Competing effects of thermal superposition and SVE-associated cooling in unsaturated soils: Controlled experiments and model-based transport decomposition

Multi-source heating and soil vapor extraction (SVE) are commonly combined in in-situ thermal remediation, but their competing effects on heat and moisture transfer in unsaturated soils remain difficult to distinguish. This study combines large-scale physical model tests with a thermo-hydro-mechanical (THM)-coupled numerical framework adapted from a previously established granular-thermodynamic formulation. Tests were conducted under single-source heating (SHS), triple-source heating without SVE (THS-NoSVE), and triple-source heating with SVE (THS-SVE), considering two initial dry densities and two gravimetric water contents. Temperature and sensor-derived corrected gravimetric water-content histories were used for model assessment. A matched THS-NoSVE/THS-SVE test with an identical heating history isolated the net SVE response for the dense and wet soil. Across the assessed curves, the range-normalized RMSE (NRMSE) was 2.9–16.2 % for temperature and 11.3–59.3 % for water content, indicating more consistent reproduction of temperature trends than transient moisture peaks. The experiments showed that multi-source heating increased inter-source temperatures; in the matched direct-heating test, SVE reduced temperature and accelerated moisture removal. Model-based term decomposition indicated that conduction dominated without extraction, while fluid-advection-carried heat transport and pressure-gradient-driven vapor transport became the principal calculated components near the extraction well under SVE. Dense and wet soil exhibited more persistent far-field moisture accumulation, interpreted by the model as a saturation-induced reduction in gas-phase mobility. The study separates experimentally observed operating responses from model-derived internal mechanisms and supports coordinated control of heating and extraction during thermal remediation.