Reducing the depth of foundations in some cases saves significant funds. The device of the foundation slab without deepening at all allows you to kill two birds with one stone - not to mess with digging a pit and erecting an underground part of the walls, and also to get a solid foundation for constructing the floor of the first floor.

But, if everything is so good, why haven't shallow foundations replaced the "ordinary" foundations yet?

Why bury foundations at all?

In the classical case, the depth of foundations corresponds to the depth of soil freezing. By the link: - you can download a calculator for calculating the depth of soil freezing (cities of Russia and the CIS) with climate maps for free. In this case, the penetration of cold into the underground of the first floor is sharply limited, and the heaving effect of the soil on the base of the foundation is excluded. Recall that frost heaving is a property of water-saturated fine (clay, loamy) soils to swell when freezing.

It is obvious that for the construction of a shallow foundation it is necessary to solve two issues: leveling the forces of frost heaving, warming.

Leveling the forces of frost heaving

If there are heaving properties of the soil at the construction site, for a shallow foundation, it is usually recommended to backfill with non-heaving material that isolates the foundations. These recommendations are described in detail in VSN 29-85 "Design of shallow foundations of low-rise rural buildings on heaving soils."

Foundation insulation should be carried out over its entire surface, that is, not only from below, but also along vertical edges.
As a non-rocky soil, it is best to use sand of coarse or medium grain size. In the conditions of the seasonal appearance of the so-called “perched water” (ground water that seeps out to the surface), a drainage device around the building will be required to avoid silting of the anti-foam bedding. Otherwise, after several seasons, the bedding may acquire heaving properties.

Insulation of the foundation and blind area

Insulation of a shallow foundation is critical. Warming will allow not only to avoid the penetration of cold from under the floor, but also to eliminate the cause of heaving. The latter is not possible at positive temperatures.
The boundary depth of soil freezing is determined not only by the temperature of the coldest five-day period in the construction region, but also by the presence of molten magma in the center of the planet. In the absence of heat deep underground, seasonal freezing of the soil would be much stronger, up to the impossibility of the emergence of life on Earth. This circumstance determines the direct expediency of insulating the blind area around the building - it will not allow the soil around the shallow foundation to freeze and penetrate under it.

1-monolithic foundation, 2-wall masonry, 3-floor base, 4-sand filling, 5-insulation, 6-waterproofing, 7-backfill, 8-blind area.

In this case, only hydrophobic materials that do not absorb moisture and have high strength characteristics are allowed as a heater. The most commonly used material is XPS, extruded polystyrene foam, often referred to as "hard foam". It can even be laid under the foundation slabs of light buildings.

Floor insulation and temperature conditions

The main difficulty in the construction of shallow foundations is to find a balance between floor insulation and temperature in the winter. This is critical for cold regions with a basement.

When constructing a shallow foundation, it is necessary to exclude freezing of the soil not only under the foundation, but also under the floor.

Very often there is an opinion that when insulating the blind area and vertical edges of the underground part of the building, floor insulation can be omitted, or it can be done with a small thickness. Allegedly, the soil array, having absorbed heat under the building, itself performs the function of a heater. But let's imagine a situation where, for some reason, the built house is not put into operation in the very first winter season. In the absence of full-fledged insulation under the floor and when the heating is turned off, freezing can occur, since the only source of heat will be deep underground. Insulated walls, ceilings and a roof, due to the lack of tightness of the building, can hardly guarantee a positive temperature in the room during severe frost outside. When you visit a country house with the heating turned off in winter, you don’t expect positive temperatures inside, do you?

Thus, the main danger for a building with a shallow foundation is freezing through the outer walls of the building. In order to avoid heaving of the soil under the floor, it is necessary either to ensure positive temperatures in the premises in winter, or to ensure floor insulation with the same thermal resistance that is required for walls in the construction region. Moreover, the second option, perhaps, is preferable - energy costs for heating the soil mass under the building will decrease, in winter, in the absence of heating, the temperature of the soil under the building will be uniform. With "partial" floor insulation while maintaining a positive temperature, freezing is possible in the corners of the building, as in the most vulnerable area.

Swedish experience

In support of the above, consider the temperature charts from the report of Swedish specialists who studied the experience of building private houses on non-buried slabs in Sweden itself. A region with a freezing depth of 2.3 m was considered. Studies were carried out with a thickness of insulation in the floor of 10cm, 20cm and 30cm. As a result, the following temperature diagrams were obtained:

As can be seen from the figure, in the absence of an insulated blind area with a large thickness of the insulation, the thermal regime of the building cannot completely warm up the soil layer. Ground freezing goes under the stain of the building. Powerful floor insulation (in terms of saving heat inside the ground) does not save the corners of the building from frost on the surface. And vice versa, with a slight warming of the floor in the case of switched on heating, freezing due to significant energy consumption for heating does not occur.

Consider the following diagram:

In this experiment, a heater 0.3 m thick was laid under the spot of the building, and 0.1 m thick under the blind area. The blind area insulation width was assumed to be 0m, 0.6m, 1.2m. The resulting diagram clearly shows the effectiveness of the insulation of the blind area. With an insulation width of 0.6 m and 1.2 m, other things being equal (in relation to the previous experiment), soil freezing does not go under the building stain.

In our country, the distribution of shallow foundations is just beginning to be used massively due to the lack of experience in such construction. In regulatory building documents, there are no requirements for the installation of insulated foundations today.

So what's the bottom line? How to properly arrange a non-buried foundation?

The device of shallow foundations can be divided into two categories - the method of isolating the foundation from heaving forces, the method of eliminating heaving with the help of insulation. Let's briefly summarize each option.

Insulation with sand bedding is a solution of the last century. Solving the issue of the impact of heaving forces on the foundations, the issue of energy consumption for heating the freezing floor is not resolved. The use of backfills made of drainage material (crushed stone, gravel) is advisable in case of difficult hydrogeological conditions (seasonal top water) in combination with drainage. With a relatively deep groundwater level, the use of non-rocky soils as a base can be recommended for heavily and excessively heaving soils. With moderate heaving, it is permissible to rest the foundation on the root soil, subject to complete (see below) insulation. In this case, it is advisable to backfill the sinuses of the trenches (pit) with non-porous soil in order to reduce the risk of deformation of the blind area.

Modern hydrophobic heat-insulating materials with high strength characteristics make it possible to build shallow foundations on heaving soils. In order to avoid the risk of deformation of the corners of the building, as well as freezing of the underground mass of soil in the event that the facility is not put into operation in the winter, it is necessary to carry out complete insulation of the basement of the building. The entire floor area, the foundations themselves (if we are not talking about a slab), the basement of the walls and the blind area must be inextricably insulated. The thermal resistance R of such insulation should be identical to the requirements for walls in the construction region. The width of the blind area insulation can be taken equal to at least the freezing depth. With a significant level of heaving properties of the root soil - 1.5 freezing depths (desirable).

The experience of construction in Sweden, Finland, Greenland and not only determines the admissibility of arranging practically non-buried foundation slabs for light houses. For this, the vegetation layer is cut, the construction site is leveled with sand, a rigid hydrophobic insulation (extruded polystyrene foam) is laid under the entire building spot, and the blind area is insulated around the entire perimeter of the building.

In the case of building a light house from gas blocks on a shallow foundation, it is especially critical to correctly

With a competent laying of the foundation for a capital building, the type of soil at the site of the construction work must be taken into account. The design of the whole house is greatly influenced by the frost heaving factor, since it can cause serious deformations of the building. Therefore, it is important to consider such details at the design stage. Shallow foundations (MZLF) are very popular among private developers, which, despite their financial affordability, are suitable for almost any housing construction if properly calculated.

Different localities contain groundwater at different levels. When moisture is found close to the freezing depth, the soil is excessively moistened, which threatens to heave the earth at low temperatures. Before making a shallow strip foundation on heaving soils, it is important to consider that heaving soils include clay soils in the form of clay, loam and sandy loam.

The height of capillary wetting directly depends on the type of soil and is called a dangerous frost border. Its thickness ranges from 30 to 3.5 meters and depends on the degree of dispersion:

• 0.3-0.5 m - near dusty soil.
• 0.5-1 m - in sandy loam.
• Up to 12.5 m - near loams.
• Up to 3 m - in clay soil.

The depth of freezing of the ground under the base largely depends on atmospheric temperature, thermal insulation and the mass of snow cover. As a result, the thicker the layer of capillary moisture, the closer the groundwater level and the lower the temperature, the higher the probability of soil heaving.

Monolithic shallow strip foundation (MZLF) for a house on heaving soils: organization features

The basis of shallow penetration in housing construction is considered to be a tape, the sole of which is no deeper than 60 cm. That is why special attention is paid to the type of soil. For example, according to construction standards, pouring MZLF on peat, sapropel and clay soils is prohibited.

The groundwater level also plays an important role - the closer the water, the more unstable the foundation structure will be. In addition, when making a shallow strip foundation, experienced builders take into account the following factors:

Site level difference.

Depth of laying.

Climate.

If the terrain on which the construction is planned is distinguished by height differences, then the arrangement of the MZLF in such conditions is quite problematic. The output can be a standard tape device or site leveling. Both options in terms of costs are almost equivalent, it is only important to prepare the right one. for pouring the base.

Advantages and disadvantages of MZLF

In many regions of Russia, the maximum period when construction work can be carried out is no more than 6-7 months. The foundation of a shallow depth does not require a lot of time with the involvement of heavy equipment, which makes it attractive to many developers. But this is not all the advantages of MZLF, experts note several more advantages:

1. Reduced consumption of building materials.
2. The possibility of independent implementation of the project.
3. With the correct calculation, the base is reliable.

Along with the listed advantages, a shallow-depth strip foundation of a monolithic type on heaving soils has a number of disadvantages:

• The impossibility of using the base in the construction of multi-storey buildings from heavy structural elements.
• With a close location of groundwater, it is necessary to equip a drainage system, which entails additional financial costs.
• Compared to piled and non-buried foundations, the cost of MZLF is higher.

It should be noted that careful , since the frame will contribute to resisting loads in all directions.

The main task in organizing the foundation of a shallow deepening is the drainage of water, when there is no water, there is no heaving. To do this, a drainage is made along the perimeter, consisting of a ditch half a meter from the base and a perforated pipe. Water through the holes in the pipe will enter the drainage well.

How to implement a shallow monolithic strip foundation with your own hands: basic processes

The preparatory stage includes cleaning the proposed building site from debris and leveling the site. If there are trees on the site, then they need not only to be cut down, but also to uproot the stumps. The necessary material and equipment is delivered to the nearby territory. The subsequent phases of the arrangement of the MZLF are performed in the sequence indicated below.

markup

It should be borne in mind that the base should be 20 cm wider than the walls being erected. A cord, pegs and a tape measure are used for marking. The procedure is carried out according to the points:

• Make measurements around the perimeter and install corner beacons.
• Check the diagonals and, if necessary, correct the position of the beacons.
• Perform a blind area at a distance of 1 m from the beacons.
• Fasten the cord marking the boundaries of the base.

earthworks

Do-it-yourself digging of a trench for a shallow strip foundation begins with the removal of a fertile layer of earth, which can later be used on the beds in the garden. They start digging from the lowest point, constantly monitoring the evenness of the bottom. The presence of sharp drops is unacceptable, since the load from the building will be unevenly distributed. The optimum depth of the ditch is 60 cm.

In the process of excavation, you need to monitor the verticality of the walls of the trench. Geotextiles are laid at the bottom of the finished ditch. Usually, the width of the roll is chosen so that the edges of the textile can be fixed on the edge of the trench. Do the same when building or walls.

Cushion and formwork organization

Coarse river sand is placed at the bottom of the ditch, additionally it is possible to use fine gravel, but subject to their layer-by-layer placement. Sand is also recommended to be laid in layers, each of them is carefully rammed and watered. Basically, the thickness of the pillow is 25-30 cm, but in some cases the figures can be increased to 50 cm, which is taken into account when calculating earthworks. Due to the porosity of the pillow, craftsmen advise separating it from concrete with a waterproofing film.

The formwork is arranged in such a way that its upper edge is 20-30 cm above ground level. It is important to install the boards without drops and gaps, this will avoid additional work on leveling the plane of the base for cladding. Supports are mounted vertically in increments of 50-60 cm; these elements prevent the formwork from being skewed under the weight of concrete.

Reinforcement

To assemble the frame, the required amount of reinforcement is prepared, the optimal section of the rods is 8-14 mm. The welding option is highly undesirable, because corrosion forms at the joints, destroying the reinforcement. Therefore, wire knitting is preferable.

Proper reinforcement involves pouring the starting layer of concrete. Its percentage of the total height of the MZLF should be at least 30%. This stage is designed to level the surface before laying the reinforcing frame. In addition, concrete protects the reinforcement from moisture.

Foundation concreting

It is no secret that for this operation it is desirable to use a high-grade concrete solution. Many developers are interested in the price to be paid for materials for a shallow strip foundation. Experience shows that in most cases, concrete M300 will be the best choice, which is a smart compromise between quality and cost.

If you plan to make the solution yourself, then it's a good idea to get a concrete mixer. In addition, it is necessary to make and other components.

The technology requires that the next layer be poured before the previous one hardens. It is impossible to fill the formwork sections in turn, even if jumpers are used - the seam sections will have low strength. After pouring, it is advisable to sprinkle the concrete with dry cement, using a sieve for this. The maximum strength of the foundation occurs in 28-30 days.

What is the price of a monolithic MZLF for a home?

Developers who prefer to trust specialists pay special attention to the prices for foundation work. It is important to consider here that a self-respecting construction company will not disclose the cost of its services over the phone only based on the size of the house you declared. The specialist will draw up an estimate of the order after studying the site and the project. Typically, the cost of laying the foundation includes several items:

• Cost of materials.
• Site preparation and planning.
• Earthworks for digging a ditch.
• Installation of formwork and production of a reinforcing frame.
• Pouring concrete solution.

The average cost of a shallow-depth strip base is from 2,600 to 3,000 rubles per linear meter. This is somewhat more expensive than pile foundation, but despite this, the majority chooses the tape. To quickly determine the prices, depending on the perimeter of the building without taking into account the walls, it is enough to use the table.


The given figures are quite approximate, because the width and height of the tape are taken into account in the final calculations. Most construction companies include in the estimate all costs for the delivery of materials to the site.

Today, despite the wide variety of different companies and firms that provide comprehensive construction services, private construction has not lost its popularity.

First of all, this is due to the fact that construction services do not cost a little money, but there are so few of them in the process of building your dream home. So you have to do everything yourself or ask friends and relatives.

The device of even the heaviest structural elements can be mastered by almost every person, so that everyone can build their own house.

However, in construction, as in any other business, there are subtleties that you need to know and take into account. If there is no exact idea of ​​what you are going to build, then it is better to seek help from professionals or ask those who have already done it.

Very often, all gaps in construction begin from the very beginning, that is, from the foundation. It seems that it is easier to put the formwork and pour concrete there. But in fact, not everything is so simple. If, for example, soil heaving or additional uneven loads on the foundation are not taken into account, then all the work will go down the drain.

Let's talk about frost heaving, find out what it is and how this process affects the strength of the foundation, and also try to figure out how to build foundations in heaving soils and how to deal with this negative phenomenon.

Heaving - what is it?

Foundation device

It is worth saying that almost the entire territory of Russia, Belarus, Ukraine and part of Western Europe is subject to seasonal freezing of soils. This is due to the fact that in winter, during severe frosts, the soil, which contains a certain percentage of moisture, simply freezes.

However, only some soils, or rather types of soils, are subject to frost heaving. These soils include:

• Clay and loamy soil types;
• Fine-grained sandy soils;
• Dusty sandy soils and others;

All these types of soils are prone to heaving when frost sets in.

What is heaving in general, and how does it manifest itself? Heaving is the ability of the soil to increase its volume under the influence of frost. In fact, heaving soil behaves like yeast dough.

This phenomenon is due to the fact that the moisture that has accumulated in the soil begins to freeze when frost sets in. As you know from the school bench, when water freezes, it increases in volume. Consequently, expanding, the moisture pushes the soil out. The increase seems small, only 1.09 times, that is, about 9 percent, however, when it comes to large volumes of soil, it becomes noticeable.

If there is no moisture in the soil, for example, when groundwater flows much below the freezing depth, then heaving is observed for the simple reason that moisture vapor is redistributed in the pores of the soil. This means that the moisture simply begins to rise up, that is, there is such a phenomenon as the capillarity of the liquid.

In this case, we can say that the soil is slightly heaving, but the very fact of the presence of this phenomenon makes it necessary to take additional precautions and protection measures when designing the foundation structure.

In general, it is on this basis that soils are usually divided into three categories:

1. Slightly heaving;
2. Medium heaving;
3. Strongly foamy;

Accordingly, the volume of changes depends on what type of soil a particular area belongs to. Some soils can deform up to 17-25 centimeters. To make these figures clear, we can cite the norm that applies to wooden houses. So, a wooden house is able to withstand heaving within 5 centimeters, and a brick house - within 2.5-3 centimeters.

Why is frost heaving dangerous for the foundation? Very simple. Expanding, the soil creates additional pressure on the foundation. When only the mass of the house presses on it, then all of it is evenly distributed over the entire area of ​​\u200b\u200bthe foundation support, but the forces of frost heaving create a tangential uneven pressure on the walls of the foundation, which leads to the emergence of lateral torsion forces in it, that is, a force arises in the foundation that able to break it and move it from its place.

Often with a high degree of heaving, the force that presses on the walls of the foundation reaches about 11 tons of force per square meter of the foundation, and the force that presses on the sole of the foundation is 80 tons of force per square meter.

So, drawing a conclusion, it can be noted that almost all soils have the property of frost heaving, which is mainly due to the presence of moisture in the soil.

Construction of a columnar foundation on heaving soil

Strip foundation on heaving soils

For the most part, such foundations are erected only when it is planned to build some fairly light building, such as a frame house, or a small bathhouse. The second case of the optimal choice of this particular type of foundation is the case when it is necessary to build a foundation at a great depth, while the choice of a strip foundation entails huge financial costs, which can reach about 40 percent of the total estimate for the entire construction.

As practice shows, the installation of columnar foundations costs one and a half, or even two times cheaper than the installation of a strip foundation, and even more so it will come out cheaper than the installation of a slab foundation.

The choice of material for the foundation depends on what kind of house is planned to be built, that is, on the mass of the building, on the height, and so on. According to the material used, columnar foundations can be divided into the following types:

• stone;
• brick;
• Concrete;
• Reinforced concrete;
• rubble concrete;

Very often, concrete structures are called monolithic. To date, when erecting columnar foundations, ready-made concrete or reinforced concrete slabs are used, that is, the foundation is made of prefabricated concrete.

The columnar foundation is erected according to three basic rules for the location of the pillars:

• Pillars must be located at the corners of the building;
• The pillars must be located at the intersection of the walls;
• The pillars must be on straight sections of the walls, so that the distance between the pillars is a maximum of 3 meters;

If we talk about the device of a columnar foundation on heaving soils, then for them all these rules apply without exception. However, there is a slight difference in the design of the pillars themselves - to reduce the load on the ground, especially if the ground is weak, the lower part of the pillars is expanded, or a larger slab is laid. If the pillar is made of brick, then this extension is made into several rows, but not less than two.

In strongly heaving soils, a columnar foundation, as a rule, is made of asbestos or metal pipes, from prefabricated reinforced concrete pillars and slabs. A brick or monolithic foundation will not work for the simple reason that their construction is very inconvenient in such soils. The thing is that in heavily heaving soils, the foundation should lie at a depth greater than the maximum depth of soil freezing.

If such a depth exceeds 1 meter, and, as a rule, it is so, then building a brick foundation at such a depth is simply not possible.

If, when constructing a columnar foundation in heaving soils, its laying exceeds a depth of more than 1 meter, and at the same time there is no water at the bottom, then it is allowed to make a foundation with a base plate of concrete or reinforced concrete.

As a rule, the distance between the pillars, when building a foundation in heaving soils, is made equal to a maximum of 2.5 meters, it can be less, but it is no longer recommended.

In order to connect all the pillars into one whole structure, it is necessary to connect them from above with strapping beams. If the distance between the posts is less than 2.5 meters, then it is allowed to make wooden beams, if more, then it is better to use ready-made reinforced concrete rand beams that form a grillage.

As for the geometric dimensions of the pillars, such indicators depend on what material they will be made of:

• Concrete and reinforced concrete - 40 centimeters;
• Rubble concrete - 40 centimeters;
• Buto flagstone - 40 centimeters;
• Brick, provided that the pillar is located above ground level - 38 centimeters;
• Brick, provided that the post will be tied up with a fence - 25 centimeters;

Since it is better to arrange posts with a square section, the size given above applies to both the length of the post and its width.

Now we should talk about the columnar foundation in heaving soils and its advantages over other types of foundations.

As already mentioned, for heaving soil, a columnar foundation will be the best solution in terms of the cost of its construction. On a columnar foundation, the tangential forces of frost heaving do not act with such great pressure as on, say, a strip foundation. However, they can be avoided or reduced to a minimum, not only by installing pillars below the freezing level of the soil.

In order to minimize the torsional force that occurs as a result of pressure on the foundation from the side, it is necessary to put an anchor plate at the base of each column. An anchor plate is a concrete slab that is larger than the width of a post and is firmly bonded to the ground. This plate will not allow the forces of frost heaving to pull out or simply budge the post.

In order to prevent a fracture of the column, it must be reinforced, and in the cement mortar, if the column is made monolithic, a plasticizer must be added to increase the elasticity of concrete. If there is no reinforcement, then the design of the column will allow minimizing the pressure, which should taper towards the top, that is, it should not have a strictly rectangular shape, but the shape of a rectangular cone.

In general, in heaving soils, and especially with their large freezing depth, the following types of columnar foundations are very effective:

• Anchor reinforced concrete;
• Monolithic concrete;
• Prefabricated concrete;

These types of frost heave forces are affected to a lesser extent than others due to the fact that they are performed with a fairly small cross section.

The device of a pillar made of bricks can be as follows:

• Sand cushion measuring 50 centimeters or more. It is made of coarse-grained or gravelly sand;
• A layer of roofing or roofing material;
• Rectangular cone of a pillar made of brick. At the same time, it should narrow exactly to ground level;
• Glue waterproofing, which is applied to the top platform of the column;
• Grillage, which can be made of precast concrete slabs;
• A brick pillar, which should be the same in width as at the base, that is, at the edge of the ground;
• Loose soil that is well compacted. It should only be applied on the outside of a wall or pole. It should start from a layer of roofing material, that is, still underground and end in the middle of a pillar that is located above the ground;
• Cement screed that covers the compacted soil;

A concrete pillar may have the following device:

• Sand cushion at least 50 centimeters thick;
• A layer of roofing or roofing material;
• The foundation is made of concrete, which is made in the form of a cone and protrudes slightly above ground level, by about 10-15 centimeters;
• Reinforced concrete belt, which is made of a reinforcing cage filled with concrete;
• Floor slab, which is made of reinforced concrete. It should lie at half the width of the post so that the same slab can be placed on the other side;
• Plate heater. It should be a continuation of the column, or rather the belt, that is, have exactly the same width;

This design of the poles allows to reduce the effect of frost heaving on the foundation, in addition, there are some additional measures, for example, to glue the pole on all sides with material that will reduce the friction force between the pole and the ground. As an additional measure, you can also insulate the ground around each post.

In order to tie all the pillars together, as already mentioned, they arrange a grillage. It helps to distribute the load that acts on a stand-alone pole between all poles, which almost completely eliminates the possibility of it tipping over or moving in a horizontal plane.

If the building is built of brick, or of concrete, of foam blocks, then the grillage must be concrete, and preferably reinforced concrete, while if the pillar also has reinforcement, then it must be rigidly connected to the reinforcement of the grillage. If the building is wooden, then the grillage can be represented by a strapping of logs.

In order to prevent the ingress of various debris and natural precipitation into the internal space between the pillars, a pick-up is arranged.

The role of the grillage is not clear. It serves not only to connect the pillars into a single structure, but also the foundation for the basement, but only if the walls are brick or concrete.

In this case, the grillage can be made in the form of a jumper, which consists of several reinforcement rods that are laid on a pre-poured concrete layer. At the same time, such a layer should be at least 70 millimeters, and the number of reinforcing bars 10-12 millimeters thick should be in the range from 4 to 6 pieces.

Thus, the grillage can be made in the form of a monolithic reinforced concrete structure or a prefabricated structure, which consists of reinforced concrete slabs.

If it is decided to manufacture reinforced concrete pillars, then there will be additional costs associated with the purchase of reinforcement. You will also need to buy either ready-made plastic formwork, or make it yourself from wood.

It is also worth noting that all construction, from the foundation to the roof, must be completed in one season. This applies only to those cases when it comes to construction on heaving soils. The fact is that if you leave the foundation without a load, but which is designed for it, this will lead to its deformation.

It should also be noted one more case when the deformation process of the foundation is possible. Such a case is the time when the house is not heated, but at the same time the depth of the foundation was taken taking into account the fact that the house will be heated from the inside.

A little about shallow foundations

As noted earlier, the most dangerous forces that act on the foundation of a private house are the forces of frost heaving. All calculations of the bearing capacity of the foundation, calculations of the depth of laying, and so on, should be carried out precisely with them in mind.

Therefore, if the foundation is built on heaving soils, then its laying depth is equal to the calculated depth of soil freezing in the most severe frost.

Yes, indeed, laying the foundation to a great depth gives its positive aspects, but this does not always happen. If the house is built from fairly light materials, then it is better to lay the foundation at a shallow depth, that is, make it shallow.

It is customary to call such a foundation a foundation, the maximum laying depth of which is 0.7 meters, if FBS rings were used in its construction, then the depth of a shallow foundation is 0.9 meters, since the height of the ring is 0.9 meters.

This figure was not invented just like that - it was taken from various studies of the depth of soil freezing.

The thing is that the depth of laying a shallow foundation is calculated as the maximum freezing depth multiplied by 0.5, since for our strip it is considered that the maximum depth of soil freezing is 1.4 meters, then, accordingly, the maximum depth of laying a shallow foundation is 0.7 meters.

Shallow foundations can be considered those foundations in which the ratio of the height of the column to the width does not exceed four. For example, a foundation with a height of 1.8 meters and a column width of 0.4 is not considered a shallow foundation, but a foundation with a height of 1.5 and a base width of 0.4 is considered so.

So, in total for a house with a low mass, three types of foundation are used:

Conditions for a reliable foundation

• Shallow;
• shallow foundations;
• Unburied foundations;

If a shallow foundation has been properly designed and properly constructed, then it is able to provide:

• Reducing the magnitude of fluctuations in seasonal heaving of the soil;
• Reducing the amount of work on its device, and, accordingly, saving time and money;
• The device of this type of foundations in almost any hydrogeological conditions;

We have already talked a little about the possible design of columnar foundations, but it is worth considering the design of a shallow foundation and a normally buried foundation in comparison.

Small foundation design

As a rule, such foundations are made either monolithic reinforced concrete or prefabricated from prefabricated reinforced concrete slabs.

In order to erect pillars, pits are dug, which have slopes, that is, which narrow as they sink into the ground. The width of the base of the pit should be 20 centimeters more on each side than the post.

The foundation of prefabricated slabs of normal penetration can have the following design:

• Sand cushion about 15 centimeters thick;
• Further, concrete blocks are laid out one on one, which have a size of 38x50x28 or 38x40x28. Blocks are connected by means of cement mortar;
• The entire pit is covered with non-rocky or slightly heaving soil;
• On the upper concrete block, that is, on the one that is located exactly at ground level, there is an adhesive waterproofing on top;
• Another concrete block;
• On top of the concrete block is a small, 3-5 cm, layer of cement;

In such a design, the distance from the edge of the ground to the top of the adhesive insulation should be approximately 15 centimeters. Thus, it turns out that the height of the pillar above ground level, taking into account the height of the extreme concrete block and the cement layer, is 45 centimeters.

The design of the foundation pillar of a small foundation can be as follows:

• Sand cushion half a meter thick;
• A concrete block that is immersed to a depth of 10-12 centimeters;
• A layer of adhesive waterproofing;
• Second concrete block;
• Cement screed 3-5 centimeters thick;

In addition, a concrete blind area is arranged on the inner side of the pillar, which is adjacent to the first block and which has a thickness from the ground level to the upper cut of the first concrete block, while it has a slope away from the pillar.

The entire pit has a depth of about 80 centimeters, and a width of about 90. As for the dimensions of the pit for a normally buried column, the width does not differ, but only at the base, but when it leaves the ground, it increases.

To choose the right concrete block of the right size, you should calculate the foundation column for the load. If it turned out to be larger than the soil on which the concrete block is located with its geometric dimensions is able to withstand, then it is necessary to replace it with another one that will have larger dimensions, and, accordingly, a large support area.

In the event that the load is high and there is no suitable concrete block, then a concrete slab can be placed under the lower block, which will act as a concrete pad. As a rule, such slabs are thinner, but longer and wider than a concrete block.

Columnar foundation with grillage

As already noted, the grillage is arranged for the stability of the pillars in heaving soils, as well as to create a support for the walls of the structure.

The grillage is arranged only after all the pillars are adjusted to a single horizontal level.

The design of the pillars that are located above the ground, in conjunction with the grillage, can be as follows:

Two adjacent lintels of the grillage are connected by means of specially left pieces of reinforcement. In addition, the grillage itself is not laid on a concrete slab, but on a reinforced monolithic belt laid on it, in which pieces of reinforcement are also left. These pieces are also attached to the lower pieces of reinforcement of the grillage lintels in the same way.

If the distance between the posts is more than 2.5 meters, then instead of the above jumpers, others with dimensions of 298x25x20 centimeters can be used, but in general, there are enough of them in the construction markets, so that everyone wears a suitable length for themselves.

It often happens that the mass of the building is greater than the calculated possible mass that the lintels can withstand. In this case, a reinforced belt is installed on top of them, in which case the design of the column with the grillage is as follows:

• Foundation block, exactly the same as in the first case, for example, FL 8-12-3;
• Wall block, for example FBS 9-5-6;
• Concrete lintels;
• Monolithic reinforced belt;

A shallow foundation of a columnar type can be either brick or monolithic, in contrast to a normally buried foundation, which, on the contrary, excludes these two types of columnar foundation.

To build a shallow foundation on heaving soils, first a hole with the appropriate dimensions is torn off and a sand cushion 50-60 centimeters thick is poured. It is worth falling asleep in layers, with a thickness of each layer of 10-15 centimeters, while each layer should be compacted and wetted with water.

After all the pillars are erected, it is necessary to adjust them to a single horizontal level. Leveling can be done with a cement mortar. After that, you can proceed to the assembly of a monolithic or precast-monolithic reinforced concrete belt. If a wooden house is being built, then the first bundle of logs or beams begins to be laid on the aligned pillars.

It should be noted that the device of a monolithic reinforced concrete belt is a very important design moment, since it is it that ensures rigidity along all the pillars, as well as their stability. Before starting the assembly of the belt, it is necessary to connect all the jumpers to each other. This can be done either by welding or by tying loops with wire.

After that, formwork is placed on top of the lintels and concrete mortar is poured.

Column foundation on heaving soils with a large freezing depth

As noted earlier, in order to mainly reduce the effect of frost heaving forces on the foundation, it must be laid below the freezing level. However, some climatic zones are so cold that the level of soil freezing reaches 2 meters in depth.

In this case, ready-made metal or asbestos-cement pipes are used for the installation of foundation pillars. In the case of the use of such pipes, the foundation can be obtained in two types:

insulated foundation

• With fittings;
• With metal rod;

The design of the foundation with reinforcement looks like this:

• Pillow of sand 10-15 centimeters thick;
• Foundation block, for example FL 6-12-3, which has dimensions of 118x60x30 centimeters;
• Asbestos-cement pipe, which must have a diameter of at least 20 centimeters;

The asbestos-cement pipe is attached to the foundation block by means of concrete mortar, in addition, it is also filled with this mortar inside.

Also inside there is a reinforcement bush, which can be pre-welded, and then simply placed inside the pipe and filled with concrete. In this case, the reinforcement should protrude 10-15 centimeters beyond the edge of the pipe, so that later it can be welded to the grillage reinforcement.

The foundation with a metal rod can have the following design:

• Sand cushion 10-15 centimeters thick;
• The supporting reinforced concrete monolithic slab, which has a width of 60 centimeters, and a height of about 40;
• Asbestos-cement pipe;

Just as in the previous case, the pipe inside is filled with concrete, but instead of reinforcement, a metal rod is used, the diameter of which is 8-10 centimeters. The asbestos-cement pipe itself has a diameter of about 20-30 centimeters.

Foundation technology with reinforcement

On heaving soils, the reinforced foundation is assembled according to its own technology. First, a foundation block is placed on a pre-prepared pillow of non-porous soil, as a rule, it is coarse-grained sand. Then an asbestos or asbestos-cement pipe is placed on it. In order for the pipe not to move, fix its position on the ground level.

After that, at the very base of the pipe, that is, where it touches the foundation block, a cement screed is made that resembles sinuses. The screed is made at an angle of 45 degrees, that is, it is a right triangle in shape, where the foundation block serves as the lower leg, and the pipe wall serves as the side leg.

After that, you can move on to the device of the next column. Only when the concrete screed is completely dry and the pillar is securely fixed to the foundation block, you can proceed to the next step. It consists in the production of backfill, which must be carried out with the same soil that was delivered or with soil of a better quality in terms of heaving.

After all the pillars have been covered, you can begin to install reinforcing bushes or metal rods. In order to prevent the metal part from shifting during concreting, it is necessary to pour cement mortar into the pipe with a height of about 10-15 centimeters before starting the installation. After that, simply insert the armature into the solution.

When reinforcing the column, it should be taken into account that each reinforcement bar must be separated from the inner wall of the pipe at a distance of 2.5-4 centimeters.

Foundation construction technology with a metal rod

On heaving soils, a foundation with a metal rod is also erected according to its own technology.

First, a concrete slab is mounted, which can be a monolithic reinforced concrete slab. Then, without waiting for the plate to dry, they begin to mount the pipe directly into the fresh solution of the plate.

In this case, the pipe should only touch the plate, and the metal core should go to a depth of 10-15 centimeters. Further, all actions are performed in the same sequence as in the previous case.

The advantages of a columnar foundation over other types when arranging them in heaving soils

Summing up, we can highlight some of the advantages of columnar foundations over other types. These advantages are observed not only during the construction of foundations on heaving soils, but also under normal conditions:

It is also worth noting another positive aspect of columnar foundations - this is that the soil under a free-standing column works much more efficiently than under a foundation tape. This suggests that even in heaving and weak soils, a columnar foundation gives less settlement than a strip foundation, provided that they exert the same pressure per unit area of ​​\u200b\u200bthe support.

Measures aimed at reducing the effect of frost heaving forces on shallow and non-buried foundations

The forces of frost heaving, when building a foundation on heaving soils, begin to act after the laying of the first brick. To avoid their influence on the construction time, layer-by-layer salinization of heaving soils is used. A trench of small depth is torn off around the foundation and table salt is thrown in. Then, after 10 centimeters, the procedure is repeated.

The required amount of salt must be taken at the rate of 26-80 kilograms per cubic meter of soil - it all depends on which heaving soils the construction is being carried out on, that is, on the degree of heaving. This should be done as follows: first, we tear off a trench 10 centimeters wide and 30-40 high, that is, on a spade bayonet, then we throw the soil back, while loosening it. Then we fall asleep salt and again mix with the soil.

On heaving soils, this is very effective, but you should be careful, as salt can damage some building materials.

Oil is also used to reduce the forces of frost heaving on heaving soils. The soil that touches the foundation is impregnated with an oil solution to a depth of 5-10 centimeters. The solution consists of the following components:

• Diesel fuel about 54 percent;
• Bitumen, which has a high degree of oxidation, on the order of 20 percent;
• Calcium oxide is about 20 percent;
• Alkylarylsulfonate, or NChK, about 4 percent;
• Water is about two percent of the total mass;

The solution can be prepared as follows:

• First, bitumen of a high degree of oxidation is poured into diesel fuel. Further, these two liquids are mixed and heated to a temperature of 45-50 degrees for about one hour;
• After that, the resulting liquid cools and mixes at normal temperature with the rest of the components for half an hour;

And finally!

As a conclusion, we can say that the device of a columnar foundation will be advisable in the following cases:

• With a sufficiently small mass of the structure;
• In heaving soils;

Indeed, it is the columnar foundation that is more effective in heaving soils, and especially if the depth of the foundation is large enough.

When choosing one or another type of columnar foundation, one should be guided by the laying conditions, hydrogeological conditions of the area and other factors that were described above.

Such foundations require accurate consideration of soil properties, impose increased requirements on the strength of building elements, the correct choice of design solutions and the quality of construction work.

There are serious theoretical justifications and a large successful practice of building low-rise buildings from any materials on these foundations. At the same time, the existing some negative experience of using shallow foundations, with an expert study, shows that The main reason for such negative situations is errors in the design and construction of buildings.

A necessary condition for the use of this type of foundation in a particular case is readiness and ability of the Customer to carry out high-quality work research, design and construction.

The use of such foundations certainly justified for wooden (log, lumber) or frame buildings, the walls of which are better able to withstand deformations.

Thermally insulated shallow foundation (TFMZ)

Heat-protected shallowly buried insulated foundation

Noteworthy, especially in areas with severe winters, are heat-protected, shallow-depth foundations that use both principles of compensation for frost heaving of the soil - increased rigidity and insulation of the foundation.

The thermal insulation of such a foundation is carried out in a lightweight version., allowing only to reduce the depth of freezing under the base of the foundation, and, consequently, the heaving force acting on the foundation.

Calculations and practice show that installation of only a vertical layer of thermal insulation to the entire height of the foundation and basement, from the base of the foundation to the outer walls of the house, capable of significantly reduce the depth of freezing soil under the foundation.

This combination allows, on the one hand, to reduce the size of the foundation heat-insulating skirt, and, on the other hand, to lighten the construction of the foundation of increased rigidity, compared to the original version without thermal insulation.

Foundation - slab, slab foundation

Foundation in the form of a monolithic reinforced concrete slab under the entire area of ​​the house- Another option for a shallowly buried foundation.

The large area of ​​support allows to significantly reduce the specific load on the ground. Reinforced reinforcement and high consumption of concrete make slab foundation is the most expensive in private housing construction.

The foundation is a slab for a private house, due to its high cost, it is advisable to use with a weak bearing capacity of the soil on the site.

The slab foundation, as well as other types of foundations, can be made with or without thermal insulation to protect against frost heaving of the soil.

should be distinguished slab foundation and a shallowly buried monolithic strip foundation with suspended

In the latter case, a monolithic reinforced concrete strip foundation and a monolithic reinforced concrete floor slab are poured over the ground.

In this option, a monolithic reinforced concrete the floor slab is not involved in transferring the load from the weight of the building to the ground, but plays the role of a floor slab and must be calculated for the standard load of floors, have appropriate strength and reinforcement.

The soil is actually used here only as a temporary formwork when constructing a reinforced concrete floor slab. This design is often called a "suspended floor on the ground."

Strip foundation with monolithic suspended floor slab often mistakenly considered a slab foundation with stiffeners. The structures are really similar, but there is a significant difference in details - reinforcement, dimensions.

In all cases, when constructing foundations, it is necessary to provide for water protection measures aimed at reducing soil heaving deformations - providing decrease in soil moisture, lowering, removal of surface water from the house by means of vertical planning, drainage ditches, flumes, trenches, etc.

shallow foundations should be use with caution for houses on steep slopes and slopes. For shallow foundations, the risk of shear (slip) is quite high due to the almost completely absent pinching in the ground.

As you can see, the choice of a fundamental design and the calculation of the foundation is a complex and responsible task. The final results primarily depend on a reliable assessment of the soils at the base of the building, which are quite difficult to obtain without surveys. The price of a mistake can be very high. An independent choice of foundation can be recommended for auxiliary, outbuildings and small garden houses.

It is wiser to order the design of the foundation for building a house to specialists.

Additional information on the construction and use of shallow foundations can be obtained from the book of one of the authors of SNiPs V.S. Sazhin "Do not dig deep foundations." Download books in djvu format 389 kb. And in PDF format 4150 kb(follow the link and select "File" > "Upload" in the menu at the top left).

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Hello!
I can't figure out the foundation! Please tell me!
We decided to build a 6X8.6 frame-panel house. Our soil is clay, loam, water from the surface of the earth is 10-15 cm! !

The choice of foundation type depends on the type of house. There are several types of foundations for wooden houses:

Tape shallow-depth of reinforced concrete;
- columnar with grillage;
- tape shallow-depth of small-sized elements;
- columnar;
- tape shallow-depth of small-sized elements on a reinforced concrete pad.

Based on my own experience, I would recommend:
1. Tape shallow-depth reinforced concrete;
2. Columnar with reinforced concrete grillage.
The pillars are buried to the depth of soil freezing.

Experts consider the tape monolithic shallow foundation, equipped with a powerful metal reinforcing cage, to be the most cost-effective, in terms of the reliability it provides. It is done as follows:

1. A geodetic survey is carried out to determine the possible level difference along the horizon. In the event of a significant difference in elevation, it may be necessary to remove part of the soil.

2. It is broken in kind of the house plan and the so-called. cast-off. The cast-off allows you to designate not only the center lines, but also the outer boundaries of the foundations and walls.

3. Earthwork technology depends on the type of foundation. For a shallow tape monolithic foundation, a trench 40-70 cm deep is dug along the perimeter of the wall (Photo 4). A sand cushion 30 cm thick is made in the trench and compacted.

4. A wooden formwork is installed, in which steel reinforcement is laid and properly fastened (Photo 5, 6).

5. When the reinforcing cage is ready, concrete is poured into the formwork. (Photo 8)

The result is a monolithic reinforced concrete frame that behaves like a floating slab or “tray” during operation. (Photo 6)
Even if underground forces set this frame in motion in the spring, it will move not in one corner, but in its entirety. Together with it, the wooden structure, standing on the frame as on a tray, will also move, but the whole will also move, without any damage: windows and doors will normally open and close at any time of the year. The sand cushion acts as a shock absorber during heaving of the soil.

It is better to make a columnar foundation with a grillage. The pillars are laid below the freezing depth so that the foundation is not subject to ground movements. It is better and cheaper to use poles made of asbestos or plastic pipes. Concrete is cast over the poles and a grillage tape is reinforced. The pitch of the foundation pillars is about 1.5 m. Such a foundation combines the advantages of a deep foundation and the low cost of a shallow one. Sincerely, Petrovich

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In your case, it is better to make a columnar foundation with a grillage. The pillars are laid below the freezing depth so that the foundation is not subject to ground movements. It is better and cheaper to use poles made of asbestos or plastic pipes. Concrete is cast over the poles and a grillage tape is reinforced. The pitch of the foundation pillars is about 1.5 m. Such a foundation combines the advantages of a deep foundation and the low cost of a shallow one. Sincerely, Petrovich