Experimental investigation on acoustic emission and damage characteristics of dehydrated lignite in uniaxial compression test

The lignite would undergo dehydration cracking at normal temperature, which has an important impact on the stability of coal-rock slope in open-pit mine. In this paper, the uniaxial compression test of lignite with different dehydration times under normal temperature and humidity control conditions was carried out, and the mechanical parameters, deformation, AE characteristics, and macro–micro crack evolution law of dehydrated lignite were obtained. After that, the correlation between the porosity and mechanical parameters of rock samples based on dehydration deformation was discussed; meanwhile, according to the macro- and microcrack evolution characteristics of dehydrated lignite, the gradual change law of crack fractal dimension was elaborated. Finally, the initial damage of dehydrated lignite was defined by the relative porosity as a variable, and the damage constitutive model of lignite subjected to the dehydration and axial load was established. The results show the dehydration of lignite at normal temperature exactly causing the deterioration of mechanical properties, which also accompanied by the shrinkage deformation, the change of fractal dimension of macro–micro cracks, and the obvious AE activity in the compression test. In addition, the established damage constitutive model, considering the characteristics of compaction stage, is in good agreement with the experimental results. The research results are of great significance to reveal the instability and failure mechanism of lignite under the action of dehydration and stress.