Experimental investigation on dynamic strength and energy dissipation characteristics of gas outburst-prone coal

We report laboratory experiments to investigate the dynamic failure characteristics of outburst-prone coal using a split Hopkinson pressure bar (SHPB). For comparison, two groups of experiments are completed on contrasting coals-the first outburst-prone and the second outburst-resistant. The dynamic mechanical properties, failure processes, and energy dissipation of both outburst-prone and outburst-resistant coals are comparatively analyzed according to the obtained dynamic compressive and tensile stress-strain curves. Results show that the dynamic stress-strain response of both outburst-prone and outburst-resistant coal specimens comprises stages of compression, linear elastic deformation, then microfracture evolution, followed by unstable fracture propagation culminating in rapid unloading. The mechanical properties of both outburst-prone and outburst-resistant coal specimens exhibit similar features: The uniaxial compressive strength and indirect tensile strength increase linearly with the applied strain rate, and the peak strain increases nonlinearly with the strain rate, whereas the elastic modulus does not exhibit any clear strain rate dependency. Differences in the dynamic failure characteristics between outburst-prone and outburst-resistant coals also exist. The hardening effect of strain rate on outburst-prone coal is more apparent than on outburst-resistant coal, which is reflected in the dynamic increase factor at the same strain rate. However, the dynamic strength of outburst-prone coals is still lower than that of outburst-resistant coals due to its low quasi-static strength. The dissipated energy of outburst-prone coal is smaller than that of outburst-resistant coal. Therefore, the outburst-prone coal, characterized by low strength, high deformability, and small energy dissipation when dynamically loaded to failure, is more favorably disposed to the triggering and propagation of gas outbursts.