Study on damage and failure characteristics of loaded gas‐bearing rock–coal–rock combination structures

Abstract

The essence of the outburst–rock burst compound dynamic disaster is the disaster behavior of the “gas‐coal‐surrounding rock” system under the comprehensive action of the stress field and the seepage field. Based on the geological occurrence characteristics of coal and rock in the roof, coal, and floor, this study combined experimental research and theoretical analysis to explore the effects of confining pressure, gas pressure, and axial loading rate on the mechanical behavior of gas‐bearing rock–coal–rock combination structures (“RCR combination”). The results show that both decreasing gas pressure and increasing confining pressure can improve the deformation capacity and bearing capacity of the RCR combination. When the gas pressure decreases from 1.5 to 0.5 MPa and the confining pressure increases from 3 to 9 MPa, the peak stress of the RCR combination increases by 15.83% and 184.02%, respectively. On increasing the axial loading rate, the peak stress of the RCR combination first increases and then decreases, and the elastic modulus continues to decrease. There is a good correspondence between stress and acoustic emission counts (AE), which can be used as a predictive index for judging rock fracture instability. Compared with rock, coal exerts much greater influence on the mechanical strength of the RCR combination. The theoretical analysis shows that the parameters m and F0 mainly affect the peak stress of the RCR combination, and the speed of stress reduction after the peak of the RCR combination is influenced by the parameter m. The coal elastic modulus exerts greater influence on the bearing capacity of the RCR combination than the rock elastic modulus. When the elastic modulus of rocks increases from 10 to 25 GPa and that of coal increases from 2 to 5 GPa, the peak stress of the RCR combination increases by 9.87% and 8.97%, respectively.