Quantitative characterization of failure evolution in raw coal and briquette based on acoustic emission

To quantitatively study the failure evolution characteristics of raw coal and briquette under triaxial compression, an acoustic emission (AE) experiment was conducted on both materials. The failure evolution of raw coal and briquette was quantitatively characterized based on AE energy. A constitutive model accurately describing the failure evolution process of raw coal and briquette was constructed. Using the Logistic function, a constitutive model of failure evolution under triaxial compression was constructed by combining failure mechanics theory with effective medium theory. The effects of parameters a and r on the failure evolution process and constitutive relationship were further analyzed. The study results show that the compaction stage of raw coal is more typical but shorter, exhibiting an obvious stress fallback characteristic. The briquette exhibits an obvious linear increase in stress before reaching peak stress, with no obvious residual strength. The failure evolution curves of raw coal based on AE energy characterization can be divided into three stages: initial almost no failure, slow start of failure, and sharp, steep increase in failure. In contrast, the failure evolution curves of briquette do not have obvious stage change characteristics. The failure evolution equations and the constitutive model obtained by fitting the Logistic function yielded correlation coefficients ranging from 0.9704 to 0.9987. This indicates that the Logistic function effectively express the characteristics of failure evolution and the failure deformation process based on AE energy characterization. The theoretical failure evolution curves of raw coal and briquette are jointly determined by parameters a and r. Parameters a and r significantly affect the ontological relationship of raw coal and have a smaller effect on that of briquette. The research results are of great theoretical significance for the stability evaluation of deep coal mining.