The Analysis Of The Deformation Monitoring Of A Subway Foundation Pit Considering The Coupling Of Seepage Flow And Soil Deformation

Metro played a key role in a city, it had to be taken service for more than 100years. The construction of the subway station pit was closely related to thetransportation safety of the city rail line, produced a direct effect on the sounddevelopment of the urban rail traffic construction, and was very important to thesafety of the around buildings and underground pipelines. In recent years, with rapiddevelopment of city construction，subway station pit engineering has been one of thehottest research topics to most geotechnical engineers. The research contents anddirections gradually become broader and deeper. The geological conditions and therequirements of the deformation standard of the foundation pit engineering vary indifferent countries.Guangxi University station was taken as the research background of this thesis,which was one of the first batch of projects of Nanning city light rail constructionengineering. The open-cut and bottom-up methods were employed as the constructionmethod, and the diaphragm wall with steel supports was made as the bracing system.The depth of the pit was 16.88~19.23m, and the standard section width was 20.7m,with a length of 465m. The construction site consists of gradeⅡalluvial terracesnorth of the Y river. The terrain was flat, and its ground elevation was 75.86~77.89 m,with a relative elevation 2.03 m. The surface was covered by urban roads surroundedby lots of high buildings. The buried depth of steady water level was about 4.0mbelow the ground elevation. The underground continuous wall had been a danger ofleakage on September 27, 2010 during the pit excavation. The deformation and axialforces of the supporting structure as well as the underground water level weremonitored during the leaking prevention process. At the same time, a plane model wasdeveloped to simulate the construction process of the foundation pit by FEM. Then,the fundamental reason for the leaking of the foundation pit was analyzed fromcombining the numerical results and in situ measured data, and the remedy measureswere put forward to prevent the water leakage, which were proved to be effective andfeasible in practice. Meanwhile, comparative analysis was done on the numericalresults of the two finite element models respectively considering the effect of thegroundwater or not. Also, special stresses were laid on analyzing the key influentialfactors and the deformation characters of the foundation pit by considering the effect of the groundwater, so as to find the deformation law of the foundation pit underdifferent construction conditions and different supporting conditions. Finally,reference and guidance were raised for the subsequent subway station foundation pitengineering in Nanning, which mainly including the design of the palisade structure,the construction order of the excavation and the formulation of the deformationmonitoring plan.