Physics of Frost Heave
Frost heave occurs in roads having fine graded, so-called frost-susceptible, material, at a depth to which the freezing front reaches during the winter. A well-built road of consistent materials and cross-section can be expected to heave relatively evenly. When inconsistencies or inhomogeneities are found in the construction of the affected subgrade, then frost heave is likely to be uneven and may well cause an uneven road surface that results in reduced travelling speed and comfort.
Although such heave can be problematic, a much greater problem usually arises in spring-time when the ice that has formed in the road construction, which was instrumental in causing the frost heave, melts and results in a very high water content in the pavement and subgrade. The increased water content often means reduced bearing capacity. For this reason many countries impose spring-thaw load restrictions on low volume roads to avoid severe pavement deterioration.