Propagation characteristics of stress waves and failure modes in gray sandstone with a gypsum-filled joint under impact loading

Dynamic mechanical properties of jointed rock mass have an important influence on the stability of geotechnical engineering. In this study, dynamic impacting experiment of gray sandstone samples with gypsum-filled joints was carried out by split Hopkinson pressure bar (SHPB) to study the influence of impact velocity and joint dip angle on wave propagation characteristics and fracture evolution of rock mass, and the failure process were captured by high-speed photography. To supplement and further study, numerical simulation was then presented. Hypermesh software was used to establish the numerical model, and then imported into LS-DYNA for calculation. The results show that the joint changes the stress wave propagation and particle vibration velocity significantly, and leads to a certain difference of stress distribution, which is the fundamental cause of 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 matrix at the non-loading end is obviously weaker than that at loading end. In addition, the initial damage and the dynamic compressive strength of rock mass increase with increasing impact velocity. The fracture is mainly caused by transverse tension in the axial direction and impact velocity influences the damage degree but cannot change the failure mode. The peak compressive strength of jointed gray sandstone decreases first and then increases with the joint dip angle, and the failure mode mainly presents as shear-tensile failure and the separation failure of joint and gray sandstone. Jointed gray sandstones are always under the dominant tensile action, especially with the joint dip angle of 45°.