Research On Dewatering Technology And Deformation Characteristics Of Ultra-deep Foundation Pit

In recent years,the construction of underground engineering in China has been accelerated comprehensively,and the dewatering of deep foundation pit has become an important factor affecting the construction of underground engineering.Dewatering of deep foundation pit is affected by complex factors such as hydrogeology,foundation pit depth,water level drop,and surrounding environment,making construction difficult.The paper takes the ultra-deep foundation pit in Qingxiushan Station of Nanning Rail Transit Line 3 as the engineering background.Aiming at the problem of large drawdown in ultra-deep foundation pit and the proportion of dewatering deformation in the total deformation,through theoretical analysis,numerical simulation and on-site monitoring and other research methods,comprehensive study of dewatering technology for ultra-deep foundation pits and dewatering deformation characteristics of ultra-deep foundation pit have been developed The main work content is summarized as follows:(1)The engineering general situation,engineering geological conditions,engineering hydrological conditions and retaining structure of ultra-deep foundation pit are introduced,and the dewatering method of foundation pit is studied.On the basis of previous geological and hydrological investigation,in view of the technical problems such as large excavation depth and deep water level drop of ultra-deep foundation pit dewatering engineering,combined with practical engineering,the dewatering design and construction of ultra-deep foundation pit are studied.In the actual construction process,the horizontal deformation of the enclosure structure,the surface settlement and the settlement of adjacent buildings are monitored on the spot.In the dewatering design of ultra-deep foundation pit,it is calculated that the length of dewatering well is 70 m and the number of dewatering wells is 26,which completes the structural design and plane layout of dewatering wells.(2)The dewatering of ultra-deep foundation pit is studied by means of Midas GTS NX finite element analysis.by comparing the horizontal deformation of enclosure structure,the settlement of surrounding surface and adjacent buildings caused by foundation pit dewatering and first dewatering and then excavation,the horizontal deformation of enclosure structure,surrounding surface settlement and adjacent building settlement caused by foundation pit dewatering are obtained,and the dewatering deformation characteristics of ultra-deep foundation pit are analyzed.The law of deformation settlement and the proportion of precipitation deformation in the total deformation are summarized and obtained.finally,the numerical simulation data and field monitoring data are compared and analyzed to verify the correctness of the numerical model.