Research On The Coal Rock Failure And Methane Flow Laws Of Short-distance And Low Permeability Coal Seams Group Under The Effect Of Repeated Excavation

Mining of protected strata in coal mine is the most effective way to deal with coal-methane outburst and to improve the gas exploitation efficiency. Now, many researches have done in the mining process of protecting strata, these researches are including overlying rock movement, stress distribution, fissure zone evolution, stress relieve, flow law of methane in coal-rock body and fissure zone. However, few studies were concentrated on stress relieve, fissure zone evolution, flow law and methane-rich of multi closed coal seams. This paper aimed to study the relation between methane move law and overlying rock evolution in closed coal seam groups; study on fissure zone evolution and methane flow law under the influence of multi exploitations. The aim of this article is to help to develop the theory on protected strata mining. Based on the study of researchers all over the world about fissure zone evolution and methane flow law, some achievements are made:(1) By field studying, the existence situation of Sichuan Coal Ming Group Company was studied. The first coal seam of 2461 mining workface has no existence of methane and can be chosed as the first step of mining. The second and third strata are protected layer. Stress relieve method and Kaiser Effect method were used to study in-situ stress of original rock body. Therefore, stress field condition of original rock body was obtained.(2) Based on triaxial compression method under different routes in methane-containing coal specimen, coal-rock mechanics and seepage character of methane-containing coal was analyzed. Furthermore, equation between coal-rock specimen and volumetric strain under the influence of pressure adding and losing was established.(3)Based on the study of coal-rock failure and acoustic emission under the influence of mining, simulate fissure failure evolution after mining, fissure evolution and prepared notch coal-rock body axial strain equation was established. There exists index relationship between box-counting dimensions and axial strain from this equation.(4)Mechanical stress estimation was studied based on quantitative determination principle GSI and Hoek-Brown. Parameters influences by structural face and overlying rock mechanic parameters were derived. Therefore, numerical simulation and similar model experiment can be promoted in a scientific and accuracy way.(5) UDEC, FLAC3 D, similar model experiment were used to study stress field and fissure field’s evolution law of coal-rock mining.(6)Based on distribution law of overlying rock based on UDEC, theory of seepage mechanics, fluid mechanics, methane movement process got from COMSOL, methane overflow movement and rich law in mined zone and overlying rock was studied during mining.(7)Based on studies above, gas drainage technology in closed coal seam group mining was optimized. Furthermore, experiment was made in field and worked well, and methane exploitation efficiency was improved.