Analysis Of The Effect On Ground Subsidence Caused By The Excavation Of Metro Tunnels In The City Centre

Metro Rail Transit can not only be able to solve many serious problems in city centers like traffic congestion and environmental pollution brought by the rapid growth of population, but also bring huge economic benefits to cities. Along with the excavation of the subway tunnel, the ground surface subsidence will be inevitable. The city center with complex environment has a more stringent requirement on the control of surface subsidence, and the underground tunnel structure in city center is also more complex, and generally, there are two forms of tunnel structures:a cross-channel among the existing tunnels and section conversion. Based on the background of Qingdao Metro Line three engineering, the finite element numerical simulation method is applied to establishing model and analyze its central metro tunnel project in this paper, and the effect on surface subsidence of excavation is studied in which a connection tunnel among existing tunnels and a tunnel with section conversion are built, the surface subsidence by the two ways of excavation are predicted and the regularity summarization is made, and the settlement data from field measurement are obtained. Combining the numerical results with the field measured data, the following findings are achieved:(1)The relationship among excavation step position, the deformation of the existing tunnel lining and the surface deformation on the process of cross-channel in the three step method of excavation are analyzed, and a reasonable settlement monitoring method are proposed;(2)By establishing model and analyzing full section excavation of section conversion, the stress change conditions of transitional surface before and after excavation, and the surface settlement rules are obtained in the process of the tunnel propelling from large cross section to small section and from small section to large cross section;(3)The surface subsidence in the course of practical excavation are monitored and compared with the simulated counterpart in the corresponding position, and the reliability of the simulation analysis results can be ensured.Research results can provide a reference for surface subsidence study in similar projects.