Determination of critical energy for coal impact fracture under coupled static-dynamic loading

Deep coal is constantly subjected to high static loading, and the accompanying mining disturbances will exacerbate the energy changes in the coal specimen. This study utilized the Split Hopkinson Pressure Bar (SHPB) system to examine the critical energy required for coal impact fracture under one-dimensional (1D) and three-dimensional (3D) coupled static-dynamic loading. The results revealed that a sufficiently large impact disturbance was required to cause deformation of the coal specimen when the initial static energy storage was low. Additionally, the coal with higher initial static energy storage was more likely to fracture under minor impact. Compared to the 1D loading, the 3D loading resulted in a higher critical impact energy and velocity for intact coal to fracture. Additionally, a model was developed to demonstrate the inherent energy evolution of coal specimen breakage under coupled static-dynamic loading, based on the relationship between energy and coal specimen deformation. Reducing the initial energy storage, weakening the dynamic absorbed energy, and increasing the critical instability energy of the coal matrix were the primary recommendations for disaster prevention. And corresponding prevention and control measures are suggested. This research can provide a scientific foundation and guidance for predicting dynamic disasters in order to ensure safe and efficient mining engineering.