Dynamic fracture behaviour and evolution mechanism of soft coal with different porosities and water contents

Abstract

Determining the effect of water content and porosity on the dynamic mechanics of soft coal is a key problem in reinforcing soft coal seams by water injection. In this study, soft coal specimens with different water contents and porosities were successfully prepared and tested using a Split Hopkinson Pressure Bar (SHPB). The results show that the effect of water content on the strength of soft coal can be divided into two stages based on the critical point of optimum water content. With the effects of increasing porosity, the optimum water content gradually increased, while the peak strength corresponding to the optimum water content gradually decreased. In addition, based on the analysis of the dynamic failure process of the coal recorded using a high-speed camera, the dynamic mechanical model varies with the distance, and the liquid bridge volume between particles was established according to the water-bearing unequal spheres models. Moreover, the mechanism of the effects of porosity and water content on the fracture expansion and dynamic strength of soft coal were further discussed.