Monitoring And FLAC Simulation Study Of Deformation Laws Of Deep Excavation In Subway Station

Design of retaining structure and study of deformation laws of deep excavation is an important problem in the construction of subway station. It has important project value to research the deformation laws of deep excavation of subway station. Relying on the deep excavation of the Reentrant line station of Beijing metro Olympic branch,the deformation laws of deep excavation of subway station are studied with the methods of theory analysis, in-situ monitoring and numerical simulation. The spatial effect of deep excavation was analyzed. The main content and conclusions are as follows:(1) The deformation principles and failure modes of retaining structure are analyzed, and the main factors affecting the stability of deep excavation are given: hydro-geologic condition, the soil press and the scale of the excavation, the design plan and the construction method.(2) The in-situ monitoring plan of deformation is designed, and the in-situ monitoring work is accomplished. The result shows that with the increment of excavation depth and the application of steel support, the deformation state of the retaining piles gradually develops form the anteverted curve towards foundation pit to bow curve and the place of Maximum horizontal displacement also move down. The horizontal deformation of the retaining piles,the axial force of the steel support and stress of retaining piles increase with the increment of excavation depth. In fact, the monitored values are much smaller than the warning value , so the support scheme is conservative.(3) By the use of finite difference software FLAC3D, a three-dimensional simulation of the entire process of excavation and support of deep excavation is accomplished.The behavior of retaining structure is analyzed, and the deformation laws of deep excavation is studied in six cases. Monitoring results and calculation results of the largest horizontal displacement of retaining pile are basically the same. (4) The spatial effect of deep excavation is analyzed by FLAC, the result shows that:the spatial distribution of the bracing structure displacements and the axial force of the steel support has strong spatial effect: spatial effect of the corner is strong.and the spatial effect of the central section weakens.The results show that the calculation of three-dimensional analysis of deep excavation is an effective means to study spatial effect.