Study On The Stability And Deformation Characteristic Of Big And Deep Subway Excavation In Beijing

ABSTRACT:In recent years, with the ever-accelerating process of urbanization, a large amount of population go into the major cities, causing constant traffic jams. In order to solve the traffic problem, Beijing speed up the construction of rail transportation. The construction of the rail transportation project makes the development of Foundation Pit Engineering to a deeper depth, larger, more complex environment direction. Due to the complexity of the excavation surrounding environment, today’s pit design concept has grown from strength control into deformation control. Pit deformation is closely related to its stability. Therefore carriying out a study on the stability and deformation characteristic excavation is very significant. The research on the stability and deformation of the excavation is were carried out through theoretical analysis, numerical simulation and on-site monitoring. The research results are as follows:(1) The current research situation of the stability and deformation of the Foundation Pit Engineering at home and abroad is summarized. The foundation stability and deformation theory is summed up.(2) Through the Pit size statistics of the cut and cover subway station in Beijing, the20m-wide pit is selected and the strgenth reduction method of the FLAC3D software is used for a two-dimensional numerical simulation. The impact of various factors on the stability of non-support pit is studied. And sensitivity to various factors are evaluated using the gray relational theory. The critical depth in stable for non-support pit with different cut slope angle in Beijing is obtained through numerical simulation.(3) The size of200m×20m×28.85m pit is selected as a standardized model and three-dimensional numerical simulation is used to study the three-dimensional deformation law for Beijing metro deep foundation (the impact of precipitation is considered), including the retaining structure deformation and the surrounding surface settlement in different location of the pit. And then the impact factors for pit deformation is studied using this three-dimensional model. And sensitivity to various factors are evaluated using the gray relational theory.(4) The monitoring results of the typical surface settlement points and horizontal displacement point for the top of the pile in Nanluoguxiang station belonged to the6th line are analyzed. Statistical analysis is carried out for the measured deformation in Beijing metro pit. And the mode of the wall deformation and surface settlement outside the pit in Beijing metro pit are obtained:The wall horizontal deformation is the belly type and surface settlement outside the pit is the groove type, which is consistent with the results of numerical simulation.