Field Test And Numerical Simulation Of Land Subsidence Due To Pumping And Recharging

Land subsidence has developed into ageological disaster that is more widespread in large cities.Due to the difficulties of monitoring land subsidence and the complexity of soil deformation,most of the research on land subsidence are based on on-site observation and experimentation for qualitative regional surveys and disasters assessment and prevention.Modem urban construction has also triggered certain land subsidence.In the ground source heat pump(GSHP)project of Tianjin Binhai New Area,in order to improve the unit efficiency of the GSHP,the method of pumping water is adopted to accelerate groundwater flow field.During this process,differential subsidence and associated issues may inevitablly emerge.In this study,the on-site pumping water test was carried out in Binhai New Area,and the water level,pore water pressure and deformation between different layers were monitored during the pumping water test.Terzaghi's one-dimensional consolidation theory has been applied in many numerical simulation software to predict subsidence problem with small size,simple boundary conditions and geological environment.In order to further understand the impact of long-term operation of ground source heat pump on the soil,this paper use GMS to establish a numerical model for the test site.The established model was verified by the results of field tests,and three different pumping methods were simulated.The main work of this paper are as follows:According to the field test,the relationship between ground subsidence and groundwater exploitation,pumping time,water depth,and pore water pressure was analyzed.The pore water pressure distribution and the compression deformation law of soil layers at diffferent depths caused bypurnping and recharging water were obtained.The influence of different period of pumping and recharging and the amplitude of water level on subsidence were obtained.The results show that in the same period of pumping and recharging water,the larger the water output,the greater the subsidence.While when the flux of water is certain,the longer the period of pumping and recharging,the greater the subsidence is.The water pumping capacity of the pumping well and the recharging capacity of the recharge well are closely related to the period of pumping and recharging and the number of period.With the increase of the number of period,the water pumping capacity of both pumping and recharging well are weakened.The ability of the effluent and recharge has also weakened over time.Under the condition of a certain flux pumping test,most of the deformation of the water-bearing sand layer occurs in the initial stage of pumping,the deformation of the adjacent aquitard is not large at the initial stage of pumping and the deformation gradually increases and tends to be stable.Through numerical simulation,it is found that recharging the aquifer can effectively inhibit the ground subsidence between the two wells.With a single well,the amount of land subsidence is positively correlated with theflux of pumping.The maximum subsidence caused by periodic pumping and recharging is basically the same as constantly pumping.But the periodic pumping and recharging can change the position where the maximum subsidence occurs,it depends on pump first or recharge first.The pumping test,pumpand recharging test are both indicated that the major deformation occurs in the silt sand layer,due to the elastic characters of sand layer,that timely replenishment to the aquifer can effectively inhibit the occurrence of subsidence.