Um ... What the Heck Is Frost Heave?

Have you ever wondered why the pavements in your area are fractured and displaced or noticed abandoned buildings that are twisted and buckled? Chances are the damage was caused by frost heave, a phenomenon that commonly occurs in regions where the soil freezes to a significant depth in winter.

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What Is Frost Heave?

The definition of frost heave is a lifting of the surface of the ground caused by the freezing of moisture in the soil. It happens in regions where the soil holds an appreciable amount of moisture that freezes during the coldest winter months, typically January and February. As the moisture freezes, it forms into circular ice lenses, so-called because of their shape, and increases in volume , forcing the soil upward. The forces exerted by deep-frozen ice are immense and can easily distort and damage structures above the frozen soil.

How to Recognize Frost Heave

There are many typical signs of frost heaves. These include uneven and cracked driveways and sidewalks. Sometimes, you'll see that a concrete slab is cracked and displaced. In homes, the effects are more serious and include bowing basement walls and cracked exterior walls. In some instances, a frost heave can push the foundation footing upward. Decks attached to a house may distort and move away from the home.

Where Does Frost Heave Occur?

Frost heave is likely in any location where the soil freezes to a considerable depth. According to the U.S. Department of Commerce's frost line map, the areas most affected by ground freezing include the central, northern and eastern regions of the United States. Most of Canada is also affected. Other factors that contribute to the likelihood of frost heave include soil that retains water and high water tables in the area.

How Do You Prevent Frost Heave?

For frost heave to occur, three conditions must be met:

• The existence of freezing temperatures for long enough for the soil to freeze

• The presence of damp, loosely packed soils with small particles that draw water upward through capillary action

• A continuous water table close to the frost depth

Frost heave mitigation measures aim to eliminate one or more of these conditions. Common measures include:

• Improving drainage. Excavate the soil around the proposed footing and slab and replace it with a layer of gravel, crushed stone or fine sand at least 6 inches deep. This allows water to drain freely and prevents capillary action.

• Placing insulation below concrete footings. Install a layer of insulation below the concrete when building. This prevents frost from penetrating the surrounding soil.

• Use frost-resistant building materials. Employ building materials such as frost-protected shallow foundations

  and insulated concrete forms (ICFs).

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How Do You Fix Frost Heave?

Older homes not built in accordance with frost-resistant building codes and practices may suffer frost heave damage. However, if this is addressed before severe damage occurs, it's generally possible to repair building foundations and prevent future frost heave. A qualified foundation repair specialist should always perform the repairs. Techniques used include improving soil drainage, soil stabilization or replacement and the installation of helical piers.

Install Drainage Systems

A drainage system will stop water from accumulating around and under the wall footings. Drainage systems typically consist of perforated pipes laid in stone or gravel around the foundations to drain the water away from the foundation. Examples include French drains and the Hydraway drainage system.

Stabilize the Soil to Resist Water Infiltration

Where possible, excavate the soil down to frost depth and replace it with a sand or dirt fill that resists capillary action, or use an impermeable clay soil. Alternatively, it's possible to inject a polymer into the soil that resists water infiltration.

Install Helical and Other Piers

Install reinforcing piers to support the building. One of the best methods is to install deep helical piers screwed into the ground. This type of pier is suitable for long-term support in sands that are susceptible to water saturation. Alternatively, a foundation specialist can install conventional concrete support piers that reach below the frost line.