• Date: 28-09-2014
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The so-called backfilling of the foundation is the process of laying soil in a trench or pit, which was previously removed from there to fill the foundation and erect the structure.

Backfilling of the soil must be carried out after the concrete of the foundation and the basement has completely solidified - when both elements of this structure can bear any load without prejudice to themselves.

This process, as a rule, occurs after the construction of the foundation and basement, but not immediately after that. Backfilling is carried out not earlier than the moment when both elements of this structure can carry any loads without damage to themselves, that is, after the concrete has completely solidified. Given sunny weather and high temperatures, this takes at least 2 weeks, and most often 3-5 weeks.

Often this rule is neglected, since the lateral pressure is almost imperceptible, but it is nevertheless very dangerous for the foundation. Therefore, backfilling is carried out only after the concrete has completely solidified and the basement has been erected.

Backfilling should never be done with sand or any other material inferior in quality to the original soil.

If the backfill is still made with sand, its compaction coefficient should tend to the compaction coefficient of the soil in its natural state.

When such backfilling of the foundation is carried out, it is necessary to establish the density of the soil using experimental data. The best density and moisture content for compaction is approximately 0.95. To determine the density and humidity in each specific area, you can refer to the data of geodetic services that were carried out at the work site earlier.

The compaction process is carried out if the natural moisture content of the soil is optimal. If this is not true, any soil must first be moistened and only then compacted. To determine the optimal soil moisture, the following indicators are taken:

• humidity for silty sands, light sandy sandy loams of large fraction is in the range from 8 to 12%, this coefficient is optimal, and waterlogging is 1.35%;
• the humidity of silty and light sandy loams is in the range from 9 to 15%, this range is considered optimal, while waterlogging for this type of soil is 1.25%;
• for heavy silty soils, light loams and light silty soils, the optimal humidity is in the range from 12 to 17%, and the moisture coefficient is 1.15%;
• the moisture content of heavy and heavy silty soils will be optimal in the range of 16-23%, the waterlogging coefficient for this type of soil is 1.05%.

Only in the laboratory, with the help of analyzes and experiments, it is possible to establish the exact moisture content of the soil. After receiving the result, it is compared with the norms and, if it is insufficient, the soil is wetted, and if it is excessive, then work is carried out to drain it. It should be borne in mind that moisturizing should not be done with ordinary water; clay or cement milk is usually used for such purposes.

This milk is prepared as follows: a small amount of cement is poured into the water or a few handfuls of clay are placed, these ingredients are stirred until a homogeneous mass. The resulting solution, in terms of viscosity and fluidity, should not differ from ordinary, without impurities, water, but turns cloudy white (this influenced the name of the liquid).

Backfilling the foundation: general principles

Backfilling is carried out no earlier than the soil moisture reaches the optimum value, and only with soil that is better and denser than the one that was excavated.

The process in which backfilling of the sinuses, plinth and foundation takes place is divided into several stages. Each of the stages consists of backfilling the soil with a layer of a maximum of 30 cm, and then compacting it. The number of steps required to complete the backfill depends on the depth of the foundation.

Backfilling is a time-consuming and complex process, in which attention should be paid to each stage, but in particular to the quality of the soil and the presence of foreign objects in it. There should not be such objects of any size in the soil, objects of an organic structure are especially dangerous for the soil, which, having rotted soon, will leave voids behind them and, as a result, will lead to a pressure difference in different parts of the foundation. Such voids and the action produced by them lead to the rapid destruction and rendering of the foundation unusable.

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Consequences of incorrect technologies and precautions

Backfilling, in which the rules are not observed or not all are observed, will cause the blind area, which was created to divert natural precipitation and groundwater from the basement, to settle in the very near future. In order to insure and protect yourself, experienced builders are recommended to initially lay the blind area under a slight slope, the value of which should be 3-4%.

This process is carried out in this way: backfilling of insufficient density or poor-quality soil sags, dragging the blind area with it. The greatest level of subsidence is usually noticeable near the wall itself, and the initial level of the slope changes, and the water flows directly along the walls. During the rainy and snowmelt season, this happens more than once or twice, and the backfill will each time be compacted to the desired level and at the same time sag. The blind area, constantly changing the angle of inclination from this subsidence, will cease to protect the walls and the basement completely. When frost sets in, the foundation, which has absorbed a lot of moisture, will freeze and may crack, which can lead to the complete destruction of the building.

The destruction and crushing of the foundation occurs, as a rule, for two reasons:

1. If a reinforced concrete version of the foundation was used, then the reinforcement in it will rust from moisture, the metal structure inside the concrete will thus expand. This will entail the crumbling of concrete and the destruction of its structure.
2. When using a brick, the water that got inside the sinuses freezes with the advent of frost and destroys the masonry along with the concrete composition between the bricks.

Wrong technology also destroys waterproofing, which is a necessary component of a good foundation.

In order to avoid all these problems with the greatest possible probability, you should try not to overload the backfilled soil. To do this, special weight-bearing structures are placed under the partitions extending from the first floor, which, as a result, do not transfer it to the backfill.

Drainage systems must also be designed and located correctly. Backfill, which has not yet gained the required density, can also be washed away by groundwater. They wash out many small particles from the soil, and this reduces the bearing capacity. To prevent the very possibility of such a nuisance, a buffer layer is arranged.

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Buffer layer: device

It is arranged between the foundation and the base of the building from high-quality gravel or crushed stone. The thickness should be at least 10-20 cm. The role of the buffer layer is to divert groundwater from the building.

Although gravel is not an unsuitable material to provide a buffer layer, crushed stone is still preferred. The point is the many sinuses that even the highest quality gravel has - moisture rises through them by capillary action and, although in small quantities, can still penetrate to the foundation. There are no sinuses in rubble, and therefore there is no such effect, which makes it a more suitable material.

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Backfill for the sinuses of the pit

The condition of the base before starting work is necessarily controlled. The condition according to which the soil should not contain foreign objects is also true for the sinuses of the pit, and must be strictly observed. There should not be any foreign objects on its bottom, especially if their diameter exceeds 10 cm. The backfill soil should in no case contain organic objects, the proportion of which in the backfill soil can be no more than 5%.

Deviation from the optimal soil moisture during work can be ≈10% for bound soils and no more than 20% for unbound ones. If this condition is met in the process of work, special attention should be paid to soils inside the sinuses, existing narrow and inconvenient places, corners for bound soils, and in unbound soils, the backfilled soil is of greater importance.

If pipes and other communications are laid in the filling cavity, soft soil is first filled to the level of the pipes, if they are located no higher than 30 cm above the bottom. Otherwise, the actions do not contradict the original instructions: first, a 30 cm layer is filled, which is tightly rammed with by carefully filling all the sinuses, and then, without tamping, soft soil is poured onto the pipes. Following this, another 15-20 cm of soil is poured and carefully compacted.

In cases where compaction of the soil is not carried out for various reasons, it is poured into a mound, the size of which is different each time and depends on the natural density of the soil. The hillock is needed so that in the future, during the natural settlement of the poured soil, pits do not form.

If the soil was compacted during backfilling, the density achieved must be checked after a while. The quality is checked in several areas, after which a common arithmetic is found and, based on this, a conclusion is made about the quality of the backfill as a whole. The best option is compaction using a special machine, while each trace should overlap the previous one by 10-20 cm. If this condition is met, there will be much less uncompacted areas or not at all.

An integral part of a private house, as well as any building structure, is a properly executed strip foundation. Without it, it is impossible to build a house; walls, ceilings and roofs rely on it. The most common foundation option for the construction of any private house is a tape monolithic reinforced concrete foundation. An important point in the construction of the foundation is the backfilling of the foundation of the house.

Foundation device technology

All modern technologies provide for the production of work on the development of a pit before laying the foundation. An exception may be when performing a pile foundation, with a grillage. The foundation pit for the future house is carried out on the basis of construction drawings, which indicate the depth, dimensions in the plan and the required angle of slope along the edge of the pit. Technologically, for the construction of the foundation, after the development of the pit, the following work is performed:

• leveling the base under the foundation, sand filling device 100 mm;
• installation of formwork from the inside and outside of the strip foundation to the height and width according to the design documentation;
• installation of the reinforcing cage;
• pouring the foundation with concrete.

After completing all these stages and holding for 5–7 days, the formwork is dismantled. The next thing to do is to waterproof the foundation surface. Waterproofing is carried out on completely dry concrete not earlier than 25–28 days after concreting at positive temperatures and dry weather.

Backfilling of the foundation, its role and necessity.

After all the work on the installation of the strip foundation and its waterproofing, the resulting voids from the outer edge of the foundation to the border of the pit should be covered with soil. Since the foundation pit is dug out with an angle of repose or a soil collapse angle other than 90 degrees, after the foundation has been erected, its waterproofing and insulation, all voids must be filled.

The inside of the pit, if the house does not provide for a basement, is also covered with soil with layer-by-layer compaction. However, the proportion of houses without a basement is a small part, so backfilling in this case is carried out only on the outside of the foundation. It is clear that without excavation of soil from the pit it is impossible to mount the foundation, and after its construction, all voids are filled with soil with mandatory layer-by-layer compaction. After that, to prevent the entry of storm water under the base of the foundation around the perimeter of the house, a concrete pavement is arranged. Therefore, the backfilling of the foundation of the house is also an important, integral part in the construction process.

Materials used for filling the foundation

An important issue in the production of work on backfilling the foundation is: what kind of soil to fill the sinuses around the foundation outside and inside the building? At the moment, several options are being considered for backfilling:

• soil excavated when digging a pit or trench for a foundation;
• clay;
• sand;
• sandy loam or loam;
• slag or rubble.

The answers to the question - what kind of soil to fill the voids around the foundation from the inside and outside of the building, will be different. To fill the sinuses outside the foundation, it is best to use sand, previously moistened with water. The next option would be backfilling with excavated soil, if it is not clay. It is categorically unacceptable to fill the sinuses outside the foundation with clay, because it absorbs moisture and keeps it in its structure like a sponge, and under different temperature conditions, the clay changes its volume. When wet, it swells and increases in volume; when it dries and loses water, it reduces its volume and at the same time cracks. Therefore, the best option would be to fill the voids around the foundation outside the building with sand. Firstly, it is easier to compact, it does not absorb water, but simply passes through itself. The volume of sand does not change with time, in this respect it is more stable. The blind area, made on a sandy backfill, will not deform over time. An important requirement is that all sinuses must be cleaned of debris before backfilling, especially for organic matter, boards - everything that can rot over time, forming additional voids.

Filling the sinuses around the foundation from the inside of the building can be done with both clay and soil excavated when digging a pit, or any other material. This, of course, applies to those cases where the basement is not provided for in the house. All backfilled soil, both outside and inside the building, must be compacted - this applies to the outer part to a greater extent.

Backfill technology outside the foundation

It is worth saying that when digging a foundation pit or trench under the foundation, it is necessary to achieve the smallest possible size of the sinuses. Optimally in the lower part of the foundation - 300-400 mm to the slope of the pit, in the upper part - 500-800 mm - this is quite enough to install and remove formwork panels. After concreting, you need to wait 5-7 days before dismantling the formwork. The optimal exposure time is 28 days, when the concrete has gained sufficient strength.

After that, it is necessary to clean the entire cavity around the foundation from debris. Before laying, the sand is moistened with water from a hose outside the pit at the place of its unloading. Now sand is covered in layers of 200-300 mm and tamped with manual rammers or a mechanical vibrating plate, if the width of the trench and the size of the vibrating plate allow. Thus, layer by layer, the entire trench is covered up to the very surface. Given that the process of dumping and compaction is not difficult, you can do it yourself. After thorough compaction of the outer surface of the sand, a concrete pavement with a thickness of 50-100 mm is started with a slope from the building to the outside. With proper sand laying and compaction, you can be sure that the blind area will not sag over time. Instead of sand, you can use sandy loam or loam.

If there is a high level of groundwater in the area and, in addition, a basement is provided in the house, it is necessary to carry out a drainage system at the level of laying the foundation before backfilling. Usually, all this is included in the construction project for the building, unless, of course, it is executed correctly and all geological nuances are taken into account. In this case, after laying the drainage system from perforated pipes, crushed stone and geotextiles, sand is filled in the same way as in the first case. When entering the house through the foundation of various engineering pipe communications, it is necessary to equip this passage with high quality by installing concrete trays and sprinkling soft soil on all sides.

Backfill technology inside the foundation

When performing work on backfilling from the inside of the foundation, you can not be afraid of temperature changes and soil soaking. Therefore, any soil is suitable for backfilling inside the building - both clay and soil left after the development of the pit. However, it also needs to be compacted in layers, better, of course, with mechanical rammers. At the same time, it is also necessary to remove all organic debris in the form of boards, branches, logs - everything that can rot over time, leaving voids. When constructing the floors of the first floor, layers of slag or sand can be made before laying the concrete screed.

Analysis of possible errors during dumping

Foundation backfilling is an important construction process and must be given due attention. If the backfilling is performed poorly or soil is used that changes its characteristics under the influence of the environment, over time, deformations can occur not only in the blind area, but also in the foundation itself, which can lead to a redistribution of stresses and cracks in the foundation and walls.

Consider the option when filling voids around the foundation outside the building with clay. First, it is impossible to compact it like sand. Secondly, the clay must be kneaded before it is backfilled, and it is almost impossible to do it correctly by hand. However, the most important thing is that it changes its volume during soaking and drying. If a concrete blind area is made on top of this clay backfill, and a storm tray is made along the edge of the blind area, then over time this entire structure will deform. There will be cracks and voids. Cracks may form between the concrete pavement and the basement of the building, and even a counterslope may appear. In this case, cracks will appear between the storm trays and the blind area. The presence of water in the clay during winter can lead to additional swelling. Therefore, it is better to use sand, as described above. It is also desirable, if there is a basement, to perform a drainage system to drain water from the bottom of the foundation. The drainage system will be very useful if the backfilling was done with sand, and the native soil in which the pit was dug is loam or clay. In this case, the drainage will divert all excess rain and groundwater into drainage wells.

Little tricks

It is quite difficult to deal with swelling of the soil. This is especially important in the area where backfilling adjoins the foundation outside the building. No matter how the soil is backfilled from the outside, there is still a risk of swelling of the soil in the winter. And, as you know, this negatively affects the integrity of the concrete blind area, which protects the foundation from soaking. As a simple option to prevent heaving of soil in the backfill area from the outside, the following method can be proposed. After mounting foam sheets on the outer surface of the strip foundation as thermal insulation, two layers of thick polyethylene film are attached on top of them and sheets of ordinary polystyrene are installed without fastening closely - from the beginning of the insulation to the border of the concrete blind area. Then backfilling with compaction is carried out. In winter, when the soil is heaving, polystyrene sheets will move along with the soil along the surface of the insulation, without tearing it off the foundation, and in spring everything will return in the opposite direction. Given the insignificance of these temperature movements, this will avoid the destruction of the blind area. It is better to reinforce the blind area during concreting with a mesh - this will enable the concrete blind area to withstand deformations in different directions.

Conclusion

The backfilling of foundations, just like any work in the construction of a residential building, is a very responsible process. Failure to comply with the elementary rules described above can lead to very tangible troubles in the future. In conclusion, it is worth noting the basic rules for backfilling: it is necessary to strictly observe the time for concrete hardening until it is completely dry, some time must also pass after the formwork is removed, it is necessary to apply waterproofing only on an absolutely dry concrete surface, before filling, carefully remove all organic debris from sinuses, if there is even the slightest suspicion of a high level of groundwater, it is necessary to take all measures for drainage, after the thermal insulation device, they start backfilling, if it is sand, it is pre-moistened with water, then the sand is laid in layers of 300 mm with compaction. After backfilling, a blind area is performed, preferably with reinforcement. When following these simple recommendations, you can be sure that the house, at least the foundation, will last a long time and will not cause any trouble to the owner.

Many developers who are faced with the construction of a house for the first time mistakenly believe that the construction of the foundation, walls and roof can be considered completed. This is far from true. After all, it is imperative to take care that during the operation of the dwelling the stove on which the entire building is located does not get damp. In addition, in areas with elevated groundwater levels, the building frame may sag or, conversely, it will bulge. It may also happen that the foundation begins to move, supported by soil layers. To avoid all these troubles, you need a properly executed backfill of the foundation.
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Essence of the question

The laying of any foundation is carried out with the obligatory execution of earthworks. This includes the formation of a pit (under the slab) or a trench (under the tape). Then formwork, reinforcement, concreting, construction of the basement are carried out. An unfilled space remains near the finished foundation - the so-called "bosoms". It must be covered with soil. This is the backfilling process in a nutshell. Before you produce it, it is necessary that events occur, the frequency and technology of which must not be violated:

• foundation pouring;
• acquisition by concrete of the required compressive strength;
• removal of the formwork frame;
• foundation waterproofing;
• laying of communications, testing of pipelines.

That is, all the processes of forming the base must be completed, ready to accept and bear the load of the structures being erected. If you do not wait for the concrete to harden throughout its entire mass, the soil poured into the sinuses can create such pressure on the foundation, due to which it will begin to collapse.

Attention! Complete hardening of concrete throughout the thickness under favorable conditions (warm sunny weather) occurs within 15 days. From the outside, any kind of foundation is covered in all cases. But from the inside, when erecting a reinforced concrete tape, it all depends on the basement. If it is planned to be built, then the back filling of the trench is not done inside the closed perimeter.

It is necessary to fill up the soil and carry out its layer-by-layer compaction with the utmost care so as not to damage the integrity of the waterproofing layer and basement walls. All work is regulated by SNiP, including 3.02.01-87 "Earth structures, foundations and foundations". The sinuses are filled to a level at which reliable drainage of surface runoff is ensured.

During return filling, it is allowed not to compact the soil, but to make a mandatory backfill along the entire length of the trench of the roller. Its dimensions should provide for the subsequent shrinkage of the soil layers. If the sinuses between the foundation and the walls of the pit are narrow, then it is better to fill them with contents with low shrinkage: crushed stone, gravel-sand mixture.

How to fall asleep: the question is not simple

In most cases, for these purposes, the same soil is used that was taken to form the foundation. But there are universal rocks: clay and sand. There are two main components: they are used for return filling. Each of the soils is used in specific cases, having its positive and negative sides.

• Backfilling the foundation with clay acts as a barrier (clay castle) for water to prevent their penetration into the foundation area. In this capacity, you can combine: pour not pure clay, but loam or another combination of soils that has a density higher than the main soil near the foundation. As an example - a log house erected on loamy soils. In this case, the sinuses and the interior space are covered with the same loam or clay extracted during the construction of the foundation. If the house is built on clay, then the backfill is made of clay. Less dense sandy loam as the main soil should be sprinkled with loam or clay.
• On heaving soils that freeze to a considerable depth, backfilling the foundation with crushed stone mixed with sand is best suited. The crushed stone-sand mixture does not retain water, does not allow it to freeze between fractional particles, which eliminates the increase in volume (heaving) of the backfill. Such a composition will not put pressure on the foundation in cold weather, creating an additional load from the forces of pushing it out. But there is also the other side of the coin. The same loose sand, passing moisture through itself, creates its accumulation at the base of the foundation. With poorly executed or poor-quality insulation, a threat to the base is created, despite even the blind area equipped around it. It is practically impossible to make it absolutely impenetrable. Additional drainage is needed to drain storm and groundwater.
• It is not recommended to use pure sand. If a "sand" decision is nevertheless made, then the degree of density of the filler should be the same or higher than the degree of compaction of the main soil in its normal state. Compaction is carried out at optimal density and moisture with a factor of 0.95. You can find out the degree of soil compaction in a particular area from geological data held in special institutions.

Attention! What is not suitable in all cases as a backfill soil is the top fertile soil layer and pure black soil.

Influence of backfill density on the state of the foundation

It depends on how to backfill the foundation, as well as how skillfully it will be done, whether the blind area will sag or not. The composition of the filling should not contain large pointed foreign objects that can break the waterproofing layer. There should not be podzolic, calcareous inclusions, organic fractions, which, decomposing and rotting, leave behind cavities - “weak” places in the integrity of the backfill. If the required density was not reached during backfilling, then the soil begins to sag, and with it the blind area, especially near the wall itself. The slope changes, and water penetrates the surface of the wall. Over time, the process will worsen, eventually the blind area will cease to fulfill its function: to protect the walls, basement and foundation from moisture. This is fraught with the destruction of the foundation and deformation of the structures of the house.

Some accents on backfilling the foundation

• When performing work, the norms and technology of work must be observed. You need to follow the sequence of steps.
• Backfilling is carried out after waterproofing works or after installation of floor slabs.
• The type of filling is influenced by the type of recycled soil and the equipment used to compact it. All processes are carried out manually, starting from areas near the walls of the fall, foundation, entry points for communication wiring, gradually moving towards the edge of the slope. At the same time, soil compaction above the pipes is carried out with extreme caution.
• Whatever material is used for backfilling, it must be compacted to avoid shrinkage of the soil. For this, a vibrating plate is used. In order not to damage the waterproofing layer of the basement walls, they are covered with asbestos-cement slabs.
• The process involves layer-by-layer tamping of each backfilled layer with a thickness of 0.3 m. At the same time, the thickness of the crumbled soil should not exceed 0.25 m.
• The upper soil layer is compacted to the level of the blind area.
• When laying communications in pipes, a soft “pillow” (0.3 m) is poured under them, it is well compacted. The pipes are being laid. Soft soil is poured on them, but without tamping. The next layer of soil is laid on top, but with subsequent compaction.

Before performing work, you need to study the requirements of building codes and strictly comply with them. Ultimately, this guarantees not only the integrity of the foundation, but the entire structure as a whole.

Usually a non-specialist, reading the instructions for building a foundation, believes that its manufacture is completed as soon as the concrete has hardened. In reality, this is not entirely true. In order for the foundation to be as reliable as possible, it is necessary to correctly fill the voids in the trench or pit after removing the formwork.

This stage of work is called backfilling the foundation. If it is not carried out, the base will not be sufficiently stable, and will also become more exposed to negative atmospheric factors.

Work should be done as competently as possible, and therefore it is important to know the intricacies of this matter. In the event that all construction is carried out by a company, it must certainly provide the customer with an act for backfilling the foundation. If suddenly the question arises whether it is necessary to backfill the foundation, there can be only one answer - of course it is necessary.

backfill materials

The first thing that is required to start work is to choose the right soil for backfilling the foundation. Unsuitable material can be a good reservoir of water, which, collecting under the base, will reduce its stability.

First of all, you should find out which soil is unsuitable for backfilling. It is strictly not allowed to use for this purpose:

• . peat;
• . crushed stone;
• . Sand and gravel;
• . chernozem;
• . heaving soil.

For backfilling the foundation, one of three types of material must be used:

• . sand;
• . clay;
• . high-quality non-heaving soil.

In this case, no further difficulties arise during the operation of the foundation. Naturally, with the proper conduct of all work.

SNiP backfilling of the foundation provides for the use of sand. This material is often used for backfilling. It is only important to observe the technology of this process.

First of all, the sand needs to be sieved in order to get rid of excessively large particles and debris. When this part of the work is completed, they move on to the backfill itself. It is produced in layers that are well compacted. When using this type of soil for backfilling the sinuses of the foundation, care must be taken to ensure that the thickness of one layer does not exceed thirty centimeters. Otherwise, it will not be possible to compact the sand qualitatively.

Tampering is given special attention. If it turns out to be insufficient, sedimentation may occur over time, after which the distribution of the weight of the base will be disturbed and, as a result, its damage will occur.

Backfilling the base with sand is convenient in cases where, due to the high level of groundwater, the base needs additional drainage. Carrying out such work is not difficult, and you can do it yourself.

Backfilling the foundation with clay is carried out according to certain rules, the violation of which will lead to an error. Like sand, clay should be clean and free of large particles. The soil containing construction debris cannot be compacted evenly, and this will lead to subsidence of its various sections.

In addition, the presence of other soil impurities in the clay is also unacceptable. After high-quality compaction, clay serves as additional waterproofing (but only if the soil moisture is not excessive, but is within normal limits).

They are also covered with clay in layers. If you use a special technique, then it is quite possible to pour a layer half a meter thick. A more powerful rammer will not process properly. When compacting the soil manually, its layer should not exceed thirty centimeters.

For high-quality backfilling of the foundation sinuses, it is important to carry out manual tamping in a certain sequence: it starts from the base wall, moving towards the edge of the pit or trench. Some difficulty is caused by the entry points to the construction of communications, since it is required to carry out ramming there especially carefully.

Backfilling the foundation of the house using clay, performed in accordance with all the rules, will ensure the reliability of the foundation for a long time.

Backfilling with soil

Backfilling a strip or monolithic foundation with soil is the most budgetary, since if the soil at the construction site is not heaving, it can be used for backfilling, extracted during digging a pit or trenches. It is very important that before starting work, the soil is freed from organic components. If this is not done, then after their decomposition, this soil (even well-compacted) will give a draft, which will adversely affect the reliability of the foundation.

Backfilling with soil is carried out in the same way as with sand and clay - in layers of thirty centimeters with their tamping before the next one. As a result, the density is maximum.

When backfilling the sinuses of the foundation, it is necessary to focus on SNiP, since in this case, without unnecessary difficulties, you can meet all the standards and avoid mistakes with materials. The better the work is done, the longer the foundation will last.

Everyone is certainly worried about the price of construction work, and backfilling is no exception. Here the cost depends on whether it is necessary to buy soil or not, and also work is carried out independently or with the involvement of specialists. Usually, craftsmen are not attracted only for backfilling, since this work is not difficult, and if a person has built the foundation himself, he will be able to fill it up according to all the standards.

Most often, such work is carried out by professionals when they build a completely house or at least a foundation. In this case, in the act they provide, the work on backfilling should be highlighted and described in detail.

To lay the foundation, earthworks are carried out: they dig a foundation pit for a slab foundation or a trench for a strip one; then formwork, reinforcing cage are installed and concrete is poured. At the same time, free space remains around the foundation - sinuses, which then need to be backfilled with soil. This is called backfilling.

The backfilling of the sinuses of the foundation is done when the foundation was poured, given to it, the formwork was removed and the waterproofing of the foundation was organized. Before backfilling, the position looks like this (in the case of ):

Or in a case like this:

Backfill outside the foundation is always done; inside the perimeter (in the case of a strip foundation), backfilling is done if the house does not provide for a basement or cellar.

At first glance, this is a very simple procedure, but disputes flare up about it, the main question of which is how to fill the sinuses of the foundation?

How to backfill?

The main question in these disputes: how to backfill, that is, what kind of soil to use for this? There are two options: sand or clay. Below are the arguments in favor of each of them, but looking ahead we can say that in some conditions you can apply any option.

Backfilling with sand

Sand, as well as gravel, sand-gravel mixture (SGM), pass water and are non-porous soil. This is the main argument in favor of backfilling the foundation with sand. The sand will not swell in winter, it will not create a load on the foundation from the forces of heaving. On the other hand: sand is a more permeable soil compared to clay, and moisture from the entire surrounding soil will drain into the sandy backfill, directly to the foundation and its base. And this creates an additional load on the waterproofing, and can lead to a decrease in the bearing capacity of the soil under the foundation.

Of course, it is necessary to make sure that rainwater is drained from the foundation, but it is unrealistic to ensure its absolute tightness in practice, and the water flowing from the blind area also needs to be diverted somewhere, otherwise it again falls into the ground, and along it in search of the easiest way again, a sand backfill will come near the foundation. So in any case, you have to do more to divert all the water (and if there is somewhere to divert it).

Clay backfill

The meaning of this solution is to create a barrier for water and prevent it from entering the backfill area, that is, to create a so-called clay castle. To do this, you can use not only pure clay, but also other types of soils: the main criterion is that the soil for backfilling should not pass water better than the entire surrounding soil. This means that if you are building a house on loam, then backfilling can be done either with the same loam or clay.

The table below shows the correspondence between load bearing soil and sinus backfill options.

In general, filling the sinuses of the foundation with the same "native" soil that was extracted looks not only logical, but also economically feasible: both clean sand and clean clay will most likely have to be bought and brought. You can also give an example of a foundation without backfilling at all, when it is used or the foundation is poured directly into such a trench:

In this case, the foundation will "coexist" with the "native" soil.

Soil compaction during backfilling

Whatever backfilling is done, the soil poured into the sinuses of the foundation must be carefully compacted. First of all, it is necessary that there is no shrinkage of this soil. For usually use a vibrating plate. Backfilling should be done with layer-by-layer compaction: a layer of no more than 30 cm was filled up, compacted, then the next one was filled up.