Strip foundation is the most common type of foundation for building a house. Therefore, everything is clear with him, but how does a shallow (MZLF) differ from it - a shallow foundation, how to calculate and how to do it?

Characteristics - design principle of operation

Shallow strip foundation or simply MZLF is similar in its laying method to its counterpart, but it has important differences:

• foundation laying depth up to 700 mm;
• located above the zone of soil freezing;
• designed for arrangement on swollen (heaving) soils.

The main feature of a shallow strip foundation is that it makes it possible to level the frost heaving of the soil. This is due to the fact that, despite the general rigidity of the structure, the MZLF, along with the weight of the entire structure, moves up and down depending on the time of year. Since the foundation is not deeply deepened, but is displaced evenly, then, therefore, it does not collapse from such vibrations.

Scheme of the device of a shallow strip foundation

1. Sand and gravel pad
2. Foundation tape
3. waterproofing layer
4. Vertical (or coating) waterproofing
5. Armature (diameter 12)
6. Armature (diameter 8)
7. plinth
8. Wall

Where to use - application

A strip shallow foundation is suitable for the construction of low-rise residential buildings and other structures from those materials that will not create significant pressure on the base of the foundation. Such structures and materials include:

• log cabins;
• cellular concrete - foam concrete, gas silicate blocks;
• lightweight bricklaying;
• frame-panel buildings.

When arranging a foundation of greater width, it is possible to build heavy houses from a bar or log on it. But in this case, the soil will freeze to a lesser depth and there is a possibility of deformation of the foundation. Thus, if it is planned to build a monumental building, it is better to equip a tape monolithic foundation.

At the same time, you should be aware that an increase in the width of the tape of shallow foundations makes it possible to build heavier houses with an attic. Large width foundation tape(respectively, the basement) helps to reduce the depth of soil freezing in the space under the floor.

What should be considered when constructing a shallow foundation

Shallow foundations are laid on heaving soils

It is forbidden to fill MZLF on biogenic organic soils, for example, peat, sapropel (deposits of freshwater reservoirs), as well as on clay. The photo shows that they are already appearance does not bode well.

• groundwater level

The closer the water is to the surface of the earth, the more unstable the MZLF will be.

Height difference

If the terrain is characterized by a significant difference in height (a house on a slope), then the installation of a shallow strip foundation on it is quite problematic. In this case, an ordinary strip foundation is equipped or a significant area under the MZLF is leveled. In terms of time and cash Both options are equivalent.

• Depth

It represents the height from the lowest point of the foundation, the so-called sole, to the zero mark (ground surface).

• Climate (depth of soil freezing)

It is quite common among builders to lay a shallow strip foundation at a height, which is calculated by the formula - freezing depth minus 20%. So you can be sure that the foundation will rise with the structure.

The minimum depth of a shallow strip foundation is regulated by SNiP II-B.1-62.

The depth of soil freezing for some Russian cities is shown in the table.

How to calculate the load on a strip shallow foundation

First of all, you should consider:

• structural features of the building;
• building height;
• planned number of floors;
• materials from which the walls will be built;
• coating weight;

Advice.
In general, the entire load can be divided into a constant (calculated before construction begins) and a variable. The latter depends on the number of inhabitants, the weight of the furniture, etc.

• trench depth;
• pillow thickness;
• foundation tape parameters;
• concrete quality.

You can additionally use

Calculation of a shallow strip foundation

1. Depth is determined by the proximity of groundwater and the depth of freezing.

2. Height above ground = 4x width.

Good to know. The height above the ground is less than or equal to the depth.

3. The width is determined by the formula:

Where, D is the width of the base of the foundation;
q is the design load on the foundation, t/m;
R - design soil resistance, t / sq.m. This indicator, for a laying depth of 300 mm, is shown in the table.

4. The thickness of the pillow is determined from the conditions of the strength of the soil of the area.

For heavily heaving soils, the formula is applied:

Where, tn is the cushion thickness;
А, С, W – coefficients;
A and C are determined according to the tables below.
And W = 0.1 or 0.06 sq.m./t for heated and unheated structures.

Above the line - for MZLF with a laying depth of 300 mm, below the line - for non-buried foundations.

Advice.
Make the calculation of MZLF using both formulas and give preference to a larger value.

The cost of a shallow strip foundation

Varies within 4-6 thousand rubles. per running metre. The price depends on the width, height, number of lintels and dimensions, for example, the cost of building the foundation of a 6x6 house will cost 70-80,000 rubles, and 10x10 \u003d 120-150,000 rubles.

Types of shallow strip foundation (shallow)

Depending on the type of MZLF, the technology of its device will differ. Therefore, you should briefly familiarize yourself with the main ones:

Tape monolithic shallow foundation

Poured directly on the construction site, resulting in a seamless tape

Tape block shallow foundation

Blocks are bought ready-made, or they are made separately, and they are only assembled at the construction site. A cement mortar is used as a fixing material.

Each of them has its own advantages and disadvantages. But, in general, the service life of the second is three times less than the first. Therefore, in this article we will dwell in detail on such a form as a monolithic MZLF.

MZLF technology or how to make a shallow strip foundation with your own hands

The instruction is easier to understand if all the work is divided into clear steps. We will not deviate from this scheme. So the tape device shallow foundation the following:

Preparatory stage

1. The place where it is planned to pour the foundation is freed from everything superfluous.

Council. Trees that are nearby, uproot along with the roots.

2. All necessary material and tools are delivered to the workplace. Moreover, it is desirable to immediately determine the location of all this stuff, so that later you do not waste time looking for it.

Marking for strip foundation

The importance of this stage is difficult to overestimate. Therefore, you need not only to “estimate” where you will dig a trench, but also to make landmarks with a rope (if possible, a laser level would be better).

How to make markings for the foundation:

1. take measurements around the perimeter;
2. hammer beacons in the corners;
3. check the diagonal between the corners;
4. if necessary, move the beacons;
5. make a blind area at a distance of at least a meter from the beacons;
6. fasten a rope to the blind area boards, which will show the edges of the foundation.

More clearly, the markup process is shown in the diagram.

How to dig a trench under the foundation

A foundation trench is a strip of excavated soil.

The depth of the trench is determined by the depth of the shallow strip foundation and cushion.

For example, the most common depth is 300 mm, the thickness of the cushion is about 200 mm depending on the quality of the soil. Then the depth of the trench will be 500 mm.

Council.
To prevent the edges of the trench from crumbling, make small slopes.

Given the type of soil, it is better to start pouring the foundation immediately. Otherwise, it will crumble, and part of the work will have to be repeated.

The sand cushion under the foundation is a mixture of sand and gravel. They can be mixed, but it is easier to pour in layers. Moisten each layer with water and compact well. Since the structure of the pillow turns out to be quite porous, it is separated from the main foundation with a waterproofing film.

In principle, natural soil can serve as the basis for a shallow-depth strip foundation, but its bearing capacity is much lower than the proposed sand and gravel pad.

Install the entire formwork structure vertically. The supports are fixed in increments of 500-600 mm. They are needed so that under the weight of concrete the formwork does not fall apart and does not warp.

Helpful advice.
Try to keep the boards close to each other tightly and without sharp drops. Then you will avoid work on leveling the surface of the finished foundation for cladding.

Filling the strip foundation

Getting concrete is an individual matter - you can buy (or rather, order) and the concrete will be delivered by a mixer or made on your own, and using it (and the second option, how to do it).

As for pouring concrete, the procedure is standard for such work - concrete is poured into the finished formwork.

Council. If the formwork is poured with water, the concrete will lie more evenly along the edges.

When pouring concrete, try to beat it off every 40-50 mm. height. This will "drive out" air bubbles that can destroy the concrete in the future.

Reinforcement of a shallow strip foundation

If a heavy load is not expected on the foundation, this step can be skipped. But still, with MZLF reinforcement it will be much stronger.

Proper reinforcement of a shallow strip foundation:

• Fill in the starting layer. This layer should be about 30% of the total height of the MZLF. The purpose of this action is to create a flat surface for laying the metal, as well as to protect it from moisture.


• Knitting reinforcement for a strip foundation. To do this, you need to tie it into blocks and lay it in a trench.


• Pour concrete to desired height.

Example reinforcing cage for strip foundation

An example of knitting reinforcement with wire.

The example shows that the bundle is made with wire. It's relative new approach to the connection, because the more familiar one is resistance welding.

But the methods of joining reinforcement by welding have several significant drawbacks, including:

1. require a welding machine and a specialist who can perform welding work;


2. due to the high temperature of the welding arc, the strength of the hardened rebar is lost;


3. welding works are not applicable for fittings with a diameter of more than 20 mm;


4. The most important thing is to increase the rigidity of the armored carcass. Since a shallow strip foundation “plays” depending on the season (being a kind of flexible foundation), increased rigidity will lead to its destruction. And as a result, it will be required.

This is what the installed reinforcement will look like

Concrete protection

To avoid overdrying and the formation of cracks, the concrete poured into the formwork is covered with a film and periodically moistened with water.

Insulation of a shallow strip foundation

• Immediately after the foundation has gained the necessary strength, construction of the house should begin. Try to do all the work in one season. Because the soil under the foundation will freeze, and the MZLF, not pressed down by the weight of the house, will deform.


• If you cannot start construction, cover the MZLF and the area near it (200-300 mm) with straw or sawdust. To protect the soil from freezing.


• During the operation of the building, try to plant perennial plants and shrubs near the shallow strip foundation. They will help to reduce the depth of freezing of the soil. And they will also be able to retain a significant amount of snow, which will also reduce the depth of freezing.

Shallow strip foundation video

Conclusion

In this article, we figured out how to make a shallow strip foundation with our own hands. Having dealt with each of the stages in detail, you will be able to prevent unfortunate mistakes and fill the foundation on which your house will stand for more than a decade. Most importantly, do not forget that before you start building, order geological research, otherwise, there is a risk that the soil on your site is not intended for the MZLF device.

For those who want to save on construction country house, a shallow strip foundation is great option. Its construction does not require special skills and even a novice builder can do it. This type of foundation is often chosen when building houses made of wood, different types cellular concrete, as well as with lightweight brickwork.

Scheme with reinforcement

A shallow strip foundation is suitable for the construction of buildings up to three floors high, while its cost is much lower than that of a deep foundation.

Definition of this type

A monolithic shallow foundation is a cross between a buried tape (to the freezing depth) and an unburied one. Shallow-depth tape - these are monolithic reinforced concrete strips that run not only around the entire perimeter of the building, but also under the bearing walls. It is located at a shallow depth (much higher than the freezing depth), due to which, during frost heaving of the soil, the reinforced concrete tape evenly rises and falls along with the building. This protects the base from destruction during seasonal temperature changes. In fact, this type of foundation is a rather rigid frame, which moves along with a fairly light building in the autumn-winter period.

The frame is a monolithic reinforced concrete structure, which is laid on a cushion of non-porous material. This design makes it possible to reduce the amount of concrete for pouring by 50-80% compared to a deep foundation, and labor costs for the construction of the zero cycle are reduced by 40-70%. In addition, this technology allows rational use of local building materials. Sand, fine crushed stone, boiler slag and others can be used as a pillow.

Foundation Advantages

1. Profitability - this type of foundation is 2-3 times cheaper than a buried one.
2. Low labor intensity of the process - a relatively small amount of excavation and formwork installation.
3. Reduced construction time (compared to a deep-laying device).
4. The possibility of arranging a small basement (when arranging non-buried foundations, a basement cannot be made).
5. Resistance to heaving phenomena.

Foundation Disadvantages

Despite a large number of advantages, a monolithic reinforced shallow foundation has one significant drawback. Its device makes sense only on soils that do not belong to the category of highly swellable, and the groundwater level at the construction site should be sufficiently low. Otherwise, a shallow tape may crack, which will lead to the destruction of the building. Brick houses with a height of 2 floors can be erected on such a basis only if there are non-porous soils on the construction site.

Device Technology

To prevent cracking of a shallow strip foundation during the operation of the building, strict adherence to the technology of the entire construction process is required. The scheme of the shallow foundation device is as follows: image 1. To perform work on the device, you will need the following materials:

• sand;
• concrete grade 250;
• wire for tying the frame;
• rebars with a diameter of 14-16 mm;
• smooth rods with a diameter of 8-10 mm;
• only;
• roofing material or mastic;
• boards for the manufacture of formwork panels;
• stakes and spacers for mounting the formwork.

Tools and fixtures

• shovel;
• tamper;
• deep vibrator for laying concrete;
• concrete mixer;
• roulette;
• kapron cord;
• construction level.

Stages of work production

1. After marking the site, proceed to earthworks. At this stage, trenches are dug 0.5 m deep and 0.6-0.8 m wide.
2. The device of the sand base 200-400 mm thick. The sand pad is moistened with water and carefully compacted in layers using improvised means or compacted with platform vibrators, which reduces the risk of settlement. The purpose of the sand base is to evenly distribute the weight of the structure over the entire area of ​​​​the sole. The better it is compacted, the better the sand will cope with this task.
3. Manufacture and installation of formwork. For formwork, boards planed on one side are suitable, from which shields are assembled. For mounting the formwork along the perimeter of the trench, spacers and support stakes are driven in. Formwork panels are installed strictly horizontally and vertically. For internal waterproofing of the formwork, for example, roofing felt or other similar material is used.
4. Reinforcing begins with laying steel reinforcing bars with a diameter of 14-16 mm along the tape. To form the frame, the reinforcement is connected with a special wire to smooth rods with a diameter of 8-10 mm. To protect the metal from corrosion, the distance from the longitudinal bars to the expected upper boundary of the foundation must be at least 50 mm.
5. After the frame is made, it is possible to start pouring the formwork with concrete mortar, each layer of which, 200 mm thick, should be carefully compacted with a deep vibrator.
6. After (this process lasts 7 days), the formwork is removed and the reinforced monolithic foundation is covered with a layer of waterproofing. To do this, use mastic or roofing material.
7. The remaining sinuses are covered with sand and carefully rammed, and from the outside the foundation is protected by a blind area.

Process Features

When constructing a shallow strip foundation, experienced craftsmen advise adhering to certain rules, the observance of which will help to avoid many problems in the future.

1. The shallow one is afraid of water, so it is very important to protect it from precipitation. To do this, it is recommended to perform a preliminary planning of the site with a slope of at least 0.03-3 cm per 1 m (if this requires adding soil, then it should be carefully compacted). In addition, it is necessary to take care of the drainage of water flowing from the roof, and also be sure to complete the blind area.
2. The sand cushion plays a very important role. So that over time it does not lose its ability to evenly distribute the load (due to silting) and instead of raising and lowering it does not start to break, it is recommended to protect it from moisture. To do this, it is recommended to line the bottom and walls of the trench with waterproofing, for example, roofing material, before filling the sand.
3. For pouring the foundation, it is preferable to use ready-made high-quality concrete and be sure to use a vibrator for compaction. If the concrete solution is prepared manually, then a sufficient number of people and several concrete mixers should be used to work. This is done in order to reduce the time for pouring, which will prevent layer-by-layer solidification of concrete. For this reason, the preparation of concrete mortar by hand is impractical and economically unjustified.
4. To avoid cracking after pouring and until the end of hardening, cover with plastic wrap.
5. It is very important not to allow the shallow foundation to remain unloaded during the cold season. The foundation, walls and roof of the house must be erected in one season. If, nevertheless, this happened, then the finished one should be carefully insulated for the winter - covered with straw, sawdust or slag so that it does not freeze.
6. To reduce the depth of freezing of the soil under the blind area, it is recommended to make a pillow of expanded clay with a thickness of 20-30 cm. For the same purpose, the site is turfed and shrubs are planted.

It is a mistake to assume that a shallow strip foundation (FMZ) 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.

In this process, miscalculations and errors are not allowed, otherwise the entire construction process may be reduced to zero or require additional investments for restoration work. In order 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 level of groundwater. It would be wise to use the services of a professional who will calculate the foundation and give the necessary recommendations.

A professional approach with the creation of a TTK (standard technological map) will ensure strict compliance with SNiP, reduce the cost of the project and labor costs. Only in this case, you can be sure - as a shallow foundation (MZLF), which 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 strip shallow foundation are as follows:

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

Of the shortcomings, it is worth noting in the first place - this is the construction of a 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 rules and regulations (SNiP), you can make a drainage system under the base of the building.

Another nuance is the pouring of concrete on heated ground. In addition, in the instructions of the TTC (standard technological map), the construction of a house on this basis is carried out within a short time - this is 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 a shallow strip foundation device includes:

• earthworks - digging the tape;
• laying a sand cushion - 200 mm;
• formwork installation;
• installation of a reinforcing cage;
• pouring concrete mix;
• drainage for a shallow foundation - on heaving soils;
• formwork dismantling.

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

For which buildings is the foundation suitable?

A shallow strip foundation for aerated concrete houses, it is also well suited for two-story buildings built of lightweight material:

• wood;
• expanded clay;
• foam concrete.

In SNiP (Foundations of buildings and structures), it is not recommended to erect buildings over two floors and exceed an area of ​​more than 100 m2. A shallow strip foundation is laid 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, a shallow foundation is 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 deep foundation allows you to save up to 70% on materials and up to 80% on labor costs.

Due to the effect of heaving forces (heaving soils) directed to the walls of the structure from the side and bottom of the base, the area of ​​\u200b\u200bthe walls decreases and the stress on the side is significantly reduced, the mass of the building regulates the heaving forces from below.

There are basic technological rules for the construction of a structure:

• dig a foundation can be 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 the forces of heaving from below and uneven pressure from above;
• laying the foundation shallow laying on prepared compacted soil, providing a sufficient coefficient of water drainage. To do this, use coarse sand or gravel. At the same time, the load is balanced during subsidence during thawing of the soil;
• a high level of groundwater provides for waterproofing work, in this case, an artificial drainage system is performed from penetration from above;
• shallow foundation needs to be insulated from above. It is necessary to build blind areas around the basement up to 1 meter wide, for this a layer of thermal insulation (extruded polystyrene foam or other insulation) is laid on the ground.

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

Laying a shallow foundation

An unburied base can be made in three ways: monolithic, using a reinforcing knitting mesh, laying in separate blocks or bricks. All methods are practical and equally easy to perform. You can choose any option, based on what material is available. To start doing construction work, you need to have an idea of ​​\u200b\u200bwhere 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 - sectional drawings of the future building, you can proceed to further steps in building a house.

Step-by-step instruction:

• Markup. A cast-off of wooden bars 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. Trench should try to dig initially flat. To check, use the spirit level, level and tape measure. The subsequent material consumption, time and labor costs largely depend on the quality of the work at this stage.
• Cushion padding. Sand of a large fraction is poured into the bottom of the trench - 20 cm, in order to compact the sand cushion, it is filled with water and tamped with a rammer. A layer of crushed stone, pebbles or expanded clay is laid on top - up to 20 cm.
• Reinforcement. It is not recommended to make a shallow foundation without reinforcing SNiP. 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 to the driven rod trimmings. A step is observed between the rods - 15-20 cm, the elements are connected to each other with a knitting wire.
• Formwork installation. The 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 against the walls of the trench. "Sanitary" openings are made - sewerage, water supply.
• Pouring concrete. The solution is prepared in a ratio of cement-sand 1: 3 - respectively. The metal frame should be filled with a solution layer 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.
• Formwork dismantling. The panels should be dismantled after the concrete has completely cured.

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

Shallow strip foundation (MZLF) is used in the construction of low-rise buildings from light piece building materials. Relatively simple design, low consumption of materials and a high level of reliability make its use a technically optimal and cost-effective solution.

A structure of this type can be made with digging a pit around the entire perimeter of a house under construction or digging trenches above the freezing point along the axes of load-bearing walls and partitions. The width and depth of the trench are determined by calculation (presented as a gallery towards the end of the article).

MZLF can be monolithic reinforced concrete or assembled from individual prefabricated concrete blocks. It is allowed to use rubble masonry or solid clay bricks, but the most durable and reliable construction is reinforced concrete monolith.

MZLF scheme.

Conditions for the use of a shallow structure

Tape device concrete foundation shallow foundation (FMZ) during the construction of a house will be appropriate in the case of:

• large depth of soil freezing;
• availability;

The lowest point of the foundation structure is always located above the level of freezing limit at a depth of no more than 1500 mm. At the same time, the greater the width of the base, the greater the weight load it can carry. The small depth of the MZLF allows it to rise along with the house during winter heaving of the soil, while remaining intact.

Reduced bearing characteristics somewhat narrow the possible range of application of the structure and allow the use of a shallow strip foundation only in the case of building houses from light building materials, which include:

• wood;
• cellular concrete blocks;
• frame-panel products;
• lightweight masonry of hollow bricks.

The width of the sole depends on the material of the building.

MZLF should not be used for building houses large area. The depth of soil freezing under the floor of such buildings will be less than in the adjacent territory. As a result, winter swelling will be uneven, which can lead to structural failure.

The use of MZLF is prohibited on clay, peat and sapropelic soils.

On weak and non-rocky soils.

On medium to heavy heaving soils.

Conditions for calculating the foundation structure

In order to calculate the MZLF and determine the depth and width of the tape, it is necessary to take into account:

• soil type to depth calculated point freezing;
• ground water level;
• freezing depth;
• distribution of weight load on the foundation;
• height differences on the building site;
• the estimated depth of laying, which is equal to the distance from the lowest point of the base to the zero mark of the building.

The depth of possible soil freezing can be determined according to SNiP 23-01-99 * "Construction climatology".

With significant height differences, the MZLF device is structurally impossible. In these cases, leveling the site or building a different type of foundation will be required.

The weight load acting on the foundation consists of a constant and a variable component. The variable includes snow and wind load, the weight of engineering equipment, furniture, plumbing, etc. To determine the constant weight component, the height of the building, the materials used, the design of the roof and floors, and other design features are taken into account.

Design calculation

The reinforced concrete monolith of the foundation rises above the ground and rests on a cushion consisting of a layer of compacted rubble covered with a layer of sand.

Depending on climatic conditions, the depth of laying of the MZLF on heaving soils is determined by the requirements of SNiP II-B1-62 and is equal to:

• when freezing up to 1 meter - at least 500 mm;
• up to 1.5 meters - 750 mm;
• more than 1.5 meters - 1000 mm.

Therefore, builders usually calculate a shallow strip foundation, taking the laying depth as a value equal to the freezing depth, minus 20-25%. Subject to this condition, the foundation for the house will be able to freely rise without destruction when the soil swells.

The height of the base above the ground can reach four times the width, but should not exceed the size of the underground part of the foundation.

The width of the structure under the bearing walls is equal to the mathematical ratio of the weight load (t / m) to the calculated soil resistance (t / m2), the value of which is given in the tables of SNiP 2.02.01-83.

The thickness of the crushed stone-sand cushion is determined by the formulas and tables given in the SNiP "Foundations and Foundations". It depends on the degree of swelling of the soil, the thermal regime of the building and the material of the walls.

Costs for the device MZLF

As practice shows, the cost of building a shallow foundation with your own hands depends on its size, design, elevation above ground level, the number of jumpers and some other factors. average price is 5-6 thousand rubles. per running metre.

Installation of monolithic reinforced concrete MZLF

After the calculations of the structure and the manufacture of the project, you can begin to make a shallow strip foundation with your own hands. Work on the MZLF device consists of several stages, which will be described in the form of step-by-step instructions:

• preparatory;
• marking;
• earthworks;
• pouring concrete;
• plinth devices;
• hydraulic and thermal insulation devices;
• sand filling and blind area devices.

To complete the work, you will need the following materials:

• sand and gravel;
• cement M400 or M500;
• steel reinforcement with a diameter of 8 and 12 mm;
• knitting wire;
• formwork boards or ready-made panel elements;
• bitumen and bituminous primer;
• brick for leveling the basement.

When installing FMZ thermal insulation, you can use polystyrene foam, which is fixed on glue and plastic nails.

Preparatory stage

Preparatory work includes clearing and possible leveling construction site. At the same time, uprooting of stumps and bushes should be carried out together with the roots in order to exclude the possibility of their germination in the future.

It is necessary to deliver all the necessary materials to the place of work and ensure their storage in such a way as to exclude damage from adverse external influences.

markup

To perform correct and accurate marking, it is best to use a construction level and measuring tape at least 10 meters long. With the help of a level, you can easily determine the necessary directions of the angles of rotation of the foundation tape. This is especially important for complex configurations.

To tension the marking cord, it is necessary to make beacons and pegs. The beacon is a U-shaped wooden structure of two stakes and a crossbar, the width of which should be greater than the width of the foundation.

Initially, the tensioned cords should run along the edge of the outer wall of the MZLF, and after the excavation work is completed, before the formwork is installed, they should also be tensioned along the internal contours.

Checking the markup is done by measuring the diagonals inside all the rectangles. They should be equal for both external load-bearing walls and partitions.

trench digging

Marking and earthworks.

The required trench depth is equal to the sum of the depth of the reinforced concrete monolith and the height of the support pad. It is determined by the calculation, which was described above.

For central Russia, a design with a cushion thickness of 200 mm and a recessed part of the foundation of 300 mm is most often used. In this case, the trench depth is 500 mm.

In order to prevent soil shedding and to be able to access the surface during waterproofing work, it is necessary to make small slopes of 150-250 mm. The width of the bottom should be taken 200-300 mm wider than necessary for the foundation itself.

Support pad for foundation

Sand pillow.

As a pillow, you can use ready-made crushed stone-sand mixtures (SCHPS), which are sold on the construction market for road work.

Another option is to layer-by-layer crushed stone and sand, with careful tamping of each layer. In this case, the crushed stone should be at least ¾ of the total thickness.

After the pillow is installed, its surface must be covered with geotextile.

This non-woven material is able to pass moisture in only one direction and will protect the foundation from its effects.

In addition, geotextiles will stop the possible germination of plants towards the concrete part of the shallow foundation of the house.

Gravel layer.

Formwork device

Formwork design for shallow band monolithic foundation installed vertically, to the full height of the concrete mixture pouring. In this case, part of it will be above ground level. It should be noted that concrete is not poured to the entire height of the foundation, since space should be left for a leveling layer of solid red brick.

To assemble the formwork, you can use boards or prefabricated small-panel structures that can be rented and not spend money on the purchase of lumber.

The upper part of the formwork walls must be connected to each other by crossbars, and the walls themselves should be supported with inclined slopes every half a meter. This will make the structure more durable and prevent it from falling apart under the pressure of the concrete mixture.

Do not forget to install sleeves made of metal or asbestos-cement pipes. They are required to enter engineering communications into the building. Since the MZLF is not a stably stable structure, the diameter of the sleeves must be taken at least 200 mm.

Formwork.

Structural reinforcement

Metal reinforcement several times increases the strength of the foundation and ensures its safety even in the most difficult operating conditions. From metal rods with binding wire it is necessary to connect the blocks with longitudinal, vertical and horizontal strings and lay them inside the formwork. In this case, the lower longitudinal strings should not touch the bottom of the trench.

It is allowed to connect rods by welding, but this technology is more complicated and, when heated, reduces the level of metal hardening. The recommended diameter of the longitudinal rods is 12 mm, vertical and transverse 8 mm. After installing the reinforcing blocks inside the formwork, you can start pouring the concrete mix.

Reinforcement schemes.
Reinforcement.

Pouring concrete into the MZLF structure

There are two options for preparing concrete mix. You can order it and buy it ready-made or make it yourself. The volumetric composition of the mixture of sand cement and crushed stone is determined as 1: 2.5: 4 for M400 cement and 1: 3: 5 for M500 cement.

Compaction of concrete is best done with a submersible construction vibrator. In its absence, you can use a manual rammer, but in this case, the concrete should be poured in layers of 30-50 mm and each individual layer should be compacted.

Thus, you can expel all air bubbles and ensure the necessary strength of the material.

In the case of hardening of poured concrete in hot and dry weather, it is recommended to cover the foundation with plastic wrap and periodically water it with water. The hardening time before the start of masonry is at least 4 days.

Foundation protection

To protect concrete monolithic construction from exposure to moisture, which can lead to gradual destruction, its surfaces are covered with hot bitumen and glued with waterproofing. Initially, the concrete is treated with a bituminous primer, which is used as a primer, and then waterproofing layers are applied.

It reduces the heat loss of the building during the cold season and prevents the possibility of moisture freezing inside the monolithic reinforced concrete structure. Installation of insulation is recommended, but not a mandatory condition for the performance of work. At this point, we are completing our guide to the construction of a strip foundation with a small depth of laying with our own hands.

Schematic sectional view: the insulation goes along the entire vertical wall of the tape combined with the base. Closed with cladding. Insulation should also be located under the blind area.
Photo of insulation.

Related videos

For the conditions of Russia, the definition of the most reliable foundation design is of particular relevance in conditions where soils with the property of frost heaving lie at the base.

When soil swells, its volume can increase significantly - by tens of centimeters, and the forces with which frost heaving forces will act on foundation structures can reach tens of tons. The deepening of the bottom of the foundation sole to a mark located below the depth of winter freezing does not save from the negative action of heaving forces, since the impact also occurs along the lateral surface.

To prevent the negative consequences of the impact of heaving forces, a special design was developed - a shallow strip foundation, or MzLF, which can be built with your own hands.

The features of the MzLF, in contrast to the conventional strip foundation, are as follows:

• the depth of a shallow strip foundation is taken regardless of the freezing depth at a mark of no more than 30-40 cm from the soil surface after planning. This minimizes the effect of negative heaving forces on side surfaces constructions;
• under the sole of the foundation, a do-it-yourself pillow is made of bulk materials - sand or ASG - a mixture of sand and gravel, the thickness of which is calculated depending on the complex conditions of the construction site. By replacing the soil under the sole, its heaving properties are eliminated, the bearing capacity of the compacted base is increased, and its deformations associated with thawing in the spring are reduced;
• the foundation is necessarily reinforced with spatial frames that turn the strip foundation into a frame system of beams lying on an elastic foundation. The system of beams, rigidly fastened together, perceives and compensates for all uneven effects of heaving forces.

We present for demonstration a tape shallow foundation according to SNiPs in the context:

MzLF device

A shallow strip foundation on heaving soils can be built with your own hands, using the instructions of a typical technological map TTK "Device of a shallow strip reinforced concrete foundation".

The MzLF technology almost completely corresponds to the technology for constructing a strip monolithic foundation, described by us in the article "", and includes the following operations:

• preparatory work - vertical layout of the site, marking and fixing the axes of the building, excavation of trenches for foundations;
• pillow device under MzLF;
• formwork installation;
• reinforcement;
• concreting;
• caring for the concrete mixture laid in the formwork;
• removal of formwork.

All these operations are described in detail in the above article, so here we will dwell in more detail on the points directly related to MzLF.

Pillow device

The cushion, due to which the heaving properties of the soil are eliminated and possible uneven deformations of the base are compensated, is the main element that distinguishes the MzLF from the usual strip foundation. The thickness of the pillow is determined by calculation (see section "").

The following bulk materials can serve as the material for the pillow device:

• coarse sand and sand of medium size;
• gravelly sand;
• crushed stone;
• blast furnace or boiler slag;
• a mixture of coarse sand (not more than 40%) and gravel (not less than 60%).

Before installing the pillow, the bottom of the trench is cleaned, then the bulk material is laid in layers, with a layer thickness not exceeding 20 cm. Each layer must be carefully rammed with electric rammers, then the next layer is filled up and rammed again. The density of the cushion after compaction should be at least 1.6 t/m³.

If groundwater is at high level and there is the possibility of soaking with top water, they provide for laying the pillow on a layer of geotextile, which also covers the structure on both sides and on top. This prevents silting of the loose cushion material.

Foundation reinforcement

Reinforcement of the MzLF is carried out by spatial frames, in which the working reinforcement is located in the upper and lower parts of the foundation section.

Let's use an example to show how the foundation is reinforced.

A conditional foundation with a section of 400x400 mm is deepened by 400 mm from the soil surface, while being reinforced with a KP-1 spatial frame. The protective layer of concrete from the sole of the foundation is 65 mm, from the side surfaces of 30 mm, from the upper plane - 30 mm.

Cushion made of ASG - a mixture of gravel and sand (40% coarse sand, 60% gravel), the thickness of the cushion is taken by calculation, the width of the cushion is 200 mm larger than the width of the foundation, that is, it protrudes 100 mm from the side surfaces of the MzLF.

The spatial frame is assembled from six longitudinal rods of working reinforcement with a diameter of 12 class A3. In this case, the connection of the frames along the length with each other should be overlapped. The length of the overlap should not exceed 20 diameters of the rods that are connected, and be at least 250 mm. The rods should be connected in a run, that is, more than 50% of the connections should not fall into one cross section.

Instead of class A3 fittings, you can use class A500C fittings, which cost 30% less and allow you to make connections by welding, which simplifies the fitting work. When connecting working rods by welding, the length of the seam should not exceed 10 diameters, in this case- not less than 120 mm.

The working rods are connected into three-dimensional frames by means of clamps made of class A1 smooth reinforcement, installed in 200 mm increments along the length.

In places where the walls intersect or adjoin each other and at the corners during the operation of the building, stress concentration occurs, so these places are reinforced by installing additional rods.

Strengthening is carried out by installing additional rods of the same working diameter of 12 mm as the working reinforcement, in the upper and lower levels of the frame. Additional rods, bent at a right angle, are attached to the intersecting working rods of the frames on the outside of the gusset using a tie wire. Additional trapezoidal rods are installed closer to the inside and welded to the connected rods according to GOST 14098-91-S23-Re for welding work.

Strengthening of the T-shaped abutment is carried out by additional trapezoidal rods, which are welded to the main rods in two levels of the connected frames.

Reinforcement at the intersection of the walls is carried out by welding additional trapezoidal rods in two levels of intersecting frames.

In this example, the width of the wall is equal to the width of the foundation. If the width of the foundation is calculated to be 600 mm greater than the width of the wall, then it is necessary to additionally reinforce the sole with flat meshes, the working reinforcement of which should be located across the sole. The diameters of the working reinforcement are accepted within 10-12 mm, class A3 or A500C, step 600 mm.

As structural reinforcement for grids, smooth reinforcement of class A1 (A240) with a diameter of 6 mm is used, or from high-strength wire of class Vr-1 with a diameter of 4-5 mm, which is laid with a step of 300 mm along the length. The connection of the working and structural mesh rods is carried out using a knitting wire at each intersection.

All reinforcement work must be done subject to requirements normative documents: SP 52-101-2003 "Concrete and reinforced concrete structures without prestressing reinforcement”, SNiP 52-01-2003 “Concrete and reinforced concrete structures”.

Rules for the production of works and special events

In addition to the main solution - the MzLF device with a compensating pillow, it is necessary to adhere to certain rules for the production of work and provide for additional measures that will help reduce the negative impact of heaving forces.

The rules for the production of works are as follows:

• all work on the MzLF device should be carried out mainly in the summer. It is not allowed to build foundations on frozen foundation soils;
• to prevent wetting of the foundation soils, it is necessary to perform a vertical layout of the site with a slope on each slope of at least 0.03 to drain surface water after precipitation from the building site and excavations for the foundation;
• if the site is located in a low place, then it is necessary to protect it from the danger of flooding with surface water from neighboring, elevated areas by means of drainage ditches;
• the process of building foundations - from preparatory work to the installation of a blind area - must be carried out in the shortest possible time, for which earthwork can only be started after all preparatory work has been completed and all materials necessary for construction have been delivered to the site;
• on the site, it is necessary to preserve the vegetation cover of the soil as much as possible, which serves as a natural soil insulator;
• after the installation of the MzLF, the sinuses of the trenches must be covered with non-rocky soil or the same material that was used to build the anti-rock cushion - sand, crushed stone or ASG - a mixture of sand and gravel with layer-by-layer compaction. This will prevent the effect of heaving forces on the vertical surfaces of the foundation;
• it is impossible to leave the foundation after the device unloaded for the winter period, that is, it is necessary to immediately erect the walls of the building to the full design height and block it.

In order to minimize the possible negative impact heaving forces, provide additional measures:

• at a level of groundwater close to the foundations, they arrange wall drainage along the perimeter of the building with the laying of drainage pipes and drainage along the slope to a low place;
• effective additional insulation of the base under the sole of the foundation, which is arranged by laying insulation under the blind area. As a heater, it is best to use extruded polystyrene foam - EPS, specially designed for use in underground structures. We wrote about the properties of EPPS and its application in the article "";
• it is recommended to reinforce the blind area made of concrete with a mesh of high-strength wire of class Vr-1 with a diameter of 4 mm with a cell of 150x150 mm. Every 6 m along the length of the blind area and at the corners, it is necessary to arrange expansion joints by inserting a wooden board. In addition, for more efficient drainage of surface water along the edge of the blind area, it is necessary to make drainage grooves with a slope that provides for discharge into a low place;

• places around the building from which the fertile layer of soil was removed, after construction works should be immediately covered with turf and it is desirable to plant shrubs. This will contribute to the warming of the soil and the retention of snow cover in winter, which also reduces the depth of soil freezing.

Calculation of MzLF

The width of the shallow foundation and the thickness of the anti-rock cushion must be taken according to the calculation.

Let's look at an example of how the MzLF is calculated. Take the option for low-rise construction- a one-story residential building made of timber with two extreme and one middle bearing wall with dimensions in the axes of 8x8 m, the middle wall is located in the middle, that is, with a step of 4 m. For wooden light houses, the problem of soil heaving is especially relevant.

Initial data:

• construction of external walls - a wall made of massive timber 150 mm thick;
• the middle wall is a massive beam 150 mm thick;
• floor height 3 m;
• coating - with wooden load-bearing beams;
• plinth 600 mm high made of monolithic concrete;
• soils - loams are semi-solid, strongly heaving, since the site is located in a lowland.

First, we determine the load per 1 linear meter of the foundation for two design sections: 1 - the outer walls bearing the coating, 2 - along the middle wall, where the coating beams rest on both sides. For self-supporting walls, we will not do the calculation, we will take the width of the foundation constructively.

• q1 = Pc x hc + Pbr x he + Pper x L/2

Pc - specific gravity of the base per 1 m2 = 1.5 t / m2 (according to table A);

hc - basement height, equal to 0.6 m;

Pbr - specific gravity of walls made of timber per 1 m² = 0.12 t / m² (according to table A);

he – floor height (3 m);

Pper = wood cover weight 0.223 t/m² (taking into account snow weight according to table A);

L - span of load-bearing walls (4 m).

We get: q1 = 0.6 x 1.5 + 0.12 x 3 + 0.223 x 4/2 = 1.72 t/m

For the middle wall:

1. q2 = Pc x hc + Pbr x he + 2 x Pper x L/2

Pbr - specific gravity of the middle wall of timber, taken according to table A = 0.12 t / m²;

Pc - weight of the plinth in the middle part = 1.5 t/m².

We get:

q2 = 1.5 x 0.6 + 0.12 x 3 + 2 x 0.223 x 4/2 = 0.9 + 0.36 + 0.892 = 2.15 t/r.m.

Table A

Determine the width of the foundation cushion by the formula:

b is the width of the foundation;

q is the load per 1 m of the strip foundation;

R is the design resistance of the soil base, which is taken according to table B, in our case for semi-solid loam R = 22.8 t / m².

Table B

We get for two sections:

1. b1 = q1 / R = 1.72 / 22.8 = 0.07 m
2. b2 = q2 / R = 2.15 / 22.8 = 0.09 m

As a result, we accept the width of the foundation from design considerations for all walls = 0.3 m.

It is also possible to calculate the width of the foundation according to the design resistance of the anti-heaving pillow, when the value of R is less than the value of Rp, where Rp is the design resistance of the soil of the anti-heam pad, which depends on the type of bulk material:

• 14 t / m² - for sand of medium size;
• 16 t/m² - for coarse sand;
• 21 t / m² - for sand and gravel mixture.

In our example, in any case, due to small loads, the width of the foundation is taken from structural considerations.

We determine the thickness of the pillow, for which two formulas are used:

From the conditions of resistance of the underlying soil:

t \u003d 2.5 x bx [ (1 - 1.2 x Rx b) / q]

where: R is the strength of the underlying soil (refractory loam R = 22.8 t/m²), determined from Table B given here.

another formula:

t \u003d (A - C x D x q) / 1 - (0.4 x C x D x q / b)

A - coefficient, determined according to table B, value A for heated structures on heavily heaving soils = 0.5;

C - coefficient, which is equal to 0.1 - for heated buildings, 0.06 - for unheated buildings;

D - coefficient, which is determined from table D, the average value for heated buildings between a width of 0.2 and 0.4 m = 1.70 + 1.29 / 2 = 1.49

Table B

Note: the values ​​above the line of the coefficient A are given for the most optimal depth of laying the base of the foundation of 0.3 m, under the oblique line - for foundations lying on the surface, that is, not buried.

We calculate the thickness of the pillow, based on the conditions of resistance of the underlying soil layer for load-bearing walls:

t \u003d 2.5 x 0.3 x [ 1 - (1.2 x 22.8 x 0.3) / 2.15)] \u003d 0.75 x (1 - 3.81) \u003d - 2.10 m

The result is a negative value, in this case the thickness of the pillow is taken equal to zero.

We calculate according to the second formula:

t \u003d (A - CxDxq) / [ 1 - (0.4 x C xD xq / b)] \u003d (0.5 - 0.1 x 1.49 x 2.15) / [ 1 - (0.5 x 0.1 x 1.49 x 2.15 / 0.3)] \u003d (0.5 - 0.32) / (1 - 0.53) \u003d 0.17 / 0.47 \u003d 0.36 m

The thickness of the pillow is taken according to the larger of the values ​​\u200b\u200bobtained when calculating using two formulas.

As a result, we accept a pillow from design considerations with a thickness of 400 mm.

Table D

Note: same as for table B.

For a quick calculation, the MzLF calculator located here is intended.

Expert opinion

The manifestation of frost heaving forces is possible only if clay or sandy soils occur at the construction site, excluding rocky and coarse-grained soils, gravelly and coarse sands under the following conditions - a sufficient depth of winter freezing, which should be at least 0.5 m, close presence of groundwater from the sole of the foundation and other possibilities of moistening or soaking the soil.

When deciding on the use of MzLF, you should carefully analyze all the conditions. The design of the foundation - the width of the pillow, reinforcement, the thickness of the anti-rock pillow must be accurately calculated.