Collaborative Research: Closing the Gap Between Theory and Evidence: Coupled Phenomena in Unsaturated Bentonite Barriers Under Variable Temperature and Chemical Conditions

膨润土是一种高膨胀粘土，其热-水-化学（THC）特性在日益增长的能源需求和保护水与环境的巨大挑战中起着至关重要的作用。具体来说，了解膨润土中耦合的四氢大麻酚现象对安全放射性、城市和危险废物处理、液体（如石油）储存设施和碳封存都很重要。尽管在过去的20年里，耦合现象的数值和概念模型取得了进展，但由于实验室测试的挑战，实验证据仍然有限。本研究采用新颖的实验方法来评估不同膨润土在不同热、水力和化学条件下的耦合现象，并改进现有的理论模型。该结果将缩小我们对膨润土THC行为的认识差距，促进科学进步，提高我们预测污染物如何通过环境遏制系统迁移的能力。该项目包括广泛参与两所大学代表性不足的本科生，促进重视和支持本科生研究经验的校园文化，并为未来的工作建立最佳实践。该项目还加强了现有的STEM外展工作，为K-12年级增加了新的土壤工程特性讲习班。粘土耦合行为的理论模型和实验数据之间的差距限制了我们评估围护屏障在现场条件变化下的长期弹性的能力。此外，最近开发的化学改性膨润土作为具有增强工程性能的屏障材料已经取得了进展，尽管人们对这种粘土在非饱和和高温条件下的性能知之甚少。鉴于我们目前对膨润土中偶联现象的理解的局限性，本研究试图回答以下问题：控制膨润土屏障中偶联现象重要性的现象系数如何随温度、浓度和饱和度变化？这项合作研究的目标是：(1)开发新的实验室测试系统，用于测量粘土在可变水力、热和化学条件下的化学传输特性；(2)定量研究了不同饱和度的传统膨润土和化学改性膨润土在高温下的四氢大麻酚耦合行为；(3)验证或改进耦合粘土行为的概念和理论模型，以推进通常用于遏制污染物的地质环境屏障的评估；(4)增加威斯康星大学普拉特维尔分校和维拉诺瓦大学本科生的研究参与。这项合作研究代表了第一次全面理解在不同温度、饱和度和化学条件下钠和改性膨润土中完全耦合现象的尝试，促进了对四氢甲烷行为的基本理论的理解和对地球环境系统长期性能的预测。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Thermal-hydraulic-chemical (THC) behavior of bentonite, a high-swelling clay, plays a critical role in the grand challenges of growing energy demand and protection of water and the environment. Specifically, understanding coupled THC phenomena in bentonite is important for safe radioactive, municipal and hazardous waste disposal, liquid (e.g., petroleum) storage facilities, and carbon sequestration. Although advances have been made in numerical and conceptual models of coupled phenomena over the last 20 years, experimental evidence remains limited due to challenges associated with laboratory testing. This research utilizes novel experimental approaches to evaluate coupled phenomena in different bentonites under various thermal, hydraulic and chemical conditions, and advance current theoretical models. The results will narrow the knowledge gap in our understanding of THC behavior of bentonites, promoting the progress of science and improving our ability to predict how contaminants migrate through environmental containment systems. The project includes extensive involvement of underrepresented undergraduate students at both universities, promoting campus cultures that value and support research experiences for undergraduates and establishing best practices for future work. The project also enhances existing STEM outreach efforts with the addition of new workshops for grades K-12 on soil engineering properties. The existing gap between advancements in theoretical models and experimental data for coupled behavior of clays has limited our ability to evaluate long-term resiliency of containment barriers subjected to changes in field conditions. In addition, recent development of chemically-modified bentonites for use as barrier materials with enhanced engineering properties has gained momentum, although the performance of such clays under unsaturated and elevated temperature conditions is poorly understood. Given the limitations in our current understanding of coupled phenomena in bentonites, this research seeks to answer the question: How do phenomenological coefficients controlling the significance of coupled phenomena in bentonite barriers change with temperature, concentration, and degree of saturation? The objectives of this collaborative research are to: (1) develop novel laboratory testing systems for measurement of chemical transport properties of clays under variable hydraulic, thermal, and chemical conditions; (2) quantify properties controlling coupled THC behavior of traditional and chemically-modified bentonites with variable degrees of saturation under elevated temperatures; (3) validate or improve conceptual and theoretical models of coupled clay behavior to advance evaluation of geoenvironmental barriers commonly used for containment of contaminants; and (4) increase undergraduate research involvement at University of Wisconsin-Platteville and Villanova University. This collaborative research represents the first comprehensive attempt at understanding fully coupled phenomena in sodium and modified bentonites under variable temperature, saturation, and chemical conditions, advancing understanding of fundamental theory for THC behavior and prediction of long-term performance of geoenvironmental systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.