Study of mechanical performance of metro station constructed by enlarging large diameter shield tunnel

A construction method that a running tunnel with two tracks is constructed by large diameter shield machine and moreover a station is built by shallow mining method to enlarge large diameter shield tunnel can be regarded as a new approach to construct metro engineering fast, efficiently, safely and economically; in more and more complicated environment which would lead to difficult layout of metro lines, increasing construction risk and making still stricter demands on construction methods of metro engineering. Taking Gaojiayuan station of Beijing metro line 14 as an engineering background, two schemes for the metro station construction by the CRD (cross diaphragm) shallow mining method to enlarge a large-size shield tunnel with an outer diameter of 10 m are introduced. Two-dimensional finite element models are used to simulate the metro station construction on the basis of the ground-structure interaction. The mechanical performance of the structure of the metro station is obtained. The numerical results show that the structural stress state varies frequently in the process of enlarged excavation. The position of maximum axial stress shifts from the shield segments to the primary lining; and the position of maximum shear stress gradually appears at the key segment. The stress state of the segments shifts from the dominative axial compression to the predominant shear. The primary lining, temporary diaphragms, top and bottom beams and temporary struts are mainly in the compressive status. Compared with other structures, the key segment and top flanges of the top beam are subjected to greater stresses during the construction; furthermore, it is suggested that they should be reinforced.