Triaxial creep damage-catastrophe instability characteristics and a nonlinear constitutive model of gas-bearing coal

Delayed coal and gas outbursts strongly relate to the transformation from creep deformation to rapid failure after extracting operations. However, the quantitative characterization of creep deformation and instability failure process of gas-bearing coal is insufficient. Hence, the long-term strain of coal samples under loading was measured under different axial, confining and gas pressures to analyse the creep damage, nonlinear deformation and catastrophic failure of the coal. It is found that the degree of creep deformation of the coal samples is closely related to the applied stress. When the applied stress is lower than the long-term strength of the samples, only decelerated and steady-state creep deformations can occur in the coal samples. The steady-state creep rate increases in the form of a power function with the creep time. However, accelerated creep failure occurs during long-term loading at a stress level exceeding the long-term strength of the sample. The gas pressure effects significantly change the creep characteristics of coal. The steady-state creep rate of coal without gas exponentially increases with increasing axial pressure, while that of gas-bearing coal linearly increases. The adsorption-induced expansion stress is proposed based on the principle of effective stress of porous media. A triaxial creep damage and catastrophic failure model for gas-bearing coal is constructed by considering the influences of damage accumulation on creep deformation. This model can quantitatively characterize the creep damage process of a coal mass under specific conditions.

Automated summary

This study aims to quantitatively characterize the creep deformation and instability failure process of gas-bearing coal. Experimental results show that the degree of creep deformation of coal samples is closely related to the applied stress, and accelerated creep failure occurs when the stress level exceeds the long-term strength of the sample. The gas pressure significantly affects the creep characteristics of coal, and a model considering damage accumulation can quantitatively characterize the creep damage process of coal.