Oxidation characteristics of unloaded coal under different initial stress

To study the oxidation characteristics of coal unloaded under different initial stress,in this paper,a compara- tive study on the micro-oxidation characteristics of the raw coal samples with easy spontaneous combustion and the un- loaded coal samples under different initial stress was carried out by using the temperature-programmed experiment,the three axial creep test of coal rock and the mercury injection experiment. The findings indicate that in the macroscopic aspects,the unloaded coal under different initial stresses is easier to oxidize than the raw coal samples,the CO produc- tion-strain curve of the experimental coal samples is similar to the axial stress-strain curve and the coal oxidation capacity changes in the “Hump” with the initial stress,When the initial stress reaches 15 MPa and the coal rock is in the stage of plastic deformation crack propagation,the contact ability of the coal sample after unloaded is significantly enhanced. When the initial stress reaches 25 MPa,the coal sample is in the stage of strain softening,the contact ability of the coal sample after unloaded is the strongest. The characteristic temperature of the experimental coal samples is a- head of the raw coal samples,that is,the period of spontaneous combustion is getting earlier. In the micro aspects,the coal total pore volume and pore size distribution collaboratively restrict oxidation reaction process,the initial stress makes the pore volume and pore size of the experimental coal samples increases,the small pore and micropore is the main contribution of O2 and coal matrix oxidation reaction area. The variation trend of volume of small pore micropore, and specific surface area with the initial stress is the same as the oxidative capacity of the experimental coal with the initial stress. Based on the experimental results,with increasing depth,the in-situ stress increased,the danger degree of coal oxidation will increase after mining unloaded. When the stress in coal seam reaches a certain critical value with the burial depth,mining coal oxidation degree of risk will be reduced after unloaded. For the same level of mining,the spontaneous combustion of coal is easier to occur when the stress is relative concentration,the difficulty degree of coal mining at the initial stage of oxidation is related to the strength of coal and the occurrence of stress.