Breaking mechanism and performance of coal subjected to water jets under high in situ stress

The effect of in situ stress on the coal-breaking characteristics of water jets remains unclear, prohibiting the deep coalbed methane (CBM) development. Water jet coal-breaking experiments under different mean three-dimensional (3D) stresses and horizontal stress differences were carried out with a self-developed in situ stress simulator. When the mean 3D stress increased, coal changed from shear and tensile failure to shear failure, and the volume of the erosion pit first decreased rapidly and then slowly. Upon increasing the mean 3D stress from 0 to 10 MPa, the volume of the erosion pit decreased by 79.7%, and the specific energy consumption increased nearly five times. With an increase in horizontal stress difference, coal transitioned from shear failure to shear and tensile failure, resulting in a shear crack farther from the erosion pit. At a horizontal stress difference of 15 MPa, the volume of the erosion pit and specific energy consumption had maximum and minimum values, respectively. Consequently, constructing a higher horizontal stress difference helps improve the coal-breaking efficiency of water jets. This study could lay the foundation for applying water jet technology in deep coal seams.