Numerical Simulation Of A Beijing Metro Foundation Pits Dewatering And Land-subsidence

The excavation of metro pit excavations are almost all related to groundwater controlling. Mostly, Metro stations are located in the downtown area of a complex surface state, the changes of water level will lead to changes in soil effective stress, and cause consolidation settlement; meanwhile, dewatering funnel has led to formation of the differences in different locations within the scope of the settlement. This uneven settlement will have varying degrees of negative impact on underground structures, pipelines, building foundations, such as deforming or even breaking down, intimidating pit excavation and property safety of the people and causing heavy losses.The dissertation relies on Ping’anli station dewatering Project of Beijing Subway Line 3, phase 2, technology and applications of dewatering are introduced briefly, and the process and the calculate results of Ping’anli station dewatering project design are decrypted detailedly.Firstly, theoretical analysis of land-subsidence caused by dewatering was made. Describes the seepage movement and continuity equation, the two-dimensional unsteady seepage flow differential equations and boundary conditions of different aquifer properties. Introduces The Terzaghi one-dimensional consolidation theory equations and differential equations of Biot three-dimensional consolidation theory(or two-dimensional form), combined with conservation of mass, basic seepage equations and saturated soil effective stress theory.Secondly, introduces the characteristics and applications of finite element numerical simulation software MIDAS/GTS and the brief modeling process. Key issues in the process of modeling such as soil constitutive model selection, determination of boundary load and seepage-stress fully coupled analysis application have been analyzed and summarized in detail.By numerical simulation on the example, find out impact on land-subsidence simulation results when deformation modulus of the soil, the groundwater drawdown, and the permeability coefficient of the aquifer changes independently.Finally, build a two-dimensional finite element analysis model with engineering example: Ping’anli station dewatering Project of Beijing Subway Line 3, phase 2. The model is built to analyze changes in seepage distribution by dewatering, to discuss the rationality of software for Unsteady Flow Simulation head function settings. Based on the seepage simulation model, a seepage-stress fully coupled analysis model is built to analyze the land-subsidence caused by dewatering(largest settlement is 5mm), and preliminary forecasts the uneven settlement at the bottom of M6 line Ping’anli Station main structure caused by dewatering(largest settlement is 3mm), which has some theoretical and practical value.