Study On Mining Technology Of Retaining Sand Proof Coal Pillar In 8₂101 Working Face

There are many thin bedrock points under the loose aquifer in China.Using the traditional theory,there is too much coal pressure,and the loss of coal resources is serious.The 8₂101 working face studied in this paper is located in the central mining area of Jiegou coal mine.The original design upper mining limit elevation is-330m,and 61.7?90.9m waterproof coal pillars are reserved,with a total of 3.687 million tons of coal.In order to further liberate a large amount of dead coal,ensure green,safe and efficient mining,and prolong the service life of the mine and the central mining area,it is very necessary to carry out the research on the mining technology of 8₂101 working face with sand proof coal pillars.Based on the research background of 8₂101 working face under the aquifer in Jiegou coal mine of Suzhou coal power plant,and on the basis of consulting the latest cutting-edge technology and research results of coal pillar reservation at home and abroad,this paper analyzes the water rich characteristics of 8₂101 working face aquifer by using the methods and means of on-site drilling sampling laboratory rock mechanical properties,hydraulic property test,overburden electrical measurement and imaging"two zones"development height,underground on-site detection,theoretical analysis and numerical simulation calculation The key technical problems such as mining grade of water body,overburden type and reasonable retention of sand control coal and rock pillar are systematically studied,and the following results are obtained:(1)8₂101 working face is located at the uppermost end of the central mining area,mainly mining 8 coal,with an inclination of 4?11°,with an average of 8°;The thickness is 2.13?3.16m,with an average of 2.65m.Based on the mining practice of 8₂10 working face underlying the contract mining area,it is comprehensively determined that the mining method of 8₂101 working face is comprehensive mechanized mining,and the full caving method is used to manage the roof.The upper limit elevation of the designed working face is-290m,and the minimum height of sand control coal pillar is 29.6m.(2)The mining of the working face is mainly threatened by the sandstone water in the roof and the four water bearing at the bottom of the loose layer.Among them,the sandstone fissure water has weak water yield and is a static reserve,which poses a small threat.The Cenozoic unconsolidated aquifer is composed of quaternary system and tertiary system,with a total thickness of 244.85?299.75m,the overlying"three partitions"thickness of 80.20?125.37m,large thickness and stable distribution.The thickness of"four aquifers"is 5.1?15.2m,the unit water inflow is 0.00016?0.04684L/(s·m),and the number of permeability coefficient is 0.00035?0.03521m/d.It belongs to the aquifer with weak water abundance.The mining grade of water body is class II,and sand proof coal pillar mining can be reserved.(3)The"two zones"of overburden failure were drilled in the underlying 8₂10 working face,and the rock samples were taken for lithology identification and physical and chemical test composition analysis.The depth of the bottom plate of the bedrock weathering zone and the lithology composition characteristics of the weathering zone were obtained;The engineering geological properties are further determined,and it is concluded that the montmorillonite in rock and soil samples has high content,the volume increases after water absorption,and the rock is easy to expand and collapse,which can close the cracks,and then play a good role in blocking water,inhibiting the development of collapse zone and fracture zone,and reducing the ability of water inrush and sand bursting.(4)The physical and mechanical properties,hydraulic properties and mineral composition of the overlying strata in the aeolian oxidation zone were analyzed and tested.According to the analysis and test results,within the range of 0?10.0m from the bedrock surface,the average compressive strength of weathered mudstone is 2.0MPa,belonging to extremely weak rock stratum;Within 10.1?20.0m from the bedrock surface,the average compressive strength of sandy mudstone and siltstone is 16.1MPa,which is a weak rock stratum.Based on the analysis of multiple drilling data in the central mining area,it is concluded that the overburden type of 8₂101 working face is soft?medium hard.(5)Two underground upward boreholes were designed and constructed in the air roadway of 8₂10 working face.A variety of sensors,electrodes and communication system devices were embedded in the overlying roof coal and rock mass of 8₂10 working face.The combined dynamic monitoring technology of high-resolution mine seismic wave and high-resolution resistivity method was comprehensively used to obtain the temporal and spatial failure evolution characteristics of overlying rock in the whole process of pre mining,during mining and post mining,that is,the maximum caving zone height after 8coal mining was 10.0?13.0m,The height of water fractured zone is 25.0?30.0m.According to the empirical formula of"Three Gorges"Mining Standard,FLAC3D numerical simulation results,multi factor fitting and engineering analogy of measured data,it is determined that the height of sand control coal and rock pillar to be reserved in 8₂101working face is 19.50?24.60m,which is less than 29.6m reserved in the design.Mining is feasible.(6)According to the mechanism of water inrush and sand burst in thin bedrock coal seam under aquifer,a series of safety control technical measures are formulated,such as first easy and then difficult,pre drainage of sandstone fissure water in mining fissures,strict control of mining height to prevent local pumping,early reinforcement of geological weak surface predicted by geophysical prospecting and so on.To sum up,from the perspective of water disaster prevention and control,8₂101working face is provided with conditions for safe mining.Figure[32]table[25]reference[86]...