Heat transfer and water migration in loess slopes during freeze-thaw cycling in Northern Shaanxi, China

Migration of heat and water during freeze-thaw cycling has always been one of the significant topics in frozen soil mechanics. This paper first carries out field tests in the heartland of Loess Plateau, i.e., Northern Shaanxi, China, on the water migration and heat transfer in loess slopes during freeze and thaw. Results indicate that the water content within a certain depth shows sudden increase during freezing, while it tends to be more uniform after thawing, strongly depending on the variation of temperature profile over depth. When modeling heat and water migration in seasonal frozen ground, two characteristic curves, i.e., soil freezing curve and water retention curve, were incorporated in an improved Harlan model. The modified Richards' equation and a nonlinear heat conduction equation considering ice-water phase change were both included. As for the effect of freeze-thaw cycling, laboratory tests were carried out to investigate how the coefficients of heat and water conductivity vary with both the degree of saturation and freeze-thaw cycles, based on which empirical models for loess were derived. A large-scale model test on the loess slope with the gradient of 1:0.75 was carried out to verify the rationality of the proposed model. Comparison of calculated curves and test data shows that the proposed method well describes the migration of both heat and water during cyclic freeze and thaw.