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Weathering
Published in Aurèle Parriaux, Geology, 2018
In contrast, fine-grained loose materials (silts and clays) are quite sensitive to freezing. They are often saturated near the surface because of the presence of perched groundwater. When this water freezes, the expanding ice pushes the grains upward, causing a slight upheaval of the soil. When these fine grounds are not saturated, a second phenomenon causes the material to disintegrate: cryosuction (Fig. 13.5a). When an ice crystal forms in a pore of finely granular soil that contains water and air, it exerts a suction potential on the water in neighboring pores (just as a dry soil does) due to the reduction of the liquid water content; this water migrates toward the ice crystal as an active film that covers the grains and freezes at the surface of the crystal. This phenomenon leads to the accretion of ice as horizontal lenses at certain places in the soil. The ice pushes the mineral material out of the soil. All this leads to significant swelling. When the soil thaws, it does not re-establish itself homogeneously: the part of the sediment occupied by the ice lenses subsides deeply. Silty materials are more sensitive than clays to cryosuction because clays are not permeable enough to allow significant migration of water toward the ice lenses.
Weathering
Published in Aurèle Parriaux, Geology, 2018
In contrast, fine-grained loose materials (silts and clays) are very sensitive to freezing. They are often saturated near the surface because of the presence of perched groundwater. When this water freezes, the expanding ice pushes the grains upward causing a slight upheaval of the soil. When these fine grounds are not saturated, a second phenomenon causes the material to disintegrate: cryosuction. (Fig. 13.5a). When an ice crystal forms in a pore of finely granular soil that contains water and air, it exerts a suction potential on the water in neighboring pores (just as a dry soil does) due to the reduction of the liquid water content; this water migrates toward the ice crystal as an active film that covers the grains and freezes at the surface of the crystal. This phenomenon leads to the accretion of ice as horizontal lenses at certain places in the soil. The ice pushes the mineral material out of the soil. All of this leads to significant swelling. When it thaws the soil does not re-establish itself homogeneously: the part of the sediment occupied by the ice lenses subsides deeply. Silty materials are more sensitive than clays to cryosuction because clays are not permeable enough to allow significant migration of water toward the ice lenses.
Effect of temperature gradients on water migration, frost heave and thaw-settlement of a clay during freezing-thaw process
Published in Experimental Heat Transfer, 2023
During the freezing process, a phase change of locally available soil water to ice occurs. However, a part of the soil water remains unfrozen even at temperatures below 0°C [1–3]. The freezing process is generally not limited to the phase transition of locally available soil water and the increase in volume caused by freezing of the in-situ water. The phenomenon of frost heave is caused by water migration, which flows from unfrozen soil to the level of phase transition [4]. This flow of water results from a negative pore water pressure, which builds up in the freezing soil, the so-called cryosuction. As a result of the cryosuction and the associated water migration, the water content can increase considerably in the frozen soil due to the formation of large ice crystals, the so-called ice lenses [5]. The zone between the base of the ice lens and the freezing front is partially frozen, with the water being partially liquid and partially frozen. This zone is referred to as the frozen fringe [6], and it influences the formation of ice lenses. Other zones between the ice lenses of the soil are dewatered and compacted due to cryosuction [7]. After thawing, the volume of the soil is normally smaller than the volume before freezing. This results in the so-called thaw-settlements [8, 9] as a difference in volume of the frozen soil and the thawed soil and the “net thaw-settlements” as a difference in volume between the state before freezing and the state after completion of thaw consolidation [10].