Numerical Simulation Analysis on Construction Process of Pile Method Pilot Tunnel of a Subway Station in Xi ' an

The emergence of subway greatly reduces the pressure of urban traffic, PBA construction method can effectively reduce the subway station construction induced surface subsidence, is one of the preferred construction method of urban subway station construction under complex ground conditions. In order to explore the law of surface subsidence induced by different excavation steps of PBA method in loess area, a three-dimensional model of subway station was established by using finite difference software FLAC based on a subway station in Xi 'an. The simulation analysis of ground settlement caused by different excavation sequences were completed, and the field deformation monitoring scheme was executed. The FLAC simulation shows that the maximum settlement of ground settlement caused by the two construction sequences of "from bottom to top" and "from top to bottom" is located at the center line of the station, and the settlement curve is in a "V" shape. The displacement of deep soil mass in the pilot tunnel "from bottom to top" construction is small, and the variation of soil structure and interaction force is small, which is convenient to control the ground settlement. The results of engineering measurement are basically consistent with those predicted by FLAC, and the FLAC simulation calculation of ground subsidence law is reasonable and effective.