Shear-rate weakening or strengthening behaviours can effectively control landslide runouts, defining sudden runaway sliding or years-long slow-creep phases. These behaviours are partly controlled by the properties of the basal material. Understanding its stress-strain-time response is crucial in physically-based assessments of landslide dynamics and the associated risk. We investigate the frictional resistance of a calcium bentonite, a kaolin and a quartz sand by means of a conventional ring-shear apparatus under normal stresses representative of landslide shear zones. Results for the fine-grained soils, in line with literature on pure clays, indicate important velocity strengthening, whereas small shear-rate effects were observed in sand. As long as effective stresses remain constant, a velocity strengthening response can exert a feedback that, under certain conditions, counteracts perturbations in boundary conditions and prevents fast runouts on pre-existing shear zones. Accordingly, we argue that specifically testing for shear-rate-dependency and incorporating observed behaviours in model formulations can be beneficial for better predicting landslide fates.

中文翻译：

---

土壤残余剪切强度的速率依赖性：对滑坡演化的影响

剪切率减弱或增强行为可以有效地控制滑坡跳动，定义突然的失控滑动或长达数年的缓慢蠕变阶段。这些行为部分受基础材料的特性控制。了解其应力-应变-时间响应对于基于物理的滑坡动力学评估和相关风险至关重要。我们在代表滑坡剪切带的法向应力下，使用传统的环形剪切装置研究了钙膨润土、高岭土和石英砂的摩擦阻力。细粒土的结果与关于纯粘土的文献一致，表明重要的速度强化，而在沙子中观察到较小的剪切率效应。只要有效应力保持不变，速度强化响应就可以产生反馈，在某些条件下，抵消边界条件中的扰动并防止在预先存在的剪切带上快速跳动。因此，我们认为专门测试剪切率依赖性并将观察到的行为纳入模型公式可能有助于更好地预测滑坡命运。