| In recent years, along with booming construction of urban railway system, underground excavation construction method gradually arises. Regarding excavation technology’s requirements on settlement control, Pile-beam-arch(PBA) method is put forward, which combines shallow-excavation and cover-excavation methods and is a strong composite support system consisting of pilot tunnel, side pile, column and top arch etc. PBA method has been successfully applied in projects such as subway station especially those emphasized on complex construction environment and strict control of settlement. However, the theory for PBA method is still far behind its practice, due to lack of comprehensive and systematical theoretical study.Based on summarization of construction technology and key problems of PBA method, this dissertation takes one subway station of large-space(Excavation of earth up to 79000m3) as the background and conduct the following study. On account of modeling and theoretical calculation, from the aspects of ground deformation, force structure and forecast of ground settlement, analyze the related construction mechanical effect, thus to provide reliable theory and guidance for construction of the subway station of large section by PBA method.The main research contents and innovation achievements are as follows:(1)Based on engineering data, this paper introduces geological conditions, structural styles of stations and construction technologies etc, and discusses the current key problems of large-space underground excavation construction projects;(2)Stimulating the main process of station construction by applying calculation method of Flac3 D numerical simulation, which offers development law of ground deformation in different construction stages, Through emphasized analysis on influence regularity of timbering parameters of pilot tunnels and excavation sequence of crown of pilot tunnel on ground deformation and ground surface settlement, this paper optimally designs construction scheme of PBA method and provides reasonable basis for construction guidance;(3)In consideration of the PBA construction process formatted a special joint support system, through using numerical simulation method specific analysis Synergy of pile-arch and force conversion. Due to side pile ultimately becomes domination under structural system, while considering the interaction of inclined force of side pile, lateral earth pressure of pile side, weight of pile body, side friction of pile and pile tip resistance, this paper simplifies the lower section of excavation face as elastic foundation beam model to obtain simplified calculation model of side pile inner force and conduct inner force expressions for side pile in hole pile method;(4)In consideration of the deficiency about forecasting methods of ground settlement caused by PBA construction, on account of modeling and fitting experience, firstly analyzes the impact of multi-cavities effect which caused by S and D, then preliminary study the application of settlement calculation through using Peck empirical formula under considering multi-cavities effect, the value obtained if buried depth of pilot tunnel remains same, only when the ratios between distances and diameters of pilot tunnels is within the range from 1.4 to 1.8, Peck theoretical formula can be used in superposition calculation of cavern excavation. |
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