4.2.5.1 Temperatures Below 0°C
The transfer of heat by conduction is the dominating factor at temperatures below 0°C (Sundberg, 1988). In the small pores of frost susceptible soils though, due to freezing point depression, some water remains unfrozen at temperatures below 0°C. This allows convection caused by so-called cryo-suction effects (see Section 4.6.2 below) and a small amount of heat transfer at temperatures below 0°C.
4.2.5.2 Temperatures Above 0°C and Below Approximately 25°C
At this temperature range, conduction of heat is still the dominating factor (Sundberg, 1988). In highly permeable soils there may be more forced convection — like groundwater flow that is natural or caused by water abstraction. High temperature gradients in permeable soils may also cause significant natural convection.
4.2.5.3 Temperatures Above Approximately 25°C
For the lower temperatures in this range, conduction is still the dominating factor (Sundberg, 1988). At higher temperatures and relatively low water content, vapour transport gets successively more important. At saturation, heat conduction is always the dominating factor. Again, high temperature gradients in permeable soils may cause more natural convection. In coarse soils at high temperature, there will be more radiation but it will still play a minor role.
