Prediction model of unfrozen water content in weak expansive soils for high-speed railway subgrade based on thermodynamic principles

Abstract

Unfrozen water content (θ_u) in weak expansive soil during freezing is a primary factor influencing uneven frost heave deformation of high-speed railway subgrades in western China. However, the mechanism underlying θ_u evolution and its prediction modeling in weak expansive soil remains unexplored. This study employs nuclear magnetic resonance technology to investigate the influence of swelling potential on the θ_u in weak expansive soils and to elucidate the underlying mechanisms. Based on thermodynamic principles, a theoretical prediction model incorporating the swelling potential parameter is thus established. The results indicated that the freezing process can be categorized into three stages, with a pronounced phase change occurring between −2 and −4 °C. Increasing swelling potential from low potential to high potential in weak expansive soil leads to a reduction in the freezing point by 2 °C, and the θ_u at −4 °C improves by 7.3 %. In addition, experimental findings demonstrated that the proposed theoretical model accurately predicts the variation of θ_u in weak expansive soil (coefficient of determination, R² > 0.95 and relative error below 15%). Finally, the model is validated using weak expansive soil samples from other regions, and the results showed that the model predictions remain in strong agreement with the measured data (R² > 0.95), with approximately 87% of data points exhibiting a relative error below 2% between theoretical and measured values. This study provides a theoretical foundation for the design of subgrades in cold regions containing weak expansive soil.

Graphical abstract

Keywords

unfrozen water content / weak expansive soil / freezing process / thermodynamic principles / theoretical model

References

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