Collaborative Research: Multiscale Investigation of Thixotropy in Soft Clays

合作研究：软粘土触变性的多尺度研究

• 批准号: 1640306
• 负责人: Guoping Zhang
• 金额: $ 34.9万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1640306&HistoricalAwards=false
• 关键词: Collaborative; Research; Multiscale; Investigation; Thixotropy

Thixotropy is a material property that describes how a substance can "thicken" over time. Simple examples of thixotropic materials available in the house are in the kitchen (ketchup), the bathroom (toothpaste), the art studio (paints), and the toy box (silly putty). Each of these materials if left untouched will become stiffer, but when the material is worked (or used) it will move more easily. This concept also is used to describe the behavior of some naturally occurring clay soils. Scientists and engineers have long observed this phenomenon in clays, but only a theorized or hypothesized explanation has been presented to date to explain the underlying mechanisms. The work in this research project aims to examine and simulate the clay particle-scale development of thixotropy under various environmental conditions (time, water chemistry, and temperature) and at different size scales. This innovative multiscale approach to understanding the mechanisms of thixotropy serves to advance the NSF mission of promoting the progress of science by filling a void of information utilizing recent advances in theory, experimentation, and computing. The new knowledge gained in this work will aid in the design and construction of engineering systems involving soft clays, such as deep pile foundations, offshore pipelines, wind farm foundations, disposal of dredged materials, drilling mud stability, and seabed clay acoustic properties, among others. The project also includes a significant outreach program to help attract under-represented minority students to STEM disciplines through publications and K-12 school activities and demonstrations.Thixotropy is a fundamental soil behavior mechanism that governs multiple time-dependent engineering properties of soft clays (e.g., the evolution of stiffness, strength, and sensitivity over time). While significant understanding of thixotropy of colloid systems has been achieved since the initiation of the field of thixotropy in the early 1920s, current knowledge on soil thixotropy is still based primarily on some pioneering work performed in and prior to the 1960s and, since then, new developments have been scarce and fragmental. Such a paucity of new findings and the disparity in thixotropy research and advancement between colloid science and soil mechanics provide an impetus to this research. Therefore, this collaborative project that integrates multiscale experimental and computational efforts is to study soft clay thixotropy. The overall goal of the project is to create the enabling knowledge on the macroscale mechanical and microscale structural mechanisms of soft clay thixotropy and hence to append some new time-dependent soil behavior to the geotechnical knowledge base. To achieve this goal, a congruent and comprehensive research program consisting of three primary thrusts is designed with synergistic collaboration among the three investigators from UMass Amherst and Drexel University with complementary expertise in macroscale mechanical testing, microscale fabric imaging, quantitative characterization of particle orientations, and coarse-grained molecular dynamics simulations. The intellectual merit of the project stems from three aspects: (1) the geotechnical knowledge base on soil thixotropy will be expanded with new understanding, particularly the effects of physico-chemical factors such as temperature and porewater chemistry; (2) both the macroscale mechanical and microscale structural mechanisms of thixotropic hardening of soft clays will be uncovered via multiscale experimental and computational research; and (3) the linkage between quantitative time-dependent clay fabric evolution and macroscale thixotropic processes will be developed. Because soil thixotropy plays an important role in many engineering problems, the project also can generate significant practical impacts to geotechnical engineering, particularly the design and construction of engineering systems involving soft clays. Examples include evaluation of pile and suction caisson setup, design of wind farm foundations, and disposal of dredged materials, among others. Moreover, the multiscale investigation methodology developed through this project can be generalized to other more complex soil research topics and can also serve as a generic approach for other basic research queries.

触变性是一种材料特性，描述物质如何随着时间的推移而“增稠”。 房屋中可用的触变材料的简单例子包括厨房（番茄酱）、浴室（牙膏）、艺术工作室（油漆）和玩具盒（橡皮泥）。 如果不受影响，这些材料中的每一种都会变得更硬，但是当材料被加工（或使用）时，它会更容易移动。 这个概念也用于描述一些天然粘土的行为。 科学家和工程师长期以来在粘土中观察到这种现象，但迄今为止仅提出了理论或假设的解释来解释其潜在机制。 该研究项目的工作旨在检查和模拟在不同环境条件（时间、水化学和温度）和不同尺寸尺度下粘土颗粒尺度触变性的发展。 这种理解触变性机制的创新性多尺度方法有助于通过利用理论、实验和计算的最新进展填补信息空白，从而推进 NSF 促进科学进步的使命。 这项工作中获得的新知识将有助于涉及软粘土的工程系统的设计和施工，例如深桩基础、海上管道、风电场基础、疏浚材料的处理、钻井泥浆稳定性和海底粘土声学特性等。 该项目还包括一项重要的外展计划，通过出版物和 K-12 学校活动和演示，帮助吸引代表性不足的少数族裔学生进入 STEM 学科。触变性是一种基本的土壤行为机制，控制着软粘土的多种与时间相关的工程特性（例如，刚度、强度和敏感性随时间的演变）。 虽然自 20 年代初触变性领域兴起以来，人们对胶体系统的触变性有了重要的了解，但目前对土壤触变性的了解仍然主要基于 20 世纪 60 年代及之前进行的一些开创性工作，自那时以来，新的进展很少且支离破碎。 新发现的缺乏以及胶体科学和土壤力学之间触变性研究和进步的差异为这项研究提供了动力。 因此，这个整合多尺度实验和计算工作的合作项目是研究软粘土触变性。 该项目的总体目标是创建有关软粘土触变性的宏观力学和微观结构机制的有利知识，从而将一些新的随时间变化的土壤行为添加到岩土知识库中。 为了实现这一目标，由麻省大学阿默斯特分校和德雷克塞尔大学的三名研究人员协同合作设计了一个由三个主要方向组成的一致且全面的研究计划，他们在宏观机械测试、微观织物成像、颗粒方向的定量表征和粗粒度分子动力学模拟方面具有互补的专业知识。 该项目的智力价值源于三个方面：（1）对土壤触变性的岩土工程知识库将有新的认识，特别是温度和孔隙水化学等物理化学因素的影响； （2）通过多尺度实验和计算研究，揭示软粘土触变硬化的宏观力学和微观结构机制； (3) 将建立定量的时间依赖性粘土结构演化与宏观触变过程之间的联系。 由于土壤触变性在许多工程问题中发挥着重要作用，该项目也可以对岩土工程，特别是涉及软粘土的工程系统的设计和施工产生重大的实际影响。 例如，桩和吸力沉箱设置的评估、风电场基础的设计以及疏浚材料的处理等。 此外，通过该项目开发的多尺度调查方法可以推广到其他更复杂的土壤研究主题，也可以作为其他基础研究问题的通用方法。

项目成果

Rigidity index of soft remolded clays during thixotropic hardening

软重塑粘土触变硬化过程中的刚性指数

• 发表时间: 2020
• 期刊: 4th International Symposium on Frontiers in Offshore Geotechnics
• 作者: Jing Peng, Don J.