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

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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.