Effects of Moisture Content and Loading Rate on Coal Samples: Mechanical Properties and Failure Mechanisms

The water content of coal seams and the advance rate of the working face are controllable factors that significantly impact coal mine disasters such as rock bursts. This study combines laboratory experiments, energy theory analysis, and numerical simulations to examine the effects of water content and loading rate on the mechanical properties, energy evolution, microcrack distribution, and failure modes of coal samples. The results indicate that, at the microscale, tensile failure is the primary mode, while shear failure is secondary. Increasing water content reduces uniaxial compressive strength and Young’s modulus while increasing peak strain. Conversely, higher loading rates enhance strength and modulus while reducing peak strain. Additionally, higher water content inhibits the storage, release, and dissipation of elastic strain energy, whereas higher loading rates accelerate these processes. While water content has minimal effect on microcrack evolution, loading rate notably affects microcrack distribution by reducing their number and concentrating them around 90°, with shear cracks appearing near the sample ends. Furthermore, loading rate critically influences failure modes, transitioning from shear to tensile with increasing rates. These findings elucidate the interplay between water content, loading rate, and coal’s mechanical behavior. This enhanced understanding of rock mechanics and engineering geology provides critical insights for preventing coal mine disasters and ensuring safe production.