WHAT IS FROST ACTION IN SOIL?

Frost Action In Soil

Frost action in a soil is a phenomena that occurs in the winter and early spring climates.There are two type of frost action Frost heavy and Frost boil.Frost heavy is a phenomenon in which the water molecules present in the pores freeze during lower temperature which results in the expansion of the soil.Frost boil is the phenomenon of loosing of the soil when the  frozen soil starts to thaw.Frost boil occurs after the frost heavy process.

Frost Heavy In Soils

Frost heavy is an upwards swelling of soil during freezing conditions caused by an increasing presence of ice as it grows towards the surface, upwards from the depth in the soil where freezing temperatures have penetrated into the soil. This results in an increase in the volume of soil because when water is converted into ice there is about 9% increase in its volume.If the porosity of soil is 45% and soil is saturated, the expansion of the soil would be (0.09 x 45) = 4.05%. In other words, there would be a heavy of about 4 cm in every one meter thickness of the soil deposit.Due to frost heavy, the soil at the ground surface is lifted.

The frost have observed in most of the soils is much more than a heavy of about 4 cm per meter.This is due to the fact that when the ice lenses are formed in the soil due to freezing of water, the water film from the adjacent soil particles is also removed.The weight of overlying soil restrains vertical growth of the ice and promote the formation of lens-shaped areas of ice within the soil.The soils which are prone to frost action are mainly silts and fine sands.These soils have large capillary rise due to relatively fine particles.

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Frost Boil In Soils

A frost boil, also known as mud boils or mud circles are small circular mounds of fresh soil material formed by frost action and cryoturbation. After the occurence of frost heavy, if the temperature rises the frozen soil thaws and free water is liberated.Thawing process starts from the upper layer and moves downwards.The liberated water is trapped in the upper layer while the lower layers are still frozen.The strength of soil in upper layer is reduced due to its softening caused by an increases in water content.The process of softening of soil due to liberation of water during thawing is known as Frost boil.

Frost boils are among the most common features of patterned ground the pervasive process shaping the topology of soils in periglacial regions.They generally from regular patterns of polygons.Frost boils are a type of nonsorted circle and are characterized from other circle by barren centres of mineral soil and intercircle region filled with vegetation and peat.It is named after skin boils due to similarities in their formation processes although subsequent research has shown other methods of formation.

Frost boil affects the structures resting on the ground surface.The effect is more pronounced on highway pavements.A hole is generally formed in the pavement due to extrusion of soil and water under the action of wheel loads.Coarse grained soils are not affected much by frost boil, as the quantity of liberated water is small and that too is drained away quickly.The soils most prone to the softening effects are silty soils.These soils have low plasticity index and become very soft with a small increase in water content.

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