Experimental investigation of mechanical characteristics and cracking behaviors of coal specimens with various fissure angles and water-bearing states

Abstract

The stability of coal pillars is of great significance for the safe and efficient operation of coal mines, and the water content and fissures affect the stability of coal pillars. In this study, uniaxial compression tests, acoustic emission (AE) analysis, and digital image correlation (DIC) analysis were carried out on coal specimens with various fissure angles and water-bearing states to investigate the effects of fissure angle and water content on the mechanical characteristics and cracking behavior of coal. The results showed that the mechanical parameters are closely related to the fissure angle and the water content. As the fissure angle increases from 15°to 75°, the peak strength initially decreases and then increases, while the elastic modulus increases linearly. The peak strength and elastic modulus of the fissured specimens decrease with increasing water content. The water content has little effect on the type of crack, but it aggravates the degree of crack propagation. As the angle increases, the degree of crack propagation and the number of cracks decrease, and the crack types are simpler. The AE b-value, full-field strain and stress level are all correlated, so they can reflect the characteristics of the failure process of fissured specimens. These results reveal the failure mechanism of fissured coal specimens with various fissure angles and water-bearing states, and provide a useful reference for reasonably evaluating the stability of coal pillars.