Energy Absorption Characteristics of Granular Buffer Layer and Dynamic Disaster Control in Coal under Impact Load

To address critical challenges associated with dynamic disasters such as rockbursts in deep underground mining and to elucidate the energy absorption mechanisms of granular geological materials, a full-scale numerical model of the split Hopkinson pressure bar (SHPB) system is developed using a coupled discrete element-finite difference method. The reliability of the proposed numerical model is validated against laboratory measurements in terms of stress wave propagation, dynamic stress equilibrium, and dynamic stress–strain responses. A systematic parametric study is conducted to quantify the effects of buffer layer configurations and incident stress wave amplitudes on the dynamic fracture behavior and energy dissipation characteristics of the bituminous coal specimens. The results indicate that buffer layer thickness, interfacial friction coefficient, and peak incident stress wave amplitude significantly influence the dynamic mechanical response, damage evolution, and energy dissipation behavior of the coal mass. An increase in the buffer layer thickness and interfacial friction coefficient leads to a pronounced reduction in peak dynamic strength and failure strain. Concurrently, the failure mode transitions from a through-going macroscopic fracture to localized microdamage, accompanied by a reduction in the total number of microcracks, which become predominantly shear-dominated. Energy dissipation is primarily governed by the granular buffer layer, which attenuates impact energy through multiple mechanisms, including interparticle sliding friction, pore compaction, and the strengthening of intergranular force chains. These processes substantially reduce the energy available for the formation of the new fracture surfaces. Under identical incident stress wave conditions, coal specimens equipped with a granular buffer layer exhibit significantly lower dynamic strength and deformability compared to those without a buffering protection. The buffer layer effectively redistributes impact-induced stress concentrations, resulting in fewer microcracks, a reduced damage extent, and a more dispersed crack distribution pattern. As the dominant contributor to energy dissipation, the granular buffer layer efficiently attenuates the incident impact energy and suppresses progressive damage and crack propagation within coal specimens, thereby demonstrating its protective effectiveness. Furthermore, this study proposes a dynamic loading control strategy for coal and gas outbursts prevention based on the coordinated regulation of energy dissipation and energy resistance. The findings provide important implications for mitigating rockbursts induced by tunnel excavation, stabilizing surrounding rock in underground excavations, and optimizing the design of protective engineering systems.