Propagation of stress wave and fragmentation characteristics of gangue-containing coal subjected to water jets

Abstract

Water jet technology has been broadly applied to extract coalbed methane (CBM) from low permeability reservoirs. However, the existing studies on the failure and damage characteristics of coal subjected to water jets have neglected the influence of gangue. To study the propagation of stress waves and the fragmentation characteristics of gangue-containing coal impacted by a water jet, a numerical model was developed for gangue- and defect-containing coal based on the smooth particle hydrodynamics (SPH) method, and was verified by using laboratory experiments. The research results indicated that gangue had a significant influence on the propagation of stress waves and the fragmentation characteristics of coal. When the stress wave propagated from coal to gangue, the total reflective and transmissive regions of the stress wave existed at the interface. The interaction process of stress waves reflected and transmitted at the interface led to the formation of shear cracks near the liquid–solid contact region and the formation of tensile cracks in the other regions, which eventually formed the obvious local fragmentation characteristics. Finally, the blocking coefficient M was defined to quantify the resistance of the gangue against the stress-wave propagation. The resistance of the gangue against the stress-wave propagation was uneven, and the maximum and minimum blocking coefficients were 0.48 and 0.15, respectively. This study could lay a foundation for understanding the breaking mechanism of coal by water jets.