Collaborative Research: A Unified Pore Water Pressure-based Paradigm for Quantifying Unfrozen Water in Frozen Soil

Climate change is exacerbating the frequency and severity of extreme phenomena on the Earth’s surface, including melting of arctic ice and thawing of permafrost in cold regions around the world. Mitigation of these hazards requires an improved fundamental understanding of soil water freezing and thawing phenomena, which will ultimately advance our ability to predict and model soil water freeze and thaw behavior. This project seeks to develop a new paradigm for quantifying unfrozen soil water content in freezing environments. Improved basic understanding of soil water freezing and thawing behavior will impact a broad range of hydrologic science applications, including the hydro-mechanical behavior of permafrost, land settlement, soil erosion, and land sliding. Education and outreach initiatives will be integrated with the research to capitalize on the collaborative nature of the project, including a summer student exchange program and a continuing education webinar series hosted by an industrial collaborator. A new theoretical framework based on a generalized soil water potential that includes both capillarity and adsorption will be formulated to quantify local pore water pressure distribution and corresponding phase change phenomena in soil. Modern laboratory approaches will be advanced to measure soil water isotherms defining the constitutive relation between water potential and water content and soil freezing curves defining the constitutive relation between soil temperature and unfrozen soil water content. Outcomes from the effort will include: clarification of fundamental relationships among soil water potential, soil water retention, and soil water freezing/thawing for a wide range of soil types and pore fluid chemistries; generalized closed-form equations for modeling soil freezing and soil thawing curves; and practical predictive relationships that may be adopted to estimate soil freezing and thawing behavior from fundamental soil properties including specific surface area and cation exchange capacity. 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.