Feasibility Study On Mining Of 7₂11 Working Face Under Aquifer In Jiegou Coal Mine

The amount of thin bedrock coal seam under loose water-bearing layer in China is large and extensive,and according to the provisions of"Water Control Rules for Coal Mines"and the calculation of traditional methods,the size of coal rock pillar left is large,pressing more coal,and the loss of coal resources is serious.The 7₂11 working face studied in the paper is located in the central mining area of Kegou mine,with the original design upper mining elevation of-330m,leaving a waterproof coal rock pillar of 61.7～90.9m,pressing 1,087,000t of coal.In order to further liberate the amount of waterproof coal left in the original design,ensure safe,green and efficient mining,and extend the service life of the central mining area,it is necessary to carry out the feasibility study of mining 7₂11working face under the water-bearing layer.It is very necessary to carry out the feasibility study of 7₂11 working face under the water-bearing layer.Based on the latest cutting-edge technology and research results,the paper analyzed the reduced waterproof coal pillar situation in the mined workings,designed and constructed pre-mining hydrological inspection holes,used on-site drilling samples,laboratory rock mechanical properties,hydraulic performance tests,theoretical analysis and numerical Using methods and means such as field drilling samples,laboratory rock mechanical properties,hydraulic performance tests,theoretical analysis and numerical simulation calculations,a systematic study was conducted on key technical issues such as water-rich characteristics of the 7₂11 working face,water body mining grade,overlying rock type,collapse zone,water-conducting fracture zone development characteristics,coal rock column type,etc.The following results were obtained.（1）7₂11 working face is located in the uppermost part of the central mining area,the main mining 72 coal,dip angle 5～10°,average 6°;thickness 2.13～2.98m,average 2.3m,combined with the mining practice of 7212 working face under the same mining area,comprehensive determine 7₂11 working face coal mining method for comprehensive mechanized mining,using all collapse method to manage the roof.The upper mining elevation of the working face is designed to be-300m,and the height of the minimum anti-sand safety coal rock column is 44.2m.（2）The working face mining is mainly threatened by the sandstone water on the roof and the four water-bearing water at the bottom of the loose layer,among which the sandstone fissure water is weakly water-rich and is static storage,so the threat is small.Neoproterozoic loose aquifer consists of the fourth system and the third system,its total thickness is 244.85～299.75m,the overlying"three compartments"thickness is 80.20～126.37m,the thickness is large,stable distribution,"four containing"thickness is 5.1～15.2m.15.2m,the unit gushing water is 0.00016～0.046034L/（s·m）,the permeability coefficient is 0.00039～0.03098m/d,belongs to the water-rich weak aquifer,the water body mining grade is II,can be left to prevent sand coal pillar mining,and the lithology of"four containing"is clay with a small amount of The clay with small amount of gravel,with more plasticity of fine particles,is easy to be bridged after mining by continuous compaction of overlying rocks,showing solidification or semi-solidification,so it is not easy to appear water gushing sand phenomenon when the coal seam is retrieved.（3）Analysis and testing of the physical and mechanical properties,hydraulic properties and mineral composition of the overburden rock and wind oxidation zone.According to the analysis and test results,the average compressive strength of weathered mudstone is 2.0MPa within the range of 0-10.0m from the bedrock surface,which is a very weak rock layer;the average compressive strength of sandy mudstone and siltstone is16.1MPa within the range of 10.1-20.0m from the bedrock surface,which is a weak rock layer.Combined with the analysis of several boreholes in the central mining area,it is concluded that the overburden rock type of 7₂11 working face is soft to medium hard type,and the regenerative water barrier performance is good after mining damage.（4）According to the"Three Undergrounds"coal mining specification,the mining grade of 7₂11 working face is II,and the overburden rock type is medium hard,and the collapse zone is strictly prohibited to develop into the range of"Four Inclusions"during the mining process,so it is necessary to set up the anti-sand safety pillar.The maximum height of the sandproof safety pillar is 21.9m,the safety pillar is 24.6m calculated according to the engineering analogy method,the safety pillar is 19.5m calculated according to the numerical simulation analysis method,the actual height of the safety pillar is 44.2m,which is 19.6m larger than the height of the engineering analogy,and 22.3m more than the requirement of the specification.It is feasible to increase the design upper recovery elevation of the working face to-300m.（5）In view of the mechanism of sudden water collapse in the thin bedrock coal seam under the water-bearing layer,a series of safety control technical measures were formulated,such as first easy and then difficult,pre-emptive release of sandstone fracture water from the mining fissure,strict control of mining height to prevent local pumping,and early reinforcement of the geologically weak surface predicted by physical exploration.In summary,from the perspective of water damage prevention and control,the 7₂11working face has the conditions for safe mining,and it is feasible to reduce the water-proof coal pillar and leave the sand-proof coal pillar for mining.At the completion of the thesis,the working face has been safely re-mined,indicating that the research results of the thesis have been verified by engineering practice and have good application prospects.Figure[53]Table[23]reference[71]...