By the depth of freezing of the soil is meant the thickness of the layer of the earth's crust, which has a negative temperature during the coldest winters with little snow. The lower boundary of the freezing zone corresponds to the contour of 0 degrees Celsius. The depth of soil freezing in the Leningrad Region is 1 - 1.5 m.
Accounting for freezing depth when laying the foundation and foundation of buildings
Seasonal freezing of soils is taken into account when laying the foundation. The lower boundary of the foundation should not be higher than the zero isotherm. It is desirable that it be 15 - 20 cm below this level. Such a foundation is called buried.
Frequent freezing and subsequent thawing of rocks can lead to their deformation, which can affect the stability of buildings and structures. Non-freezing rocks are more stable, therefore they should be the support for the foundation and foundation.
The freezing depth of the soil determines the preferred foundation design. It can be screw, tape, columnar, plate, etc.
Factors affecting the depth of freezing
Various factors influence the depth of freezing of the soil. Climatic (weather) is the most significant, and it is on its basis that maps of the depth of seasonal freezing of the soil are built. However, the microclimatic factor is also important, which depends on the topography, building density, the size of the settlement (in cities the minimum temperatures are much higher), the presence or absence of woody vegetation, etc.
Of great importance are the properties of the soil. Different types of rocks freeze at different speeds and deform differently. Loose, water-saturated rocks will give more deformations during the freezing-thawing cycle.
Depth of soil freezing in the Leningrad region
The climatic conditions in our country are such that the main part of the territory is in the zone of freezing soils, which is due to the geographical location. In the Leningrad Region, the depth of soil freezing is less than the average for Russia. This is due to the location of the city near the western borders of the Russian Federation, where the influence of the warm Atlantic is maximum.
In the most favorable conditions is the Krasnodar Territory: there the depth of seasonal freezing is minimal (less than 80 cm). An increase in the depth of freezing is noted when moving in a northeastern direction, which is associated with an increase in the role of the Asian anticyclone leading to air cooling. In the Leningrad Region, the depth of soil freezing is 100 - 140 cm, increasing within the limits of these figures from west to east. In the future, global climate change may lead to a decrease in these indicators, however, while winters remain quite cold, despite the general trend of warming.
Standard depth of soil freezing (SNiP)
Normative soil freezing is an easily determined quantity. The norms and rules established in SNiP for the design of construction works allow taking into account and eliminating the main risk factors, which gives a guarantee of the durability and reliability of the buildings being constructed. SNiP "Foundation of Buildings and Structures" is a regulatory legal framework designed for designers, engineers, individuals, architects. It was created by the efforts of geologists and engineers back in Soviet times, but it continues to be successfully used at the present time. In accordance with documents 2.02.01-83 and 23-01-99, the depth of the designed foundation is determined based on the following factors:
- Construction and weight of the building.
- The functional purpose of the house under construction.
- The total depth of seasonal freezing for a given region.
- Hydrological and geological conditions of the area.
- The depth of the foundations of neighboring buildings.
- Features of the terrain.
- Physical characteristics of the soil (density, porosity, presence or absence of voids, soil lamination, etc.).
Calculation of soil freezing depth
The depth of soil freezing is defined as the square root of the sum of the average monthly temperatures, provided that they are negative - M, multiplied by the coefficient - K, which is a reference value and depends on the type of soil. For clay K - 0.23, for fine sand - 0.28, for coarse sand - 0.3, for rocks consisting of large fragments - 0.34. Coarse material freezes more than fine-grained. Also, the depth of freezing depends on the water content in the soil: the more it is, the faster the freezing occurs. The degree of soil deformation determines the rate of expansion.
The most pronounced frost swelling in clay and fine soils. In these cases, the volume of the rock during freezing can increase up to 10 percent. For rocky soils, the indicator is almost zero.
