In-situ Monitoring And FLAC Simulation Study Of Deformation Laws Of Deep Excavation In Metro Station In Xi'an

Design of the retaining structure and stability analysis of deep excavation in metro station is one of the key issues in metro construction. The study on the theory of deformation laws and monitoring of deep excavation in metro station in Xi'an has great significance to guide informational construction in deep excavation in northwest. In this paper, it uses the method that combines with the theoretical analysis, in-situ monitoring and numerical simulation followed the background of deep excavation of South Gate metro station. The main jobs are as follows:(1) The main factors affecting the deformation of deep excavation are analyzed, and the deformation principles and failure modes of retaining structure are studied. The research shows that the hydro geological conditions, the foundation size and earth pressure, design decision, the rationality of the construction methods and organization, and the pit seepage greatly impact the deformation of deep excavation. The deformation of deep excavation consists of three parts: the wall deformation, the bottom heave of the pit and the Surrounding ground settlement. The failure pattern of deep excavation contains the bow-shaped deformation mode, the buried-type deformation mode, the forward-type deformation mode, and the kick-type deformation mode.(2) The comparison of different support programs and the selection argument is completed. It proposes the design program of retaining structure of deep excavation of South Gate metro station, and gives the preliminary design focus on supporting pile and steel support selectively.(3) It designes the in-situ monitoring plan of deformation, and accomplishes the in-situ monitoring work. At the same time, it focuses on deep analysis of the horizontal deformation of the retaining piles, the axial force of steel support, ground settlement around foundation. The results show that displacement of pile is a direct reflection of deformation of the retaining structure, while the steel support of the foundation significantly limiting deformation. The analysis tells that the design program of retaining structure is basically rational and monitoring is feasible.(4) By the use of the software FLAC^3D, a three-dimensional simulation of the entire process of excavation is accomplished, and the discipline of the displacement of the excavation and pile and the ground settlement around foundation is given under five cases. It indicates that the calculated results are identical with the measured ones. Also, the impact on the loess collapsibility of the deformation of deep excavation in Xi'an is analyzed. The results show that pit deformation decreases along with the cohesion increases.