Strength Characteristics of “Natural” Fractured Sandstone Affected by Impact Direction

Studying the strength characteristics of “Natural” fractured sandstone affected by impact direction is of great importance to ensuring the long-term stability of underground engineering structures. In this research, the “Natural” distribution of fractures is initially obtained through biaxial compression simulation, and the distribution characteristics of fractures under varying confining pressures are analyzed. Subsequently, the “Natural” fracture distribution is extracted and rotated by 0, 90°, 180°, and 270° as a whole for transplantation into the SHPB numerical model of the Particle Flow Code. On this basis, the relationship between the impact strength of “Natural” fractured sandstone and factors such as static compressive strength, fracture distribution information, and impact direction is examined through dynamic loading simulation. The results indicate the following: 1) When the biaxial compression confining pressure is low, the sliding surface of the specimen is relatively distinct. As the confining pressure increases, the sliding surface becomes more challenging to identify. 2) With the increase in the biaxial compression level and confining pressure, the impact strength and corresponding time of the specimen exhibit a decreasing trend. When the impact strength exceeds 20 MPa, the tangent slope of the stress–strain curve in the pre-peak elastic stage of the specimen remains consistent. 3) When the impact direction is perpendicular to the maximum principal stress direction of biaxial compression, the number of fractures has a more significant impact on the impact strength. In contrast, when the impact direction is parallel to the maximum principal stress direction of biaxial compression, the influence of the fracture number on the impact strength is relatively minor. 4) To further analyze the influence of the fracture number on impact strength, the concept of the inverse value of the distributed fracture number is introduced. Under different impact directions, the variations of the inverse value and the impact strength with the biaxial compressive strength of the specimen are generally synchronous. 5) The dependence of impact strength on the impact direction is closely associated with the macroscopic fracture surface. The presence of the macroscopic fracture surface effectively impedes the transmission of stress within the specimen, changing the propagation path and range of the impact stress under different impact directions.