单斜构造煤层采空区降雨淋滤渗流作用下重金属污染物迁移模拟试验OA

This study takes the typical coal mining area of Dongshan town,Qujing City,Yunnan Province as the study area.As a representative region of karst landforms in Southwest China,the study area features dense distribution of coal seams and non-ferrous metal minerals.The karst pipelines-fracture networks are intertwined,resulting in an extremely complex karst groundwater systems.The strata in the study area exhibit an overall monoclinic structure,with rock formations oriented at 27° ∠ 9° and strata sloping toward the northeast,forming a typical monoclinic hydrogeological structure.Continuous seepage of Acidic Mine Wastewater(AMD),caused by rainfall infiltration and leaching,has servely polluted both surface water and groundwater in the region.Consequently,this area among the most heavily polluted groundwater zones in the karst region in Southwest China,and tracing the source of groundwater pollution remains challenging. The purpose of this study was to conduct an in-depth analysis of the dominant flow activities within monoclinic hydrogeological structures in coal mine goafs under the influence of rainfall,as well as to investigate the migration mechanism of heavy metal pollutants in groundwater.The research primarily focused on:(1)The effects of dominant flow and fracture development on the migration rate of heavy metals in the goaf;(2)The influence of the collapse funnels on the migration direction and distance of heavy metals.By combining laboratory seepage tests with numerical simulation method,both an experimental sandbox model and a numerical goaf model were developed.Four experimental conditions were established in the indoor sandbox experiment:T1 simulated the natural leaching of coal gangue exposed to rainfall in an open-air environment;T2 simulated the migration of heavy metals driven by dominant flow within the goaf.T3 simulated the migration of heavy metals following roof collapse in the goaf;and T4 simulated the migration of heavy metals in naturally buried coal gangue strata under rainfall.The sandbox was filled with soil and coal gangue from a goaf coal mine in Dongshan town,Qujing City,Yunnan Province.Leachate obtained through static leaching supplemented the dominant flow,and changes in the concentrations of Mn2+and Zn2+were reflected throughout the process.Additionally,to further simulate the long-term migration behavior of elevated concentrations of Mn2+in goaf strata,the numerical model was employed to represent the migration of heavy metals in monoclinic tectonic strata by setting different working conditions and using the porous medium dilute mass transfer equation and Richards equation. The results of the sandbox experiment show that the dominant flow through the middle and lower fractures of the backfill of the close coal seam significantly enhances the migration,diffusion and accumulation of Zn2+and Mn2+.Additionally,the presence of the overlying soil layer in the T3 experiment causes the hysteresis of Mn2+release.Numerical simulation results directly show that the collapse funnel in the collapse area accelerates the migration of Mn2+pollution plumes,with the collapse of the goaf increasing the migration distance of Mn2+by 9.65 m.Moreover,the dominant flow within the monoclinic structure after leaching shortens the downward migration period of Mn2+by 8 years and extends the horizontal migration distance by 29.85 m.Mn2+released from coal seam#6 penetrated the strata horizontally and reached surface rivers within 15 years,shortening the migration period by 10 years.Furthermore,after the collapse of the goaf,the upward migration and diffusion distance of Mn2+increased by 9.65 m,indicating that the collapse funnel provides an favorable channel for the upward migration of Mn2+. The following conclusions are drawn:(1)The presence of dominant flow in monoclinic goaf generates acidic mine wastewater faster than fracture flow,resulting in the heavy metal Mn2+to more readily contribute to regional groundwater pollution through dominant diffusion in the aquifer of the karst area in Southwest China.(2)The existence of collapse funnels in the monoclinic goaf facilitates the rapid upward migration of heavy metal Mn2+,which further leads to surface water pollution.(3)Long-term simulation results show that acidic mine wastewater in the goaf creates a low-concentration area of Mn2+near the dominant flow side of the downward rock strata of the goaf under the action of dominant flow.