Brittleness evaluation of gas-bearing coal based on statistical damage constitution model and energy evolution mechanism

Abstract

Accurate assessment of coal brittleness is crucial in the design of coal seam drilling and underground coal mining operations. This study proposes a method for evaluating the brittleness of gas-bearing coal based on a statistical damage constitutive model and energy evolution mechanisms. Initially, integrating the principle of effective stress and the Hoek-Brown criterion, a statistical damage constitutive model for gas-bearing coal is established and validated through triaxial compression tests under different gas pressures to verify its accuracy and applicability. Subsequently, employing energy evolution mechanism, two energy characteristic parameters (elastic energy proportion and dissipated energy proportion) are analyzed. Based on the damage stress thresholds, the damage evolution characteristics of gas-bearing coal were explored. Finally, by integrating energy characteristic parameters with damage parameters, a novel brittleness index is proposed. The results demonstrate that the theoretical curves derived from the statistical damage constitutive model closely align with the test curves, accurately reflecting the stress-strain characteristics of gas-bearing coal and revealing the stress drop and softening characteristics of coal in the post-peak stage. The shape parameter and scale parameter represent the brittleness and macroscopic strength of the coal, respectively. As gas pressure increases from 1 to 5 MPa, the shape parameter and the scale parameter decrease by 22.18% and 60.45%, respectively, indicating a reduction in both brittleness and strength of the coal. Parameters such as maximum damage rate and peak elastic energy storage limit positively correlate with coal brittleness. The brittleness index effectively captures the brittleness characteristics and reveals a decrease in brittleness and an increase in sensitivity to plastic deformation under higher gas pressure conditions.

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