Understanding the mechanical properties and fracturing behaviours of coal is significant for the safety of underground mining engineering. Coal failure characteristics are highly influenced by the anisotropy and loading conditions. In this study, the coupled biaxial static and dynamic tests are conducted on coal specimens with five bedding orientations θ (i.e., 0°, 30°, 45°, 60°, and 90°) with respect to the normal direction to loading. A Triaxial Hopkinson bar (Tri-HB) system is adopted to apply the biaxial quasi-static stress first and then dynamic loading at four impact velocities (i.e., 10, 13, 17, and 21 m/s). Real-time processes of coal fracturing are recorded by two high-speed cameras, and accordingly, full-field deformation and ejection velocities are identified by the three-dimensional digital image correlation (3D-DIC) technique. Moreover, the internal fracture morphology of coal specimens is characterised using synchrotron-based X-ray computed tomography (CT). Experimental results show that at similar strain rates, the peak stress against θ shows a “U” shape with the lowest value at θ = 60°. The peak stress increases with increasing impact velocity, while its growth rate exhibits a downward trend revealing a decreasing sensitivity to strain rate. Coal ejection velocities are positively rate-dependent, and the highest ejection velocity is found shifting from θ = 45° to θ = 90° with increasing impact velocity. The average fragment size of coal specimens is negatively related to impact velocities and energy absorption, and the finest fragmentations are observed at around θ = 45°. Dynamic behaviours of coal under biaxial pre-stresses are dependent on bedding structures and strain rates, while the bedding effect becomes weak as strain rate increases.

了解煤的力学特性和断裂行为对地下采矿工程的安全性具有重要意义。煤的破坏特性受各向异性和加载条件的影响很大。在这项研究中，对煤样品进行了双轴静态和动态耦合试验，该煤样品具有相对于加载法线方向的五个层理方向θ（即0°，30°，45°，60°和90°）。采用三轴霍普金森杆（Tri-HB）系统首先施加双轴准静态应力，然后以四个冲击速度（即，10、13、17和21 m / s）。两个高速摄像机记录了煤压裂的实时过程，因此，通过三维数字图像相关（3D-DIC）技术识别了全场变形和射出速度。此外，使用基于同步加速器的X射线计算机断层扫描（CT）对煤样品的内部断裂形态进行了表征。实验结果表明，在相似的应变率下，针对θ的峰值应力呈“ U”形，在θ处的最小值 = 60°。峰值应力随着冲击速度的增加而增加，而其增长率却呈现出下降的趋势，表明对应变率的敏感性降低。煤的喷射速度与速度成正比，并且 随着冲击速度的增加，最高的喷射速度会从θ  = 45°变为θ = 90°。煤样品的平均碎片尺寸与冲击速度和能量吸收呈负相关，在θ  = 45°附近观察到最细的碎片。煤在双轴预应力下的动力学行为取决于层理结构和应变率，而层理效应随着应变率的增加而变弱。