Mobilization of Sand Particles and Erosion Progression Under Various Permeating Fluids

众所周知，管涌会导致堤坝和土坝的灾难性破坏，人们对管涌的研究已经有近世纪了。 在典型的土壤侵蚀实验研究中，通常采用自来水或去离子水作为渗透流体，因此对土壤侵蚀行为的认识大多局限于以相对纯净的水作为渗透流体的情况。 在现场，通过土坝或堤坝的渗透流体可能含有泥浆（在泥浆墙安装的情况下）或来自上游土壤侵蚀的渗透流体中携带的细粉。细粒含量可具有各种尺寸、浓度和其它物理化学特性。 在恒定水头条件下的孔蚀试验中，我们进行了可重复的室内试验，结果表明，不同渗透流体对砂土管涌的影响有显著差异。 膨润土泥浆和水，含有1%的无粘性的罚款并没有引起管涌的进展，在一个较长的时间内，而水和水与0.1%的罚款造成的预形成管涌孔扩大到一侧的土柱在不到40分钟。 在具有无粘性细粒的流体的情况下，这种观察是违反直觉的，这是基于目前的知识，即具有较高密度和粘度的渗透流体倾向于施加较高的水力剪切应力并引起更多的侵蚀。 目前的认识和最近的实验室观测之间的差距是由于缺乏基本的了解悬浮液-流体-土壤相互作用。 本研究的假设是，渗透流体的物理化学特性（粘度，流体密度，离子强度，pH值，并可能悬浮液的表面电位）和流动条件的累积有助于砂的侵蚀。 本研究的主要目的是确定悬浮液-流体-土壤相互作用的物理化学机制，并提供不同的渗透流体和水力条件下的砂的不同侵蚀行为的基本解释。 本研究将回答以下三个问题：（1）是哪种力主导着粒子的移动：粒子间的伦敦-范德华力和电双层力，还是流体动力？(2)具有不同物理化学特性（颗粒浓度、尺寸、粘度、流体密度、静电表面电位、离子强度、pH值）的各种渗透流体如何对驱离力产生影响？ 哪个是主导因素？(3)流速（即，层流和湍流）改变了上述每个因素在颗粒去除中的作用？ 将对十一种渗透流体的物理化学特性进行实验量化。 微观流动实验和实验室孔侵蚀实验使用的11种流体将进行揭示在不同的水力条件下的颗粒驱逐过程中的上述特征的个人角色。这项研究将产生变革性的知识，因为它将提供现实的理解，管涌进展土坝和堤坝。 它还将指导我们现实地评估和修复许多自然和建筑基础设施，例如在自然河岸栖息地保护中，在河床或桥梁基础冲刷中，水流可以以不同的流速携带不同浓度的各种颗粒，以及在管道工程中，雨水，废水或石油可能具有不同的粘度或携带各种颗粒负荷。 这笔资金还将为PI提供教育机会，指导研究生成为未来独立和自信的研究人员，及时将多学科研究方法和成果整合到研究生和本科生课程中，并与K-12学生和代表性不足的本科生进行外联和参与研究，以吸引未来的人才到STEM领域。 在这个项目中开发的知识将通过网站、在大学和高中的演示以及PI和学生撰写的出版物进行传播。

Piping is known to cause catastrophic failures of levees and earthen dams, and has been studied for nearly a century. In the typical experimental studies on soil erosion, tap water or de-ionized water is used as permeating fluid; therefore, the understanding of soils' erosion behavior is mostly limited to situation where relatively pure water is the permeating fluid. In the field, permeating fluids through earthen dams or levees may contain slurry (in the case of slurry wall installation) or fines that are carried in the permeating fluid from the upstream soil erosion. The fines content may have various sizes, concentrations, and other physicochemical characteristics. Our repeatable laboratory experiments in hole-erosion tests under constant head have revealed that the piping progression of a sand differed significantly with different permeating fluids. Bentonite slurry and water that contains 1% cohesionless fines did not induce piping progression during a prolonged period, while water and water with 0.1% fines caused the pre-formed piping hole to enlarge to the side of the soil column in less than 40 minutes. This observation is counter-intuitive in the case of fluid with cohesionless fines, based on the current knowledge that permeating fluid with higher density and viscosity tends to exert higher hydraulic shear stress and cause more erosion. The gap between the current knowledge and the recent laboratory observation is due to the lack of fundamental understanding of the suspension-fluid-soil interaction. The hypothesis of this research is that the physicochemical characteristics (viscosity, fluid density, ionic strength, pH, and possibly suspension's surface electric potential) of the permeating fluids and the flow conditions accumulatively contribute to the erosion of sand. The main objective of this research is to identify the physicochemical mechanisms of suspension-fluid-soil interactions and provide fundamental explanations for the different erosion behaviors of sand under various permeating fluids and hydraulic conditions. The research project will answer the following three questions: (1) Which forces dominate the particle dislodging: inter-particle London-van der Waal forces and electrical double layer forces, or the hydrodynamic forces? (2) How do the various permeating fluids with different physicochemical characteristics (particulate concentration, size, viscosity, fluid density, electrostatic surface potential, ionic strength, pH) contribute to the dislodging forces? Which is a dominating factor? (3) How does the flow rate (i.e., laminar and turbulent flows) change the role of each of the aforementioned factors in particle dislodging? The physicochemical characteristics of eleven permeating fluids will be experimentally quantified. Microscopic flow experiments and laboratory hole erosion experiments using the eleven fluids will be conducted to reveal the individual roles of the aforementioned characteristics in the particle dislodging process at different hydraulic conditions. This research will yield transformative knowledge because it will provide realistic understanding of the piping progression in earthen dams and levees. It will also guide us to realistically evaluate and remediate many natural and built infrastructures, such as in natural riparian habitat protection, in riverbed or bridge foundation scouring where flows can carry various particles with different concentrations at different flow rate, and in pipeline engineering where storm water, wastewater, or oil can have different viscosity or carry various particle loadings. This funding will also provide educational opportunities for the PI to mentor graduate students to become future independent and confident researchers, to timely integrate multidisciplinary research methodologies and outcomes into graduate and undergraduate courses, and to outreach to and involve K-12 students and underrepresented undergraduate students in research in order to attract future talents to the STEM fields. The knowledge developed in this project will be disseminated through websites, presentations in university and high schools, and publications written by the PI and students.