Thermal Gradient's Impact on Segregation Frost Heave of Unsaturated Soil

Abstract

The thermal gradient is a key factor that causes and affects water migration and frost heave deformation (referred to as partial frost heave) of soil in cold regions. To investigate the influence of thermal gradient on the freezing behavior of soil in cold regions, this study used a self-developed experimental device to observe the freezing process of unsaturated soil columns with water supply under different average thermal gradients (ATGs). The deformation field of the soil freezing process was obtained using PIV technology, and the influence of thermal gradient on the migration of unsaturated soil moisture and the freezing deformation process was analyzed. The test results demonstrate the following: (1) The maximum frost heave (17.2 mm), total water uptake (270 ml), segregation crack width (11.3 mm), and peak strain (1.43) occur at the critical ATG of 1.7 °C∙cm⁻¹. (2) The thermal gradient within the frozen fringe (TGFF), but not the ATG, affects water migration, peaking at 1.1 °C·cm⁻¹ (critical ATG) and being correlated linearly with the frost heave amount ($H_v=12.36\times \text{TGFF}+4.12$). (3) Our model $V_0=1.85\times {10}^{-10}\times \text{TGFF}$ (R² = 0.97) enables the accurate prediction of the water migration rate (with a < 7 % error), providing a new method for analyzing frost heave mitigation in engineering projects. A value below the critical ATG (e.g., thermal insulation at 1.7 °C·cm⁻¹) minimizes frost damage in cold-region infrastructure. These findings reveal the effect of the critical ATG on frost heave, ensuring the prevention or control of frost heave in cold region engineering projects.