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Frost penetration is the depth at which frost is beneath the pavement or soil, also known as the frost line or frost depth. There are two ways to calculate frost penetration: theoretically or using field tests. Typically during the theoretical method, information from a freeze index is used. Results from a field test, however, tend to be more accurate. [a]

If frost is present beneath pavement, it can damage the concrete and cause cracking and other failure. Freezing is caused by an increase in moisture content, ice expanding, and ice lenses. Ice lenses are layers of solid ice parallel to the surface of the soil below surface level. They can cause the greatest magnitude of displacement in pavement structures. In order to avoid or minimize damage and frost penetration, drainage systems and optimized thermal properties of the structure should be put in place. [b]