Study On Movement Law Of Overlying Rock Failure And Seepage Failure In Gubei Coal Mine

The Double-Huai(Huainan and Huaibei)coal-fields have huge coal reserves and have been an important energy base in China,but the thick Quaternary loose layer overlying the coal seam is a huge safety hazard when the coal seam is mined.In the early days of coal mining,the backwardness of theoretical research and technical equipment led to too conservative when leaving the safety coal rock pillar.With the depth of theoretical research and technical progress of mining equipment and roof management equipment,it is significant to reduce the original safety coal rock pillar and increase the upper limit of mining to improve the resource utilization rate and relieve the energy pressure,so it is necessary to carry out the research on the movement law of overburden damage and resistance to penetration damage.The paper investigates the overburden damage law and the risk of sudden water collapse under the influence of mining,taking the 1542(3)working face of Gu Bei coal mine as an example,and studies cutting-edge domestic and international papers on the permeability damage law of the "red layer".On the basis of this,FLAC3 D numerical simulation was constructed to simulate the mining process,and the height of hydraulic fracture zone and collapse zone were determined comprehensively.Based on the drilling data,simulation results,calculation formulae and the "three down" mining specification,the water mining level and the height of sandproof coal rock column of 1542(3)working face were determined and the risk of sand collapse was evaluated,and the following results were obtained.(1)The average coal thickness is 4.7m,the mining height is 4.5m,the recoverable reserve is 635,000 t,the average dip angle is 5°,the original design sandproof coal pillar height is 58.1m,after the study,it is determined that the safe coal rock pillar is 39.4m,and the value of waterproof coal pillar is reduced to 18.7m,saving coal mine resources 32,000 t,the coal mining method is comprehensive mechanized coal mining,the highest point roof elevation is-429.3m,the bedrock surface of its corresponding position The elevation is verified by drilling to be-389.9m.(2)In order to explore the overburden damage law,physical exploration works were carried out on the nearby working face 1552(3)with similar overburden conditions,and the overburden damage law was compared with that of working face 1542(3)after mining.Two boreholes with a total volume of117 m were arranged in the windrow of the working face,and electrodes were buried in the boreholes to detect the overburden damage characteristics below 12 m in height,reflecting the range of mining collapse zone;below 28 m in height,the electrode current ratio was around 0.7,reflecting the range of hydraulic fracture zone.(3)In order to explore the rock properties of the coal seam roof,a total of 7 boreholes were designed and constructed in the roof of the down-slope,with a total volume of 210 m,mainly for medium sandstone,fine sandstone,sandy mudstone and mudstone,according to the results of rock mechanical property testing,the rock nature above the working face is different,and the boreholes over the weathering zone are not leaking,the color is mostly earthy yellow,and the degree of weathering fragmentation is high,indicating that the weathering zone can effectively block the loose aquifer of the nascent boundary from The weathering zone can effectively block the infiltration and recharge of the bedrock by the loose aquifer of the Cenozoic.(4)According to the hydrological data,the lower aquifer is less covered on the working face of 1542(3),and the main source of sand collapse risk is the "red layer".The pumping test of the "red layer"was carried out through the borehole,and it was calculated that the unit water influx of the "red layer"was 0.00161L/(s.m),and the permeability coefficient was 0.015m/d;the "red layer "red layer"samples for granularity analysis experiments,fine grain content of about 27.5%,sand content of about67.57%,gravel content of about 4.93%,"red layer" to meet the soil grading inhomogeneity coefficient Cu ? 5,and most of the gradation curvature coefficient in line with the Cc = 1 3 conditions.The fractal dimension of the soil in the "red layer" is 2.45,and the fractal dimension of the pore space between fractal particles is 0.882,which belongs to the soil with good grading.Combined with the data of permeability coefficient,water influx,grading coefficient and fractal dimension,it reflects that the "red layer" in the study area is characterized by weak water-richness and poor permeability.According to the "three down" mining specification,the water body mining grade is II,and the water-conducting fracture zone is allowed to pass through the "red seam",but the collapse zone is not allowed to ripple through the "red seam",and the coal pillar set up is an anti-sand coal pillar.(5)The Mohr-Columb intrinsic model was selected to establish the model,and the deformation and damage characteristics of the overburden rock were deduced from the model,and the height of the collapse zone was 20 m and the height of the hydraulic fissure zone was 60m;the formula method calculated the height of the collapse zone as 20.18 m and the height of the hydraulic fissure zone as69.71m;by analogy with the collapse ratio of 4.2 in the adjacent working face,the height of the collapse zone was 18.9m and the fissure ratio was 11.86,resulting in the height of the hydraulic fissure zone as 53.37 m.The height of the water-conducting fissure zone is 53.37 m,and the height of the sand-proof coal column is 39.4m,and the height of the water-conducting fissure zone is greater than 40 m,which means that the water-conducting fissure zone penetrates the "red layer" and needs to be evaluated for anti-permeability damage.(6)To determine the hydraulic slope as the evaluation standard of the overlying rock layer against infiltration damage,the critical hydraulic slope formula at home and abroad is chosen to arrive at the critical hydraulic slope value of 1.48 for the "red layer";according to the actual conditions of the project,the actual hydraulic slope value is calculated to be 0.66,which is less than the critical hydraulic slope value,so there is no risk of sand collapse.Figure [26] table [27] reference [70]...