Recharge Test And Numerical Simulation Study Of Fengyi Bridge South Station To Fengjing Section Of Fangshan Line Of Beijing Subway

According to the purpose of recharge,groundwater recharge of subway foundation pit can be divided into two types,one is environmental control type and the other is water resources protection type.Water resource protection recharge is different from environment control recharge because of its large amount of recharge water and its location is often within the influence radius of precipitation,which leads to the frequent occurrence of groundwater recharge and circumfluence.Recharge disturbs foundation pit dewatering,which increases the difficulty of foundation pit dewatering.Therefore,feasibility of recharge of gravel phreatic aquifer,influence of recharge on water inflow of foundation pit dewatering,and effect analysis of different recharge schemes have been studied through dewatering of foundation pit of Fengyiqiao South Station ~Fengjing in Fangshan Line of Beijing Metro.Specific research contents include:1.Through on-site monitoring of water inflow,recharge and surrounding groundwater level of foundation pit dewatering,it is found that the sand and pebble layer has strong recharge capacity,and the ratio of irrigation to pumping can reach 1:1,which indicates that it is feasible to recharge.With the increase of recharge water,the groundwater level of foundation pit and the water inflow of foundation pit increase,which proves that recharge groundwater flows back to the area of foundation pit and affects the dewatering of foundation pit.2.A three-dimensional numerical seepage model for dewatering and recharge of subway foundation pit has been established.Based on the established numerical model,combined with mathematical analysis method,the influence of recharging on dewatering of foundation pit has been studied,and the influence of recharging on water inflow of foundation pit has been calculated.The results show that the recharge water accounts for 25%-31% of the water inflow into the foundation pit.At the same time,it is found that there are some differences between numerical methods and analytical methods,but both methods can be used in the study of foundation pit dewatering and recharge engineering,and can be checked each other.3.Based on the established numerical model,the effect of formation permeability coefficient on the effect of recharge has been studied.Changing the formation permeability coefficient and remaining parameters unchanged,it is found that the formation permeability coefficient increases,the maximum water level in the recharge area remains unchanged,and the water level in the precipitation area rises.It shows that under the same conditions,the higher the formation permeability coefficient,the more obvious the phenomenon of recirculation and recirculation,and the greater the interference to foundation pit dewatering.4.Based on the established numerical model,the influence of the distance of the recharge area on the effect of recharge has been studied.Changing the location of the recharge area,the remaining parameters remain unchanged.It is found that with the distance between the recharge area and the precipitation area increasing,the maximum water level of the recharge area remains unchanged and the water level of the precipitation area decreases.In this numerical model,the recharge area is 1900 m away from the dewatering area,which does not interfere with the dewatering of foundation pit.5.It is necessary to consider the coupling effect between dewatering and recharge in engineering,accurately predict the influence of recharge on foundation pit dewatering,and then coordinate the design of dewatering and recharge schemes,in order to achieve the control goal of foundation pit groundwater level.