Numerical Simulation Study On The Influence Of Underground Filling And Mining Of Kunyang Phosphate Mine On The Groundwater Environment

A large amount of waste rock and tailings generated in the process of phosphate mining are piled on the surface,occupying a large amount of arable land,and have a certain impact on the ecological environment.Therefore,underground backfill mining method has become a research hotspot in underground phosphate mining.The core of the filling mining method is to transport the cement,waste rocks,tailings and phosphogypsum and other filling slurry mixed in a certain proportion to mined-out area for filling.This method can not only solve the surface environmental problems caused by a large amount of waste rock and tailings stacking,but also can avoid the environmental geological problems caused by the subsequent collapse of the goaf by filling the goaf.For large-scale irrigating and filling of the goaf,the change in the permeability coefficient of the filling layer will inevitably cause a certain degree of impact on the groundwater environment of the filling area.This paper took the second mine area of Kunyang Phosphate Mine in Yunlin as an example,deeply studied the potential impact of underground backfill mining of Kunyang Phosphate Mine on the groundwater environment through the combination of data collection,on-site hydrogeological survey and groundwater numerical simulation.The main research results are as follows:(1)The research results of different water volume scenarios show that the flow system of multi-layer monoclinic structure aquifers has leakage recharge.Under the condition of natural flow field,deep confined aquifers recharge shallow aquifers through leakage.(2)The seepage field changes significantly before and after the comented filling.correspondingly,the impact on the groundwater level of the monoclinic structure aquifer is more obvious,and the shallow and deep aquifers have obvious changes in the water level on both sides of a "watershed".In the upstream of watershed level contour,affected by the decrease in the hydraulic conductivity of the filled aquifer after cemented filling,the deep aquifer receives less leakage recharge and the groundwater level rises,while the groundwater level in shallow aquifer drops due to the decrease in the leakage recharge of the deep aquifer;In the downstream of watershed level contour,the groundwater level changes are just the opposite.(3)Under the condition of mining pumping and drainage,the groundwater level of different aquifers will be affected to a certain extent.Among them,the groundwater level of the overlying aquifer of the mining layer has dropped the most significantly.And affected by the leakage recharge,the groundwater level of the underlying aquifer also dropped to a certain extent.(4)Before and after the cemented filling,the pollution caused by the different pollution sources in the third layer upstream and downstream of the watershed to the overlying second aquifer was reduced to a certain extent.The main reason is that after the cemented filling,the hydraulic exchange between the second and third aquifers weakened.(5)Before and after the cemented filling,the pollution degree near the pollution sources in the upper and lower reaches of the watershed of the underlying fourth aquifer decreased,which was mainly related to the decrease in hydraulic conductivity of the third aquifer.The strength of the fourth confined aquifer leakage recharged to the third aquifer is weakened,so the advection and mechanical dispersion between the two aquifers are reduced to varying degrees.