A model of unfrozen water content in rock during freezing and thawing with experimental validation by nuclear magnetic resonance

The unfrozen water content of rock during freezing and thawing has an important influence on its physical and mechanical properties. This study presented a model for calculating the unfrozen water content of rock during freezing and thawing process, considering the influence of unfrozen water film and rock pore structure, which can reflect the hysteresis and super-cooling effects. The pore size distribution curves of red sandstone and its unfrozen water content under different temperatures during the freezing and thawing process were measured using nuclear magnetic resonance (NMR) to validate the proposed model. Comparison between the experimental and calculated results indicated that the theoretical model accurately reflected the water content change law of red sandstone during the freezing and thawing process. Furthermore, the influences of Hamaker constant and surface relaxation parameter on the model results were examined. The results showed that the appropriate magnitude order of Hamaker constant for the red sandstone was 10−19 J to 10−18 J; and when the relaxation parameter of the rock surface was within 25–30 μm/ms, the calculated unfrozen water content using the proposed model was consistent with the experimental value. •Theoretically derived formula for unfrozen water film calculation.•Considering the super-cooling effect and hysteresis effect during freezing-thawing.•The calculation model of unfrozen water content was proposed and verified by experiments.