Ice lenses are formed by the migration and solidification of unfrozen water during soil freezing, which can lead to the upwards displacement of the ground surface known as frost heave. The complicated interplay between heat and mass transport that causes ice lens formation has been addressed by several theoretical models, but uncertainties remain that require further experimental constraints. In particular, the initiation of ice lenses has long posed theoretical difficulties. We performed a series of stepwise freezing experiments in fine granular materials to observe the initiation and growth of ice lenses. Our experiments demonstrate clear and systematic relationships between the behavior of ice lenses, and the particle size and cooling temperature. Ice lenses are thicker when formed in sediments with smaller particle sizes and the initial formation position is further from the cooled boundary when it is set to lower temperatures. Our temperature measurements and photographic documentation demonstrate that ice lenses are formed below the nominal melting temperature, at a location that is sufficiently distant for the freezing velocity to have slowed below a threshold. We compared our experimental results to numerical predictions of ice lens formation that were applied to our experimental conditions. Our experimental trends are consistent with predictions of our simple, initial model. However, important quantitative differences motivate a refined treatment that emphasizes the kinetics of liquid supply from the pore space through the thin films that separate ice lenses from particle surfaces. We obtained good quantitative agreement between our experimental measurements and the refined model predictions, emphasizing the importance of kinetic effects as a control in ice lens initiation and growth.

We investigated the effects of microparticles and grain size on the microstructural evolutions and mechanical properties of polycrystalline ice. Uniaxial compression tests were conducted using fine-grained pure ice and silica-dispersed ice under various conditions. Deformation behavior of fine-grained ice was found to be characterized by stress exponent n ≈ 2 and activation energy Q ≈ 60 kJ mol−1. The derived strain rates of fine-grained ice were ≈ 1 order of magnitude larger than those of coarse-grained ice obtained in previous studies, and they were found to be independent of particle dispersion and dependent on the mean grain size of ice, with grain size exponent p ≈ 1.4. Work hardening was observed in dislocation creep, while the strain rate continued to decrease. These results indicate that the deformation mechanism of fine-grained ice is different from typical dislocation creep, often associated with n = 3. Although microparticles restricted grain growth, there was little direct effect on the deformation of fine-grained ice. Microstructural observations of the ice samples indicated that the grain boundaries were straight and that the subgrain boundary densities increased after deformation. Our experiments suggest that grain size and boundaries play important roles in the deformation processes of polycrystalline ice.

Polycrystalline ice is known to exhibit macroscopic anisotropy in relative permittivity (ɛ) depending on the crystal orientation fabric (COF). Using a new system designed to measure the tensorial components of ɛ, we investigated the dielectric anisotropy (Δɛ) of a deep ice core sample obtained from Dome Fuji, East Antarctica. This technique permits the continuous nondestructive assessment of the COF in thick ice sections. Measurements of vertical prism sections along the core showed that the Δɛ values in the vertical direction increased with increasing depth, supporting previous findings of c-axis clustering around the vertical direction. Analyses of horizontal disk sections demonstrated that the magnitude of Δɛ in the horizontal plane was 10–15% of that in the vertical plane. In addition, the directions of the principal axes of tensorial ɛ in the horizontal plane corresponded to the long or short axis of the elliptically elongated single-pole maximum COF. The data confirmed that Δɛ in the vertical and horizontal planes adequately indicated the preferred orientations of the c-axes, and that Δɛ can be considered to represent a direct substitute for the normalized COF eigenvalues. This new method could be extremely useful as a means of investigating continuous and depth-dependent variations in COF.

Ice lenses are formed during soil freezing by the migration and solidification of premelted water that is adsorbed to ice-particle interfaces and confined to capillary regions. We develop a model of ice lens growth that clearly illustrates how the freezing rate dependence on particle size and soil microstructure changes in response to changes in the relative importance of permeable flow and thin-film flow in governing the water supply. The growth of an ice lens in fine-grained porous media is primarily constrained by low permeability in the unfrozen region. In contrast, the constraints offered by the film flow decrease the lens growth rate adjacent to larger particles. The trade-off between resistance to permeable flow and film flow causes the growth rate for ice lenses to be maximized for particles of intermediate size. Moreover, because film flow along particle surfaces adjacent to a growing lens is not strongly affected by the microstructure of the pore space, our analysis predicts that lensing in coarse-grained porous media is insensitive to the pore microstructure and porosity, but the permeable flow that governs lens formation in fine-grained porous media causes their growth to be much more affected by these details.