Research On Risk Analysis And Control Of Existing Subway Station Affected By The Adjacent Construction Of Deep And Large Foundation Pit In Beijing

With the continuous development of the urban metro network,the construction of subway has led to the development of the real estate along the line. Subsequently, it appears more and more foundation pit construction near subway. Due to environment and line selection restrictions,the foundation pit engineering near existing subway becomes some new characteristics, such as more larger,tighter,deeper and closer. Deep and large foundation pit near existing subway is bound to cause disturbance to the surrounding soil of subway,which lead to subway station structure and track produce deformation. It will cause guideway irregularity,affect passenger comfort, and even affect the safe operation of subway train when severe. Subway line is different from the general building,which allowable deformation is extremely strict,generally measured in millimeters.Therefore, risk analysis and control research of deep foundation pit adjacent to the existing subway station has important practical value to ensure safe operation of the train during the construction of foundation pit,which aslo guide construction of similar projects.The paper systematically studies risk control of deep and large foundation pit adjacent to the existing subway station,including ANSYS numerical simulation analysis, foundation pit construction scheme comparison,monitoring data and numerical simulation data comparison analysis and the risk control measures.The main contents are as follows:(1)The research status of deformation of foundation pit construction and its influence on subway is summarized. Survey the construction of more than 20 excavation adjacent to subway in Beijing to analyze the specialized design of adjacent subway foundation pit support. The results show that:when the net level length of pit and subway less than about 15m, foundation pit support usually used pile-pillared or double-row piles. Otherwise, single-row pile/double piles and anchor support system will be used.(2)Based on the practical engineering, the paper analyzed the impact of "pistol-shaped" irregular excavation on the deformation of subway station structure and track with 3D finite element model. And combined with the actual monitoring data, the reliability of numerical simulation is verified. The results show that:the structural deformation of the subway station which is near the long side of foundation presents parabola, and the short side station presents nonlinear growth.(3) The development process and deformation law of subway station following excavation are analyzed under different conditions. The factors, such as the foundation pit excavation plan, excavation depth,the diameter of the piles, the distance between the piles are considered the effect on the deformation of subway station. The results show that:the foundation close to the subway construction, its block length should be controlled at about 30 meters, and each excavation depth should be controlled at around 2 meters. This can effectively control the impact of excavation on subway construction.(4) For the construction of the deep foundation close to subway station, this paper puts forward the risk control measures from the management and technical aspects, which would provide references for design and construction of similar engineering.