Analysis of the ground deformation to large cross- section tunnel by Pipe-roof Pre-construction Method

Urban underground engineering construction may have bad influence on the environment and even cause disasters. Pipe-roof Pre-construction Method(PPM) had been used in building a metro station of line No.2 of Shenyang subway. It´s very important to analyze and evaluate the deformation of the environment in order to ensure the safety of constructing procedure. So, based on the detailed study of geological conditions and PPM, Flac^3D software combined with field monitoring data in stations earthwork phase is used. And then, research on the surface and vault settlement, arch feet headroom convergence and tunnel structure deformation law is presented. The results show that: (1) numerical simulation is close to the monitoring data, which ensures the large cross-section single arch tunnel construction safety, and provides guidance for the first successful application and research of this method in China mainland area. (2) The surface deformation and vault subsidence could be less by using PPM to build large sections tunnel, and in the whole PPM construction process of surface subsidence caused by the proportion is less too, which could meet the requirements of controlling the surface subsidence target. (3) It deserves further research and extension for the PPM to build underground space, because it has obviously social and environmental benefits, and can be used to build traversing urban traffic hub of the underground engineering.