Tensile Fracture Behaviour of Stratified Sandstone Under Static and Dynamic Loading

Stratified sandstone is frequently subjected to coupled tensile stress from dynamic and static loads in underground engineering construction. Additionally, as underground engineering projects are constructed, the dynamic load, pretensile stress, and bedding force direction will change. To investigate this phenomenon, dynamic-static tensile tests were conducted on stratified sandstone using an improved split Hopkinson pressure bar (SHPB). The dynamic tensile strength, dynamic impact factor (DIF), anisotropy coefficient, and energy distribution characteristics of sandstone are among the key parameters that were investigated. Additionally, the fracture surfaces of the sandstone samples were scanned via a 3D scanner, enabling the analysis of surface roughness, fractal dimension, roughness height, and slope evolution patterns. The loading conditions and bedding angle significantly affect the strength of sandstone. Sandstone samples with a higher bedding angle have lower strength while increasing impact pressure increases the strength. Moreover, the strength of sandstone is weakened by pretensile stress. The DIF and anisotropy coefficient are strongly affected by the impact pressure and pretensile stress. The speed at which cracks spread in sandstone increases with impact pressure, but cracks do not spread along weaker bedding planes. Significant internal damage and numerous microcracks develop at high pretensile stresses, which further decreases the anisotropy of stratified sandstone. The DIF of sandstone is directly proportional to the impact pressure, while it is inversely correlated with the pretensile stress. Little incident energy is transferred or absorbed; instead, most energy dissipates as reflected energy. As the impact pressure increases, more incident energy is used to fracture the rock. According to the 3D scan of the fractured sandstone surfaces, high-impact pressure causes the fracture surfaces to become steeper and rougher, and exhibit more indentations. These characteristics suggest more complex internal crack propagation paths. The presence of pretensile stress further increases the roughness of the fracture surfaces.