Frozen Ground

Frozen ground is soil or rock with a temperature below 0°C. The definition is based entirely on temperature and is independent of the water and ice content of the soil or rock. The large increase in soil strength on freezing has been utilized by engineers in the construction of frozen earth structures. The ice becomes a bonding agent, fusing together adjacent soil particles or blocks of rock to increase their combined strength and make them impervious to water seepage. Excavation and other work can proceed safely inside, or next to, a barrier of strong, watertight frozen earth. In cold regions, perennially frozen ground (or permafrost) remains at a temperature below 0°C continuously from year to year. Moisture in the form of water and ground ice may or may not be present. Seasonally frozen ground involves temperatures below 0°C only during the winter season. In the northern hemisphere the southern limit of cold regions extends to about the 40th parallel. Engineers identify this southern limit by the depth of seasonal ground freezing, the 300-mm depth of frost penetration.