Research On Safety And Influence Of Existing Subway Station Affected By Bilateral Deep And Large Foundation Pit

With the development of city subway network, in range of the metro control protection, it appears more and more foundation pits construction near subway station. Subway lines’allowable deformation control value are very strict, usually measured in millimeters.Deep and large foundation pit adjacent to existing subway is bound to cause disturbance to the surrounding soil of subway,which lead to deformation of subway station structure and track.It will result in track irregularity and affect passengers’comfort, seriously even endanger the safe operation of subway train. 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.In this paper, safety research on a bilateral deep and large foundation pit adjacent to subway station has been researched comprehensively and systematicly, includeing ANSYS numerical simulation analysis, SIMPACK multibody dynamics analysis and risk control measures.The main works and achievements are listed as below:1.Comprehensively sum up risk control about the foundation pit adjacent to existing subway station project related data. Summraize the content of peripheral deformation law of foundation pit and deformation characteristics of foundation pit adjacent to subway station and the subway car dynamic effects due to track deformation, the existing subway structure status is rated "one level".2.Study the optimal excavation scheme of double side foundation pit based on numerical simulation and AHP:The earth surface’ final settlement, the lateral deformation of diaphragm walls,the deformation of track structure,time-step deformation of track structure,deforamation difference of deformation joint 5 indexes caused by bilateral deep and large foundation pit were analyzed, The results show that:the south side of the foundation pit caused about 60%-80% of total structure deformation.Establish a multi-level model about 5 indexes by intrucduting AHP, the excavation scheme order is "north before south"< "south before north"< "the excavation at the same tine".3.Establish ANSYS finite element model to optimizate the analysis of foundation pit construction scheme:Based on the excavation scheme of "north and south at the same time", optimize ansysis the scheme of excavation from three aspects of the depth of exaction and the choice of retaining structure and the parameters of diaphragm walls.The results show that:With a thickness of 1200mm,embedded depth of 10m diaphragm walls,track structure deformation will reduced by about 11%～16% compared with the design condition. When single-step excavation depth of a foundation pit is 3m, lateral deformation of diaphragm walls will reduce by about 9%～10% compared with the design condition.4.Establish SIMPACK dynamic model to evaluate vehicle dynamic performance:The train safety are in "excellent" grade before and after construction,but train stability becomes "qualified" from "good". It seems although the construction of foundation pit impact on comfort is greater than the effect on the safety of the train, two indexes meet the specification requirements.5.Put forward the risk control measures about deep and large foundation pit adjacent to exsiting subway station:According to the latest research results, this crossing project’risk is rated to "special level". From the perspective of risk of foundation pit and safety of existing structure puts forward corresponding control measures.