The formation of aggregates consisting of snow, water, and tephra has been reported in small-scale experiments on three-phase flows containing tephra, water, and snow, representing lahars triggered by snowmelt. Such aggregates reduce the mobility of mud flow. However, the formation mechanism of such aggregates under various conditions has not been investigated. To elucidate the formation conditions and mechanical properties of the aggregates, we performed mixing experiments with materials on a rotating table and compression tests on the resulting aggregates with a universal testing machine in a low-temperature room at $$0\,^{\circ }\text {C}$$ 0 ∘ C . From experiments with varying component ratios of the mixture and tephra diameter, the following results were obtained: (i) the aggregate grew rapidly and reached maturity after a mixing time of 5 min; (ii) the mass of aggregates increased with snow concentration, exhibiting an approximately linear relationship; (iii) single aggregates with large mass formed at lower and higher tephra concentrations, whereas multiple aggregates with smaller mass were observed at intermediate concentrations; (iv) the shape of the aggregate satisfied the similarity law for an ellipsoid; (v) the compressive mechanical behavior could be modeled by an empirical nonlinear model. The obtained mechanical properties of the aggregates were independent of the experimental conditions; (vi) scaling analysis based on the Reynolds number and the strength of the aggregates showed that the aggregates cannot form in ice-slurry lahars. Our findings suggest that low-speed lahars containing snow and ice are likely to generate aggregates, but snow and ice in the ice-slurry lahars are dispersed without such aggregates.

中文翻译：

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火山灰-水-雪流中聚集体的形成条件和力学性能

由雪、水和火山灰组成的聚集体的形成已在包含火山灰、水和雪的三相流的小规模实验中报告，代表由融雪引发的火山泥流。这种骨料降低了泥浆流的流动性。然而，这种聚集体在各种条件下的形成机制尚未得到研究。为了阐明骨料的形成条件和力学性能，我们在旋转台上对材料进行混合实验，并在 $0\,^{\circ } 的低温室中用万能试验机对所得骨料进行压缩试验\text {C}$$ 0 ∘ C 。从混合物的不同组分比例和火山灰直径的实验中，获得了以下结果：(i) 骨料快速生长并在混合 5 分钟后达到成熟；(ii) 聚集体的质量随着雪浓度的增加而增加，呈现近似线性关系；(iii) 在较低和较高的火山灰浓度下形成大质量的单个聚集体，而在中等浓度下观察到质量较小的多个聚集体；(iv) 集合体的形状满足椭圆体的相似定律；(v) 压缩力学行为可以通过经验非线性模型进行建模。获得的骨料力学性能与实验条件无关；(vi) 基于雷诺数和聚集体强度的标度分析表明聚集体不能在冰浆泥浆中形成。