Frost line
Frost limit denotes the height above or below a constant height at which frost - i.e. temperatures below 0 ° C - occurs or can occur. Specifically, a distinction is made between three meanings:
- In meteorology , a (variable) height above sea level is meant in certain weather conditions or at certain (annual) times.
- In construction and agriculture , the (fixed) depth in the ground below the surface is meant in which frost can occur (exception: permafrost soil ).
- In geography and ecology , however , what is meant is the (static) climatic altitude limit in the mountains , which represents the upper limit of the year-round and permanently frost-free areas. It is also called the absolute frost limit .
Frost lines in the mountains
The physical reason for the upwardly definable (changeable) frost limit lies in the general vertical gradient of the air , which averages −6 ° C per 1000 meters of altitude. If, for example, 3 ° C currently prevails at an altitude of 1000 m , the 0 ° C limit will be around 1500 m . Neither the variable nor the absolute frost line (as a rule) coincide with the snowfall line or the snow line.
The local location of the frost lines also depends on other conditions. Amongst other things:
- solar radiation
- Exposure (orientation of a slope to the sun)
- Slope of a mountain slope
- Vegetation (types and density)
- Soil and rock types
- Wind conditions
Ground frost
The frost boundaries in the ground are to be distinguished from the air. In the ground , the temperatures a few centimeters below the surface of the earth are usually higher than above. A snow cover also has an insulating effect. Conversely, the nocturnal radiation can cause frost to be stronger than the local average.
Frost lines in the ground
In terms of depth, the frost line is understood as the depth below the surface of the earth below which negative soil temperatures do not occur. In the ground and in the entire interior of the earth, the temperature increases downwards, in mines by an average of 30 ° C per kilometer. However, conditions are more complicated near the surface because the top soil layers vary greatly. The temperature gradient towards the earth's surface is weakened by groundwater flows, strong moisture penetration or rocky soil that conducts heat well . The conditions towards the poles of the permafrost boundaries also deviate from this. In the case of poorly heat-conducting soil layers, the seasonal fluctuations in temperature are significantly reduced after just a few meters.
The depth limit is basically dependent on the climatic zone . In Germany's geographical latitudes it is assumed that the frost line is about 80 cm deep.
Frost protection in surveying and construction
The frost limit denotes the maximum depth of penetration of the frost into the ground. It depends on the climate, the local situation, the water content and the type of soil. In Central Europe, the frost line is between 0.80 and 1.50 m below the surface. The 80 cm depth must be observed for all foundations , foundations and measuring pillars in order to prevent the concrete from lifting up due to frost . Due to the freezing effect, stones can also gradually come to the surface. Therefore, survey points and important boundary points must reach at least this depth.
As a rule, a layer of gravel is poured under buildings and traffic routes as frost protection . This means that the rainwater is diverted and can no longer cause the ground to uplift when it freezes. Otherwise cracks and frost breakouts will occur .
To supply the construction and agricultural industries with current data that measure weather stations in addition to the air temperature and that of the soil at various depths.
In regions of permafrost such as in Siberia , the frost line can often not be reached with reasonable structural effort, so that special precautions for the foundation of structures are necessary.
Individual evidence
- ↑ DIN 1054: 2010-12 "Subsoil - Proof of safety in earthworks and foundations - Supplementary regulations to DIN EN 1997-1" p. 40.