Evolution of mechanical state and failure tendency of loaded outburst coal

The loaded outburst coal body is destroyed under the action of internal and external stresses, which induces coal and gas outburst(abbreviated as “outburst”). In order to further understand the coal body failure mode and mechanical action mechanism in the process, the coal body mechanical state, failure mode and tendency during the outburst process were analyzed based on the results of large-scale outburst physical simulation test. The research results show that in the early stage of outburst, the low-strength coal body is destroyed under the combined action of high gas pressure gradient and stress, causing gas pressure and stress to fall at the same time. In the middle stage of outburst, the coal body will once again show a certain bearing capacity, which will increase the stress and gas pressure. When the ultimate bearing capacity of coal body is reached, the coal body will be destroyed again, causing the stress and gas pressure to continue to decrease. In the later stage of outburst, the internal and external loads of the coal body cannot reach its destructive strength, resulting in a sharp rise in the stress and a slower rate of gas pressure decrease. The stress exerted by the gas on the coal body during the outburst process can be equivalent to the tensioning action, and the temperature change can be equivalent to the compression action on the coal body. During the outburst process, the effective stress concentration zone will repeatedly transfer to the deep part of coal body, and gradually return to the original position when the outburst is terminated. The effective stress value shows an intermittent decrease and increase process. With the continuous development of outburst, the central position of the stress circle of the outburst coal body in the stress relief zone and the abutment stress zone will periodically approach the origin of the diagram of, but the distance moved in each cycle will gradually decrease. In addition, the maximum principal stress direction of the coal body in the stress relief zone will change during the outburst process, and the principal stress difference in the later stage of outburst basically shows a continuous increase process. However, the principal stress difference in the abutment stress zone generally shows a process of first decreasing and then increasing. During the dynamic evolution process of compression and tension state, the outburst coal body shows an intermittent tendency to be destroyed and stable. The outburst coal in the stress relief zone and the abutment stress zone will enter another stable state immediately after experiencing a mechanical state that tends to fail.