Excessively heaving soils. What is heaving soil? Slab foundation is the best option

Heaving soils cause many problems for builders. In winter, they can greatly increase in volume, putting increased pressure on the foundations of the building. At the same time, the structure rises unevenly from the ground, and serious cracks appear on the walls. Before you fight a phenomenon, you need to understand what it is.

A difficult issue during independent construction is determining what kind of soil is available: heaving or non-heaving. According to GOST 25100-2011, all bases are divided into five groups according to the degree of frost heaving:

excessively heaving;
highly heaving;
medium heaving;
slightly heaving;
not heaving.

The last group can be called conditional. There are practically no types of soil in which frost heaving forces will never arise. The category of safe foundations includes only coarse rocks and granite, the occurrence of which on the surface is extremely rare.

Soil type does not have as much influence on the likelihood of frost heave forces occurring. The factor causing this phenomenon is not the soil, but moisture and negative temperatures. If certain conditions are met, negative phenomena can occur in almost any area.

The susceptibility of soil to heave is influenced by such properties as:

capillary activity;
filtration ability.

According to these indicators, clayey soils become the most dangerous types of soil. These include clay, loam and sandy loam. These soils do not filter water well, retain it and do not allow it to pass into deeper layers. The liquid remains dangerously close to foundations.

Types of soils.

At the same time, clays are characterized by high capillary activity. For comparison, sandy types of soil are capable of drawing water up to about 30 cm. This property is relevant when precipitation falls or snow melts. Moisture extends only 30 cm from the source. In this case, the foundations are protected from frost heaving by a blind area of standard meter width. Clay can attract moisture to a distance of 1.5 m; to protect it from atmospheric moisture, you will need to build a very wide blind area to prevent damage.

If the groundwater level is high, even conditionally non-heaving soil types (coarse and medium sand) can lead to problems. The danger of frost heaving in sand can also appear under the influence of other factors (for example, a house is located on a site with a slope, even a slight one).

Why is frost heaving dangerous?

The combined effect of moisture and low temperatures on the soil leads to an increase in its volume. For any building, uneven deformations that are characteristic of frost heaving pose a particular danger. This is due to the fact that the soil under the outer walls is slightly heated by the building, and in the middle of the house the temperature is above zero.

A crack caused by heaving.

External walls, and especially corners, can rise relative to the initial level by 15 cm. In this case, deformations under the internal walls do not occur or they are small. Uneven lifting leads to the appearance of inclined cracks in the walls.

Frost heaving also has a negative impact on the side surface of the foundation.

Ways to fight

To prevent heaving soils from causing problems during operation, it is necessary to combat the causes of frost heaving of clays and other types of soils at the stage of foundation construction. Methods of control depend on the scale of the problem and the type of supporting part of the house. Most often, activities are provided in a complex.

Buried foundations

Every builder knows that to effectively combat frost heaving, it is necessary to lay the building supports below the depth of soil freezing. This value is found using special tables and maps or calculated using the formula from the SP “Foundations of buildings and structures”. But taking such measures is not always enough. When laid deeply, it is possible to avoid impacts on the base of the foundation, but tangential forces remain that act on its lateral surface. They can be decomposed into:

vertical, which in some cases are capable of lifting structures;
horizontal, bending foundations.

The strength of frost heaving depending on the depth of its occurrence.

Control methods depend on the type of structure and foundations. For massive buildings with deep foundations, one or more of the following measures can be recommended:

coating waterproofing, which not only protects the foundation material from getting wet, but also impairs the adhesion of the soil to it (prevents structures from being lifted);
insulation is carried out for the same purpose; extruded polystyrene foam is often used, which also takes on the function of protecting against moisture;
drainage and filling the sinuses with coarse or medium sand allow moisture to be removed from the building;
an insulated blind area prevents freezing of the soil in the immediate vicinity of the house, which means it eliminates one of the factors necessary for the occurrence of heaving;
competent calculation and execution of reinforcement will allow the elements to withstand horizontal influences.

If the building is made of lightweight materials or has only one floor, it is recommended to use foundations using TISE technology. Such supporting elements are piles that widen towards the bottom. Due to the increased cross-section, it becomes almost impossible to pull the element out of the soil.

To protect this type of foundation from horizontal influences, you will have to consider the following points:

competent calculation of the working reinforcement of the pile;
rigid coupling of the pile to the grillage using reinforcement;
calculation of the grillage for increased soil pressure on the side surface.

With a large freezing depth, installing a buried foundation with insulation, waterproofing, drainage and a warm blind area is not economically profitable. It will be easier to build shallow supports. Deepening will be justified only if:

the need for a basement or ground floor;
poor soil strength indicators closer to the surface.

Shallow foundations

Such designs have several advantages. They reduce the cost of building foundations and reduce the time required to complete the work. Shallow foundations can be used when the groundwater level is sufficiently high (at least 1.5 m).

The following measures used in the complex will help protect these types of building support elements:

. This design will reduce the depth of freezing of the base. The exact mark for safe laying of the sole depends on the climate, the thickness of the insulation and the width of the blind area. In most cases, it is advisable to use a protective strip 1 m wide with insulation 5-10 cm thick. The depth of the foundation will be 0.7 - 1 m.
. If you forget about the thermal insulation of the base, the foundation of the house will become an excellent conductor of cold under its own sole. For work, it is recommended to use extruded polystyrene foam (penoplex). It is fixed to the entire height of the supporting part of the house: from the sole to the base. The thickness of the insulation above the blind area is on average 100 mm, and below you can use penoplex with a thickness of 50 mm. Additionally, the material protects foundations from moisture, increasing their service life.
. The system eliminates the second factor in the occurrence of frost heaving: moisture. For drainage to work effectively, it must be positioned correctly. The pipe is laid next to the building site, but not under it. Drainage should be located below freezing or in a place where it does not occur (within the range of the insulated blind area). If pipes are laid in frozen ground, they may break in winter. You will also need to observe the recommended slopes of the drainage pipes, which depend on the cross-sectional diameter.

If it is not possible to install drainage (the work is highly complex, there is nowhere to drain it, etc.), you can only get by with a blind area. In this case, the protective strip around the perimeter of the building is made wide. It should completely prevent access of atmospheric moisture to the foundations. For clays, the width should be more than 1.5 m. Landscaping around the building is done so that the slope of the site is in the direction from the house.

The method is applicable if the following conditions are simultaneously met:

good strength characteristics of the base under the black soil layer;
low natural soil moisture;
deep occurrence of groundwater;
absence of slopes towards the building on the site.

With proper selection of the type of foundation and timely adoption of measures to combat frost heaving, serious problems during operation of the house can be avoided. A careful approach to the issue will allow you to find an effective option that requires the least labor and financial costs.

excessively heaving;
highly heaving;
medium heaving;
slightly heaving;
not heaving.

The susceptibility of soil to heave is influenced by such properties as:

capillary activity;
filtration ability.

Types of soils.

Why is frost heaving dangerous?

A crack caused by heaving.

Frost heaving also has a negative impact on the side surface of the foundation.

Ways to fight

Buried foundations

vertical, which in some cases are capable of lifting structures;
horizontal, bending foundations.

The strength of frost heaving depending on the depth of its occurrence.

Control methods depend on the type of structure and foundations. For massive buildings with deep foundations, one or more of the following measures can be recommended:

coating waterproofing, which not only protects the foundation material from getting wet, but also impairs the adhesion of the soil to it (prevents structures from being lifted);
insulation is carried out for the same purpose; extruded polystyrene foam is often used, which also takes on the function of protecting against moisture;
drainage and filling the sinuses with coarse or medium sand allow moisture to be removed from the building;
an insulated blind area prevents freezing of the soil in the immediate vicinity of the house, which means it eliminates one of the factors necessary for the occurrence of heaving;
competent calculation and execution of reinforcement will allow the elements to withstand horizontal influences.

To protect this type of foundation from horizontal influences, you will have to consider the following points:

competent calculation of the working reinforcement of the pile;
rigid coupling of the pile to the grillage using reinforcement;
calculation of the grillage for increased soil pressure on the side surface.

More information about TISE: Do-it-yourself TISE foundation.

the need for a basement or ground floor;
poor soil strength indicators closer to the surface.

Shallow foundations

The effect of an insulated blind area.

The following measures used in the complex will help protect these types of building support elements:

Insulated blind area. This design will reduce the depth of freezing of the base. The exact mark for safe laying of the sole depends on the climate, the thickness of the insulation and the width of the blind area. In most cases, it is advisable to use a protective strip 1 m wide with insulation 5-10 cm thick. The depth of the foundation will be 0.7 - 1 m.
Insulation of the vertical part of the foundation. If you forget about the thermal insulation of the base, the foundation of the house will become an excellent conductor of cold under its own sole. For work, it is recommended to use extruded polystyrene foam (penoplex). It is fixed to the entire height of the supporting part of the house: from the sole to the base. The thickness of the insulation above the blind area is on average 100 mm, and below you can use penoplex with a thickness of 50 mm. Additionally, the material protects foundations from moisture, increasing their service life.
Drainage. The system eliminates the second factor in the occurrence of frost heaving: moisture. For drainage to work effectively, it must be positioned correctly. The pipe is laid next to the building site, but not under it. Drainage should be located below freezing or in a place where it does not occur (within the range of the insulated blind area). If pipes are laid in frozen ground, they may break in winter. You will also need to observe the recommended slopes of the drainage pipes, which depend on the cross-sectional diameter.

Location of the drainage pipe.

The method is applicable if the following conditions are simultaneously met:

good strength characteristics of the base under the black soil layer;
low natural soil moisture;
deep occurrence of groundwater;
absence of slopes towards the building on the site.

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Special properties of heaving soils

A special property of foundations that can swell is a significant increase in volume as a result of winter freezing.

How to identify heaving soils? Substrates that have the property of swelling when freezing include only clayey (including loam) and sandy soils (silty, fine and medium-sized). Gravelly and coarse sands are not classified as heaving sands.

Sandy, clayey soils and their varieties have a fine-porous structure, that is, they consist of small mineral particles, between which there are many small cavities. These cavities or pores may contain moisture. When the temperature drops below zero, the moisture in the soil freezes, turning into ice, which, as is known, always increases in volume compared to the original volume of water. As a result of the freezing of water in the pores, an increase in the entire volume of the base occurs, called frost heaving.

Foundations are divided according to the degree of heaving, which depends on the level or depth at which groundwater lies. For clay bases, the fluidity index is also important. We present the following table with a gradation according to the degree of heaving of different types of soil.

Degree of soil heaving

Degree of soil heaving	Fine sand, Z	Silty sand, Z	Sandy loam, Z	Loam, Z	Clay, Z	Flow index Jl	Relative heaving strain Efh
Non-heaving soils	> 0,75	> 1	> 1,5	> 2,5	> 3
Soils are slightly heaving	0,5 - 0,75	0,75 - 1	1 - 1,5	1,5 - 2,5	2	0 - 0,25	0,01 - 0,035
Soils are medium heaving		0,5 - 0,75	0,75 - 1	1 - 1,5	1,5 - 2	0,25 - 0,5	0,035 - 0,07
Soils are highly heaving	-					>0,5	> 0,07

The main indicator is the relative heaving deformation Efh, which is determined by the ratio of the amount of rise in the surface of the intumescent base to the thickness of the frozen layer.
The Z index is the difference between the groundwater level and the depth of seasonal freezing, the value of which is 1.2 m for heated buildings and 1.5 m for unheated buildings.

If the degree of heaving in terms of indicators Z and Jl (fluidity) differs, then a larger value is accepted.

Since heaving foundations exhibit their negative properties when saturated with water, there is another classification method that takes into account the conditions for moistening the foundations of buildings according to the nature of the terrain.

That is, if, according to the Z and Jl indicators, the base is classified as slightly heaving, but the construction site is located in a lowland or basin, then it should be considered that the soils are highly heaving.

Thus, heaving soil is sandy or clayey soil that is subject to moisture and seasonal freezing.

Distribution of heaving soils in Russia

Since sandy and clayey foundations are ubiquitous, we can assume that the location of soils with heaving properties covers almost half of the territory of Russia. This includes:

western regions of the Russian Federation: Kaliningrad, Pskov and Leningrad regions and the Republic of Karelia;
middle zone of the Russian Federation: Vladimir, Kaluga, Ivanovo, Kostroma, Ryazan, Moscow, Smolensk, Tver, Tambov, Tula, Yaroslavl, Belgorod, Bryansk, Vologda, Voronezh, Kirov, Kursk, Lipetsk, Oryol, Penza, Samara, Saratov, Ulyanovsk regions , Chuvash Republic;
the southern parts of the Arkhangelsk and Murmansk regions, Khabarovsk Territory, the Republic of Yakutia, the Krasnoyarsk Territory, the Irkutsk and Tyumen regions, the Komi Republic;
Amur, Chita, Novosibirsk, Omsk, Kemerovo regions, Republics of Buryatia, Komi, Tyva, Altai, Sverdlovsk region, Republics of Tatarstan and Bashkortostan, Volgograd region, Rostov region, Republic of Kalmykia;
northern parts of the Krasnodar and Stavropol territories.

The permafrost zone is excluded, which covers most of the territories of Yakutia, the Krasnoyarsk Territory, the Tyumen and Arkhangelsk regions, and the Komi Republic. The permafrost zone is distinguished by the fact that the soil there freezes hundreds of meters deep, so the problem of heaving soils is irrelevant for this zone.

In the same way, the problem of frost heaving is irrelevant for regions where the foundations of buildings are mainly rocky and coarse-clastic soils - these are all the North Caucasus republics and the southern part of the Stavropol Territory.

In addition, the problem of heaving does not matter for territories where the bases practically do not freeze - this is the southern part of the Krasnodar Territory and the Republic of Dagestan.

The depth of freezing, along with the level of groundwater, are the determining factors influencing the amount of possible swelling of the base. For example, in regions close to Lake Baikal, where the freezing depth can reach 2.5 m, the surface rise during swelling can reach 30-40 cm; in the Moscow region, with a freezing depth of 1.5 m, the surface rise is 15-18 cm.

The influence of heaving soils on foundations

Frost heaving causes a significant increase in its volume - the amount of surface rise can amount to more than tens of centimeters. In this case, forces arise, the magnitude of which reaches tens of tons. Even if you lower the base of the foundation below the depth of seasonal freezing, this will not prevent the negative influence of heaving forces, since they also act on the side surfaces.

The heaving of the soil is also manifested in the fact that after the foundation thaws during warming, it settles, that is, the structure of the foundations is periodically affected by multidirectional forces.

The weight of structures can compensate for heaving only if a building is constructed at least three floors high with massive concrete or stone walls. For low-rise buildings of one or two floors, especially those made of lightweight structures - wooden frames and logs, lightweight concrete blocks and bricks - a special foundation for heaving soil must be selected and calculated.

The main danger of the negative impact of heaving forces lies in their unevenness. Different parts of the foundations of a building are always in different conditions. Freezing occurs only along the perimeter of the heated building; under the foundation on which the middle walls rest, the base does not freeze.

Uneven freezing under the building

In addition, along the perimeter of the enclosing external walls, the base freezes unevenly - on the shady, northern side there is more freezing, on those sides where the sun warms up there is less freezing. The amount of freezing is also affected by the thickness of the snow cover, the architecture of the building, and the nature of the development of the site.

All these factors cause uneven impact of heaving forces on different sections of foundations and uneven deformations in structures, causing the most unfavorable consequences - the occurrence of cracks and other damage in enclosing and load-bearing structures, which can lead to their destruction.

The foundation on heaving soils must have features that can minimize or eliminate the negative impact of this type of foundation.

Expert opinion

If the foundation of the building contains soils with heaving properties, you should be especially careful when choosing the type of foundation. After many years of practice, the MzLF design has proven itself to be very effective - we describe its design, reinforcement and calculation in detail in the article “Shallow strip foundation: depth calculation, foundation preparation, do-it-yourself reinforcement and calculation calculator.”

In addition to choosing the most suitable type of foundation when building on heaving foundations, it is necessary to take additional measures aimed at preventing soaking and freezing: installing drainage, insulating the blind area, filling the sinuses with compacted bulk material.

Heaving soils are the number one problem for builders. In winter, when the cold comes, they increase in size, compressing the foundations and lifting them. As a result, cracks appear on the structure of the latter. They fight this phenomenon in different ways, but to start the fight, you need to understand what it is.

Type of heaving soil

What is heaving and non-heaving soil is a question that can be answered if you understand why such processes occur inside the soil. The thing is that expansion (heaving) occurs due to water drops frozen inside the soil. This means that she must retain these drops within herself.

Therefore, the main properties of the soil that lead to heaving are capillary activity and the ability to filter water. If the soil is loose, for example, with a high sand content, then water easily passes through it into the lower water horizons without being retained. Such soils do not belong to the category of heaving soils.

But those types of soils in which water is retained are classified as “heaving”. These are clay, loam and sandy loam. But there is a point related to capillary activity. For sand types it is lower, because sand absorbs precipitation to a depth of 30 - 40 cm. At the same time, clay types gradually absorb moisture to a depth of 1.5 m. Therefore, in the first case, you can get by with blind areas around the foundation with a width of 1 m, in the second, the value will have to be increased to 1.5 - 2.0 m. This relates to the question of how to deal with heaving.

At a high level of groundwater, even non-heaving soils can expand. Therefore, soil heaving must be treated from the point of view of the presence or absence of factors that lead to such a property of the earth. You can also add the location of the house here. If it is being built on a site with a slope, then there is a high probability that such terrain will lead to heaving of some sections, especially those located below.

Let’s not forget about the region where the house is being built. If this is the south, where the level of soil freezing is low, then there is no need to talk about heaving. Even clay bases covered with a standard blind area can easily withstand low temperatures in winter. In the north this is expressed more clearly. In some northern regions, the ground freezes to 2 - 2.5 m, which means that soil heaving occurs regardless of the type of soil.

Classification

Classification of soils according to the type of swelling divides the types into several subgroups. Heaving ones include:

excessively or very heaving;
very heaving;
moderate;
weak degree.

And non-heaving soils stand separately.

The last definition can be called purely conditional, because there is no land that does not freeze and swell. It all depends on the soil moisture and its cooling temperature. Of course, we can say that purely stone soil will not swell. But this variety is extremely rare in places where people live. Usually these are mountains.

That is, it turns out that the type of soil does not greatly affect frost heaving. The main reasons are soil moisture and air temperature. Therefore, the question of how to determine which soils are heaving and which are not is posed incorrectly. All of them can swell to some extent.

Wrestling rules

The easiest way to combat soil heaving is to fill the foundation structure below the freezing depth of the ground. Since the soil presses on the foundation from all sides, the most dangerous pressure is vertical. To avoid this, you need to fill the structure so that nothing presses on it from below. And since the buried foundation is poured below the freezing level, there is therefore no frost heaving of the soil in its lower part. Accordingly, the structure will not rise.

There are other ways to fight.

Waterproofing. It not only protects the foundation from the negative effects of moisture, but also creates an intermediate layer between the soil and the concrete structure, which impairs adhesion. In this case, the soil will partially slide over the surface of the foundation, which means the pressure on it will also decrease.

Thermal insulation. This is still the same intermediate layer.
Drainage. An effective way to lower the level of groundwater, which will reduce the concentration of moisture inside the soil at the depth of pouring the foundation structure.
Blind areas. Here you not only need to maintain their width, but also try to insulate them. For example, pour a layer of expanded clay with a thickness of at least 15 - 20 cm under the concrete mortar. The blind areas serve as a drainage system for atmospheric precipitation, and the insulation will inhibit the penetration of low temperatures.

During the heaving process, horizontal loads also act on the foundation, which creates bending pressure. A dangerous factor that, if construction operations are carried out incorrectly, will tear the structure. A reinforcing frame made of metal reinforcement helps to avoid this trouble. Here it is important to make an accurate calculation, taking into account the dimensions of the metal profile and the dimensions of the frame itself.

It is easier if a shallow foundation is poured under the house, which is built above the freezing level of the soil. To protect it from heaving, you just need to lay a blind area with insulation and insulate the base. When the groundwater level is high, drainage is also carried out. If the building is being constructed in the northern regions, then the entire foundation must be insulated: from the base to the upper edge of the base.

Conclusion on the topic

In any case, soil heaving is precisely pressure. Therefore, its weakening must be approached comprehensively. That is, to build blind areas, lay a reinforcing frame in the foundation formwork before pouring the concrete solution, carry out measures for hydro- and thermal insulation, assemble a drainage system for removing atmospheric precipitation in the first place, and in the second place lower the groundwater level. This property of the earth can be treated in different ways, but it should not be neglected under any circumstances. If you miss something, you will get cracks throughout the entire foundation structure, which will weaken the foundation of the building.

How to determine soil heaving on your own

The phenomena of soil heaving are very dangerous processes for the foundations of low-rise buildings. They occur in moist and moisture-saturated silty, fine-sandy and clayey soils (clays, loams, sandy loams) when they freeze seasonally. The water-saturated mass increases when it freezes. This increase in soil is called frost heaving of the soil.

In clays or fine sands, water, due to the capillary effect, rises from the groundwater level.

The water rise reaches:

In silty sands – 0.51.1 m;
- in sandy loam – 11.8 m;
- in loams – 45.5 m.

In coarse sands, pebbles, crushed stone, and gravel, there is no capillary effect, i.e. the water does not rise, and the soil remains moist strictly at the groundwater level. Such soils are considered non-heaving.

According to the degree of heaving, soils are divided into:

Low heaving – heaving is about 4%;
- medium heaving – heaving is about 8%;
- highly heaving – heaving is about 12%.

So, with a freezing depth of 1.3 m for highly heaving soil, the heaving will be: 1.3x12/100 = 0.16 m, i.e. 16cm.
The heaving of the soil depends both on its composition and on the level of groundwater.

In order to determine the groundwater level (GWL) at the construction site, it is necessary to dig a hole up to 2 m deep. If, over time, there is no water in the pit, then a well is drilled another 1.5 m with a garden drill. If water appears in the well, measure the distance from the ground surface to the groundwater level with a regular bar.

Knowing the type of soil (which is also determined visually) and groundwater level, you can determine the degree of heaving of any soil.

So, slightly heaving soils are soils if the groundwater level is below the calculated depth of seasonal freezing:

For silty sands - 0.5 m or less;
- for sandy loam - 1.0 m or less;
- for loams – 1.5 m or less;
- for clays - 2.0 m or less.

Medium heaving soils are soils if the groundwater level is below the calculated depth of seasonal freezing:

For sandy loam - 0.5 m or less;
- for loams – 1.0 m or less;
- for clays – 1.5 m or less.

Strongly heaving soils are soils if the groundwater level is below the calculated depth of seasonal freezing:

For sandy loam - 0.3 m or less;
- for loams – 0.7 m or less;
- for clays – 1.0 m or less.

It should be noted that a mixture of gravel or coarse sand with clay or silty sand will fully apply to heaving soils.

Heaving soil

Heaving soil is a soil that is susceptible to frost heaving. The value that shows how prone the soil is to heaving is the degree of frost heaving, which is defined as the relative change in the volume of the soil during freezing:

Where E is the degree of heaving, H is the height of frozen (swollen) soil, h is the height of the soil before freezing.

The degree of heaving shows how much the volume of soil changes when it freezes. Heaving soils are soils in which the degree of heaving is greater than 0.01, i.e. This is the kind of soil that, when frozen to a depth of 1 m, increases in volume by more than 1 cm.

What soils are heaving?

Heaving occurs due to the fact that the moisture contained in the soil freezes, and, as is known, ice has a lower density than water and therefore occupies a larger volume. An increase in the volume of water during freezing leads to heaving, so which soils are heaving and which are not depends on the water content in them: the more there is in the soil, the more it swells. All clayey soils are classified as heaving. clays, loams and sandy loams. Unlike sand, clay has many pores and retains moisture well; water does not seep between the smallest particles of clay and does not go into the deeper layers of the earth. Therefore, the higher the clay content, the more heaving the soil is.

Construction of a foundation on heaving soil

Heaving forces are quite strong and are capable of lifting entire buildings, so the construction of a foundation on heaving soil should only be carried out with measures taken against heaving. The most radical way is to replace the soil with non-heaving gravel or coarse sand. In this case, they dig a large pit to a depth greater than the freezing depth, remove the heaving soil and instead fill it in and compact it well with sand, which is an excellent foundation for the foundation, does not retain moisture and has a high load-bearing capacity. This method is perhaps the most reliable, but also the most expensive - it involves a very large amount of land work.

Another way to build a stable foundation on heaving soil is to lay it at a depth below the freezing depth. In this case, heaving forces will not act on the base of the foundation, but heaving will act on the side surface. And although this impact is an order of magnitude smaller, it can create problems: heaving soil will freeze to the side surface of the foundation and, when moving up/down, will drag it along with it. The tangential heaving force can reach 5 tons per square meter of surface. A 6 m by 6 m house strip foundation laid to a depth of 1.5 m will have a total lateral surface area of 36 m2, and the total tangential heaving force can lift up to 180 tons. This will be enough to lift a wooden house, because its weight cannot balance the effect of heaving. Therefore, laying the foundation on heaving soil below the freezing depth is used in the construction of heavy brick and monolithic reinforced concrete houses.

The third way to reduce the influence of heaving soil on the foundation is insulation. This option is most suitable for the construction of shallow foundations for light houses and is to avoid freezing of moisture in heaving soil. By laying a layer of insulation on the ground, you can ensure that the soil around the foundation never freezes. The width of the insulation strip must correspond to the freezing depth: if the ground freezes to 1.5 m, then a 1.5 m wide strip around the foundation must be insulated. The thickness of the insulation depends on its thermal insulation properties and climatic conditions.

Another measure that can be taken when building a foundation on heaving soil is water drainage, because if there is no water, then there will be no heaving. To drain water contained in the soil, drainage is installed around the perimeter of the foundation. half a meter from the foundation, they dig a ditch to the depth of its foundation, lay a perforated pipe wrapped in filter fabric in it at a slight slope and fill it with coarse sand or gravel. The water contained in the soil will flow to the drainage pipe, enter it through the holes and be discharged through it into the drainage well. For natural drainage of water, it is necessary that somewhere there is a lower area of the terrain where the water will be drained. To drain precipitation water around the foundation, you need to make a blind area and storm drainage.

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Clay soil is soil that is more than half composed of very small particles less than 0.01 mm in size, which are in the form of flakes or plates. Clay soils include sandy loam, loam and clay.

This article discusses the main types of soils - rocky, coarse, sandy and clayey, each of which has its own properties and distinctive features.

Freezing of the soil leads to heaving and a negative impact on the foundation of the building. The depth of freezing depends on the type of soil and climatic conditions.

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.

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.

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.

Date of publication: 27.10.2010 14:27:54

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Which foundation is more reliable when building on heaving soils?

Heaving soil is a soil mass that expands in the winter and puts strong pressure on the foundation walls. It leads to the destruction of the structure, its “pushing” out of the pit.

Impact of heaving pressure on the foundation

There are types of structures for construction in such conditions and a list of rules for work: from the correct foundation depth to reinforcement.

Calculation of heaving intensity in the area

To calculate the degree of soil heaving at a construction site with your own hands, you need use the formula: E = (H - h) / h. wherein:

E – corresponds to the degree of soil heaving;
h – height of the soil mass before freezing;
H – height of the soil mass after freezing.

To calculate the degree, it is necessary to take appropriate measurements in summer and winter. The soil can be considered heaving whose height has changed by 1 cm when freezing by 1 m. In this case, “E” will be equal to the coefficient 0.01.

Soils that have a high moisture content are more susceptible to heaving processes. When it freezes, it expands to the state of ice and thereby raises the ground level. Heaving soils are considered to be: clayey soils, loams and sandy loams. Clay, due to the presence of a large number of pores, retains water well.

What is heaving soil and why is it dangerous? (video)

How to remove the effects of heaving on the ground?

There are simple ways to remove heaving around the foundation with your own hands:

Replacing the layer of soil under and around the base with a non-heaving layer.
Laying the foundation on a soil mass below the freezing layer.
Insulation of the structure to prevent soil freezing.
Drainage

The first method is the most labor-intensive. To do this, you need to dig a foundation pit. depth below the freezing level of the ground, remove the heaving soil, and fill in its place with heavily compacted sand.

It shows high load-bearing capacity and does not retain moisture. The large volume of excavation work makes it the least popular, although it is an effective way to combat heaving. This technique is effective for laying low-rise buildings, shallow recesses, for example, a barn.

A feature of the second method is the removal of the influence of heaving on the base of the foundation, but its preservation when exposed to the walls of the foundation. On average, the lateral pressure on the walls is 5 t/1 m2. With its help, you can build brick houses.

The third method allows you to make a shallow foundation for a private house with your own hands in heaving conditions. The essence of the method is to lay insulation along the perimeter of the foundation to its entire depth. The calculation of the material is done as follows: if its height is 1 m, then the width of the insulation should be 1 m.

To drain water around a house or barn, you need to build drainage. It is a ditch at a distance of 50 cm from the building, the depth of which is the same as the level of the structure. A perforated pipe is laid in the drainage trench at a technical slope and wrapped in geotextiles, and then filled with gravel and coarse sand.

Below we will consider the types of bases that can be used on soil prone to heaving.

Shallow strip foundation on heaving soils

An effective way to make a strong foundation for a house or barn is a shallow (low depth) strip foundation on heaving soils. This is a concrete strip with reinforcement elements, arranged around the entire perimeter of the building and in places where load-bearing walls lie. To build a shallow foundation with your own hands, you must follow these steps:

Dig a pit/trench. 50-70 cm deep. The width is calculated based on the width of the base itself plus formwork, insulation or waterproofing, as well as decor.
Lay the slopes of the open trench with waterproofing. For this purpose, roofing felt and film are used.
Fill the excavation with layers of compacted sand, 20-30 cm each. To compact the material, it is periodically moistened with water.
Place formwork from any available material (board, laminated plywood).
Lay a hydroprotective barrier on the sand.
Make a reinforcing belt with a rod diameter of 12 mm.
Fill the shallow foundation with concrete mortar.
Lay the second layer of the reinforcing belt into the shallow foundation using a liquid mortar (a feature that is required only by the shallow type of foundation)

Welding is not used to connect reinforcement. To make the non-buried foundation more rigid, a 20 cm long wire is used.

Columnar foundation on heaving soils

The structure can be used to lay a house or barn on heaving soils, the freezing level of which does not exceed one and a half meters. The columnar foundation was based on ready-made piles. Their height reaches 3-4 m.

Strip foundation with drainage on heaving soil

If you plan to build a small building, then such types of piles as driven ones made of wood or reinforced concrete, as well as screw ones, are effective. Wood is a less durable material for foundation purposes.

The columnar foundation is laid below the soil freezing level, so only lateral heaving pressure is maintained. Compared to buried strip structures, it is insignificant, since the area of the pile is smaller.

Among all types of foundation pillars, screw piles for foundations are the most convenient. To make a columnar foundation with their help, you do not need to drill wells. The screw blades will do all the work.

All watery types of soil are accessible to the pile structure: swampy, damp areas. To give the building rigidity, the pillars are connected with support-anchor platforms. To do this, the pillars are screwed into the ground.

On their surface you need to make formwork, lay out a reinforcement frame stitched with metal wire and fill it with concrete mixture. Calculation of the level of the concrete strip is equal to the soil surface or slightly below.

TISE technology is a new way to combat heaving

For laying a foundation with your own hands, the most affordable design is TISE. It is a support-column foundation. the piles of which are connected by a grillage. Chise can be used for brick, frame or stone construction.

Among the advantages of laying TISE piles with your own hands: cost-effectiveness (comparing a shallow strip foundation and TISE, the difference is 4 times in favor of the second), the ability to do without special equipment and electricity, and the possibility of conveniently laying communications.

The resistance to heaving of the TISE structure is ensured by the presence of space between the grillage and the soil. With its help, you can minimize the slope of the site, for example, use its stepped design if the slope of the construction site is more than 10˚.

TISE foundation on heaving soil

The TISE foundation is necessarily reinforced along the perimeter of the tape. The number of rods is calculated so that their total diameter is 8 cm. Using reinforcement, you need to make two belts: top and bottom.

Formwork for TISE structures is done as follows:

Cover the pillars with waterproofing.
Place wooden stakes in the ground so that their top point coincides with the zero level.
Cover the entire width of the grillage and flush with sand.
Nail the boards to the stakes and align them to the zero level.
Protect the TISE formwork with waterproofing.

Slab foundation under heaving conditions

There are other ways to construct a foundation on heaving soils. In addition to TISE, shallow and columnar foundations, slab foundations are used. This is a monolithic reinforced concrete slab. which resists heaving due to the large sole area.

It is effective with a simple building design, when the foundation is a square or rectangle. Calculation of materials shows that this is the most expensive, but no less reliable type of structure. Made from concrete or reinforced concrete.

A monolithic foundation requires a low base. The calculation of the width of the monolithic slab is made depending on what material is used to build the walls.

The average indicator corresponds to parameters from 15 to 35 cm. 15 cm is suitable, for example, for wooden structures, and 20 cm for brick ones. To lay utility lines in the slab, holes of the appropriate diameter are made in advance.

Which type of foundation to choose - shallow, columnar, slab or TISE - depends on the ability to use technology, the size of the house, its configuration and the financial capabilities of the developer.

Heaving phenomena are insidious and unceremonious processes that occur in wet clayey, fine sandy and dusty soils during their seasonal freezing. They cannot be ignored, which is clear to anyone, even a developer with little knowledge of construction. Many people realized this when they discovered a crack in the brick wall of a country house in the spring, saw the skewed door and window openings of a frame country house, and noticed a dangerously tilted fence.

Heaving phenomena are not only large deformations of the soil, but also enormous forces - tens of tons, which can lead to great destruction.

The difficulty in assessing the impact of heaving soil phenomena on buildings lies in some of their unpredictability, due to the simultaneous impact of several processes. To better understand this, let's describe some concepts associated with this phenomenon.

Frost heaving, as experts call this phenomenon, is due to the fact that during the freezing process, wet soil increases in volume.

This happens because water increases in volume by 12% when it freezes (which is why ice floats on water). Therefore, the more water in the soil, the more heaving it is. Thus, a forest near Moscow, standing on very heaving soils, rises in winter by 5...10 cm relative to its summer level. Outwardly it is invisible. But if a pile is driven more than 3 m into the ground, then the rise of the soil in winter can be tracked by the marks made on this pile. The rise of soil in the forest could be 1.5 times greater if there were no snow cover to cover the soil from freezing.

Soils according to the degree of heaving are divided into:

– highly heaving – heaving 12%;

– medium heaving – heaving 8%;

– slightly heaving – heaving 4%.

With a freezing depth of 1.5 m, highly heaving soil is 18 cm.

The heaving of soil is determined by its composition, porosity, and groundwater level (GWL). Likewise, clayey soils, fine and silty sands are classified as heaving soils, and coarse sandy and gravel soils are classified as non-heaving soils.

Let's look at what this is connected with.

Firstly.

In clays or fine sands, moisture, like a blotter, rises quite high from the groundwater level due to the capillary effect and is well retained in such soil. Here wetting forces between water and the surface of dust particles appear. In coarse-grained sands, moisture does not rise, and the soil becomes wet only according to the groundwater level. That is, the thinner the soil structure, the higher the moisture rises, the more logical it is to classify it as more heaving soil.

The water rise can reach:
– 4...5 m in loams;
– 1...1.5 m in sandy loam;
– 0.5...1 m in dusty sands.

In this regard, the degree of soil heaving depends both on its grain composition and on the level of groundwater or flood waters.

Slightly heaving soil
– 0.5 m – in dusty sands;
– at 1 m – in sandy loams;
– 1.5 m – in loams;
– at 2 m – in clays.

Medium heaving soil– when the groundwater level is located below the calculated freezing depth:
– 0.5 m – in sandy loams;
– at 1 m – in loams;
– 1.5 m – in clays.

Heavily heaving soil– when the groundwater level is located below the calculated freezing depth:
– by 0.3 m – in sandy loams;
– by 0.7 m – in loams;
– by 1.0 m – in clays.

Excessively heaving soil– if the groundwater level is higher than for highly heaving soils.

Please note that mixtures of coarse sand or gravel with silty sand or clay will fully apply to heaving soils. If there is more than 30% silt-clay component in coarse soil, the soil will also be classified as heaving.

Secondly.

The process of soil freezing occurs from top to bottom, with the boundary between wet and frozen soil falling at a certain speed, determined mainly by weather conditions. Moisture, turning into ice, increases in volume, displacing itself into the lower layers of the soil, through its structure. The heaving of the soil is also determined by whether the moisture squeezed out from above will have time to seep through the soil structure or not, and whether the degree of soil filtration is sufficient for this process to take place with or without heaving. If coarse sand does not create any resistance to moisture, and it flows away unhindered, then such soil does not expand when frozen (Figure 23).

Figure 23. Soil at the frost line:
1 – sand; 2 – ice; 3 – freezing limit; 4 – water

As for clay, moisture does not have time to escape through it, and such soil becomes heaving. By the way, soil made of coarse sand, placed in a closed volume, which may be a well in clay, will behave like heaving (Figure 24).

Figure 24. Sand in a closed volume is heaving:
1 – clay; 2 – groundwater level; 3 – freezing limit; 4 – sand + water; 5 – ice + sand; 6 – sand

That is why the trench under shallow foundations is filled with coarse-grained sand, which makes it possible to equalize the degree of humidity along its entire perimeter and smooth out the unevenness of heaving phenomena. The trench with sand, if possible, should be connected to a drainage system that drains the perched water from under the foundation.

Third.

The presence of pressure from the weight of the structure also affects the manifestation of heaving phenomena. If the soil layer under the base of the foundation is strongly compacted, then the degree of heaving will decrease. Moreover, the greater the pressure per unit area of the base, the greater the volume of compacted soil under the base of the foundation and the less the amount of heaving.

Example

B Moscow region (freezing depth 1.4 m) a relatively light timber house was erected on medium-heaving soil on a shallow strip foundation with a laying depth of 0.7 m. When the soil completely freezes, the outer walls of the house can rise by almost 6 cm (Figure 25, a). If the foundation under the same house with the same depth is made columnar, then the pressure on the soil will be greater, its compaction will be stronger, which is why the rise of the walls due to soil freezing will not exceed 2...3 cm (Figure 25, b).

Figure 25. The degree of soil heaving depends on the pressure on the base:
A – under the strip foundation; B – under a columnar foundation;
1 – sand cushion; 2 – freezing limit; 3 – compacted soil; 4 – strip foundation; 5 – columnar foundation

Strong compaction of heaving soil under a shallow strip foundation can occur if a stone house of at least three floors in height is erected on it. In this case, we can say that the heaving phenomena will simply be crushed by the weight of the house. But even in this case, they will still remain and can cause cracks to appear in the walls. Therefore, the stone walls of a house on such a foundation should be erected with mandatory horizontal reinforcement.

Why are heaving soils dangerous? What processes take place in them that frighten developers with their unpredictability?

What is the nature of these phenomena, how to deal with them, how to avoid them, can be understood by studying the very nature of the ongoing processes.

The main reason for the insidiousness of heaving soils is uneven heaving under one building

Soil freezing depth- this is not the calculated freezing depth and not the foundation depth, this is the real Freezing Depth in a specific place, at a specific time and under specific weather conditions.

As already noted, the depth of freezing is determined by the balance of the power of heat coming from the bowels of the earth with the power of cold penetrating into the soil from above during the cold season.

If the intensity of the earth's heat does not depend on the time of year and day, then the influx of cold is affected by air temperature and soil humidity, the thickness of the snow cover, its density, humidity, pollution and degree of heating by the sun, the development of the site, the architecture of the structure and the nature of its seasonal use (Figure 26).

Figure 26. Freezing of the building site:
1 – foundation slab; 2 – estimated freezing depth; 3 – daytime freezing limit; 4 – night freezing limit

The unevenness of the thickness of the snow cover most significantly affects the difference in soil heaving. Obviously, the depth of freezing will be higher, the thinner the layer of snow blanket, the lower the air temperature and the longer its effect lasts.

If we introduce such a concept as frost duration (time in hours multiplied by the average daily subzero air temperature), then the freezing depth of clay soil of average humidity can be shown on the graph (Figure 27).

Figure 27. Dependence of freezing depth on snow cover thickness

Frost duration for each region is an average statistical parameter, which is very difficult for an individual developer to assess, because this will require hourly monitoring of air temperature throughout the cold season. However, in an extremely approximate calculation this can be done.

Example

If the average daily winter temperature is about -15 °C, and its duration is 100 days (frost duration = 100 24 15 = 36000), then with a snow cover 15 cm thick the freezing depth will be 1 m, and with a thickness of 50 cm - 0 .35 m.

If a thick layer of snow cover covers the ground like a blanket, then the freezing line rises; at the same time, both day and night its level does not change much. In the absence of snow cover at night, the frost line drops significantly, and during the day, when the sun warms up, it rises. The difference between the night and day levels of the soil freezing limit is especially noticeable where there is little or no snow cover and where the soil is very moist. The presence of a house also affects the depth of freezing, because the house is a kind of thermal insulation, even if no one lives in it (the underground vents are closed for the winter).

The site on which the house stands may have a very complex pattern of soil freezing and rising.

For example, medium heaving soil along the outer perimeter of a house, when frozen to a depth of 1.4 m, can rise by almost 10 cm, while drier and warmer soil under the middle part of the house will remain almost at the summer level.

Uneven freezing also exists around the perimeter of the house. Closer to spring, the soil on the south side of the building is often wetter, and the layer of snow above it is thinner than on the north side. Therefore, unlike the north side of the house, the soil on the south side warms up better during the day and freezes more strongly at night.

From experience

In the spring, in mid-March, I decided to check how the soil “walks” under the built house. At the corners of the foundation (on the inside) rods were concreted into paving slabs, along which I checked the subsidence of the foundation from the weight of the house. On the northern side the soil rose by 2 and 1.5 cm, and on the southern side by 7 and 10 cm. The water level in the well at that time was 4 m below the ground.

Thus, the unevenness of freezing in the area manifests itself not only in space, but also in time. The depth of freezing is subject to seasonal and daily changes within very large limits and can vary greatly even in small areas, especially in built-up areas.

By clearing large areas of snow in one place of the site and creating snowdrifts in another place, you can create noticeable uneven freezing of the soil. It is known that planting shrubs around the house retains snow, reducing the freezing depth by 2–3 times, which is clearly visible in the graph (Figure 27).

Clearing narrow paths of snow does not have much effect on the degree of soil freezing. If you decide to fill a skating rink near your house or clear an area for your car, you can expect greater unevenness in the freezing of the soil under the foundation of the house in this area.

Lateral adhesion forces frozen soil with the side walls of the foundation is the other side of the manifestation of heaving phenomena. These forces are very high and can reach 5...7 tons per square meter of the lateral surface of the foundation. Similar forces arise if the surface of the pillar is uneven and does not have a waterproofing coating. With such strong adhesion of frozen soil to concrete, a vertical buoyancy force of up to 8 tons will act on a pillar with a diameter of 25 cm, laid to a depth of 1.5 m.

How do these forces arise and act, how do they manifest themselves in the real life of the foundation?

Let's take, for example, the support of a columnar foundation under a light house. On heaving soil, the depth of the supports is set to the calculated freezing depth (Figure 28, a). Given the light weight of the structure itself, the forces of frost heaving can lift it, and in the most unpredictable way.

Figure 28. Raising the foundation by lateral adhesion forces:
A – columnar foundation; B – columnar-strip foundation using TISE technology;
1 – foundation support; 2 – frozen soil; 3 – freezing limit; 4 – air cavity

In early winter, the frost line begins to drop down. Frozen, strong soil grabs the top of the pillar with powerful adhesion forces. But in addition to increasing the adhesion forces, the frozen soil also increases in volume, causing the upper layers of the soil to rise, trying to pull the supports out of the ground. But the weight of the house and the forces of embedding the pillar in the ground do not allow this to be done while the layer of frozen soil is thin and the adhesion area of the pillar with it is small. As the freezing line moves downwards, the area of adhesion between the frozen soil and the pillar increases. There comes a moment when the adhesion forces of frozen soil to the side walls of the foundation exceed the weight of the house. The frozen soil pulls out the pillar, leaving a cavity below, which immediately begins to fill with water and clay particles. Over the course of a season, on heavily heaving soils, such a pillar can rise by 5–10 cm. The rise of the foundation supports under one house, as a rule, occurs unevenly. After the frozen soil thaws, the foundation pillar, as a rule, does not return to its original place on its own. With each season, the unevenness of the supports coming out of the ground increases, the house tilts, falling into disrepair. “Treatment” of such a foundation is a difficult and expensive job.

This force can be reduced by 4...6 times by smoothing the surface of the well with a roofing felt jacket inserted into the well before filling it with concrete mixture.

A buried strip foundation can rise in the same way if it does not have a smooth side surface and is not loaded on top with a heavy house or concrete floors (Figure 4).

The basic rule for recessed strip and column foundations (without expansion at the bottom): The construction of the foundation and loading it with the weight of the house should be completed in one season.

The foundation pillar, made using TISE technology (Figure 28, b), does not rise due to the lower expansion of the pillar due to the adhesion forces of heaving frozen soil. However, if it is not expected to be loaded with a house during the same season, then such a pillar must have reliable reinforcement (4 rods with a diameter of 10...12 mm), which prevents the extended part of the pillar from being separated from the cylindrical one. The undoubted advantages of the TISE support are its high load-bearing capacity and the fact that it can be left for the winter without loading from above. No amount of frost heaving will lift it.

Lateral adhesion forces can play a sad joke on developers who make a columnar foundation with a large margin of load-bearing capacity. Extra foundation pillars may indeed be unnecessary.

From practice

A wooden house with a large glassed-in veranda was installed on foundation pillars. Clay and high groundwater levels required the foundation to be laid below the frost depth. The floor of the wide veranda required an intermediate support. Almost everything was done correctly. However, over the winter the floor rose by almost 10 cm (Figure 29).

Figure 29. Destruction of the veranda ceiling due to the adhesion forces of frozen soil to the support

The reason for this destruction is clear. If the walls of the house and veranda were able to compensate with their weight the adhesion forces of the foundation pillars with frozen soil, then light floor beams were unable to do this

What should have been done?

Significantly reduce either the number of central foundation pillars or their diameter. The adhesive forces could be reduced by wrapping the foundation pillars with several layers of waterproofing (tar paper, roofing felt) or by creating a layer of coarse sand around the pillar. Destruction could also be avoided by creating a massive grillage tape connecting these supports. Another way to reduce the rise of such supports is to replace them with a shallow columnar foundation.

Extrusion– the most tangible cause of deformation and destruction of the foundation laid above the freezing depth.

How can this be explained?

Extrusion is required daily allowance the passage of the freezing boundary past the lower supporting plane of the foundation, which occurs much more often than the lifting of supports from lateral adhesion forces having seasonal character.

To better understand the nature of these forces, let’s imagine frozen soil in the form of a slab. In winter, a house or any other structure becomes securely frozen into this stone-like slab.

The main manifestations of this process are visible in the spring. The side of the house facing south is quite warm during the day (you can even sunbathe when there is no wind). The snow cover melted, and the soil was moistened with spring drops. Dark soil absorbs sunlight well and warms up.

On a starry night in early spring especially cold (Figure 30). The soil under the roof overhang freezes heavily. A ledge grows from below a slab of frozen soil, which, with the power of the slab itself, strongly compacts the soil underneath due to the fact that wet soil expands when it freezes. The forces of such soil compaction are enormous.

Figure 30. Slab of frozen soil at night:
1 – slab of frozen soil; 2 – freezing limit; 3 – direction of soil compaction

A 1.5 m thick slab of frozen soil measuring 10x10 m will weigh more than 200 tons. The soil under the ledge will be compacted with approximately the same force. After such exposure, the clay under the protrusion of the “slab” becomes very dense and practically waterproof.

The day has come. The dark soil near the house is especially heated by the sun (Figure 31). As humidity increases, its thermal conductivity also increases. The freezing line rises (under the ledge this happens especially quickly). As the soil thaws, its volume also decreases; the soil under the support loosens and, as it thaws, falls under its own weight in layers. Many cracks form in the soil, which are filled from above with water and a suspension of clay particles. At the same time, the house is held by the forces of adhesion between the foundation and the slab of frozen soil and the support along the rest of the perimeter.

Figure 31. Slab of frozen soil during the day:
1 – slab of frozen soil; 2 – freezing limit (night); 3 – freezing limit (day); 4 – defrosting cavity

As night falls cavities filled with water freeze, increasing in volume and turning into so-called “ice lenses”. If the amplitude of the rise and fall of the freezing boundary in one day is 30–40 cm, the thickness of the cavity will increase by 3–4 cm. Along with the increase in the volume of the lens, our support will also rise. Over several such days and nights, the support, if it is not heavily loaded, sometimes rises by 10–15 cm, like a jack, resting on very strongly compacted soil under the slab.

Returning to our slab, we note that the strip foundation violates the integrity of the slab itself. It is cut along the side surface of the foundation, because the bitumen coating with which it is covered does not create good adhesion between the foundation and the frozen soil. The slab of frozen soil, creating pressure on the ground with its protrusion, begins to rise itself, and the fracture zone of the slab begins to open up and fill with moisture and clay particles. If the tape is buried below the freezing depth, then the slab rises without disturbing the house itself. If the depth of the foundation is higher than the freezing depth, then the pressure of the frozen soil raises the foundation, and then its destruction is inevitable (Figure 32).

Figure 32. Slab of frozen soil with a fault along the foundation strip:
1 – plate; 2 – fault

It is interesting to imagine a slab of frozen soil turned upside down. This is a relatively flat surface, on which at night in some places (where there is no snow) hills grow, which turn into lakes during the day. If you now return the slab to its original position, then exactly where the hills were, ice lenses are created in the ground. In these places, the soil below the freezing depth is highly compacted, and above, on the contrary, it is loosened. This phenomenon occurs not only in built-up areas, but also in any other place where there is unevenness in the heating of the soil and in the thickness of the snow cover. It is according to this scheme that ice lenses, well known to specialists, appear in clayey soils. The nature of the formation of clay lenses in sandy soils is the same, but these processes take much longer.

Raising a shallow foundation pillar

The foundation column is lifted with frozen soil by passing the freezing line daily past its base. Here's how the process happens.

Until the moment the soil freezing line drops below the supporting surface of the pillar, the support itself is motionless (Figure 33, a). As soon as the freezing line drops below the base of the foundation, the “jack” of heaving processes immediately starts working. The layer of frozen soil located under the support, increasing in volume, lifts it (Figure 33, b). Frost heaving forces in water-saturated soils are very high and reach 10…15 t/m². With the next warming up, the layer of frozen soil under the support thaws and decreases in volume by 10%. The support itself is held in a raised position by the forces of its adhesion to the slab of frozen soil. Water with soil particles seeps into the gap formed under the sole of the support (Figure 33, c). With the next decrease in the freezing limit, the water in the cavity freezes, and the layer of frozen soil under the support, increasing in volume, continues to rise the foundation column (Figure 33, d).

It should be noted that this process of lifting the foundation supports is daily (multiple) in nature, and the extrusion of the supports by adhesion forces with frozen soil is seasonal (once per season).

With a large vertical load on the pillar, the soil under the support, strongly compacted by pressure from above, becomes slightly heaving, and water from under the support itself is squeezed out through its thin structure during the process of thawing the frozen soil. In this case, practically no lifting of the support occurs.

Figure 33. Raising the foundation pillar with heaving soil;
A, B – upper level of the frost line; B, D – lower level of the frost line;
1 – grillage tape; 2 – foundation pillar; 3 – frozen soil; 4 – upper position of the frost line; 5 – lower position of the frost line; 6 – mixture of water and clay; 7 – mixture of ice and clay

Heaving soil is a soil mass that expands in the winter and puts strong pressure on the foundation walls. It leads to the destruction of the structure, its “pushing” out of the pit.

There are types of structures for construction in such conditions and a list of rules for work: from to reinforcement.

Calculation of heaving intensity in the area

To calculate the degree of soil heaving at a construction site with your own hands, you need use the formula: E = (H - h) / h, wherein:

E – corresponds to the degree of soil heaving;
h – height of the soil mass before freezing;
H – height of the soil mass after freezing.

What is heaving soil and why is it dangerous? (video)

How to remove the effects of heaving on the ground?

There are simple ways to remove heaving around the foundation with your own hands:

Replacing the layer of soil under and around the base with a non-heaving layer.
Laying the foundation on a soil mass below the freezing layer.
Insulation of the structure to prevent soil freezing.
Drainage

The first method is the most labor-intensive. To do this, it is necessary to remove the heaving soil at a depth below the freezing level of the ground, and fill in its place with heavily compacted sand.

Below we will consider the types of bases that can be used on soil prone to heaving.

Shallow strip foundation on heaving soils

An effective way to make a strong foundation for a house or barn is a shallow (low depth) strip foundation on heaving soils. This is a concrete strip with reinforcement elements, arranged around the entire perimeter of the building and in places where load-bearing walls lie.. To build a shallow foundation with your own hands, you must follow these steps:

, 50-70 cm deep. The width is calculated based on the width of the base itself plus formwork, insulation or waterproofing, as well as decor.
Lay the slopes of the open trench with waterproofing. For this purpose, roofing felt and film are used.
Fill the excavation with layers of compacted sand, 20-30 cm each. To compact the material, it is periodically moistened with water.
Place formwork from any available material (board,).
Lay a hydroprotective barrier on the sand.
Make a reinforcing belt with a rod diameter of 12 mm.
Fill the shallow foundation with concrete mortar.
Lay the second layer of the reinforcing belt into the shallow foundation using a liquid mortar (a feature that is required only by the shallow type of foundation)

Welding is not used to connect reinforcement. To make the non-buried foundation more rigid, a 20 cm long wire is used.

Columnar foundation on heaving soils

The columnar foundation is laid below the soil freezing level, so only lateral heaving pressure is maintained. Compared to buried strip structures, it is insignificant, since the area of the pile is smaller.

TISE technology is a new way to combat heaving

For laying a foundation with your own hands, the most affordable design is TISE. It is a structure whose piles are connected by a grillage. Chise can be used for brick, frame or stone construction.

Slab foundation under heaving conditions

There are other ways to construct a foundation on heaving soils. In addition to TISE, shallow and columnar foundations, slab foundations are used. This is one that resists heaving due to the large area of the sole.

A monolithic foundation requires a low base. The calculation of the width of the monolithic slab is made depending on what material is used to build the walls.

What type of foundation to choose - shallow, columnar, slab or TISE - depends on the ability to use technology, the size of the house, its configuration and the financial capabilities of the developer.

Soil heaving, caused by the ability of the soil to retain water in its structure, is a serious enemy of strip foundations. Particularly critical is the uneven heaving of the underlying soils, leading to uneven loads on the foundation. Most often, uneven heaving of soils can be caused by the presence of heterogeneous underlying soils under a shallow strip foundation. Also, uneven heaving can be caused by uneven heating of the soil from the sun, differences in soil insulation (including uneven coverage of the soil near the house with snow), and the presence of heated and unheated rooms on the same foundation. In addition to clay soils, heaving soils include silty and fine sands, as well as coarse soils with clay aggregates that have a moisture content above a certain level at the beginning of the freezing season.

The list of heaving soils according to GOST 25100-95 is given in the table:

Table. Soil heaving.

Degree of soil heaving (GOST 25100-95) / % expansion	An example of soil requires research to decide on classification)
Almost non-heaving soils< 1%	Hard clayey soils, low-water-saturated gravelly soils, coarse and medium sands, fine and silty sands, as well as fine and silty sands containing less than 15% by weight of particles smaller than 0.05 mm. Coarse soils with filler up to 10%
Slightly heaving soils<1-3,5 %	Semi-solid clay soils, moderately water-saturated silty and fine sands, coarse-grained soils with filler (clayey, fine sand and silty sand) from 10 to 30% by weight
Medium heaving soils< 3,5-7 %	Tight plastic clay soils. Water-saturated silty and fine sands. Coarse soils with aggregate (clayey, silty sand and fine sand) more than 30% by weight
Highly heaving and excessively heaving soils > 7%	Soft plastic clay soils. Water-saturated silty and fine sands.

For an overview of the most important properties of soils and their suitability for construction, we suggest referring to the summary table:

Table. Soil characteristics(Table adapted from Section R406.1 of the International Residential Code - 2006)

Priming	Drainage capabilities of soils	Potential for ground level rise due to freezing. (Vertical and tangential components of frost heave forces)	The potential for soil expansion when frozen. (Horizontal components of frost heaving forces)
Boulder, pebble, crushed stone, gravel, wood. The sand is gravelly and coarse.		Minor	Minor
Silty gravel, silty sands			Minor
Clay gravel, sand-clay gravel mixture, clay sands			Minor
Silty and fine sand, fine clay sand, inorganic silt, clay loam with moderate plasticity			Minor
Low- and medium-plastic clays, gravelly clays, silty clays, sandy clays, lean clays			Slight to moderate
Plastic and fatty clays
Inorganic silty soils, fine micaceous sands
Organic non-plastic silty soils, silty refractory clay
Clay and silty clay of medium and high plasticity, plastic silty soils, peat, sapropel.	Unsatisfactory

The heaving of soil is determined by its composition, porosity, and groundwater level (GWL). The higher the groundwater level, the more the soil will expand when it freezes. The ability to retain and “suck” water from the underlying layers is ensured by the presence of capillaries in the soil structure and their suction of water. When soil expands with freezing water (ice), it begins to increase in volume.
This happens due to the fact that water increases in volume when it freezes by 9-12%. Therefore, the more water in the soil, the more heaving it is. Heaving is also higher in soils with poor drainage characteristics. When the soil freezes from above (from the ground level or level), the still unfrozen water is squeezed out by ice into the underlying layers of the soil.
If the drainage properties of the soil are insufficient, then the water is retained and quickly freezes, causing additional expansion of the soil. At the interface between positive and negative temperatures, ice lenses can freeze, causing additional soil rise. The greater the density of the soil, the fewer capillaries and voids (pores) there are where water can be retained and, therefore, the less potential for expansion when freezing.
By definition, a shallow strip foundation is laid at the depths of the seasonally freezing soil layer. When the soil freezes and begins to move, a force begins to act on the foundation, the vector of which is applied perpendicular to the base of the foundation (provided that the base lies in the horizon).
Under the influence of this force, the application of which is often uneven along the length of the foundation, the foundation and the building itself may also be subject to uneven movements. In addition to upward pressure, when frozen, heaving soil can exert pressure both horizontally and tangentially to the vertical plane of the foundation strip.

The strength of frost heaving depends on the magnitude of negative temperatures and the duration of their action. Maximum frost heaving of soil in Russia occurs at the end of February - March. If you are building a shallow shallow foundation on highly heaving soil, you will have to think about how to reduce the impact of not only the tangential components of frost heaving forces, but also their horizontal components. The soil freezing to the foundation can not only provide lateral compression of the foundation, but also pinching it by lateral adhesion forces and lifting, which can cause deformation of the foundation (especially critical for prefabricated strip foundations made of blocks).
Therefore, if you decide to build a shallow strip foundation on heavily or excessively heaving soil, it is better for you to choose a rigid monolithic reinforced concrete frame as a foundation, rather than a prefabricated strip foundation made of blocks. In addition, a number of measures will have to be taken to reduce the friction force between the foundation and the soil, and thermal engineering measures to reduce the forces of frost heaving.

Table. Standard depth of seasonal soil freezing, m.

City		Loams, clays	fine sands	Medium and coarse sands	Rocky ground

Vladimir

Kaluga, Tula

Yaroslavl

Nizhny Novgorod, Samara
Saint Petersburg. Pskov
Novgorod
Izhevsk, Kazan, Ulyanovsk
Tobolsk, Petropavlovsk
Ufa, Orenburg
Rostov-on-Don, Astrakhan

Bryansk, Orel
Ekaterinburg

Novosibirsk

What can be done to reduce the impact of frost heaving forces on the foundation:

Provide good drainage of seasonally freezing soil near the foundation.
Ensure drainage of storm and melt water using hard or soft pavement.
Insulate the surface of freezing soil near the foundation.
Consider the possibility of soil salinization with substances that do not cause corrosion of concrete and reinforcement.

The simplest and most inexpensive way is horizontal insulation of the soil around the building (which we will discuss in detail below) and vertical insulation of the strip foundation. In addition to reducing heat loss at home (from 10 to 20%), insulation of the underground part of the foundation with polystyrene foam also plays an important role in reducing friction between the soil and the foundation during heaving and compensating for soil expansion.

Proper drainage plays an important role in reducing soil heaving. To reduce the forces of frost heaving, it is necessary to dehydrate the soil as much as possible in the immediate vicinity of the shallow strip foundation. To do this, the trenches for the strip foundation are lined with geotextiles, after casting the foundation and performing waterproofing and insulation of the foundation, drainage pipes for ring drainage around the entire house are laid at the bottom and filled with a drainage mixture of sand and expanded clay, or simply sand. The wall drainage membrane also helps to drain water deeper into the drainage pipes.
In particularly difficult soil conditions, you can resort to complete or partial replacement of the soil underlying and adjacent to the shallow strip foundation.

The role of large deciduous trees in the movement of heaving soils is not considered at all in the domestic construction literature. Meanwhile