Moisture-path-dependent thermal resistivity hysteresis of compacted soils for energy and geotechnical systems

Poor understanding of soil heat transfer and thermal resistivity accelerates the deterioration of buried energy and geotechnical infrastructure systems, with consequent effects on their short- and long-term safety and reliability. This study presents a unified, cross-textural framework that quantifies the effect of soil grain size on hysteresis (wetting and drying pathways)-driven alterations in soil thermal resistivity across complex soil textures and moisture contents. We conducted a series of standardized experiments on representative soil types spanning coarse-grained to fine-rich soils under controlled wetting and drying moisture states, from which we characterized soil-class-specific hysteresis behavior. Results demonstrate that wetting and drying pathways produce systematically distinct thermal resistivity responses, with the wetting path exhibiting values up to 255% higher than those of the drying path. This variation is governed by particle-size distribution, the associated pore-network characteristics, and the water-retention capacity of each soil type. The drying path, obtained by allowing compacted saturated soils to lose moisture naturally, most accurately represents in-situ soil thermal conditions compared to the wetting path, and is recommended as a candidate for a measurement path for infrastructure design. Based on these experimentally validated results, we propose a new, relatively close-to-field-representative framework for standardized thermal dry-out curve generation, guided by three physically distinct moisture states (oven-dry condition, hygroscopic moisture content, and optimum moisture content), and applicable across soil types regardless of classification. Collectively, these findings provide robust guidelines for reliable, efficient, and relatively close to field-representative characterization of soil thermal resistivity, advancing measurement protocols and design practice for buried and geotechnical infrastructure.