Dynamic behaviour and failure mechanism of coal subjected to coupled water-static-dynamic loads

The stability of a coal pillar dam in a coal mine underground reservoir is affected by water pressure, static geo-stress, and coal mine earthquakes. Thus, it is essential to accurately evaluate the dynamic behaviour of coal under coupled water-static-dynamic loads to reasonably design a coal pillar dam. In this study, an innovative test system was developed based on a split Hopkinson pressure bar (SHPB) device, and a series of impact tests of coal under the coupled action of impact load, static axial preloading, and water pressure were performed with this system. The effects of coupled water-static-dynamic loads on mechanical behaviours, including strength and deformation characteristics, failure mode, and energy dissipation of the coal samples were systematically investigated. Results showed that the dynamic deformation process of the coal samples can be divided into three stages: linear elastic deformation stage, crack unstable propagation stage, and post-peak failure stage. Impact and higher axial static loads were the two negative factors that made the coal samples more prone to damage. In contrast, the presence of water pressure positively affected the sample, which improved the dynamic strength and reduced the failure strain of the sample. Energy dissipation characteristics showed that water pressure enhanced the energy utilisation efficiency of the sample. Furthermore, the microcosmic mechanism of free water protecting coal from the fractures was also examined.