Segregation and levee formation in geophysical mass flows and their feedback on runout distance

地球物理质量流中的离析和堤坝形成及其对跳动距离的反馈

基本信息

批准号：
NE/E003206/1
负责人：
Nico Gray
金额：
$ 33.7万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FE003206%2F1
关键词：
Segregation levee formation geophysical mass

项目摘要

It is crucially important to be able to predict the distance to which a hazardous natural flow of rocky debris might travel; this is the flow runout distance. Runout distance has to be known for accurate assessment of the risks posed in populated areas by geophysical mass flows, such as snow slab avalanches, debris-flows and pyroclastic flows. In the high solids fraction regions of these flows the large and/or low-density particles commonly segregate to the surface, where the velocity is greatest, and are transported to the margins to form bouldery flow fronts. In pyroclastic and debris-flows the flow mobility results from high basal pore pressures that reduce the frictional resistance to motion. Since the pore pressure is dissipated much more rapidly amidst the coarse clasts than in the finer grained material, the bouldery margins experience much greater frictional resistance to motion than the flow interior. This can lead to frontal instabilities and surge waves on steep slopes. On shallow slopes, where the large/low density particles are able to come to rest, the flow front spontaneously organizes itself so that the more resistive bouldery material accumulates at the sides to form lateral levees. There are two mechanisms by which the large/low density particles can move to the side:- (i) they can be shoved en masse out of the way by the material behind or (ii) they can be over-run and recirculated by size/density segregation until they reach a stable position in the levee. Both mechanisms are active in most flows. Somewhat paradoxically, an increased resistance to motion in these bouldery perimeters can lead to much longer runout distances. This is because the levees form a channel that resists lateral spreading of the interior flow, in effect constraining the flow to push forward. This proposal aims to study the processes of segregation, flow mobility and levee formation, using a powerful combination of large-scale flume tests and field experiments, small-scale laboratory experiments and theoretical and computational modelling. This will significantly improve our ability to predict the motion and maximum runout distance of potentially hazardous geophysical mass flows, and will give sedimentologists an improved understanding of the parent flows that form deposits including coarse lobate terminations and levees.

能够预测危险的岩石碎片自然流可能传播的距离至关重要；这是流量跳动距离。为了准确评估地球物理质量流（例如雪板雪崩、泥石流和火山碎屑流）对人口稠密地区造成的风险，必须知道跳动距离。在这些流的高固体分数区域中，大的和/或低密度的颗粒通常偏析到速度最大的表面，并被输送到边缘以形成巨石流前沿。在火山碎屑流和泥石流中，流动流动性是由高底孔压力引起的，高底孔压力降低了运动的摩擦阻力。由于孔隙压力在粗碎屑中的消散速度比在细粒材料中快得多，因此巨石边缘所经历的运动摩擦阻力比流动内部大得多。这可能会导致陡坡上的锋面不稳定和浪涌。在浅斜坡上，大/低密度颗粒能够停下来，流动前沿自发地组织起来，使得阻力更大的巨石材料在侧面积聚，形成侧向堤坝。大/低密度颗粒可以通过两种机制移动到一侧：- (i) 它们可以被后面的材料一起推开，或者 (ii) 它们可以根据尺寸越过并再循环/密度分离，直到它们到达堤坝中的稳定位置。这两种机制在大多数流程中都处于活动状态。有点矛盾的是，这些巨石周边运动阻力的增加可能会导致更长的跳动距离。这是因为堤坝形成了一个通道，阻止内部水流的横向扩散，实际上限制了水流向前推进。该提案旨在通过大规模水槽试验和现场实验、小规模实验室实验以及理论和计算模型的有力结合，研究离析、水流流动和堤坝形成的过程。这将显着提高我们预测潜在危险的地球物理质量流的运动和最大跳动距离的能力，并使沉积学家更好地了解形成沉积物的母流，包括粗叶状终端和堤坝。