Study On Numerical Simulation Of Mechanical Effect Of PBA Method For City Subway Station With Shallow Buried

With rapid development of subway construction in recent years, the construction technology of metro station constantly to progress, much new construction method and new process is thereupon generated. PBA method is a new construction method formed with the organic combination of some mature technique, such as small guide hole, supporting arch, and grouting pile, which absorbes technical achievements of top-down method on the basis of traditional shallow tunneling method. This method has been practiced several times in metro construction of Beijing, economic and social benefits have been gained.This paper is based on the practical engineering of the shallow buried metro station in Beijing. 2D plastic finite-element model of PBA standard cross section is respectively established, and the whole excavation process is simulated by using the general finite element calculation program ANSYS. Study is done to analysis the change law of internal force of main arch and grouting pile, stress of top beam, and ground settlement is which is obtained via numerical simulation of the whole construction process. Study is also done to compare different construction scheme of PBA method, and compare the construction effection of PBA method and CRD method in different surrounding rock grades. The results show that:â‘ The whole supporting system constituted by arch, beam and pile is generated during construction process, earth pressure is transferred from main arch and backfilled concrete to beam, then from top beam to pile. With deeply excavation, the axial force and bending moment of pile increases constantly, but internal force of arch maintains relatively stable, and keeps almost unchanged after the secondary lining of subway holl poured, stability of upper structure is therefore guaranteed.â‘¡The hall-plate which is constructed timely improved horizontal stiffess of the whole supporting system, therefore, ground settlement is controlled to some extend. Finally, the invert construction order is the most effective method of all to control settlement, the half-invert one takes second place, and the ordinal one is relatively worse.â‘¢During construction process by CRD method, with the erection and demolition of temporary supports, load bearing path of support structure is constantly changing, which enduce a large excavating disturbance. In contrast, PBA mehod transmits force directly, and takes anvantage of little ground settlement.when the station is shallow buried with bad geological condition.