LAUSR

To study the mechanical responses of rock joints within a wide range of shear rates, this study develops a horizontal gripping mechanism to improve a double shear test device. Artificial rock joints, including planar and regular asperities with dip angles of 15° and 30°, are produced for conducting double shear tests under constant normal load within the shear rate range of 10−2–101 mm/s. Experimental results demonstrate that, though normalized by applied normal stress, the shear stiffness of the planar joints has a semi-logarithmic linear relationship with normalized shear rates. For rock joints with regular asperities, the shear rate, asperity dip angle, and normal stress influence the failure modes of asperities. When the shear rate is lower than the threshold shear rate, the asperity dip angles after the shear process and the peak dilation angles of the 15° regular joints increase with increasing the shear rate, whereas these two parameters tend to decrease in the cases of the 30° regular joints. The peak friction angles of both planar and regular rock joints have a semi-logarithmic linear relationship with normalized shear rates. The increasing peak friction angles of rock joints at different shear rates after sliding or local cut-off failures are derived mainly from increased basic friction angles. Both the basic friction angles of rock joints and the shear strength of asperities rise as the shear rate increases when asperity cut-off occurs. However, the quantitative effect of these two factors on the increase of peak friction angle requires further study.