Mechanical and failure properties of rocks with a cavity under coupled static and dynamic loads

In this study, a series of one-dimensional coupled static and dynamic loading tests were performed by using a modified split Hopkinson pressure bar. Intact prismatic sandstone specimens and specimens with a prefabricated internal circular cavity were tested. The results show that, the dynamic strength of intact specimens and specimens with a cavity decreases with the increase of axial static pressure under 20-70% of the uniaxial compressive strength (UCS). However, the combined dynamic-static strength of intact specimens and specimens with a cavity increases slightly with the increase of the axial static pressure. Besides, the total strain of specimens under coupled axial static and dynamic loads is approximately a fixed value (about 1.16%). Under a low axial static pressure (20-40% of UCS), dynamic load plays a major role in rock failure, resulting in tensile splitting failure in intact specimen; under a medium axial static pressure (60% of UCS), both of static and dynamic loads play a major role in rock failure, resulting in a composite tensile-shear failure in intact specimen; under a high axial static pressure (70% of UCS), static load plays a major role in rock failure where shear failure occurs in intact specimens. However, for the specimen with an internal cavity, no matter how large the axial static pressure is, X-shaped shear failure occurs under the combined axial static and dynamic loads.