and thorough study and evaluations were carried on the construction mechanics of the PBA tunnel. The research methods include theoretical analysis, model tests, numerical simulation and in-situ monitor data analysis as well. The main achievements include:(1) Taking the pile buried under the excavation surface as elastic foundation beam, under the combined actions of pressures of arch and the soil and braces, a internal force calculation model was achieved. Formulas to calculate internal force were derived in three cases: supported by multiple braces, the worst condition, considering P-? effect.(2) Considering the pressure of the arch and the soil, by simplifying the stability analysis mode of the pile, potential functions of the pile was derived. Using cusp catastrophe model of large deformation, the necessary destabilization condition of pile is obtained. Large flexural rigidity and excellent mechanical properties of soil and less loading make for stability of pile. (3) Taking plastic pipe as model pile, by changing the diameter, spacing, buried depth and supporting condition of pile bottom, the variation characters of soil pressure, displacement and internal force of the pile were bained. Calculations according to the tests were also conducted to compare with the results of the tests. The effects of displacement control by different parameters were also analyzed.(4) Numerical simulations according to the tests were also conducted to compare with the results of the tests. Based on North Gongti Road station of Beijing metro line 10, 2D analysis of PBA with divisional excavating was conducted. 3D analysis, mainly focused on distance between the working faces of two pilot tunnels and on the bench length of main tunnel, was also performed to simulate the excavation procedures of PBA.(5) Take North Gongti Road station of Beijing metro line 10, 3D analysis were performed to simulate the construction procedures of preliminary supporting system of tunnel intersection. The interaction behaviors and arch settlement of preliminary supporting system of tunnel intersection as well as the stress characteristics of the assistant supporting components in tunnel intersection were analyzed.(6) Using numerical simulation, the internal forces of arch and pile, the ground displacement field and the ground surface settlement of CRD tunneling method and sequential construction and reverse construction of PBA were gained and analyzed and compared with in-situ monitoring results.(7) A multiobjective fuzzy optimization model of construction scheme decision was derived and a case was conducted according to the case of the North Gongti Road station of Beijing subway line 10.