The Research Of Foundation Pit Dewatering Of Tumour Hospital Station Project In Tianjin Metro Line No.5 And 6

For nearly 30 years,with the rapid development of urban construction in our country,high-rise buildings are arising,underground space engineering scale is increasing,which technologies are improving,such as,subway station,underground tunnel,base of bridge,etc..These complicated engineering have been largely promoting the rapid development of the theory and technology level of foundation pit engineering.The main content of foundation pit engineering contains geotechnical engineering survey,design and construction of foundation pit supporting structure,control of groundwater,earth excavation of foundation pit,project monitoring and environment protection etc..Foundation pit engineering usually includes two big systems that are foundation pit excavation and supporting system.Foundation pit dewatering is an important process of foundation pit excavation and supporting,so when the dewatering scheme is designed,not only to ensure the construction safety in the future,also to ensure the minimum to reduce the level of confined water.Rational optimization of foundation pit dewatering scheme is to minimize the area around the ground subsidence.Relying on the tumour hospital station engineering of Tianjin metro line No.5 and 6,according to the engineering geological and hydrogeological conditions,combined with special pumping test results,a reasonable scheme of foundation pit dewatering is putted forward in this paper.And optimizing some problems caused by the application of the scheme a number of problems,for example,the stability problems of base plate of foundation pit and ground subsidence problems caused by foundation pit dewatering.The main body of foundation pit engineering lays out 26 drainage wells in No.1 area;Setting up 9 drainage wells in No.2 area of foundation pit,3 wells that outside the pit for standby decompression and observation in the third confined water.Because the relatively uneven thickness of water-resisting laye of the second confined water and the third confined water in No.2 area of foundation pit,and partial thin lens,hydraulic connection is good,the more obvious flow supply exists.Through the sudden surge stability calculation,the maximum value of stability coefficient is 0.96 whih is less than 1.05 that the standard requires,the instability of foundation pit bottom maybe existing.Using the traditional method of pressure balance,shear model of bar foundation pit proposed by Liang Yongran and plastic hinge line theory model,the stability problem of base floor of foundation pit excavation is discussed in No.2 area of the subject in this paper.It is found that the calculation results are conservative using the traditional soil pressure balance method and the shear stress strength model of bar foundation pit that did not consider the strength of soil and the size of base plate of foundation excavation,and stability safety coefficient of foundation pit floor is low.The safety stability coefficient of foundation pit bottom of the plastic hinge line theory model that considering of the strength of soil and size is higher,in accordance with the actual situation.For ground subsidence problems caused by foundation pit dewatering,3 d finite difference method is used to simulate the environmental problems caused by foundation pit dewatering,and the simulation result is further discussed,which provide theoretical basis for the design and construction of drainage dewatering.