Study On The Evolution Of Groundwater Seepage Field During The Closure Of Fushun West Open-Pit Mine

Fushun West Open-pit Mine is located in Fushun City in the eastern part of Liaoning Province.After more than 100 years of mining,it has formed a giant pit with a length of 6.6 km from east to west,a width of 2.2 km from north to south,a vertical depth of 420 m,and an area of 10.87km~2.In 2019,the West Open-pit Mine was shut down,and the transformation from mining to governance began.At present,there are mainly two ideas for the comprehensive management of the West Open-pit Mine.One is to partially backfill the mine pit,and then take ecological restoration,landscape transformation and other measures to transform it into an urban green space and industrial heritage display area for tourism resource development,referred to as the backfill and water storage plan.The other is to use the negative terrain of the open-pit mine to transform it into a pumped storage power station,namely the pumped storage hydroelectricity(PSH)plan.The implementation of the backfill and water storage plan will inevitably cause the water level of the mine pit to rise,which may lead to slope instability.The PSH plan needs to consider the impact of the cyclical rise and fall of groundwater level caused by repeated pumping and injection of water in the reservoir on the stability of the slope.This article clarifies the hydrogeological conditions of the study area through data collation and analysis and on-site investigation,establishes a numerical model of groundwater flow in the West Open-pit Mine,and conducts numerical simulations of the backfill and water storage plan and the PSH plan,summarizes the evolution law of the groundwater flow field during the closure process,and provides reference for the selection of the closure plan.The main research results of this article are as follows:1.The evolution of the groundwater flow field in Fushun West Open-pit Mine and its surrounding area during the natural water storage process after uniform step backfilling to-50m was simulated.The results showed that the groundwater level rise during the implementation of the plan can be divided into two stages:backfilling and water storage.The trend of water level rebound in both stages is first rapid and then slow,and the water level rebound rate in the backfilling stage is greater than that in the water storage stage,and when the water was stable,the water level in the mine was 78.8 m.During the backfilling process,the amount of water inrush in the mine ranged from 22,000 to 41,000 m~3/d,which was negatively correlated with the water level rebound rate.2.The evolution of the groundwater flow field during the staged backfilling from west to east and the natural water storage process in the east was simulated.The results show that the groundwater level rebound during the implementation of the plan can be divided into three stages:early stage of backfilling,middle and late stage of backfilling,and water storage stage.The water level in the early stage of backfilling rose rapidly,the rising rate in the middle and late stage was relatively gentle,and the water storage stage was first rapid and then slow.When the water storage was stable,the water level in the mine was about 80m..The amount of water inrush in the mine during the backfilling process was negatively correlated with the net storage capacity of the aquifer,ranging from 28,000 to 52,000 m~3/d.3.The operation of the pumped storage scheme was simulated,and the results show that the water level of the downstream reservoir during the operation of the pumped storage scheme fluctuated by about 17.5m,and the water level in the rest of the pit did not change significantly under the seepage control condition of the reservoir basin,except for the periodic fluctuation of groundwater level near the reservoir area with the reservoir water level.The influence of the leakage coefficient of the reservoir basin on the range of groundwater level change and the amount of water inrush in the mine was further studied.The results show that the smaller the leakage coefficient,the smaller the range of groundwater level change and the more stable the amount of water inrush in the mine.At the same time,the decrease of the leakage coefficient will lead to an increase in the amount of water inrush,with a maximum value of about 53,000m~3/d.The influence of the pumping and storage time on the groundwater level around the reservoir is also studied,the results show that the shortening of the pumping and storage time will lead to an increase of the variation of groundwater around the reservoir.4.Water level changes,water influx changes and slope stability of different pit closure program were compared.After a comprehensive comparison that backfilling to-50 m and water storage program with a small influx of water during the construction period,more water storage capacity after the end of the backfill,higher slope stability in backfill and water storage process and relatively low cost of treatment,etc.,can take into account the safety of the advantages of open pit terrain at the same time.