Foundation depth. An example of determining the depth of the foundation How to determine the depth of the foundation with a basement

At the stage of designing a foundation for a steam room, the most difficult moment is the correct calculation and laying of the foundation. But, if you can somehow figure out its type and design on your own, based on the possibilities of the budget and the popularity of a particular type in a certain area, then what is the correct depth of the foundation is another question.

Why are foundations buried in the ground at all? Yes, because several forces always act on the foundation of any house at once: the gravity of the structure itself, the movement of soils invisible to the eye, landslides and precipitation. That is why it is so important to put the bath on a really solid and solid foundation, thus transferring to it all the calculated loads. And how to correctly calculate this depth, the article will tell.

Foundation depth: dispelling myths

Yes, it seems that the simplest solution is to bury the same bath deeper, and it will last a hundred years. In fact, this is not so, and today there are a lot of myths among builders about how deep the foundation should be.

The deeper the better?

Even among fairly experienced architects, there is a myth that the deeper the foundation, the stronger it is. Of course, you can understand the desire of the customer to save money, as well as the foreman, who is trying to convey to the fact that with a foundation “at random” it will not work. But digging deeper does not mean that it will turn out stronger.

So, the depth of the zero level is determined by many parameters - and it is better to entrust this issue to specialists. Engineering and geological surveys are being carried out, the type of soil is being investigated, the level of groundwater and its freezing are being measured. The design feature of the building also decides a lot: the number of floors, superstructures, wall material - and the bath in this parameter is just less demanding on the power of the base than a residential building. More details about determining the depth of the foundation can be found in a small interesting book by V.S. Sazhin “Do not dig foundations deep”.

Does depth really always “save”?

But it is far from always necessary to strive to make the foundation deeper if the soil is restless - in fact, there are methods on how to compact and harden any soil. And therefore, if the bathhouse will not be built at all massive, there is no point, as builders like to say, "to bury money in the ground."

So, the first thing to do is to study the problem well. For example, if water is often visible at or close to the surface, proper drainage around the foundation will save. After all, it is pointless to strengthen the foundation in this case by increasing the support - the zero level will continue to “walk”, and it will take a lot of money for such a method. There really is no lack of depth here.

But if landslides are observed along the perimeter, the foundation is washed away and even starts to sag somewhere - it is not necessary to strengthen it, but the soil. So, silicification is good for sandy soil - the soil around the foundation is poured with a mixture of liquid glass with water, one to one, and the resulting wet sand is well tamped. Or chemical reagents are used: wells of small diameter are drilled, and special resin compounds are pumped into them. Durable and inexpensive, and for weak soils - what you need.

We determine the depth by the formula

Here is a standard formula by which you can calculate the depth of the foundation:

Hp = mtmHн, Where:

• Hn - depth of soil freezing,
• mt - 0.7-1, the coefficient of influence of the heat of the building on the freezing of the soil near the outer walls,
• m - 1.1, coefficient of working conditions.

Soil type, temperature and other parameters

So, how to correctly calculate the depth to which the bath should be laid?

Average temperature of the region

Many today, of course, rely on average calculations and pour foundations 90 cm deep, but experienced builders always make sure in case of a cold winter and reach 1.10 m and no less! Moreover, frosts in Russia are certainly not uncommon. Why, and since Soviet times, the foundation has been laid to a depth of 110 cm - so even in frosty winters, heaving of the soil cannot disturb anything.

Do we heat the basement?

Unheated structures are laid 10% deeper than the level of soil freezing depth, and heated structures - 20-30% higher. Another point: under the inner walls of the bath, the foundation can be deepened less - allowed by building codes. But not less than 40 cm is important!

Soil freezing depth

So, in all areas - their own characteristics of the soil, its density and water saturation. Take an interest in such characteristics from the owners of neighboring buildings. But pay attention: if there is a reservoir nearby, then the winter swelling of the soil may be much larger than expected. How to find out the normative depth of soil freezing in your area? Use this map here:

soil properties

What is seasonal soil heaving? This is underground water, which freezes in winter, increases in volume (remember school physics) and pushes out what is in this soil. In the spring, it melts and lowers the ground again.

For example, according to official information, 80% of soils in the Moscow region are heaving. These are clays, loams and sandy loams, and all this swells a lot in seasons. On peat soil, there is no need to talk about depth at all: the only possible foundation here is a floating slab.

No less important for determining the required depth of laying the tape and any other foundation is water saturation: if it is clay and it is heaving, then the foundation will have to be deepened significantly. In extreme cases, it is better then to use a stove - for a small bathhouse, that's what you need.

In general, the ideal condition for any foundation is when groundwater is above the freezing depth of the soil. After all, when they cross, groundwater freezes and “swells” the soil, and unevenly, which leads to a warp of the foundation. And these are cracks and even worse. Because the force of seasonal swelling of the soil is 10-15 t / m2, not bad, right?

Shallow foundations - benefit or competent calculation?

And, finally, when determining the depth of the foundation, you need to pay attention not so much to the type of soil, but to the array of walls and their material. So, profiled timber and logs, from which the Russian bath is built most often, is a flexible and elastic material. After all, a tree is a fibrous structure, and then it works great for deformation, and quite easily survives any movements of the foundation. That is why it is recommended to build a steam room from a log house on a strip shallow foundation with a depth of only 50 cm - this is enough. A frame bath can also have the same basis - after all, all its elements are connected by corners, and therefore you also don’t have to worry about cracks and deformations.

Of course, shallow foundations are most often erected in order to save money on the construction of a bath: there is little earthwork, and the coarse sand used replaces the soil and helps to reduce the degree of deformation. Such foundations can move imperceptibly to the eye, but massive buildings from this can completely collapse. After all, such wall material as brick and stone will not tolerate vibrations and stretching. Both stone and brick are fragile, and therefore, regardless of the weight of such a bath, the foundation for it is necessary, as they say, unshakable - such that it does not tilt even a millimeter. Otherwise, the walls in the first year will “please” by no means small, rapidly growing cracks.

And even after such information, you find it difficult to correctly calculate how deep you need to dig the foundation for your bath? Welcome to the "" section!

The depth of the foundation is a design value that depends on the type of building or structure, the climatic zone, the soil on the site and the level of groundwater. This value is also influenced by the design of the building (with or without a basement), the principle of its use (with or without heating), the number of storeys and weight.

Speaking objectively, this is the amount by which the foundation will need to be buried in order for it to provide a stable support for the structure. They are of two types:

According to building codes, in order to withstand the forces of frost heaving, the sole must be deepened 15-20 cm below the freezing level for the soil. When this condition is met, the foundation is called "deep" or "deep".

With a freezing depth of more than 2 meters, earthworks have very large volumes, the consumption of materials is also high and the price is very high. In this case, other types of foundations are considered - pile or, as well as the possibility of laying above the standard freezing point. But this is possible only if there are soils with a normal bearing capacity, the obligatory insulation of the basement and foundation, as well as the installation of an insulated blind area. In this case, the laying depth decreases several times and is usually less than a meter.

Sometimes the foundation is poured directly on the surface. This is an option for outbuildings, and most likely made of wood. Only she, in such conditions, is able to compensate for the resulting distortions.

Preliminary survey

Before you start planning your house, you must decide where on the lot you want to put the house. If there are already geological studies, take into account their results: in order to have fewer problems with the foundation, it has a minimum cost, it is advisable to choose the “driest” site: where the groundwater is as low as possible.

Further, geological studies of the soil are carried out in the selected place. To do this, pits are drilled to a depth of 10 to 40 meters: it depends on the structure of the layers and the planned mass of the building. Wells are made at least five: at those points where corners are planned and in the middle.

The average cost of such a study is about $ 1,000. If a large-scale construction is planned, the amount will not greatly affect the budget (the average cost of a house is 80-100 thousand dollars), but it can save you from many problems. So in this case, order a study from professionals. If you want to put up a small building - a small house, a summer house, a bathhouse, a gazebo or a platform with a barbecue, then it is quite possible to do the research yourself.

We explore geology with our own hands

To check the geological structure of soils with our own hands, we arm ourselves with a shovel. At all five points - at the corners of the future structure and in the middle - you will have to dig deep holes. Size: meter per meter, depth - at least 2.5 m. We make the walls even (at least relatively). After digging a hole, we take a tape measure and a piece of paper, measure and record the layers.

What can be seen in the cut:

Often difficulties arise when trying to distinguish clay-containing soils. Sometimes it is enough just to look at them: if sand predominates and there are inclusions of clay, you have sandy loam in front of you. If clay predominates, but there is also sand, it is loam. Well, the clay does not contain any inclusions, it is hard to dig.

There is another method that will help you make sure that you have determined the soil correctly. To do this, a roller is rolled up from the moist soil (between the palms, as once in kindergarten) and bent into a bagel. If everything crumbled - it is low-plastic loam, if it fell into pieces - plastic loam, if it remained intact - clay.

Having decided on what soils you have in the selected area, you can begin to choose the type of foundation.

The depth of the foundation, depending on the level of groundwater

All design features are described in SNiP 2.02.01-83*. In general, everything can be reduced to the following recommendations:

As you can see, basically the level of laying the foundation of the foundation is determined by the presence of groundwater and how much the soils in the region freeze through. It is frost heaving that causes problems with foundations (or a change in the level of groundwater).

Soil freezing depth

To roughly determine to what level the soils freeze in your area, just look at the map below.

Using this map, you can roughly determine the level of soil freezing in the region (to increase the size of the picture, click on it with the right mouse button)

But this is averaged data, so for a particular point it is possible to determine the value with a very large error. For inquisitive minds, we present a method for calculating the depth of soil freezing in any area. You will only need to know the average temperatures for the winter months (those with negative monthly averages). You can calculate for yourself, the formula and calculation example are posted below.

D fn is the depth of freezing in this region,

Do is a coefficient that takes into account soil types:

• for coarse soils, it is 0.34;
• for sands with good bearing capacity 0.3;
• for loose sands 0.28;
• for clays and loams, it is 0.23;

M t - the sum of the average monthly negative temperatures for the winter in your area. Find metrology service statistics for your region. Choose the months in which the average monthly temperature is below zero, add them up, find the square root (there is a function on any calculator). Substitute the result into the formula.

For example we're going to build on clay. Average winter temperatures in the region: -2°C, -12°C, -15°C, -10C, -4°C.

The calculation of soil freezing will be as follows:

1. M t \u003d 2 + 12 + 15 + 10 + 4 \u003d 43, we find the square root of 43, it is 6.6;
2. D fn \u003d 0.23 * 6.6 \u003d 1.52 m.

We got that the estimated depth of freezing according to the given parameters: 1.52 m. That's not all, consider whether heating will be necessary, and, if so, what temperatures will be maintained in it.

If the building is unheated (bathhouse, cottage, construction will take several years), a multiplying factor of 1.1 is applied, which will create a margin of safety. In this case, the foundation depth is 1.52 m * 1.1 = 1.7 m.

If the building is heated, the soil will also receive a portion of its heat and it will freeze less. Therefore, in the presence of heating, the coefficients are decreasing. They can be taken from the table.

Coefficients that take into account the presence of heating in the building. It turns out that the warmer it is in the house, the less depth you need to deepen the foundation (to increase the size of the picture, click on it with the right mouse button)

So, if the temperature in the premises is constantly maintained above + 20 ° C, the floors are with insulation, then the depth of the foundation will be 1.52 m * 0.7 = 1.064 m. This is already a lower cost than deepening by 1.52 m.

The tables and maps show the average level for the last 10 years. In general, it is probably worth using data for the coldest winter in the last 10 years in the calculations. Abnormally cold and snowless winters occur with approximately the same frequency. And in the calculations it is desirable to focus on them. After all, it will not calm you down if, after standing for 9 years, on the 10th your foundation will crack due to a too cold winter.

How deep to dig the foundation

Armed with these figures and the results of the study of the site, you need to select several options for foundations. The most popular - and columnar or pile. Most experts agree that with the normal bearing capacity of the soil, their sole should be 15-20 cm below the freezing depth. How to calculate it, we told above.

The foundation depth is the level to which the foundation needs to be deepened.

• The sole should rest on the ground with good bearing capacity.
• The foundation must sink into the bearing layer by at least 10-15 cm.
• It is desirable that groundwater is located lower. Otherwise, it is necessary to take measures to divert water or lower its level, and this requires very large funds.
• If the bearing soil is too deep, it is worth considering the option of a pile foundation.

Having chosen several types of foundation, having determined the depth of laying for them, an approximate calculation of the cost of each is carried out. Choose the one that is more economical.

Also note that to reduce the depth of the foundation, you can use insulated u. During the construction of a shallow strip foundation, a blind area is required.

shallow foundation

Sometimes a deep foundation is very expensive to build. Then they consider pile (pile-grillage) or shallow foundations (shallow). They are also called "floating". There are only two types of them - a monolithic slab and tape.

The slab foundation is considered the most reliable and easily predictable. It has such a design that it can receive significant damage only with gross miscalculations in the design. However, it can also be corrupted.

However, developers do not like slab foundations: they are considered expensive. They take a lot of material (mainly reinforcement) and time (for knitting the same reinforcement). But sometimes a slab foundation is cheaper than a deep-laid tape or even a pile foundation. So don't discount it right away. It is optimal if they want to build a heavy building on heaving or loose soils.

A shallow tape can have a depth of 60 cm or more. At the same time, it must rest on soil with normal bearing capacity. If the depth of the fertile layer is greater, then the depth of the strip foundation increases.

With shallow strip foundations for light buildings, everything is very simple: they work well. A combination with a log cabin or timber frame is an economical and at the same time reliable option. If there are bends in the tape, then elastic wood copes with them perfectly. A frame house feels almost as good on such a basis.

It is necessary to calculate more carefully if they are going to build rear ones from light building blocks (aerated concrete, foam concrete, etc.) on a shallow strip foundation. They react to changes in geometry not in the best way. Here you need the advice of an experienced and, of course, a competent specialist with extensive experience.

But under a heavy house, it is unprofitable to put a shallow strip foundation. To transfer the entire load, it must be made very wide. In this case, most likely, slab will be cheaper.

How shallow foundation works

This type is used when it is too expensive to deal with heaving forces and does not make sense. In the case of shallow foundations, they are not fought. You could say they are being ignored. They just make the foundation and the house rise and fall along with the swollen soil. Because they are also called "floating".

All that is needed is to ensure a stable position and a rigid connection of all parts of the foundation and elements of the house. And for this you need the right calculation.

If you want to calculate the depth of the foundation, you need to familiarize yourself with the basic concepts. There are several approaches to solving the problem, taking into account a number of factors. The foundation is the basis of the structure, so experts are closely looking at the ground.

Depth calculation

When preparing for the construction of a new house or cottage, it is not always possible to contact the designers who make the necessary measurements. Private developers can take an irresponsible approach to the issue, as a result, there are problems with the design.

The concept of calculating the depth of the foundation involves the designation of the level of the sole relative to the zero mark.

For the calculation, the state of the soil is taken into account, the features of the terrain and the type of building itself are analyzed. The structures differ in shape and size. Additional factors include weather conditions, designers are interested in the average temperature, the amount of precipitation per year. Depth calculation affects the following factors:

• operational properties;
• indoor moisture level;
• floor condition;
• building microclimate;
• overall level of sustainability.

Depth calculation

If you do not go into details, the calculation of the depth is carried out according to the formula - Hp = mt * m * Hn. The soil freezing coefficient is taken as the basis (in the formula it is denoted as mt). Separately, the indicator of temperature and the depth of solid soil is taken into account.

Consideration of a columnar, strip foundation

• bottom laying;
• supports;
• foundation slab;
• sand filling.

In order to calculate the depth of the strip foundation, geological aspects are taken into account, it is recommended to draw up an action plan:

1. analyze the soil
2. find out the features of the landscape;
3. clean up the construction site;
4. estimate the mass of the structure;
5. determine the main load points.

In the form of calculating the depth of the foundation, the need to determine the freezing of the soil is indicated. To get a complete picture, it is also recommended to study the nature of the soil in a small and medium depression.

There may be problems with the aquifer on the site, builders often do not pay attention to height fluctuations.

GOST 25100 spells out how to calculate the depth of the foundation for a house, so it is recommended to delve into the basic rules. Regarding soil freezing, average parameters are considered. To determine the indicator, annual data for the region are taken; statistics cannot be dispensed with. When taking a sample, attention is paid to the temperature, the level of the slope (difference) of the earth.

To make it clearer, it is recommended to consider everything with an example. First of all, the average temperature in the area is taken, the content of sandy loam and sand in the ground is taken into account. For example, the indicator is 0.23%. The size of the soil is also taken into account (on average, exponential 0.3). The freezing coefficient starts from 1.5 to 2.5 meters. Thus, when multiplying the indicators, a value of 0.6 meters is obtained.

Online calculation

• soil type;
• foundation;
• occurrence of groundwater;
• soil freezing;
• average temperature;
• region is specified.

Some sites require you to enter the building type (heated, unheated, residential, commercial).

The seasonal freezing index is calculated by the formula - the thermal regime coefficient is multiplied by the freezing depth. To prevent users from paying for expensive design work, it is recommended to simply look at the statistical tables. Depending on the temperature, data have already been collected regarding the average freezing depth.

Information is presented separately for soil with and without a basement. The user, for his part, must take into account the restrictions on the foundation. If we consider structures longer than 5 meters, an error is introduced. In some cases, the building is adjacent to another foundation, then the formula changes.

Calculating a room with a basement is considered more laborious. When estimating the average temperature, it is recommended to round it down. According to GOST, there are rules for calculating the freezing parameter in areas where the average temperature is negative. An additional constant is introduced in the formula - the thermal protection coefficient. This is due to the fact that a boiler room can be installed in the building. Due to the operation of heating equipment, the level of soil freezing changes and the initial calculations will not be true.

Ground density

When calculating the depth of laying, the formula changes depending on the density of the soil. Designers know that rocky, sandy, clay surfaces are encountered. Sometimes it is homogeneous or mixed. Builders have to work on sandy loam, gravel, loam.

It is not possible to make a bookmark without an accurate calculation.

To maximize the safety of the structure, it is recommended to clarify the data on the occurrence of solid soil. In some cases, the indicator is 2.5 meters, the average parameter is 0.8 meters.

The calculation of the depth of the foundation is impossible without determining the water level. Considering a strip or column foundation, in any case, it suffers from precipitation. The complexity of laying communications is also taken into account. Builders are trying to solve the problem in certain areas by installing an additional sole. Under the ground, water lies in various depressions, since there is a classification of waters:

• ground;
• artesian;
• soil;
• mineral.

Builders are largely interested in soil and groundwater. They are located at a depth of 3-5 meters. As a result of precipitation, the liquid can move, rise to the surface or fall. The main force is gravitational influence. The average groundwater level is affected by the amount of snowfall. After the winter period, the process of thawing is actively taking place. In addition to the possible destruction of foundations, fluid contamination is observed.

Interstratal water also affects the foundation, as it is enclosed in impervious layers of the earth. This indicator is constant, the aquifer does not change depending on the season. Interstratal waters are under pressure and can be static or circulating.

To find out the exact indicator, a drill with a diameter of 6 inches is used. Sometimes it is required to make a well with a deepening of more than 3 meters. The situation is simplified if there is a well nearby. In this case, it is enough just to lower the rope or tape.

Conclusion

You can calculate the depth of the foundation yourself. There is a general formula, but changes are made depending on climatic conditions and the type of structure. To ease the lot of the designer, there are online calculators that are on the net.

Any building needs a high-quality, reliable, properly designed and equipped foundation - the foundation. It is a support platform that takes over and ensures the distribution of both the loads created by the building and the forces of the soil, atmospheric phenomena and other external factors.

One of the most important stages in the design of a supporting structure, regardless of its type, is the determination of the required depth. Many developers mistakenly believe (and numerous instructions compiled by unqualified authors only exacerbate 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 many more factors that need to be taken into account and analyzed: construction features, engineering and geological conditions, site topography, groundwater flow rate, etc.

Foundation laying methods

Knowing the methodology for determining the required depth of the 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 arrangement 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 performed by them, because the wrong choice of the depth of laying in the future will lead to catastrophic consequences - the processes of deformation and subsequent destruction of the support will begin, and with it the higher building.

Following elementary logic, one can come to 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 learn how to do it right.

You build deeper - it lasts longer

Even experienced workers in the construction industry are often mistaken in believing that an impressive laying 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 necessarily performed, which involves preliminary engineering and geological studies, determining the type of soil on the site, finding the level of groundwater passage, etc. Much also depends on the design features of the building being erected (material, number of floors, superstructures, etc.). For example, less stringent requirements will be imposed on the foundation for a bath, other things being equal, than on a support designed for use in conjunction with a residential building, but determining the optimal depth of laying must be equally responsibly and competently approached in both cases.

Helpful advice! The above points are detailed in the book “Do not dig foundations deep” by V.S. Sazhin. Recommended for review.

Download file - V.S. Sazhin "Do not dig deep foundations." Calculations, tables, foundation design, rules for choosing support structures, rules for reinforcement

Does depth alone matter?

As noted, the foundation should not be buried in all situations, even if construction is carried out on not the most calm ground - there are building technologies that can increase the hardness and density of almost any soil. In view of this, if the construction of a compact private bath is planned, and not a huge residential building, there will be no point in “digging money into the ground”.

Along with this, the characteristic features of the construction site should be taken into account. For example, a common problem is the high passage of groundwater. In the case of the construction of a bath, this issue can be resolved by arranging effective drainage around the supporting structure, and not by deepening the foundation.

Landslides are another common problem. 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 expedient to strengthen the soil, and not the foundation.

For example, in the case of sandy soils, the silicification technology works well, which involves treating the soil around the supporting structure with a mixture that includes equal parts of water and liquid glass. The sand moistened with such a composition is carefully compacted. As a result, the soil becomes more durable.

Another effective method involves the use of special chemicals. In this case, small wells are drilled at the construction site, resin compositions are poured into the ground through the resulting recesses, which leads to effective strengthening of weak soil with minimal financial costs.

Regulatory and technical provisions

The provisions regarding the optimal depth of the support structures are fixed by the relevant regulatory documentation. In this case, this is SNiP number 2.02.01-83.

Download file. SNiP 2.02.01-83. SP 22.13330.2011. FOUNDATIONS OF BUILDINGS AND STRUCTURES.

What determines the depth of the support structures?

At this stage of design, attention is paid to the following points:

• the purpose and dimensions of the building to be erected on the support;
• the level of loads created by the structure;
• the depth of arrangement of the supporting structures of the nearest and adjacent buildings;
• the level of passage of engineering communications;
• features of the terrain;
• 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 probability of soil erosion at supporting structures erected near water bodies;
• indicator of the level of seasonal freezing of the soil.

When determining this value, the average index of the largest annual freezing depths is used. For the correct calculation, it is necessary to take information obtained during at least 10 years of observation. Directly for observations, a flat, not snow-covered area is selected. The groundwater level, at the same time, should be lower in relation to the index of seasonal freezing of the soil.

If the results of long-term observations are not available (and this is exactly what often happens), the corresponding thermal engineering calculations are performed. For regions in which the soil does not freeze more than 250 cm, it is permissible to use the following formula for determining the standard freezing depth indicator.

The coefficient Mt in the above formula indicates the total value of the absolute average monthly sub-zero 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 coefficient d0 is determined by the type of soil on the site. The dependency is the following:

• clay and loamy soils - 0.23 m;
• dusty, fine sandy and sandy soils - 0.28 m;
• medium, large, as well as gravel sands - 0.3 m;
• coarse fragments - 0.34 m.

What is the estimated freezing depth?

The following formula is used to find it.

The coefficient dfn here indicates the standard freezing depth (guidance for determining this indicator was given above).

The kh index is a coefficient referring to the effect of the thermal regime of the building. In the case of external support 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 indicator of the estimated freezing depth is carried out in accordance with the heat engineering calculation and in situations where the supporting structure is equipped with permanent thermal insulation. Also, this provision is relevant for situations where the features 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 baths.

The indicator of the laying depth, 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 rate is not taken into account.

The calculated value may also be disregarded if:

• the foundation is built on fine sandy soil and during the studies the absence of heaving was confirmed, as well as in situations where preliminary studies and subsequent design measures made it possible to establish that the deformation processes that occur during freezing and thawing of the soil do not adversely affect the operational suitability of the structure ;
• it is planned to carry out appropriate measures aimed at preventing soil freezing.

Use the following table to find the depth of support structures for heated buildings with unheated underground and cellar layouts. Count from the floor of the first floor to the basement.

From theory to practice

Previously, you had the opportunity to get acquainted with the list of factors taken into account in the foundation design process, and also received a theoretical understanding of the main design measures at the foundation planning stage. Now you are invited to find out how the determination of the optimal laying depth is carried out in practice.

What are we paying attention to?

Previously, a rather extensive list of factors determining the optimal depth of the foundation was given. In practice, developers pay attention to only a few of them. About this in the table.

Table. Depth Determinants

Factors	Explanations
	During the study of engineering-geological conditions, a soil layer is determined that can take on the functions of a natural bearing base for the supporting structure. In practice, when determining the depth of laying, the following rules are followed: Depth of laying - from 50-70 cm; Deepening of the supporting structure into the natural bearing layer - from 10-20 cm; If possible, the supporting base is laid lower in relation to groundwater. By following this rule, the developer saves himself from the need to build a drainage system. In this case, there will be no violation of the natural structure of the soil. If there is no opportunity to go deep below the groundwater level due to any circumstances, they resort to arranging a drainage system, tongue-and-groove fastening of the walls of the pit, as a result of which the total cost of carrying out the necessary earthworks increases significantly.
	Among the significant climatic factors that are of greatest importance in determining the depth of laying of supporting structures for various purposes, there are, firstly, the depth of soil freezing on the site, and secondly, the features of soil thawing, associated primarily with the level of groundwater passage. Some types of soils in the process of freezing are susceptible to heaving, 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 heaving is mainly caused by the movement of moisture contained in the underlying soil layers to the freezing front. In view of this, great importance in determining the optimal depth of arrangement of the supporting structure should be given to the indicator of the level of groundwater passage during the cold season. The heaving category includes silty clay 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 level of freezing, if groundwater passes less than 200 cm below the freezing point.
	Among the significant design features of the erected structure, affecting the final value of the depth of the foundation, there 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 utilities and their overall characteristics; The nature of the loads acting on the supporting structure, and their magnitude. As a rule, in the presence of underground facilities, the supporting structures are buried 50 cm below the floor of those. In the case of arranging a columnar support structure, the mentioned indicator can increase up to 150 cm.

Important! After determining the optimal depth of laying for all significant factors, the largest indicator found is selected, and it is he who is used as a calculated one.

There are quite a few varieties of supporting structures, among which the most common in private construction are strip, columnar and slab foundations. Next, you are invited to familiarize yourself with the recommendations regarding the optimal laying depth of each of them.

Belt supports

The tape 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 design of the strip base is a reinforced concrete strip, equipped under the walls and partitions of the building. The base receives the loads created by the parent structure and ensures their uniform distribution on the ground.

Important! The bearing capacity of the soil on the site must exceed the loads transmitted by the foundation structure from the building. Information regarding the necessary was covered in detail in the relevant publication.

The belt type base is suitable for use on homogeneous soils with little or no heaving. It is better that groundwater passes as low as possible. It is not recommended to equip concrete tapes in flooded areas.

The considered foundation is prohibited for use on peat and other biogenic organic soils. Also, the use of such a design should be refrained from if the construction site is located on heterogeneous soil or at the junction of different types of soil. It is not recommended to use a strip foundation on water-saturated dusty sandy soil and water-saturated clay soils.

When determining the configuration and geometric parameters of the support base, the following factors should be taken into account:

• loads created by the higher building;
• soil characteristics (heaving, bearing capacity indicators);
• local climate;
• properties of building materials.

The minimum allowable depth for arranging a tape 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 impact on the support from below. Under the influence of these forces, the base will be compressed and pushed up. To reduce the intensity of the severity of these effects, the deepening of the foundation is carried out.

Helpful advice! In addition to deepening the support structure, the severity of frost heaving of the soil can be controlled by providing thermal insulation of the support, installing a non-removable heat-protected formwork at the stage of foundation arrangement, as well as by providing drainage and organizing drainage, soil compaction, its partial or complete replacement.

In accordance with current building codes, the smallest allowable depth of a strip concrete support on all low-rocky and non-rocky soils (with the exception of clay and rocky soils) is 450 mm. When working on rocky ground, due to the physical impossibility of providing significant deepening, it is allowed to arrange a supporting structure directly on the soil surface. When arranging a tape support structure on clay soils and other heaving type soils, the base is deepened by at least 750 mm (an average of 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 loam, sands), as well as at low bearing capacity of the surface soil layers, the strip foundation can be deepened to the level of the soil balls, which are characterized by stable properties and higher bearing capacity.

You can use the values ​​in the following table as a guide.

Estimated freezing depth of conditionally non-porous 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
over 3 meters	from 1.5 to 2.5 meters	1m
	from 2.5 to 3.5 meters	1.5 m

Helpful advice! Regardless of the conditions on the ground, the maximum allowable depth indicator in economic and generally reasonable terms is 250 cm.

If the foundation is settled on sandy, non-rocky soil, you can ignore the freezing depth indicator. It is also possible to get rid of the dependence on the freezing depth by providing vertical insulation of the foundation and horizontal thermal insulation of the soil.

The values ​​given above may change if the groundwater is relatively close to the surface. Under such circumstances, the foundation will have to be deepened to a more substantial level. You can refer to the values ​​given in the following table.

Owners of sites located on heaving soils with high groundwater should consider using a different support structure, for example, pile-grillage. Such a base is not afraid of groundwater and frost heaving.

The indicators of the standard freezing depth are presented in the table.

This design is based on supporting pillars, equipped in the corners of the building and at the intersections of walls and partitions. If necessary, additional supports are built under heavy walls, massive beams and in other areas characterized by increased load.

In order to ensure the uniform distribution of loads created by the parent structure, as well as to organize the work of the pillars as an integral supporting structure and to increase the stability of the foundation to the forces acting on it, a grillage is equipped, represented by strapping beams connecting the elements of the supporting structure.

• in the construction of buildings that do not have basements;
• in the construction of buildings with light walls made using frame, panel and similar technologies;
• when erecting 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 necessary, to minimize the severity of frost heaving forces (pillars are less susceptible to the mentioned phenomenon compared to tape 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, no more than 20% of the cost of the entire house is usually spent on its arrangement (for comparison, in the case of other types of foundations, this figure can increase to 30% or more).

Secondly, through individual supports, a more efficient distribution of loads occurs than through a continuous strip base. The pillars provide equivalent indicators of pressure on the soil, as a result of which there is a decrease in the severity of precipitation compared to the previously considered belt structures. This makes it possible to reduce the total area of ​​the base.

Support-columnar structure - photo

When determining the optimal indicator for the depth of the pillars, pay attention to the following factors:

• soil freezing depth. This parameter remains significant in the design of any foundation. Ideally, the posts should be buried 20-30 cm below the mentioned mark, but this is not always necessary. Exceptional cases will be dealt with separately;
• type of soil and features of its composition. The best option is sandy soil. Water passes almost instantly through such soil, plus its bearing capacity is maintained at a very high level. Construction on peatlands and silty soils should be avoided. The only possible option in this case comes down to a partial (even better - complete) replacement of the existing soil with sandstone;
• depth of groundwater. This point is determined in the course of relevant previous studies. Almost 100% confirmation of the high level of groundwater can be the presence of any natural reservoir nearby. In this case, they resort to the organization of drainage systems or a waterproofing device.

In addition to natural factors, the designer should pay attention to the following points:

• estimated weight of the finished building;
• the weight of the supporting pillars;
• the weight of the internal arrangement of the building and the people in it;
• temporary loads, such as snow.

The most pronounced negative impact on the supporting structures is exerted by the forces of frost heaving. 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 that 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 low-load buildings, for example, such as a private bath, has its own exceptional features.

The foundations of such structures are subjected to heaving forces, in most cases exceeding the total loads created by the overlying structure. Due to this difference, in the end, various deformations of the support 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 shallow or shallow type of support structure.

Shallow supports are called supports, the laying depth of which is 50-70% of the normative index of soil freezing. For example, in accordance with the normative indicator, the soil freezes by 150 cm. In this case, a shallow foundation must be deepened by at least 75 cm.

If the soil is heaving and freezes deeply, it will be necessary to make an in-depth support structure, equipped, as already noted, 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 affected by heaving forces.

If stones, non-reinforced concrete, small blocks, bricks are used to equip the supports, the foundation walls should taper upwards - 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 sidewalls of the pillars with materials that help reduce soil friction. Such materials include a variety of greases, polymer films, epoxy resins, bituminous mastics, etc.;
• insulation of the upper soil ball 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.

1. Firstly, a columnar foundation cannot be used on weak soils, as well as soils prone to horizontal movements, because. poles are characterized by low resistance to overturning. To level the lateral shifts, a rigid reinforced grillage is equipped. In the case of its application, the cost of erecting a columnar foundation is practically equal to the cost of pouring a reinforced tape.

   

2. Secondly, it is better not to equip the pillars in areas located on weakly bearing (peat, water-saturated clay, etc.) soils, especially in the case of the construction of heavy houses (using reinforced concrete floor slabs, with brick walls with a thickness of 50 cm, etc. .d.).

   

3. Thirdly, it is better not to build anything on columnar supports if the site is located in an area with significant elevation changes (more than 200 cm).

   

   In areas with difficult terrain, a columnar base is not the best option.

Plate supports

A monolithic slab supporting structure is characterized by high rates of reliability, strength and durability, but it also requires appropriate labor and material investments for the arrangement. The use of such supports is appropriate when working on weak varieties of soil, for example, soils with a high content of organic matter.

In the case of using a plate, a decrease in pressure on the soil is noted. This happens because the slab rests on the base with the entire surface, which ensures a uniform distribution of the loads created by the parent structure.

On a slab foundation, buildings can be built from any materials. 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 above types of foundations, the depth of the foundation 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 becomes and the deeper it is laid.

Slab foundation structures are not deepened to the level of freezing. Non-buried supports are completely 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 provide 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 “pillow” of sand and gravel with a total thickness of about 30 cm is arranged under the slab. The slab is reinforced over the entire area. Such a 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, subsidence, heaving, etc.

Among the disadvantages of this design, it should be noted a large amount of earthworks, as well as increased costs for the purchase of high-quality reinforcing elements and concrete. The materials used must meet the following minimum requirements:

• brand of concrete - from M200;
• fittings - steel, with a diameter of at least 1.2 cm.

Thus, a monolithic reinforced concrete slab is well suited for use on soils with high groundwater, as well as on weak and heterogeneous soils. Under such circumstances, the cost of arranging the slab structure will be justified and appropriate. Otherwise, experts recommend paying attention to more cost-effective solutions in the form of the columnar and tape bases discussed above.

In addition, you are invited to familiarize yourself with tables characterizing various types of soils, as well as reflecting the dependence of the indicator of the depth of the supporting structure on the characteristics of the soil and the height of the passage of groundwater.

Successful work!

Video - Foundation Depth

When laying the foundation of a building, the type and number of storeys of the house, its weight, terrain features, and all soil characteristics are taken into account. These factors determine the type and depth of the foundation. The last parameter is calculated according to SNiP 2.02.01-83 Foundations of buildings and structures.

Foundation classification by depth

In the regulatory building base, foundations, depending on the depth, are divided into three types:

1. Buried. They are a solid foundation for heavy buildings on all types of soil.
2. Shallow. The depth of laying a shallow foundation does not reach the place where the soil has already frozen. They are used on solid soils, with a high level of groundwater, in the construction of structures that do not have basements and basements.
3. Unburied. They are used in the construction of light structures on heaving and soils with increased heaving, soils with low subsidence, as well as in the construction of heavy buildings on rocky soils.

Factors determining how deep the foundation should be:

• rise height and general groundwater level;
• characteristics of the climate of the area, indicators of hydrogeological surveys;
• location of the construction site;
• building structure, the nature of the loads exerted on the foundation.

If other structures are located next to the house under construction, when calculating the depth of the foundation, I take into account the technical characteristics of their foundation.

There is a general rule: the foundation is laid so that the maximum level of groundwater rise is below the foundation. Then the time and cost of construction are significantly reduced.

The depth of the foundation, depending on the geological characteristics, is determined by two factors:

1. The presence of moisture in the soil.
2. Groundwater level and its impact on frost heaving of the soil in the region.

The strip foundation is poured at a height of at least 0.5 m higher than the groundwater.

With high soil moisture, the foundation material will get wet and gradually collapse from this. If we take into account that the main material for the formation of foundations is concrete, then the destructive effect of moisture during slight frosts increases several times.

Accounting for moisture concentration in the design has differences depending on the type of foundation under the foundation of the building:

1. Soils are rocky, sandy of large and medium fractions, gravelly, coarse-grained, having sand as a filler. They have no restrictions on the depth of the foundation in terms of groundwater levels.
2. The foundation in clay, loam, in soil consisting of large fragments filled with dust-clay fractions is always designed below the freezing level of the soil, regardless of the level at which the groundwater is located.
3. For fine sand and dusty soil, the location of groundwater in relation to the level of soil freezing is important. If the waters pass at a level of 2 meters down from freezing, then it does not matter what the depth of the foundation should be.

How climate affects the calculation of the depth of the foundation

The climatic conditions of the region where construction work is underway affect the depth of soil freezing. With a certain degree of approximation, this value can be determined from the maps "Boundaries of soil freezing depths". More accurate calculations can be made in relation to a narrow construction site.

Calculation of the standard indicator

For areas where the soil freezes over more than 2.5 m, the standard freezing depth indicator is calculated using the formula:

where M t is the total number of absolute average monthly negative temperatures for a given region, d 0 is a coefficient depending on the type of soil.

To calculate M t, the data are taken from the statistics service. The coefficient d 0 is 0.34 for coarse clastic soils, for loam and clay - 0.23, for coarse, medium and gravelly sands - 0.3, for fine sandy and dusty soils - 0.28.

How to take into account the heat transfer of a building

In order to determine the depth of freezing of a structure in real conditions, use the formula:

In this expression, the coefficientk htaken into account two factors:

1. The building is heated and the ground will warm up additionally, so k h will be lowering. It is taken in special tables, where the gradation is based on the presence of a basement, basement and average daily air temperature in rooms that are adjacent to the foundation.
2. In the absence of heating. In this case, k h is a margin of safety equal to 1.1 for all types of buildings.

We study the features of soils

Before calculating the depth of the foundation, the type of soil is determined. This service can be ordered from specialists or performed independently.

On the fertile soil layer, no foundations are poured. It is completely removed.

Below the fertile layer is one or more layers suitable for soil construction:

1. Rocky soil that does not require deepening of a strip and monolithic foundation. It does not swell in winter, moisture does not accumulate in it, it does not undergo subsidence.
2. Gravel, stones, crushed stone, coarse sand create a reliable foundation, on which the depth of the foundation is from 0.5 m.
3. Clay soil freezes to a level of 0.5-1 m, is mobile when wet, has uneven shrinkage. But if there is not much precipitation in the region, and groundwater is very deep, the foundation is laid at a depth of at least 0.75 m.
4. Fine-grained sand has increased mobility and loses its stability with strong moisture. With deep groundwater, it is recommended to deepen to a more stable base. The depth of freezing of sandy soil, in which there are clay particles, is from 0.6 to 2 m.
5. The unreliable type of peat soil is used for building on a columnar foundation.

When determining the type of soil yourself, consider the following:

• the clay is dense, it is difficult to dig it, it does not crumble when rolled into a roller;
• the sandy loam will consist of sand with clay fractions, and the rolled flagellum will crumble;
• loam is based on clay and interspersed with sand (any figure from such a mixture will break apart).

Knowing the type of soil already allows you to proceed to determine the type of foundation and the depth of its laying.

Building features and foundation depth

The first thing to consider is the weight of the entire structure. Larger buildings require deeper foundations. The bearing capacity of the soil is also taken into account.

During the construction of a frame one-story building on heaving soils, the foundation is deepened by 0.5 m, and for a 2-3-story building this figure will be at least 1.5 m. When replacing a beam with a brick, the depth of the foundation will also increase.

To take into account the bearing capacity of the soil, the weight of the entire building, foundation, communications and internal equipment per unit area is calculated. If the standard indicator does not correspond to the calculated one, the parameters of the foundation are changed.

When designing the foundation, the design features of the structure and its location are taken into account:

• the foundation is located below the basement floor by at least 0.4 m;
• the level of the foundation is aligned with the foundation of all buildings that are in close contact with the structure under construction;
• it is desirable to bypass the main communications by construction, but if this does not work, then the foundation is laid under the pipes.

Depth level of the belt support

The tape type foundation is easy to install and design, suitable for most types of building structures. Recommended for use on soil with mild heaving, not recommended where soil water saturation is high.

The depth of the strip foundation is determined by the parameters:

• the level of soil freezing;
• groundwater flow height;
• severity of soil heaving.

The combination of these factors leads to the fact that the heaving of the soil will increase with an increase in the depth of soil freezing and the proximity of groundwater. Such soil will squeeze the foundation from below and push it up. The deep location of the foundation reduces the intensity of such processes.

The standards define the minimum depth indicators:

• 0.45 m in low-heaving soils;
• 0 m on rocky ground;
• 0.75 m in heaving soils;
• at the level of stable soil occurrence with water-saturated and mobile upper soil layers.

The maximum depth of penetration is 2.5 m for all types of soil.

In order not to decide what the depth of the foundation depends on, you can equip the thermal insulation of the soil and the insulation of the foundation, mount it.

Other types of foundation

The columnar base is used for light buildings. Such a foundation is effective where the soil freezes strongly. It is lowered into the ground below the freezing point by 10-25 cm.

To lay piles and select their type, soil properties are determined. Such a base is made mainly of concrete. Deep pile foundations are lowered to a depth of 1 m or more, which depends on the bearing capacity of the structure.

The most stable version of the foundation of the building is slab or solid. Formed from reinforced concrete slabs. It is buried down to 50 cm in any soil.

Determining the depth for laying the foundation is a complex task, which must be solved at the design stage of the building structure.

What to look for when building foundations - video