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Construction of a shallow strip foundation. Do-it-yourself shallow strip foundation for a house Do-it-yourself shallow strip foundation

Shallow strip foundation(MZLF) is a type of strip foundation, which is located 0.3-0.7 m below the zero level. The construction of this type of foundation requires a minimum of financial and labor costs. MZLF is excellent for light buildings erected on various soils. The foundation has its advantages and disadvantages, as well as a special construction technology.

Shallow strip foundation: scope of application, pros and cons

The bearing capacity of MZLF, in comparison with foundations of other types, is assessed as average and largely depends on the type of soil on the site. A shallow foundation is suitable for the construction of country houses, timber buildings, frame houses, as well as outbuildings, bathhouses, barns, etc. For brick houses, large cottages made of foam concrete and aerated concrete blocks, a shallow foundation is not suitable. For such buildings, an excellent option would be a combined foundation on piles, for example, a shallow pile-strip type on bored supports.

It is advisable to build a foundation of this type on slightly heaving and non-heaving soils. The ideal option is sandy and sandy loam soils with low moisture content. The groundwater level must be at least 0.5 m below the laying depth. On clay, the construction of an MZLF is accompanied by difficulties, because Most clayey soils are classified as medium- and high-heaving soils. We will consider the features of constructing a foundation with a shallow laying depth on heaving soils below.

The advantages of this type of base include

economical, concrete consumption is 30% lower than when constructing a conventional recessed strip foundation or a foundation with a monolithic floor slab;
ease of construction, you can build it yourself without the involvement of workers and special equipment;
small amount of excavation work - a narrow trench with a depth of no more than 0.7 m is dug;
small area of contact between the structure and the ground.

Among the disadvantages of MZLF they note

pouring is carried out at stable temperatures above +10 C;
limited use due to small bearing capacity
construction is possible only on a flat surface with a slope of no more than 5 degrees;
lack of a basement in the house.

Expert opinion

Sergey Fedorov

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If you are planning to build an MZLF foundation and “freeze” the construction, then keep in mind that you cannot leave the foundation unloaded for the winter! When the soil freezes, it will push out the monolithic tape, which will lead to a violation of its integrity.

Features of the design of a shallow foundation

Shallow monolithic strip foundation erected on a flat surface. When building a house on a slope, you will have to combine MZLF with pile foundation, using supports to level out the height difference. In terms of strength and resistance to deformation, the structure must comply with SNiP 2.03.01-84.

Sectional view of the foundation shallow looks like this:

Features of MZLF that must be taken into account during calculation and construction:

The depth of the foundation base depends on the depth of soil freezing.
Be sure to install a cushion made of dry bulk materials: a mixture of coarse sand and gravel.
At high level groundwater Drainage is performed under and around the foundation.
The base on which the monolithic tape is installed is compacted as much as possible.
It is necessary to arrange a blind area to drain rainwater and snow.

Taking these features into account, we can conclude that the backfill and blind area are an integral part of the shallow foundation. Requirements for the blind area are specified in SNiP 2.02.01–83.

Calculation of a shallow strip foundation

Calculating the MZLF, which is being built on low- and non-heaving soils, is not difficult. During the calculation, three main parameters are determined:

Laying depth

Determined on the basis of SN “Foundations and Foundations”. The document specifies the following minimum depth values for the foundation base:

when the soil freezes less than 2 m - 50 cm;
when the soil freezes to a depth of 3 m - 75 cm;
when the soil freezes more than 3 m - 100 cm.

For most regions middle zone the laying depth of the MZLF will be 50 cm. For light buildings, for example a frame barn or a small country house this parameter can be reduced to 30 cm.

Width of monolithic tape

In order not to make complex calculations, we recommend taking the width of the sole based on the table:

Wall and ceiling materials	Number of floors	MZLF sole width, m
Lightweight walls brickwork or aerated concrete with reinforced concrete floors	1	0,6
	2	0,8
	3	1,2
Wooden frame walls with wooden floors	1	0,4
	2	0,4
	3	0,6
Log walls with wooden ceilings	1	0,3
	2	0,4
	3	0,6
Walls made of timber with wooden floors	1	0,2
	2	0,3
	3	0,4

Height above ground level

The higher the monolithic strip rises above ground level, the better the floors of the house will be protected from dampness and cold. However, the height of the foundation to maintain stability and load-bearing capacity must correlate with its width. The best option: the height of the tape above the zero mark is equal to its width.

Expert opinion

Sergey Fedorov

Professional builder. 18 years of experience

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Example: The laying depth is 50 cm. The width of the monolithic tape according to the table is 30 cm. This means that the height above ground level will be 30 cm, and the height of the entire monolithic tape will be 80 cm. The height of the ground part of the MZLF should not be lower than the snow level. The snow depth value depends on the region (you can find it on the Internet). For regions of the middle zone, this value does not exceed 8-10 cm.

Calculation of MZLF on heaving soils

When building a house on heaving soils, more complex calculations are made, the purpose of which is to determine the heaving deformation. It is quite difficult to make such a calculation yourself, so you need to entrust it to professional designers or use a ready-made table:

Name and degree of soil heaving	Number of floors of the building	Width of foundation base b, m	Thickness of the pillow t, m	Foundation design option	Reinforcement option
clays, loams and sandy loams, fine and silty sands, moist - medium sandy	1	0,3 / 0,2	0,6/0,7	G.	3
	2	0,3 / 0,2	0,5 / 0,6	G.	3
	3	0,3 / 0,2	0,4 / 0,5	G.	3
clays, loams and sandy loams, fine and dusty sands, moist - highly heaving	1	0,3 / 0,2	0,7 / 0,8	G.	4
	2	0,3 / 0,2	0,6 / 0,7	G.	4
	3	0,3 / 0,2	0,5 / 0,6	G.	4

In column 2 “Sole width” and column 3 “Cushion thickness”, the values for heated and unheated rooms are indicated through the sign /. The column “Reinforcement option” indicates the minimum number of reinforcing bars that must be used to reinforce the monolithic strip.

Construction of a shallow foundation: construction technology

The technology for constructing MZLF is not complicated; filling can be carried out according to SNiPs 3.03.01-87, 2.02.01-83 or according to our instructions. Reason for frame house 10 x 10 m can be poured in 1-2 days. Before you start pouring, you need to decide where you will take the concrete solution. There are two options:

1order concrete class B22.5...B17.5 at the nearest RBU. In this case, the mixture will be delivered to you at the specified time by a concrete mixer truck. If the ABS cannot reach the pouring site, then a special hose is used through which the concrete solution will be supplied to the formwork. Ordering a sleeve will slightly increase the cost of ABS services. In addition, you will have to pay for every hour of downtime of the special vehicle.
2 prepare concrete yourself. At the same time, you will not depend on RBU and will spend significantly less money, however, the quality of the concrete mixture will be slightly lower. When mixing concrete, the recipe must be strictly followed. To prevent concrete from starting to set ahead of time, you can use special additives. You can begin preparing concrete immediately after installing the formwork.

Installation of MZLF: step-by-step instructions from A to Z

Preparatory work and marking

The installation of a shallow foundation begins with site preparation, which consists of removing debris and uprooting stumps. The top layer of soil with vegetation is cut off. If necessary, leveling and filling of soil is carried out, followed by compaction.

The marking is carried out as follows: the perimeter of the future foundation is established, beacon pegs are driven into the corners. Ropes are stretched along the future monolithic tape.

Expert opinion

Sergey Fedorov

Professional builder. 18 years of experience

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The diagonal between the corners must be strictly 45 degrees. You can check the evenness of the markings using a tape measure and a building level.

Construction of trenches and cushions

The depth of the trench depends on the depth of the foundation and the thickness of the cushion. The width of the trench is made 10 cm wider than the calculated thickness of the monolithic tape. This is necessary for installing the formwork. When constructing MZLF on loose soils, the slopes of the trench can be strengthened with boards. Pillowing is necessary to reduce the impact of frost heaving forces on the foundation. The thickness of the cushion, as a rule, is 20-30 cm for slightly heaving and non-heaving soils. For heaving ones - determined according to the table given above.

For corners where the walls of the future house intersect, it is necessary to strengthen the reinforcement frame by installing additional vertical rods, which are welded to the longitudinal rods. This reinforcement allows the strip foundation to withstand critical loads acting at the intersections of the walls.

You can lay the reinforced frame on a prepared cushion, but it is better to do it on the starting layer of concrete. The thickness of the starting fill should not exceed 20% of the entire height of the tape. Concrete pouring helps create a more even surface on which the reinforced frame is laid. If you decide not to fill the starting layer, then support fungi should be used to raise the reinforced frame above the surface of the pillow by 5-7 cm.

Expert opinion

Sergey Fedorov

Professional builder. 18 years of experience

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The reinforced frame should be located in space, nowhere in contact with the bedding and formwork.

Pouring concrete

Filling should be done at a temperature of +10 C and above. Before pouring, the formwork must be moistened, then the concrete will lie more evenly. The mixture must be poured in layers, the layer thickness should not exceed 40 cm, optimally 20-30 cm. Each layer is subjected to 5-10 minutes of vibration compaction. This technology does not allow voids to form inside the concrete. To supply the concrete mixture to the formwork, you must use an elastic sleeve or chute.

Layer-by-layer foundation pouring

After pouring is completed, the formwork is covered with a vapor-proof film. Hardening of the concrete lasts 25-30 days, after which the formwork is dismantled and the gaps between the foundation and the trenches are filled with soil.

Insulation of a shallow foundation

Professional builders recommend be sure to insulate the MZLF. It is recommended to do this immediately at the time of construction of the structure. An insulated foundation will protect the floors of the house from dampness and cold, which is especially important when arranging the floor “on the ground”. In this case, in the absence of thermal insulation, all the heat from the floor will go into the ground.

There are external and internal thermal insulation MZLF. External - when the insulation is attached to the outside of the monolithic tape, internal - from the inside. External insulation is considered mandatory, but internal insulation is usually done if the house has a basement. What insulation should I use? There are a lot of options. The most popular are:

Penoplex. Dense thermal insulation, excellent heat conservation. Its service life is significantly longer than that of conventional foam. Penoplex is resistant to rodents, mold and practically does not absorb moisture. In terms of price/quality ratio it is best material for thermal insulation of shallow foundations.
Expanded polystyrene. The extruded material is slightly inferior to penoplex in terms of physical and mechanical properties. However, the price of polystyrene foam boards is 20-30% cheaper. It can be used in dry and dusty soils with minimal moisture.
Polyurethane foam. Liquid spray thermal insulation is an expensive option, but it has many advantages: no joints between slabs, a service life of at least 50 years, minimal water absorption and resistance to aggressive environments.

It is not recommended to make a prefabricated foundation on heaving soils. The forces of frost heaving will push out individual elements, which will lead to the destruction of the foundation.

At correct execution of all work on the installation of FBS, a prefabricated foundation of a small foundation will last 70-80 years. This is exactly the service life that reinforced concrete blocks have.

For the construction of small houses, as well as various outbuildings the best option grounds is shallow foundation. Its construction will not take much time, and the entire process can be completed independently. In order for a shallow 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 main differences between a shallow foundation

Depth regular 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 is also decreasing. Not only concrete, but also red brick and concrete blocks are suitable for its manufacture.

A shallow foundation also has its disadvantages: it is only suitable for the construction of one-story buildings of a small area; requires the arrangement of a drainage system on heaving soils. Such a foundation can be poured only in the warm season, and it cannot be left unloaded for the winter. When the soil freezes, it pushes out light foundation, damaging its integrity.

Foundation construction technology

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

So, to work you will need:

roulette;
plumb line or level;
wooden pegs or iron rods;
thick fishing line;
pick-up and bayonet shovel;
geotextiles;
sand;
crushed stone;
reinforcement with a cross section of 12 or 16 mm;
formwork materials;
polyethylene;
concrete solution;
trowel.

The area for a 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 place the beacon from the peg. A fishing line is pulled between the pegs, secured, then perpendicular lines are drawn from each corner. Having connected the beacons into a rectangle, they check the perimeter along the diagonals. If the angles and sides of the marking are equal, you can mark the internal perimeter, according to the project.

The width of the foundation strip is usually 40 cm, so inside the markings it is necessary to mark the internal boundaries of the base. To do this, step back 40 cm in both directions from each outer corner along the stretched fishing line. These points are marked with beacons, and then they retreat from them beyond the perimeter by 20-30 cm and drive in pegs. This is necessary for more accurate designation of angles, both external and internal. In addition, while digging, closely spaced pegs can accidentally get caught and knock down the markings.

The soil is removed to a depth of 70 cm, counting is carried out from the lowest marking point. The walls of the trenches must be strictly vertical, which is periodically checked with a building level. If the soil is crumbling, wooden supports should be installed as you move along the perimeter. When the trenches are ready, check the horizontal level of the bottom and 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 use regular 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 secured with something, for example, with bricks. This will not allow the geotextile to move while compacting sand and laying reinforcement.

In an area with clay soil, the thickness of the cushion 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, tamping it thoroughly each time. For better compaction, layers of sand are shed with water. A layer of gravel about 10 cm thick is poured on top of the sand cushion, and it is also compacted well. After this, the formwork can be installed.

Assembly and installation of wooden formwork

Smooth boards with a thickness of 2 cm or more, durable plywood, and OSB boards are suitable for formwork. The sheet material is cut into pieces with a width of 40 cm, and the boards are knocked down into panels. It is more convenient to connect the formwork elements with self-tapping screws, then dismantling the structure is much easier. When assembling the panels, it should be taken into account that the inner side should be as smooth as possible, otherwise all irregularities will appear on the foundation walls. Since wood strongly absorbs water from the solution, the formwork should be covered with plastic film.

When required quantity The panels are ready, they begin to install the formwork. Parts of the formwork are placed on both sides of the trenches, leveled horizontally and vertically, and knocked down along the upper edge with transverse bars at certain intervals. Next, the structure is strengthened with spacers from the outside so that the formwork walls do not come apart when pouring. At the end of the installation, you should make sure that there are no gaps or cracks in the formwork, and that the walls are positioned strictly vertically.

On the inner walls of the shields, mark the level of filling the solution; 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 markings on the walls, many builders use fishing line: they stretch it inside the formwork and secure 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. Rods are cut from the reinforcement to fit the width and length of the trenches, and then tied into a lattice. The dimensions of a standard cell are 30x30 cm. Soft wire is used for binding, but it is not advisable to weld the frame: welding reduces the tensile strength of the metal, which leads to cracks in the base. In addition, welded grating is more susceptible to corrosion.

Having laid the lattice on the bottom, tie the frame with reinforcement at the joints. If the height of the base exceeds 30 cm, the reinforcing frame should be made two-level. To do this, knit a 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, or reach the concrete pouring level. Metal protruding from the foundation will quickly rust from rain and snow, which means the strength of the foundation will be reduced.

The strength of a shallow foundation directly depends on the quality of the concrete. For filling, it is recommended to use a solution of grade M200 or higher. When making the solution yourself, pour 1 part of cement into a container, add 3 parts of sifted sand and 4-5 parts of fine gravel or crushed stone. If everything is done manually, first mix the dry ingredients, and then gradually add water.

Although the height of the foundation is small, it is recommended to fill the trenches in layers. This will help compact the solution better and distribute it more evenly. The first layer is poured 20 cm thick, leveled if possible and pierced to the bottom with a piece of reinforcement in several places. Particular care should be taken to pierce 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 frame rods, at the joints of the walls, and get rid of air voids.

The last layer of concrete is leveled along the line, the surface is smoothed with a trowel, and then sprinkled with dry cement through a sieve. This contributes to faster setting and strengthening of the solution; in addition, the surface sprinkled with cement does not crack when drying. 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 extend the service life of a shallow foundation, it is recommended to insulate its outer walls with polystyrene foam boards or polyurethane foam. It is advisable to make a blind area 1 m wide along the perimeter of the base, and additionally install drainage ditches in flooded areas.

The construction of such a foundation has slight differences. Used bricks can be used, as long as they are fired and intact. You can make the foundation blocks yourself, which will allow you to save a little on materials.

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

mark the area and dig trenches;
lay geotextiles, a sand cushion and a layer of crushed stone;
knit and lay out reinforcement, the top of which should not reach approximately 5 cm to the edge of the trench;
fill the holes with concrete level with the ground, level the surface;
after the concrete layer has set and hardened, several rows of blocks or bricks are laid out with mandatory bandaging 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, it does not need to be insulated, but the masonry can be immediately plastered with mortar. If the described technology is followed, the foundation will last for several decades.

Video - Do-it-yourself shallow strip foundation

The most cost-effective and easy-to-build option for foundations for houses made of brick, wood or aerated concrete, built on normal soils that are not prone to heaving.

The page provides detailed information on the calculation method and technology for constructing a shallow strip foundation. You will also watch videos that explain the most important aspects of creating a strip foundation with your own hands.

Shallow strip foundation - calculations

There are two types of calculations that must be performed when designing a shallow strip foundation: the first is the calculation of its load-bearing capacity and dimensions, the second is the calculation of the materials required to create the foundation.

Calculating the bearing capacity is a complex process; it is necessary to take into account a very large number of factors: the depth of freezing and soil resistance, the deformation loads that the soil will exert on the future foundation, the weight of the structure and many others.

Rice. 1.1: Shallow strip foundation

You can calculate the required materials from start to finish yourself. To do this, you need to know the dimensions of the foundation, on the basis of which further calculations will be made for such materials as:

Concrete;
Reinforcement and wire for knitting;
Crushed stone and sand;

As an example, we provide a calculation of the materials required to create a shallow strip foundation 40 cm wide and 60 cm deep for a house with a wall perimeter of 54 m (length - 9 m, width - 6 m).

To calculate the materials, we need to determine the volume of the foundation: the perimeter of the tape must be multiplied by its width and length

54*0.4*0.6 = 12.96 m3;

Calculation of materials for compacting bedding

To create a compacting bedding, fine crushed stone and sand are used. Soil compaction is necessary in order to reduce the deformation and buoyancy loads that the soil exerts on the foundation.

Rice. 1.2: Sealing pad diagram

We calculate the volume of the bedding layers (they will be the same, since the thickness of the layers is identical): 56 (length similar to the perimeter of the base) * 0.4 (w) * 0.1 (t) = 2.24 m3.

The weight of 1 m3 of crushed stone and sand is data that can be found in any construction reference book: 1 m3 of sand weighs 1440 kg, crushed stone - 1600 kg. Now we calculate the mass of materials we need:

Sand mass: 2.24*1440 = 3225.6 kg;
Mass of crushed stone: 2.24*1600 = 3584 kg.

Concrete mass calculation

Concrete- the main part of the cost estimate for the construction of a shallow strip foundation. If you have a concrete mixer, you can do it directly on the work site, or order a machine for ready-made concrete.

To fill a shallow strip foundation, according to the current SNiP, it is necessary to use concrete of the M300 standard, since concrete of a lower density will not provide the required load-bearing capacity of the foundation strength.

Rice. 1.3: Structure of M300 concrete used for pouring foundations

The nominal mass of 1 m3 of M300 concrete is 2389 kilograms. To determine total weight required concrete we need to multiply the volume of the foundation tape (12.96 m3) by the weight of 1 m3 of concrete:

12.96*2389 = 30,961.44 kg.

Since concrete tends to shrink when hardening, the mixture must be taken with a margin of 3-4% of the required weight:

30961.44 * 0.03 = 928.9 kg;

Total we need 31.9 tons of M300 concrete.

Calculation of materials for base reinforcement

Any strip base requires mandatory reinforcement with a reinforced frame consisting of two horizontal belts, which are connected by vertical jumpers.
To create a horizontal contour of the frame, hot-rolled reinforcement A3 (12 mm in diameter) and reinforcement A1 (8 mm) are required. for jumpers. The frame connection is made with knitting wire.

Based on the total duration of the foundation strip, you can calculate the length of the required reinforcement A3:

54*4 (number of frame contours) = 216 m;

In addition, we will need an additional 10 m of reinforcement to strengthen the corners of the frame. The total length of the A3 rods is 226 meters.

Rice. 1.4: Reinforcement of a shallow strip foundation

Now we determine the amount of reinforcement A1 for the jumpers. Considering that the frame must be recessed ten centimeters deep into the foundation, and the height of our base is 60 cm, the height of the vertical lintel will be 40 cm.

We calculate the total number of vertical rods: (54/0.2)*2 = 540 pcs;
Which allows you to determine the required length of reinforcement: 540 * 0.4 = 216 m.

One frame connection requires approximately 20 cm of wire. Based on the total number of jumpers (540 pcs), we calculate the number of connections and the length of the binding wire:

540*2 = 1080 connections;
1080*0.2 = 216 m of wire for knitting.

Shallow strip foundation - construction technology

Construction shallow strip foundation begins with marking the territory. To do this, pegs made from scraps of reinforcement and string are used, with the help of which the contour of the future foundation is marked on the ground according to the project.

Land works

If the walls of the pit crumble during digging, it is necessary to make temporary supports from boards. It is also extremely important to monitor the verticality of the bottom of the trench, since any slopes will increase the consumption of materials to create a compacting cushion.

Upon completion of digging and leveling the walls of the pit, we begin arranging the bedding. The first ball is sand. It must be poured out in layers, 3-5 centimeters, and each layer must be spilled with water and compacted so that the sand receives maximum density.

Rice. 1.4.1: Formation of sand bedding

A layer of crushed stone is poured on top of the sand, which also needs to be compacted using a hand tamper.

Installation of formwork

To create the formwork, boards 20 mm thick are used, which are fastened together using bars and screws or a metal corner.

Rice. 1.5: Formwork for shallow strip foundations

Along the outer contour of the formwork, spacers are installed from wooden beam, the spacer spacing is 50 centimeters, they are necessary to ensure that the formwork does not deform from the weight of the concrete.

Inside the formwork, the boards must be covered with oilcloth, since the laitance of liquid concrete can leak into the cracks between them. Upon completion of installation on the formwork, we mark the level at which the filling will be performed.

Reinforcement

The technology for reinforcing a shallow foundation in accordance with the requirements of SNiP does not require mandatory strengthening of the middle part of the foundation, since it does not experience critical loads. It is enough to arrange the frame along the upper and lower contours of the tape.

Such a frame consists of two vertical belts of A3 reinforcement with a diameter of 13 mm, which are connected by vertical jumpers made of smooth 8 mm reinforcement. The frame is fixed with knitting wire.

The most convenient way to knit wire by hand is to use a crochet hook. Fixing one knot requires 20-25 cm of wire bent in half.

Rice. 1.6: Layout of reinforcement in the frame to strengthen the strip foundation

The reinforcement frame is knitted in a place convenient for you, and only then the finished part of the structure is placed inside the formwork. It is extremely important to correctly connect the reinforcement at the corners of the foundation, since it is in this place that the bearing and deformation loads on the foundation are maximum.

At corner joints it is necessary to install additional L-shaped reinforcements made of reinforcement with a diameter of 13 mm. No less reliable are U-shaped connections, which you can see in the image below.

Rice. 1.7: Connection diagram for reinforced frame corners

Pouring concrete

To fill the foundation with concrete, it is recommended to order the ready-made mixture in the required volume, since one-step pouring provides better final strength of the foundation.
If you are deprived of this opportunity and are forced to prepare concrete yourself, be guided by the proportions of cement, sand and crushed stone shown in the image.

Rice. 1.8: Pouring concrete into a shallow strip foundation

After pouring concrete into the formwork, it must be treated with a vibration compactor or a hammer drill with an appropriate attachment. Compaction allows you to remove air bubbles from the concrete, which negatively affect the final strength of the foundation.

Upon completion of compaction, the concrete is leveled using a rule and covered with oilcloth or tarpaulin. If the foundation is being built in the hot season, in order to avoid cracking, the concrete must be regularly moistened during the maturation process. The concrete foundation reaches its design strength in 3-4 weeks.

Do-it-yourself shallow strip foundation (video)

A video that examines in detail the technology for creating formwork for a shallow strip foundation.

We make the reinforced frame for the strip foundation correctly.

Let's figure out how to properly knit reinforcement into a frame to strengthen a strip foundation.

Features of pouring concrete into strip foundation formwork.

A classic for low-rise development is one with a low construction budget. The monolithic lattice structure allows floors to be built on the ground, has high spatial rigidity, and is suitable for any wall materials.

Shallow strip foundation step by step

The operation of any foundation is complicated by uneven heaving forces and insufficient design soil resistance. The technology became possible thanks to a set of measures to eliminate swelling:

the topsoil layer is replaced with sand, crushed stone depending on the level of groundwater level
the blind area is insulated to a width of 0.6 - 1.2 m
the perimeter of the building is equipped with ring drains
backfilling of trench sinuses is carried out with inert material

There is no heaving in non-metallic materials, excess moisture is removed by drainage, and the heat insulator retains the geothermal heat of the subsoil. It is better to carry out all work at the foundation pit stage in order to reduce the construction budget.

Calculation of parameters

Shallow strip foundation is not regulated in depth only if the above measures are taken to compensate for heaving forces. The calculated settlement must be within acceptable values, otherwise it is necessary to supplement the structure with bored piles. The standard parameters of the MZLF provide a 2-3 times greater load-bearing capacity for 2-storey brick cottages with an attic:

For MZLF tape, two reinforcement belts and anchoring in L-shaped and T-shaped joints are usually sufficient. Longitudinal rods 8 – 16 mm, reinforcement A400 (“corrugated”), clamps, anchors made of rods 6 – 8 mm smooth reinforcement A240.

Full-scale axle offset

Shallow strip foundation marked in a standard way. Instead of pegs, it is better to use cast-offs, consisting of two pointed bars with a crossbar between them. If you level all the cast-offs, mark with dashes the axis of the wall, the side edges of the tape, the cords can be removed during excavation work and tightened later to install the formwork. They are taken outside the perimeter of the MZLF (1 - 1.5 m) so that the soil underneath does not crumble. When breaking down you need to consider:

MZLF is not recommended if there is a height difference of one and a half meters between adjacent walls. The lateral movements of the soil are too significant; reinforcement of the belt with piles and retaining walls will be required, which will significantly increase the construction budget.

Trench development

Even with the maximum depth of the MZLF tape, all work can be done independently. Special equipment is needed for pits, but here you can get by with trenches. When excavating soil, common mistakes made by individual developers are:

Therefore, it is recommended to remove black soil from the entire perimeter with a bayonet. The dimensions of the pit are 1.2 m larger than the size of the foundation. This distance is necessary for insulating the blind area. Inside the trenches for the MZLF tape, additional trenches for drainage with a cross-section of 30 x 30 cm are required.

Drainage system

Clay soils swell only when they are abundantly wetted with groundwater. Drainage reduces heaving forces by 40% without additional measures. To create an underground sewer circuit, it is necessary to perform the following work:

To increase the service life of the system, the bottom layer of the natural filter is laid on geotextiles, with which the entire structure is covered on top after backfilling.

Substrate

Adding non-metallic material to the bottom of the trench is necessary to solve the following problems:

leveling the base
drainage to prevent concrete from getting wet
elimination of heaving forces

In different regulatory documents the thickness of the sand and crushed stone cushion varies from 20 to 80 cm or is four times the width of the MZLF tape. In practice, a thickness of 40 cm is more often chosen, making it layer by layer (10 cm) with mandatory compaction (vibrating plate, rammer, wetting with water). You can alternate layers in any order, taking into account the distance from the base of the MZLF to groundwater.

Footing

A monolithic strip foundation is poured into formwork, which drains the concrete with a lower underlying layer with high drainage qualities. Some of the cement will leave along with the liquid, and the structure will experience a decrease in strength. Therefore, the following technology is used:

The footing allows you to reduce the protective layer (bottom) of concrete of the MZLF tape to 1.5 - 3 cm, lay a waterproofing carpet on top of it (2 - 3 layers roll material). The supporting surface of the foundation and the strength of the structure are increased, in which the cement laitance is completely preserved. It is convenient to mount formwork panels on the screed; you can additionally mark the axes. Plastic supports for fittings do not tip over when installing frames.

Reinforcement

With a height of MZLF from 70 cm (together with base part) it is inconvenient to lay reinforcement cages inside the formwork. Therefore, first the tape is reinforced, then shields are installed around the frames. The work is carried out in stages:

The ideal option is to bend the rod 90 degrees, launch it onto the adjacent wall, and overlap it with the next rod. The adjacent rod in the same row, on the contrary, is launched from another wall so that the joints are located at a distance of 60 - 80 cm minimum. The lower, side protective layers are created by polymer parts placed on the rods at intervals of 0.7 - 1 m. The rods of one wall laid in the corners on the rods of another without bending are considered an interruption of the reinforcing belt, even when connected by welding.

Longitudinal rods are made from A400 reinforcement with a periodic section of 8 – 16 mm. Anchors, transverse, vertical rods, clamps made of smooth 6 - 8 mm A240 reinforcement.

Formwork

Therefore, at shallow depths of MZLF, it is recommended to install formwork panels to the entire height of the tape with a 7 cm margin. When installing the top edge of the shield above the design level, concrete is guaranteed not to splash out during vibration compaction and leveling.

Depending on the height of the foundation, the formwork panels are made of edged boards or plywood. This will allow the use of lumber after stripping at the stage of manufacturing partitions and roofing.

In the absence of an underground (floors on the ground), ventilation ducts in the MZLF strip are not needed. If beam ceilings are used, pipes must be installed in the formwork panels. The total area of the vents should be about 1/400 of the size of the base part.

Concreting

The mixture is laid inside the formwork in layers, in one direction. The thickness of the layer depends on the size of the nozzle of the deep vibrator used for compaction. The normal quality of the tamping is indicated by the absence of large crushed stone, air bubbles on the surface, and the presence of cement laitance.

It is prohibited to drop concrete from a height of 1 - 1.5 m; gaps inside the formwork are larger than 2 mm. MZLF is characterized by small volumes of work, which makes it possible to fill the tape per appointment. If stage-by-stage concreting is planned, vertical partitions are installed in the middle thirds of straight sections. After pouring, the first three days require a wet compress (sawdust constantly moistened with water) or watering the surface from a watering can.

Protection of MZLF from moisture, soil heaving

After stripping, concrete structures are protected from moisture and swelling in several ways:

Volumetric or complex waterproofing is considered the most effective. In the first case, concrete is modified with special additives during mixing or impregnated with Penetron to impart moisture-repellent characteristics. In the second option, concrete structures are treated with a primer, coated with mastics, and covered with films, rolls, and membrane materials.

It is a mistake to believe that a shallow strip foundation (FMF) does not require special knowledge and experience in construction. The choice of any type of foundation, as well as its construction, are the most difficult and critical stages in the construction of a house as a whole.

Miscalculations and mistakes are not allowed in this process, otherwise the entire construction progress may come to naught or require additional investments for restoration work. To avoid mistakes, it is necessary to find out the qualitative composition of the soil of the site, calculate the weight of the future structure, and find out the groundwater level. It would be wise to use the services of a professional who will calculate the foundation and give the necessary recommendations.

Professional approach with the creation of TTK (standard technological map), will ensure strict compliance with SNiP, reducing project costs and labor costs. Only in this case can you be sure of the quality of the shallow foundation (MSLF) that meets all the parameters of SNiP.

Advantages and disadvantages of a shallow foundation

Any construction method has its pros and cons, and the construction of a shallow foundation is no exception. The advantages of building a house on a shallow strip foundation are as follows:

can be installed do-it-yourself shallow strip foundation from “A” to “Z”;
may not be used construction equipment - no need to bury the foundation deep;
possibility of insulation strip base, as well as “warm floor” technology devices;
high strength designs;
low cost project even if the work is performed under a contract by a construction company.

Among the disadvantages, it is worth noting first of all - this is the construction of the structure on heaving soils. In order for the building to gain sufficient strength, a blind area is made around the entire structure. Following all the norms and rules (SNiP) you can do drainage system under the base of the building.

Another nuance is pouring concrete onto heated soil. In addition, according to the TTK instructions (standard technological map), the construction of a house on this basis is carried out within a short time - up to 5 months.

Cost of work

The cost of a shallow strip foundation can be calculated by cubic meters, on average it comes out to 15 thousand rubles per 1 cubic meter, or 3 thousand rubles per linear meter. The cost of installing a shallow strip foundation includes:

excavation work - digging out the tape;
laying a sand cushion - 200 mm;
installation of formwork;
installation of reinforcement frame;
pouring concrete mixture;
drainage for shallow foundations - on heaving soils;
dismantling of formwork.

This is calculated if the installation of a shallow strip foundation is ordered from a professional organization. The calculations should include the cost of reinforcement - 12 mm in diameter, the cost of sand and delivery of the material. For high-quality waterproofing of shallow foundations, reinforced glass insulation with hot bitumen mastics is used.

For which buildings is the base suitable?

A shallow strip foundation for a house made of aerated concrete; it is also well suited for two-story buildings built from lightweight material:

wood;
expanded clay;
foam concrete.

SNiP (Foundations of Buildings and Structures) does not recommend the construction of buildings of more than two floors and exceeding the area of more than 100 m2. A shallow strip foundation is placed on clay, but it is worth remembering that the typical dimensions of buildings on clay and loamy soil should not exceed 6x6 m.

Features of a shallow strip foundation

To save time and money in private housing construction, shallow foundations are used. The main advantages of this structure are high reliability and low cost. The use of shallow strip foundations occurs in buildings with different walls: logs, gas blocks, panels. Unlike other types of foundation, the design of a buried foundation allows you to save up to 70% on materials and up to 80% on labor costs.

Due to the influence of heaving forces (heaving soils) directed at the walls of the structure from the side and below the base, the area of the walls decreases and the stress on the side is reduced significantly, the mass of the building regulates the heaving forces from below.

There are basic technological rules for constructing a structure:

bury the foundation no deeper than 30-40 cm;
grounds should be 10 cm wider than the thickness of the walls;
on heaving soils, the foundation should be created as a monolithic reinforced concrete structure capable of balancing heaving forces from below and uneven pressure from above;
laying the foundation shallow laying on prepared compacted soil, providing a sufficient coefficient of water drainage. For this, coarse sand or crushed stone is used. In this case, the load during subsidence during soil thawing is balanced;
high groundwater levels require waterproofing work, in this case artificial system drainage from penetration from above;
shallow foundation requires insulation from above. It is necessary to build a blind area around the base up to 1 meter wide; for this, a layer of thermal insulation (extruded polystyrene foam or other insulation) is laid on the ground.

Is it necessary to insulate? A layer of thermal insulation will save the base from frost heaving and the effects of temperature loads. The blind area around the house is insulated so that the soil underneath does not freeze, but, on the contrary, itself becomes a source of heat, stabilizing the temperature situation under the house.

Laying a shallow foundation

A non-buried base can be made in three ways: monolithic, using reinforced knitting mesh, laying in separate blocks or bricks. All methods are practical and equally easy to implement. You can choose any option based on what material is available. To start practicing construction work, you need to have an idea of where to start, as well as the order of further stages of construction.

First, marking and design are carried out; for this, they conduct reconnaissance of the area, study the properties of the soil in order to decide how deep it is necessary to lay the foundation for the future structure. Having drawn up a project - cross-sectional drawings of the future building, you can begin further steps in building the house.

Step by step instructions:

Marking. A cast-off made of wooden blocks is installed, which are nailed to the pegs - at a distance of 1.5-2 meters from the outer edge of the intended corners of the base. Nails are nailed onto the bars, onto which a tape or rope is pulled to mark the lines of the future trench.
Earthworks. You should try to dig trenches that are initially level. To check, use a spirit level, level and tape measure. The subsequent consumption of material, time and labor largely depends on the quality of work at this stage.
Laying the pillow. Coarse sand is poured into the bottom of the trench - 20 cm to compact the sand cushion, it is filled with water and compacted with a tamper. A layer of crushed stone, pebbles or expanded clay is laid on top - up to 20 cm.
Reinforcement. SNiP does not recommend making a shallow foundation without reinforcement. For reinforcement, a rod with a cross section of 12 mm is used. The frame consists of 2-3 rows of reinforcement; horizontal rods are tied onto driven rod scraps. The spacing between the rods is 15-20 cm; the elements are connected to each other with knitting wire.
Installation of formwork. Formwork is made from formwork panels or boards. The formwork should rise 30 cm above ground level. After installation, the walls are fixed with spacers, pressing them against the walls of the trench. “Sanitary” holes are made - sewerage, water supply.
Pouring concrete. The solution is prepared in a cement-sand ratio of 1:3, respectively. Metal frame should be filled with a layer of solution of at least 3 cm. To prevent the accumulation of air and give strength, the solution is compacted, air bubbles are expelled with a probe or stick.
Dismantling of formwork. The panels should be dismantled after the concrete has completely hardened.

If groundwater is close, you should think about waterproofing. An inexpensive way to produce high-quality waterproofing is to use bitumen.