Changes in shear velocity can strengthen or weaken the frictional resistance of joints/faults in natural systems, but the mechanism remains unclear. We investigated the shear behavior of a rough basalt fracture in well-controlled, repeatable shear tests under constant and dynamic normal load conditions at different shear velocities. Normal load vibrations, simulating a dynamic normal load, were applied to the upper block of a fractured basalt sample. Simultaneously, a shear load was applied to the bottom block, providing a constant shear velocity. The peak shear strength increased with increasing shear velocity under constant normal load conditions. The peak shear strength decreased at a lower shear velocity under normal load vibrations. When the shear velocity exceeded the critical value, v_c, the peak shear strength increased. The apparent coefficient of friction reduced under normal load vibrations. The reduction in the dynamic coefficient of friction increased with increasing shear velocity. We identified a phase shift between the peak normal load and peak shear load with peak shear load delay (D1) and a phase shift between peak normal load and the peak coefficient of friction with the peak coefficient of friction delay (D2). D1 and D2 were dependent on the quasi-static coefficient of friction and shear velocity, and both decreased with increasing shear velocity. D1 decreased with the increasing quasi-static coefficient of friction, while D2 was almost constant with changes in the quasi-static coefficient of friction. A new shear strength criterion was proposed for a rough joint under a constant shear velocity and normal load vibrations.

剪切速度的变化会增强或削弱自然系统中关节/断层的摩擦阻力，但机理尚不清楚。我们在恒定的和动态的法向载荷条件下，在不同的剪切速度下，在控制良好的可重复剪切试验中研究了玄武岩粗裂缝的剪切行为。模拟动态法向载荷的法向载荷振动被施加到断裂玄武岩样品的上部块体上。同时，将剪切载荷施加到底部砌块，以提供恒定的剪切速度。在恒定的正常载荷条件下，峰值剪切强度随着剪切速度的增加而增加。在正常载荷振动下，峰值剪切强度在较低的剪切速度下降低。当剪切速度超过临界值时，v _c，峰值剪切强度增加。在正常负载振动下，表观摩擦系数减小。动态摩擦系数的减小随着剪切速度的增加而增加。我们确定了峰值法向载荷和峰值剪力载荷之间的相移（具有峰值剪切载荷延迟）（D1），以及峰值法向载荷和峰值摩擦系数之间的相移（具有峰值摩擦延迟）（D2）。D1和D2取决于准静态摩擦系数和剪切速度，并且都随着剪切速度的增加而减小。D1随着准静态摩擦系数的增加而减小，而D2随着准静态摩擦系数的变化而几乎恒定。