Breakage mechanism analysis of bedded sandstone impacted by abrasive water jet using an integrated SPH-DEM-FEM and cohesive element method

Abrasive water jet (AWJ) is an emerging technique for improving the drilling efficiency for geothermal energy development. Rock bedding significantly influences the effectiveness of rock breaking during drilling. In this study, to investigate the damage modes and the mechanism of the bedded sandstone under abrasive water jet erosion, smooth particle hydrodynamics (SPH) and discrete element method (DEM) are used to establish the jet, and cohesive elements are inserted into finite elements to model the bedded sandstone, simulating the process of water and abrasive into the nozzle to form an abrasive water jet impacting bedded sandstone. The numerical results showed that the depth and diameter of fractures in bedded sandstone decrease and then stabilize as the bedding angle increases under AWJ, and the error in the ratio of erosion hole diameter and depth between the simulated and experimental results was <10.8 %. In addition, two damage modes of the bedded sandstone were determined, which include Case I damage mode: the sandstone is well consolidated, and the damage is in the form of erosion holes (0°≤α≤60°), dominated by the tensile damage, and Case II damage mode: the rock is fractured along the bedding and splits into two halves (60°<α≤90°), and the process can be divided into two stages during this mode. The first stage is the impact kinetic energy carried by the jet to form a crater, and the second stage is the water wedge effect to fracture the rock. The results of this study complement the damage mechanism of fractured bedded rocks by AWJ, which provides a theoretical reference for the application of AWJ to break bedded rocks in subsurface energy extraction.