Constitutive model of scale effects in uniaxial compression for gas-saturated coal

Gas coal has also scale-dependent mechanical properties like many other rock materials. It becomes significant to select its mechanics parameters for determining critical conditions of coal and gas outburst and other application in fields such as the underground excavation design of room and pillar. Based on the Weibull theory, a scale constitutive model in uniaxial compression for gas-saturated coal is raised. The scale-dependent variation of ultimate compression strength under different gas pressure is specifically studied. We discuss the effects of interfacial friction during testing and modify our model according to the testing results. Results show that, the ultimate compression strength of coal samples decreases as gas pressure and the ratio of height to diameter increase. The differences between theoretical and experimental results for ultimate compression strength mainly depend on the interfacial friction. The model reasonably agrees with the testing results after modifying, and it can reflect the law of changeable uniaxial compressive strength with the coal sample size and describe almost the whole process of uniaxial loading.