Research Of Ground Subsidence Caused By Foundation Pit Dewatering And Control Measures In Songhua River Street Station Of Shenyang Metro

In recent years,along with more and more basement of high-rise buildings,underground garage,subway stations and other projects,it need excavated foundation pit in construction process inevitably.In the process of the excavation,that is necessary to control groundwater reasonably.When encountered groundwater in deep foundation pit construction now,foundation pit dewatering is a scheme that used widely and more mature of the technical.But foundation pit dewatering will impact on the surrounding environment inevitably,the ground subsidence is likely caused.The foundation pit dewatering of Songhua River Street Station was selected as an example which based on line 10 of Shenyang metro.The deformation of strata subsidence mechanism caused by foundation pit dewatering was researched under the typical geological conditions of Shenyang area,the relative deformation law was analyzed,control measures were proposed.The conclusions were reached as following.According to the research status at home and abroad,the adverse effects of groundwater in deep foundation pit engineering were analyzed,various methods and its applicable condition of foundation pit dewatering were analyzed and summarized,the calculation method of ground subsidence which was caused by foundation pit dewatering were summarized that was commonly used in engineering,the process of seepage and consolidation theory derivation were analyzed.After contrasted Terzaghi consolidation theory with BIOT consolidation theory,the pore pressure was solved by BIOT theory and the change of the pore pressure was solved at the same time,this displacement solution was more realistic than indirect estimation of consolidation settlement by Terzaghi theory.Primary consolidation settlement could be calculated only by Terzaghi theory approximately,and then the degree of consolidation of each time was calculated by the pore pressure changes to solve the settlement.While two parts of the initial settlement and primary consolidation settlement could be solved by BIOT theory at the same time,but the secondary consolidation settlement part didn't included.According to the survey data of the Songhua River Street station in Shenyang subway,the engineering geological and hydrogeological conditions of the Songhua River Street station was discussed,the physical and mechanical indexes of each soil layers was given.The station Foundation pit dewatering of the Songhua River Street station was designed.By calculation,the number of dewatering wells was designed to 30.The specific technical requirements of dewatering construction plan and environment monitoring was raised.According to the dewatering design,application to the amount of ground subsidence induced by dewatering wascalculated by the software of Lizheng deep Foundation pit.The results showed that the maximum drawdown and the largest settlement appeared in the central of the pit,with the Central pit distance increased;both of the drawdown and settlement decreased gradually,presented funnel-shaped distribution.Beyond the boundaries of the foundation pit dewatering,the absolute value of ground subsidence was small,and the inhomogeneous subsidence was not obvious.The foundation pit dewatering had little effect on the existing buildings.The dewatering design was reasonable and feasible,the construction could be undertaken.The settlement observation should be strengthened during construction.According to the practice,The influence factors of ground settlement was analyzed,including the basic structures and solidification history of the soil mass,the initial groundwater level,the Layout method of the dewatering wells,the duration of dewatering,the water inflow of each well.In response to these factors,measures of reduced settlement could be proposed accordingly,including reasonable arrangement of well point,taking water retaining structure,the dewatering speed control,reducing the load of foundation pit surrounding,strengthening the monitoring and forecasting during construction.The safety of foundation pit and surrounding environment could be ensured.The actual project construction could be guided by relevant conclusions which were reached but still some deficiencies were also existed,further study was suggested during the process of engineering construction.A system that combined with various research methods for evaluation and prediction of ground settlement could be set up which could be comprehensive consideration in depth of foundation,foundation pit dewatering,forms of support structure and surrounding environment situation to fully guide the engineering practice.