In order to disclose the mechanism of coal and gas outburst the variation of stress and strain during coal damage is analyzed and theoretical equation of coal creep damage is proposed on basis of previous studies. According to theoretical equation of coal creep damage and by considering the roles of gas the theoretical creep equation of coal containing gas is established. By use of the theoretical creep equation of coal containing gas the creep fitting curve and relevant parameters is got. The research results show that the creep experiment results and theoretical model curve is consistent comparatively and the theoretical creep equation of coal containing gas can satisfactorily describe the mechanical properties of coal containing gas creep damage. The researches have important theoretical significance to the prevention of coal and gas outburst in coal mines.
Coal and gas outburst is that coal and gas suddenly burst out together from coal wall in a very short time during coal mining with strong dynamic effects and it is easy to trigger serious gas explosion which can cause significant casualties and property losses. The essence of coal and gas outburst is the rheological behavior of coal containing gas[1]. Therefore, it is great significance to study the mechanism of coal and gas outburst for coals containing gas creep characteristics. At present some researches have been done on the coal creep damage. Shugang Cao and Xuefu Xian[2,3] presented the generalized visco-elastoplasticity model to describe the creep properties of coal-rocks. Zhenhua Li[4] proposed the creep model of rock differ from that of coal. Four-parameters Burgess models could be used to describe the marble's creep properties berger, while generalized Maxwell model for coal's creep properties. Jianzhong Liu[5] used the Nishihara model to reflect the creep characteristics of coal-rock. Yongdong Jiang[6] adopted the elasto-viscoelastic-viscoplastic model to describe the creep properties of sandstone. Xuefu Xian[7] approached the five-substance visco-elastoplasticity-rheological model to discuss the creep characteristics of coal. Youping Zou[8] modified the generalized elastoplasticity model, and then the new model would better describe the three stages of creep deformation when coal-rock were under long-time stress. Shugang Cao and Jin Bian[9–11] improved the elasto-viscoelastic-viscoplastic model. Later, Jia Wei [12] raised the modified Nishihara model, which could give a excellent description of rock's accelerated creep stage. Jianping Zuo[13] put forward the rheological Nishihara model of deep rock under the thermodynamic process. Zhechao Wang and Qingzhong Fan[14–17] improved the Burgers model by adding damage variable and hardening function, and built the nonlinear creep equation of soft rock. It represented the three creep stages of soft rock in a uniform way without segmenting the creep curves with several steps or introducing Threshold value. Considering the inhomogeneity in the accelerated creep stage of coal, Xueqiu He[18] brought up the generalized K-B model, which gave the whole creep curves of coal. Yuchun Liu[19] established the nonlinear viscoelastic-plastic creep model by adding the rheological index. It could better reflect the three creep stages of rock, fully describing the accelerated creep characteristics.