Experimental study on dynamic failure characteristics of coal and rock under different loading rates

Airside roadway is known for being the primary location where coal or rock dynamical disasters occur. Verifing the dynamic manifestation and damage characteristics of the coal-rock system in air-side roadway during mining operations is crucial for ensuring safe and efficient production in mining areas. Using a high-frequency vibration acquisition and in-hole imaging three-axis dynamic-static load test system, the true triaxial single-side hanging experiments were performed on coal-rock samples under different loading rates to reveal the influence mechanism of loading rate on coal-rock dynamic failure. The research findings are summarized as follows: 1) Under different loading rates, the damage and failure of the coal-rock system progressively shift from the hanging face to deeper regions. At lower loading rates, the coal-rock system undergoes adaptive adjustments, and its failure characteristics and acoustic emission signals exhibit clear precursor patterns. Prior to reaching bearing instability, the coal-rock on the hanging side experiences tension expansion, leading to the outflow of coal dust particles from deeper regions. Acoustic emission signals persist in a state of “high frequency, high energy.” However, as the loading rate increases, crack development is suppressed, resulting in a sudden increase in stress at the tip of primary cracks. Consequently, the hanging coal-rock layer fractures and ejects, generating a significant amount of kinetic energy from local particle ejection. The acoustic emission signals transition into a state of “high frequency, low energy” without exhibiting any precursor information. 2) Tensile failure predominates on the hanging face of the coal-rock. With an increase in the loading rate, the failure pattern in the deeper coal-rock transitions from flexural tensile failure to a combination of tensile-shear failure and shear failure. 3) At lower loading rates, the coal-rock system exhibits well-developed cracks, weakened strength, and substantial energy release. However, as the loading rate increases, the peak strength, degree of fragmentation, ejection mass, and kinetic energy of the coal-rock system all experience significant growth, resulting in a more rapid dynamic manifestation. The increase in loading rate serves as a positive stimulus for the dynamic failure of coal-rock. © 2023 China University of Mining and Technology. All rights reserved.