Numerical analysis on the mechanical performance of supporting structures and ground settlement characteristics in construction process of subway station built by Pile-Beam-Arch method

Pile-Beam-Arch (PBA) method is an effective approach to control the surface settlement induced by excavation to construct the subway station, especially when the station is located in the urban area with dense buildings. Based on the numerical analysis model of practical engineering, the whole construction stages of the subway station built by PBA method are simulated in this paper. The mechanical performance of supporting structures (such as piles, beams, arches, secondary lining and backfill concrete) and surface settlement characteristics during construction are investigated. The results show that the pre-supporting system of piles, beams and arches is formed in the stage of soil excavation under main tunnel arch; Station hall plate and backfill concrete are two key structures to ensure the support stiffness of PBA supporting system. In addition, compared to the bottom-up method, the top-down method for the secondary lining construction can obviously reduce the internal force of supporting structures and the surface settlement. Combined with in-situ monitoring data, three increase stages of surface settlement and the corresponding settlement ratio are gained and the characteristic of surface settlement trough is also analysed. This study is helpful for further understanding the support mechanism of PBA method and the increase law of the ground settlement during the construction of the station built by PBA method.