Frost heaves are bulges in the surface of the ground that can cause damage to man-made structures. In cold weather, frost heaves can affect roads, houses, patios, fences and even gardens. In some cases, the heave is minor enough that it only causes slight movement, leaving the structure intact but affecting its cosmetic appearance. In other cases, the damage is much more severe.
How Frost Heaves Work
Frost heaves are thought to function due to the formation of an ice lens. Though the surface of the earth reflects the current temperature outside, the temperature of the soil rises the lower it gets underground. When the surface ground freezes, a frost line forms where the temperature in the earth departs from freezing temperatures. At the frost line, groundwater freezes, forming a thin sheet of ice called an ice lens. As water turns to ice, it expands. The expansion of the ice lens causes the surface soil to bulge upward, resulting in a frost heave.
Frost heaves form in cold temperatures where water is present. One simple solution to this problem is to get rid of the water. Install a good drainage system wherever frost heaves may occur. Though this solution is theoretically simple, it can be difficult to carry out in practical terms. For example, frost heaves affect fences because water at the bottom of each pot hole pools up and freezes there, causing expansion and movement of the poles. To properly drain a fence line, you would need to dig out a trench under each pole. This technique effectively eliminates the occurrence of frost heaves, but requires significant effort to implement.
Use Better Soil
The type of soil you build structures on can also affect the occurrence of frost heaves. Some soil types, like silt, are very susceptible to frost heaves. Silt has small pores and is very permeable, so water seeps into the soil and stays there. In cold weather, that water freezes and causes frost heaves. Gravel resists water the best, due to its large pores. Water tends to drop below gravel rather than pooling up. If you’re building a road, house or other structure and are worried about frost heaves, build only on top of gravel.
Another method for avoiding frost heaves is to install footings on structures. Footings, which are typically constructed of poured concrete or firmly compacted gravel, ensure that posts are firmly grounded below the frost line. When the ground freezes, the footing anchors the post to a lower area of the ground that doesn’t freeze, so the post does not surge upward with the frost. Besides helping to prevent frost heaves, footings also have the added benefit of contributing structural support to the building.
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