High speed granular debris flows: new paradigms and interactions in geomechanics

泥石流(通常称为泥石流)是一种土壤、岩石和水一起高速下坡的快速滑坡。这些自然灾害的传播距离很长，并对它们在其流动路径中遇到的生命和基础设施构成风险。在泥石流事件中，固体颗粒大小和流体分离，使大颗粒集中在前部，导致高冲击力。这使得泥石流的行为既危险又物理复杂，因此有几种数学和数值颗粒流理论竞相解释他们的运动。本研究旨在通过在模型泥石流沟道内进行一系列新颖的实验室尺度试验，提高我们对泥石流及其对遇到的障碍物的冲击应力的理解。在二维模型实验中，土壤和岩石将被丙烯酸颗粒取代，并使用光弹性方法来确定材料向下流动时单个颗粒中的力，而不考虑流体的相互作用。然后将结果与现有的二维颗粒流理论进行比较，以确定哪种理论在颗粒运动和颗粒中诱导的应力方面与结果最匹配。在3D实验中，土壤和岩石将被玻璃颗粒取代，水将被光学匹配的流体取代，这将使混合物几乎透明。然后，穿过系统的激光平面将在其中心创建流动的可视切片，因此在高速运动期间，在明亮的流体背景下，2D粒子切片将显示为黑色。通过高速摄影捕捉到这一行为，将能够与3D颗粒流理论在流体存在时的颗粒运动和远离井壁边界效应方面进行比较。在3D的第二系列测试中，代表流动或基础设施的结构性障碍的障碍物将被放置在玻璃和流体泥石流模型的路径上，以便检查其与障碍物的相互作用。除了使用更传统的技术外，还将使用一种新的方法--全息干涉计量术--进行试验，以确定结构本身的变形和应力如何与泥石流模型的颗粒撞击有关。这种方法能够检测到整个物体上非常小的变形，因此非常适合于研究多个颗粒与不同形状和大小的障碍物之间的复杂相互作用。总体结果将是几个数据集，可以用来更好地对泥石流进行数值模拟，其中唯一包括泥石流对结构物和结构物对泥石流的影响。希望这些成果能够更好地设计防止泥石流的屏障，加强和保护自然和建筑环境，从而更好地保护人类生命。

Debris flows (often called mudflows) are a type of rapid landslide where soil, rocks and water flow together at high speed downslope. These natural hazards travel for long distances and pose risks to lives and infrastructure that they encounter in their flow paths. During a debris flow event, solid particle sizes and fluid segregate so that large particle are concentrated in the front, leading to high impact forces. This renders their behaviour both dangerous and physically complex so that there are several mathematical and numerical granular flow theories competing to explain their motion.This research seeks to improve our understanding of debris flows and the impact stresses they can cause to obstacles they encounter, by conducting a series of novel laboratory scale tests in 2D and in 3D on flows confined within model debris flow channels. In the 2D model experiments, the soil and rock will be replaced by acrylic particles, and a photoelastic method used to enable the forces in the individual particles to be determined as the material flows downslope without considering fluid interactions. The results then will be compared against current theories of granular flow in 2D in order to determine which theories best match the results in terms of particle motion and stresses induced in the particles. In the 3D experiments, the soil and rock will be replaced by glass particles and the water by an optically matched fluid which will render the mixture virtually transparent. A laser plane passing through the system then will create a visual slice of the flow at its centre, so that the 2D slice of particles will appear as dark against a bright fluid background during high speed motion. Capturing this behaviour via high speed photography will enable comparison with granular flow theories in 3D in terms of particle motion in the presence of fluid and away from sidewall boundary effects.In the second series of tests in 3D, an obstacle, representing a structural barrier to the flow or infrastructure, will be placed in the path of a model glass-and-fluid debris flow so that its interaction with the obstacle can be examined. As well as using more conventional techniques, the use of a novel method, holographic interferometry will be trialed to determine how the deformation and stresses in the structure itself are related to particle impacts from the model debris flow. This method can enable the detection of very small deformations over a whole object so is ideally suited to examining the complex interactions of multiple particle impacts with obstacles of differing shape and size.The overall outcomes will be a several datasets that can be used to better model debris flows numerically, which uniquely includes both the influence of a debris flow on a structure and a structure on a debris flow. It is hoped that the results may lead to better design of barriers to debris flows, enhancing and protecting the natural and built environment and hence leading to greater protection of human life.