Shallow strip foundation for the house. Do-it-yourself shallow strip foundation for a house. Video - Do-it-yourself shallow strip foundation

In private low-rise construction shallow strip foundation are used as the most economical and, moreover, reliable construction solution. This type of foundation combines a number of advantages inherent in buried and non-buried foundations, so its use is quite widespread.

What is the difference between a shallow foundation?

To carry out the foundation of a buried structure, a pit is required with a depth below the level of soil freezing. In areas with severe winters, this depth exceeds one and a half meters, so you can’t do without heavy equipment on the site. A shallow strip foundation is a base made along the perimeter of all load-bearing walls, while the depth of the structure usually does not exceed half a meter.

The advantages of a shallow foundation include:

• Ease of implementation and low cost of work;
• The possibility of building a foundation without the use of construction equipment;
• Strength sufficient for the construction of small houses, baths or frame buildings;
• The possibility of warming the basement;
• A wide range of materials and technologies for its construction: it can be monolithic, made by pouring concrete, or made of concrete blocks or bricks.

Among the shortcomings, it should be noted its insufficient strength for buildings built on heaving soils. This problem can be solved by sand filling and drainage, which will reduce the load from the soil.

A shallow foundation cannot be made on frozen ground, and also left unloaded for the winter, so the time frame for pouring the foundation and building walls is quite short and amounts to middle lane 4-5 months.

Materials for making a shallow foundation

The easiest and fastest way to make a shallow foundation is to pour a monolithic concrete base. However, options are also possible: the foundation can be made of concrete blocks or.

For a monolithic foundation, concrete of a grade of at least 200 is used, as well as reinforcement from a metal bar D12-D16. Filling is carried out either immediately or in horizontal layers, there should not be vertical joints in the foundation - this will lead to its destruction.

If the concrete is prepared independently, and it is impossible to prepare large volumes immediately, you can make a shallow foundation from do-it-yourself concrete blocks.

Technology for the implementation of a monolithic shallow foundation

1. The fertile layer of soil is removed from the site and markings are made using pegs and nylon twine. Carefully measure the angles, compare the distances between the walls with the project. By marking, they dig a trench up to 70 cm deep. In this case, it is necessary to start from the lowest corner of the site, and align the horizontal plane of the trench along it. The walls of the trench must be strictly vertical. If the soil is loose, you can install props.

   

2. Geotextiles are laid at the bottom of the trench - a construction fabric that allows water to pass through, but prevents soil particles from entering the sand. The geotextile is laid in such a way that its edges are higher than the planned sand bedding.

   

3. The bottom of the trench with the laid geotextile is covered with coarse sand. Backfilling is carried out in layers, with each layer being shed with water and compacted. The height of the sand bed depends on the type of soil. On sandy soils, 20 cm of sand is enough; on saturated clay soils, its layer should be half a meter.

   

4. A formwork made of boards is installed over the trench, continuing the walls of the trench. The boards are fastened with nails or self-tapping screws, while the ends of the nails sticking into the formwork should be avoided, otherwise the formwork will then be difficult to disassemble. On the formwork from the inside, mark the level of pouring concrete. When marking, use the building level.

   

5. Reinforcing bars are placed in the prepared formwork. The metal bar is cut to the size of the walls in the longitudinal and cross section, and with the help of knitting with wire, they are attached to the reinforcing lattice. All corners and joints of the walls must be tied with perpendicular reinforcement bars - this will preserve their tensile strength during soil movements. If the height of the foundation is more than 30 cm, several layers of reinforcement are required. Welding cannot be used when attaching a bar for several reasons: a corrosion-unstable area appears at the welding site, in addition, a hardened bar loses its tensile strength during welding and may burst during operation. As a result - a crack in the foundation, gradually transmitted to the wall of the building.

   

6. Start pouring concrete formwork. The first layer is poured and the concrete is evenly distributed over the formwork, punching it in several places with a bar to remove air voids. Each subsequent portion of concrete must be poured before the previous one has set, so it is better to pour it in a large team. The very last layer is leveled according to the markup, smoothed with a rule and sprinkled with dry cement using a sieve - this measure leads to a stronger setting of the upper part of the foundation and prevents cracking when it dries.

   

7. Concrete maturation lasts 28 days and depends on weather conditions. At the same time, the construction of light buildings can be started in a couple of weeks, for the construction of a brick house, you will have to wait for the entire ripening period.

Technology for the implementation of a shallow foundation of concrete blocks

This technology allows you to perform a shallow foundation in stages, which is important when building a foundation with your own hands. At the same time, concrete blocks can be made independently.

1. The form for blocks is made of plywood in the form of a rectangular frame with walls, but without a bottom, while it is more expedient to make it into 4-6 blocks, dividing the structure with removable partitions. All parts are impregnated with machine oil - this facilitates the removal of finished blocks. The bottom is a flat surface covered with polyethylene.
2. Concrete is mixed: take 1 part of cement, 4 parts of sand mixed with crushed stone, expanded clay or other filler. Fiber can be added if desired. The resulting dry mixture is poured with water and mixed, the resulting concrete should be thick enough, but freely fit into the mold.
3. Fill the form halfway and lay the chopped reinforcing mesh. Fill the form completely, leveling the surface of the concrete. You can also make blocks hollow by inserting glass bottles into the mold.

Products are dried for 2-3 days at positive temperature, after which they are taken out of the mold and dried for another 2 weeks.

Laying the foundation as a whole does not differ from a monolithic one, the only difference is that the formwork above the soil surface is not performed, a monolithic base is poured from concrete in the ground, reinforcing it with a bar, and the ground layer is laid out from concrete blocks in several rows, using ordinary cement for masonry solution.

An economical and at the same time the most reliable foundation is the dream of every novice developer. But is such an option possible? Quite. Direct confirmation of this is a shallow tape base. The arrangement of such a foundation does not require large financial and time costs, but the result of the work is very pleasing - you get a high-quality and durable foundation. Moreover, you can even build it with your own hands, without the involvement of professional builders. To make sure of this, let's look at each stage of the construction of a shallow foundation. And in addition, we advise you to watch the installation video - it will allow you to understand in more detail the technology of laying the base.

Distinctive features of a shallow foundation

Before proceeding to the analysis of the laying technology, we will designate the main features of the shallow-depth strip base:

• is a frame in the form of a monolithic tape of reinforced concrete, outlining the perimeter of the future structure;
• costs two times cheaper than a deep-seated foundation;
• suitable for the construction of one- and two- and three-story buildings made of wood, concrete, stone and brick;
• can be used on non-rocky areas, as well as on weakly, medium and strongly heaving soil;

Important! In the last two cases, it is necessary to ensure high-quality soil drainage.

• arrangement involves a minimum amount of land work;
• makes it possible to build a small basement or cellar in the perimeter of the building;
• for laying it is not necessary to use special equipment.

A shallow foundation cannot be built on frozen ground, so all work must be completed before the onset of frost. The laying of the base is carried out in four stages.

Stage 1: Trench preparation

The first step is to prepare trenches into which concrete will subsequently be poured.

First, mark the site on which the foundation will be located. Then accurately determine the corners of the future design - they should be as even as possible. Next, proceed to create the foundation - dig trenches around the perimeter of the marked area. The optimal foundation depth is 50 cm. The width of each trench should be at least 60-80 cm.

When the recesses are dug, you need to compact the soil - arrange a special pillow on it. If the site is based on silty fine sand, the soil must first be covered with geotextile - it will prevent the site from silting up and protect the foundation cushion from weeds, which are likely to grow in it due to high humidity.

The pillow itself should reach a height of 30-50 cm - this will be enough to give the foundation the necessary strength. First, sand is poured with a layer of 15-20 cm. It must be thoroughly moistened and compacted. Then fill in 15-20 cm of gravel. Moisten and tamp the base again. Further, waterproofing is carried out - sheets of roofing material are laid.

When the work is completed, check the level of the resulting base surface - it must be strictly horizontal.

Stage 2: Arrangement of formwork

The next step is to work with the formwork. For its construction you will need a large number of boards. Keep in mind that when concrete is poured onto the formwork, serious mechanical stress will occur, so stock up on a solid board - its thickness should be at least 5 cm.

Boards need to be knocked down in the form of shields. The optimal connection pitch is 80 cm. If the pitch is wider, the structure will not be strong enough. Finished wooden panels can be fixed to the base using props or support bars. The latter must be installed every 60-70 cm. The recommended section of the bars is 50x50 mm. The shields must be tightly fixed between the installed bars or supports. After mounting the formwork, cover the panels with dense polyethylene or glassine.

From the outside, it is also desirable to strengthen the formwork structure with special supports so that it does not deform during subsequent installation work.

Stage 3: Base reinforcement

High-quality reinforcement is a guarantee of the integrity and durability of the entire structure of a shallow foundation, so this step should not be skipped in any case.

First, build a reinforced frame. To do this, prepare metal rods 14-18 mm in diameter. Their length can be any, but experts recommend using long products - 2-5 m. Remember: the longer the rods, the fewer connections and the stronger the base of the foundation. Metal products are laid around the entire perimeter of the foundation on a pillow, thereby forming a frame.

For the arrangement of a reinforced skeleton, rods of a smaller section are usually used - up to 10 mm. The length of the products should be slightly wider than the trench. All reinforcement is installed strictly perpendicular to the frame elements. There are two ways to connect them: more reliable - electric welding, and more affordable - wire tying. The latter must be very flexible in order to be easy to work with.

Advice. For the convenience of mounting the reinforcing skeleton, you can use trimmings of plastic pipes: saw them on a circular saw to make rings 5 ​​cm high, install the resulting products on the base and fix the reinforced structure on them.

Stage 4. Concrete pouring

The most important stage is the direct pouring of the foundation. It can also be divided into several stages:

1. Mixture preparation. If you are laying the foundation yourself, you will probably decide to prepare the concrete mix yourself. There is nothing difficult in this. The main thing is to buy high-quality consumables: concrete itself, crushed stone and sand. It is desirable that the latter be of a large fraction - it adheres better. The mixture is made from concrete, sand and water in a ratio of 1:3:1. After thorough mixing, 5 parts of crushed stone are added to the composition.
2. Filling the mixture. When the composition is thoroughly mixed, you can pour it into the prepared trenches. To prevent the formation of air chambers during the solidification of the foundation, the concrete must be compacted after laying. This can be done both manually - using a wooden rammer, and using a special vibropress. The composition must be poured not in one go, but as it is compacted. Check the level regularly while the concrete is drying.
3. After the final solidification of the foundation, fill the remaining layers between the trenches of the foundation with earth and tamp it down.

As you can see, it’s really not difficult to equip a shallow strip foundation with your own hands. Stick to the general technology and follow the installation rules that professional builders have long taken out - compliance with these two conditions will lead you to a positive result, even if you are pouring the foundation for the first time.

Shallow strip foundation: video

Strip foundation: photo

Among all the options for building a foundation, shallow enjoys particular popularity.

It allows save on earthworks and required materials, provide a reliable foundation for the future structure and, which may be especially attractive, to complete all the work on one's own.

What you need to know and how to deal with this task, we will tell.

What is a shallow foundation?

The name itself already quite accurately defines the features of this type of foundation: it buried into the ground, but finely, not deep. But seriously, on average, the depth of such a foundation is 50 cm, Oh really not deep, and quite capable on one's own dig a trench without involving labor and equipment from outside.

It is a concrete reinforced tape, on which subsequently erected outdoor and internal bearing walls. Best conditions for using a shallow foundation - non-foamy soils and low-rise structure made of non-heavy materials, which include:

1. , frame-panel structures;
2. Cellular concrete - expanded clay blocks, foam concrete etc.;
3. Lightweight brickwork.

Considering that in most cases such a foundation is located higher the level of soil freezing, it is necessary to take into account the soil and ensure styling matching pillow. You can read more about this in dedicated to technology. devices such pillows under the foundation.

Device

The shallow foundation is quite simple by design. On the sandy(sand and gravel) cushion concrete is poured into the formwork of the desired configuration and size. Its necessary strengthen fittings.

cured coating waterproofed. The depth of occurrence depends on the weight of the structure, the characteristics of the soil. The height of the foundation above the ground should not be more height of the underground part of the foundation.

The possibility of using such a foundation can be limited the complexity of the terrain (construction on a slope), as well as the ground. Use on sapropelic and peat soils of a shallow foundation excluded.

How to make a calculation?

To calculate the parameters of a shallow foundation, you need to know some soil parameters and future construction, including level groundwater flow, depth soil freezing, calculated the weight buildings, snow, calculated resistance soil, etc. In general terms, we will describe the calculation technology.

Initial data

For the initial data, we will take a one-story house by measurement 10x8 m with walls made of aerated concrete with block sizes 600x300x200mm and one internal load-bearing wall. The density of this material is approx. 500 kg/m³. Rough calculation, taking into account door and window openings, as well as one load-bearing internal wall, will show that the weight of the walls can be 15 t.

Similarly, one can calculate the weight attic floor, gender, roofing, snowy loads(for example, for the Moscow region it is 160 kg/m2). This needs to be added the weight insulation materials, facing brick(if it will be used), metal for doorways, etc.

And don't forget about useful load, which consists of people, furniture, equipment, dogs, cats, cages with budgerigars, etc. In order not to catch your Barsik for the purpose of weighing, the value payload taken equal to 180 kg/m2. This value is somewhat redundant, but allows to take into account all possible loads inside the premises.

Calculation

Suppose that the final value of the weight of the house turned out to be 130 tons. Now let's define the calculated pressure on the ground, for which we will divide the weight buildings on the area of ​​the base of the foundation. Let us assume that the planned foundation will be width 35 cm. Then the area of ​​​​its base will be approximately 15.4 m². 130 divided by 15.4 and we get that estimated the specific pressure on the ground is 8.44 t/m².

Next, this value is compare with calculated soil resistance. For example, for alumina this value is 10 t/m². This means that the previously selected size of the foundation provide that the soil will support the building.

Given that width foundation should be more wall width approx. 10 cm, you may need to increase the width of the base of the house. This will lead to an increase masses foundation and will need to be done recalculation, but even a slight increase in the width of the foundation will provide stock by ground load.

Construction technology

After everything is calculated, it's time to start working on laying foundation. It can be divided into several stages.

markup

According to plan marked out territory for the future building, with the help of pegs and a stretched rope, the perimeter of the work is determined.

Advice! It is desirable to remove the top fertile layer of soil over the entire area.

Trench

dug out trench desired depth. It is necessary not to forget to take into account not only the dimensions of the foundation, but also the pillows under it. Width trenches should be more the width of the base of the house so that nothing interferes with the formwork.
After all the soil is taken out, it begins styling pillows.

At first recommended lay geotextile, which will prevent mixing sand with soil. Sand, pre-moistened, is laid in layers on 15-20 cm and carefully rammed down using vibrating plates.
After the formation of the pillow is completed, you can proceed to installation formwork.

How to make a waterproofing strip foundation with your own hands:

formwork

Most commonly produced from boards, but you can buy it at a hardware store, made metal or plastic. When installing formwork necessary keep a close eye on verticality walls and holding permanent distances between them. For strengthening, pegs, bars are used, spacers are nailed on top, which will help later keep poured cement mortar.

Formwork walls can be pull off wire. The inner walls of the boards should be smooth. Steel, asbestos-cement or other pipes should be installed in advance for ensure underground ventilation.

They are installed perpendicular formwork and covered with sand, which prevents concrete from getting into them and deformation when pouring the foundation.

Reinforcement

After completion formwork installation before starting to pour concrete, necessary provide for it. In the case of the construction of light buildings, reinforcement can be neglect, in other cases, perform it extremely recommended.

Used rebar diameter 10-16 mm, which is located longitudinally along the entire length of the foundation. Usually, in the lower and upper parts of the future foundation of the house, two reinforcement bars are laid, retreating from the edges by several, recommended by 5 centimeters. transversely steel bars with a diameter 6-8 mm. They are connected to each other with a wire.

For reinforcement enough arrange 2 reinforcement belts, but for high altitude foundation and heavy loads, the number of belts can be increase.

Beyond the need use welding equipment, with this method of connection, due to heating, the structure of the metal and its mechanical characteristics change. increased rigidity at the welding site can become reason for the gap during pouring with concrete, or may subsequently create internal stresses in the foundation, preventing it from responding to temperature fluctuations.

pouring concrete

Concrete grades are often used for foundations. M200. The finished mixture is poured in layers approximately 15-20 cm.

Attention! Preferably every layer tamp down using a vibrator or rammer, or at least a piece of rebar pierce surface to remove possible air pockets.

The next layer must be poured before solidification the previous one. After graduation concreting, the foundation is needed shelter film and leave to harden, from time to time wetting water.

Pre-hardening will take place in 3-4 days, then it will be possible dismantle formwork. For further work concrete will be usable through 2-3 weeks.

Blind area what is it?

protects foundation from soil erosion by melt water, precipitation, diverting unwanted moisture from the base of the house. In addition, it can also serve path around the house.

Her device not difficult. It consists of two parts:

• Foundations. To do this, a layer of sand is laid, or several layers of gravel and sand.
• decorative coating. In the simplest case, this is a layer of concrete, but you can use a rock, pour asphalt, fill with gravel.

The slope of the blind area away from the house should be at least 1.5˚. Optimal if the height difference between the edges is 8-10 mm.

Between the wall and the blind area you need to leave expansion joint order width 2 cm. Roofing material, expanded polystyrene is laid in it, sand or other waterproofing material.

The width of the blind area should be not less the width of the eaves of the house so that the water rolling down from the roof gets on her and not on the ground. In addition, another point can affect the dimensions - the insulation of the foundation.

Why is foundation insulation necessary?

After the foundation concrete has completely hardened, it must be covered several layers of bituminous mastic and shelter waterproofing material, for example, roofing material. Next step - . Reinforcement laid in concrete conducts cold well, and insulation measures will reduce this unfortunate effect.

In addition to actually improving the temperature indicators of the structure, there is another important moment.

Soil heaving

Considering the shallow depth of the foundation, higher freezing boundaries, it is affected by vertical and tangential forces of frozen soil. This is compensated cushion under the foundation, and lateral forces can be compensated by laying insulation under the pavement.

A good option would be to use extrusion polystyrene foam, which is buried to a shallow depth under decorative pavement coverage. Knowing depth soil freezing (recall, for the Moscow region it is about 1.4 m), if the width of the laid insulation, and, in fact, the blind area, will be not less this value, the soil at the point of contact with the foundation will not freeze.

AT video below is shown in detail device finely ruined strip foundation:

When the bath is planned to be quite massive, but the ground is solid fine and low-moisture sands, then the most rational option for building a zero level is a shallow strip foundation, the approximate depth of which is 20, 40 and 60 cm. In this article, we will consider in detail the stages of construction of such a foundation option .

What are the disadvantages of a conventional recessed foundation?

Firstly, soil heaving processes cannot occur under the sole of a traditional buried foundation, and therefore there are no normal perpendicular frost heaving forces towards the soil surface.

Secondly, as already mentioned, the unjustified price of building such a foundation for the construction of a 1-2-storey bath is also important, but a shallow foundation - with your own hands - allows you to save up to 80% of costs.

Thirdly, in addition to the natural heaving forces, tangents are also of considerable importance - which sometimes exceed the norm. And the larger the area of ​​​​contact of the foundation with the ground, the more important these forces will be. After all, shallow strip foundations always have a minimum area of ​​​​contact, and therefore their tangential forces are almost zero. Whereas in traditional recessed ones they are large and can even raise both the foundation and the whole building. That is why deep foundations without special measures to reduce such forces will not give any guarantees of the absence of heaving. In addition, in this case it is not used at all. load bearing capacity the upper layers of the soil, and therefore the solution is inefficient.

Stages of construction and their features

Stage I. Pillow laying

Once the trench has been dug, the soil must be compacted. In the case when shallow foundations are built on heaving soils, the old-fashioned method of impregnation with water is no longer justified - a vibrating plate is definitely needed here. Where the soil is normal, it will go well, and where it is mixed, it will stop, and it will not even be possible to push it - it is advisable to replace the earth in this place. But the pillow in the area where there is one fine and dusty sand, it is desirable to protect it with geotextiles - so that there is no silting with the parent soil. It will also protect the pillow from weeds that may grow into it and from water intrusion.

The device of a shallow foundation is such that the width of the pillow should be 30 cm wider than itself. First, sand is poured, on it - 10 cm of gravel and roofing material (preferably on geotextiles). But, if it is necessary to insulate a shallow foundation, then it is better to use fixed formwork and polystyrene foam - it is now especially popular among attendants.

Stage II. Formwork construction

It is better to build formwork for a shallow foundation from support posts in the form of 10x2 cm boards and support posts in the form of 50x50 bars, which stand every 60 cm. Be sure to finish the formwork with glassine.

Stage III. Foundation reinforcement

It is better to reinforce such a foundation like this: 5 reinforcing bars in the lower and upper chords. The most suitable for this is a longitudinal reinforcement of 12 mm and a transverse reinforcement of 20 mm. The distance between the longitudinal reinforcement should be left about 15 cm. In this case, the corners are reinforced in an overlap and tied with wire.

To make it convenient to put fittings, special stands can be made under it - from scraps of plastic pipes. It is not difficult to cut them on a home circular in the form of rings 50 mm high, and then place them under the reinforcement.

Stage IV. Pouring concrete

The best brand for a shallow strip foundation is concrete B15 F100 P4 M200. For the pour itself, a mixer and a concrete pump are often used - this will greatly facilitate the whole process.

How to avoid annoying mistakes?

Shallow foundations have been built for a long time - and have been appreciated by both builders and scientists. There is also a shallow slab foundation, and columnar - not only tape. And all their shortcomings have always been dictated by perfect mistakes in the process of construction or design.

The correct use of waterproofing tape is extremely important in construction - if the rules are not followed, then more resources will be required for construction

So, the most common mistake is that the higher the tape at a shallow foundation, the better. In fact, such apparent pluses can easily turn into unpleasant minuses.

Firstly, thoughtlessly increasing the height of the tape will entail a significant increase in rigidity - and reinforcement will have to be increased. And this is already unjustified costs.

Useful tips on how to build an inexpensive bath can be found in the article

Secondly, any wooden or - building is flexible enough, and in combination with the same flexible right shallow foundation creates one balanced structure, which will not be afraid of even the deformation of the soil due to frost heaving. And when instead of a tape of 40 cm, all 80 cm are built, the result is a rigid foundation, which, under the influence of the load of the building on one side and the frosty forces of heaving on the other, will simply crack one day - because it “stands to the last”.

That is why, if 40 cm is not enough for the plinth - it can be made in the form of brickwork, or another monolithic tape with separation in the form of waterproofing - it is she who will ensure two years of sliding when bending. So the tape will turn out both high and without loss of flexibility. Moreover, it is already possible to reinforce an additional tape many times less than the main one.

For the construction of houses of a small area, as well as various outbuildings the best option The foundation is a shallow foundation. Its construction will not take much time, and the whole process can be done independently. In order for the shallow-depth strip foundation to be as strong as possible with your own hands, you need to correctly calculate its parameters and strictly follow the pouring technology.

The depth of a conventional foundation is at least 1.5 m, and in cold regions - up to 2 m. The shallow foundation is located at a depth of up to 70 cm, which greatly facilitates the digging of trenches and reduces construction time. Since the area of ​​such a foundation is several times smaller, the consumption building materials also decreases. For its manufacture, not only concrete is suitable, but also red brick, as well as concrete blocks.

The shallow foundation also has its drawbacks: it is suitable only for the construction of one-story buildings of a small area; requires arrangement drainage system on heaving soils. Such a foundation can be poured only in the warm season, and you can not leave it for the winter without a load. When freezing, the soil pushes out a light foundation, damaging its integrity.

Foundation construction technology

The fastest version of the strip foundation is concrete monolithic. It is erected from blocks or bricks if it is not possible to prepare a large amount of mortar and pour the base at a time. To ensure that the construction process is not interrupted, all the necessary tools and materials should be prepared in advance.

So, for work you will need:

• roulette;
• plumb or level;
• pegs made of wood or iron bars;
• thick fishing line;
• pick and bayonet shovel;
• geotextile;
• sand;
• crushed stone;
• reinforcement with a section of 12 or 16 mm;
• formwork materials;
• polyethylene;
• concrete mortar;
• trowel.

The area under the shallow foundation should be relatively flat, with dense homogeneous soil. The location of the house relative to the site is determined and a peg is driven in at the site of one of the corners of the facade. Measure the distance to the second corner and again put the beacon from the peg. A fishing line is pulled between the pegs, fixed, then perpendicular lines are drawn from each corner. By connecting the beacons into a rectangle, check the perimeter along the diagonals. If the angles and sides of the marking are equal, you can mark the inner perimeter, according to the project.

The width of the foundation tape is usually 40 cm, so inside the markup it is necessary to mark the internal boundaries of the base. To do this, 40 cm in both directions retreat from each outer corner along the stretched fishing line. They mark these points with beacons, and then retreat from them by 20-30 cm beyond the perimeter and drive in pegs. This is necessary for a more accurate designation of corners, both external and internal. In addition, during digging, closely spaced pegs can be accidentally hooked and knock down the markings.

The soil is taken out to a depth of 70 cm, the count is taken from the lowest marking point. The walls of the trenches must be strictly vertical, which is periodically checked building level. If the soil is crumbling, wooden supports should be installed as you move along the perimeter. When the trenches are ready, they check the horizontal level of the bottom, correct defects.

To avoid shrinkage and deformation of the strip foundation, a sand cushion is required. It is recommended to use coarse-grained river sand, which better resists compression. To protect the sand cushion from erosion, the bottom and walls of the trenches are covered with geotextiles. You can also take ordinary polyethylene, the main thing is that the sand does not mix with the soil. The material is spread inside the trenches, and its edges are brought up and fixed with something, for example, with bricks. This will prevent the geotextile from moving during sand compaction and rebar placement.

On the site with clay soil the thickness of the pillow should be at least 50 cm, but if the soil is predominantly sandy, 20 cm is enough. The sand is poured in 2-3 steps, each time carefully ramming it. For better compaction, layers of sand are shed with water. A layer of gravel about 10 cm thick is poured over the sand cushion, and it is also well rammed. After that, you can mount the formwork.

Shallow strip foundation - trench

Assembly and installation of wooden formwork

For formwork, flat boards with a thickness of 2 cm or more, durable plywood, OSB boards are suitable. Sheet material is cut into pieces with a width of 40 cm, the boards are knocked into shields. It is more convenient to connect the formwork elements with self-tapping screws, then it is much easier to dismantle the structure. When assembling shields, it should be taken into account that inner side should be as smooth as possible, otherwise all the irregularities will appear on the walls of the foundation. Since the tree strongly absorbs water from the solution, the formwork should be upholstered with plastic wrap.

When the required number of panels is ready, proceed to the installation of the formwork. Parts of the formwork are placed on both sides of the trenches, leveled horizontally and in height, and knocked down along the upper edge with transverse bars at regular intervals. Further, the structure is strengthened with struts from the outside, so that when pouring, the formwork walls do not disperse. At the end of the installation, make sure that there are no gaps and cracks in the formwork, and that the walls are strictly vertical.

On the inner walls of the shields, the level of pouring the solution is noted; do this along the entire perimeter of the trenches so that the surface of the shallow foundation lies in the same horizontal plane. Instead of marking on the walls, many builders use fishing line: they stretch it inside the formwork and fix the ends with nails. This must be done after installing the reinforcing frame.

Frame installation

The reinforcing frame is knitted from reinforcement with a diameter of 12 cm or more. Bars are cut from the reinforcement along the width and length of the trenches, and then they are tied into a lattice. The dimensions of a standard cell are 30x30 cm. A soft wire is used for bonding, but it is undesirable to weld the frame: welding reduces the tensile strength of the metal, which leads to cracks in the base. In addition, the welded grating is more prone to corrosion.

Having laid the grate on the bottom, the frame is tied with reinforcement at the junctions. If the height of the base exceeds 30 cm, the reinforcing frame should be made two-level. To do this, knit the second layer of gratings, and then connect them to the bottom layer with vertical rods. The reinforcement should not touch the walls of the trenches and formwork, and also reach the level of pouring concrete. The metal protruding from the foundation will quickly rust from rain and snow, which means that the strength of the foundation will be reduced.

The strength of a shallow foundation directly depends on the quality of the concrete. For pouring, it is recommended to use a solution of brand M200 and higher. At self-manufacturing 1 part of cement is poured into the container, 3 parts of sifted sand and 4-5 parts of fine gravel or crushed stone are added. If everything is done manually, the dry ingredients are first mixed, and then water is gradually poured in.

Although the height of the foundation is small, it is recommended to fill the trenches in layers. This will help to better compact the solution and distribute it more evenly. The first layer is poured with a thickness of 20 cm, leveled if possible and pierced to the bottom with a piece of reinforcement in several places. Particular attention should be paid to the corners. The second layer is poured immediately after the first, without waiting for the concrete to set. Again distribute the solution in the corners, under the bars of the frame, at the joints of the walls, get rid of air voids.

The last layer of concrete is leveled along the fishing line, the surface is smoothed with a trowel, and then sprinkled with dry cement through a sieve. This contributes to a faster setting and hardening of the mortar, in addition, the surface sprinkled with cement does not crack when dried. The finished foundation should be covered with a film from scorching rays and from rain for 28 days, until the concrete is completely dry.

To prolong the service life of a shallow foundation, it is recommended to insulate its outer walls with polystyrene foam boards or polyurethane foam. Along the perimeter of the base, it is desirable to make a blind area 1 m wide, and additionally equip drainage ditches in flooded areas.

Shallow foundation of brick or blocks

The construction of such a foundation has slight differences. Brick can be used second-hand, the main thing is that it be burnt and intact. Blocks for the foundation can be made by hand, which will save a little on materials.

So, the construction of the foundation is carried out as follows:

• mark the site and dig trenches;
• lay geotextiles, a sand cushion and a layer of rubble;
• they knit and lay out reinforcement, the top of which should not reach about 5 cm to the edge of the trench;
• fill the pits with concrete flush with the ground, level the surface;
• after setting and hardening of the concrete layer, lay out several rows of blocks or bricks with mandatory dressing of the seams;
• the outer walls of the foundation are insulated, and covered with cement plaster on top.

If the foundation is intended for utility rooms, you can not insulate it, but immediately plaster the masonry with mortar. Subject to the described technology, the foundation will last for several decades.

Video - Do-it-yourself shallow strip foundation