Optimum Design Of Automatic Recharge Scheme For Soft Soil Foundation Pit

With the rapid development of urban infrastructure in China,foundation pit engineering is developing in the direction of "deep,long and wide".In practice,a series of groundwater activities,such as foundation pit seepage and dewatering,will lead to ground deformation around the deep foundation pit and affect the safe use of buildings.In the process of foundation pit construction and excavation,leakage has become one of the greatest risk sources.According to statistics,engineering accidents caused by leakage of retaining structure and water gushing from foundation pit account for more than 50% of the total accidents in foundation pit construction,especially in soft soil foundation pit.Therefore,the problem of groundwater balance in foundation pit construction has become a hot issue in geotechnical engineering.Based on the soft soil deep foundation pit project of Daliang Station of Foshan Metro Line 3 in Guangdong Province,combined with the excavation method of the foundation pit construction,the field monitoring survey data and the engineering geological conditions,this paper systematically analyses the recharge scheme of the foundation pit and how to realize the automatic control.The main research contents are as follows:(1)Based on the analysis of monitoring data of groundwater level,horizontal displacement of wall,surface settlement and building settlement in the knife handle section of foundation pit of Daliang Station,the variation law between groundwater level and seepage of foundation pit is obtained.Through on-site investigation of foundation pit leakage,the causes and ways of foundation pit leakage are clarified.In order to effectively control the groundwater level of the foundation pit,a single well recharge test was carried out,and the variation law of groundwater level outside the foundation pit after recharge was obtained.(2)In order to optimize the recharge scheme of the foundation pit,ABAQUS numerical software is used to simulate and analyze the single well recharge of the knife holder section of the foundation pit in Daliang Station.The simulation data are compared with the field data,and the reliability of the numerical model is verified.On this basis,the influence of single well recharge on seepage field and displacement field of foundation pit is studied.The effects of different filter length,diameter,recharge pressure and different distance between recharge well and foundation pit under the same recharge pressure on seepage field,displacement field and foundation pit leakage are analyzed,and the optimum parameters of single well recharge are obtained.(3)Based on the previous experience of recharge design and the design optimization of single well recharge parameters,a preliminary recharge optimization scheme is established.After comparing and analyzing the results with single well recharge simulation,the influencing factors of recharge are obtained.On this basis,the different design parameters of different influencing factors are combined to optimize the selection of various recharge schemes,and finally the optimization scheme of recharge is determined.(4)In order to realize automatic recharge,the automatic control program written by Python et al.has been successfully applied to the automatic recharge control equipment,and a set of automatic recharge system equipment has been formed with the self-designed automatic water level monitoring wells and automatic recharge wells.According to the actual situation of the site,an automatic recharge scheme is designed.