Rheology mechanism and constitutive equation based on meso-damage factor are studied for the whole rheology process of coal-rock using rock rheology apparatus in uniaxial compression. A new rheology experimental apparatus is set up, including rheology loading system and computerized tomography scanning system, which can gain meso-damage image of coal-rock during coal-rock creep. Rheology experimental work shows that there are three typical creep stages: instantaneous creep stage I, stable development of deformation stage II, and accelerated deformation to failure stage III. CT image changes taken during the experiment indicate the three creep stages as well. Based on the results of rheology experiment obtained and processed CT images, a creep constitutive equation is derived using damage factor. The study lays the theoretical foundation for understanding the mechanical behavior of coal-rock in response to dynamic phenomena in underground coal mines.
Coal-and-gas outburst constitutes one of the most severe natural disasters confronted by coal mines. Its delay in outburst manifests rheological characteristics of coal-rock. Many scholars conducted extensive studies on the time effect of coal-rock rheological outburst [1,2]. Xueqiu He et al. came up with coal-rock rheology-mutation theory, taking into account the rheological properties of coal [3,4]. Having investigated the creep damage properties of coal-rock, Shugang Cao, Xuefu Xian et al. put forward generalized visco-elasto-plastic model and a method monitoring deviatoric stress of creep damage . Ruanjiang Chen et al. proposed two nonlinear compound rheology models for creep body and fissure plastic body . Vyalov in 1986 brought forward modified Bingham law taking into consideration the nonlinear relationship between rheological rate and stress, namely, the coefficient of viscosity of "viscous pot" in Bingham model is not a constant, but a variable instead. The coefficient is an empirical expression of time and stress level . These models are helpful in determining the rheological properties of coal-rock, and deriving the general characteristic curve of rheology. However, most of these models started from stress-strain change, and most of the parameters can be inversely obtained only according to regression curve. Only a few of them analyze creep process in forward direction from the quantified damage factor within coal-rock. Experiments have proved that, rock mass parameters, such as elastic modulus, strength and viscosity, generally decrease with time. In the meantime, it is also a deterioration process of material properties. To study the deterioration mechanical behavior of rock by rheological damage mechanical approach, internal variable (damage factor) can be introduced to characterize the deterioration of rock mechanical properties, while the damage evolution of rock mass actually reflects the time-dependent weakening of some rheological mechanical parameters. Considering the rheological rock mechanical parameters unsteady will more directly and objectively reflect the nonlinear and viscous time effect characteristics of rock mass. In this paper, CT scanning experiment was performed to reveal the meso-damage change law within coal-rock mass in its rheological process, and the constitutive model for coal-rock rheology considering meso-damage factor was studied. Fit was made based on the calculation results from the model and the experimental results.