| In order to ensure the smooth progress of the foundation pit engineering,the foundation pit precipitation plays a crucial role.Reducing the groundwater level at the foundation pit can ensure that the construction surface of the foundation pit is in a dry state,and is conducive to the safe excavation of the foundation pit.Therefore,the rationality of the precipitation scheme largely determines the economy and safety of the foundation pit project.However,there is no accurate calculation method for slim foundation pit dewatering design at present.Given the relevant parameters involved in the traditional calculation method are too simplified,to makes a scientific quantitative analysis of groundwater in the slim foundation pit engineering,which may cause too little dewatering to meet the requirements of dewatering or too much dewatering to cause adverse effects on the surrounding environment,moreover the traditional calculation method is only applicable to the foundation pit of one-time precipitation,does not accord with the actual situation of dewatering construction of narrow and long foundation pit.In view of the above problems,based on the actual project,this paper studies the design method of deep foundation pit dewatering in slim subway station by using the research methods of theoretical calculation,indoor test,nondestructive testing and field monitoring.The main research contents and results of this paper are as follows:(1)Considering the characteristics of slim foundation pit dewatering construction,this paper proposed the "big well method" dewatering theory based on dewatering unit.Slim foundation pit could be divided into several rectangular dewatering units.Given the interaction effect of each dewatering unit,the total water inflow of each dewatering unit is calculated according to the sequence of units.A preliminary dewatering scheme is proposed relying on actual projects and theoretically the groundwater level can be guaranteed to meet the drawdown requirements.control point and the limit value of single well yield as the restraint condition,establishes mathematical model with the water yield of each single well as the design variable,uses Python to solve the model.Then futher the optimized dewatering scheme,and determined a final scheme.The results show that,compared with the first dewatering scheme,the number of dewatering wells in the optimized scheme is reduced by 4,and the total water inflow is reduced by 3815.509 m3/d.The final optimized dewatering scheme effectively reduces the number of dewatering wells and the water inflow,to make the dewatering scheme more reasonable.(3)Based on the optimization dewatering scheme,MIDAS GTS NX finite element analysis software is used for analyzing the groundwater seepage change near the foundation pit and the water head change at the key position of the foundation pit.The research shows that the simulation results of the final optimized dewatering scheme show that the groundwater level is on-12.4m to-14.0m,below-12.2m,which verifies the feasibility of the final dewatering scheme.At the same time,the required dewatering depth decreases in turn with the excavation direction of foundation pit,which verifies the reliability of the dewatering theory of "large well method" based on dewatering unit.(4)The variation of groundwater level in the foundation pit was analyzed by field monitoring and compared with the numerical simulation results.The results show that after the precipitation is stable,the groundwater level at the bottom of the foundation pit is between-12.6m and-14.5m.The underground water level can meet the dewatering requirements and is basically consistent with the numerical simulation results.This proves the feasibility of the final dewatering scheme and further verifies the reliability of the dewatering calculation method based on the“objective function theory",which provides a reference for the optimization of foundation pit dewatering in the future. |
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