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Rocks in the deep underground are likely subjected to both hydrostatic confining pressure and dynamic compression–shear load. Thus, accurately characterizing the dynamic properties and failure mechanism of hydrostatically confined rocks under combined compression–shear impacting is crucial for the stability assessment of deep underground rock structures. In this study, on the basis of an improved split Hopkinson pressure bar (SHPB) apparatus, the combined dynamic compression–shear tests are performed on inclined cylindrical sandstone specimens with hydrostatic confining pressures. During the test, the dynamic force balance of rock specimens can be well satisfied using the pulse shaping technique. Our results show that the hydrostatic confining pressure and dynamic loading rate help strengthen the load-carrying capacity of rocks. In contrast, the shear component in the dynamic load limits the dynamic peak stress of rocks. As hydrostatic confining pressure increases, the failure surface based on the Drucker–Prager criterion gradually expands outward. Under dynamic loading, the compressive deformation modulus of rocks decreases with increasing shear component in the dynamic load, contrary to its response to hydrostatic confining pressure. Fragmentation analysis indicates that the hydrostatic confining pressure and the shear component of dynamic loading restrict the fracture behavior of rocks. Besides, as the specimen inclination angle and the hydrostatic confining pressure increase, the failure pattern of rock specimens changes from the tensile-dominated failure with a truncated conical surface to the shear-dominated failure with a single shear plane along its short diagonal. [ABSTRACT FROM AUTHOR]

Cracked rocks are quite susceptible to dynamic loading from drilling, blasting, and impacting events. Understanding the dynamic response of cracked rocks under dynamic loadings is crucial for the assessment of rock structure stability. In this study, dynamic compression tests were carried out on rock specimens with multiple parallel cracks using a split Hopkinson pressure bar apparatus. Effects of strain rate and crack intensity on dynamic responses, including strength and deformation properties, progressive failure behavior, rock fragmentation characteristics, and energy dissipation of cracked rock specimens, were systematically investigated. Stress–strain curves migrate from class I curves into class II with increasing strain rate. Dynamic strength shows clear rate dependence while dynamic elastic modulus is independent of strain rate. Progressive failure behavior of cracked rock specimens under high loading rates was analyzed using high-speed photography and digital image correlation technique. Results show that the X-shaped shear failure mode is the final failure modes of all specimens, regardless of crack intensity. Fragmentation analysis indicates that increasing strain rate intensifies fragmentation, decreases mean fragment size, and increases fractal dimension of rock fragments. At low strain rates, specimens remain unbroken or slightly spilt; at high strain rates, specimens are systematically pulverized. Energy utilization efficiency decreases while energy dissipation density increases with increasing strain rate. For a given strain rate, crack intensity has no significant influences on energy dissipation and fragmentation characteristics of cracked rock specimens under dynamic loading. [ABSTRACT FROM AUTHOR]