The article describes the features of solid slab foundations. The scope of their application, operational and design differences are discussed in great detail. Applied issues related to the technology of construction of foundation slabs are brought to the fore.

This is a continuation of the series of articles about foundations, and we have already published a lot of interesting material. Therefore we recommend:

A slab foundation, also known as “solid”, also known as “floating”, or “Swedish, Scandinavian slab”, is a solid slab located under the entire area of ​​the building, buried in the ground, or laid on it. There are several design options for slabs - box-shaped, flat, ribbed, prefabricated from road reinforced concrete products, monolithic, with extensions at the corners, with or without reinforcement, insulated and cold... They all have their own distinctive features and specific scope of application. For private suburban construction, in terms of economic and functional characteristics, flat monolithic reinforced concrete slabs with a thickness of 20 to 40 cm with insulation have proven themselves to be the best. We will talk about them further.

Why choose a slab foundation

In low-rise construction, which is what we are actually interested in, this type of foundation for many reasons will be preferable to its competitors (both strip and pile structures). This is explained by advantages of both a purely technical and construction-related nature.

Strengths of solid foundations

Universality in foundation geology. A floating structure can be correctly used on all types of soils, including weak-bearing, heaving, horizontally mobile, high groundwater levels, permafrost...

There are some restrictions on the terrain - it is difficult to build such a foundation on a slope; most likely, piles will be preferable. However, there are American-tested technologies for constructing slabs on hillocks, which in their design (in the lower part of the site) have elements of high monolithic strips. Another “centaur” suitable for such places is a pile foundation with a low grillage in the form of a monolithic slab.

Good load-bearing capacity. This quality is due to the specific mechanics of the “house/slab/soil” interaction. In the next chapter we will look at this point in detail. In short, the slab has a large support area, so the pressure on the foundation soil is very low (from 0.1 kgf/cm2). Consequently, a two-story stone house on a slab can be built with confidence. They say that the elevator shaft of the Ostankino Tower stands on a monolithic slab.

High spatial rigidity. It is due to the absence of seams and joints, the use of rigid reinforcement, the massiveness of the structure and high material consumption. The slab foundation is excellent for houses with “inelastic” walls, which are very afraid of even the smallest (1–3 mm) movements of the supporting structure - brick, aerated concrete, cinder block, shell rock and other mineral materials.

In the presence of excessively heaving soils and significant sensitivity of buildings to uneven deformations, it is recommended to build them on shallow and non-buried monolithic reinforced concrete slabs, under which cushions made of non-heaving materials are placed.

SP 50–101–2004 “Design and installation of foundations and foundations of buildings and structures.”

Good insulating properties. When properly executed, it does not allow water to pass through and prevents heat loss through the floor.

Simple construction technology, built quickly. Easy to mark, minimum excavation work, simplified formwork design, easy to reinforce and concrete. Can be manufactured by low-skilled builders.

Conditional disadvantages of a slab foundation

Technically, it is very difficult to combine a solid slab and a basement in a structure.

The slab can be poured only in favorable weather (it is slightly inferior to prefabricated and pile driven foundations).

High price. Increased material consumption (concrete, reinforcement), of course, leaves its mark. But if you look at the problem as a whole, the picture changes dramatically - we save a lot on other materials, construction stages, and production operations:

• the slab becomes the subfloor of the first floor - no need to make an overlap;
• You can lay a water heated floor in the mass of the slab, rather than pouring a separate screed for it;
• for the manufacture and fastening of formwork panels, less boards or sheet materials are needed (at least twice as much as strip structures);
• no need to pay for removal/planning of a large volume of selected soil;
• the height of the external walls is reduced, since it is possible to obtain a lower base (and these are expensive facade finishing materials, labor costs...);
• lifting equipment, concrete pumps, excavators, driving pile drivers, drilling machines are not needed, everything is limited to mixer vehicles;
• you can build it yourself and not hire highly paid professional builders, there is less risk of suffering financially from the “human factor” (simpler technology).

It turns out that the main disadvantage of slab foundations is the low awareness of domestic developers about their advantages. But in the northern part of the USA and Scandinavian countries, monolithic slabs have become the No. 1 foundation.

The principle of operation of a slab foundation

Situation

The building density is growing, people increasingly have to build on “bad” soils (weak, constantly wet, heaving, frozen...).

Modern projects of country houses have become much more complex in terms of architectural and planning solutions: different parts of the building are built at different heights (options of one and a half floors, attached garages, special solutions for staircases and landings...), uneven distribution of load-bearing walls over the building area. Houses are now bigger, higher, heavier.

Problem

On top of the foundation and on the natural foundation there are uneven impacts from the house. From below, complex soils either tend to form local failures under the building, or forces of frost heaving push the building out, and then, when thawed, sag. There is a danger of deformation and destruction of supporting structures.

Solution

Increase the supporting area of ​​the foundation, reducing the load from the house on the natural foundation.

Maximize the spatial rigidity of the foundation and evenly redistribute the pressure from top to bottom.

Use a heat insulator to separate the heated rooms from the ground under the house - thus eliminating uneven freezing under the building (in winter, the ground under the slab does not thaw).

All these methods of dealing with “unevenness” are inherent in the principle of operation of an insulated monolithic slab. This is a kind of single platform under the house, which is not subject to local bending (if properly designed), and without deformation is able to actually move with the ground - “float”.

Features of designing a slab foundation

Slab design differs significantly from methods for developing other types of foundations. Here, engineers also take into account all the main soil parameters and all loads (weight of structures, operating weight, snow pressure). SP 20.13330.2011 has not been canceled.

However, the slab foundation must be considered as a single, jointly working “slab-above-foundation part” structure. Therefore, in this case, special attention is paid to a detailed study of specific components of the building and the supporting structure as a whole; drawings of the house are created and calculated, indicating diagrams of load distribution and their directions.

The whole problem lies in the difficulty of competently modeling bending loads, possible rolls that the slab experiences, and, accordingly, calculating its thickness, configuration, and the need for reinforcement, including local reinforcement. The most efficient design of foundation slabs is carried out using special computer systems that produce very detailed working drawings. That is why we recommend ordering a foundation slab calculation from a specialized organization; the cost of such work will range from 5 to 10 thousand rubles.

The most widespread are slabs with a thickness of 20 to 40 cm, but one detail is very interesting: most calculations show that different slab thicknesses can be used for the same house if the percentage of reinforcement is correctly manipulated.

For example, a solid foundation for some abstract building. At 20 centimeters, it is necessary to carry out local “additional reinforcement” of especially loaded areas and not make mistakes in the calculations; at 25 centimeters, the frame can be knitted evenly, without particularly risking. But a 30-centimeter slab, when compared with a 25-cm structure, will not allow you to save on reinforcement, but it will use much more concrete.

Exceptionally competent calculation allows you to cast slabs even with a thickness of 15–18 cm.

Note that it is possible to significantly increase the resistance of the slab to punching, while reducing its overall thickness (read material consumption) by making local thickenings of the foundation in the area of ​​the corners, the junction of load-bearing walls, along the entire perimeter, under the columns. Such reinforced slabs are often called “American”; in cross-section they look like a prism.

The slab foundation cannot be smaller in area than the house; all cantilever sections must be taken into account. For example, if the building will be faced with brick or other heavy materials, then the slab must be laid in large sizes to provide a supporting area for the cladding.

Slab foundation construction technology

Since slab foundations are often used in very difficult geological conditions, the most stringent requirements are imposed on the planning and construction of floating structures, which are stipulated by many regulatory documents, for example, SNiP 3.03.01–87 “Load-bearing and enclosing structures” or SP 50–101– 2004 “Design and installation of foundations and foundations of buildings and structures.” Naturally, only high-quality materials should be used for the construction of foundation slabs.

The construction of all solid foundations is carried out approximately according to the same scheme:

• Design.
• Marking (only the outlines of the building are taken into reality).
• Removing turf, sampling soil (if cushion/drainage is necessary).
• Laying buried communications (water, sewerage).
• Installation of cushion and drainage.
• Installation of hydro- and thermal insulation.
• Assembling a “warm floor”.
• Knitting and laying of reinforcement cage.
• Assembling and unfastening formwork.
• Concreting.
• Stripping.

Let's look at these operations in more detail.

We have more or less figured out the design. If you are building something serious, it is better to order the development of a foundation project from engineers, and you will definitely save your nerves and money.

We have already discussed the issues of carrying out preparatory work and carrying out markings in situ in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement.”

As for earthworks. If soil replacement (massive cushions) and insulation are not required, then it is enough to remove only the top fertile layer, otherwise, the soil of the natural foundation is removed in the required volume. Sometimes, before excavation, it makes sense to level the building area - to make bedding. Then the additional material is very carefully compacted with a vibrating plate.

The most important condition is that the bulk soil under a slab foundation should not be inferior to the mainland (natural) in any way.

There is no need to worry that it will be difficult to maintain communications under the slab. Everything is done as usual: where there will be a technical room, a pit is always made in the slab for entering communications (foam is laid near the pipes, or a contour is made from formwork), the smaller it is, the better for the rigidity of the foundation. In any case, the pipes cannot be sealed tightly. Under the slab, communications run in a trench and are covered with drainage materials. Read about drainage of communication lines in the article “How to make drainage on a site.”

The cushion is an artificial base, it is designed to replace “bad” soils. The material for the cushion is most often a mixture of sand and crushed stone, which have good drainage properties, have little compression, and do not heave. The sand and gravel cushion is laid in layers of 100 mm, and each layer is carefully compacted with a vibrating platform. If clean sand is used, it must be spilled with water.

It is necessary to periodically check the horizontalness of each layer of pillows.

In areas with unfavorable water balance, it is recommended to lay several drains under the slab (cushion) to drain water.

Most technological maps for the production of solid foundations suggest laying geotextiles under the cushion, which prevents sand and gravel from silting (read: losing properties that are important to us).

In order for the hydro- and thermal insulation to fit well and not be deformed by the mass of concrete, the upper part of the cushion must have the most even plane possible. Some manufacturers of floating foundations even prefer to make a preparation screed from sand concrete.

The cushion is covered with a thick polyethylene film or other waterproofing materials that will prevent laitance from leaking during concreting. The sheets are laid overlapping and glued/soldered.

A layer of insulation up to 100 mm thick is laid on the waterproofing. Previously, they used polystyrene foam, but now everyone has switched to extruded polystyrene foam. Some builders believe that insulation is not a necessary layer, but it reduces heat loss through the slab and does not allow the soil under the slab to thaw uncontrollably and unevenly even under heated rooms. If you want to use a warm floor, you will not heat the ground, but let all the heat into the house. In the technological maps of foreign companies, it is recommended to lay the insulation (and pillow) outside the slab.

Heated floor pipes are laid out directly onto EPS sheets using a special mesh; naturally, they are not insulated with any materials in order to better transfer heat. Some heating routes can also pass through this layer - they are carried out in sleeves and heat insulators. All ends are removed from the pit for communications, the system is ringed and crimped. Under pressure, air pumped into the pipes prevents them from deforming when pouring concrete.

Reinforcement is perhaps the most difficult operation in the construction of floating foundations. This is where the most mistakes are made, both technological and design.

Let's start with the main thing. According to SP 52–103–2007, the minimum percentage of reinforcement for a reinforced concrete slab is 0.3%. It is calculated as follows: take a cross section of the slab and calculate its area, calculate the total cut area of ​​all reinforcing bars, and compare these indicators. If the metal content of concrete is insufficient, then increase the diameter of the reinforcement or the number of rods (reduce the pitch). For thick slabs, a third tier of metal is used, located in the thickness of the slab. Practice shows that most often it is enough to lay two layers of reinforcement with a diameter of 12–14 mm, and a pitch of 150–250 mm.

Do not forget that in loaded areas (columns, load-bearing wall inside a building...) additional reinforcement may be required by laying auxiliary longitudinal rods within the punching prisms.

Depending on the design of the building, it sometimes makes sense to install vertical reinforcement outlets under load-bearing walls and columns (SP 52-103-2007), which will provide additional rigidity to the “slab-above-foundation part” system.

The presence of a protective layer of concrete is a prerequisite for high-quality reinforcement. The reinforcement cage meshes are displayed on special polymer mushroom stands. The fungi of the lower tier are small, about 4–5 cm. The intermediate fungi (between two meshes) have a height depending on the thickness of the slab, so that about 5 cm of concrete (protective layer) remains above the upper reinforcement. The fungi are placed one above the other, their total number (step) should ensure sufficient resistance of the frame to the loads arising during concreting.

It is prohibited to use all kinds of linings made of wood, stone, and metal.

It is recommended (SP 63.13330.2012) to connect the ends of the frame, the upper and lower tier, with U-shaped elements made of reinforcement. The reinforcing bars should not come into contact with the formwork, since a protective layer of concrete with a thickness of at least 40 mm should be provided.

A frame of viscous reinforcing bars is made using wire. The use of electric arc welding is allowed, but then it is necessary to use class A500c fittings, or similar, with the index “C”.

Due to the large volume of reinforcement work, it may be advisable to use standardized factory-made welded mesh. The joints obtained after laying must be placed in a “checkerboard” order - the joints of the finished mesh of the lower tier of reinforcement must be overlapped by the entire mesh of the upper tier.

The floating foundation formwork is very easy to assemble; you just need to level each side of the perimeter. Please note that a lot of concrete is used, and the pressure on the shields will be quite serious - so lift them off the ground very well.

The formwork should be wrapped inside with polyethylene to prevent laitance from leaking through the cracks. As an option, you can lay EPS sheets near the formwork, then they will reliably “stick” to the concrete and provide vertical insulation of the slab.

Expanded polystyrene is also used to separate buildings adjacent to the house, which require their own foundation (garage, porch, terrace...).

A separate small formwork contour is made for the pit for communications.

You can read about formwork and reinforcement in the article “Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement.”

The nuances of making a monolith can be found in our publication “Strip foundation. Part 3: concreting, final operations.”

Concreting must be done in one work shift. The most rational way would be to order the delivery of concrete with a mixer and pour the foundation directly from the tray. For concreting remote areas, you can use a homemade gutter.

Concrete must be compacted with an in-depth vibrator.

For the manufacture of slab foundations, concrete is used with characteristics that are regulated by SP 52–103–2007. Most construction companies producing floating foundations offer to order concrete with the following performance properties:

• strength class from B22.5 (grade not lower than M300);
• water resistance coefficient from W8;
• frost resistance from F200;
• mobility P-3;
• possibly sulfate resistant if groundwater is high.

Taking into account domestic realities, it is better for a private developer to order concrete at least a grade higher than the standardized one - there will be a greater chance of obtaining the design strength class.

Next, you should carry out manipulations to care for the concrete. When the slab reaches 50% strength, the formwork can be removed. We examined these works in detail in the article “Strip foundation. Part 3: concreting, final operations,” we will add that the next day after pouring the floating foundation, the upper plane of the slab should be rubbed down - this will be a good base before installing any floor coverings.

In Northern Europe and the USA, floating foundations have been actively used for more than half a century; over time they have proven their reliability, functionality and economic attractiveness. In our country, the slabs also found their developer. From year to year, solid foundations are becoming more and more popular, since in many cases there is simply no alternative to them.

Turishchev Anton, rmnt.ru

http://www. rmnt. ru/ - RMNT website. ru

They are a type of shallow, or rather, non-buried foundations, the depth of which is 40 - 50 cm. Unlike shallow strip and column foundations, they have rigid spatial reinforcement along the entire load-bearing plane, which allows them to withstand alternating loads that arise during uneven movement without internal deformation soil.

Foundations that, together with the soil, move seasonally are called floating. Their design is a solid or lattice slab made of cast-in-place reinforced concrete, precast cross-beams or precast slabs with a monolithic cover (Fig. 1).

The construction of a slab foundation is associated with the consumption of concrete and reinforcement and may be advisable when constructing small and compact houses or other buildings when a high base is not required and the slab itself is used as a floor. For higher-class houses, foundations are often installed in the form of ribbed slabs or reinforced cross strips.

The large support area of ​​the slabs makes it possible to reduce the pressure on the ground to 10 kPa (0.1 kgf/cm2), and the cross stiffening ribs create a structure that is sufficiently resistant to alternating loads that occur during freezing, thawing and subsidence of the soil. For their construction, high-strength concrete (not lower than class B12.5) and reinforcing bars with a diameter of at least 12 - 16 mm are used. The relatively large consumption of concrete and reinforcing steel can be considered justified if all other technical solutions for foundations under these conditions cannot guarantee their reliable operation. In buildings where the floors are located low above the ground level, such foundations can be even more economical than columnar foundations (there is no need to install a basement floor and grillage).

A solid, non-buried slab as part of the spatial system “slab - superfoundation structure” ensures the perception of external force influences and possible deformations of the soil foundation and eliminates the need for various kinds of measures to prevent uneven deformations of the soil, which usually require significant resources in conditions of weak, sandy and heaving soils.

The use of non-buried foundation slabs allows reducing concrete consumption by up to 30%, labor costs by up to 40% and the cost of the underground part by up to 50% compared to buried foundations. To protect such foundations from freezing, they must be insulated.

Frost-resistant shallow foundations are a practical alternative to more expensive deep foundations in cold regions with seasonal ground freezing and potential for frost heave. Shallow laying of frost-resistant foundations is achieved by installing thermal insulation placed in the most important places - practically around the house. Thus, it becomes possible to carry out foundations with a laying depth of 40 - 50 cm even in very harsh climates. The technology of frost-resistant shallow foundations has gained wide recognition in the Scandinavian countries. Frost-resistant foundations are made in the form of a monolithic reinforced concrete slab 25 - 20 cm thick with thickened edges - contour ribs, and foam insulation (foam plastic) is used to protect against frost (Fig. 2).

Fig.2. Scheme of an insulated monolithic foundation slab with thickened ribs: 1 - continental soil; 2 - compacted sand cushion; 3 - monolithic reinforced concrete slab; 4 - insulation with waterproofing; 5 - concrete blind area	Rice. 3. Scheme of reinforcement of a monolithic slab: 1 - reinforcing bars AIII, d 12-16 mm; pitch 200 mm; 2 - reinforcing bars AIII, d 8 mm, pitch 400*400 mm; 3 - protective layer of concrete 35 mm thick

Heat escaping from the house into the ground through the foundation slab, plus geothermal heat, causes the frost line to rise up along the perimeter of the foundation. Experts know that heat from a building actually reduces the depth of freezing around the perimeter of the foundation. In other words, the frost line rises near any foundation if the building is heated or insulated at ground level.

Foundation perimeter insulation prevents heat loss and transfers heat through the foundation slab into the soil beneath the building's foundation. At the same time, geothermal heat sources radiate heat towards the foundation, which reduces the frost depth around the building.

When building houses using frost-resistant foundations, one of the problems that builders face is that polypropylene decomposes under the influence of ultraviolet radiation and has insufficient impact resistance. Vinyl chloride plastic in the form of a roll 610 mm wide, 15 m long is well suited for these purposes. The upper outer edge of the foundation is wrapped with film, starting from the inner edge of the slab. The plastic is easily bonded to the edge of concrete and polypropylene foam with a mastic compatible with the foam. Flexible vinyl chloride plastic is glued in place.

It is important to note the cost savings when constructing frost-resistant foundations in comparison with traditional ones. It accounts for approximately 3% of the total mandatory costs of building a house.

Solid slab foundations are also installed buried in the form of a monolithic slab under the entire building (Fig. 3). Such structures ensure the most uniform distribution of the load on the foundation and, as a result, uniform settlement of the building, and also protect basements well from groundwater backing up.

Solid foundations are erected on weak or heterogeneous soils when it is necessary to transfer significant loads to them. Such structures have proven themselves well in low-rise construction, especially if it is necessary to organize a basement or semi-basement under the building. The construction of basement or semi-basement premises affects another important aspect of design and construction - waterproofing (waterproofing, etc.) of foundations from groundwater and moisture. A competent assessment of the hydrological situation at the construction site, the correct choice of water protection scheme and high-quality work are the main conditions, the fulfillment of which largely determines the trouble-free operation of both the underground and above-ground parts of buildings.

Violation or destruction of the structure of a building is almost always associated with violations or destruction of its foundation. This may occur due to errors made during design or construction. Only with a responsible approach to the entire range of work - from design to practical implementation - can you build a reliable house that will last for many decades. Options for installing non-buried slab foundations are shown in Fig. 1.

On soft soils, characterized by increased compression, the best option for foundation of a house is a solid foundation. The beginning of construction work on the construction of a house is associated with determining the quality of the soil at the construction site, the depth of groundwater, the level of freezing and the material from which the construction will be carried out. In addition, it is necessary to determine the number of storeys of the building, because the load exerted directly on the base of the house depends on this. The construction of a solid foundation is necessary in cases where the load on soft soil is quite large. Such a foundation is a monolithic concrete slab located under the entire area of ​​the building.

Features of a monolithic foundation

The main feature of a solid monolithic foundation is that it can withstand a high degree of load, since the slab is made using a reinforced frame that occupies the entire area of ​​the building. Such a base has a flat, smooth surface and therefore can serve as a basement floor.

To install a solid foundation, it is necessary to erect formwork and allows construction to be carried out on any soil.

Even moving soil is incapable of damaging the integrity of the structure, and the evenly distributed load makes it possible to erect buildings on such a foundation, both the lightest and the heaviest, consisting of two or more floors.

Installation of a solid foundation is justified when carrying out construction work on buildings:

• on soil with a high sand content;
• in wetlands;
• on subsidence and peat soils.

A solid foundation is also irreplaceable in areas where a characteristic feature is the presence of soil close to the surface.

The use of a solid foundation is necessary when constructing buildings in soils prone to significant swelling. A slab made of reinforced concrete is located over the entire area of ​​the building being constructed and does not lose its strength and shape, moving, if necessary, along with the soil.

Work on the construction of a solid foundation

First of all, before starting work, you will need to perform a calculation to determine:

• slab thickness;
• slab laying depths;
• total base area.

In order to significantly increase the strength of the building, the area of ​​its base is increased by one or even two meters in each direction. When performing calculations, it is necessary to take into account the bearing capacity of the soil and the increase in load due to interior walls, ceilings, installed furniture and equipment. To obtain more accurate results, add 150 kg/m2 to the weight of the building itself, then the resulting number must be divided by the area of ​​the house. The brand of cement used to prepare concrete is also taken into account.

M500 grade cement makes it possible to obtain a composition that, when hardened, can withstand a load of 500 kg/m2; accordingly, the thickness of the base slab will be at least 50 centimeters.

Using reinforced concrete slabs, builders receive a reliable and durable foundation for light frame structures and heavy multi-story buildings.

Installation of a solid foundation

Pouring a monolithic slab

Reinforced concrete solid foundations are erected in several stages:

• marking the site intended for construction;
• erection of formwork;
• installation of reinforcement frame;
• pouring concrete.

To build a small house of a regular shape, you can use ready-made reinforced concrete slabs, but if the project of the future building is drawn up taking into account the wishes of the owners and the house has non-standard shapes and sizes, then it is necessary to pour concrete in accordance with the available data.

Marking

Before you begin marking the site, you should carefully prepare the site, getting rid of debris and vegetation. Then you need to use a level to achieve a perfectly flat surface on which the markings will be carried out. Transferring the plan of the future house drawn up according to the project to the surface of the earth requires the use of special marks, pegs, and laces. The construction thread should not be made of nylon. A stretchable cord is not able to maintain its shape and size, which means that the markings made will be inaccurate. Watch the video on how to mark the foundation.

After the pit is ready, a sand and gravel cushion is placed at the bottom, which must be thoroughly compacted. Trenches are laid across the future foundation over its entire area, the bottom of which is lined with geotextiles, and then covered with gravel and crushed stone. This is necessary drainage.

Formwork and frame

The formwork for a solid foundation is placed, protruding beyond the pit by 20 cm along the entire perimeter. The bottom of the pit is covered with a layer of crushed stone, the thickness of which must be at least 20 centimeters, and a solution based on a cement-sand mixture is poured on top of it, performing the first screed and creating a flat surface. It is covered with rolled waterproofing materials and the construction of formwork begins. Along the entire perimeter of the pit, supports are dug in for boards or panels, from which the formwork will be erected. The work is carried out under level control. Watch the video on how to install formwork for a solid foundation.

A reinforced mesh is laid on the surface of the first screed, rods are installed vertically at a distance of 20 cm, to which the lower mesh and, later, another upper mesh are tied.

The structure is fastened using annealed wire. The use of welding will lead to the formation of bridges that promote the development of corrosion.

Pouring concrete

When starting the final stage of work, you must remember that to create a reinforced concrete slab, you can order a ready-made solution, or you can prepare it yourself. But the hardening time is only 3-5 hours, and therefore you may not have time to prepare the concrete yourself. Therefore, it is worth spending money and ordering a mixer with ready-made concrete. The supplied solution is distributed over the base area using a rule, and then compacted using a vibrator.

There should be no metal components visible above the surface of the finished slab, so using a level, even before pouring begins, the height corresponding to the thickness of the foundation is marked on the vertical rods.

Foundations of different types can be erected under suburban and multi-storey buildings. For example, in some cases, solid slab foundations are poured under houses. Such grounds, in turn, can also be classified into several types. Before starting to pour a solid foundation, of course, its design must be drawn up.

Necessity of application

Slab foundations are one of the most reliable types of house foundations. In this regard, they are superior to tape and columnar ones in any case. However, the area of ​​this type of structure is very large. They are solid foundations - a single thick slab under the entire house.

The construction of such structures is, of course, very expensive. In addition, for example, when building a low-rise country house, foundations of this type, unlike others, cannot be filled with concrete using homemade means. In this case, the cement mortar has to be ordered ready-made. Liquid concrete is poured into the formwork when constructing such a foundation from a tank using a hose. And this, of course, makes the construction of the foundation even more expensive.

Due to the high cost, foundations with a solid slab are built under houses quite rarely. Their construction is considered advisable mainly only when the building is built on non-static soils. In this case, a solid slab can maintain the integrity of other building structures during movements.

Also, foundations of this type can be erected under various types of small-area buildings. For example, sometimes garden gazebos are built on such a foundation. Most often, under such structures, of course, columnar foundations are built. A solid foundation, however, in this case can also be a good solution.

The slab under the gazebo or small extension, of course, will be very small in size. If the concrete depth is shallow, it won’t take much. In addition, it will be possible to fill the slab under the gazebo without the use of special equipment and assistants - manually at a time.

Main types by filling method

When building houses, solid foundations can be erected:

not buried;

shallow;

strongly buried.

The first can only be used in areas where there is no frost heaving. They build exclusively lightweight houses of small area on shallow foundations. The thickness of such structures, depending on the type of soil, can vary between 30-50 cm. Sometimes heavy brick houses are built on such foundations. But the use of non-buried foundation slabs under such structures is allowed only on rocky soils.

Shallow foundations are usually erected during the construction of small private houses. The pit under them is dug very shallow. In most cases, when pouring such a foundation on an area according to the markings, the top fertile layer of soil is simply removed. Deeply buried foundations are built only on heaving soils under heavy buildings.

Types by design

In this regard, solid foundations are distinguished:

monolithic;

lattice.

The first type of foundation is a regular concrete slab. Solid monolithic foundations are the simplest and most popular type of such structures. But on very unreliable soils, foundations with stiffeners can also be installed. The latter are poured directly under the slab.

Sometimes the ribs at the lattice bases can be directed upward. In this case, the walls of the building are erected on them using approximately the same technology as on strip foundations. When using this type of solid foundation in a building, among other things, it is possible to equip a basement. This is how deep slab foundations, for example, are often poured.

Design

When developing drawings of a solid foundation, of course, first of all you should decide on its thickness. When constructing high-rise city buildings, such calculations are made exclusively by specialists using various kinds of formulas.

In individual construction, a design for a solid reinforced concrete foundation for a small house can be developed independently. In this case, most likely, you won’t even have to calculate anything. There are standard indicators for the thickness of such foundations for certain types of buildings, which can be used as a guide in the process of drawing up a project.

So, for example:

gazebos and light extensions are erected on solid foundations 100-150 mm thick;

under light frame private houses, as well as one-story log and cobblestone houses, foundations of this type are most often poured to a depth of 200-300 mm;

under concrete structures or brick or two-story log buildings, solid foundations with a thickness of 250-350 mm are erected;

under two- or three-story houses made of brick or concrete, it is necessary to pour slab foundations at a depth of 300-400 mm.

Load collection

If you wish, of course, you can independently make a more accurate calculation of the solid foundation when building a country house. The collection of loads when pouring such a structure is determined taking into account:

constant pressure from the roof, ceilings, walls, etc.;

temporary loads - snow, furniture, people.

The permanent load is calculated depending on the materials used to assemble the building structures and their parameters. According to the standards, the mass of the walls should be taken minus the openings.

The weight of the slab itself when performing calculations of solid foundations:

• not taken into account on sandy soils;

  on clayey ones it is divided in half;

  on quicksand it is taken into account completely.

The snow temporary load on the foundation is determined according to Table 10.1 SP. In this case, the parameter is taken for this specific area. Uniformly distributed loads for residential buildings are assumed to be 150 kg/m2. The weight of very heavy objects that are supposed to be placed in the house is taken into account separately.

Selection of materials

The collection of loads on such foundations is calculated in the same way as on columnar and strip foundations. A solid foundation, like any other, is poured in most cases, of course, from a concrete mixture. Having determined the thickness of such a foundation, you can easily calculate the amount of material required for its construction.



Concrete for the construction of solid foundations is usually used grades B15-B25. You can, of course, pour slab foundations using a higher quality and durable mortar. However, this is usually considered impractical due to the increased cost of work. One of the undoubted advantages of slab foundations in any case is increased strength.

In addition to concrete, to build such a foundation you will also need materials such as sand, reinforcing bars and waterproofing. To assemble the formwork you will need to prepare boards. According to the standards, lumber with a thickness of at least 30 mm must be used to create a pouring form for the slab base of a house. Before pouring the solution, it is recommended to cover the formwork boards with plastic film.

Concrete and reinforcement

Calculate the amount of material required to fill such a base, in addition to the thickness of the slab, taking into account the fact that:

at the edges the foundation should extend beyond the building by at least 10 cm;

the reinforcement rods for the slab should be 6 cm shorter than it;

rods are installed when pouring in increments of 40 cm;

the sand cushion should also extend 10 cm beyond the building;

When pouring, the waterproofing material is laid with a small margin.

It is advisable to use roofing felt as a waterproofing agent for pouring such a foundation.



Work order

Slab foundations are poured in several steps. A pit of the designed depth is first dug on the site.

At the next stage, when arranging a solid slab foundation, a multi-tiered reinforcement frame connected with the use of wire is installed on the sand cushion. In order for the volumetric mesh to subsequently appear in the thickness of the concrete, special plastic stands or bars 5 cm thick are first placed at the bottom of the pit.

At the final stage, concrete from the tank is poured into the pit. During the process of laying the mixture, any defects that appear are manually eliminated. From time to time, the concrete layer in the pit is pierced with shovels to eliminate air bubbles. At the final stage, carefully level the surface of the slab.

To fill a lattice solid foundation, longitudinal trenches are dug in the pit before filling with crushed stone. The concrete poured into them subsequently forms ribs.



The final stage

After the foundation is poured, it is advisable to cover the slab with plastic film. Subsequently, the slab should be periodically moistened with water for 2 weeks. This will avoid the appearance of surface cracks. It is allowed to erect walls on such a foundation, as on any other, only after the concrete has fully matured. That is, approximately 28 days after pouring.

At the moment, even a small building requires a reliable foundation. It is the key to the strength of the structure and its durability. But when building a house or other similar structure, the same question arises: what foundation is best to use and what technology should it be poured using? The answer lies in a number of factors: the number of floors in the building, its area, weight, soil characteristics and much more. But in the vast majority of cases, the best option is a solid foundation. We will talk below about how to do all the work of filling it yourself.

The most in demand is a solid monolithic foundation in unstable soils - they have weak bearing capacity. It is also great in places where water is close to the surface. It is also indispensable for construction on old landfills, in sandy areas and where the soil is prone to significant swelling due to temperature changes. It is simply necessary when a building is erected on subsiding, weak-bearing, waterlogged, peaty soils. The main advantage of such a foundation is obtaining an acceptable supporting area on a relatively small plot of land. It is used in the construction of both massive heavy houses and small private buildings. The foundation is truly universal and can be used in almost any conditions, which is a big plus. How is a slab foundation constructed? Peculiarities The standard device for a solid foundation is a solid reinforced concrete slab, which is placed over the area of ​​the building being constructed. In fact, such a structure can partially move along with the soil without losing its shape and strength. Such a monolithic structure significantly increases the building’s resistance to any loads that may appear due to land subsidence or changes in weather conditions, which is very important for our climate zone with cold winters and hot summers. The tiled foundation consists of three main elements: fittings D12 A3; geotextiles; sand cushion. How to lay a solid foundation with your own hands? Stages of work The main thing to remember is that at all stages of construction, in order to avoid unpleasant consequences, you cannot do anything at random. Accurate calculations and application of knowledge in practice according to the prepared plan will allow you to efficiently do what every man is obliged to do - build a house. Start with calculations of key parameters The first thing you need to do is calculate a solid foundation with maximum accuracy. You must determine how thick the slab will be, as well as the area and depth at which it will be laid. Keep in mind that the area of ​​the slab is slightly larger than the area of ​​the house being built. It is best when it is one to two meters wider in each direction. This will not be a big blow to your budget, but it will significantly add strength to the building. The area of ​​the foundation is calculated relative to the total weight of not only the building, but also the foundation itself. Don't forget that he puts pressure on himself. It is also necessary to take into account the bearing capacity of the soil where construction will take place. For ordinary dry soil it is approximately 2 kg per 1 cm2. Important! Be sure to also take into account the weight of the floors between rooms in the house, the roof, and even ordinary snow, which will put pressure on the building from above for several months a year. Please note that there will still be furniture, appliances and the residents themselves. Thus, you need to add another 150 kg/m2 to the resulting weight. When you get the total weight of the future building, divide it by the area. Now you can calculate the parameters of the foundation, also taking into account the type of soil. If your house is planned to have two floors, the miscalculation remains the same. If the weight is 300 tons, and the area is 100 m2, then the load per 1 cm2 will be 300 g. In this case, if you use M500 concrete, the foundation can be quite thin - about half a meter. The strength of concrete is 150 kg per 1 cm 2. Preparatory work The construction of the foundation occurs in several stages: First, you need to completely clear the area chosen for construction of all foreign objects. The surface should be as level as you can ensure. To achieve optimal results, you will have to be sure to use a level. Although not the fastest, the free way is to level the surface with a shovel. We recommend purchasing all materials for work in advance so that the process is not interrupted for additional purchases. When the surface becomes smooth and you have completely cleared it of foreign objects, you can start marking. It is necessary to fix marks in key places. You will also need to remove the top layer of soil. This is about half a meter. The top soil has weak bearing capacity, so it should be disposed of immediately. The process is labor-intensive, so we advise you to use an excavator or involve more people in the work. Doing this on your own will take a lot of time and effort. When you have prepared the pit, place a bed of sand and gravel on its bottom. You can use crushed stone instead of gravel. The quantity ratio becomes 2:3. This pillow needs to be compacted tightly. Thanks to it, the pressure on the soil is distributed evenly, moisture from the soil will freely flow under the house, and the force of frost heaving of the foundation will decrease. Lay trenches for reservoir drainage along the future foundation. It is necessary to lay geotextiles on their bottom, and pour crushed stone on top. We also recommend placing plastic pipes in the trenches. They also need to be sprinkled with crushed stone, and so that they do not become clogged, they must be protected with the same geotextile. But before you pour a solid slab foundation, you will need to do one more set of works. Reinforced frame and formwork Install rotary pit wells in the corners. The fact is that the foundation will most likely stand on soil with high humidity. Water will accumulate next to it. To avoid water collecting under the entire foundation, formwork is also installed. It must be installed in such a way that it extends beyond the proposed foundation by at least 15 cm. Now, another layer of crushed stone (20 cm) must be poured onto the bottom of the pit. Pour about 4 cm of concrete on top of it - it will act as the first screed. We recommend pouring a mixture of concrete and sand onto the crushed stone before pouring concrete - this will level the surface. Form the formwork for pouring the concrete. To do this, you need to dig racks along the entire perimeter of the foundation and nail any boards to them. Be sure to do this while checking the level. To form a reinforced frame, you will need two iron meshes: lower and upper. They must be connected by vertical rods that are placed 20 cm from each other. To connect them, use a special knitting wire. We do not recommend using welding. In this case, bridges are formed that are highly susceptible to corrosion. Only now can the foundation be poured, the solid slab of which, thanks to the previous steps, will be a truly reliable support. Pouring the slab This is the final and one of the most labor-intensive stages of creating a solid foundation. To implement it you will need a lot of time and effort. If possible, get yourself a couple of assistants who will help you prepare the solution and pour it into the formwork. To prepare the mixture, use ready-made dry mixtures, concrete ordered from manufacturers, or prepared yourself. Make a choice depending on your budget, time and effort. For concrete you will need cement, gravel and sand. You can use crushed stone instead of gravel. Pour the finished concrete into the formwork up to the sides. Important! Keep in mind that after 3-4 hours the concrete begins to set and harden, so everything needs to be done as quickly as possible, and the solution must be prepared right before you pour it. The foundation is ready! Features of columnar foundations It is also necessary to say a few words about the use of columnar foundations, because columnar and solid foundations are quite similar to each other, and the technology for creating both is quite simple, for which it has earned great popularity. Let's look at the key differences and features of the fill. Also begin work by clearing the area and making initial markings. Determine the number of pillars to be installed and dig holes of at least 0.6 m in the right places. The depth depends on the properties of the soil. Difficulties arise only in swampy areas. Here you need to make the base about a meter deep and at the same time a little wider. Cut the reinforcement according to the height of the foundation pillars and the roofing material, which needs to be rolled into a tube with a diameter of about 10 cm (it is better to make two layers) and wrapped around the reinforcement. Place a sheet of roofing material at the bottom of the hole so that the soil does not absorb moisture from the concrete. Now you can pour the first layer of concrete (10-20 cm) into the hole. Immediately insert the reinforcement with the roofing felt film on it into the hole. When you have filled the first ten centimeters, start adding soil around the post. It will prevent concrete from flowing out from under the tube. Thus, we fill the column to the top and move on to the next one. And so on until the last. The main advantage of such a foundation is its low cost and significant time savings. You also need to pay attention to the absence of the need to use removable formwork, which significantly saves time. Due to the fact that the post is wrapped in roofing felt, the soil does not freeze to it during the cold season and does not push it out - the roofing felt simply slides. A bag of cement will be enough for 5-8 columns. But it is still inferior in strength to a solid concrete slab, so it is not suitable for large and heavy buildings. Now nothing will stop you from starting the construction of a new house yourself and finishing it in the shortest possible time. And there is no longer any need to hire an expensive team of builders for work that you can actually do yourself.