Soil Freezing in Different Regions of Russia: The Best Study

What determines the depth of soil freezing?

Soil freezing depth is the maximum depth to which the soil freezes in winter.

Each soil has some characteristics of behavior under certain conditions. This fact must be taken into account during the creation of any foundation project in any territory, in any region. There is a dependence of the depth to which the soil freezes on its rock (type). This depth is also determined by:

• climate (temperature regime) in a specific area;
• the presence or absence of groundwater, its depth;
• base density;
• degree of soil heaving.

The degree of freezing depends on the listed factors. Taking into account all the conditions, a type of foundation is selected that can best ensure the strength of the building in a certain area.

How deep should the foundation for a house be, depth calculation

Thus, soil freezing has a negative impact. In order to prevent heaving forces from acting on the base of the foundation, it must be laid to a depth below the freezing depth.

The depth of soil freezing depends, firstly, on the type of soil: clay soils freeze slightly less than sandy soils because they have greater porosity. The porosity of clay ranges from 0.5 to 0.7, while the porosity of sand ranges from 0.3 to 0.5. Secondly, the depth of freezing depends on climatic conditions, namely on the average annual temperature: the lower it is, the greater the depth of freezing.

Standard freezing depths (according to SNiP data) in centimeters for different cities and soil types are presented in the table.

The actual freezing depths will actually differ from the normative ones given in SNiP, because the normative data are given for the worst case - the absence of snow cover. The standard soil freezing depth presented in this table is the maximum depth. Snow and ice are good heat insulators, and the presence of snow cover reduces the depth of freezing. The soil under the house also freezes less, especially if the house is heated all year round. Thus, the actual depth of freezing of the ground may be 20-40% less than the standard one.

Soil freezing can be reduced by insulating the soil around the house. A strip of good insulation 1.5-2 meters wide, laid around the house, can ensure a minimum freezing depth of the soil surrounding the foundation of the house. Thanks to this technique, it is possible to lay shallow foundations, which are laid at a depth above the freezing depth, but due to the insulation of the soil they remain stable.

Forces of frost heaving of soils

Frost heaving is an increase in soil volume at subzero temperatures, that is, in winter. This happens because the moisture contained in the soil increases in volume when it freezes. The forces of frost heaving act not only on the base of the foundation, but also on its side walls and are capable of squeezing the foundation of a house out of the ground.

Ground water level

Groundwater is the first underground aquifer layer from the surface of the earth, which lies above the first impermeable layer. They have a negative impact on the properties of the soil and the foundations of houses; the groundwater level must be known and taken into account when laying the foundation.

Heaving soil is a soil that is susceptible to frost heaving; when it freezes, it increases significantly in volume. Heaving forces are quite strong and are capable of lifting entire buildings, so it is impossible to lay a foundation on heaving soil without taking measures against heaving.

Soil bearing capacity

The load-bearing capacity of soil is its basic characteristic that needs to be known when building a house; it shows how much load a unit area of ​​soil can withstand. The bearing capacity determines what the supporting area of ​​the house's foundation should be: the worse the soil's ability to withstand the load, the larger the foundation area should be.

Average annual air temperature

The average annual air temperature is the arithmetic average of temperatures for all months of the year. The need to insulate the foundation and the soil around it, as well as the possibility of laying a shallow foundation, depends on it.

Date of publication: 07.10.2010 14:49:25

Instead of a foreword. Smart and friendly people pointed out to me that this case should be assessed only in a non-stationary setting, due to the enormous thermal inertia of the earth, and take into account the annual regime of temperature changes. The completed example was solved for a stationary thermal field, therefore it has obviously incorrect results, so it should be considered only as some kind of idealized model with a huge number of simplifications showing the temperature distribution in a stationary mode. So, as they say, any coincidence is pure coincidence...

As usual, I will not give a lot of specifics about the accepted thermal conductivities and thicknesses of materials, I will limit myself to describing only a few, we assume that other elements are as close as possible to real structures - the thermophysical characteristics are assigned correctly, and the thicknesses of materials are adequate to real cases of construction practice. The purpose of the article is to obtain a framework understanding of the temperature distribution at the Building-Ground boundary under various conditions.

A little about what needs to be said. The calculated schemes in this example contain 3 temperature boundaries, the 1st is the internal air of the premises of a heated building +20°C, the 2nd is the outside air -10°C (-28°C), and the 3rd is the temperature in the soil at a certain depth at which it fluctuates around some constant value. In this example, the value of this depth is 8 m and the temperature is +10 ° C. Here someone can argue with me regarding the accepted parameters of the 3rd boundary, but a dispute about the exact values ​​is not the purpose of this article, just as the results obtained do not claim to be particularly accurate and can be linked to any specific design case. I repeat, the task is to obtain a fundamental, framework understanding of the temperature distribution, and to test some established ideas on this issue.

Table of soil freezing depth by region of Russia

To facilitate the work of designers, SNiP 2.02.01-83* was developed, containing design standards for various types of foundations. In addition, an application has been created for this SNiP, which has the form of a map of the Russian Federation and contains standards for the depth of freezing of soils for each of the territorial zones. To make this information convenient, it is formatted as a table. For some Russian cities, freezing coefficients are listed here:

Clause 2.25 of this SNiP specifies the factors that determine the depth of the foundation:

• the purpose of the construction project, its design features;
• level of load on the foundation;
• depth of placement of communication systems;
• relief;
• freezing depth;
• engineering and geological features of the territory;
• hydrological situation.

Some of these factors have coefficients determined through the classification of buildings. The freezing rate is the average statistical value of the greatest freezing depths on the site, provided that snow is removed from it and freed from water flowing underground for at least ten years.

How to calculate soil freezing depth

Clause 2.27 of SNiP 2.02.01-83* allows you to determine the freezing depth norm when the area being determined does not provide ready-made values. To determine the parameter, the formula Dfn=d0√Mt (Mt is a coefficient equal to the sum of temperatures in the cold season below zero within the region). When such observations are not available, the value is taken based on observations from a meteorological station located in an area experiencing the same weather and climate. d0 is a value expressed in m, which is separate for soil types:

• loam - 0.23;
• sandy loam - 0.28;
• gravelly sand, coarse or medium in size - 0.30;
• with large debris - 0.34.

If a standard value is available, it is possible to determine the depth of soil freezing (df), which is taken into account when determining the parameters of the foundation according to the formula df = kh ∙ dfn. kh is the heat coefficient for a construction project, determined according to the table in relation to the foundation of the external walls of a heated room. For the outer part of the foundation of a room that is not heated, kh = 1.1 (does not apply to regions where the average annual temperature is below 0 - for these regions a special calculation is used, which is based on the parameters of permafrost soil).

Calculator for calculating soil freezing depth

Effect of snow cover thickness

According to SNiP, the value of freezing depth also depends on the thickness of the snow layer that lies on a given soil in winter. The graph of this dependence is well illustrated in the graph below.

Graph of soil freezing versus snow cover thickness

This circumstance goes logically contrary to the generally accepted procedure for clearing the area around the house from snowdrifts. People, trying to restore order, without realizing it, create a zone of uneven soil freezing on their site. This can damage the foundation, the ground under which can freeze very much and begin to deform the foundation.

With additional insulation of a shallow strip foundation, it is not afraid of frost deformations

In order to create additional insulation of the foundation, as a tip, it will help to plant a low shrub around the perimeter of the house, which will be able to collect snow and protect your foundation from the cold.

• Author: Maria Sukhorukikh
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Types of soil and their characteristics

The table of soil freezing depth for regions of Russia has approximate values. Even in the same region, soils can vary in structure and density, and their behavior can be different when exposed to water, as well as during temperature fluctuations.

The structure of rocky soil almost does not change due to the influence of climate factors, since the basis of such soil is stone. Therefore, rocky soil is suitable for use as a foundation directly after completion of preparatory work.

Gristly soil is a mixture of sand, soil, clay and a significant amount of gravel. The specificity of this soil is its resistance to washout.

Sandy soil is reliable as a base when it contains no small and dusty fractions. The shrinkage of the building leads to a noticeable increase in the density of the soil and its subsidence, if there is almost no heaving in it.

Sandy loam and loam are suitable for building construction only in some cases, subject to certain parameters. For such soil, the correct choice of foundation type is of no small importance, since solidification of rocks leads to severe heaving.