Frost depth
The frost depth describes how far the frost has penetrated the subsoil . The frost penetration depth indicates the maximum value observed in a region.
Soil temperatures near the surface are mainly determined by the air temperature and climatic influences. So it is quite natural in Europe that temperatures below freezing point occur in the ground during the winter season. Permafrost soil can occur in regions with months of frost .
In connection with the depth of frost, a distinction is made between two different causes of frost damage :
- Elevations due to frost (increase in volume of the soil)
- Subsidence due to thawing of the ice in the ground
Agriculture and Forestry
The water between the individual soil particles freezes to ice. This process increases the volume of water in the soil pores by approx. 9 to 11 percent. Since the soil has a pore volume of 25 to 35%, depending on the type of soil, the influence of a change in soil volume is to be estimated at 2 to 4%. After several frosts with different depths of frost, the arable soil begins to freeze . The depth of frost also has an influence on the seeds stored in the ground and on stratification and vernalization .
If there is ground frost with a depth of a few centimeters over a longer period of time , roots will tear off in winter crops as the frozen crumb layer rises and falls . If there is a great depth of frost, there is a risk of frost drying . Both low and high frost depths can lead to the wintering of agricultural crops.
The frost penetration depth indicates the maximum vertical depth to which the ground freezes and the ground frost penetrates during longer periods of frost .
This depth depends on the air temperature above the ground, the solar radiation and the albedo of the ground, the snow cover and, in particular, on the thermal conductivity of the ground itself, which varies greatly depending on the constituents, porosity and water content .
The depth of frost penetration observed over a longer period of time is decisive for the selection of crop and frost crops. In regions with high frost penetration depth, the plants are selected according to the known frost hardness . The permafrost soil is a special case of plant cultivation , which only thaws on the surface of the terrain even in summer and the depth of the frost penetration remains.
Road construction
In construction, especially in road construction , systems must contain a water-permeable frost protection layer made of gravel , in which water contained in the soil can run off. Freezing water leads to ice lenses and, as a result, to the formation of potholes .
The empirical values of the construction industry for the frost line in Central Europe are between about 120 cm ( boundary stones in Austria) and 60 cm (heavily used roads in northern Germany). Based on the climatic conditions, Germany is divided into three frost zones that have an impact on road construction.
In an average winter half-year , the depth of frost penetration relevant for road construction depends mainly on the thermal conductivity of the road structure and the surrounding soil . For medium-severe cold spells that are rough formula gives a good approximation where the frost index is (roughly the accumulated cold degrees of concerning. Days). Assuming it is 500 (500 ° C · day), the result is 100 cm, and with a safety margin ultimately the 120 cm, which is usual in road construction.
This value can be reduced to ½ to ¾ meters for less stressed structures or for floors with a greater thermal capacity .
Buildings
The increase in volume during the conversion of water to ice has very far-reaching consequences for buildings. The increase in the volume of the soil causes so-called frost uplifts . Cohesive soils are particularly susceptible to these effects, as the pores are very small and mostly filled with water.
For the structural processing of a structure, it is important to know how far the frost can penetrate the subsoil. The temporal distribution of the surface temperatures is important for determining the frost penetration depth. To describe the cold period, the frost index is used, which is composed of the number of frost days multiplied by the average frost temperature . As a first approximation, the frost penetration depth can now be determined using this Brown frost index. In Germany, the minimum depth for frost-free foundations is regulated in DIN 1054. In this standard, it is at least 80 cm, but may be prescribed even higher by regional supplementary decrees or meteorological empirical values.
If a structure is not founded deeper than the frost penetration depth, frost uplifts can occur, which lead to uneven movements of the structure. These movements are almost always expressed in the formation of smaller or larger structural cracks.
literature
- Gassner, Gustav : Contributions to the physiological characteristics of summer and winter manual plants in particular of cereal plants. Botanik magazine , Berlin 1918.
- Klapp, Ernst : Textbook of arable and plant cultivation. 5th edition, Berlin 1958.
- Petr, Jiri : Weather and Yield. Developments in Crop Science. Amsterdam, Oxford, New York, Tokyo, Prague 1991. ISBN 0-444-98803-3 .
- Manfred G. Raupp: What the grandfather already knew. Thoughts on the development of agriculture in Staffort. Written in memory of Gustav W. Raupp (1905–1985), Stutensee-Staffort 2005.
Individual evidence
- ^ Bernhard Wietek : Foundation. 4th edition. Manz-Verlag, 2002, ISBN 3-7068-1206-1 .
- ^ Brown, WG: Difficulties associated with predicting depth of freeze or thaw. Canadian Geotechnique Journal, 1964; Vol. 1, 215-226.