An analysis of flow-like motion of avalanches based on physical modeling experiments
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摘要:
流态化运动是高速远程滑坡的主要运动形式，是揭示高速远程滑坡运动机理的重要基础。基于粒子图像测速（PIV）分析方法，采用物理模型试验对不同粒径组成条件下的颗粒流内部的速度分布、剪切变形及流态特征进行了研究，并对高速远程滑坡流态化运动特征进行了讨论分析。结果表明：碎屑流流态化运动特征与颗粒粒径呈显著的相关性，随着粒径的减小或细颗粒含量的增加，颗粒流底部相对于边界的滑动速度以及整体的运动速度均呈逐渐减小的趋势，颗粒流内部剪切变形程度增加，颗粒的运动形式由“滑动”向“流动”转变；当颗粒粒径较小或细颗粒含量较高时，颗粒流内部剪切速率增大的趋势在颗粒流底部更加显著，反映了粒径减小有助于促进颗粒流内部剪切向底部的集中；在同一颗粒流的不同运动阶段及不同纵向深度，其流态特征具有显著差别，颗粒流前缘及尾部主要呈惯性态，颗粒间以碰撞作用为主，而主体部分则主要呈密集态，颗粒间以摩擦接触作用为主；在颗粒流表面及底部，颗粒间相互作用方式主要是碰撞作用，中间部分则以摩擦作用为主；对于不同粒径的颗粒流，随着粒径的增大或粗颗粒含量的增加，颗粒流内部颗粒的碰撞作用加强，颗粒流整体趋于向惯性态转变。
Abstract:Flow-like motion is the main forms of rock avalanche emplacement, which is the foundation to reveal the dynamic mechanisms of rock avalanches. In this paper, a series of physical modeling experiments based on the Particle Image Velocimetry（PIV）analysis method are conducted to research the internal velocity distribution, internal shear behavior and flow regimes of the granular flow under different grain size conditions. The flow-like motion of rock avalanches and the corresponding deposit features are further discussed and analyzed based on the experimental results. The research results show that the flow-like motion of the granular flow is significantly correlated with the grain size. With the decreasing grain size or the increasing fine particles content, the slip velocity at the bottom of the granular flow and the bulk velocity decrease gradually, the degree of internal shear of the granular flow increases, and the motion form of the granular materials changes from “sliding” to “flowing”. When the grain size is smaller or the content of fine particles is higher, the increasing trend of the internal shear rate is more prominent at the bottom of the granular flow, which indicates that the reduction in grain size promotes shear localization at the bottom of the granular flow. The granular flow regime is different at different locations of the granular flow. The leading and trailing edges of the granular flow are mainly inertial regime, and the interaction between particles is dominated by collisions, while the particle interactions in the main body is dominated by frictional contact. On the surface and bottom of the granular flow, the interaction between particles is mainly collision, while particle interaction in the middle part is mainly frictional contact. For the granular flow with different grain sizes, with the increasing grain size and coarse particles content, the particle collisions in the granular flow are enhanced, and the flow regimes tend to be more inertial.
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Key words:
- granular flow /
- flow-like motion /
- shear rate /
- flow regime /
- rock avalanche
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表 1 试验工况设计
Table 1. Design of experimental conditions
粒径组成 编号 工况条件 平均粒径/mm 内摩擦角/（°） 质量/kg 单粒径 M1 d=0.25～0.5 mm 0.38 26.7 8 M2 d=0.5～1 mm 0.75 28.2 M3 d=1～2 mm 1.5 28.1 M4 d=2～5 mm 3.5 31.0 M5 d=5～7 mm 6.0 33.0 多粒径 F1 D=1.5 3.96 32.2 F2 D=2.0 3.41 31.4 F3 D=2.5 2.14 30.6 F4 D=3.0 0.75 28.4 F5 D=3.5 0.30 28.1 
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