Do-it-yourself foundation: step-by-step instructions for self-construction of the foundation. Solid foundation: types, classification, need for application, composition, calculation and application Solid foundation

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

The most demanded is a solid monolithic foundation in unstable soils - they have a weak bearing capacity. It is also great for places where water is close to the surface. It is also indispensable for construction in 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, weakly bearing, swampy, peaty soils. The main advantage of such a foundation is obtaining an acceptable footprint on a relatively small piece of land. It is used in the construction of both massive heavy houses and small private buildings. The foundation is really universal and can be used in almost any conditions, which is a big plus. How is the tiled foundation? Peculiarities The standard solid foundation device is a solid reinforced concrete slab, which is placed over the area of ​​the building under construction. In fact, such a structure can partially move with the soil without losing its shape and strength. Such a monolithic structure significantly increases the resistance of the building to any loads that may appear due to subsidence of the earth 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: armature D12 A3; geotextile; 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. An accurate calculation and application of knowledge in practice according to a prepared plan will allow you to do what every man is obliged to do - to build a house. Start with calculations of key parameters The first thing you need to do is to calculate the 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 ​​\u200b\u200bthe plate is slightly larger than the area of ​​\u200b\u200bthe house being built. It is best when it is wider by one or two meters in each direction. This will not be a strong 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. Do not 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 cm 2. Important! Be sure to also take into account the weight of the floors between the rooms in the house, the roof and even ordinary snow, which for several months of the year will put pressure on the building from above. Please note that there will still be furniture, appliances and the residents themselves. Thus, another 150 kg / m 2 must be added 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 calculation remains the same. If the weight is 300 tons, and the area is 100 m 2, then the load per 1 cm 2 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 takes place in several stages: First you need to completely clear the site chosen for construction from all foreign objects. The surface should be as even as you can ensure this. To achieve the optimal result, you will definitely have to use a level. Although not the fastest, but 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 even and you completely clean it all of third-party objects, you can start marking. In key places it is necessary to fix marks. You also need to remove the top layer of soil. It's about half a meter. The top soil has a weak bearing capacity, so it should be disposed of immediately. The process is time-consuming, so we advise you to use an excavator or involve other people in the work. It will take a lot of time and effort on your own. When you prepare the pit, lay a pillow of sand and gravel on its bottom. You can use crushed stone instead of gravel. The ratio of quantity becomes 2:3. This pillow needs to be tamped tightly. Thanks to it, the pressure on the soil is distributed evenly, moisture from the soil will freely go under the house, and the force of frost heaving of the foundation will decrease. Lay trenches for reservoir drainage along the future foundation. Geotextiles must be laid on their bottom, and crushed stone should be poured 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, protect them with the same geotextile. But before pouring a solid slab foundation, you will need to do one more set of works. Reinforced frame and formwork Install excavation swivel wells in the corners. The fact is that the foundation, most likely, will stand on soil with high humidity. Water will accumulate next to it. To avoid collecting water under the entire foundation, formwork is also installed. It must be installed in such a way that it extends beyond the intended foundation by at least 15 cm. Now it is necessary to fill up another layer of rubble (20 cm) at the bottom of the pit. Pour about 4 cm of concrete on top of it - it will act as the first screed. Before pouring concrete on crushed stone, we recommend also pouring a mixture of concrete and sand - this will level the surface. Form the formwork for pouring concrete. To do this, along the entire perimeter of the foundation, you need to dig in racks, and nail any boards to them. Be sure to do this according to the level. To form a reinforced frame, you will need two iron meshes: lower and upper. They must be connected with vertical rods, which are placed 20 cm apart. To connect them, use a special knitting wire. We do not recommend 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 really reliable support. Slab pouring This is the final and one of the most time-consuming stages of creating a solid foundation. It will take you a lot of time and effort to do it. If possible, take a couple of assistants who will help you prepare the mortar and pour it into the formwork. To prepare the mixture, use ready-made dry mixes, concrete ordered from manufacturers or prepared on your own. Make a choice depending on your budget, time and effort. You will need cement, gravel and sand for concrete. Gravel can be used instead of gravel. Pour the finished concrete into the formwork up to the very sides. Important! Keep in mind that already after 3-4 hours the concrete begins to set and harden, so everything must be done as quickly as possible, and the mortar should 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. Consider the key differences and features of the fill. Also start work with clearing the territory and initial marking. Determine the number of posts 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 a 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 must be rolled into a tube with a diameter of about 10 cm (it is better to make two layers) and wrap the reinforcement. Place a sheet of roofing material at the bottom of the pit so that the soil does not absorb moisture from the concrete. Now the first layer of concrete (10-20 cm) can be poured into the pit. Immediately push the reinforcement into the pit with a roofing film put on it. When you fill in the first ten centimeters, start pouring earth around the column. It will prevent the concrete from flowing out from under the tube. Thus, fill the column to the top and move on to the next one. And so to 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 column is wrapped with roofing material, the soil does not freeze to it in the cold season and does not push it out - the roofing material simply slides. At the same time, a bag of cement will be enough for you for 5-8 columns. But in terms of strength, it is still inferior 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 on your own and finishing it as soon as possible. And it's no longer necessary to hire an expensive team of builders for a job that you can actually do yourself.

Solid foundations are: slab beamless, bar-beam and box-shaped (Fig. 18.1). Box-shaped foundations have the greatest rigidity. Solid foundations are made with especially large and unevenly distributed loads. The configuration and dimensions of the solid foundation in the plan are set so that the resultant of the main loads from the structure passes approximately the center of the sole.

In some cases of engineering practice, when calculating solid foundations, the approximate distribution of the reactive pressure of the soil according to the law of the plane is sufficient. If on a solid foundation, loads are rarely distributed, unevenly, it is more correct to calculate it as a slab lying on a deformable foundation.

Under the action of the reactive pressure of the soil, a solid foundation works like an inverted reinforced concrete floor, in which the columns; serve as supports, and the foundation structural elements experience bending under the action of soil pressure from below. In accordance with what is stated in subchapter 17.3, for solid foundations, the calculation of slabs on a compressed layer of limited depth and, in some specified cases, based on bed coefficients, is of practical importance for solid foundations. The solution of such problems is beyond the scope of the course.

Fig.18.1. Solid reinforced concrete foundations

a - slab beamless; b - slab-and-beam; c - box-shaped

In buildings and structures of great length, solid foundations (except for end sections of short length) can be approximately considered as independent strips (ribbons) with a width, the main unit, lying on a pliable foundation. Their calculation on a base with a bedding coefficient corresponds to that described in subchapter 17.3, and the calculation on a compressed layer of limited depth is explained below.

Beamless foundation slabs are reinforced with welded meshes. Grids are accepted with working reinforcement in one direction; they are stacked on top of each other in no more than four layers, connecting without overlapping in the non-working direction and overlapping - without welding in the working direction. The upper grids are laid on the frame-stands.

Slab-and-beam solid foundations are reinforced with welded meshes and frames. On fig. 18.1 shows an example of reinforcing the foundation of a multi-storey building. Double longitudinal and transverse meshes are laid in the thickness of the slab. The most stressed zone is additionally reinforced with a double layer of longitudinal meshes. For local bending, the slab is reinforced with top reinforcement grouped into grids of three working rods; gaps are left between them for access to the lower reinforcement. In the ribs, flat frames are combined into spatial frames by welding of transverse rods and are connected with slab reinforcement with pins.

A slab of unit width, isolated from a solid foundation together with a base, is considered as a plane problem under plane deformation according to the classification of the theory of elasticity.

1 - columns; 2 - ribs; 3 - plates

Fig.18.1. An example of the construction of a solid slab-and-beam

foundation

a - diagram of the foundation design in plan; b-layout welded

grids in plan; c - details of reinforcement of foundations; g - welded

First of all, they are the type of house (brick one-story, brick more than 2 floors, foam concrete house, light frame or panel house, etc.) which determines the weight of the building, and, accordingly, its pressure on the ground. In addition, the determining parameter is also the type of soil, the depth of seasonal freezing and the level of groundwater.

When the load on the foundation is high and the soil is weak, solid foundations are used. They are a solid reinforced concrete slab under the entire building area.

There are two types of solid foundations: from slabs and from cross tapes. They are erected from monolithic reinforced concrete to give the foundation spatial rigidity.

Slab foundations erected under the entire area of ​​the building are a solid or lattice slab made of monolithic reinforced concrete or precast cross reinforced concrete beams with rigid sealing of butt joints. Most often they are used in weak heterogeneous soils with a high level of groundwater, as well as in cases where the load on the foundation is large, and the base soil is not strong enough. Such a foundation well withstands all vertical and horizontal movements of the soil, the slab moves with it, protecting the house from destruction. Thanks to this feature, he received another name - floating.

The use of foundations of this type is practiced mainly in low-rise construction, as well as with a small and simple form of the building. They are built, as a rule, on problematic soils: wet or with a high level of groundwater. The disadvantage of this type of foundation is its cost, they are quite expensive due to the high costs of earthworks, concrete and metal reinforcement. Nevertheless, if the use of foundations of another type cannot provide the structure of the house with the necessary stability, it is advisable and more than justified to use solid foundations. This applies to small and compact houses or other buildings where a high plinth is not required, and the slab itself is used as a floor (for example, garages, saunas, etc.). For houses of a higher class, foundations in the form of ribbed slabs or reinforced cross tapes are more often arranged.

When building solid foundations, there are some points that need to be given special attention. First of all, this concerns the process of preparing the foundation for the foundation. The top fertile soil layer has a very low bearing capacity, and also tends to be compressed. Therefore, it must be removed to a depth of up to 0.5 meters. As a pillow, a mixture of crushed stone and sand is used in a ratio of 60/40, respectively. A well-placed and compacted pillow reduces the likelihood of swelling of the lower part of the foundation when the temperature drops. Secondly, it is necessary to evenly distribute the pressure on the ground and allow groundwater to pass unhindered under the building. The sand cushion does not accumulate moisture in itself, and the deep-set building prevents the ground from freezing in winter, thereby providing greater stability to the house.

The thickness of reinforced concrete foundation slabs is calculated during the design, as a rule it is 200-300 mm. Reinforcement is carried out in the upper and lower parts of the slab from rods with a thickness of at least 12 mm in increments of 200 * 200 or 300 * 300 mm. The thickness of the sand cushion is selected depending on the bearing capacity of the soil, the level of groundwater and the mass of the house, and ranges from 200 to 500 mm.

A slab (monolithic) foundation is a structure around the entire perimeter of which a solid slab is installed, for example, made of reinforced concrete. Such a solid, mainly reinforced concrete product is located, under the entire area of ​​\u200b\u200bthe building. Such a foundation is able to cope with any loads that a subsequently erected structure can exert on it. The slab foundation is divided into 2 types: buried and non-buried. The device of a slab foundation with your own hands is quite possible to carry out on your own and without involving the hands of professionals in the workflow.

It should be noted that such a basis for construction requires serious investments in time and money and is one of the most costly options in modern construction. Most often, monolithic foundation slabs are used in the construction of private sector houses. This choice is especially relevant in building plots, where soil and soil are distinguished by some weakness. Regardless of the distinctive properties of the soil, a slab monolithic foundation should be installed on a previously prepared base of sand and gravel, carefully compacted cushion.

Slab foundations of a recessed type for buildings are made slightly recessed into the ground, that is, it does not deepen to the level of soil freezing. The non-buried version is completely built on the same level with the ground. Another common name in the construction industry for a non-buried foundation is a "floating slab". Such a “slab” is installed to a depth of no more than one meter, and the bottom layer of sand and gravel really creates the appearance of a “floating” solid monolithic base.

The slab foundation can be built not only from reinforced concrete, but also from a concrete slab. All internal and external walls are erected on this solid foundation. Thus, the load exerted on it is distributed extremely evenly over the entire plane, and this minimizes the pressure on the ground. This technology guarantees an increase in the stability of the foundation to the loads that the soil exerts on it. A solid foundation is not afraid of ground movements due to heavy rainfall or freezing and thawing. Moving imperceptibly along with the layers of soil, a monolithic slab prevents the possibility of deformation of the building structure erected on it.

Slab foundation: features

Everyone who thinks about what a slab foundation is, in the process of studying this issue, begins to note the inherent advantages of such a foundation for any building. For buildings of medium weight, for example, for houses made of blocks with one or two floors, it is the slab version of a solid foundation that can be called the ideal solution. A monolithic base for a house can be erected on loose and subsidence soils. And the types of overlaps do not play any role.

To guarantee the high quality of such a foundation can only be the observance of the correct technology of its construction at all stages. By accurately calculating the composition and sequence of all the "layers of the pie" of the structure, you can build a really reliable foundation that will not fail under any circumstances. The only drawback of such a foundation is its comparative high cost. However, a reliable construction of this type does not require the presence of underground sections and the creation of additional ceilings, which, in principle, makes it not much more expensive than other options that require additional structural extensions, and, therefore, investments.

Structures built on this basis are distinguished by a high degree of durability. The reliability of such buildings is the higher, the more precisely during construction all existing and developed construction rules were observed. The slab foundation belongs to the classical type of foundations for buildings, and has long established itself in the global construction industry. Such a foundation is necessarily reinforced over the entire area of ​​\u200b\u200bthe structure, which guarantees its resistance to various types of loads. This can also explain the absence of deformations of an already finished building, even with uneven ground movements. Often, during the construction of an object that is being built on a slab foundation, it is this monolithic slab that is taken as the basis for the floor of a building under construction. In general, the use of this type of basis is quite universal.

Solid foundation: the subtleties of the device

The monolithic foundation is able to withstand sudden changes in temperature, it is completely insensitive to the frequent “whims” of such weakly bearing soils, such as peat. Its reliability adds to its attractiveness and speaks in favor of this choice.

The positive qualities of solid foundations are obvious:

• time-tested high degree of reliability;
• complete exclusion of the possibility of penetration into the structure of water from the ground;
• very high resistance to soil pressure;
• the possibility of building such a foundation on any, without exception, soils, even with really bad and unstable soil;
• ease of installation;
• the possibility of building a building from any building materials;
• high quality waterproofing.

During the construction (erection) of slab-type foundations, the primary task of the developer is the correct calculations. Then work begins on the laying, as well as earthworks and the device of the pit itself. At this stage, it is necessary to drain groundwater, in other words, drainage. The dug pit is thoroughly tamped with the help of special equipment. At the next stage, they begin to form a pillow for the future monolith.

The pillow under the slab foundation consists of a mixture of sand and gravel, while geotextiles must be present. The issue of waterproofing is also an important point in construction. Waterproofing material for this type of foundation must be laid in 2 layers. Then it is poured with an even layer of concrete mortar. After that, the reinforcement of the entire structure is made. When the fittings are installed, the pit is completely filled with fresh mortar, after hardening of which, the foundation will be built with your own hands and can be used both as a base for the house and, at the same time, as the floor of the basement.

Do-it-yourself monolithic base for a house

The most common is such a "layer" of a solid foundation:

1. soil (compacted);
2. sand pillow (20 - 35 cm);
3. mandatory geotextile;
4. small gravel;
5. first layer of concrete;
6. 2 layers of continuous waterproofing;
7. expanded polystyrene (extruded);
8. polyethylene protective film;
9. reinforced concrete slab.

Many people think about how to make a slab foundation. However, in reality, the installation of such a structure is quite simple, but it requires physical and time costs, as well as the obligatory observance of simple, but mandatory technologies at all stages of construction. A solid foundation has several varieties, depending on which the “layers” and the technology of its construction differ. If the project provides for a deep foundation, it would be more appropriate to build a basement.

The types of slab foundation include the following types:

• reinforced (reinforced concrete);
• slab trellised or solid;
• the plate is ribbed or smooth;
• "Swedish" insulated solid plate;
• a simple monolith consisting only of concrete.

At the same time, the type of reinforcement used and the brand of concrete are selected taking into account the subtleties of the structure, project and soil. Before starting work on the construction of a slab foundation, it is necessary to make geological analyzes of the soil. Only if these indicators are available, it is possible to correctly calculate the desired thickness of the sand cushion.

Do-it-yourself monolithic slab foundation will require patience and really high physical costs from builders. However, to do such work on your own, with the help of, for example, family members, relatives and friends, means saving on the wages of a team of workers. And the construction of a monolithic foundation for a future house, although it is not an easy process, still gives extremely positive and reliable results. The performance characteristics of such a foundation, no doubt, will meet any expectations.

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

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

• Strip foundation. Part 1: types, soils, design, cost
• Strip foundation. Part 2: preparation, marking, excavation, formwork, reinforcement
• Strip foundation. Part 3: concreting, final operations
• Strip foundation. Part 4: assembly of concrete block structures

A slab foundation, also known as “solid”, or “floating”, or “Swedish, Scandinavian slab”, is a solid slab located under the entire area of ​​\u200b\u200bthe 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 ... All of them have their own distinctive features and a specific scope. 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 in the best way. 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 tape and pile structures). This is explained by the advantages, both of a purely technical and near-construction nature.

Strengths of solid foundations

Universality in the geology of foundations. The floating structure can be correctly applied on all types of soils, including weakly bearing, heaving, horizontally mobile, with a high level of groundwater, permafrost…

There are some restrictions on the relief - it is difficult to build such a foundation on a slope, most likely, piles will be preferable. However, there are technologies proven by the Americans for erecting slabs on hillocks, which in their design (at the bottom of the site) have elements of high monolithic belts. Another “centaur” suitable for such places is a pile foundation with a low grillage in the form of a monolithic slab.

Good bearing capacity. This quality is due to the specific mechanics of the "house / slab / soil" interaction. In the next chapter, we will take a closer look at this point. Briefly - the plate has a large area of ​​​​support, so the pressure on the base soil is very low (from 0.1 kgf / cm 2). Therefore, a two-story stone house on a slab can be safely erected. 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 the high material consumption. The slab foundation is great 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 pillows of non-heaving materials are arranged.

SP 50-101-2004 "Design and installation of bases and foundations of buildings and structures."

Good insulating characteristics. With proper execution, it does not let water through, prevents heat loss through the floor.

Simple construction technology, built quickly. Easy to mark, minimum excavation, simplified formwork design, easy to reinforce and concrete. Can be made by builders with low qualifications.

Conditional disadvantages of the slab foundation

It is technically very difficult to combine a solid slab and a basement in a structure.

It is possible to pour the slab only in favorable weather (it loses a little 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, then the picture changes dramatically - we save a lot on other materials, construction stages, production operations:

• the slab becomes the rough floor of the first floor - no need to make an overlap;
• in the mass of the slab, you can lay a water heated floor, and not pour a separate screed for it;
• for the manufacture and fastening of formwork panels, less boards or sheet materials are needed (at least twice as compared to strip structures);
• no need to pay for the removal / planning of a large volume of selected soil;
• the height of the outer walls is reduced, since a lower plinth can be obtained (and these are expensive facade finishing materials, labor costs ...);
• lifting equipment, concrete pumps, excavators, driving headframes, drilling machines are not needed, everything is limited to mixer cars;
• you can build on your own and not hire highly paid professional builders, there is less risk of financially suffering from the "human factor" (simpler technology).

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

The principle of operation of the slab foundation

Situation

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 (one and a half floors, attached garages, special solutions for flights of stairs and landings ...), uneven distribution of load-bearing walls over the building area. Houses are now bigger, taller, heavier.

Problem

On top of the foundation and on the natural foundation, there are uneven effects from the house. From below, complex soils either tend to form local dips under the building, or push the building out with the forces of frost heaving, and then, thawing, sink. There is a danger of deformation and destruction of load-bearing structures.

Solution

1. Increase the footprint of the foundation, reducing the load from the house on a natural foundation.
2. To maximize the spatial rigidity of the foundation, to evenly redistribute the pressure “from top to bottom”.
3. Use a heat insulator to separate the heated premises from the ground under the house - thus, to eliminate the uneven freezing under the building (in winter, the ground under the stove does not thaw).

All these methods of dealing with “irregularities” are based on 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 bends (with proper design), and without deformation is able to actually move along with the ground - “float”.

Design features of the slab foundation

The design of slabs differs significantly from the methods of developing other types of foundations. Here, engineers also take into account all the main soil parameters and all loads (mass 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” 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 the distribution of loads, their direction.

The whole problem lies in the complexity of competently modeling bending loads, possible rolls that the slab experiences, and, accordingly, calculate 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 the calculation of the foundation slab in a specialized organization, the cost of such work will be from 5 to 10 thousand rubles.

The most widespread are slabs with a thickness of 20 to 40 cm, while 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 make local "additional reinforcement" of especially loaded zones and not make mistakes in the calculations, at 25 centimeters - the frame can be knitted evenly, without much risk. But a 30-centimeter slab, when compared with a 25-cm structure, will not allow saving on reinforcement, but much more concrete will go to it.

An exceptionally competent calculation allows pouring plates 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 total thickness (read material consumption) by making local thickenings of the foundation in the area of ​​\u200b\u200bthe corners, the junction of the 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 than the house in area; 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 "Bearing and enclosing structures" or SP 50-101- 2004 "Design and installation of bases 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:

1. Design.
2. Marking (only the contours of the building are taken out in kind).
3. Sod removal, soil sampling (if cushion / drainage is needed).
4. Laying of buried communications (water, sewerage).
5. Pillow, drainage device.
6. Installation of hydro and thermal insulation.
7. Assembly of "warm floor".
8. Knitting and laying of the reinforcing cage.
9. Assembling and fixing the formwork.
10. Concreting.
11. Stripping.

Let's look at these operations in more detail.

We have more or less figured out the design. Build something serious - it is better to order the development of a foundation project to engineers, definitely save your nerves and money.

We have already discussed the issues of preparatory work, the removal of markup in nature in the article.

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

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

The pillow is an artificial base, it is designed to replace "bad" soils. The most common material for the pillow is a mixture of sand and gravel, which have good drainage properties, shrink a little, and do not swell. The sand and gravel cushion is laid in layers of 100 mm, and each cake is carefully rammed with a vibrating platform. If clean sand is used, then it must be spilled with water.

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

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

Most of the technological maps for the manufacture of solid foundations suggest laying geotextiles under the pillow, which does not allow sand and gravel to silt (read, lose important properties for us).

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

The pillow is covered with a dense polyethylene film, or other waterproofing materials that, during concreting, will prevent leakage of cement laitance. The sheets are overlapped and glued/soldered.

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

Underfloor heating pipes are laid out directly on XPS sheets using a special mesh, of course, they are not insulated with any materials in order to better give off heat. Some heating routes can also pass in this layer - here they are in sleeves and heat insulators. All ends are taken out of the pit for communications, the system is ringed, pressed. Under pressure, the 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 most errors, both technological and design, are made.

Let's start with the main one. According to SP 52-103-2007, the minimum percentage of reinforcement of a reinforced concrete slab is 0.3%. It is calculated as follows: they take a cross section of the slab and calculate its area, calculate the total area of ​​the cut of all reinforcing bars, 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 step of 150-250 mm.

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

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

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

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

The ends of the frame, the upper and lower tiers, are recommended (SP 63.13330.2012) to be connected to each other with U-shaped reinforcement elements. Reinforcing bars should not come into contact with the formwork, as a protective layer of concrete with a thickness of at least 40 mm should be provided.

The frame is made with viscous reinforcing bars with wire. It is allowed to use electric arc welding, but then it is necessary to use fittings of class a500s, or similar, with index "C".

Due to the large amount of reinforcement work, it is advisable to use unified prefabricated welded meshes. The joints obtained after laying are necessarily bred in a “chessboard” order - the joints of the finished meshes of the lower tier of reinforcement must be overlapped by a whole mesh of the upper tier.

The formwork of the floating foundation is very easy to assemble, it is only necessary to align 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 spread them very well from the ground.

The formwork should be wrapped with polyethylene from the inside to prevent leakage of cement laitance through the cracks. Alternatively, it is possible to lay XPS sheets near the formwork, then they will reliably “stick” to the concrete and provide vertical insulation of the slab.

Expanded polystyrene is also separated by buildings associated with the house, which require their own foundation (garage, porch, terrace ...).

A separate small formwork circuit is made for a 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 manufacturing a monolith can be found in our publication.

Concreting must be done in one work shift. It would be most rational 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 chute.

Concrete must be compacted without fail with a deep 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 the water table is high.

Taking into account domestic realities, it is better for a private developer to order concrete, at least a grade higher than the standard one - there will be more chances to get the design strength class.

The next step is to take care of the concrete. When the slab gains 50% strength, the formwork can be removed. We examined these works in detail in the article “Strip Foundation. Part 3: concreting, final operations ”, we add that the next day after pouring the floating foundation, the upper plane of the slab should be rubbed - 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; they have proven their reliability, functionality and economic attractiveness over time. In our country, the plates also found their developer. From year to year, solid foundations are becoming more popular, since in many cases there is simply no alternative to them.

Turishchev Anton, rmnt.ru