The intrinsic mobility of very dense grain flows
The intrinsic mobility of very dense grain flows
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DOI：
10.1016/j.epsl.2022.117389
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发表时间：
2022-02
影响因子：
5.3
通讯作者：
Wei Hu;Qiang Xu;M. McSaveney;Run-qiu Huang;Yujie Wang;Ching-Shyang Chang;H. Gou;Yangshuai Zheng
中科院分区：
文献类型：
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作者：
Wei Hu;Qiang Xu;M. McSaveney;Run-qiu Huang;Yujie Wang;Ching-Shyang Chang;H. Gou;Yangshuai Zheng
在大型山体滑坡和地震断层破裂中，经常报告具有严重后果的自然灾害的高度机动性。到目前为止，高流动性的机制一直是个谜。在本研究中，我们对四种不同矿物的颗粒进行了高速旋转剪切实验，在正应力为1 Mpa、转速为2m/S的条件下，所测试的含有可破碎颗粒的干密颗粒流动本质上具有很高的流动性。颗粒流迅速减弱到非常低的粘度(约500Pa.s)，这与颗粒组成无关。我们发现，当流动开始时，颗粒被压碎成一种特殊的分形结构，其中大多数较大的颗粒被小得多的颗粒所包围。这种特殊的结构为从颗粒上的划痕所指示的磨损产生和传播声能提供了有利的条件。划痕在较大的颗粒中产生非常高频率的弹性能量(振动)，这深刻地削弱了所有颗粒的接触，使得颗粒质量像巨型洪水一样流动。更小的颗粒在岩石雪崩沉积物中冲刷巨石时留下的颤动痕迹表明，自然界中也发生了同样的过程。这一发现对于解释大应变和高应变率下致密颗粒流动的行为是重要的。
High mobility of natural disasters with severe consequences is often reported in large landslides and in earthquake fault ruptures. The mechanism of high mobility keeps to be mysterious to date. In this study, we used high-speed rotary shear experiments under normal stress 1 MPa and with a rotary speed of 2 m/s on grains of four different minerals to show that the tested dry dense grain flows with crushable grains are highly mobile intrinsically. Granular flow quickly weakens to a very low viscosity (about 500 Pa.s), which is independent of grain composition. We find that when flow begins, grains are crushed to a special fractal structure in which most larger grain is surrounded by much smaller grains. This special structure provides a favourable condition for generating and propagating acoustic energy from the abrasion indicated by the scratches on the grains. The scratching generates very high frequency elastic energy (vibration) in the larger grains, which profoundly weakens all grain contacts so that the grain mass flows like a giant flood. Chatter-marked scratches made by smaller grains scouring across boulders in rock-avalanche deposits suggest that the same processes occur in nature. This finding is important for the explanation of the behaviour of dense grain flows at large strains and high strain rates.