| At the influence of the"four high and one disturbance"environment,the gas pressure and gas content in deep mining coal seam are larger than that in shallow coal seam,resulting in fewer available protective layers.The traditional protective layer mining mode in coal seam encounters tremendous challenges.There is no suitable coal seam as the technical condition of protective layer mining.Thus,gas control has become an urgent problem to be solved in mine safety production.In view of the deep strong-outburst coal seam groups in Luling Mine cannot meet the technical conditions of traditional coal seam protective layer mining,a new regional gas control technology of mining soft rock reserved as the protective layer mining was put forward in this paper,which innovate the protective layer mining methods.Based on the co-mining of pressure-relief antireflective coal and gas in soft rock protective layer zone as the main research line,the soft rock protective layer mining of Luling Mine in Huaibei was taken as engineering background.This paper adopted a research idea of multi-disciplinary cross-permeability and a research method of multi-means comprehensive application,to develop the pressure-relief mechanical effect and application of soft rock protective layer mining in deep strong-outburst coal seam groups.Moreover,the pressure-relief mechanism and gas migration law in overburden fissure field were revealed for soft rock protective layer mining.In addition,a matching three-dimensional pressure-relief gas extraction technology system was formed,and the field industrial tests were performed.The finding verified the positive effect of the research results on guiding simultaneous extraction of deep coal and pressure-relief gas.The main achievements of this paper are as follows:(1)The composition,microstructure and pore characteristic of No.8 coal were studied in Luling Mine.It was found that the developments of micropore and keyhole are high,while the developments of mesopore and macropore are low for No.8 coal.Such a pore structure was one of the main factors that cause its strong outburst risk.In addition,the regional gas control scheme of?1 mining area was analyzed.The results showed that the No.10 coal within the coal seam groups cannot meet the conditions of protective layer mining.Thus,a new regional gas control method of mining soft rock reserved as the protective layer mining was put forward.The mudstone containing kaolinite clay was selected as the horizon of protective layer mining.By arguing from different aspects,it was feasible to choose the soft rock protective layer as the mining method.(2)The effect of different confining pressure,gas pressure and stress paths on mechanics and seepage characteristics of gassy coal mass by using the solid-gas coupling experiment device.The results showed that the confining pressure inhibited the deformation and failure of gassy coal mass,and the permeability decreased exponentially with the increase of confining pressure.Moreover,the weaken mechanism of filling gas on the mechanics of gassy coal mass were analyzed.By the simplifying the pressure-relief effect of the protective layer mining used as the stress path of loading axial compression and unloading confining pressure,the unloading confining pressure was found to cause the decreased strength of gassy coal mass and the post-yield permeability increased.In addition,it revealed the antireflective mechanism of the protective layer pressure-relief mining.(3)The related theoretical problems of soft rock protective layer mining were analyzed,to form five technical conditions that can be optimized for soft rock protective layer mining.The pressure-relief mechanics model of overburden strata and numerical computational mechanics model were established by using the theoretical analysis and numerical computation.The pressure-relief mechanism of soft rock protective layer mining was revealed,and the unit stress of protected coal seam lower than 0.5 times of original rock stress was used as the mining stress pressure-relief critical index.In addition,the influence law of different mining technical parameters(mining thickness,interlayer spacing,and working face length)on the pressure-relief effect of protected layer were obtained.Based on the results of numerical computation,the mining technology parameters of the working face first mined were also optimized for?11 soft rock protective layer in Luling Mine,including 2 m mining thickness,59 m layer spacing,and 105 m working face length.(4)The mining effect of soft rock protective layer mining was analyzed.Through the theoretical analysis and numerical calculation methods,the influence laws of different lithology on the stress environment in front of the stope were obtained.Moreover,the soft rock protective layer mining stress path was determined under the geological conditions of Luling Mine,and the mining-induced mechanics characteristics test was carried out.It was found that the pressure-relief effect of the soft rock protective layer mining can cause the dilatancy of coal and rock mass.In contrast to the coal seam protective layer mining method,the obtained pressure-relief antireflective degree was different for the different protective layer mining methods.By the qualitative analysis of the same geological conditions,the coal seam protective layer mining was more favorable to pressure-relief gas extraction after mining than the soft rock protective layer mining.(5)The working face of?11 soft rock protective layer in Luling Mine reserved as test background,the pressure-relief similar test model of soft rock protective layer was constructed.During the mining of soft rock protective layer,the development characteristics of fracture was analyzed,and the fracture development area of overburden was determined.Based on the key strata theory,the dynamic evolution process of overburden mining fissures was revealed by using the model of internal and external double-trapezoidal-platform zones.The formation and expansion process of fissures network after soft rock protective layer mining were quantitatively described by fractal theory.The fissure evolution process was revealed for soft rock protective layer mining.It was found that the pressure relief gas source after soft rock protective layer mining was the gas gush from adjacent layer.Based on the results of COMSOL numerical simulation,the pressure-relief gas migration law was revealed in overburden mining fissure field.(6)The pressure-relief gas extraction method was established for soft rock protective layer mining.By the integrated research methods such as field measurement,the growth altitude of the overburden“two belts”was judged after?11 soft rock protective layer mining under the geological condition of Luling Mine.Based on the surrounding roadway arrangement of?11 soft rock protective layer mining,the matching three-dimensional pressure-relief gas extraction technology system was formed.In addition,when soft rock protective layer mining combined with pressure-relief gas extraction,the maximum residual gas pressure and residual gas content of the protected layer are 0.25-0.35 MPa and 4.87-5.01 m~3/t,respectively.The mining practice showed that the gas control effect is remarkable.Figure[130]Table[23]References[212]. |
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