Mining Mode And Engineering Application For “Coal-Water” Dual-resources Mine Under The Threat Of Roof Water Hazard

China's coal reserves are among the best in the world.As a big consumer of coal,China is also the largest producer of raw coal in the world.However,there are many hydrogeological conditions in our country,and the water filling condition is very complicated.Water disaster has a high proportion of heavy accidents in coal mines,and has become the second biggest killer after gas accidents.According to the statistical data,the coal mine drainage in China amounted to 7.17 billion m3.Because of the high cost caused by large amount of drainage,the coal mine enterprises are overburdened.In addition,a large amount of drainage results in the continuous decline of the groundwater table and the tension of production and living water in the coal mining area and the surrounding areas.If the mine water is directly discharged,it will causes pollution of surface water and groundwater.Besides,it also makes ecological environment in mining area become more deteriorate.What is more serious is that the per captia of water resource in China is only one fourth of per capital value of worldwide,and the distribution is uneven across our country.The coal resource and water resource show reverse distribution in China,and most of the coal mines mainly distribute in the North China and Northwest China,of which 70% of mines are short of water,and 40% of mines are seriously lack of water.Therefore,most coal mines in China suffer from the threat of roof water hazards,and there are also contradictions and conflicts among the three aspects of drainage,water supply and ecological environment protection in coal mining areas.Under the engineering background of Xingyuan coal mine and Jinjie coal mine,the paper mainly focuses on the following contents based on the conflict and contradiction among the green development for coal resource,the water resource supply and the protection of ecological environment,and the main results are as follows:(1)This paper discussed geological factor,mining factor and time factor which have impact on development height of water-flowing fractured zone.The mining thickness and overburden property are the main controlling factors.According to 32 sample data,the author built a RBF neural network model that could accurately predict the development height of overburden water-flowing fractured zone of fully mechanized caving mining.The results show that the predicted values of 7 samples are very close to the real value.Therefore,the model based the RBF neural network enable to correctly predict the development height of water-flowing fractured zone in fully mechanized caving mining face.(2)The author proposed the concept and connotation of “Coal-Water” dual-resources mine and then developed the techniques and methods for “Coal-Water” dual-resources mine.i.The concept of “Coal-Water” dual-resources mine is the mining techniques and methods which aim to realize the target of control of water inrush,protection and utilization of water resource and protection of ecological environment and make the trinity achieve the best.ii.The connotation of “Coal-Water” dual-resources mine is that: we regard groundwater as resources when mining coal resources.The negative effect which caused by “disaster attribute” could be eliminated by using reasonable mining techniques.By utilization of mine water resource,we are supposed to exploit positive effect of “resources attribute” and avoid to disturb and damage the water aquifer structure,which can develop both coal and water resources,protect ecological environment and realize sustainable development in mining area.And eventually we can reach the Win-Win goal of water harards control,protection and utilization of water resource and improvement of ecological environment in mining area.iii.The author proposed the techniques and methods of “Coal-Water” dual-resources mine by optimization of mining method,parameters and mining technology,optimization and combination of multinity,underground separation discharge of clean water and sewage,intervention of hydrogeological condition,filling mining based on the specific filling-water hydrogeological conditions of main mineable coal seams.(3)Efficient longwall mining method ignores the impact on water resources and ecological environment,so the enterprise cost is incomplete and enterprise benefit is at the cost of environment.Based on the full cost theory,longwall mining method is high efficiency but low benefit,while shortwall mining method and limited mining and intermittent slicing mining are high benefit but low efficiency,where the enterprise pursues sustainable high-benefit.Mining engineering is a comprehensive work to coordinate safety,resources,ecology and the environment,coal mining is only one of the subsystems.Longwall fully-mechanized coal mining or fully-mechanized top coal caving method for thick coal seam pursue the goal of high yield,high efficiency,high recovery rate,but does not consider post-mining environmental negative effects.Based on the system theory,the ultimate pursuit of coal enterprises is the overall maximize benefit of the entire mining engineering system,rather than the best efficiency of subsystem.When the longwall mining technology could not protect the underground water,it would be a good way to using high-benefit shortwall mechanized coal mining method(such as,strip mining,room and pillar mining)or limited mining or intermittent slicing mining,in some geological conditions.(4)The mining mode of “Coal-Water” dual-resources mine: under the guidance of the connotation and concept of “Coal-Water” dual-resources mine,the mining mode is a optimization and combination of mining method and water-preventing technology and control measures,to establish method sets for solving water-protecting coal mining,reasonable utilization of water resouces and ecological environment protection.(5)Mining mode is consist of two parts,the water prevention and control engineering measures and the mining technology.The former adopts prevention,water cutoff,dewatering,drainage,and interception to realize the water body isolation,control,unwatering,transformation.The latter includes comprehensive mechanized coal mining method/comprehensive mechanized coal mining method,limited mining shortwall mechanized mining and filling mining.This paper constructs 8 kinds of “Coal-Water” dual-resources mining modes,these are,“leaving a safe coal pillar+ comprehensive mechanized coal mining method/comprehensive mechanized coal mining method” mode,“leaving a safe coal pillar + limited height mining/stratified intermittent mining” mode,“mining and dewatering + underground separation discharge of clean water and sewage + mine drainage quality-divided utilization + comprehensive mechanized coal mining method/comprehensive mechanized coal mining method” mode,“advanced drainage + underground separation discharge of clean water and sewage + optimization and combination of multinity + comprehensive mechanized coal mining method/comprehensive mechanized coal mining method” mode,“intervention of hydrogeological condition + advanced drainage + underground separation discharge of clean water and sewage + optimization and combination of multinity + comprehensive mechanized coal mining method/comprehensive mechanized coal mining method” mode,“natural hydrogeological conditions + shortwall mechanized mining” mode,and “natural hydrogeological conditions + filling mining” mode.(6)Taking the thin bedrock area of No.4 mining area in Xingyuan coal mine as engineering background,this paper analyzed the characteristics of the aquifer at the bottom of the Cenozoic loose layer,and drawn the thickness isoline of bedrock by using Surfer software,and proposed the different mining mode of "Coal-Water" dual-resources mine in thin bedrock area,and investigated the mining and pillar width and overburden moving law of shortwall mechanized mining.i.Based on aquifer thickness,clay layer ratio in the aquifer,drilling unit water inflow and permeability coefficient,this paper established the grade evaluation model of water abundance of aquifer by using extension matter-element model and Arcgis software.The weight of each index was determined by analytic hierarchy process method(AHP).According to the grade evaluation results,it was concluded that the overall water abundance grade of the aquifer at the bottom of the Cenozoic loose layer is medium to strong and the water abundance grade is very strong in the southwest and eastern part of the thin bedrock area.ii.The plastic zone at the edge of coal pillar gradually yield under the influence of mining,which unilateral yield zone width of coal pillar is 2.2~2.6m.If the width of coal pillar is less than or equal to the sum of the bilateral yield zone width,the yield zone would run through the whole coal pillar after the next bordroom was mined.The vertical stress of the coal pillar shown “arch-shaped” state.iii.The stability evaluation system of coal pillar was put forward,including: firstly,the width between coal pillar yield zone and coal pillar should be matched to avoid the emergence of critical coal pillar,otherwise it will lead to the high stress concentration of coal pillar,and avoid causing the sudden instability of coal pillar,which is not conducive to the formation of the pressure arch;secondly,bed separation is produced in the deformation process of overlying strata containing a main key stratum,which form the stable pressure arch supporting weight of overlying rock;thirdly,the yield coal pillar has enough strength to support the overlying strata weight under the pressure arch,which should be the maximum stable pressure arch after the whole section is extracted.iv.According to the flow direction of aquifer under the lower part of the Quaternary in mine field,the adopted mode of “intervention of hydrogeological condition + advanced drainage + comprehensive mechanized coal mining method/comprehensive mechanized coal mining method” is a feasible technical scheme.That is,firstly,curtain grouting was implemented in the northwest boundary of the mine field,which can pre-intercept groundwater recharge.If the mode of "natural hydrogeological conditions + shortwall mechanized mining " is applied,the schemes of mining width 5m with pillar width 4m,mining width 5 with pillar width 5,and mining width 6m with pillar 5m have a reliable safety factor.(7)Shallow coal seam,thin bedrock,and strong rich loose pore aquifer,weathering bedrock fissure aquifer or burning rock aquifer,are the essential condition of water inrush and sand inrush of Jurassic Coalfield in North Shaanxi Province.Based on the background of Jinjie coal mine,the paper discussed the relationship between coal seam and water-resisting layer and aquifer in dangerous area of water and sand inrush,and discusses the feasibility of “Coal-Water” dual-resources mining mode.The rule of water-flowing fractured zone of overlying rock strata with different coal mining methods was also studied by using FLAC3 D software in this paper.i.The water controlling and sand controlling capacity of the rock(soil)layer between the coal seam and the aquifer becomes weakened or even disappeared induced-by mining in the thin bedrock area where the Baode Formation of Neogene and Lishi Formation of Quaternary missed.ii.Based on the numerical simulation results,the relationship between the height of water-flowing fractured zone and the mining width is Hli=0.01995x2-1.08809x+24.36,Hli is the height of water-flowing fractured zone,m,x is the mining width(25?x?70),m.When 10<x<25,the the height of water-flowing fractured zone is 7.1m.When 5?x?10,the overlying strata form a structure similar to the "beam",the immediate roof can temporarily stabilized for a few days,after caved similar to the formation of a caving belt.iii.The height of water-flowing fractured zone are 34.4m?16.2m?9.6m?7.1m,when the elastic modulus of filling material are 0.05GPa?0.1GPa?0.2GPa?0.4GPa,respectively.The fitting relation is Hli = Ef-0.5025(Hli is the height of water-flowing fractured zone,m,Ef is the elastic modulus of filling material,GPa).When the elastic modulus is minor value,there are two types of cracks in the overburden,that is,the upstream fissures and the downstream fissures,all because the tensile stress exceeds the maximum tensile strength of the rock strata.