Shallow strip foundation for a house. Construction of a shallow strip foundation Installation of formwork under a shallow foundation

Foundation work is not considered the most difficult construction work, but in terms of responsibility these are one of the most critical building structures. Most mistakes during foundation construction lead to very serious consequences; correcting them is very difficult and expensive, and in some cases impossible. All foundation calculations must be carried out in accordance with the provisions of SNiP 2.02.01–83.

File for download. SNiP 2.02.01–83. Foundations of buildings and structures. SP 22.13330.2011

During calculations the following are taken into account:

• loads acting on the base of the foundation;
• soil indicators, presence and location of groundwater;
• maximum permissible deformations and load-bearing characteristics;
• characteristics of climatic zones and foundation depth.

These are very complex calculations, we will not dwell on them. For the simplest structures, builders take standard parameters for a given climate zone and soil characteristics as the foundation. They already have a large margin of safety, which ensures the reliability of the design.

Shallow strip foundation- options

Introductory table of the approximate width of the strip foundation

Minimum tape width depending on the number of storeys	Tape width, cm The bearing capacity of the soil is 0.72 kgf/cm2. Example: silty, fine micaceous sands, silty sands, silty clay	Tape width, cm Soil bearing capacity 1 kgf/cm2 Example: clay, sandy clay, silty clay, silty inorganic silt	Tape width, cm The bearing capacity of the soil is 1.4 kgf/cm2. Example: sand, clayey coarse sand, silty crushed stone, clayey crushed stone	Tape width, cm Soil bearing capacity >1.92 kgf/cm2. Example: gravelly sand, gravel, crushed stone
Frame house 1st floor	30	30	30	30
Frame house 2 floors	38	30	30	30
Frame house 3 floors	58	43	30	30
Frame house, lined half-brick, 1st floor	30	30	30	30
Frame house, lined half-brick, 2 floors	53	40	30	30
Frame house, covered "half-brick" 3 floors	81	60	40	30
Brick house, 1 brick laying, 1st floor	40	30	30	30
Brick house, 1 brick, 2 floors	73	53	35	30
Brick house, 1 brick, 3 floors	106	81	53	40

Tape width depending on wall material

A shallow strip foundation is one of the most frequently used options in private construction; in all respects it satisfies most developers. The construction of the foundation can be divided into three stages: marking, digging a trench and constructing formwork, pouring concrete and leveling.

Let's look at each stage in detail. We will talk about the stages of construction of a shallow reinforced foundation on a sand bed.

Work must be done carefully and slowly. It’s better to lose an extra hour or two during marking than to have problems later with the finished foundation tape.

Step 1. Drive wooden pegs around the perimeter of the foundation. In order to align the dimensions and angles of the tape, you need to prepare a basic device in the form of small benches. Drive two pegs into the ground at a short distance from the corners of the foundation and attach horizontal boards to them.

Step 2. Strengthen the nails in the boards and tie ropes to them. Try to first check the angle between the ropes with an ordinary large square. This will give you an approximation of the foundation lines.

Step 3. Align the corners of the tape; they should be exactly 90°. This must be done by checking the diagonals. The dimensions of the two diagonals cannot differ by more than two centimeters. Such scatter can be easily removed during the construction of the building box.

Step 4. Do not remove the ropes; use them to carefully mark the position of the tape with a shovel; it is advisable to dig a trench as deep as the bayonet of the shovel (about 20 centimeters).

Step 5. Now you can remove the ropes and continue digging the trench. Decide right away where you will put the land. It can be taken outside the perimeter of the building or leveled under it. In any case, the fertile layer must be completely removed.

Step 6. The width of the trench is equal to the width of the walls of the building. If the soil on the site is dense, then there is no need to do formwork in a trench; if the walls are crumbling, then you will have to do formwork along the entire height of the foundation.

The depth of the trench is within 60÷80 cm, taking into account a sand cushion up to twenty centimeters thick.

Video - Marking for the foundation

Foundation marking schemes	Description

Manufacturing

You can use second grade edged boards or special waterproof plywood. We will take boards 20÷25 mm thick and 20 cm wide; to assemble the panels we will use slats and scraps of boards.

Step 1. Production of formwork panels. There is no need to make them very large; then it will be difficult to install and dismantle. The length of the shields depends on their height, but in any case, try to ensure that the total weight of the structure does not exceed 50–60 kilograms. This weight can be done without special effort lift together. Try to fit the boards without large gaps, nail the vertical posts at a distance of 50–60 centimeters. More accurate indicators depend on the parameters of the foundation tape.

Shields – photo

Use nails for nailing; self-tapping screws will not only increase the cost of the formwork, but will also create problems during its disassembly. Almost all lumber after dismantling the formwork can be used for further construction of the building, it is advisable not to damage it again. You are unlikely to be able to accurately calculate the length of the shields; leave a margin of approximately 1.5÷2 meters in length; you will make this shield after accurately installing all the previous ones. In this position it will be possible to take exact measurements up to the corner and make the shield of the required length.

Step 2. Start laying out the formwork for the foundation. This kind of work cannot be done alone; you need to call an assistant. Lower all the panels one by one into the trench, fix the position with pegs and corner stops. Spacers should be inserted between the panels so that they do not change their position while fixing the formwork. Spacers do not work while concrete is being poured, they are only important during the assembly of the formwork. We advise you to immediately prepare spacers for the template; the quantity is determined taking into account the length and height of the foundation strip and the parameters of the panels.

Step 3. Fix the panels securely; it is better to place corner supports more often than to level the foundation later. Place your shields along the rope and constantly monitor their position. The joints of the boards are sealed with a board; fastening must be done in this place. Drive the pegs as deep as possible; the corner supports to the shields must be fixed with special small stops made from scraps of boards. You must exclude even the slightest possibility of violating the integrity of the formwork while pouring concrete. Such an “accident” always comes at a cost.

Step 4. During the installation of formwork, it is always necessary to provide for its subsequent dismantling. This means that the nails should be driven into places where they can be removed. Place all dismountable units only on the outer accessible side of the formwork.

Step 5. Check that the formwork is installed correctly. Pay attention not only to the linearity of the planes, but also to the reliability of fixation. Apply multidirectional forces to the formwork - if even slight vibrations of the structure are detected, immediately install additional stops. Remember that correcting formwork installation errors while pouring concrete is an extremely thankless task.

Assembled formwork - photo

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Video - Making formwork

Step 6. Place plastic tubes in the formwork at the locations of the ventilation ducts and inlet engineering communications. Secure the top boards of the formwork panels with boards or tie them with wire to prevent expansion.

Our foundation must be reinforced - its load-bearing capacity increases significantly. For reinforcement, construction reinforcement of periodic profile Ø 10 mm is used. The reinforcement can be tied together, which takes a very long time, but you can only lay horizontal bars while pouring concrete. We, of course, choose the second option. In terms of strength, a strip foundation loses almost nothing, and much less work and money will be required.

If everything is fine, you can start pouring concrete.

Pouring concrete

We will make the concrete ourselves from grade 400 cement, sand and gravel or crushed stone.

Nowadays, such heavy physical work is no longer done manually; you need to purchase or borrow a small concrete mixer with a drum volume of approximately 0.2 m3.

Before starting work, you need to calculate the required amount of building materials; calculations are made taking into account the total volume of the foundation tape. It’s easy to calculate the volume; multiply the length by the width and height. For one cubic meter of concrete you will need 325 kg of cement, 760 kg of sand and 1100 kg of crushed stone. These are approximate figures, they are needed only to guide the amount of materials. When purchasing materials, increase their quantity by 10%. You need to buy even more sand for a sand cushion.

No one weighs individual ingredients to the nearest gram when making concrete. When preparing concrete, take two shovels of sand and three shovels of crushed stone or gravel for one shovel of cement. Water is used as needed, the specific amount is determined experimentally, and the concrete must have optimal viscosity.

Step 1. Pour a layer of sand ≈15÷20 centimeters thick into the trench. The sand needs to be compacted well; use any available means for this or make a simple device.

Step 2. Fill in concrete mixture along the perimeter of the building, do not allow large differences in height. If you have an electric vibrator, great, it can compact the concrete along the entire height of the foundation. If tamping is done manually, then the concrete layer should not exceed 25–30 centimeters in height.

Step 3. Simultaneously with pouring, pay attention to the “behavior” of the formwork; if you detect any bulges or curvatures, immediately take measures to eliminate them.

Step 4. We decided that we would perform the foundation reinforcement in a simplified way. The rods are placed directly on the concrete. In total, we will have four rows of reinforcement in the tape, two in each layer. Cover the sand cushion with a layer of concrete approximately 30-40 centimeters thick. Level it horizontally and lay two rows of reinforcement. You shouldn’t try too hard, the rods will then become filled with mass, and a small angle of inclination (if any remains) will not have any negative effect.

Step 5. Continue pouring the foundation around the perimeter, when twenty to thirty centimeters remain to the top of the tape, lay the second row of reinforcement. Make sure that the ends of the reinforcing bars overlap by approximately 20÷30 centimeters.

Step 6. Align the zero level of the strip foundation; the variation in height in the corners cannot exceed two centimeters. Use a stretched rope; with its help you will perform the leveling faster and with better quality.

It is highly advisable to fill the entire foundation within one working day.

In most cases, this is possible for baths, but it all depends on the specific size, ability to organize construction work, professionalism and the number of workers. If you have to leave part of the work for the next day, then the liquid concrete in the formwork must be leveled horizontally as much as possible. The presence of “steps” with large differences in height significantly reduces the load-bearing characteristics of the foundation. The formwork should be removed two weeks after pouring the concrete. If the weather outside is hot and dry, it is recommended to moisten the concrete generously with water several times a day. A quickly drying foundation will not have the calculated strength indicators.

Why? Concrete is a unique material. IN ideal conditions the strength of concrete structures is constantly increasing. During the first 14–15 days, concrete gains 70–80% of maximum strength, then the rate of increase in strength slows down and after 30–40 years its strength increases by only a fraction of a percent. But it is increasing! Of course, this only happens in cases where the structure is not affected by precipitation, temperature changes, external forces, etc. That is why it is not recommended to remove the formwork in less than two weeks. Do not rush to dismantle it; during this time it is better to prepare for the next stage of construction.

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Video – Seminar on pouring the foundation

Now that you already have general concepts about foundation construction technology, we can give a few practical advice. With their help, it will be possible not only to simplify and facilitate a number of construction works, but also to improve their quality and reduce cost.

How to make concrete

A lot depends on the proper organization of work; we give advice from experts who have solid practical experience.

The concrete mixer must be in a stationary place, and ready-made concrete is transported to the foundation by wheelbarrows.

There are some “craftsmen” who advise dragging the concrete mixer along the foundation as it is filled. They transport water, sand, cement and gravel separately in buckets to each new location. Looking at this “technology” is both funny and painful. This organization of work increases the labor intensity at least twice and increases the time by the same amount.

What do we recommend? The concrete mixer must be stationary; install it taking into account the possibility of access. Place a barrel of water with a volume of approximately 200 liters near the concrete mixer. Bring sand and gravel to separate piles, and let the cement lie on pallets in bags. All materials must be available for filling into a concrete mixer without transfer.

Throw a bag of cement onto the pile of sand and use a shovel to cut it approximately in half. Half a bag of cement is just the norm for one batch of concrete. Turn on the concrete mixer, pour one and a half to two buckets of water into it, take half a bag of cement with your hands and pour it into the water. You can immediately throw gravel or crushed stone; the pebbles will break up small piles of cement well. Next, throw sand and gravel into the mixer one at a time. The calculation is simple - for one shovel of cement you need two shovels of sand and four shovels of gravel.

The specific amount depends on the size of your shovels; for the first batch, you can measure the amount of cement in half the bag, this will give you a rough idea. In the future, you will gain experience and you will already be able to determine the quality of concrete by eye by the viscosity of the mass. If the solution is too thick, add water in small portions. If it turns out liquid, add sand; gravel has almost no effect on the viscosity of concrete; it absorbs little water. I had to add a lot of sand - throw another shovel of cement into the concrete mixer. The cement that spilled onto the sand is picked up and used.

With water, you also can’t guess right away; the amount of water depends on the moisture content of the sand and gravel. For the first batch, it is better to take slightly less water and then add it as needed. Too much water can cause trouble - there won't be enough volume in the concrete mixer to add large amounts of sand and gravel.

Ready concrete must be transported to the foundation by wheelbarrows. When planning the organization of work, it is necessary to provide for such a number of people that the work proceeds in an assembly line manner, without anyone expecting anyone. The time for pouring the foundation with concrete should be equal to the time it took to make it. These indicators are influenced by many factors: the distance to the foundation strip, the volume of the concrete mixer, the professionalism and hard work of the workers.

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Important

Perhaps this is all we can advise beginners; in the future you will gain your own experience and you will be able to change and improve the algorithm for making concrete.

How to assemble formwork

Absolutely all individual nodes work in bending or compression. Why are we talking about this? And then, when assembling the formwork, there is no need to use huge nails and then bend them five centimeters on the back side. Not a single nail works to pull out. In corner stops, the nails are subject to bending forces and very insignificant pulling forces. Using normal nails will not reduce the strength of the structure, but it will make your work much easier during its dismantling.

Most of the boards after formwork are used for further construction - after removing the formwork, immediately disassemble it and clean the boards. There are cases when high-quality boards are used for formwork - we recommend covering them with plastic film. Install the film on the inside of the formwork, fix it with an ordinary stapler. The cost of the film is pennies compared to the cost of lumber. No master will process boards contaminated with cement on machines, and polyethylene will keep the materials in their original condition.

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How to dig a trench

It would seem that nothing is simpler - dig deeper and throw further. But those who have never dug themselves think so. Each job has its secrets, here are just a few of them.

1. First you need to trim the grass roots along the entire length of the trench. Using a shovel, cut the turf along the line on both sides of the foundation strip to a depth of approximately ten centimeters. This will not only make it easier to remove the sod, but will also make the edges smooth.
2. The first excavated soil should be thrown away as far as possible from the edges of the tape. You will still have to throw it further than you might think. It's easier to do this before you get too deep. Over time, the trench will become deeper, and more effort will have to be spent to throw out the earth. And if you have already made a mound near the edges, then you will have to transfer it too.
3. Increase the depth by the spade bayonet along the entire length of the trench, immediately leveling the edges. Then clean up the loose soil with a shovel, starting work from the place where you finished digging with a bayonet shovel. This way you won’t be compacting the soil yourself. When you’ve finished clearing the ground, repeat it all over again, work with a bayonet shovel along the entire length, then clean the bottom of the trench.

Video - How to dig a trench for a foundation

We guarantee that in this way you will be able to dig the foundation much faster and without “heroic feats of labor.” It is impossible to talk about all the intricacies of construction work in one article. Do not perform monotonous work for a long time, this accelerates physical and mental fatigue; if possible, change it after an hour or two.

We can give you one universal advice: Look for logic in every work. All actions should be aimed at one thing - obtaining maximum results with minimal losses. It doesn’t matter what the loss is: time, money or effort. If you listen to our advice, then work will always be a joy, not a punishment. Especially if it is done with your own hands and for yourself.

Video - Do-it-yourself shallow strip foundation

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 routing), 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 work shallow foundation(MZLF), corresponding to all 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 device of a shallow strip foundation is ordered in 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 standard sizes 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, shields. 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;
• a high groundwater level requires waterproofing work, in this case an artificial drainage system is installed to prevent 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 reinforcing 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 doing construction work, you need to have an idea of ​​where to start, as well as the sequence 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 instruction:

• 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.
• Excavation. 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. A step of 15-20 cm is maintained between the rods; 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. The metal frame should be filled with a layer of solution of at least 3 cm. To prevent air accumulation 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.

At low-rise construction wooden or brick houses, as well as buildings made of aerated concrete and foam concrete, a strip shallow foundation (MSLF) is most often used. This type of foundation combines the advantages of recessed and non-recessed structures, but its cost is much lower.

To determine the main differences between a shallow strip foundation and how to self-installation, consider its features, advantages and disadvantages.

Features of MZLF

For a standard buried foundation, it is necessary to dig a pit, the depth of which will be below the freezing level of the soil. If you live in a region characterized by harsh winters, then the depth of such a trench can reach 1.5 m, so during construction you will have to use heavy construction equipment.

If we consider the structure of a shallow strip foundation, then it represents a foundation laid along the perimeter of all load-bearing walls Houses. However, its depth rarely exceeds 50 cm.

Among other advantages of structures of this type, it is worth highlighting:

• The possibility of constructing a strip foundation for a house from aerated concrete, foam concrete and other lightweight materials, without the use of an excavator and mixer.
• Smaller volume building material and reduced labor costs.
• High structural strength.
• Large selection of materials and installation methods. For example, you can arrange a ribbon monolithic foundation, fill the base with concrete or make a more complex structure from brick.

Also, thanks to MZLF, you can easily insulate basement rooms.

Among the disadvantages of this light base It is worth noting the fact that a shallow strip foundation on heaving soils will have insufficient strength. The fact is that during the changing seasons, such soil sinks and rises, which can, in turn, lead to deformation of the shallow belt. However, this problem can be solved with the help of a drainage layer and sand filling, which will significantly reduce the load from the soil.

Important! MZLF cannot be laid on frozen ground or left unloaded in winter. The foundation should be poured in a short time, before the onset of frost.

For more information about MZLF, watch the video:

In order to make a shallow strip foundation with your own hands, you must first assess the type of soil that prevails on your site.

Assessment of soil composition and type

In order to determine the type of soil, it is not necessary to order an expensive service to study the geology of the site; it is enough to use the “old-fashioned” method. To do this, dig holes at several points, take some earth in your hand and try to roll it into a ball. If:

• The ball is rolled tightly, and its consistency resembles plasticine, then this is clay soil.
• After pressing the ball, cracks appeared on it - loam.
• The ball crumbled, then it was sandy loam.
• If you can’t roll a ball at all, then there is sand in front of you.

For each individual breed, it is necessary to calculate the required resistance in kg/cm2. This is necessary to determine the bearing capacity of the foundation, which, according to SP 22.13330, will be the following values ​​for:

• loam – from 1.8 to 2.8;
• sandy loam – 2-3;
• watered clay – 1-2;
• plastic clay – 2-3;
• medium-dense clay – 3-5;
• dense clay – 4-6;
• gravel with sand – 5;
• sand of different fractions – 3-5;
• wet sand – 2-3.

After assessing the composition of the soil, it is necessary to calculate the design and volume of building material.

Calculating MZLF

To make a shallow strip foundation with your own hands, you need to decide on the type of foundation and its dimensions. Let's say we plan to build a base with an area of ​​15 m2, with a width of 5.5 m and a length of 6.5 m, with 4 horizontal rows of reinforcement and 2 vertical ones.

Based on this, we get the following approximate drawing of the future fundamental foundation.

For such a construction you will need:

• 402 m of reinforcement (120 m for horizontal rows, 192 m for vertical rows and 90 m for connecting rods);
• 2.02 “cubes” of lumber for formwork;
• 153 bags of cement (50 kg each);
• 19,100 kg of sand;
• 27,550 kg of crushed stone.

This is an example of a standard MZLF design, 1,600 mm high. The depth is calculated using the following parameters:

• 0.4 m if the base is protected from heaving soils;
• 0.45 m for sandy soil with low groundwater levels;
• 0.5 m if clay soil predominates with a freezing level of 1 m;
• 0.75 if the freezing mark reaches 1.5 m;
• 1 m for soils with a freezing depth of 2.5 m.

In addition, pay attention to other types of foundation.

Types of shallow foundation structures

There are several types of MZLF, presented in the table below.

Based on this classification, we will consider recommendations for choosing the type of a particular design:

• When constructing heated buildings with walls made of lightweight brick or aerated concrete, it is recommended to focus on the following indicators:

• For heated frame houses, with wooden floors it is recommended:

• For unheated log buildings:

After theoretical calculations, you can proceed directly to the construction of the foundation.

Construction of a shallow strip foundation

To build a non-buried strip foundation with your own hands, you need to complete the following stages of work:

Preparing the trench

Before making a shallow strip foundation, remove from the area allocated for construction top part soil and mark the foundation. To do this, take wooden stakes and nylon thread and measure the corners. After this, check the distance between the walls with your project and dig a trench about 70 cm high and 30 cm wide.

Make sure that the walls of the trench remain vertical and the bottom is level. At the next stage, it is necessary to cover the trench with geotextile, which will prevent mixing of the sand cushion and soil.

After this, coarse sand (fine sand should not be used) or a mixture of sand and crushed stone, 10-15 cm high, is poured into the bottom of the trench. Backfilling should be done in layers, with each subsequent layer moistened and compacted. The final height of the sand cushion depends on the type of soil. It is recommended to lay insulation (for example, roofing felt) on top of the prepared waterproofing layer, this way you will insulate a shallow strip foundation.

Formwork

Formwork made from edged boards or OSB is installed on top of the insulating layer. It is best to make removable formwork by fastening its walls with ties in increments of 0.5 to 1 m.

On the back of the formwork, mark the concrete pouring level.

Reinforcement

Place reinforcement bars in the formwork, having previously cut the rods in accordance with the dimensions of the walls, both in cross and longitudinal sections. In corners and at wall joints, perpendicular reinforcement rods must be tied to increase the strength and durability of the reinforced frame.

Healthy! If the height of the foundation exceeds 30 cm, then you will need several layers of reinforcement.

For more information about MZLF reinforcement, watch the video:

Fill

To fill the foundation, you can purchase a ready-made cement-sand mixture or make it yourself:

Concrete grade	Sand fraction	Crushed stone share	Share of cement	Durability level
M 300	1,9	3,7	1	At 22.5
M 250	2,1	3,9	1	IN 20
M 200	2,8	4,8	1	At 15
M 150	3,5	5,7	1	At 12.5

After pouring the first layer, holes must be punched in the concrete surface using a rod. This is necessary so that all the air comes out of the solution.

Each subsequent layer of cement-sand mixture must be poured before the previous one sets, so it is better to hire a team for the work.

The final layer of concrete must be leveled according to the markings on the formwork. After this, it is recommended to reinforce the concrete in order to increase the strength of the foundation and avoid cracking of the surface. To do this, sprinkle the concrete that has not yet set with dry cement (it is most convenient to use a regular sieve for this).

Final processing

After 3-5 days, when the base has set, carry out vertical waterproofing of the foundation. You can do this in several ways:

1. Coat the surface with bitumen mastic in 2-3 layers.
2. Cover the foundation with roll material based on polymer or fiberglass.
3. Saturate the surface with the penetrating mixture.

The foundation will finally gain strength in 28 days, after which it will be possible to continue building the house.

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; it is removed by drainage sewerage excess moisture, 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. Standard parameters of MZLF provide 2 - 3 times the load-bearing capacity for 2-storey buildings brick cottages with 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 increases, the strength of the structure, in which the cement laitance. 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

When the height of the MZLF is from 70 cm (together with the plinth 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 the other 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 mark, 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 tape 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.

When erecting small buildings on a suburban area, a shallow strip-type foundation can be designed for the construction. The foundations of low-rise buildings are usually laid at a height of 0.6-1 m. Below the surface level, the structure is buried at a distance of about 0.5 m. The small dimensions of the shallow foundation are compensated by the strength properties of the concrete used and the design of the reinforcement frame. When constructing small buildings (baths, outbuildings etc.) you can determine the main areas and dimensions of a shallow foundation yourself.

Table for calculating the load per 1 m² of foundation.

Principles for calculating shallow foundations

The difficulty of carrying out calculations when designing a strip foundation, first of all, lies in determining the hydrogeological properties of the soil at the construction site. If there is a suspicion that groundwater is close to the surface of the construction site, it is preferable to involve specialists in conducting research and design. On heaving soils, the groundwater level can change over time and affect the strength of the foundation.

It is permissible to install a shallow foundation for a bathhouse if the site has sandy or homogeneous hard soil and the groundwater is located far from the surface, at least 0.5 m below the freezing depth of the soil. If the construction site has complex moving soil, the base must be increased.