Despite the fact that the foundation is considered the basis for any building, it is not always capable of supporting the weight of the structure on its own. In addition, any base is monolithic or prefabricated concrete structures connected to each other.

If soil movement occurs or groundwater rises to the base, the inevitable destruction of the foundation will begin. Therefore, the pillow under the foundation plays a vital role here and it must not only be selected correctly, but also made in strict accordance with building codes.

Why do you need a pillow under the foundation?


It is used as an excellent natural waterproofing of the sole and prevents water from entering the subfloor. As a rule, such building elements are not reinforced, except for the pillow block. Why else is it needed:

  1. It creates a strong and reliable surface under the lower edge of the load-bearing base.
  2. Blocks groundwater, prevents it from rising above the permissible level, this is the primary layer of waterproofing.
  3. Provides an even, strong base without subsidence.
  4. A foundation on a sand cushion is more resistant to soil heaving and is also practically impervious to small seasonal soil movements.

The concrete pad can withstand enormous loads, and if reinforcement is also used, then it can withstand vertical and horizontal seismic shifts of low power.

What types of foundation pillows are there?


Considering that the structure of any pillow under the foundation is approximately the same, there are several types of them, which differ in design and filling material:

  1. Sand cushion for the foundation. It is made from sifted river sand, and fine gravel can also be used as filling. This pillow has a thickness of 25-30 cm, is additionally moistened with water and compacted.
  2. Crushed stone cushion for foundations. It is distinguished by its massiveness, thickness and design, because it is made from medium and fine crushed stone, and sand is used as a filter.
  3. Concrete pad for the foundation. Here we use ready-made concrete blocks, placed directly on the bottom of the trench or pit. All blocks are connected to each other by reinforcement, concrete mortar and are additionally covered with waterproofing on both sides. As a rule, such a foundation cushion is more practiced for massive large buildings, because it is heavy and the thickness is calculated individually in each case.

It is also possible to provide for the reinforcement of the pillow and the foundation at the same time, and this will further increase the strength of such a structure.

Sand foundation cushions


Sand pillows are made in cases where there is an abundance of sand as a building material, and a private developer wants to save money on building a house. It is also simple to set up and is needed for almost all small structures.

Advantages:

  • low cost of building materials;
  • small thickness of the compacted layer;
  • this is an excellent natural waterproofing, because water does not linger in the sand;
  • provides moderate loads on the foundation as a whole;
  • protects the sole from being washed away and destroyed by groundwater.

Why do you need a sand cushion foundation? It is used not only as waterproofing and a primary layer of non-heaving soil. It is often used to replace unsuitable or weak soil layers at a construction site. The layer height often varies, depending on the terrain profile and soil type. But you should always take coarse-grained sand, the thickness should be at least 20 - 25 cm, if blocks are used when constructing the foundation, then the thickness can be greater.

After the sand is evenly scattered along the bottom of the trench, it must be leveled and compacted. Changes in height should not be allowed, because then the foundation will begin to “walk.” As compaction proceeds, the sand must be regularly moistened to ensure high-quality adhesion of all particles and to achieve maximum density of the foundation cushion.

Features of sand cushions for foundations


Despite their versatility, they are not so easy to make. To begin with, you only need to tamp with a special tool, old-fashioned methods are not used. You also need to take into account the level groundwater, features and seasonal fluctuations in their level.

If the groundwater horizon is located too high, directly under the sand cushion for the foundation, then it is necessary to make a drainage system. The reason for this is simple: sand is hygroscopic, so over time the water will simply wash away the foundation cushion and the foundation will sag.

So, where is it better to use sand cushions for foundations:

  • if the groundwater level is relatively deep and there are no strong seasonal fluctuations;
  • if you plan to build a light structure, because sand does not withstand heavy loads. This problem is eliminated by block structures or crushed stone;
  • when a one-story building is being built.

The more floors, the heavier the structure as a whole, and it is too expensive to create or strengthen the existing foundation.

Crushed stone cushion for foundations


It is more durable than sand, it is made from crushed stone of the 20/40 mm fraction, and lies on a layer of finer building material. As a rule, coarse river sand is excellent as bedding. What is sand used for? To create a dense platform, the layer thickness is often up to 15 cm, this is also a natural waterproofing layer.

Why do you need a crushed stone cushion:

  1. It is durable, so multi-story buildings can be erected on it.
  2. The terrain and soil type have virtually no effect on the characteristics.
  3. Crushed stone is resistant to groundwater and does not wash out when compacted thoroughly.
  4. This is a natural drainage system, and the layer of sand underneath is excellent waterproofing.

When arranging, you need to remember that it consists of sand and crushed stone. After leveling the layer of crushed stone, it must be compacted to the level of the zero mark, and free spaces must be eliminated as much as possible. air gaps. Gravel along with crushed stone is great for this, but it is a little more expensive.

The calculation is carried out in such a way that each side of the bottom layer of the base is larger size future structure by 15 - 20 cm. This is achieved using formwork, and the front part is covered with a layer of waterproofing for greater reliability.

Block pillow for foundations


Block pillow under the foundation on this moment considered the most reliable and durable, especially if you make the correct and high-quality reinforcement load-bearing structures. But blocks are expensive, so they are not very popular in private construction. In addition, they are massive and heavy, so it’s simply impossible to do without powerful construction equipment.

How to properly make a foundation cushion from blocks:

  1. First, the soil is prepared. It must first be leveled and compacted. Then a layer of crushed stone up to 10 cm thick is laid on it.
  2. Along the perimeter of the trench, formwork is installed with a thickness similar to that of the future foundation. The thickness, as a rule, is up to 30 cm, but this is only if the base is filled with concrete mortar and concrete blocks are not used. You can pour a layer of sand on the bottom and compact it, or you can use small crushed stone.
  3. Then reinforcement is made inside the formwork. Wire, rods or composite materials are suitable for such purposes. The reinforcement is done in such a way that it is possible to connect not only the foundation cushion blocks themselves, but also the base itself. This will result in a rigid and durable structure that is not subject to horizontal displacement.
  4. After reinforcement, the pouring process begins concrete mortar. The grade of concrete is selected individually, taking into account the mass of the future structure and the type of soil, as well as climatic conditions.

If factory blocks are used in the construction of the sole, then the technology remains the same, only here it is necessary to provide for vertical and longitudinal reinforcement of the structure, and crushed stone does not need to be used here.

The foundation is not just the basis on which the future house will be built, but also one of its most important parts. This means that the strength and durability of any structure depends on the correct installation. The foundation cushion also plays a fairly significant role in this context.

This element is needed to create a stable and level platform for the foundation and reduce its level of settlement. If the layer is not laid well enough, the foundation will sooner or later shift, which will gradually lead to the destruction of the building as a whole. It is the pillow under the foundation that allows you to ensure the permissible load on bottom part grounds.

There are three main types of foundation cushions: sand, crushed stone, concrete.

In order to make a sand layer, the following building materials will be required:

  • sand of coarse or medium fraction without clay inclusions;
  • building level;
  • wooden pegs;
  • twine;
  • tamper (or vibrating plate);
  • roofing felt or other waterproofing material.

First, all crumbling soil should be removed from the bottom of the pre-dug trench. Lay the bottom with roofing felt or geotextile with an overlap (at least 10 cm). The designated building materials will avoid mixing sand with soil. When performing work, it is very important to ensure compliance with the horizon line. For this purpose, the required level is established using twine and wooden pegs. A layer of sand is poured onto the carefully laid material. The filling must be done in small portions, while simultaneously wetting the bulk material with water.

Each layer in mandatory compacted. Experts recommend compacting the sand until traces begin to remain on the surface. The thickness of the sand layer should not exceed 10 cm.

Today the sand cushion is optimal choice for all those builders who are interested in reducing the cost of building a foundation without compromising its quality characteristics.

Sand helps soften the load and significantly reduces the harmful effects of moisture on the foundation.

To summarize the above, the main advantages of a sand pillow are:

  • ease of filling the pillow;
  • low thermal conductivity;
  • availability of building material;
  • ease of compaction.

There can only be one disadvantage of a sand cushion. It is not intended for multi-story construction.

Most often, the choice in favor of a sand pillow is made in the following cases:

  • if the groundwater level is deep enough relative to the ground surface;
  • if the construction of the building is planned from relatively light building material (for example, frame structures or foam blocks);
  • during the construction of one-story buildings and structures.

Crushed stone pillow

Crushed stone pillows are just as widely used as sand pillows. In this case, coarse river sand or crushed stone (gravel) ranging in size from 20 to 40 mm is used.

First, sand is poured onto the bottom of the trench (no more than 10-15 cm). This layer is compacted and soaked. Crushed stone is poured onto the compacted layer. Usually a layer of about 20 cm thick is sufficient. The crushed stone layer is also compacted.

Recently, crushed stone cushions have been used more and more often for foundations. Although such a base is inferior in strength characteristics to a layer of concrete, it is much better than sand.

The crushed stone used for work consists of crushed rocks, stones and boulders. There are several main types of crushed stone:

  • limestone;
  • slag;
  • secondary;
  • granite;
  • gravel.

For the foundation cushion, fine crushed stone is most often used. Usually we're talking about about the following sizes: 3x8, 5x10, 10x20, and also 5x20 mm. And only for foundations for heavy buildings it is recommended to choose medium-fraction crushed stone.

In terms of temperature stability and strength characteristics, granite stands out among crushed stone. But crushed gravel is most often chosen for the foundation cushion. Its advantages are relatively high strength, low cost and minimal radioactive background.

Just like a layer of sand, a layer of crushed stone acts as a kind of filter that effectively prevents capillary rise of water. Since capillary movement occurs through the surface energy of the particles, their size and shape are particularly important. In this case, it makes sense to use large-porous materials for the pillow. And sand turns out to be far from the best option.

Concrete pad

Unlike pillows made of sand and crushed stone, concrete option somewhat more expensive. But in fact, its high price is completely justified.

For its construction you will need the following materials:

  • concrete;
  • Not a large number of crushed stone;
  • metal rods;
  • boards;
  • rammer (vibrating plate).

A layer of crushed stone (about 10 cm) is placed at the bottom of the trench and thoroughly compacted. The crushed stone substrate serves as a base, so it must be strictly horizontal. Next, formwork made of boards is installed on the crushed stone. To increase the strength of the structure, it is reinforced. Concrete is poured into the formwork with a metal frame. All you have to do is wait for it to dry completely.

Which specific layer option for the foundation to choose is calculated individually in each case. And if you have any doubts, it makes sense to seek help from professionals. They will not only tell you which pillow option to choose: crushed stone, sand or concrete, but if necessary, they will also help you do the actual work of equipping the base for the foundation.

Laying the foundation of a house is the first and most important stage of construction, but this is preceded by preparing the foundation under the entire building area on the site.

The type of foundation, its design and characteristics depend on the bearing capacity of the soil at the construction site, as well as the strength of the house that will be built subsequently.

Even at the design stage, it is necessary to determine the properties of the soil and determine which backfill for the foundation, sand or crushed stone, will be relevant as preparation.

It is somewhat incorrect to raise the question of choosing a backfill for a foundation made of sand or crushed stone. The key to a strong and stable home is a strong and reliable foundation, which must meet a number of requirements:

  • High strength and density of the soil, capable of withstanding the distributed load of further development;
  • Groundwater should not linger under the foundation, therefore the high drainage capacity of the soil is important;
  • When wet or dry, the base should not lose its basic characteristics.
  • It should not contain organically active components;
  • The presence of flammable or rotting plant residues is not allowed.
  • Cold heaving of the soil is not allowed;
  • Uneven shrinkage or deformation is not allowed.

In progress construction work the foundation should not deform even under the load of the involved construction equipment or the activity of builders.

The strength of the surface layer should be sufficient to accommodate all the necessary elements, such as reinforcing frame, formwork, etc.

bedding device

Since it is not possible to select the type of soil on the site in advance, you should work with what you actually have. If the soil does not meet the specified requirements, a foundation filler is used from:

  • sand;
  • gravel;
  • sand and gravel mixture (SGM);
  • gruss (crushed fragmentary rock);
  • crushed stone;
  • skinny concrete.

Since the properties of each of the listed materials differ, as do the methods of their use, the choice of backfill should be made based on the final requirements for the base under the foundation.

The main conclusion: backfilling the foundation with sand or gravel is needed to adjust the properties of the soil on which the house will be built. It is part of the foundation preparation activities and is not an absolute component.

Anyway the type of soil is first determined optimal type foundation(tape, pile, monolithic slab, etc.) and after that, if necessary, select the type of bedding that will be required.

High-quality training under strip foundation or monolithic slab is pouring the bottom of the pit with lean concrete to level the level and prepare a solid foundation. Sand or gravel are for the most part a low-cost alternative to reduce overall construction costs.

Sand

A simple and quite effective option for backfilling the foundation. Well compacted mechanically the sand cushion is capable of taking on the same strength and density as the main soil, and at the same time is easily shaped to accommodate all the unevenness of the bottom of the pit.

Advantages of sand for backfilling:

  • With high-quality compaction, you can achieve a foundation strength equal to the original value for the soil;
  • Fills all the unevenness of the pit well and transfers the load evenly;
  • Sand retains drainage properties;
  • Easily shaped and leveled;
  • Does not require the use of heavy construction equipment.

Flaws:

  • Weak mechanical strength of transverse point load.
  • Sand is washed away by groundwater over time.

Sand for backfilling is ideal when using ready-made reinforced concrete blocks and slabs, allowing the load to be transferred evenly over the entire base.

Sand for backfilling is selected from coarse and medium fractions without clay inclusions. Even with complete compaction, the drainage properties of the base are preserved, and cold heaving has almost no effect on the strength of the base.

The thickness of the bedding can range from 10 to 60-70 cm depending on the properties of the soil. The depth of soil freezing in many regions of the country exceeds 30 cm, and cold heaving can appear even under a well-insulated foundation during prolonged winter cold spells.

The optimal height for adding sand is considered to be 45-60 cm. Such a layer of sand is difficult to compact at a time, so the material is gradually filled in layers 5 cm thick and gradually compacted and necessarily moistened.

It is quite difficult to determine the required amount of water to moisten the sand. A common mistake is excessive moistening of the sand, from which the entire mass becomes plastic and diverges more to the sides of the tamper than becomes compacted.

The volume of liquid should be determined individually so that the sand is easily crushed in your hands, maintaining the shape of a cake. On the other hand, during mechanical compaction, water should not protrude on top of the sand.

The degree of sand compaction is determined quite simply. If there are no traces left on the prepared sand cushion when walking on it, then the base is ready for further work.

Gravel

Medium and coarse gravel is used for backfilling in situations where the maximum throughput of the drainage layer should be ensured under the base of the foundation in combination with distributed drainage system, aimed at draining groundwater from the base of the foundation.

Gravel is often used as a cheap substitute for lean concrete when preparing and strengthening the soil for a foundation. To do this, it is compacted and mixed with the soil mechanically or manually.

However this is not The best decision, since without a binder, which can be cement, such a foundation is susceptible to erosion by groundwater with subsequent loss of load-bearing strength.

More often in demand is ASG - a sand and gravel mixture to form a level area under the foundation. In combination with sand, the mixture is easier to impart density and strength comparable to that of the parent soil on construction site, while maintaining the drainage capabilities of the bedding.

Advantages of gravel backfill:

  • Low water capacity of the substrate, liquid is poorly retained in it, and the surface area of ​​gravel for wetting is much lower than that of sand;
  • The strength of the bedding and its high load-bearing capacity and resistance to erosion or lateral loads.

Flaws:

  • Under heavy loads, even distributed, gravel bed can “sink”, reducing its own strength and the strength of the parent soil;
  • It is difficult to level the bedding surface;
  • When pouring concrete, part of the cement laitance falls aimlessly through the bedding, weakening the main body of the foundation.

If gravel is used for backfilling under a strip foundation or monolithic slab, then, of course, it should be pre-insulated to prevent the concrete from weakening. However, this often entails more costs than when using initially lean concrete.

Which is better sand or crushed stone

The requirements for preparing the foundation pit for the foundation require strict instructions in the construction project based on an analysis of the bearing capacity and properties of the parent soil.

The best preparation for a strip foundation or monolithic slab is lean concrete and only in some cases is it possible to replace concrete with sand, gravel or ASG to reduce overall costs. At the same time, sand has a wide range of advantages and is more practical.

Gravel is suitable only in cases where high throughput if necessary, arrange a drainage layer with low water capacity. At the same time, it is difficult to isolate the bedding from the volume in which the foundation will be poured.

The gravel backfill goes well with pile foundations, where it is enough to remove excess moisture from under the base of the house, and at the same time there will not be a significant load on the bedding itself.

Under strip foundation

By definition, sand bedding is needed only when ready-made reinforced concrete slabs and blocks are used in order to distribute the load evenly along the base plane.

With the help of sand it is easier to level the bottom of the pit, and tamping gives the sand the necessary density and bearing capacity.

However, this is only relevant if it is possible to place a massive vibrating plate in the trench for mechanical compaction of sand. In most cases, it is safer to use a lean concrete footing to level the base and prepare it.

Sand is also relevant in case of significant differences in height along the bottom of the prepared trench. To reduce costs and reduce the volume of solution for the concrete base, sand or crushed stone is added with layer-by-layer compaction and moistening.

Under a monolithic slab

It is important to strictly level the base of the pit and prepare the soil for installation of the reinforcing frame and pouring. Either lean concrete or sand compacted in layers is used.

stages of construction of a monolithic foundation

Sand is mainly used in cases where it is necessary to significantly raise the bottom of the foundation pit after removing the entire fertile soil layer to the base of the parent soil.

When forming the bedding, it is important to pre-distribute trays for water drainage, communication lines that will pass through the foundation slab, and also mark the required planes of the future foundation.

According to the requirements, a base is formed under the monolithic slab not strictly in one plane, but with a slight elevation in the center of the building and with a slope of 2-3% in all directions, for effective removal of moisture from the substrate of the future foundation.

Particular attention is paid to the quality of sand compaction. So, the density of the backfill for the foundation should be from 1.65 t/m3 and preferably not less than the density of the parent soil with an error within 0.05 t/m3.

The height of the backfill is determined as the difference between the level of the bare base of the soil after removal of the fertile layer and the design level of the foundation base.

Under a pile foundation

The backfill primarily performs the function of drainage to drain groundwater, and also acts as a substitute for the fertile layer of soil in order to remove the volume of material containing organic or combustible inclusions from under the foundation.

backfill device for pile foundation

For these purposes, it is best to use large and medium gravel and crushed stone. Expanded clay bedding is often used, which further increases thermal insulation properties grounds.

High-quality and fast installation of systems:

Beginners in the construction business are often interested in a rather pressing question: what to use for the foundation cushion: sand or crushed stone? The foundation of the house has always been and continues to be one of the most important building elements for any private home. The durability and reliability of the structure itself often depends on how the foundation is built: if you deviate from the norms, distortions and cracks in the walls are possible, and restoration repairs in the house will never be completed. Therefore, the foundation usually needs to be laid with special care, observing all possible building regulations. And one of them is properly produced bedding.

What to use for the foundation cushion: sand or crushed stone? We asked both professional builders and those who tried to build a house with their own hands for special opinions. We will tell you what they say in our article today.

Requirements for a pillow under the foundation: To understand which material to use most effectively, you need to know what criteria apply to the pillow (bedding). So, the material should not be heaving, but in the event of a change in temperature and natural conditions(drying, freezing or thawing) but also not lose its declared properties. Also - do not contain flammable or herbal additives, and when pressing, also perform drainage functions.

What types of bedding are there?

According to the above requirements, materials such as crushed stone and gravel are used. Sand – gravelly, coarse, sometimes medium. Sometimes - concrete or mixtures. But the most commonly used cushions are sand and crushed stone. It is considered mandatory for strip foundations, for example. The European standard is 25 cm. But in our conditions, a pillow is sometimes used up to 80 cm (on average 30-50)!

It all depends mainly on what kind of soil is on the site: heaving or not. And also on how close to the surface the soil waters lie and on the possibility of floods in the area. So, before constructing a building on a site, experts recommend conducting a thorough soil and water study.

You can do this yourself if you are well versed in this, or you can order it from special companies that do this. True, you will have to pay, but then you will already know exactly what kind of pillow (and what thickness) to use for the base, and it will also become more clear what kind of foundation to build!

Triple cushion: Quite a commonly used option in private developments. The bottom line is that after digging a trench, the backfill for the foundation is prepared, alternating sand, crushed stone, and concrete (each layer is at least 20 centimeters).

The layers are thoroughly compacted using tools (roller, vibrator, vibrator): manually and mechanically. According to the norm, the pillow should have a density of at least 1.6 t/m3.

Sand backfill

A bedding under the foundation is also made from clean sand. The material taken is coarse and gravel. Less often - the middle fraction. Small is not used due to its increased instability. When compacting sand into a pre-dug trench, sand is taken wet or specially wetted for these purposes. This way the compaction process itself works better and the instability of the material goes away.

A sand pillow is the most accessible and cheapest option. It is well suited for those who decide to save on the foundation. And it’s quite simple to arrange it. And its main advantage is that it is an excellent barrier between soil water and the foundation itself, and well accepts increased loads from the foundation. By the way, the quality of the tamper you made can be checked folk method: if you step on the sand and no traces remain, then the process was carried out efficiently.

A layer of clay is placed and compacted under the substrate, which is designed to protect the foundation of the building from rising groundwater. This option, contrary to the opinion of some users, does not seem appropriate from the point of view of elementary physics of materials. The clay layer will indeed retain rising water, but due to its consistency it will also increase the heaving of the soil, thereby worsening the bearing capacity of the foundation. So when constructing a sand substrate, it is best to use coarse, clean, compacted sand.

Crushed stone backfill

Many people prefer to use it without fail. Such a foundation cushion has increased strength compared to sand. Crushed stone, as is known, has several fractions. So, in the place most transitional from the ground, you need to use 10-15 cm of fine crushed stone (some, by the way, recommend using coarse or gravel sand for these purposes). After this comes medium crushed stone. This layer should be 20-25 cm. It is leveled and thoroughly compacted by special means, for example, a vibrating plate.

A characteristic feature of crushed stone, which is artificially crushed stone, is its sharp corners. Thus, when compacting, you need to ensure that the gap (free space) between units of material is as small as possible.

According to construction standards, the size of the pillow should extend 15-20 cm in each direction, that is, be larger than the base itself.

A crushed stone cushion is feasible for almost all buildings of varying complexity and floors.

The advantage is that it does not matter what type the structure is built from. And some disadvantage in comparison with sand is the high cost of such bedding.

Let's sum it up

When comparing and choosing what to use for a foundation cushion: sand or crushed stone, foundation laying experts advise paying attention to some nuances. First, examine the soil on the site, since sand bedding is not suitable for everyone.

Secondly, you should also focus on the type of structure being built. If this is a small outbuilding or shed, then the best option(to also save money) there will be a sand cushion, since it is the cheapest option. But if we are talking about a residential building and even several floors, it is better to use crushed stone as the most durable option. In addition, it is possible to use mixed options (for the same savings): sand/crushed stone or sand/crushed stone/concrete.

People who are far from construction most often don’t even think about why everyone needs it?

There are people who quite frankly believe that it is needed in order to have something to put the walls on: “Well, really, shouldn’t we put them on the ground? We need something harder."
Of course, most more or less enlightened people understand that a foundation is necessary in order to evenly transfer the load from the above-ground part of the building to the ground. And since the weight is even one-story house

is quite large, it is believed that its foundation should be something monumental and monolithic. This belief is due to the fact that nowadays they are made of monolithic or precast reinforced concrete. People have already forgotten that in the old days, foundations were made not only of concrete, but also of wood and stone. A gravel foundation is not an ordinary foundation where gravel and sand serve as filler. concrete mixture

, this is a foundation built without any binder at all.

Why gravel foundation?

Why did the question suddenly arise about the relevance of such a foundation? Because in some cases, this particular version of the load-bearing foundation of a house may be the only one possible to use. At the usual concrete foundation

  • There are some disadvantages that can be avoided by making a foundation of only gravel:
  • Concrete foundations conduct water well. Therefore, in soils saturated with water, moisture through diffusion very quickly spreads to the entire body of the foundation, and when negative temperatures begin to freeze, it first causes the appearance of microcracks in concrete, and then can lead to serious destruction of parts of the foundation, which is very dangerous for the entire structure .

To avoid this, various types of waterproofing are used, forming a literally “fur coat” around it. To protect the walls of a building from dampness, it is used horizontal waterproofing, cutting off capillary moisture of the foundation from penetration into the walls. But with the slightest destruction, the process extends to the walls of the house.

Therefore, in some cases saturated with water, it makes sense to resort to the construction of a gravel foundation. It’s clear that you can’t put a high-rise building on it, but for small house with one or two floors it is quite suitable.

Gravel belongs to the category, therefore capillary moisture, which easily spreads in concrete, cannot rise along it.

Thus, there are a number of positive aspects that determine its use as the only material for foundation construction:

Gravel foundation technology

So, for the construction of a gravel foundation, only gravel or stones are used, not bound by any mortar.
The construction of the foundation occurs as follows:

    1. A narrow trench needs to be dug along the entire perimeter of the future building. Its depth should be at least 10 - 15 cm lower than the freezing depth of the soil in a given region.
    2. The base of the trenches is given a slight slope for better water flow. Therefore, you need to first decide where exactly the drainage well should be located, into which water from under the foundation will flow. To avoid silting of the trench due to the penetration of small particles of surrounding soil, it must be covered with geotextiles.
    3. If the house is built on clay soils, the absorbing properties of which are low, then a trench can be laid along the bottom drainage pipe, equipped with holes and wrapped in filter cloth. This will prevent soil particles from clogging the holes. This pipe must be connected to a drainage well, which is located below the trench.
    4. Next, the trench is filled with gravel or crushed stone with a particle size of 25 - 30 mm. Every 25–30 cm, a layer of crushed stone is compacted tightly. At this stage, it is quite possible to get by with manual tamping.
      Important! Gravel or crushed stone must be washed from dust, as it can contribute to capillary suction of water from the ground.

Then using solid polystyrene floor slabs from the ground. But this is optional.

  1. On top of crushed stone and a layer of insulation (subject to its use), formwork is placed around the perimeter of the house and poured concrete slab, the task of which is to uniformly transfer the weight of the above-ground part of the house to the gravel foundation.
  2. If you plan to build a house from lightweight materials (adobe, foam concrete), you can not cast a slab for the entire area of ​​the house, but use only a reinforced concrete belt located directly above the foundation along the perimeter of the house.

Where you should not use a gravel foundation:

  • You should not use this method of constructing a foundation in areas with highly expansive soils that spontaneously expand when frozen (soil heaving).
  • Also, you should not use this method on soils that can bear only a small load - less than 10 t/kV. m. In such a situation, you can get out of the situation by increasing the width of the foundation, but this will increase the cost of the project.

Thus, having carefully studied the geology of the site and decided on the size of the house (and therefore its weight), in order to reduce the cost of construction, you can use the construction of a gravel foundation.