The issue of laying depth is relevant for any type of foundation for a house. The correct choice of this value will ensure the strength and reliability of the structure (subject to construction technology). The depth of the foundation must be set in strict accordance with regulatory documentation.
According to clause 12.2 of SP 50-101-2004, the depth of the required foundation of any house depends on:
- the purpose of the object, its design solutions and loads from overlying elements;
- depth of laying in the ground of the house's utility lines;
- terrain of the site and planning marks;
- characteristics of the foundation soil;
- climatic features of the construction area.
To put it simply, for private construction, the minimum depth required to lay the base of the foundation in the soil is determined by the following factors:
- foundation type;
- soil type;
- presence or absence of a basement;
- groundwater level (GWL) in the soil;
- depth of soil freezing in winter.
The mark of the sole in the presence of basements or basements is taken to be 30-50 cm below the floor mark. The foundation must be buried so that at least 50 cm remains to the groundwater level.
The depth of soil freezing is taken into account for columnar and strip foundations. The slabs are usually laid above the freezing mark, and the piles rest significantly lower (the length is calculated based on the bearing capacity).
Laying depth depending on freezing
Soil freezing is dangerous because if there is water in it, it expands, turning into ice. Displacements occur that can lead to damage to the foundation. If you place the tape or poles without special measures on unstable heaving soil that deforms in winter, the consequences will be disastrous.
Before digging a pit or trench, determine the standard depth to which the soil freezes. For private housing construction, you can be guided by the average value, but if you need to determine the exact standard value, then calculations are made according to formula 5.3 SP “Foundations of buildings and structures.”
If there is no desire to calculate in detail what the minimum laying depth that is necessary for the foundation should be, take the already calculated freezing values from the table presented below, depending on the region of construction and the type of soil. Previously, the freezing depth could also be determined from the SNiP “Building Climatology and Geophysics” maps, but after editing these maps were removed from the updated edition (SP). SNiP can be used for reference purposes. The table is presented for some Russian cities.
| City | Construction on | |||
| coarse soil | sandy soil (medium or coarse fraction) | sandy soil (silty or fine), sandy loam | Clay and loamy bases | |
| Arkhangelsk | 231 cm | 204 cm | 190 cm | 156 cm |
| Belgorod | 159 cm | 140 cm | 131 cm | 108 cm |
| Vladivostok | 199 cm | 175 cm | 164 cm | 134 cm |
| Volgograd | 145 cm | 128 cm | 119 cm | 98 cm |
| Vorkuta | 346 cm | 305 cm | 285 cm | 234 cm |
| Ekaterinburg | 231 cm | 204 cm | 191 cm | 157 cm |
| Ivanovo | 213 cm | 188 cm | 175 cm | 144 cm |
| Irkutsk | 274 cm | 241 cm | 225 cm | 185 cm |
| Kaliningrad | 71 cm | 62 cm | 58 cm | 48 cm |
| Kemerovo | 274 cm | 241 cm | 225 cm | 185 cm |
| Krasnodar | 15 cm | 13 cm | 13 cm | 10 cm |
| Lipetsk | 195 cm | 172 cm | 160 cm | 132 cm |
| Magadan | 295 cm | 261 cm | 243 cm | 200 cm |
| Moscow | 163 cm | 144 cm | 134 cm | 110 cm |
| Orenburg | 225 cm | 198 cm | 185 cm | 152 cm |
| Petrozavodsk | 196 cm | 173 cm | 161 cm | 132 cm |
| Rostov-on-Don | 97 cm | 86 cm | 80 cm | 66 cm |
| Samara | 228 cm | 201 cm | 188 cm | 154 cm |
| Saint Petersburg | 145 cm | 128 cm | 120 cm | 98 cm |
| Ulan-Ude | 306 cm | 270 cm | 252 cm | 207 cm |
| Khabarovsk | 281 cm | 248 cm | 231 cm | 190 cm |
Values for cities not included in the table can be found on maps from SNiP by interpolation or take the value for the nearest point. The type of soil is determined by drilling or digging holes. First you need to familiarize yourself with GOST “Soils. Classification".
Standard depth of soil freezing in the European part of Russia. Previously, these maps were in regulatory documentation, but now they can only be used for reference.
The estimated soil freezing depth is calculated by multiplying the standard depth by the correction factor given in Table 5.2 SP “Foundations of buildings and structures”.
| Constructive solution for the house | Coefficient depending on the calculated air temperature in volumes (°C) adjacent to the foundation* | ||||
| 0 | 5 | 10 | 15 | >20 | |
| Without a basement with floors built on the ground | 0,9 | 0,8 | 0,7 | 0,6 | 0,5 |
| Without a basement with floors built on the ground on joists | 1,0 | 0,9 | 0,8 | 0,7 | 0,6 |
| Without a basement with floors built on an insulated basement floor | 1,0 | 1,0 | 0,9 | 0,8 | 0,7 |
| With a basement | 0,8 | 0,7 | 0,6 | 0,5 | 0,4 |
*For unheated basements the value is +5 °C, for residential premises according to GOST “Residential and public buildings” - +20 °C.
The depth of the foundation for the house is taken to be no higher than the freezing depth (in the absence of additional measures).
Dependence on the location of groundwater
Before digging, it is also necessary to determine the depth of groundwater in the soil, since it significantly affects the depth required for laying and its dependence on freezing. What the minimum depth should be is determined according to Table 5.3 SP “Foundations and Foundations”.
| Soils on which the sole is supported | Sole depth | |
| if groundwater is located at a distance of less than 2 m from the base of the foundation | if groundwater is located 2 or more meters below the base of the building support | |
| Coarse and rocky rocks, sandy soil (gravelly, coarse and medium fraction) | Does not depend on freezing | Does not depend on freezing |
| Sandy soil (fine and dusty) | Depends, assumed to be no less than the freezing depth | |
| Sandy loam | ||
| Clayey and loamy bases, coarse-grained rocks with silty filler | Depends, at least 1/2 freezing depth is assumed | |
Advice! It is not recommended to build a house on a shallow sandy or dusty foundation. To prevent problems, soil with poor performance characteristics is replaced with another more durable one.
GWL should be measured in the spring, when the soil is most saturated with moisture. To study, it is better to choose several points, one of them in the lowest part of the site. The distance from the sole to the groundwater level must be at least 50 cm.
Dependence on the type of foundation
The depth of the foundation is also determined depending on the chosen design solution for the foundation of the house. The recommendations can be summarized in one table.
In addition, foundations can be:
- recessed
This mainly applies to columnar and strip bases. But it is also applicable for slabs (more often the slabs are made shallow or not buried).
Shallow foundations
This type of foundation is suitable for use in the following cases:
- construction of a light house without a basement or plinth;
- high groundwater level (but more than 1 meter from the ground surface);
- fairly good strength characteristics of the foundation soil.
Scheme of an insulated shallow strip foundation
When constructing such a foundation, you do not have to dig deep into the ground, which reduces labor and time costs. The minimum for conditionally non-heaving soils (sandy, coarse-clastic) can be as follows:
- with a freezing depth of up to 3 m - 0.5 m;
- up to 3 m - 0.75 m;
- more than 3 m - 1.0 m.
To prevent damage to the structure due to frost heaving and water, the following measures must be taken:
- Waterproofing. Like any other foundation, a shallow foundation requires reliable protection from moisture. The blind area protects the structure from rain and melt water. Bitumen mastic is applied to the vertical part of the foundation along the entire height or roll waterproofing materials (linocrom, waterproofing) are glued.
- Insulation foundation height and installation of a warm blind area. Extruded polystyrene foam (penoplex) can be used as a thermal insulation material. The thickness of the insulation is selected using thermal engineering calculations. For most regions of the country, 100 mm of penoplex will be required. Mineral wool cannot be used as thermal insulation. The insulation is laid outside along the entire height and under the concrete or asphalt blind area.
- Sand cushion. It prevents frost heaving. It is laid from medium or coarse sand with layer-by-layer compaction. The thickness of the cushion depends on the actual strength characteristics of the soil, on average it is 30-50 cm.
- Drainage of groundwater and rainwater from the design. Storm sewers also take on this function. Even with a fairly low level of groundwater, these measures are necessary, since during the period of rain or melting snow, the soil is highly saturated with moisture. If you allow the foundation to be exposed to water and low temperatures at the same time, the consequences may be irreversible. The most common type of drainage is wall drainage. The pipe with holes is laid in a layer of gravel wrapped in geotextile. The maximum distance from the drainage pipe to the foundation is 1 meter. The laying depth is 30-50 cm below the base of the foundation.
In the case of shallow foundation slabs, a modern solution will be (USP). This is the base that houses the underfloor heating system and some utilities. For production, permanent formwork made of expanded polystyrene is used, which subsequently plays the role of insulation.
The depth of the foundation is one of the decisive factors affecting the durability and reliability of the foundation. It is important to take into account all the requirements, and if they cannot be met, take the necessary measures to protect the structure.
Advice! If you need contractors, there is a very convenient service for selecting them. Just send in the form below a detailed description of the work that needs to be performed and you will receive proposals with prices from construction teams and companies by email. You can see reviews about each of them and photographs with examples of work. It's FREE and there's no obligation.
Used in individual construction laid to frost depth soil strip, slab or columnar foundation. Piles are immersed to layers with bearing capacity, which can lie at any level. The base of the foundation, located below the freezing mark, does not experience loads from heaving forces. However, these forces still act on the side walls of strip foundations, piles, pillars, trying to pull them out of the ground to the surface.
Why do soils swell?
Largely soil, on which the construction of foundations takes place, contains particles of clay. This material does not allow moisture to pass through, but is saturated with it during rains or groundwater. When freezing, the droplets inside the clay increase in volume several times, the volume of the soil increases by 10 - 12%.
For example, in regions with depth freezing 1.5 m, the earth is capable of rising on the site by 12 - 17 cm, pushing out the concrete structures placed in it. The main problem of frost heaving is as follows:
- The clay content in different layers is not the same
- some contain more moisture than others
- the soil swells unevenly, warping individual sections of the foundation
Light buildings cannot balance these underground forces, which sometimes reach 5 t/m2. Increasing depth the occurrence of the base of the strip foundation, the developer completely solves the problem of swelling under the base. However, the area of the lateral surfaces on which tangential loads act increases. Even if they can't pull out the pole, the tape from soil completely, at the moment the base of the foundation is raised by 10 - 15 cm, soil from adjacent layers is poured into these voids.
When thawing, the reinforced concrete structure cannot return to its original position; next winter the whole cycle is repeated in the same order. Thus, after just a few years, the building finally warps, falls into disrepair, and becomes unsuitable for use.
Methods to neutralize heaving forces
To protect against freezing soils on depth The following technologies are most effective for foundation immersion:
In practice, several of these methods are usually used in combination. This allows you to reduce swelling to a minimum that is safe for the operation of the foundation in specific conditions.
What foundations are buried below the freezing mark?
A deep-lying strip is expensive for the developer, so this type of foundation is used in projects with an underground floor. Most often below the mark freezing foundations are located:
- columnar - in 90% of cases the sole has a widening, often not related to the body of the column, so heaving forces must be compensated by this method
- strip – for cottages with a usable basement floor
- pile - these structures are laid at great depths by default, since in the upper level a layer with bearing capacity is extremely rare
A slab foundation is considered the most expensive foundation. When it is buried below the freezing mark, the budget increases many times over.
This foundation is used due to tradition, since it has an unreasonably high construction budget. Foundation strip buried below the mark freezing, doubles the price of m2 of housing:
However, immersed in depth below the freezing mark, tape remains practically the only way to get a warm underground or a full-fledged underground level. This is true for small areas where horizontal development is undesirable. The number of storeys for individual development is regulated by three floors, so the basement significantly increases the comfort of living.
Protection against heaving forces for buried belts is standard:
- insulation of external walls
- backfilling with sand, ASG
- thermal insulation of the blind area
- drainage around the perimeter of the sole
The insulation protects the waterproofing material and contracts, taking on some of the heaving forces. The second method completely eliminates the presence of clay rock near the walls of the belt. The warm blind area prevents the soil from freezing; moisture is removed by drainage.
For shallow tape, almost all of the listed methods of combating heaving forces are used. However, these cottage foundations cannot 100% replace a buried tape in terms of ease of use, although they can withstand serious loads.
Light buildings at MZLF are practiced mainly on sands and sandy loams. Despite the comprehensive protection against heaving, the likelihood of soil lifting still remains. Light walls will not be able to load the foundation enough to compensate for heaving forces. In this case, foam concrete, aerated concrete blocks or brickwork are recommended.
On flat areas with normal geological conditions, a columnar foundation is an economical solution for lightweight buildings. The maximum service life of the structure is provided by pillars, the sole of which is located below the retaliation freezing in the region. Only outbuildings, MAFs, can rest on shallow pillars.
The most popular are monolithic or glass columnar foundations, which in any case must be waterproofed and filled with inert material on the sides to avoid heaving forces. Both among individual developers and in the construction literature, columnar foundations often include hanging bored piles in shells, the base of which is lowered below the level freezing.
Unlike a pile, a pole is constructed in an excavated hole, rather than in a hole drilled in the ground. The technology looks like:
- marking - according to cast-offs taken outside the corners of the building, cords are pulled along the axes of the pillars
- soil development - a hole is dug under each pillar, taking into account the access of workers to concrete work
- preparation - 20 cm layer of sand, 20 cm layer of crushed stone with compaction with a vibrating plate every 10 cm of non-metallic materials, pouring the footing (5 - 10 cm), waterproofing the base with hydroglass insulation (2 layers)
- widening - slab 10 - 20 cm with horizontal reinforcing mesh (rods 12 mm of periodic section) with the release of a vertical reinforced frame to the entire height of the column
- formwork - panels, asbestos-cement, large-diameter polyethylene pipe
- concreting - laying the mixture, compacting with the tip of an internal vibrator
- waterproofing - after stripping on days 4 - 15 after concrete has gained 70% strength
- backfilling - the bosoms of the pit are filled with ASG or sand with layer-by-layer compaction of the material
Thus, the location of the base of the pillar below the freezing mark guarantees the absence of heaving forces from below. Backfill minimizes tangential pull-out loads on the column.
Due to the maximum construction budget of a floating slab, these structures are rarely buried below the level freezing. However, a slab foundation submerged to this depth is the most durable of all existing ones and allows the construction of a full-fledged basement floor. The design looks like:
Prefabricated loads from the building are transferred to the basement walls and are evenly distributed by the slab over the foundation pad made of inert materials (crushed stone, sand). The safety margin of deep-laid slabs is many times greater than the required value, allowing the construction of 3-story brick mansions with heavy roofs, wall cladding, and facades.
There are coffered slabs poured over the metal into formwork of complex configuration:
This is the most economical option to get a classic slab foundation with a wine cellar or an underground structure for storing vegetables and placing communications. The depth of the cellar base is guaranteed to be below the freezing mark. This allows you to preserve the geothermal heat of the subsoil, which prevents heaving soils from freezing. Waterproofing of structures is mandatory, since even with a low groundwater level, groundwater can have seasonal level changes.
Pile foundation
Unlike all existing foundations, for piles the mark freezing doesn't really matter. The minimum permissible immersion depth of screw and bored structures for housing is 3 m, which is much greater than the freezing mark in most regions.
The area of the lateral surfaces of the piles (diameter 15 - 60 cm) is insignificant, the pulling forces of heaving soils in this case are minimal. However, the bearing capacity of pile foundations depends 70% on the calculated resistance of the soil under the heel. Therefore, geological surveys are carried out in the building area or test drilling is carried out. 
In the latter case, the depth of the bearing layer (calculated resistance 4 - 6 kg/cm2) is determined by a sharp increase in the tightening force. After which, all piles are immersed to this level, resting on the bearing layer.
Thus, of all existing foundations, the following are not buried below the freezing mark:
- floating slab - due to the maximum supporting surface, two-layer reinforcement, it successfully resists soil movements, insulating the sole (a version of the Swedish USHP slab) completely eliminates heaving forces, the ground cannot freeze
- shallow-depth MZLF tape - the soil under the sole is replaced with inert material, the blind area is insulated, and ring drainage is laid
- shallow pillars - used exclusively for outbuildings, often require repairs on heaving soils
All other foundations are immersed below the freezing mark in the region, ensuring maximum bearing capacity and service life of the structure.
Deepening the base of the foundation below the freezing mark allows you to stabilize the geometry of the spatial structure and increase durability. However, this method for an individual builder is more expensive than shallow-depth MZLF tape, screw piles, and bored piles. Therefore, it is used exclusively if there is a basement floor in the project.
This is an architectural and construction structure that plays a very important role in the construction of a house. The longevity of the entire building depends on its stability and strength, as well as a guarantee against all sorts of heavy and expensive repairs to the basement of the walls, the blind area and the foundation itself. Due to a weak, poorly made foundation, even the most spectacular, beautiful architecture can end up in a deplorable state and lose its appearance. As a result of improper construction of the foundation, the destruction of the house occurs, which begins from below the ground and from above from the roof. Many cases from the practice of construction and operation of low-rise suburban buildings indicate significant problems that arise after a certain period of operation of the house. These include: loss of heat in the house, the appearance of mold, dampness and cracks. All these problems are the result of many reasons, including the incorrectly chosen location of the house on the site.
Excessive heat loss leads to high costs for fuel and for repairs not only of the enclosing structures of walls, roofs, ceilings, sealing cracks, seams and joints, but also for the necessary repairs of the foundation itself. If heat loss is associated with the destruction of hydro and thermal insulation, then additional efforts to restore them may be insignificant, but when the problem concerns the base itself, the foundation, then the costs of repairing it can be very significant.
Conclusion: Before you start building a personal home on your own, you need to become familiar with all the construction processes in a sequential cyclical order. As a rule, construction begins from the bottom up. At the same time, you should know and remember many of the subtleties of construction and craftsmanship, and most importantly, decide in advance on the organization of the construction plan on your site. That is, carry out the entire appropriate set of preparatory work, prepare and place building materials, structures and parts on the site in the order in which you should use them according to the existing house design.
Difficulties and complications that arise during the construction of a house, often associated with physical environmental phenomena and natural climatic conditions, such as: temperature and humidity, precipitation (snow, rain), wind and its main direction (the so-called “wind rose”), its strength and pressure, pressure on the walls and roofing. Taking these factors into account during design and construction is aimed at ensuring an optimal microclimate inside the house, in which the human body does not experience physical and psychological discomfort.
Insolation– irradiation of the surfaces of the walls and roof of the house with direct rays of the sun has a significant impact on the architectural and planning solution of the house. Insolation has light, thermal and biophysical effects on humans. The impact of insolation on humans and the environment is twofold... On the one hand, insolation is favorable and cannot be avoided; on the other hand, excessive solar activity (radiation) causes light discomfort, overheating and ultraviolet overexposure, which dictate the use of sun protection devices. These properties insolation Architects use it very well in the process of designing a particular house, especially a country house. They design structures of various shapes on facades (on the south side): special sun protection devices in the form of canopies of various shapes, canopies, covered terraces, loggias, balconies, decorative reflective screens (vertical and horizontal), lowering and rising awnings, etc. The structures used not only cover the walls of the house from direct sunlight, so that part of the structure is in the shade, but these planes also decorate the house, making its architectural motifs more expressive and picturesque. If a house is built in the south, where there is a lot of sun, then its architecture can be very diverse and impressive. But it must be remembered that when designing and constructing a house, the conditions of reasonable sufficiency must be observed. After all, excessive shading by large pockets, niches, as well as excessive landscaping lead to the rapid formation of dampness, mold, small cracks on the external planes of the house, and as a result, the destruction of the base of the structure, its foundation, occurs.
Many Construction Materials have a porous structure and, therefore, can allow dampness and moisture to pass through, which rise up and down through capillary vessels hidden from view, which certainly affects foundation condition. House foundation can also be destroyed if the soil is very waterlogged, in particular from the effects of ground moisture. If the foundation of the house was made heavy, then it will subsidence, destruction of waterproofing, blind areas, etc. As a rule, the foundation begins to collapse on the side where the foundation soil is waterlogged, where shading predominates and there is no ventilation.
Important to remember, that very often, in practice, there are situations when haste in quickly completing the construction of a house, a shortage and replacement of one building material with another, various miscalculations and errors during the construction of a building lead to the fact that a residential building begins to collapse before the start of operation. As a result, the entire load falls on the base of the house, its foundation. Therefore, a carefully prepared foundation and a well-executed foundation will ensure reliable operation of any house - both a one-story garden house and a multi-story modern mansion.
Regions of the country differ in their natural and climatic conditions, therefore, depending on this, during the winter cold period, soils can freeze to different depths, which leads to their swelling. Clay soils, loess, sandy loams and silty sands are especially susceptible to such changes. The soils subside under the weight of the erected house, as a result of which the integrity of the building structures is compromised. To prevent this from happening, special measures must be taken even at the stage of laying the foundation, namely:
- strengthen the soil by laying a sand layer or introducing cement or bitumen;
- carry out drainage work;
- provide protection from uneven soil moisture in a pit or trench;
- reduce foundation construction time made of waterproof materials, while the space between the foundations and the walls of the pit or trench must be filled with soil as soon as possible.
The non-chernozem zone of Russia is characterized by heaving soils, which include clays, loams, sandy loams and fine sands. Non-heaving (medium- and coarse-grained sands, gravelly sands, clastic and rocky rocks) are much less common.
When calculating, constructing and laying the foundation, it is necessary to remember that heaving forces at low temperatures act from bottom to top tangentially on the sides of the foundation, amounting to 6-10 tons per 1 sq.m. and almost always exceed the vertically directed forces arising under the weight of the house structure itself (this is especially typical for light buildings).
To prevent frost heaving or reduce its severity, when laying the foundation you should:
- make the side surfaces of the foundation sloped;
- treat the side surfaces of the foundation with a composition that prevents them from freezing with the soil;
- insulate the blind area, which will reduce the depth of soil freezing. The blind area is a strip of land that is covered with insulating material. The main purpose of the blind area is to prevent moisture from penetrating under the foundation;
- lay drainage to drain the soil.
The depth of the trench that needs to be dug to lay the foundation depends on a number of circumstances:
- soil freezing depth;
- soil structure;
- availability and ground water level;
- natural and climatic conditions, defining depth of soil freezing.
In addition to the quality of the soil, it is necessary to know the depth of its freezing. The depth of the foundation should be greater than the depth of soil freezing, which for the middle zone is 80-100 cm.
The depth of the foundation also depends on the groundwater level. If the groundwater level is low (more than the freezing depth plus 2 m), it is recommended to lay the foundation at least half a meter. At a higher groundwater level (up to 2 m freezing depth), it is recommended to lay the foundation at the freezing depth and install it on a bed of sand and gravel.
The minimum depth of the foundation is 0.5 m for sandy soils, for clay soils - 0.7 m.
The minimum thickness is 50 cm from rubble stone, from rubble concrete - 35 cm.
Table for determining the foundation depth for low-rise construction:
| Soil type | Groundwater horizon relative to estimated freezing depth |
Bookmark depth foundation |
| Rocky | Doesn't matter | Regardless of freezing depth |
| Crushed stone, pebbles, coarse and medium-grained gravelly sands, gravel | Doesn't matter | Regardless of freezing depth - 0.5 m |
| Clays, sandy loams, loams, silty and fine-grained sands | The groundwater horizon is at or above the calculated freezing depth | Not less than the calculated freezing depth |
The depth of soil freezing depends on the natural and climatic zone in which the house is being built. Since the territory of Russia is located in the Northern Hemisphere, most of it experiences soil freezing in winter, although, naturally, it will be different, for example, in the Arkhangelsk and Saratov regions. For each geographical zone there is a standard freezing depth. This is the depth at which the temperature is 0°C in winter, and -1°C for clay and loamy soils. During long-term observations in places cleared of snow, its average value was established. It was taken as a starting point. The depth of soil freezing ranges from 80 cm in the south to 240 cm in the north.
The estimated freezing depth for laying the foundation of a residential building, which is constantly heated in winter, can be reduced compared to the standard by a certain amount if the floor is located on:
- soil - by 30%;
- logs - by 20% (logs are logs or metal beams, laid horizontally and serve as a support for the floor);
- apply vertical reinforcement to connect the upper and lower surfaces of the foundation;
- beams - by 10%.
Close groundwater and increased humidity as a result are among the main factors influencing the depth of soil freezing in winter. According to the laws of physics, when water freezes, it increases in volume (by about 10%), which causes heaving of soil layers within the freezing depth. As a result, the foundation is pushed out in winter and the opposite process - tightened - in the spring, which occurs along the perimeter of the foundation with varying intensity, i.e. unevenly. Such circumstances can lead to deformation of the foundation and cracking, and subsequently even destruction. The swelling force is so great (approximately 120 kN per 1 sq.m.) that it can lift almost any house, but not equally in different areas. The only way out is competent laying of the foundation.
Sometimes builders play it safe and lay the foundation (even with an insignificant depth of soil freezing) to a depth of more than 1 m. In this case, the base of the foundation is located on layers of non-freezing soil. This can be justified with increased load (more than 120 kN per linear meter of strip foundation), when a brick or stone house with a height of 2-3 floors is being built. When constructing walls from relatively lightweight building materials (timber, foamed concrete, etc.), the load per linear meter does not exceed 40-100 kN. Deformation of the foundation during heaving can be caused by frictional forces acting from adjacent layers of soil. In addition, if the erected structure is quite light, the load-bearing capacity of the buried foundation is used only by 10-20%. Consequently, 80-90% of materials and funds that will be invested in zero-cycle work are spent irrationally, almost in vain.
! Thematic articles and materials posted on the website www.site are for informational purposes only and in no way constitute a guide to action. Please turn to professionals when building a house, repairing and finishing!
We select the depth of foundations taking into account the following factors:
Design features of buildings and structures.
The nature of bedding, type and condition of soils.
Groundwater level position.
The magnitude and nature of the loads acting on the base and foundations.
Depths of seasonal freezing and thawing.
Depths of foundations of nearby significant buildings and structures.
During the construction process, the underground part of the load-bearing structures included in the zero cycle consists of concrete blocks of basement walls and reinforced concrete foundation slabs. Layer II was adopted as the base of the foundations.
We determine the depth of the foundation from the following parameters:
When choosing the foundation depth, we use an analysis of the engineering and geological conditions of the construction site. Due to the fact that the plant layer contains a lot of organic substances, has high compressibility, and there is a layer of deep freezing, it is impossible to accept this layer as the basis of the foundation. This layer must be cut off and the foundation laid. Considering that the level of the sole should be at least 1 m above the ground level (108.4 m).
According to the conditions of SNiP, the depth of the foundation must be no less than the calculated depth of soil freezing. The coefficient k n = 0.6 for buildings with a basement and an average indoor air temperature of +10 0 C will be equal to 0.6.
Estimated freezing depth:
d = k n * d n = 0.6 * 0.9 = 0.54 m
The height of the foundation cushion is 0.3 m.
The foundation rests on dense silty sands.
Conclusion: we accept the foundation depth as 2.0 m
Before installing the foundation, it will be necessary to carry out work to strengthen the foundation and carry out drainage work.
4. Determining the dimensions of the foundation base
The main dimensions of small foundations in most cases are determined based on the calculation of the foundations based on deformations. In this case, design considerations, the nature of the operating loads, the operating conditions of the soil foundation, as well as their strength and deformation characteristics are taken into account.
In accordance with structural design standards, all loads are considered to be applied at the center of gravity of the foundation base. The main calculation method is calculation based on deformations, i.e. for the second group of limit states. When calculating foundation deformations using design schemes, the average pressure under the base of the foundation 
should not exceed the calculated resistance of the foundation soil 
.
1 – wall; 2 – foundation block;
3 – base; 4 – foundation cushion;
5 - waterproofing; 6 – blind area;
7 – load-bearing layer; 8 – underlying layer.
The criteria for choosing the dimensions of the foundation base are based on the conditions for calculating the foundations of boundary states. The calculation is carried out on a linearly deformed basis, which is used when the following conditions are met:
For centrally compressed (i.e. for our foundations) P ≤ R.
Where P is the average pressure under the base of the foundation of external stress;
R – design resistance of the foundation soil.
The average pressure under the base of the foundation is found by the formula:
Where N is the resulting vertical force at the edge of the foundation, kPa;
A - area of the base of the foundation, m 2;
Design soil resistance:
γ c 1 and γ c 2 – coefficients of operating conditions, taking into account the characteristics of various soils at the base of foundations;
=1.25 – (since 
);
=1.2 (since L/N<1,5)
k – 1.1 (since the physical and mechanical characteristics of the soil are accepted according to SNiP 2.02.01-83);
=1 (if the width of the sole is less than 20m);
Мγ, Мq, Мс – dimensionless coefficients according to SNiP depending on 
.
At 
=
Мγ=0.69
=25 kPa - specific soil adhesion, kPa;
=0,57
;
d 1 =2.0m (foundation depth);
γ / - specific gravity of the soil located above the base of the foundation.
γ – specific gravity of the soil located under the base of the foundation.
kN/ 
Let's accept 
R= 371.59 
Let's define P:
Under a self-supporting wall:
(at 
)
<
R=371,59
For an external load-bearing wall:
(at 
)
<
R=371,59
For interior wall:
(at 
)
<
R=371,59
Because all conditions are met, we accept the width of the foundation base 
, we accept foundation pillows of the brand Fl 12.12.
Any building needs a high-quality, reliable, properly designed and equipped foundation - a foundation. It is a supporting platform that takes over and ensures the distribution of both the loads created by the building and the forces of soil influence, atmospheric phenomena and other external factors.
One of the most important stages in the design of a supporting structure, regardless of its type, is determining the required depth. Many developers mistakenly believe (and numerous instructions compiled by unqualified authors only aggravate the situation) that the depth of the foundation should be determined based solely on the level of soil freezing. Yes, this is one of the most significant indicators, but in reality there are much more factors that require consideration and analysis: construction features, engineering and geological conditions, site topography, groundwater flow level, etc.
Methods for laying a foundation
Knowledge of the methodology for determining the required depth of a support will allow you to design and ultimately obtain the most reliable structure that can serve for decades without any problems or complaints. Even if you plan to entrust the installation of the support to third-party specialists, having understood the nuances of the calculation in question, you will be able to control the correctness of the actions they perform, because An incorrect choice of depth in the future will lead to catastrophic consequences - processes of deformation and subsequent destruction of the support, and with it the higher building, will begin.
Following elementary logic, you can come to approximately the following conclusion: the deeper you lay the foundation, the better it will withstand all kinds of influences, and the longer it will last. In practice the situation is different. Next, you are invited to familiarize yourself with the most popular myths about the depth of the foundation and find out how to do it correctly.
The deeper you build, the longer it lasts
Even experienced workers in the construction industry are often mistaken in believing that an impressive foundation depth under any circumstances is a guarantee of the reliability and durability of the structure. In some situations this works, but you should not think that a large foundation depth will be a 100% guarantee of high support strength.
In practice, a qualified and rather voluminous calculation is required, which involves preliminary geotechnical research, determining the type of soil on the site, finding the level of groundwater, etc. Much also depends on the design features of the building under construction (material, number of floors, superstructures, etc.). For example, the foundation for a bathhouse, all other things being equal, will be subject to less stringent requirements than a support designed for use in conjunction with a residential building, but determining the optimal depth of installation must be approached equally responsibly and competently in both cases.
Helpful advice! The above points are presented in detail in a language that is interesting and understandable to the common man in the book “Do not bury the foundations deep” by V.S. Sazhina. We recommend you read it.
File for download – V.S. Sazhin “Do not bury the foundations deep.” Calculations, tables, foundation design, rules for choosing supporting structures, reinforcement rules
Is depth alone important?
As noted, the foundation does not have to be buried in all situations, even if construction is carried out on not the calmest soil - there are construction technologies that can increase the hardness and density of almost any soil. In view of this, if the construction of a compact private bathhouse is planned, and not a huge residential building, there will be no point in “burying money in the ground.”
Along with this, the characteristic features of the construction site must be taken into account. For example, a common problem is high groundwater flow. In the case of building a bathhouse, this issue can be resolved by arranging effective drainage around the supporting structure, and not by deepening the foundation.
Another common problem is landslides. The presence of such can lead to catastrophic consequences in the form of sagging, deformation and destruction of the supporting structure. In this case, it would be more appropriate to strengthen the soil rather than the foundation.
For example, in the case of sandy soils, silicatization technology works well, which involves treating the soil around the supporting structure with a mixture containing equal parts of water and liquid glass. The sand moistened with this composition is carefully compacted. As a result, the soil becomes more durable.
Another effective method involves the use of special chemical reagents. In this case, small wells are drilled at the construction site, and resin compositions are poured into the ground through the resulting depressions, which leads to effective strengthening of weak soil with minimal financial costs.
Regulatory and technical provisions
The provisions regarding the optimal depth of support structures are fixed in the relevant regulatory documentation. In this case, this is SNiP number 2.02.01-83.
File for download. SNiP 2.02.01-83. SP 22.13330.2011. FOUNDATIONS OF BUILDINGS AND STRUCTURES.
What determines the depth of support structures?
At this design stage, attention is paid to the following points:
- the purpose and dimensions of the building that will be erected on the support;
- the level of loads created by the structure;
- the depth of arrangement of supporting structures of nearby and adjacent buildings;
- level of passage of engineering communications;
- terrain features;
- significant engineering and geological features of the construction site. These include: soil properties, features of existing strata, etc.;
- hydrogeological features of the area and the nature of their potential changes during construction work and during the subsequent operation of the structure;
- the likelihood of soil erosion near supporting structures erected near water bodies;
- indicator of the level of seasonal soil freezing.
When determining this value, the average indicator of the greatest annual freezing depths is used. To carry out the calculation correctly, you need to take information obtained during at least 10 years of observation. A flat, non-snowy area is selected directly for observations. The groundwater level, in this case, should be lower in relation to the indicator of seasonal soil freezing.
If the results of long-term observations are not available (and this is what often happens), the corresponding thermotechnical calculations are performed. For regions where the soil does not freeze to a depth of more than 250 cm, it is permissible to use the following formula for determining the standard freezing depth.
The coefficient Mt in the above formula indicates the total value of the absolute average monthly subzero temperatures in winter for a particular region. This information should be clarified individually by contacting the nearest hydrometeorological station or by reading the relevant reference information.
The d0 coefficient is determined by the type of soil on the site. The dependency is as follows:
- clayey and loamy soils – 0.23 m;
- silty, fine sandy and sandy loam soils – 0.28 m;
- medium, coarse, and gravelly sands – 0.3 m;
- coarse clastic – 0.34 m.
What is the estimated freezing depth?
To find it, use the following formula.
The dfn coefficient here indicates the standard freezing depth (guidance for determining this indicator was given above).
The kh indicator is a coefficient that refers to the impact of the thermal regime of the structure. In the case of external supporting structures of heated buildings, this parameter is taken from the following table.
When arranging the foundations of unheated buildings, this coefficient is taken equal to 1.1.
The determination of the calculated freezing depth is carried out in accordance with thermal engineering calculations and in situations where the supporting structure is equipped with permanent thermal insulation. This provision is also relevant for situations where the peculiarities of the temperature operation of a building under construction can have a significant impact on the temperature indicators of the soil, for example, in the case of bathhouses.
The laying depth indicator, which is relevant for heated structures, is also accepted in the case of the construction of external and internal foundations. In the second case, the calculated freezing index is not taken into account.
The calculated value may also not be taken into account if:
- the foundation is built on fine sandy soil and during the research the fact of the absence of heaving was confirmed, as well as in situations where preliminary studies and subsequent design measures made it possible to establish that deformation processes occurring during freezing-thawing of the soil do not have a negative impact on the serviceability of the structure ;
- It is planned to carry out appropriate measures aimed at preventing soil freezing.
To find the depth of arrangement of supporting structures of heated buildings, the layout of which includes unheated crawl spaces and basements, use the following table. Count from the ground floor floor to the basement.
From theory to practice
Previously, you had the opportunity to familiarize yourself with the list of factors taken into account in the foundation design process, and also received a theoretical understanding of the main design activities at the foundation planning stage. Now you are invited to find out how to determine the optimal burial depth in practice.
What do we pay attention to?
Previously, a fairly extensive list of factors was given that determine the optimal depth of foundation. In practice, developers pay attention to only a few of them. About this in the table.
Table. Factors that determine burial depth
| Factors | Explanations |
|---|---|
| During the study of engineering geological conditions, a soil layer is determined that can take on the functions of a natural load-bearing foundation for the supporting structure. In practice, when determining the depth of burial, the following rules are followed: Laying depth – from 50-70 cm; Recession of the supporting structure into the natural load-bearing layer - from 10-20 cm; If possible, the supporting foundation is laid lower in relation to groundwater. By following this rule, the developer saves himself from the need to construct a drainage system. In this case, there will be no disturbance to the natural structure of the soil. If there is no possibility of going deeper below the groundwater level due to any circumstances, they resort to arranging drainage and tongue-and-groove fastening of the pit walls, as a result of which the total cost of carrying out the necessary excavation work increases significantly. |
|
| Among the significant climatic factors that are of greatest importance in determining the depth of installation of support structures for various purposes are, firstly, the depth of soil freezing in the area, and secondly, the characteristics of soil thawing, associated primarily with the level of groundwater passage. Some types of soils undergo heaving during freezing, i.e. increase their volume. In such conditions, the foundation of the structure must be laid strictly below the freezing depth point. The appearance of the mentioned frost heave is caused mainly by the movement of moisture contained in the underlying soil layers to the freezing front. In view of this, when determining the optimal depth of installation of a supporting structure, great importance should be given to the level of groundwater flow during the cold season of the year. The heaving category includes silty-clayey soils and varieties of soils consisting of fine and silty sand. When performing construction work on such soils, the depth of the support arrangement is determined by the freezing level indicator, if groundwater passes less than 200 cm below the freezing point. |
|
| Among the significant design features of the structure under construction that influence the final value of the foundation depth are: Availability of basement/basement premises and their dimensions; Availability of pits and their dimensional characteristics; Availability and dimensions of supporting structures for various equipment, for example, a sauna stove; Availability of underground communications and their dimensional characteristics; The nature of the loads applied to the supporting structure and their magnitude. As a rule, in the presence of underground premises, supporting structures are buried 50 cm below the floor of such premises. In the case of a columnar support structure, this figure can increase to 150 cm. |
Important! After determining the optimal burial depth based on all significant factors, the largest found indicator is selected, and it is this that is used as the calculated one.
There are quite a few types of supporting structures, among which the most common in private construction are strip, column and slab foundations. Next, you are invited to familiarize yourself with the recommendations regarding the optimal depth of each of them.
Tape supports
The strip-type foundation ranks first in popularity among private developers. Such structures are characterized by easier construction and lower financial costs when compared with monolithic slab supports.
The strip base design is a reinforced concrete strip installed under the walls and partitions of the building. The foundation absorbs the loads created by the superstructure and ensures their uniform distribution on the ground.
Important! The load-bearing capacity of the soil on the site must exceed the loads transmitted by the foundation structure from the building. Information regarding the necessary ones was discussed in detail in the corresponding publication.
The tape-type base is suitable for use on homogeneous soils with no or mild heaving. It is better for groundwater to flow as low as possible. It is not recommended to install concrete strips in flooded areas.
The foundation in question is prohibited for use on peat and other biogenic organic soils. You should also refrain from using such a design if the construction site is located on heterogeneous soil or at the junction of different types of soil. It is not recommended to use strip foundations on water-saturated silty sandy soils and water-saturated clay soils.
When determining the configuration and geometric parameters of the support base, the following factors must be taken into account:
- loads created by a higher building;
- soil characteristics (heaving, bearing capacity indicators);
- local climate;
- properties of building materials.
The minimum permissible depth for arranging a strip support structure is determined by the level of soil freezing, the height of groundwater, as well as the characteristics of soil heaving. The dependence is as follows: the deeper the soil freezes and the closer the water passes to the surface, the stronger the heaving of the soil, and the more pronounced the effect on the support from below. Under the influence of these forces, the base will be compressed and pushed upward. To reduce the intensity of these impacts, the foundation is deepened.
Helpful advice! In addition to deepening the supporting structure, the severity of frost heaving in the soil can be regulated by providing thermal insulation of the support, installing permanent heat-protected formwork at the stage of foundation construction, as well as by ensuring water disposal and organizing drainage, soil compaction, and its partial or complete replacement.
In accordance with current building codes, the minimum permissible depth of a strip concrete support on all low-heaving and non-heaving soils (except for clay and rocky soils) is 450 mm. When working on rocky soil, due to the physical impossibility of ensuring significant depth, it is allowed to construct a supporting structure directly on the soil surface. When arranging a strip support structure on clay soils and other heaving type soils, the base is buried at least 750 mm (on average, 90-100 cm is maintained).
If the soil is excessively soft and there is a possibility of its mobility (this group includes water-saturated soils, sandy loams, sands), as well as with low bearing capacity of the surface soil layers, the strip foundation can be buried to the level of the soil balls, characterized by stable properties and higher bearing capacity.
You can use the values given in the following table as guidelines.
| Estimated freezing depth of conditionally non-heaving soil | Estimated freezing depth of slightly heaving soil of solid and semi-solid consistency | |
|---|---|---|
| up to 2 meters | up to 1 meter | 0.5 m |
| up to 3 meters | up to 1.5 meters | 0.75 m |
| more than 3 meters | from 1.5 to 2.5 meters | 1m |
| from 2.5 to 3.5 meters | 1.5 m |
Helpful advice! Regardless of local conditions, the maximum permissible depth in economic and generally reasonable terms is 250 cm.
If the foundation is built on sandy, non-heaving soil, you can ignore the freezing depth indicator. You can also get rid of the dependence on freezing depth by providing vertical insulation of the foundation and horizontal thermal insulation of the soil.
The above values may change if groundwater is located relatively close to the surface. Under such circumstances, the foundation will have to be deepened to a more significant level. You can use the values given in the following table as a guide.
Owners of plots located on heaving soils with high groundwater should consider using another support structure, for example, a pile-grillage. Such a foundation is not afraid of groundwater and frost heaving.
Indicators of standard freezing depth are presented in the table.
This design is based on support pillars located in the corners of the building and at the intersections of walls and partitions. If necessary, additional supports are constructed under heavy partitions, massive beams and in other areas characterized by increased load.
In order to ensure uniform distribution of loads created by the higher structure, as well as to organize the operation of the pillars as a solid supporting structure and to increase the stability of the foundation to the forces acting on it, a grillage is constructed, represented by strapping beams connecting the elements of the supporting structure.
- during the construction of buildings that do not have basements;
- during the construction of buildings with light walls made using frame, panel and similar technologies;
- when constructing brick walls if there is a need to ensure deep laying;
- with a higher resistance of the columnar foundation to sedimentary processes in the soil (compared to other types of foundations);
- if it is necessary to minimize the severity of frost heaving forces (pillars are less susceptible to the mentioned phenomenon compared to strip and slab structures);
- under other conditions, when the use of a strip foundation is economically unprofitable or impractical due to any circumstances.
The columnar support structure has a number of advantages.
Firstly, its arrangement usually costs no more than 20% of the cost of the entire house (for comparison, in the case of other types of foundations, this figure can increase to 30% or more).
Secondly, through individual supports there is a more effective distribution of loads than through a continuous strip base. The pillars provide equivalent pressure on the soil, resulting in a decrease in the severity of settlement compared to the previously considered strip structures. Thanks to this, it becomes possible to reduce the total area of the base.
Support-column structure - photo
When determining the optimal depth of pillars, pay attention to the following factors:
- depth of soil freezing. This parameter remains significant when designing any foundation. Ideally, the pillars should be buried 20-30 cm below the mentioned mark, but this is not always necessary. Exceptional cases will be considered separately;
- type of soil and features of its composition. The best option is sandy soil. Water passes through such soil almost instantly, plus its bearing capacity remains at a very high level. Construction on peat bogs and muddy soils should be avoided. The only possible option in this case comes down to partial (even better, complete) replacement of the existing soil with sandstone;
- depth of groundwater. This point is determined by relevant previous research. Almost 100% confirmation of a high groundwater level can be the presence of any natural body of water nearby. In this case, they resort to organizing drainage systems or installing waterproofing.
In addition to natural factors, the designer must pay attention to the following provisions:
- estimated weight of the finished structure;
- weight of support pillars;
- the weight of the internal furnishings of the building and the people in it;
- temporary loads, for example snow.
The most pronounced negative impact on supporting structures is caused by frost heaving forces. In view of this, the construction of almost any foundation is preceded by an assessment of the degree of heaving of the soil. Most developers adhere to the principle according to which, when working on heaving type soils, foundations are laid on average 200-300 mm below the calculated freezing depth in the cold season. Along with this, the construction of lightly loaded buildings, for example, such as a private bathhouse, has its own exceptional features.
The foundations of such structures are subject to heaving forces, in most cases exceeding the total loads created by the structure above. Because of this difference, various deformations of the support ultimately occur.
In view of this, when planning the construction of a bathhouse or any other building without a basement on soil prone to seasonal heaving, it is better to give preference to a non-buried or shallow type of support structure.
Shallow supports are those whose depth is 50-70% of the standard soil freezing index. For example, in accordance with the standard indicator, the soil freezes to 150 cm. In this case, a shallow foundation must be buried at least 75 cm.
If the soil is heaving and freezes deeply, you will have to make a buried support structure, which, as already noted, is installed on average 20-30 cm below the freezing point. Under such circumstances, prefabricated and monolithic pillars made of reinforced concrete perform well. Such structures are slightly susceptible to heaving forces.
If stones, unreinforced concrete, small blocks, bricks are used to equip the supports, the foundation walls should taper upward - thanks to this, firstly, an even distribution of the loads created by the structure will be ensured, and secondly, the consumption of building materials will be reduced.
Among the additional measures that help reduce the severity of frost heaving forces, the following provisions should be noted:
- covering the sides of the pillars with materials that help reduce soil friction. Such materials include a variety of greases, polymer films, epoxy resins, bitumen mastics, etc.;
- insulation of the upper ball of soil around the supporting structure. An excellent option is the construction of an insulated blind area.
There are a number of restrictions, the presence of which is a direct contraindication to the use of columnar supports.
- Firstly, a columnar foundation cannot be used on weak soils, as well as soils prone to horizontal movement, because The pillars are characterized by low resistance to overturning. To level out lateral shifts, a rigid reinforced grillage is installed. If it is used, the costs of constructing a columnar foundation are almost equal to the costs of pouring reinforced tape.
- Secondly, it is better not to install pillars in areas located on weak-bearing (peaty, water-saturated clay, etc.) soils, especially in the case of the construction of heavy houses (using reinforced concrete floor slabs, with brick walls 50 cm thick, etc. .d.).
- Thirdly, it is better not to build anything on columnar supports if the site is located in an area with significant elevation differences (more than 200 cm).
In areas with difficult terrain, a columnar base is not the best option
Slab supports
A monolithic slab support structure is characterized by high levels of reliability, strength and durability, but also requires appropriate labor and material investments for arrangement. The use of such supports is advisable when working on weak types of soil, for example, soils with a high organic content.
When using a slab, there is a decrease in pressure on the soil. This happens because the slab rests on the base with its entire surface, which ensures uniform distribution of loads created by the superstructure.
Buildings from any materials can be built on a slab foundation. In particular, such supports are often chosen for use in combination with stone structures, i.e. buildings built from blocks, bricks, etc.
As in the case of the types of foundations discussed above, the laying depth is determined in accordance with the characteristic features of the soil and the loads created by the structure: the higher they are, the thicker the slab is made and the deeper it is laid.
Slab foundation structures are not buried to the freezing level. Non-buried supports are generally erected at ground level. In construction practice, the so-called “floating slab” - such a foundation is deepened to a maximum of 1 m, and the forces of the underlying compacted sand and gravel layer ensure the visibility of a “floating” reinforced concrete slab. This design is characterized by greater resistance to deformation effects from the soil.
The most popular is the shallow type of slab foundation, laid to a depth of 200-500 mm. A compacted “cushion” of sand and crushed stone with a total thickness of about 30 cm is installed under the slab. The slab is reinforced over the entire area. This design is characterized by high resistance to variable loads that occur during temperature changes and lead to heaving of the soil.
Shallow
type of slab foundation
Thus, slab foundations are suitable for use on problematic soils: mobile, subsiding, heaving, etc.
Among the disadvantages of this design, it is necessary to note the large volume of excavation work, as well as the increased costs of purchasing high-quality reinforcing elements and concrete. The materials used must meet the following minimum requirements:
- concrete grade – from M200;
- reinforcement – steel, with a diameter of at least 1.2 cm.
Thus, monolithic reinforced concrete slab is well suited for use on soils with high groundwater levels, as well as on weak and heterogeneous soils. Under such circumstances, the costs of arranging a slab structure will be justified and appropriate. Otherwise, experts recommend paying attention to more cost-effective solutions in the form of the above-mentioned columnar and strip bases.
Additionally, you are invited to familiarize yourself with the tables characterizing various types of soils, as well as reflecting the dependence of the depth of the supporting structure on the characteristics of the soil and the height of groundwater passage.
Happy work!
Video - Foundation depth