关键词: 加载速率, 含水率, 声发射, 分形维数, SEM

Abstract: To investigate the influence of mining rate on the development of fracture structures in water-bearing coal after implementing water injection for rockburst prevention in the working face, uniaxial compression tests at various loading rates were conducted on coal samples with different moisture contents (Dr, Se, Sa). The mechanical properties and acoustic emission characteristics of these water-bearing coal samples were analyzed under different loading rates. Using fractal dimension and scanning electron microscope (SEM), the fracture mechanism of the microstructure of these coal samples was revealed. The results show that an increase in water content weakens the peak strength of coal samples, induces a delay in acoustic emission ringing count and energy signals, and the lubrication effect of water reduces the proportion of tensile cracks in coal samples. Particle hydration is the primary reason for the reduction in brittleness and the alteration of fracture characteristics, with fractures transitioning from brittle to plastic and from transgranular to intergranular. An increase in loading rate inhibits the full propagation of internal cracks in coal samples, enhances their peak strength and elastic modulus, and reduces cumulative damage during the initial loading stage, resulting in acoustic emission ringing counts and energy signals gradually approaching their peak values. The cumulative energy of acoustic emissions shifts from a pattern of long-term slow increase followed by short-term sudden increase to a pattern of short-term slow increase followed by short-term sudden increase. The faster the loading rate, the smaller the slope of the k-value on the lg(M_Leq/M)-lgL_eq curve (where M is the total mass of the fragments, M_Leq is the mass of fragments smaller than the equivalent side length L_eq), the larger the fractal dimension, the less fragmented the coal sample, and the brittleness of the coal sample is enhanced, altering its fracture morphology. The research results can provide a solid experimental basis for rapid, safe, and efficient production in working faces.

Key words: loading rate, moisture content, acoustic emission, fractal dimension, SEM