Elementary theory of bed-sediment entrainment by debris flows and avalanches
Elementary theory of bed-sediment entrainment by debris flows and avalanches
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DOI：
10.1029/2011jf002189
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发表时间：
2012-07-19
影响因子：
3.9
通讯作者：
Iverson, Richard M.
中科院分区：
文献类型：
--
作者：
Iverson, Richard M.
泥石流或雪崩与下伏沉积层之间的质量和动量交换分析有助于解释和预测床-沉积物夹带率。初步分析评估了库仑滑块的行为，夹带床料，因为它下降了一个统一的斜坡。分析表明，块的动量可以不稳定地增长，即使在有限的卷吸效率的存在。一个更详细的，深度集成的连续分析的相互作用，可变形的机构确定的机械控制夹带效率，并表明夹带率满足跳跃条件，涉及剪切牵引和速度不连续的流动床边界。卷吸率E的显式预测来自对流速剖面和边界剪切力的合理假设。对于库仑摩擦牵引力，预测夹带率是敏感的孔隙流体压力，开发在床沉积物，因为它是覆盖。在最简单的情况下，河床沉积物完全液化，液化速率方程简化为E = 2 μ（1）gh（1）cos θ（1 - lambda（1））/（v），其中θ是倾斜角，mu（1）是水流的库仑摩擦系数，h（1）是其厚度，lambda（1）是其液化程度，（v）在横杠（1）上的是其深度平均速度。当λ（1）值在0.5 ~ 0.8范围内时，该方程预测的卷吸率与在湿沉积物床几乎完全液化的大规模泥石流实验中测得的0.05 ~ 0.1 m/s的卷吸率一致。床层液化的倾向取决于几个因素，包括沉积物孔隙度、渗透率和厚度，以及床层被覆盖时发生的压缩和剪切变形速率。
Analyses of mass and momentum exchange between a debris flow or avalanche and an underlying sediment layer aid interpretations and predictions of bed-sediment entrainment rates. A preliminary analysis assesses the behavior of a Coulomb slide block that entrains bed material as it descends a uniform slope. The analysis demonstrates that the block's momentum can grow unstably, even in the presence of limited entrainment efficiency. A more-detailed, depth-integrated continuum analysis of interacting, deformable bodies identifies mechanical controls on entrainment efficiency, and shows that entrainment rates satisfy a jump condition that involves shear-traction and velocity discontinuities at the flow-bed boundary. Explicit predictions of the entrainment rate E result from making reasonable assumptions about flow velocity profiles and boundary shear tractions. For Coulomb-friction tractions, predicted entrainment rates are sensitive to pore fluid pressures that develop in bed sediment as it is overridden. In the simplest scenario the bed sediment liquefies completely, and the entrainment-rate equation reduces to E = 2 mu(1)gh(1) cos theta(1 - lambda(1))/(v) over bar (1), where theta is the slope angle, mu(1) is the flow's Coulomb friction coefficient, h(1) is its thickness, lambda(1) is its degree of liquefaction, and (v) over bar (1) is its depth-averaged velocity. For values of lambda(1) ranging from 0.5 to 0.8, this equation predicts entrainment rates consistent with rates of 0.05 to 0.1 m/s measured in large-scale debris-flow experiments in which wet sediment beds liquefied almost completely. The propensity for bed liquefaction depends on several factors, including sediment porosity, permeability, and thickness, and rates of compression and shear deformation that occur when beds are overridden.