Frost heave is a common problem in colder climates of the United States and throughout the world. When the temperature drops below freezing, the moisture in the ground will freeze and expand. The expansion of the frozen water (ice) causes the soil and other materials at the ground surface to be pushed up. If a foundation or pavement has been built over an expanding ground surface, the material could crack if the frost heave is severe enough.
Frost heave results when water freezes beneath a layer of soil. As the water freezes, the newly formed ice expands and pushes the overlying soil upward. If soil is soaked with water before freezing occurs, frost heave can result.
There are several factors that make an area susceptible to frost heave. If there is a continuous supply of water beneath the soil, such as a shallow water table, the soil could be subject to frost heave during freezing conditions. The particle size of a soil can also contribute to soil susceptibility. Silty and loamy soils are most susceptible to frost heave in cold climates.
Frost heave sometimes causes severe damage to structures. If the foundation of a building becomes cracked, it can become a safety hazard. Highways, car parks and other paved surfaces can also be affected by frost heave. Often times, the cracks and damage from frost heave is more of an aesthetic issue, but it can also be dangerous, especially if the cracks are on a surface that people constantly walk on, such as a sidewalk.
The depth of penetration of frost, also known as the frost line, is different in every area. It is important to know the frost line in an area when constructing large buildings or other structures because frost heave could result in any soil above the frost line. A common "safety depth" used in construction is 4 feet.
Preventing Frost Heave
If you live in a cold climate, frost heave can be prevented by digging holes for posts, fences and other structures at least 4 feet into the soil. If the foundation or fence structures are placed into the soil below the frost line, structures should not shift too dramatically during a freezing event. Deep beds should be dug for walkways, garden borders and other forms of decorative structures on your property.