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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Granular mixture deflation and generation of pore fluid pressure at the impact zone of a pyroclastic fountain: Experimental insights
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Granular mixture deflation and generation of pore fluid pressure at the impact zone of a pyroclastic fountain: Experimental insights

机译：粒状混合物通气和发热喷泉冲击区的孔隙流体的产生：实验见解

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We present the results of analogue laboratory experiments on pyroclastic fountain collapse. Mixtures of air and glass beads ranging in size around 75 +/- 15 mu m, with Stokes number of similar to 10(-3)-10(1) and representative of 0.1-1 mm sized particles in nature, were released from a hopper at heights of 0.45-2.95 m above the base of a horizontal channel. Free fall caused continuous dilation of the granular material and led to mean particle concentrations of similar to 9-36 vol%, with concentration inversely proportional to drop height, before the particles impacted the channel base. Decoupling between the particles and the ambient air upon impact caused deflation of the mixture, which then propagated laterally as a dense granular flow overridden by a dilute suspension. Measurements at the impingement surface revealed that pore fluid pressure, generated through high air-particle relative velocity during deflation, counterbalanced up to similar to 50% of the weight of the emerging granular flow. The runout distance of the dense flow increased linearly with the fall height, similar to published results on unidirectional flows generated from collapse of packed granular columns. This suggests that the runout of flows resulting from release of granular material is controlled essentially by conversion of potential to kinetic energy and that the initial particle concentration is a second order parameter. We conclude that fountaining of pyroclastic material containing large amounts of particles with Stokes numbers of the order 10(-3)-10(1) can generate dense pyroclastic flows with some degree of pore fluid pressure. (C) 2021 Elsevier B.V. All rights reserved.
机译：我们介绍了对Pyroclastic喷泉塌陷的模拟实验室实验结果。范围约为75 +/-15μm的空气和玻璃珠的混合物，具有类似于10（3）-10（1）的Stokes数量，并且本质上具有0.1-1mm尺寸粒子的代表性，从a中释放料斗高于水平通道底部0.45-2.95 m的高度。自由落体引起粒状材料的连续扩张，并导致与9-36体积％的平均颗粒浓度，浓度与下降高度成反比，在颗粒撞击通道基座之前。在冲击时颗粒和环境空气之间去耦，导致混合物的放气，然后作为稀释悬浮液覆盖的致密粒状流动横向传播。撞击表面的测量显示，通过在放气期间通过高空气颗粒相对速度产生的孔隙流体压力，同样达到新出现的粒状流量的50％。致密流的跳动距离随着秋季的高度线性增加，类似于从填充粒状柱的塌陷产生的单向流动的公开结果。这表明由粒状材料释放产生的流动的跳动基本上通过转换动力能量来控制，并且初始颗粒浓度是二阶参数。我们得出结论，含有大量颗粒的喷射含有大量颗粒的尖端10（-3）-10（1）可以产生具有一定程度的孔隙流体压力的致密的吡焦流。 （c）2021 Elsevier B.v.保留所有权利。

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