Energy Release Law Of Tectonic Coal Under The Unloading Pressure And Its Influence On Outburst Development

In the process of coal mining,tectonic coal is mostly accompanied by abnormal occurrence of stress and gas,with the characteristics of high energy storage and low instability conditions,which is the key prevention and control area of outburst disasters in China.At present,there is a lack of research on the mechanisms of stress and gas energy release during the development of tectonic coal outburst.The bottleneck is the coupling release mechanism of stress energy（deformation energy）and gas energy,which leads to disasters.In this thesis,the tectonic coal of 13th Ping Coal Mine is selected as the research object.The effects of unloading pressure on gas expansion energy release of coal are analyzed from microscopic point of view by means of spectral experiment and gas adsorption experiment.The effect of pulverization on the adsorption/desorption characteristics of coal samples with different particle sizes were analyzed using the adsorption/desorption experimental apparatus,and the effect of unloading pressure on the desorption/diffusion characteristics of tectonic coals was investigated.Based on the unloading instability characteristics and desorption kinetics experiments,the order of magnitude relationship between deformation energy and gas expansion energy was calculated,and the indirect control mechanism of deformation energy release on gas expansion energy release was obtained,and the influence mechanism of deformation energy release and gas expansion energy release on the continuous development of outburst was revealed.The main conclusions are as follows:（1）The results of XRD,Raman spectroscopy and FTIR show that the influence of confining pressure on the long-term evolution of microcrystalline structure and aromatization degree of coal can be ignored.The quantitative indexes of aromaticity（fa）,stacking degree（L_c）,aromatic layer number(N_ave),peak position difference（G-D₁）,aromatic layer distance(d₀₀₂)and peak intensity ratio(I_D1/I_G1)of coal have little difference before and after confining pressure.（2）N₂/CO₂ adsorption method showed that increasing the unloading pressure rate was beneficial to pore development,promoting gas desorption and diffusion,and creating conditions for gas expansion energy accumulation.When the unloading pressure rate increased from 0.01MPa/s to 0.1MPa/s,the pore volume of micropores,macropores and total pore volume of coal samples increased by 10.16%～10.58%,6.78%～8.92%and 8.78%～9.32%respectively;the specific surface area of micropores,macropores and total specific surface area increased by 9.69%～12.19%,12.25%～22.10%and 9.56%～11.98%respectively.（3）The speed of initial diffusion（?p）of coal sample is 15.70 mm Hg,indicating a high capacity for gas release.The research on desorption/diffusion characteristics of tectonic coal under different unloading pressure has been carried out.The results show that the unloading pressure rate,the higher the gas desorption capacity,the higher the initial gas desorption volume,the gas desorption rate and the effective diffusion coefficient（D_e）;the opposite result is obtained by increasing the confining pressure.This is mainly due to the influence of pore structure.The larger the unloading pressure rate,the more small-grained coal samples are unloaded and the more developed pore structure with>2 nm pore size,which promotes gas desorption and diffusion,is conducive to gas expansion energy accumulation,and promotes outburst development.The larger the confining pressure,the smaller the proportion of small size coal samples,which is not conducive to pore development and reduces the gas desorption and diffusion capacity.（4）Based on the group’s previous research results on the stress release characteristics of tectonic coal,and combined with the experimental content of this thesis,quantitative characterization and calculation of the stress energy and gas expansion energy of coal under different unloading pressure.Results show that the larger the unloading pressure rate is,the larger the gas expansion energy is.The larger the confining pressure,the smaller the gas expansion energy.Experimental results show that gas expansion energy ranges from 100 KJ/t to 650 KJ/t.Coal deformation energy under three sets of confining pressures is 25.86 KJ/t,60.24 KJ/t and 140.33 KJ/t respectively.It is concluded from experimental research and theoretical derivation that in actual outburst,deformation energy and gas expansion energy have the same order of magnitude,which is about 10²-10³ KJ/t.And the outburst energy relationship is verified by the case of Pingdingshan outburst accident.（5）The study shows that the dynamic unloading will disrupt the stress balance inside the coal,prompting the release of deformation energy.The destabilization of coal to occur in the expansion phenomenon cause the release of gas expansion energy.The deformation energy and gas expansion energy can provide the crushing energy and transporting energy needed to transport the coal in the outburst process.At the outburst development stage,coal is spewed out at a high speed,which leads to the aggravation of pulverization,increases pore volume and specific surface area,promotes gas desorption,and enables coal mass to be cast farther away at a faster speed.At the same time,the coal behind the outburst experiences rapid unloading pressure,which is conducive to the accumulation of gas expansion energy and creates conditions for the continuous development of outburst.The thesis contains 57 figures,17 tables and 160 references.