Experimental investigation on the hydro-thermal variation and frost heave during the unidirectional freezing process of sandy soil

Through conducting the unidirectional freezing model test under an open system, this study explores the variation characteristics of the temperature field, unfrozen water content and frost heave of sandy soil. The lower cold plate temperature results in a faster cooling rate and a larger absolute temperature gradient within the soil column, and the stable frozen area increases nonlinearly. With the dry density of sandy soil increasing, the stable temperature decreases and then increases, and the lowest temperature occurs under a dry density of 1.9 g/cm 3 . Weak upward moisture migration appears during the freezing process, and the unfrozen water content decreases rapidly with the temperature falling below the freezing point, with values being higher along the freezing path than the thawing path. Frost heave in sandy soil is significantly affected by high dry density, and it transitions from non-frost heaving to weak frost heaving when the dry density reaches 2.1 g/cm 3 . Additionally, considering the influence of saturation transformation on the moisture migration and heave deformation, a thermal-hydro-deformation coupling model was developed to describe the freezing process of sandy soil, which was validated with the measured data of the model test. This research reveals the freezing characteristics of sandy soil, and it will contribute to the thermal-mechanical stability analysis of artificial freezing engineering such as subway tunnel in water-rich sandy strata.