Experimental research on the anisotropic properties of sandy slate

In this study, the effect of joint on the anisotropy of a homogeneous, stiff, and intact sandy slate from a typical hydropower station is investigated by selecting and making jointed rock samples with jointed angles of 0°, 30°, 45°, 60°, and 90°. Accordingly, an acoustic measurement and a triaxial compression test are conducted on these jointed rock samples. The research results show that the joint angle significantly influences the rock mass anisotropy. In other words, the average value of the longitudinal wave velocity of the jointed rock samples is smaller than that of the intact rock. Furthermore, the value of the longitudinal wave velocity increases with the increase of the joint angle and is the largest when its spreading direction is in line with the joint inclination. The stress–strain curve, elastic modulus, peak strength, and failure mode of the joint rock samples are found to have anisotropic features. The failure stage occurs in samples with joint angles of 0°, 30°, and 90°. The stress–strain curve of the samples with joint angles of 45° and 60° tends to be horizontal. Meanwhile, the elastic modulus and the compression strength displayed a U-shaped distribution with an increase of the joint angle and the smallest value that belongs to samples with joint angles of 30° and 60°. The peak value ratio of the elastic modulus and the compression strength gradually decrease when the confining pressure increases, indicating that the anisotropy of the samples has weakened (i.e., the increase of the confining pressure decreases the anisotropy of the sandy slate strength). The failure mode of the samples with different joint angles is presented as follows: the samples with a 0° joint angle exhibit a tensile splitting damage; the samples with a 90° joint angle exhibit compression–shear damage; the samples with a 30°joint angle exhibit the combination of slide and compression–shear damage; and the samples with 45° and 60°joint angles exhibit slide damage along the joint surface.