In cold regions, the soil temperature gradient and depth of frost penetration can significantly affect roadway performance because of frost heave and thaw settlement of the subgrade soils. The severity of the damage depends on the soil index properties, temperature, and availability of water. While nominal expansion occurs with the phase change from pore water to ice, heaving is derived primarily from a continuous flow of water from the vadose zone to growing ice lenses. The temperature gradient within the soil influences water migration toward the freezing front, where ice nucleates, coalesces into lenses, and grows. This study evaluates the frost heave potential of frost-susceptible soils from Iowa (IA-PC) and North Carolina (NC-BO) under different temperature gradients. One-dimensional frost heave tests were conducted with a free water supply under three different temperature gradients of 0.26°C/cm, 0.52°C/cm, and 0.78°C/cm. Time-dependent measurements of frost penetration, water intake, and frost heave were carried out. Results of the study suggested that frost heave and water intake are functions of the temperature gradient within the soil. A lower temperature gradient of 0.26°C/cm leads to the maximum total heave of 18.28 mm (IA-PC) and 38.27 mm (NC-BO) for extended periods of freezing. The maximum frost penetration rate of 16.47 mm/hour was observed for a higher temperature gradient of 0.78°C/cm and soil with higher thermal diffusivity of 0.684 mm 2 /s. The results of this study can be used to validate numerical models and develop engineered solutions that prevent frost damage.
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A thermomechanical model for frost heave and subglacial frozen fringe
Ice-infiltrated sediment, or frozen fringe, is responsible for phenomena such as frost heave, ice lenses and metres of debris-rich ice under glaciers. Understanding frozen fringes is important as frost heave is responsible for damaging infrastructure at high latitudes and sediment freeze-on at the base of glaciers can modulate subglacial friction, influencing the rate of global sea level rise. Here we describe the thermomechanics of liquid water flow and freezing in ice-saturated sediments, focusing on the conditions relevant for subglacial environments. The force balance that governs the frozen fringe thickness depends on the weight of the overlying material, the thermomolecular force between ice and sediments across liquid premelted films and the water pressure required by Darcy flow. We combine this mechanical model with an enthalpy method that conserves energy across phase change interfaces on a fixed computational grid. The force balance and enthalpy model together determine the evolution of the frozen fringe thickness and our simulations predict frost heave rates and ice lens spacing. Our model accounts for premelting at ice–sediment contacts, partial ice saturation of the pore space, water flow through the fringe, the thermodynamics of the ice–water–sediment interface and vertical force balance. We explicitly account for the formation of ice lenses, regions of pure ice that cleave the fringe at the depth where the interparticle force vanishes. Our model results allow us to predict the thickness of a frozen fringe and the spacing of ice lenses in subaerial and subglacial sediments.
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- PAR ID:
- 10436697
- Date Published:
- Journal Name:
- Journal of Fluid Mechanics
- Volume:
- 964
- ISSN:
- 0022-1120
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Glaciers and ice streams flowing over sediment beds commonly have a layer of ice‐rich debris adhered to their base, known as a “frozen fringe,” but its impact on basal friction is unknown. We simulated basal slip over granular beds with a cryogenic ring shear device while ice infiltrated the bed to grow a fringe, and measured the frictional response under different effective stresses and slip speeds. Frictional resistance increased with increasing slip speed until it plateaued at the frictional strength of the till, closely resembling the regularized Coulomb slip law associated with clean ice over deformable beds. We hypothesize that this arises from deformation in a previously unidentified zone of weakly frozen sediments at the fringe's base, which is highly sensitive to temperature and stress gradients. We show how a rheologic model for ice‐rich debris coupled with the thermomechanics of fringe growth can account for the regularized Coulomb behavior.
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Abstract Glacier-erosion rates range across orders of magnitude, and much of this variation cannot be attributed to basal sliding rates. Subglacial till acts as lubricating ‘fault gouge’ or ‘sawdust’, and must be removed for rapid subglacial bedrock erosion. Such erosion occurs especially where and when moulin-fed streams access the bed and are unconstrained by supercooling or other processes. Streams also may directly erode bedrock, likely with strong time-evolution. Erosion is primarily by quarrying, aided by strong fluctuations in the water system driven by variable surface melt and by subglacial earthquakes. Debris-bed friction significantly affects abrasion, quarrying and general glacier flow. Frost heave drives cirque headwall erosion as winter cold air enters bergschrunds, creating temperature gradients to drive water flow along premelted films to growing ice lenses that fracture rock, and the glacier removes the resulting blocks. Recent subglacial bedrock erosion and sediment flux are in many cases much higher than long-term averages. Over glacial cycles, evolution of glacial-valley form feeds back strongly on erosion and deposition. Most of this is poorly quantified, with parts open to argument. Glacial erosion and interactions are important to tectonic and volcanic processes as well as climate and biogeochemical fluxes, motivating vigorous research.more » « less
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Abstract Flow through partially frozen pores in granular media containing ice or gas hydrate plays an essential role in diverse phenomena including methane migration and frost heave. As freezing progresses, the frozen phase grows in the pore space and constricts flow paths so that the permeability decreases. Previous works have measured the relationship between permeability and volumetric fraction of the frozen phase, and various correlations have been proposed to predict permeability change in hydrology and the oil industry. However, predictions from different formulae can differ by orders of magnitude, causing great uncertainty in modeling results. We present a floating random walk method to approximate the porous flow field and estimate the effective permeability in isotropic granular media with specified particle size distributions, without solving for the entire flow field in the pore space. In packed spherical particles, the method compares favorably with the Kozeny‐Carman formula. We further extend this method with a probabilistic interpretation of the volumetric fraction of the frozen phase, simulate the effect of freezing in irregular pores, and predict the evolution of permeability. Employing no adjustable parameters, our results can provide insight into the coupling between phase transitions and permeability change, which plays important roles in hydrate formation and dissociation, as well as in the thawing and freezing of permafrost and ice‐bed coupling beneath glaciers.
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Frost action in soils causes a significant effect on the performance of roadways. This effect is more pronounced in the regions that are experiencing seasonal subfreezing temperatures as the soil undergoes multiple freeze-thaw cycles. Apart from the subfreezing temperature, the frost action is also affected by the soil type as the void ratio and hydraulic conductivity of soils control the presence and movement of water for the growth of ice lenses. Frost heave is mainly attributed to silty soils, but significant frost heave can also occur in clay and sandy soils under favorable environmental conditions. For the present study, frost heave and thaw settlement of clayey and sandy soils, subjected to a one-dimensional freeze-thaw cycle, is investigated to determine how the frost action varies with soil types. Soil specimens were subjected to ten freeze-thaw cycles. Total heaving, heave rate, and water intake were measured as a function of time during testing. The moisture content of the soils after ten freeze-thaw cycles was also measured. The amount of pore water and external water supply affects the total heave during freeze-thaw cycles. Therefore, the effect of moisture availability during the freeze-thaw cycles was also investigated by comparing the results of specimens with or without an external water supply. Results of the study suggested that significant frost heave occurred in both clay and sandy soils. In addition, the application of ten freeze-thaw cycles provided a better estimation of the total heave than that observed with two freeze-thaw cycles (typical/standard numbers of freeze-thaw cycles). The maximum heave (40.9 mm) and heave rate (5.01 mm/day) were found to be higher in clay soil. The presence of an external water supply contributed to the frost action, and total heave was seven times higher in soils with an external water source. Soil with a free water supply showed 1.1–1.7 times higher moisture content after ten cycles compared to the soils with no external water supply. These results were used in estimating the frost heave potential of soils in different environmental conditions.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/jfm.2023.366
