Propagation Characteristics of Stress Waves and Failure Modes of Gray Sandstone with a Gypsum-Filled Joint Under Impact Load

To investigate the effects of the impact velocity and joint dip angle on stress wave propagation and fracture evolution of rock masses, dynamic impact experiments of the gray sandstone samples with gypsum-filled joints were carried out by split Hopkinson pressure bar (SHPB), and the failure process was captured by high-speed photography. The numerical simulation was then presented. HYPERMESH software was used to establish the numerical model, which was then imported into LS-DYNA for calculation. The results show that the joint significantly changes stress wave propagation and particle vibration velocity and leads to a certain difference of stress distribution, which is the fundamental cause of the different failure modes. Not only P waves but also shear waves perpendicular to the particle vibration direction are generated in the joint, and the particle vibration velocity in the matrix at the non-loading end is obviously weaker than that at the loading end. In addition, the initial damage and the dynamic compressive strength of the rock masses increase with increasing impact velocity. The fracture is mainly caused by transverse tension in the axial direction, and the impact velocity influences the damage degree but does not change the failure mode. The peak compressive strength of the jointed gray sandstone decreases first and then increases with the joint dip angle, and the failure mode mainly presents as shear-tensile failure and separation failure of the joint and gray sandstone. Jointed gray sandstones are always under dominant tensile action, especially with a joint dip angle of 45°.