The requirements for the foundation are very high.

The strength and reliability of the foundation are among the main, but not the only tasks assigned to the supporting structures.

• Unburied. It is created on absolutely immovable soils - rocks, strong stable soils. It is extremely rare.
• Shallow. It is used for construction on solid soils that are not subject to frost heaving. The depth of laying is less than the level of winter freezing of the soil.
• Buried. The depth of such a tape is slightly below the level of soil freezing. It is used for the most massive and heavy buildings, suitable for most types of soil and hydrogeological conditions.

The choice of a suitable type is determined by the analysis of all the conditions of the site - the composition of the soil, the number and properties of layers, the depth of soil water, etc.

What building is it suitable for?

Tape bases are a reliable support for buildings made of various materials:

• Tree.
• Foam and aerated concrete.
• Brick.
• Concrete plates.

The material and the number of floors determine the weight of the building, on which the design parameters of the tape depend - the degree of penetration and thickness. Along with the characteristics of the soil, the parameters of the building are the main material for performing engineering calculations in the design.

How to calculate depth

strip foundation depends on the type of foundation. E if construction is planned option, it is necessary to rely on the tabular data of SNiP, showing the depth of soil freezing in a given region.

During the construction of a shallow type of tape, the composition of the soil, the presence and depth of groundwater are taken into account. It is customary to refer to the optimal depth of 0.75-1 m, but on stable and dry soils, the depth can be slightly reduced.

NOTE!

The most common immersion depth for shallow tape is considered to be 0.7 m.

How does a shallow strip foundation work

almost completely repeats the in-depth version, only with a lower level of immersion.

There is a trench in which a drainage layer of backfill is created and a concrete tape is poured.

The design of the base has fewer possibilities than a full-fledged tape, but, for relatively small low-rise buildings, its bearing capacity is quite enough.

Do-it-yourself step-by-step installation instructions

Consider the procedure for creating a strip foundation:

• Preparation.
• Site marking.
• Digging a trench.
• Laying and arrangement of the drainage system.
• Creation of sandy.
• Formwork manufacturing.
• Reinforcing cage installation.
• Pouring concrete.
• Exposure for hardening.
• Stripping.
• Waterproofing and insulation tape.
• Further work.

The order of actions does not change under almost any circumstances, since all stages are the result of previous operations.

Surface marking

The beginning of work consists in removing the top layer of soil and marking the site. For this, wooden stakes are used, which are installed at the intersection points or corner points of the future trench.

The width is selected based on the design parameters of the base, but not less than 20 cm more than that of the tape. This is important, since it will be necessary to install the formwork inside the trench, and subsequently to ensure a sufficient thickness of the backfill layer of the sinuses.

trench preparation

Digging a trench is done with an excavator or manually. The second option is difficult, but if there are difficulties with the delivery or approach of construction equipment to the site, it is quite possible. Excavated soil is stored on the sides of the trench or immediately removed from the site.

It is necessary to ensure the same depth, but there is no need to try too hard and level the bottom to centimeters. Trench corners are manually leveled regardless of digging method.

Drainage device

The drainage system makes it possible to remove groundwater from the sand cushion layer, eliminating the possibility of heaving loads in winter.

There are different types of systems:

• Open. It is created on the day surface and is designed to drain rain or melt water. Used on dry soils with deep groundwater.
• Closed. Consists of a system of pipelines placed in a trench near the tape. It serves to remove groundwater from a layer of sandy backfill (cushion), it is used on soils with the presence or seasonal change in the level of groundwater.

In practice, the closed type is most often used, since there is a danger of water in most cases. A system of pipelines for special purposes is installed, receiving and discharging moisture into the drainage well.

For high-quality drainage, the installation of a filtration piping and a slope for the natural movement of water are required. The filtration layer cuts off small organic particles, preventing the inner surface of the drainage pipes from silting up.

This contributes to extending the life of the system and reduces the risk of failures.

Pillow

The sand cushion is an important and indispensable element of the foundation design. Its thickness is different, on average it is 20 cm.. Usually clean river sand is used or alternately a layer of sand 10 cm, fine gravel 10 cm and again a 5 cm leveling sand layer.

After backfilling of each layer, a thorough compaction is carried out using construction vibrators or hand tools. It is recommended to shed the layers with water, this contributes to a better sealing of the pillow.

NOTE!

Experts recommend to be guided by the following quality criteria for the compaction of the backfill layer: there should be no footprints on the surface when walking. This is important as cushion settlement is not acceptable as it will cause the belt to deform with unpredictable consequences.

Formwork installation

To create the formwork, edged boards with a thickness of 25-40 mm are used (depending on the size of the tape). First, next to the trench, shields are assembled with a width slightly greater than the height of the tape.. As the assembly progresses, the shields are lowered into the trench and fixed outside with inclined stops and vertical support bars.

From the inside, crossbars are installed that determine the distance between the shields, equal to the width of the tape. The formwork must be strong, ready to receive loads during pouring and solidification of concrete. There should not be any gaps, all gaps over 3 mm must be filled with tow or clogged with slats.

This will eliminate the unproductive consumption of concrete when flowing into the cracks.

Reinforcement

The reinforcement is designed to compensate for tensile axial loads that concrete cannot withstand. It freely accepts a lot of pressure, but the tape is unstable in bending and immediately breaks.

For reinforcement, a reinforcing belt is created, the main element of which is horizontal working rods made of metal or fiberglass ribbed reinforcement.

To support the rods in the required position, smooth rods of smaller diameter are used, from which vertical elements (clamps) are made, which, in combination with the working rods, form a spatial lattice.

Its dimensions are such that the horizontal rods are immersed in concrete to a depth of 2-5 cm.

Working rods are selected based on the width of the tape. Their diameter for a shallow base is in the range of 12-14 mm (with a width of 30-40 cm) or 16 mm with a larger width.

Rebar knitting

The reinforcement cage elements are connected in two ways:

• Electric welding.
• Knitting with soft steel annealed wire.

The first option is used for thick rods and is practically not used in the construction of shallow foundations. The assembly of the armored belt most often occurs by knitting.

A soft wire is used, which quite reliably holds the elements of the frame, but has a certain degree of freedom, which makes it possible to maintain the integrity of the frame when loads occur during pouring.

For knitting, a special tool in the form of a hook is used. A piece of wire about 25-30 cm long is folded in half. The resulting half-loop wraps around both connected rods in a diagonal direction, the ends rise up.

Then they grab the fold loop with a hook and, leaning on the second free end, make 3-5 rotational movements, due to which both rods are tightly and firmly connected to each other.

The operation is simple, usually the skill is developed on the first day.

The choice of concrete for pouring

There are quite a few grades of concrete designed for different conditions and loads. Since a shallow strip foundation is mainly used in low-rise private construction, concrete grade M200 will be the best choice.

It is able to provide the necessary strength and load-bearing capacity of the tape with a relatively low dead weight.

For those who wish to approach the issue more carefully, we can recommend using an online calculator to calculate the grade and amount of concrete. The result obtained should be duplicated on another resource in order to protect yourself from possible errors.

fill

Filling must be done as quickly as possible, ideally at once. Breaks in pouring for more than a day are unacceptable, in such cases it is necessary to withstand concrete until it is completely hardened and only then continue work. The quality and degree of strength of such a tape is much lower than that of a simultaneous casting.

This condition is most easily met using ready-mixed concrete, which is delivered directly to the site in a mixer. It turns out significant time savings, and the quality of concrete in any case will be better than that of a home-made solution.

It is necessary to pour from several points, trying to distribute them as evenly as possible along the length of the tape. This will allow you to get a casting with the same parameters around the entire perimeter, which will ensure high strength of the base.

Features of waterproofing

The effect of moisture is extremely detrimental to a shallow tape. Penetrating into concrete, water sooner or later freezes and breaks the material from the inside. Under no circumstances should this be allowed.

There are two types of waterproofing that you can do:

• Horizontal. Protects the lower and upper plane of the tape against the penetration of moisture from the lower layers of the soil and from rain or melt water flowing from the walls. The lower waterproofing is laid before the installation of the formwork and the reinforcing belt, and the upper one is made after the concrete has completely hardened in parallel with the vertical waterproofing. Both layers consist of roofing material, laid in two layers with bituminous mastic.
• vertical. It is applied to the outer and inner surface of the tape after stripping and complete drying. Materials of different types of action are used - impregnation, coating or pasting. Impregnations are the most effective, but they appeared relatively recently and are little known to builders.

Warming issues

Tape insulation prevents the formation of condensate. There are two options - external and internal insulation. In the first case, the insulation is mounted outside, in the second - from the inside.

Experts recommend performing both types of insulation at the same time, since it is not possible to achieve the expected result separately. Considering the specifics of placement, it is necessary to use moisture-proof types of heat insulators - foundation foam, liquid polyurethane foam, polyethylene foam, etc.

Mineral wool should not be used in this case, since it is able to absorb water with a complete loss of performance.

Proper care of concrete after pouring

After pouring for 10 days, it is necessary to regularly water the surface of the tape with water.:

• The first 3 days - every 4 hours.
• The next 7 days - 3 times a day.

The tape must be hidden from the scorching rays of the sun under a layer of polyethylene. Sprinkling with water makes it possible to somewhat equalize the moisture content of the outer and inner layers of the tape, reducing loads and the risk of cracks.

The final hardening of concrete takes a very long time, but you can continue working with the tape after 28 days.

Stripping

Demoulding is the process of dismantling the formwork. It can be produced no earlier than 10 days after pouring.

You should not try to speed up the process, the foundation is too important an element of the building to take risks and rely on chance.

Basic Mistakes

Most often, a sediment of a sand cushion occurs due to poor-quality compaction of the backfill layer. In addition, the use of unsuitable materials is often encountered, in particular, concrete of the wrong brand.

Some unscrupulous suppliers ship low quality material to save money. Experienced experts recommend ordering heavier concrete - instead of M200, take M250. The difference in cost and weight is small, but there is hope that the material will be more durable.

In addition, they often try to reduce the cost of money and labor by refusing and. These procedures require some time, but compared to the service life of the base, they are carried out very quickly and cannot be neglected.

Useful video

In this video you will learn how to install a strip foundation:

Conclusion

Creating a strip foundation is not so much a difficult task as it requires a complete understanding of the meaning of all stages and the high-quality implementation of the necessary actions.

For an unprepared person with no experience, it is recommended not to deviate from the technology and strictly comply with the requirements of SNiP.

This will help build a solid and high-quality shallow strip foundation.

In contact with

This page provides information about reinforced concrete strip foundations. We will consider the varieties of these bases, their scope, calculation features and construction technology - from marking to concreting the foundation tape.

The strip foundation is a closed reinforced concrete contour, arranged along the supporting structures and contributing to a uniform distribution of the mass of the building over the entire area. There is effective resistance to buckling processes occurring in the soil, which eliminates the possibility of distortions and subsidence.

What is strip foundation

The strip foundation is a monolithic reinforced concrete or prefabricated strip that repeats the perimeter of the walls of the structure. The tape is laid under the internal and external walls of the building, its cross section is identical both in the longitudinal contours and at the intersections.

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In comparison with the technology of mounting slab foundations, the construction of a strip foundation is simpler in execution and requires less material. The operational characteristics of the tape allow you to build on it the following types of buildings:

• Heavy houses with walls made of concrete, brick or stone, weighing more than 1000 kg / cubic meter;
• Buildings with reinforced concrete and metal floors;
• Light houses made of timber, logs and wood panels.

Important: the height of structures erected on a strip foundation varies between 1-5 floors. Such bases are suitable for construction in places where there is a risk of uneven soil shrinkage associated with frost heaving or soil heterogeneity. The reinforced frame of the tape provides a uniform redistribution of the loads acting on the foundation, which protects the walls from deformation.

The operational durability of strip foundations depends on their type:

• Monolithic reinforced concrete tapes - up to 150 years;
• Prefabricated brick strips - up to 50 years;
• Prefabricated tapes from reinforced concrete blocks - up to 75 years.

Strip foundations (deep) are used when it is necessary to equip the basement floor - the contours of the tape (1.5-2 m high) form the walls of the basement. In order to save building materials, deep laying tapes are often equipped with different perimeter configurations - the outer contours of the foundation deepen below the soil freezing limit (by 30-40 cm), and the inner contours are placed at a depth of 50-60 cm.

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In conditions of dry clay and sandy soils, the minimum depth of laying the foundation tape is 60 cm. On heavily heaving soil with a low freezing limit, such foundations are practically not used due to the financial inexpediency of laying the tape to a great depth. An alternative in this case are pile foundations.

Types of strip foundations

Tape bases are of 2 types:

• monolithic
• prefabricated.

Monolithic strip foundations are distinguished by the presence of a reinforcing cage, which is subsequently poured with concrete mortar directly at the construction site. Thanks to this technology, the continuity of the structure is ensured. Prefabricated bases are formed from prefabricated reinforced concrete blocks.

Between themselves block structures fastened with cement mortar and reinforcement method. There are strip foundations according to the degree of deepening: deep-buried, shallow-buried. The depth is determined, depending on the bearing characteristics of the soil and the expected design load.

Strip foundation technology

It is rational to carry out the construction of a strip foundation in the warm season, from April to October. The construction of the tape does not require the involvement of special equipment, it is only necessary to have a concrete mixer and small-scale mechanization - a welding machine, a grinder, an electric drill.

Stage number 1 - preparatory work and marking

Construction begins with the preparation of a building site - the territory is cleared of debris and stones, vegetation and tree roots are removed. It is necessary to remove a layer of fertile soil (sod) to the depth of a shovel bayonet. If the site has a natural slope, the site is leveled at one horizontal level.

Important: marking the axes of the foundation is carried out using cast-off boards and wire or construction cord. The run-down shield consists of two stakes driven into the ground, which are connected by a horizontal belt. The twine on the shield is fixed using a self-tapping screw or a nail screwed into the board.

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When marking the contours, the shields are carried out beyond the axes of the foundation at a distance of 1-2 meters, so that in the process of digging a trench, the structures do not interfere with work. The design outlines of the foundation are transferred to the site - initially the external contours of the building are indicated, then the width of the tape retreats from them and the twine is pulled along the inner contour.

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The marking of the internal walls of the building is carried out upon completion of the breakdown of the external axes. In the process of work, you need to check the right angles of the markup. This is done according to the Egyptian triangle method - in one of the corners from the intersection on the first twine, a mark is made at a distance of 3 m, on the second - with an indent of 4 m. Next, the diagonal is measured, with the right right angle its value is 5 m.

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Stage number 2 - digging a trench and backfilling the compacting pad

The trench for the foundation tape can be developed manually or using excavators. When using special equipment, the bottom of the trench must be leveled at one horizontal level.

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Upon completion of the formation of the trench, the compacting pad is backfilled. Its thickness is selected based on the degree of heaving of the soil; under normal conditions, a bedding 20 cm thick is used, consisting of two identical layers of crushed stone and sand. Sand is poured first, which is watered and manually compacted. If necessary, gravel can be replaced with fine gravel.

Stage number 3 - formwork installation

To create formwork, planed boards with a thickness of over 0.5 cm are used. It is acceptable to use boards processed on one side (a smooth surface is installed inside). The boards are knocked down into shields with a height equal to the height of the ground part of the foundation and are installed along the perimeter of the trench.

Important: the formwork must be fixed with the help of side braces and the upper transverse bar, which prevent the deformation of the form under the pressure of concrete. Make sure that the nails and screws that connect the shields do not protrude onto the inner surface of the formwork.

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It is important to achieve the verticality of the formwork walls, which is controlled by the level. The part of the formwork raised above the ground forms the basement part of the foundation tape. Holes are pre-cut in the shields for the placement of sewer and water communications, into which metal pipes are installed to form cavities in the reinforced concrete structure.

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The formwork walls and the internal surfaces of the trench must be covered with a waterproofing material that will prevent leakage of water and cement laitance from the concrete mixture.

Stage number 4 - assembly of the armored carcass

To reinforce the foundation, a double-circuit frame is used, consisting of an upper and lower longitudinal belt connected by vertical bridges. The number of rods in the longitudinal belts is selected based on the width of the tape (3-5 pcs), rods with a diameter of 12 to 16 mm are used. Vertical jumpers are placed in increments of 20-30 cm.

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For convenience, the frame is assembled outside the trench, after which the finished structure is placed inside the formwork. Each side of the frame should be removed from the contours of the concrete body of the foundation at a distance of 4-5 cm, special mushroom stands are used to raise the frame above the bottom of the trench, it is not recommended to use bricks for this purpose.

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Important: at the junction of the walls and the corner parts of the foundation, the frame is joined using curved reinforcement and is additionally reinforced with L-shaped rods. Cross docking cannot be used, as it reduces the strength of the structure.

Stage number 5 - concreting

For concreting the foundation tape, concrete grade M200 or M300 is used. When self-mixing, the proportions 1:2:4 (cement-sand-aggregate) are used. As a filler, fine-grained crushed stone with a particle size of 40-70 mm is used.

It is important to achieve the optimal consistency of the composition - when stirring with a shovel, it should not flow around a metal surface, but should be mixed with considerable effort. When using excessively liquid concrete, the aggregate may settle at the bottom of the trench, which should not be allowed.

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When pouring the foundation, gutters are used - it is impossible to pour concrete from a height of more than 1 m from the bottom of the trench, this can lead to its delamination. Do not allow intermediate hardening of concrete, the layers must be poured before the previous layers have set. After concreting, the tape must be pierced with a reinforcing bar in order to remove air cavities from it.

Dismantling of the formwork is carried out after 5-7 days after pouring the foundation, it takes 25-30 days for the concrete to fully cure.

Frame reinforcement technology

The strength of the foundation is provided by the reinforcing structure, without which it is impossible to form an integral foundation. Reinforcement work includes several stages:

• formwork installation - a plank frame is installed along the perimeter of the future building, the walls of which are lined with parchment on the inside, thanks to which it will be easy to remove it later;
• driving vertically arranged reinforcing bars into the soil - the length of the reinforcement is comparable to the depth of the base. It is necessary to deepen the bars at a distance of 50 mm from the walls of the formwork, while they are introduced into the ground in increments of up to 600 mm;
• installation of supports on the bottom (height up to 100 mm), on top of which horizontally arranged reinforcing bars are laid: the function of supports can be performed by halves of bricks installed on the edge;
• horizontal rows connected to vertical rods;
• fixing structural elements at intersections by welding or wire.

Useful materials

The concept of "strip foundation" characterizes only its form. In practice, for low-rise buildings, there are several options for manufacturing a base of this shape. We will briefly talk about some and give instructions for the step-by-step construction of a monolithic foundation.

Tape depth options

There are two types of tape in depth. If the sole is no deeper than 60 cm, then this is a shallow foundation.

This also includes bases when the sole is on the surface of the ground. And to be more precise, a little lower, given that the site is leveled. In practice, such a foundation in its pure form is placed where there is no fertile layer. Such conditions are rare. In most cases, there is a humus layer on the construction site, so the scheme for arranging an unburied foundation looks like this:

• completely cut off the fertile layer along the entire base of the future structure;
• a layer of sand is covered (if necessary, improve the bearing capacity of the soil - also crushed stone);
• water, level and tamp the pillow;
• put the formwork for the tape.

1. Concrete floors on the ground, raised to the height of the basement.

1. Basement with underground and floors on the floor.

But the foundation deepened into the ground up to 60 cm is more common.

All these options are common in private construction, when the project does not provide for a basement. It has been proven that the heaving forces at a shallow depth are compensated by the weight of a low-rise building, and the bearing capacity of a shallow-depth tape is sufficient to withstand the load.

The sole of the buried lies in the ground below the freezing point.

This type is the most durable, but it is also the most material-intensive. It is laid when a basement or an underground technical floor is needed to accommodate engineering systems equipment.

Classification by technology

According to the manufacturing method, there are three types of base tape: prefabricated, monolithic, combined. And already these technologies have their subspecies.

The prefabricated base is assembled, as a rule, from concrete blocks (FBS).

They also use a more “small format”: ceramic brick or cinder block. But even for a solid building block foundation, the bearing capacity is weakened by the seams - and even the reinforcing belts cannot fully compensate for this. Therefore, in its pure form, a brick or cinder block foundation is rare, and building blocks go to the base of combined foundations.

If for FBS a mortar is needed to fill the irregularities of the spoon and there are no special requirements for the brand (the adhesion strength of the blocks is provided by weight), then when using “small forms”, a full-fledged masonry mortar is required. In addition to the FBS assembly, medium-sized natural stone foundations are also popular.

And the popularity is explained simply - high decorative properties.

Combined foundations can also have different technological schemes. For example, an underground part made of reinforced concrete plus a brick base.

There are two types of monolithic tape: with rubble stone, poured with concrete, and from reinforced concrete.

In the first version, the reinforcing role is assigned to a small rubble stone. Unlike a “clean” rubble foundation, a rubble concrete foundation provides for: formwork installation, laying a pillow, pouring a small layer of concrete, laying the first row of stone into it, pouring a mortar layer, laying the second row, etc. The distance between the stones is about 5 cm, and the ratio of the volumes of mortar and stone is approximately 1:1.

The attractiveness of this type of foundation is in reducing the volume of concreting, and, consequently, the cost of materials.

But the most reliable is a monolithic concrete tape with a reinforcing frame.

Monolithic strip foundation

Manufacturing technology has the following sequence.

On the ground, a pit is marked (for a deep foundation) or a trench system (for a shallow foundation). Carry out excavation work.

If the tape is shallow and communications enter / exit under the sole, then they dig a trench for them and lay sleeves for laying pipes under the tape. Align (plan) the bottom of the pit or trenches. They fall asleep, level, moisten and ram the sand and gravel cushion. The total thickness of the pillow is up to 30 cm (the ratio and volume of the parts depend on the characteristics of the soil), and the width of the pillow is 30 cm wider than the heel of the foundation. Install the formwork.

The materials are edged board and timber. It is allowed to use an edged board with a wane, but so that there are no gaps between them.

To simplify the assembly procedure, it is possible to make shields from boards and timber on the ground. The wall thickness of the formwork must withstand the pressure of the concrete. The strength of the formwork is increased by connecting the racks along the horizon with steel wire and reinforcing the side stops on the ground on one or both sides.

For a deep foundation, when constructing a basement, it is recommended to install a non-removable foam formwork.

At the formwork of the buried foundation, holes are cut out for sleeves for engineering communications. For sleeves, pieces of plastic or asbestos-concrete pipes are used. The diameter of the sleeve is chosen based on the dimensions of the passing pipes and the insulation layer. At the time of work on the arrangement of the foundation, the sleeves are filled with sand and the holes are closed.

Install reinforcing frame. The diameter of the reinforcement, the mesh parameters depend on the design indicators of the bearing properties. The main purpose of the "iron" is to improve the resistance of the foundation to fracture and to lateral loads, the compressive strength of the concrete stone is already high. The distance between the reinforcement and the walls of the formwork is at least 50 mm.

The concrete is poured in layers. If there are access roads, and a concrete plant is nearby, then it is better to use a ready-mix.

Otherwise, the mixture is prepared by themselves, observing the proportions to obtain the required grade.

The optimal layer thickness is up to 20 cm. And the filling of the layer should be continuous around the entire perimeter. Each layer is compacted in one of the ways: with a deep vibrator or bayoneted with a piece of reinforcement (for small volumes).

After pouring the last layer, it is covered with a plastic film (this is a necessary condition for the normal hydration of concrete). It is allowed to cover the basement of the foundation with burlap and periodically moisten it. The first seven days are critical, when the concrete stone gains 70% of the design strength.

Four weeks later, the formwork is removed. Then carry out waterproofing. The choice of materials and technology depends on the nature of the soil and the level of groundwater. Roll materials are popular, which are deposited on a prepared surface.

Strip foundations are the most common, but not applicable on all soils. To begin the construction of such a foundation, it is necessary to carefully examine the soils and decide how thick and how high the tape should be.

In this article, we will describe in detail all the stages of the construction of a strip foundation, starting from digging a trench, reinforcing, formwork and ending with pouring concrete.

Geology of the soil under the foundation

This is the most important stage by which the following data are determined:

1. Soil type and its design resistance.
2. Freezing depth.
3. Ground water level.
4. The degree of heaving of the soil and its uniformity.

After geology, you can proceed to the design of the foundation itself.

Depending on the architectural solution, that is, the initially planned building, the weight of the house is determined, including the weight of the foundation, snow, wind and payload. The type of foundation, in our case, tape, can be buried and shallow.

The next step is to determine the parameters of the foundation itself, namely:

1. Foundation width.
2. The height of the recessed part.
3. Above ground height.
4. Is drainage required?

To determine the width of the foundation, it is necessary to divide the weight of the house by the area of ​​\u200b\u200bthe foundation support, and the resulting value should be less than the calculated soil resistance by 20%.

To increase the area of ​​​​the foundation support, a broadening (heel) is made, which distributes the load over a larger area.

We wrote about this in more detail in our previous article - how to calculate the weight of the house.

For a deep foundation, the laying depth should be 20 cm below the freezing depth. For a shallow foundation, it all depends on the soil, or rather on heaving, freezing depth and groundwater level.

For an approximate determination of the depth of a shallow foundation, see the table.

1. The maximum height of the above-ground part of the strip foundation should not exceed four widths of the foundation strip.
2. The above-ground part should be smaller than the underground part.
3. The optimal height of the aerial part is 40-50 cm.

Performing site markings

According to the finished project, it is necessary to carefully measure all the corners of the future foundation and set the pegs. The stakes are placed along the outer and inner perimeter of the foundation, a cord is stretched between the stakes, defining the contours for digging the foundation trench.

At this stage, a trench is being dug, the depth of which should be under the foundation project, taking into account the sand cushion and formwork. There are two ways to dig a trench: with a tractor using a narrow bucket, and manually (with shovels). The tractor will cope much faster, but with shovels it turns out smoother and more accurate.

The sand cushion is made about 20 cm thick, wetted with water and well compacted.

In some cases, it will be much more convenient to first tie the frame in a trench, and only then expose the wooden formwork.

Frame reinforcement steps:

1. Stones or bricks 5-6 cm high are laid at the bottom of the trench, the task of which is to raise the reinforcing cage in order to create a protective layer of concrete from below.
2. Further, longitudinal reinforcements are laid out on the bottom, not rods, previously bent at the corners.
3. Next, pre-made clamps are put on the bottom row of reinforcement, they are also frames, they are also transverse reinforcement.
4. Clamps and a row of lower reinforcement are connected with knitting wire.
5. If the height of the tape is more than 80 cm, then structural rows of reinforcement are added, one row or more.
6. Further, the upper longitudinal reinforcement bars, L-shaped clamps at the corners are added to the frame and are connected with wire.
7. To provide a protective layer of concrete on the sides of the foundation, special plastic rings are used to help hold the frame in position.

We strongly advise you to read our article about the calculation of the reinforcement of a strip foundation, in which all the nuances for the selection of reinforcement and the scheme for reinforcing corners are described in detail.

The formwork is knocked down from wooden boards, and reinforced with many bars, which additionally rest against the ground on pegs. Also, to strengthen the formwork, metal wire ties are used, or studs are tightened in plastic tubes.

The installation of the formwork must be approached very responsibly, since liquid concrete has a large bursting force, especially if the height and width of the formwork are large. Quite often, formwork bursts for inexperienced builders, and concrete flows to the ground. To avoid this situation, reinforce the formwork as much as possible. And remember that more concrete pressure is created at the bottom.

Do not forget about the installation of sleeves for communications (water, sewerage).

It is very important that the foundation be monolithic, and in order to achieve this state, it is necessary to pour concrete into the trench in one go. Manually, with a concrete mixer, this is unlikely to be achieved, therefore it is better to order the delivery of ready-made concrete in mixers.

1. The time between delivery of concrete trucks should not exceed two hours.
2. Pouring is best done in layers, pulling the concrete around the entire perimeter.
3. For a more plastic (liquid) concrete mix, ask to add a plasticizer to the mixer.
4. Excess water in concrete reduces grade strength, increases the number of shrinkage cracks and increases the number of pores in concrete, making it less moisture resistant. Avoid excess water during the kneading process.
5. During pouring, you need to use a deep vibrator, which compacts the concrete and expels air.
6. Try to level the plane of the foundation tape as much as possible.
7. During the week, it is necessary to shed the surface of the foundation with water, this will avoid shrinkage cracks and help the concrete gain brand strength. We also recommend covering the tape with foil.

The foundation is ready. It remains to perform vertical and horizontal waterproofing, as well as an insulated blind area, which reduces the depth of freezing and removes excess water from the foundation.

About how long the foundation should stand, we wrote a separate article, which discusses options for settling from 10 days to six months.

Everyone knows the old proverb that a real man must do three things in his life: plant a tree, raise a son and build a house. With the last point, there are especially many questions - what material is better to use, choose a one- or two-story building, how many rooms to count, with or without a veranda, how to install a foundation, and many others. Among all these aspects, it is the foundation that is fundamental, and this article will be devoted to its tape type, its features, differences, and construction technology.

Peculiarities

Despite the fact that there are several types of bases for the house, preference in modern construction is given to strip foundations. Due to its durability, reliability and strength, it occupies a leading position in the construction industry around the world.

Already from the name it is clear that such a design is a tape of a fixed width and height, laid in special trenches along the boundaries of the building under each of the outer walls, thus forming a closed loop.

This technology gives the foundation ultimate rigidity and strength. And due to the use of reinforced concrete in the formation of the structure, maximum strength is achieved.

Among the key features of the tape type foundation are the following:

• the reliability and long service life already mentioned above;
• rapid construction of the structure;
• accessibility in terms of cost relative to its parameters;
• the ability to install manually without the use of heavy equipment.

According to GOST 13580-85, a strip foundation is a reinforced concrete slab, the length of which is from 78 cm to 298 cm, the width is from 60 cm to 320 cm and the height is from 30 cm to 50 cm. After calculations, the brand of the base is determined with a load index of 1 up to 4, which is an indicator of the pressure of the walls on the foundation.

In comparison with pile and slab types, the tape base, of course, wins. However, the columnar foundation overpowers the base with tape due to the significant consumption of materials and increased labor intensity.

This number is affected by:

1. soil characteristics;
2. the total area of ​​the basement;
3. type and quality of building materials;
4. depth;
5. dimensions (height and width) of the tape itself.

The service life of a strip foundation directly depends on the correct choice of a site for construction, compliance with all requirements and building codes. Taking into account all the rules will extend the service life for more than one decade.

An important feature in this matter is the choice of building material:

• a brick foundation will last up to 50 years;
• prefabricated structure - up to 75 years;
• rubble and monolithic concrete in the manufacture of the base will increase the service life up to 150 years.

purpose

Tape technology for the construction of the foundation can be used:

• in the construction of a monolithic, wooden, concrete, brick, frame structure;
• for a residential building, a bathhouse, an economic or industrial building;
• for the construction of fences;
• if the building is located on a site with a slope;
• great if you decide to build a basement, porch, garage or basement;
• for a house where the wall density is more than 1300 kg / m³;
• for both light and heavy buildings;
• in areas with heterogeneous bedded soil, which leads to uneven shrinkage of the base of the structure;
• on loamy, clayey and sandy soil.

Advantages and disadvantages

Among all the many advantages, it is worth mentioning some of the disadvantages of the strip foundation:

• with all the simplicity of the design, the work itself is quite laborious;
• difficulties with waterproofing when installed on wet ground;
• unsuitable option for soils with a weak bearing property due to the large mass of the structure;
• reliability and strength are guaranteed only with reinforcement (reinforcement of the concrete base with steel reinforcement).

Kinds

By classifying the selected type of foundation according to the type of device, it is possible to distinguish between monolithic and prefabricated foundations.

Monolithic

Assume the continuity of the underground walls. They are characterized by low construction cost in relation to strength. This type is in demand in the construction of a bathhouse or a small wooden house. The disadvantage is the large weight of the monolithic structure.

The technology of a monolithic foundation involves a reinforcing metal frame, which is installed in a trench, after which it is poured with concrete. It is due to the frame that the necessary rigidity of the foundation and resistance to loads are acquired.

Cost per 1 sq. m - approximately 5100 rubles (with the characteristics: slab - 300 mm (h), sand cushion - 500 mm, concrete grade - M300). On average, a contractor for pouring a 10x10 foundation will take about 300-350 thousand rubles, taking into account installation and the cost of materials.

prefabricated

The prefabricated strip foundation differs from the monolithic one in that it consists of a complex of special reinforced concrete blocks interconnected by means of reinforcement and masonry mortar, which are mounted with a crane at the construction site. Among the main advantages is the reduction of installation time. The downside is the lack of a single design and the need to attract heavy equipment. In addition, in terms of strength, the prefabricated foundation is inferior to the monolithic one by as much as 20%.

Such a foundation is used in the construction of industrial or civil buildings, as well as for cottages and private houses.

The main costs will go to the haul and hourly rental of a truck crane. 1 running meter of prefabricated foundation will cost at least 6600 rubles. About 330 thousand will have to be spent on the basis of a building with an area of ​​​​10x10. Saving will allow laying wall blocks and pillows with a small distance.

There is also a tape-slot subspecies of the structure, which is similar in its parameters to a monolithic strip foundation. However, this base is adapted for pouring exclusively on clay and non-rocky soils. Such a foundation costs less due to the reduction of land work, since the installation takes place without formwork. Instead, they use a trench that visually resembles a gap, hence the name. Slotted foundations make it possible to equip a garage or utility room in low-rise, non-massive buildings.

Important! Concrete is poured into wet ground, since in a dry trench some of the moisture goes into the ground, due to which the quality of the foundation may deteriorate. Therefore, it is better to use concrete of a higher grade.

Another subspecies of the prefabricated strip foundation is the cross one. It includes glasses for columns, base and intermediate plates. Such foundations are in demand in row building conditions - when a columnar foundation is located in close proximity to a foundation of the same type. Such an arrangement is fraught with subsidence of structures. The use of cross foundations involves the contact of the lattice of the end beams of the building under construction with the already constructed and stable structure, thereby allowing the load to be evenly distributed. This type of construction is applicable for both residential and industrial construction. Among the shortcomings, the laboriousness of the work is noted.

Also, for a tape type foundation, a conditional division can be made relative to the depth of the foundation. In this connection, according to the magnitude of the load, buried and shallow-buried species are distinguished.

Deepening is carried out below the established level of soil freezing. However, within private low-rise buildings, a shallow foundation is acceptable.

The choice in such typing depends on:

• mass of the building;
• the presence of a basement;
• soil type;
• height difference indicators;
• groundwater level;
• soil freezing level.

The definition of these indicators will help in choosing the right type of strip foundation.

The recessed view of the foundation is designed for a house made of foam blocks, heavy buildings made of stone, brick, or multi-storey buildings. For such foundations, significant height differences are not terrible. Perfect for buildings in which the arrangement of the basement is planned. It is erected 20 cm below the level of soil freezing (for Russia it is 1.1-2 m).

It is important to take into account the frost heaving buoyancy forces, which should be less than the concentrated load from the house. To confront these forces, the foundation is set in the shape of an inverted "T".

The shallow-depth tape is distinguished by the lightness of the buildings that will be located on it. In particular, these are wooden, frame or cellular structures. But its location on the ground with a high level of groundwater (up to 50-70 cm) is undesirable.

The key advantages of a shallow foundation are the low cost of building materials, low labor intensity and short installation time, unlike a deep foundation. In addition, if it is possible to get by with a small cellar in the house, then such a foundation is an excellent and low-cost option.

Among the shortcomings, one can single out the inadmissibility of installation in unstable soils., and such a foundation is not suitable for a two-story house.

Also, one of the features of this type of foundation is the small area of ​​the side surface of the walls, and therefore the buoyant forces of frost heaving are not afraid of light construction.

To date, developers are actively introducing the Finnish technology for installing foundations without deepening - pile-grillage. A grillage is a slab or beam that connects the piles to each other already above the ground. The new type of zero-level device does not require the installation of shields and the installation of wooden bars. In addition, the hardened concrete does not have to be dismantled. It is believed that such a structure is generally not subject to heaving forces and the foundation is not deformed. Installed on the formwork.

In accordance with the norms regulated by SNiP, the minimum depth of the strip foundation is calculated.

materials

The strip foundation is mainly assembled from brick, reinforced concrete, rubble concrete, using reinforced concrete blocks or slabs.

Brick is suitable if the house is supposed to be built frame or with thin brick walls. Since the brick material is very hygroscopic and easily destroyed due to moisture and cold, such a deep foundation is not welcome in places with a high level of groundwater. At the same time, it is important to provide a waterproofing coating for such a base.

The popular reinforced concrete base, despite its low cost, is quite reliable and durable. The composition of the material includes cement, sand, crushed stone, which are reinforced with a metal mesh or reinforcement bars. Suitable for sandy soil when erecting monolithic bases of complex configuration.

A strip foundation made of rubble concrete is a mixture of cement, sand and large stone. Sufficiently reliable material with length parameters - no more than 30 cm, width - from 20 to 100 cm and two parallel surfaces up to 30 kg. This option is perfect for sandy soils. In addition, a prerequisite for the construction of a rubble concrete foundation should be the presence of a gravel or sand cushion 10 cm thick, which simplifies the process of laying the mixture and allows you to level the surface.

The foundation of reinforced concrete blocks and slabs is a finished product manufactured at the enterprise. Among the distinguishing features are reliability, stability, strength, the ability to use for houses of various designs and types of soil.

The choice of material for the construction of the strip foundation depends on the type of device.

The base of the prefabricated type is made:

• from blocks or slabs of the established brand;
• concrete mortar or even brick is used to seal cracks;
• completed with all materials for hydro- and thermal insulation.

• the formwork is constructed from a wooden board or polystyrene foam;
• concrete;
• material for hydro- and thermal insulation;
• sand or gravel for a pillow.

Rules for calculation and design

Before a project is drawn up and the parameters of the building foundation are determined, it is recommended to review the regulatory construction documents, which describe all the key rules for calculating the base and tables with established coefficients.

Among these documents:

GOST 25100-82 (95) “Soils. Classification";

GOST 27751-88 “Reliability of building structures and foundations. Basic provisions for the calculation ";

GOST R 54257 "Reliability of building structures and foundations";

SP 131.13330.2012 "Construction climatology". Updated version of SN and P 23-01-99;

SNiP 11-02-96. “Engineering surveys for construction. Basic Provisions”;

SNiP 2.02.01-83 "Foundations of buildings and structures";

Manual to SNiP 2.02.01-83 "Manual for the design of the foundations of buildings and structures";

SNiP 2.01.07-85 "Loads and impacts";

Manual to SNiP 2.03.01; 84. "Manual for the design of foundations on a natural basis for the columns of buildings and structures";

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

SNiP 3.02.01-87 "Earth structures, foundations and foundations";

SP 45.13330.2012 "Earth structures, foundations and foundations". (Updated version of SNiP 3.02.01-87);

SNiP 2.02.04; 88 "Foundations and foundations on permafrost soils".

Let us consider in detail and step by step the calculation plan for the construction of the foundation.

To begin with, a total calculation of the entire weight of the structure is made, including the roof, walls and ceilings, the maximum allowable number of residents, heating equipment and domestic installations, and the load from precipitation.

You need to know that the weight of the house is determined not by the material from which the foundation is made, but by the load that is created by the entire structure from various materials. This load directly depends on the mechanical features and the amount of material used.

To calculate the pressure on the sole of the base, it is enough to summarize the following indicators:

The first point is calculated by using the formula snow load = roof area (from the project) x set snow mass parameter (different for each region of Russia) x correction factor (which is affected by the angle of inclination of a single or gable roof).

The established snow cover mass parameter is determined according to the zoned map SN and P 2.01.07-85 "Loads and impacts".

The next step is to calculate the potentially valid payload. This category includes household appliances, temporary and permanent residents, furniture and bathroom equipment, communication systems, stoves and fireplaces (if any), additional engineering routes.

There is an established form for calculating this parameter, calculated with a margin: payload parameters = total structure area x 180 kg/m².

In the calculations of the last point (the load of parts of the building), it is important to list all the elements of the building to the maximum, including:

• directly reinforced base itself;
• ground floor of the house;
• the bearing part of the building, window and door openings, stairs, if any;
• floor and ceiling surfaces, basement and attic floors;
• roof covering with all the resulting elements;
• floor insulation, waterproofing, ventilation;
• surface finishing and decorative elements;
• the whole set of fasteners and hardware.

Moreover, to calculate the sum of all the above elements, two methods are used - mathematical and the results of marketing calculation in the building materials market.

Of course, there is also the option of using a combination of both methods.

The plan for the first method is:

1. breaking complex structures into parts in the project, determine the linear dimensions of the elements (length, width, height);
2. multiply the obtained data to measure the volume;
3. with the help of all-Union technological design standards or in the manufacturer's documents, establish the specific gravity of the building material used;
4. having set the parameters of volume and specific gravity, calculate the mass of each of the elements of the building, using the formula: mass of a part of the building \u003d volume of this part x parameter of the specific weight of the material from which it is made;
5. calculate the total mass allowed under the foundation, summing up the results of the parts of the structure.

The method of marketing calculation is guided by data from the Internet, the media and professional reviews. The specified specific gravity is also summed up.

The design and sales departments of enterprises have accurate data, where it is possible, by calling them, to clarify the nomenclature or use the manufacturer's website.

The general parameter of the load on the foundation is determined by the summation of all calculated values ​​- the load of the parts of the structure, useful and snow.

approximate specific pressure = mass of the entire structure / dimensions of the area of ​​\u200b\u200bthe sole of the base.

Having determined these parameters, an approximate calculation of the geometric parameters of the strip foundation is permissible. This process occurs according to a certain algorithm established in the course of research by specialists from the scientific and engineering departments. The scheme for calculating the size of the foundation depends not only on the expected load on it, but also on the construction documented standards for deepening the foundation, which, in turn, are determined by the type and structure of the soil, groundwater level, and freezing depth.

Based on the experience gained, the developer recommends the following parameters:

Soil type	Soil within the estimated freezing depth	The interval from the planned mark to the groundwater level during the freezing period	Foundation installation depth
Non-porous	Coarse clastic, gravel sands, coarse and medium size	Not standardized	Any, regardless of the freezing limit, but not less than 0.5 meters
heaving	The sand is fine and dusty	Exceeds the freezing depth of more than 2 m	Same indicator
	Exceeds the freezing depth by at least 2 m	Not less than ¾ of the calculated freezing level, but not less than 0.7 m.
loam, clay	Less than the estimated freezing depth	Not less than the calculated level of freezing

The width parameter of the strip foundation should not be less than the width of the walls. The depth of the pit, which determines the base height parameter, should be designed for a 10-15 cm sand or gravel cushion. These indicators allow us to determine in further calculations: The minimum width of the base of the foundation is calculated depending on the pressure of the building on the base. This size, in turn, determines the width of the foundation itself, pressing on the soil.

That is why it is so important to make an examination of the soil before starting the design of the structure.

• the amount of concrete per pour;
• the volume of reinforcing elements;
• amount of material per formwork.

Rubble stone:

• basement depth - 2 m:

• basement wall length - up to 3 m: wall thickness - 600, foundation footing width - 800;
• the length of the basement wall is 3-4 m: the thickness of the wall is 750, the width of the base of the foundation is 900.

• basement depth - 2.5m:

• basement wall length - up to 3 m: wall thickness - 600, foundation footing width - 900;
• the length of the basement wall is 3-4 m: the thickness of the wall is 750, the width of the base of the foundation is 1050.

Rubble concrete:

• basement depth - 2 m:

• basement wall length - up to 3 m: wall thickness - 400, foundation footing width - 500;
• basement wall length - 3-4 m: wall thickness - 500, foundation base width - 600.

• basement depth - 2.5m:

• basement wall length up to 3 m: wall thickness - 400, foundation footing width - 600;
• the length of the basement wall is 3-4 m: the thickness of the wall is 500, the width of the base of the foundation is 800.

Clay brick (ordinary):

• basement depth - 2 m:

• basement wall length up to 3 m: wall thickness - 380, foundation footing width - 640;
• the length of the basement wall is 3-4 m: the thickness of the wall is 510, the width of the base of the foundation is 770.

• basement depth - 2.5m:

• basement wall length up to 3 m: wall thickness - 380, foundation footing width - 770;
• the length of the basement wall is 3-4 m: the thickness of the wall is 510, the width of the base of the foundation is 900.

Concrete (monolith):

• basement depth - 2 m:

• basement wall length up to 3 m: wall thickness - 200, foundation footing width - 300;
• the length of the basement wall is 3-4 m: the thickness of the wall is 250, the width of the base of the foundation is 400.

• basement depth - 2.5m;

• basement wall length up to 3 m: wall thickness - 200, foundation footing width - 400;
• the length of the basement wall is 3-4 m: the thickness of the wall is 250, the width of the base of the foundation is 500.

Concrete (blocks):

• basement depth - 2 m:

• basement wall length up to 3 m: wall thickness - 250, foundation footing width - 400;
• basement wall length 3-4 m: wall thickness - 300, width of the base of the foundation - 500.

• basement depth - 2.5m:

• basement wall length up to 3 m: wall thickness - 250, foundation footing width - 500;
• basement wall length 3-4 m: wall thickness - 300, width of the base of the foundation - 600.

Further, it is important to optimally adjust the parameters by adjusting the norms of the specific pressure on the sole soil in accordance with the calculated soil resistance - the ability to withstand a certain load of the entire structure without its settlement.

The calculated soil resistance should be greater than the parameters of the specific load from the building. This item is a significant requirement in the process of designing the foundation of a house, according to which, in order to obtain linear dimensions, it is necessary to simply solve an arithmetic inequality.

When drawing up a drawing, it is important that this difference is 15-20% of the specific load of the structure in favor of the value of the soil's ability to withstand pressure from the building.

In accordance with the types of soil, the following design resistances are displayed:

• Coarse clastic soil, crushed stone, gravel - 500-600 kPa.
• Sand:
  • gravelly and large - 350-450 kPa;
  • medium size - 250-350 kPa;
  • fine and dusty dense - 200-300 kPa;
  • medium density - 100-200 kPa;

• Sandy loam is hard and plastic - 200-300 kPa;
• Loam hard and plastic - 100-300 kPa;
• Clay:
  • solid - 300-600 kPa;
  • plastic - 100-300 kPa;

100 kPa = 1kg/cm²

By correcting the results obtained, we obtain the approximate geometric parameters of the foundation of the structure.

In addition, today's technologies make it possible to significantly simplify calculations using special calculators on developers' websites. By specifying the dimensions of the base and the building material used, you can calculate the total cost of building the foundation.

Installation

To install a strip foundation with your own hands, you will need:

• round and corrugated fittings;
• steel galvanized wire;
• sand;
• edged boards;
• wooden bars;
• a set of nails, self-tapping screws;
• waterproofing material for the foundation and formwork walls;
• concrete (mainly factory-made) and related materials.

markup

Having planned to build a structure on the site, it is worthwhile to first examine the place where the construction is planned.

There are certain rules for choosing a place for the foundation:

• Immediately after the snow melts, it is important to pay attention to the presence of cracks (indicate the heterogeneity of the soil - freezing will lead to rise) or dips (indicate the presence of water veins).
• The presence of other buildings on the site makes it possible to assess the quality of the soil. You can make sure that the soil is homogeneous by digging a trench at the corner of the house. The imperfection of the soil indicates the unfavorability of the place for construction. And if cracks are noticed on the foundation, then it is better to postpone construction.
• As mentioned above, conduct a hydrogeological assessment of the soil.

Having determined that the selected site complies with all standards, you should proceed to marking the site. First of all, it needs to be leveled and rid of weeds and debris.

For marking work you will need:

• marking cord or fishing line;
• roulette;
• wooden pegs;
• level;
• pencil and paper;
• hammer.

The first marking line is decisive - it is from it that all other borders will be measured. It is important to establish an object that will serve as a guide. It can be another structure, a road or a fence.

The first peg represents the right corner of the building. The second is installed at a distance equal to the length or width of the structure. Between themselves, the pegs are connected with a special marking cord or tape. According to the same scheme, the rest are clogged.

Having defined the external boundaries, you can move on to the internal ones. For this, temporary pegs are used, which are installed at a distance of the width of the strip foundation on both sides of the corner markings. Opposite marks are also interconnected by a cord.

A similar method establishes the lines of load-bearing walls and partitions. Suggested windows and doors are marked with peg.

Excavation

When the marking stage is completed, the cords are temporarily removed and trenches are dug under the outer load-bearing walls of the structure along the entire perimeter of the marking according to the marks on the ground. The internal space breaks out only if it is planned to equip a basement or basement.

The established requirements for earthworks are specified in SNiP 3.02.01-87 on earthworks, foundations and foundations.

The depth of the trenches must be greater than the estimated depth of the foundation. Do not forget about the obligatory preparatory layer of concrete or bulk material. If the dug excavation significantly exceeds the depth, taking into account the margin, this volume can be replenished with the same soil or gravel, sand. However, if the search exceeds more than 50 cm, you should contact the designers.

It is important to take into account the safety of workers - the excessive depth of the pit requires strengthening the walls of the trench.

In accordance with regulatory documents, fastenings are not required if the depth is:

• for bulk, sandy and coarse soils - 1 m;
• for sandy loam - 1.25 m;
• for loam and clay - 1.5 m.

Typically, for the construction of a small building, the average trench depth is 400 mm.

The width of the excavation must correspond to the plan, which already takes into account the thickness of the formwork, the parameters of the underlying preparation, the protrusion of which beyond the side boundaries of the base is allowed at least 100 mm.

The usual parameters are the width of the trench, equal to the width of the tape plus 600-800 mm.

Important! In order for the bottom of the pit to be a perfectly flat surface, a water level should be used.

formwork

This element is a form for the intended foundation. The formwork material is most often wood because of its affordability in terms of cost and ease of implementation. Removable or non-removable metal formwork is also actively used.

In addition, depending on the material, the following types differ:

• aluminum;
• steel;
• plastic;
• combined.

Classifying the formwork depending on the type of construction, there are:

• large-panel;
• small-panel;
• volume-adjustable;
• block;
• sliding;
• horizontally movable;
• hoist.

Grouping varieties of formwork by thermal conductivity, they differ:

• insulated;
• uninsulated.

The formwork structure is:

• deck with shields;
• fasteners (screws, corners, nails);
• props, racks and frames for support.

For installation you will need the following materials:

• lighthouse board;
• board for shields;
• fight from longitudinal boards;
• tension hook;
• spring bracket;
• ladder;
• shovel;
• site for concreting.

The amount of materials listed depends on the parameters of the strip foundation.

The installation itself provides for strict adherence to the established requirements:

1. the installation of the formwork is preceded by a thorough cleaning of the site from debris, stumps, plant roots, and the elimination of any unevenness;
2. the side of the formwork in contact with the concrete is perfectly cleaned and levelled;
3. fastening takes place in such a way as to prevent shrinkage during concreting - such deformation can adversely affect the entire structure as a whole;
4. formwork panels are connected to each other as tightly as possible;
5. all formwork fastenings are carefully checked - the compliance of the actual dimensions with the design ones is checked with a barometer, a level is used to control horizontality, and a plumb line is used to control verticality;
6. if the type of formwork allows it to be removed, then for reuse it is important to clean the fasteners and shields from debris and traces of concrete.

Step-by-step instructions for arranging continuous formwork for a strip base:

1. Lighthouse boards are installed to level the surface.
2. With a gap of 4 m, formwork panels are fastened on both sides, which are fastened with braces for rigidity and spacers that provide a fixed thickness of the base tape.
3. The foundation will turn out to be even only if the number of shields between the lighthouse boards is the same.
4. The bouts, which are longitudinal boards, are nailed to the sides of the shields for horizontal alignment and reliability.
5. The scrums are stabilized by slanted struts that allow the shields to be vertically aligned.
6. Shields are fixed with tension hooks or springy brackets.
7. Solid formwork is usually obtained with a height of more than a meter, which requires the installation of stairs and platforms for concreting.
8. If necessary, the disassembly of the structure occurs in the reverse order.

Installation of a stepped structure goes through several stages. Each next tier of formwork is preceded by another similar tier:

1. first stage formwork;
2. concreting;
3. second stage formwork;
4. concreting;
5. according to the same scheme, the required parameters are installed.

The installation of stepped formwork is also possible at once, similar to the assembly mechanism of a solid structure. In this case, it is important to adhere to the horizontal and vertical arrangement of the parts.

During the formwork phase, the planning of the ventilation openings is an essential issue. Air vents should be located at least 20 cm above the ground. However, it is worth considering seasonal flooding and varying the location depending on this factor.

The best material for the ventilation hole is a round plastic or asbestos-cement pipe with a diameter of 110-130 mm. Wooden beams tend to stick to the concrete base, which makes it difficult to remove them afterwards.

The diameter of the vents is determined depending on the size of the building and can reach from 100 to 150 cm. These ventilation holes are located in the walls strictly parallel to each other at a distance of 2.5-3 m.

With all the need for air, there are cases when the presence of holes is not required without fail:

• the room already has ventilation vents in the floor of the building;
• between the foundation pillars, a material with sufficient vapor permeability is used;
• a powerful and stable ventilation system is available;
• vapor-tight material covers the sand or soil compacted in the basement.

The correct choice of reinforcement is facilitated by an understanding of the variety of material classifications.

Depending on the manufacturing technology, fittings may vary:

• wire or cold rolled;
• rod or hot rolled.

Depending on the type of surface, the rods:

• with a periodic profile (corrugations), providing maximum connection with concrete;
• smooth.

By purpose:

• rods used in conventional reinforced concrete structures;
• prestressing rods.

Most often, reinforcement according to GOST 5781 is used for strip foundations - a hot-rolled element applicable for conventional and prestressing reinforced structures.

In addition, in accordance with the grades of steel, and hence the physical and mechanical properties, the bars of the reinforcement differ from A-I to A-VI. For the manufacture of elements of the initial class, low-carbon steel is used, in high classes - properties close to alloy steel.

In the planned areas with the highest load, mounting fittings are installed in the direction of the expected additional pressure. Such places are the corners of the structure, areas with the highest walls, the base under the balcony or terrace.

When installing a reinforcement structure, intersections, junctions and corners are formed. Such an incompletely mounted assembly can lead to a crack or subsidence of the foundation.

That is why, for reliability, we use:

• paws - L-shaped limb (internal and external), attached to the outer working part of the reinforcement frame;
• transverse clamp;
• amplification.

It is important to remember that each class of reinforcement has its own specific parameters for the allowable bending angle and curvature.

In a solid frame, the parts are connected in two ways:

• Welding, which involves special equipment, the availability of electricity and a specialist who will do it all.
• Knitting, possible with a simple screw hook, mounting wire (30 cm per intersection). It is considered the most reliable method, albeit time-consuming. Its convenience lies in the fact that, if necessary (bending load), the rod can be moved slightly, thereby relieving pressure on the concrete layer and protecting it from damage.

You can make a hook if you take a thick and durable metal rod. A handle is made from one end for more convenient use, the other is bent in the form of a hook. Having folded the mounting wire in half, a loop is formed at one end. After that, it should wrap around the reinforced knot, winding the hook into the loop so that it rests on one of the “tails”, and wrap the second “tail” with mounting wire, carefully tightening it around the reinforcing bar.

All metal parts are carefully protected with a layer of concrete (minimum 10 mm) to prevent acid corrosion.

Calculations of the amount of reinforcement that will be needed for the construction of a strip foundation require the determination of the following parameters:

• dimensions of the total length of the foundation tape (external and, if there are internal lintels);
• the number of elements for longitudinal reinforcement (you can use the calculator on the manufacturers website);
• the number of places of reinforcement (the number of corners and junction nodes of the foundation tapes);
• overlap parameters of reinforcing elements.

The norms of SNiP indicate the parameters of the total cross-sectional area of ​​​​the elements of longitudinal reinforcement, which will be at least 0.1% of the cross-sectional area.

fill

It is recommended to pour a monolithic foundation with concrete in layers of 20 cm thick, after which the tier is compacted with a concrete vibrator to avoid voids. If concrete is poured in winter, which is undesirable, then it is necessary to insulate it with the help of improvised materials. In the dry season, it is recommended to use water to create the effect of dampness, otherwise it may affect its strength.

Concrete consistency must be the same for each layer, and pouring must be done on the same day, since a low level of adhesion (a way of bonding surfaces of dissimilar solid or liquid consistency) can lead to the formation of cracks. In the event that it is impossible to pour in one day, it is important to at least pour plenty of water on the surface of the concrete and, in order to preserve dampness, cover it with plastic wrap on top.

The concrete must set. After 10 days, the walls of the base are treated from the outside with bituminous mastic and a waterproofing material (most often roofing material) is glued to protect against water penetration.

The next stage is backfilling the cavities of the strip foundation with sand, which is also laid in layers, while carefully tamping each tier. Before laying the next layer, the sand is poured with water.

A properly installed strip foundation is the key to many years of operation of the building.

It is important to clearly maintain a constant depth of laying the foundation over the entire area of ​​​​the construction site, since minor deviations lead to a difference in soil density, moisture saturation, which compromises the reliability and durability of the foundation.

Among the common omissions in the construction of the foundation of a building are mainly inexperience, inattention and frivolity in installation, as well as:

• insufficiently thorough study of hydrogeological properties and soil level;
• the use of cheap and low-quality building materials;
• the unprofessionalism of the builders is demonstrated by damage to the waterproofing layer, crooked markings, an unevenly laid pillow, and a violation of the angle;
• non-compliance with the terms of formwork removal, drying of the concrete layer and other time steps.

In order to avoid such errors, it is fundamentally important to contact only specialists involved in the installation of the foundations of structures, and try to follow the stages of construction. If, nevertheless, the installation of the base is planned independently, it would be preferable to consult with specialists in this field before starting work.

An important topic in the construction of the foundation is the question of the recommended time of year for such work. As mentioned above, winter and late autumn are considered undesirable times, since frozen and soggy soil leads to inconvenience, slowdown in construction work, and, importantly, shrinkage of the foundation and the appearance of cracks in the finished structure. Professionals indicate that the optimal time for construction is warm and dry periods (depending on the region, these intervals fall on different months).

Sometimes, after the construction of the foundation and the operation of the building, the thought comes of expanding the living space of the house. This issue requires a close analysis of the state of the foundation. With insufficient strength, construction can lead to the fact that the foundation will burst, sag, or cracks will appear on the walls. Such an outcome can lead to the complete destruction of the building.

However, if the condition of the foundation does not allow you to complete the premises, do not be upset. In this case, there are some tricks in the form of strengthening the foundation of the structure.

This process can be carried out in several ways:

• with minor damage to the foundation, it is sufficient to restore the hydro- and heat-insulating layer;
• more costly is the expansion of the foundation;
• often use the method of replacing the soil under the base of the house;
• using various types of piles;
• by creating a reinforced concrete jacket that prevents collapse when cracks appear on the walls;
• reinforcement with monolithic clips strengthens the base over the entire thickness. This method involves the use of a double-sided reinforced concrete cage or tubes that inject a solution that freely fills all the voids in the masonry.

The most important thing when building any type of foundation is to correctly determine the required type, conduct a thorough calculation of all parameters, perform all actions step by step exactly according to the instructions, follow the rules and advice of experts and, of course, enlist the support of assistants.

Strip foundation technology - in the next video.