The Aquifer Destruction Mode And Risk Control In Closed Coal Mine Areas

Coal mining practice has shown that coal mining has caused severe pollution and damage to the groundwater environment in the mining area.In recent years,the state has introduced relevant policies,closed and integrated tens of thousands of small coal mines.The safety and environmental problems brought by the mine closure are becoming more and more serious,of which the impact of aquifers has appeared in many areas,with water burst in mine shaft,groundwater table lowering,aquifer water quality deterioration,and string layer pollution problems,thus produces major influences to the groundwater system,which also brought a series of water environment security risks.However,there is no clear technical standard and management for the destruction of aquifer in our country,the existing technical standards or specifications can not be fully applied to the management of aquifers in mine closure.Therefore,it is necessary to strengthen the research on the evaluation and management technology of the groundwater aquifer destruction in mine closure.Based on the investigation of countrywide coal mine materials and typical aquifer destruction cases in the country,three models of coal mine aquifer damage are proposed,ground collapse stress-driven,hydrodynamic change driven,and pollution driven;Based on the damage mechanism of aquifer,this paper constructs an index system and applicable model to evaluate the risk of coal mine aquifer destruction in mine closure,establishes the countermeasure and technical process of the risk management of the closed pit mine.In the end,the typical case of pollution-driven aquifer damage in hongshan-zibo coal mine were studied.The main research results of this paper are as follows:(1)The destruction forms of the coal aquifer and typical cases studyThrough participat the work of mine geological environment protection and land reclamation program compilation in China,combined with the data-collection and investigation of the aquifer destruction of coal mine closure,and a related survey was conducted on 9,995 closed mines in 2017,selective analyse the typical cases as the Guoyang No.1 Mine and the Fengfeng coal mine,the aquifer destruction modes based on the overall structural level,groundwater dynamic level and hydrochemical level were obtained.The destruction of the aquifer structure mainly in the upper and down floor of coal layer arising collapses,water-fractured fractures,separations and bends,causing groundwater in the aquifers to leak downhole or causes aquifer inrush.The water level change of aquifer is mainly characterized by the formation of groundwater depression cone in the mining stage,and the groundwater level rises rapidly submerging the mines and lanes after the coal mine closure.The pollution models of aquifers main include: Leaching pollution by abandoned mine solid waste;Infiltration pollution by abandoned mine subsidence water,solid waste and coal gangue leaching solution;String pollution by roof layer water flowing fractured;String pollution by bottom layer of polluted mining fissure;String pollution by bad drill enclosed layer;String pollution by fault or collapse column string.(2)Groundwater aquifer destruction mode in closed coal mine areas was put forward.By sorting out the geologic environment problems of the national closed pit coal mine area,we conducted in-depth investigation and study on the typical cases of the aquifer destruction,and summarized the main performance of the aquifer damage in the coal mining.On the three levels of aquifer structural control layer,aquifer hydrodynamic layer,and aquifer water quality degradation,the various forms of aquifer damage were combed.Based on this,three models of coal mine aquifer damage are proposed,ground collapse stress-driven,hydrodynamic change driven,and pollution driven.(3)The evaluation index system and evaluation model for the damage risk of abandoned aquifer aquifer are constructed,and raising risk management strategies and methods.Based on the analysis of the aquifer failure modes and the risk factors of damage,comprehensive consideration was given to all possible factors affecting aquifer damage,three first-level indicators and 12 secondary evaluation indicators were selected to establish the evaluation index system of aquifer damage risk,including aquifer structural damage,aquifer level changes,and aquifer water quality deterioration.Cluster analysis,expert consultation,and statistical analysis methods were used to evaluate and grade all the selected indicators.The weights of all indicators were calculated and assigned using the analytic hierarchy process method and expert scoring method.Based on the principle and method of superposition index method,we established a comprehensive index model for aquifer damage risk assessment by using weighted summation method.Based on risk assessment theory,the risk management processes for mine closing was developed,including preliminary investigation,risk assessment and risk management,and risk prevention.And formulate the management model for the risk of aquifer destruction in view of the mine life cycle.(4)An example application for the risk assessment of pollution-driven aquifer damage in Hongshan-Zibo,Shandong province.Taking the Hongshan-Zibo closed pit mining area as an example,which is the typical case of aquifer water quality deterioration in closed pit coal mine.Through field experiments and isotope analysis methods,the causes of deterioration of water quality in the austilitic gray aquifer of the mining area were analyzed.The tracer experiments and isotope analysis showed that the water pollution in mine closure area is caused by the poor water supply wells in the mining area.Based on the comprehensive index model of aquifer damage risk assessment established in the thesis,the risk assessment of the aquifer destruction in the Hongshan-Zibo closed pit mining area was performed.The results showed that the comprehensive index of the damage risk of the Ordovician limestone karst aquifer in the Hongshan Mining Area was 7.9914,indicating that the aquifer damage risk level is high.On the basis of this,the management countermeasures for the risk of aquifer destruction in the Hongshan Mining Area was formulated,including the three stages of preliminary investigation,risk assessment and risk prevention and control.The specific measures to deal with the risk of aquifer destruction are discussed,including 1)Pre-control of production mines.2)Reasonable selection of mining methods and reserve of waterproof coal pillars.3)Blocking of crossstratapollution wells.4)Reasonable use of pit water and control mine water level.5)Post-treatment of groundwater pollution.The research results deepened the understanding of abandoned mine destruction to aquifer mechanism and modes.The aquifer destruction risk evaluation index system of abandoned mine was based on sufficiently.The abandoned mines aquifer destruction risk assessment and the risk management technology provided important technical support for the resource-exhausted mining groundwater environmental protection.