Flowslide High Fluidity Induced by Shear Thinning
Flowslide High Fluidity Induced by Shear Thinning
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DOI：
10.1029/2022jb024615
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发表时间：
2022-11
期刊：
影响因子：
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通讯作者：
Wei Hu;Yan Li;Qiang Xu;Run-qiu Huang;M. McSaveney;Gong-hui Wang;Yuxu Fan;J. Wasowski;Yangshuai Zheng
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文献类型：
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作者：
Wei Hu;Yan Li;Qiang Xu;Run-qiu Huang;M. McSaveney;Gong-hui Wang;Yuxu Fan;J. Wasowski;Yangshuai Zheng
降雨引起的泥石流和随后的泥石流由于其高速和长距离的爆发，是最常发生和最具破坏性的自然灾害。人们普遍认为，剪切引起的超孔隙压力控制着流滑运动中的高流动性。然而，水槽实验表明，即使在没有超孔隙压力的情况下，流动滑动也能表现出高流动性，这表明即使是饱和颗粒物质也具有内在的剪切速度依赖流化机制。为了进一步了解饱和颗粒材料的流动性，我们进行了排水环剪实验。通过透明剪切室，可以直接观察试样的剪切带厚度和速度梯度，从而可以很好地确定试样的流变性。即使在没有超孔隙压力的情况下，颗粒土也表现出明显的剪切减薄，这可以很好地解释除了超孔隙压力外，流滑动力学中的高流动性，特别是在快速剪切过程中。环形剪切装置中的声发射（ae）为流变机理提供了额外的证据。随着声发射功率的增大，快速剪切作用减弱了颗粒体系的宏观表观粘度。我们提出，随着剪切应变速率的增加，颗粒压力的增加会减弱颗粒层之间的摩擦接触，从而减弱表观粘度，反之亦然。通过声发射测量与无量纲数分析相结合，我们认为剪切减薄是导致流滑梯超高流动性的最关键机制之一。
Rainfall‐induced flowslides and the subsequent debris flows are the most recurrent and destructive natural hazards due to their high velocity and long‐distance runout. It is widely accepted that shear‐induced excess pore pressure controls the high fluidity in flowslide movement. Nevertheless, flume experiments demonstrate that flowslides can exhibit high fluidity even in the absence of excess pore pressure, demonstrating that even saturated granular matter has an intrinsic shear‐velocity‐dependent fluidization mechanism. Herein, drained ring shear experiments were conducted to obtain a further understanding of the fluidity of the saturated granular material. By means of a transparent shear chamber, the shear‐zone thickness and the velocity gradient within samples could be directly observed and thus its rheology could be well determined. The granular soil showed substantial shear‐thinning even in the absence of excess pore pressure, which could well explain the high fluidity in flowslide dynamics in addition to excess pore pressure, especially during rapid shear. Acoustic emissions (AEs) in the ring shear device provided additional evidence of the rheological mechanism. The macroscopic apparent viscosity of the granular system was weakened by rapid shear accompanied by increasing AE power. We propose that increasing grain pressure associated with increasing shear strain rate weakens intergranular frictional contacts between granular layers, thus weakening the apparent viscosity, and vice versa. By using AE measurements combined with dimensionless number analysis, we suggested that shear‐thinning is one of the most pivotal mechanisms accounting for the ultra‐high fluidity in flowslides.