NUMERICAL STUDY ON THE SCHEMES FOR METRO STATION CONSTRUCTION BY ENLARGING LARGE-DIAMETER SHIELD TUNNEL

摘要

With the rapid development of urban rail transit, more and more complicated environmental problems come forth in Beijing, which lead to difficult layout of underground lines, increasing construction risk, and so on. In order to construct metro fast, efficiently, safely and economically in complicated environment, a new-style 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 is presented in this paper. Two schemes for a planned station of Beijing metro by enlarging large-diameter shield tunnel are introduced. Based on the ground-structure interaction, two-dimensional finite element models are used to simulate the metro station construction. The structural stresses of the shield segments, the primary lining and the temporary supporting system are obtained, as well as the ground surface displacement. The numerical results indicate that: (1)The scheme for metro station construction by enlarging large-diameter shield tunnel with an outer diameter of 10m is feasible in practical engineering. (2)During the enlarged excavation, the structural stress state changes frequently. The stress state of the segments shifts from the dominate axial compression to the predominate shear. The primary lining and the temporary supporting system are chiefly in the compressive condition. (3)Compared with other structures, the key segment is subject to greater shear stress during the construction.