Ground frost penetration in Sweden

Observations on which this report is based were made in the period 1962-66. They were made in natural soil and water- main trenches and were done to establish methods of determining depth of frost penetration, paying special attention to the question of depth, of soil cover over water and sewer mains to prevent freezing. Observations were carried out at 21 stations using special probes at different depths to measure temperature and thermal conductivity, both in bare and snow covered areas. Field observations were used to verify calculation methods. A calculation method was used to determine the frost penetration for five different types of soil at varying mean annual temperatures and minimum winter temperatures. Observations showed that the heat insulating capacity of snow is less than could be expected from its thermal conductivity, mostly because the structure of the snow is continually changing. Therefore an equivalent conductivity was used which depends on the mean annual temperature. Special treatment was given to the depth of soil required over water-mains, which allows for the heating effect of the water carried in the pipes. For the frost protection of service pipes to buildings a practical method suggested is to use electrical heating to compensate for heat losses. The calculated frost penetration method compared well with actual measurements.