The shear behaviour of granular materials at high velocities is crucial for understanding the high mobility of rapid landslides and the low-friction mechanisms behind them. Here, a numerical ring shear model driven by granular shear platens was developed, and this model was validated in terms of the kinematics and mechanics of the granular material. The granular material was then accelerated at different accelerations to high shear velocities (ranging from 0.001 m/s to a maximum of 5.0 m/s). The results indicate that with increasing shear velocity, the shear behaviour of granular materials transitions from a single behaviour to a composite behaviour. The composite shear behaviour is important for both the shear flow state and the frictional characteristics. The velocity profile reveals the transition of granular materials from uniform shear flow to composite shear flow consisting of locally high-shear-rate layers and slow creep layers; the volume of granular materials transitions from global expansion at the onset of shearing to local expansion; and particle velocity fluctuations and contact force fluctuations change from being uniformly distributed and relatively small at the beginning of shearing to rapid growth in local areas. Furthermore, with increasing shear velocity, the frictional characteristics become nonuniform. Local areas exhibit positive velocity-related friction effects, whereas the friction of the particles in other regions slightly decreases. Particle fluctuations represent an important factor that leads to the composite shear behaviour of granular materials. This study provides valuable insights into the shear behaviour of particles in rapid landslides.

中文翻译：

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颗粒材料快速剪切行为的数值研究及其对快速滑坡的意义


颗粒材料在高速下的剪切行为对于理解快速滑坡的高流动性及其背后的低摩擦机制至关重要。在这里，开发了一个由颗粒剪切板驱动的数值环剪切模型，并在颗粒材料的运动学和力学方面验证了该模型。然后以不同的加速度将颗粒材料加速到高剪切速度（范围从 0.001 m/s 到最大 5.0 m/s）。结果表明，随着剪切速度的增加，颗粒材料的剪切行为从单一行为转变为复合行为。复合剪切行为对于剪切流态和摩擦特性都很重要。速度剖面揭示了颗粒材料从均匀剪切流到由局部高剪切速率层和慢速蠕变层组成的复合剪切流的转变;颗粒材料的体积从剪切开始时的全局膨胀转变为局部膨胀;粒子速度波动和接触力波动从剪切开始时均匀分布且相对较小转变为局部区域的快速增长。此外，随着剪切速度的增加，摩擦特性变得不均匀。局部区域表现出与速度相关的正摩擦效应，而其他区域中颗粒的摩擦力略有降低。颗粒波动是导致颗粒材料复合剪切行为的重要因素。这项研究为快速滑坡中颗粒的剪切行为提供了有价值的见解。