Understanding dynamic shear behaviours of rock under quasi-static confinement and dynamic loads is not only of great importance in underground engineering structures, but also beneficial to reveal earthquake mechanics regarding pre-stressed rocks fracturing from initial intact to rapid shear sliding. Here we propose a dynamic shear test setup and present full-field observations of stressed rock failure at high shear rate (up to = 220 s) and sliding at high slip velocity over 10 m/s in the order of coseismic slip, with the integration of a novel triaxial Hopkinson bar (Tri-HB) and high-speed three-dimensional Digital Image Correlation (3D-DIC) techniques. Dynamic shear strength and friction coefficient are determined during the dynamic shear test under confinement, with different shear strain rates and pre-stresses. The dynamic shearing process can be divided into three stages, i.e. shear deformation, fracture degradation and dynamic frictional sliding. The high energy density of shear fracture band is observed, the rate and stress state dependences of rock shear strength and dynamic frictional coefficient are revealed. The dynamic shear strength of granite follows the Mohr-Coulomb criteria under varying pre-stresses and strain rates. The gouge materials with size of 1∼10 μm are generated within the high-rate shearing zone, and this appears to control the frictional resistance. The results could help determination of rock shear strength and post-shear failure, as well as explain the shear rupture and the resistance to slip mechanism of rock faults and strong near-surface earthquake events.

中文翻译：

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静态和高速率耦合作用下花岗岩的动态剪切行为


了解岩石在准静态约束和动荷载作用下的动态剪切行为不仅对于地下工程结构具有重要意义，而且有利于揭示预应力岩石从初始完整断裂到快速剪切滑动的地震力学。在这里，我们提出了一种动态剪切测试装置，并提出了高剪切速率（高达 = 220 s）下受力岩石破坏和按同震滑移顺序以超过 10 m/s 的高滑移速度滑动的全场观察，并积分新型三轴霍普金森棒（Tri-HB）和高速三维数字图像相关（3D-DIC）技术的研究。动态剪切强度和摩擦系数是在不同剪切应变率和预应力约束下的动态剪切试验中确定的。动态剪切过程可分为剪切变形、断裂退化和动摩擦滑动三个阶段。观察到剪切断裂带的高能量密度，揭示了岩石剪切强度和动摩擦系数的速率和应力状态依赖性。在不同的预应力和应变率下，花岗岩的动态剪切强度遵循莫尔-库仑准则。在高速剪切区内会产生尺寸为 1∼10 μm 的凿孔材料，这似乎控制了摩擦阻力。研究结果有助于确定岩石的剪切强度和剪切后破坏，并解释岩石断层和强近地表地震事件的剪切破裂和抗滑移机制。