Study On The Law Of Ground Subsidence And Its Control Method For Excavation Of Foundation Pit Of Subway Station

The construction of urban subway can not only solve the problem of urban traffic congestion,but also stimulate employment,create output value and enhance urban vitality.In recent years,with the rapid development of the domestic and western cities,more and more cities are in line with the construction of the subway.In order to alleviate the problem of transportation,most cities take the construction of the subway as the first choice.As the ancient capital of the Six Dynasties and the more developed cities in the Midwest of Taiyuan,the construction of subway is the top priority for future development.Now,with the construction of Taiyuan metro line two,Taiyuan will soon usher in the first subway line,which is very important for this historical and cultural city.Although the subway has the advantages of expanding the urban underground space and alleviating the ground traffic jam,it is undeniable that the construction of the subway may also damage the buildings and other shallow buried facilities around the subway stations and the lines.In particular,the city where the subway has not been built,the related aspects of the research are insufficient,the project case is not much,the experience is deficient,therefore,it is necessary to study the influence of the excavation of the foundation pit of the subway station on the surface subsidence of Taiyuan metro station.This paper,taking Taiyuan Metro Line No.2 Hua Zhang Jie Street Station as the project background,through the collection of materials,engineering investigation,outdoor pumping and indoor geotechnical test,to understand the hydrogeological conditions in the region and determine the physical and mechanical indexes of the parameters in the study area.Using the obtained data and considering the influence of percolation,the FLAC^3D numerical simulation software is used to establish a three-dimensional numerical model,and the influence and control method of the foundation pit excavation on the surface subsidence under different working conditions is simulated and analyzed.Through numerical simulation,the influence law of different soil parameters on the surface subsidence of the excavation of the foundation pit is obtained,and the different methods for controlling the surface subsidence are explored,and the following conclusions are drawn.?1?Fen River floodplain area has relatively special hydrogeological conditions,and groundwater is relatively abundant,which is easy to cause impact on foundation pit construction.The measured data indicate that the surface subsidence of the foundation pit of Hua Zhang Jie station has exceeded the control value,so we should take some measures to control the ground settlement.?2?the change of soil parameters does affect the surface subsidence,and the variation of soil parameters varies.The change of each parameter should be analyzed according to the actual conditions of this parameter;the soil parameters which are directly applied to the soil test should be obviously deviated from the actual soil,and the soil parameters should be determined through the experiment.According to the change range,the adjustment range of the soil parameters around the station is given by calculation.The results of the simulated surface subsidence are basically close to the actual measurement.the influence degree of each parameter is different,in which the permeability coefficient is contrary to the other parameters,the greater the permeability coefficient,the greater the surface subsidence value,and the soil ginseng obtained by Table 4-2.The adjustment range can provide reference for similar engineering problems in Taiyuan area later.?3?the deeper the depth of the dewatering well is,the smaller the surface subsidence value is.With the increase of depth,the magnitude of surface subsidence decreases.The larger the spacing between the wells is,the smaller the surface subsidence value is.Under the same precipitation time,the decline of surface water slows down,and the water pressure at the same elevation is larger.The permeability coefficient of the water stop curtain has no significant influence on the surface subsidence,especially the permeability coefficient of the water stop curtain is getting smaller and smaller,and its influence on the surface subsidence is almost invariable.The influence of the depth of the water stop curtain on the surface subsidence is remarkable.If the water stop curtain is too shallow,the seepage effect of the groundwater will be more obvious,the surface subsidence value increases,but the effect of the water stop curtain over a certain depth has little effect on the effect of the water stop.The total number of recharge wells has little effect on surface subsidence.The surface subsidence value becomes smaller with the increase of the pumping ratio,but the surface subsidence should not recharge after the control value.Otherwise,the pumping in the pit outside the pit will result in the increase of the cost of the project.?4?Aiming at Hua Zhang Jie station,the surface settlement control effect is best when the depth of well depth 24m,the distance of pumping well distance 10m,the depth 28m of the water stop curtain and the permeability coefficient of the water stop curtain are 10^-9cm×s^-1.The results are constructive for the construction of foundation pit of Hua Zhang Jie station,and provide reference for the control of surface subsidence of the same type of foundation pit in Taiyuan..