What kind of sand is used to cushion the foundation. Pillow for different types of foundations. Positive characteristics of river sand

In search of information about the construction of the foundation with your own hands, you must have come across such a concept as a sand cushion. It is nothing more than a layer of sand under the sole of the foundation. From this article you will learn about why a sand cushion is generally needed under the foundation, how thick it should be, as well as how and from what sand to make it.

The device of a sand cushion under the sole of the foundation

We will assume that you have already marked the foundation and determined its main parameters, then the sequence of work in the manufacture of a sand cushion can be represented as follows:

• we dig a pit or trenches (depending on the type of foundation) to the estimated depth (depending on the soil on the site, more in this article);
• we scrupulously level the bottom of the trench (pit), especially important if the excavator has worked;
• we fill the pit (trench) with layers of sand 200 mm each with moderate moistening of the material and its strong tamping. The sand must be compacted so hard that no marks from the sole of the boot remain on its surface;
• backfilling and tamping is carried out until a sand cushion under the foundation of the required thickness is obtained (about the thickness below). Moreover, it is necessary to ensure that the surface of the layer is as even and leveled as possible on the horizon - a very important condition

After that, it is already possible to start reinforcing, install removable or fixed formwork and pour concrete.

The need for laying a sand cushion

The process described above seems to be quite simple. But why do you need a sand cushion at all, is it really impossible to do without it? We will highlight several reasons why in some cases it is better to take care of the device of this layer:

• sand can replace the problematic base soil under the foundation of the house. For example, there may be clay - heaving soil, which manifests itself when the soil freezes and thaws;
• sand, even its slight layer, allows you to level the bottom of the pit or trench, which is very important for the subsequent stages of the construction of any foundation;
• the sand cushion resists compression and is an intermediate link between the foundation and the base soil. Even though the soil usually becomes stronger with increasing depth (due to natural compaction under the influence of the mass of the overlying layers), replacing its surface layers with sand helps to reduce the settlement of the building. In addition, the cushion “breaks” the capillary bridge and additionally protects reinforced concrete from moisture.

What kind of sand to use

When building a sand cushion under the foundation, it is best to use coarse gravel sand. The use of a fine and fine fraction is undesirable, due to a significant deterioration in the resistance of such a material to compression - there will be large shrinkages. Pure river sand of medium fraction is quite suitable for the construction of a sand layer. We draw your attention to the fact that not only sand, but also any other material with a sufficient value of compressive strength and, of course, non-rocky or less heaving than the native soil of the site can be used for the device of an anti-heaving pillow. To increase the life of the sand cushion, to protect it from silting at high GWL, before filling the sand into the trench (pit), it is necessary to lay geotextiles or any other material that prevents sand from mixing with the soil.

The thickness of the sand cushion under the foundation

As a rule, the thickness of the sand cushion is assigned based on the specific conditions for the construction of the foundation. Usually it is taken equal to 10-20 cm - in this case there is no question of saving concrete for the foundation, and sand is used solely to level the base. As for the shape of the section, it is better to arrange a trapezoidal sand cushion, tapering downward at an angle of 30 degrees. The maximum thickness of the pillow for the strip foundation is taken equal to three times the width of the strip. If you decide to lay a shallow strip foundation, then we recommend that you additionally familiarize yourself with the information provided in VSN 29-85.

Sand belongs to bulk materials with high density and is successfully used both in construction and for the installation of treatment facilities.

Creating a sand cushion is one of the important stages of construction. Unfortunately, not all experts will be able to answer the question of the need to place it under the foundation and what kind of sand should be used.

Functions

If the question arises what kind of sand is needed for a pillow under the foundation, it is first necessary to figure out what functions this embankment performs.

• Leveling.
• Substitute.
• Compensatory.

The leveling function is relevant in situations that can be called ideal. The soil is homogeneous, immovable and does not contain impurities of organic soil or clay. Therefore, the task of sand is limited to leveling the trench bottom or the bottom of the pit.

In cases where organo-mineral soil (peat) is under the future construction, you can be sure of the mobility of the soil and a decrease in its bearing capacity. To avoid the destruction of structures, it is necessary to remove a large amount of soil until the moment when the organic layer is over. The great depth formed after the excavation of organic soil is covered with sand.

Deformation compensation is the main task of sand when performing the third functional purpose. Clay and other heaving soils, being under the support of the house, significantly affect the distribution of loads. Which, as you know, can lead to the complete destruction of slabs or concrete tape.

How it works

The pillow, which performs leveling functions, in thickness, as a rule, does not exceed 200 mm. The sand is once poured to the bottom of the trench and leveled. Then it is slightly moistened and gently rammed. All other varieties of this necessary element directly depend on the size of the base of the foundation. Their calculation is made individually in each case.

Material selection

What kind of sand to use for the foundation pad? Unfortunately, few people think about this issue. Construction continues with the material that will be delivered to the site. But the basic properties of the building material itself greatly affect the strength of the structure.

It should be noted which sand for the foundation cushion should not be:

• With small grains. The greater the size modulus, the better and better the embankment for the foundation. The pillow will be easier to compact and be affected by moisture.
• Dirty. The presence of large stones or particles of organic soils in the bulk material radically changes the physical properties of the cushion. Particularly dangerous particles of clay. The presence of its impurities in the sand contributes to greater soil mobility, reducing its bearing capacity. Clay retains moisture, which will negatively affect the sand cushion.
• The sand used for the pillow under the foundation must be washed without fail. It is best to use river sand or quarry sand. Also, the best solution would be the use of gravel material.

The use of river sand significantly increases the cost of construction work. An order of magnitude cheaper will be quarry sand, thoroughly washed with a huge amount of water from impurities of clay and silt.

The foundation of any home is actually a key part of it. Even if the walls, ceilings and roof are built to last, a poor-quality base can easily destroy everything. Therefore, it must be built with special care.

You can often hear disputes about the need for moisture protection and insulation. Along with these questions, there is another one: is it worth making a pillow under the foundation? And along with it, a number of others appear: how to make it, what material to choose for this, etc. We will try to answer these and other questions further.

Functions, materials for creation

First, let's talk about why we need a sand (or any other) pillow under the foundation. It performs several functions in different cases:

1. Makes the bottom of the pit/trench even.
2. Protects the base from moisture.
3. Reduces the load on the soil and compensates for its movements.
4. Replaces problem soil.

Dealt with the appointment. Now let's move on to what this foundation is created from. According to this criterion, the fundamentals are:

1. Sandy.
2. Gravel (or crushed stone).
3. Concrete.
4. Combined (from sand and gravel).

There are other materials that are used to create a foundation pillow.(for example, industrial waste). But still they are not found under the base as often as the above. We will take a closer look at them.

Sand

This material is quite often used to create a layer between the foundation and the foundation. To understand why you need a conventional sand cushion for foundations, you should say what exactly it does under the base:

1. Sand well removes rain and melt precipitation.
2. Some species absorb groundwater, preventing them from penetrating into seams and crevices.
3. When heaving, it acts as a shock absorber.

A sand cushion under the foundation is needed in the following cases:

1. When to replace loose soil.
2. For prefabricated bases (for example, a pillow for foundations is made of sand).
3. To eliminate capillary moisture when the underground part of the base is deepened to a small level (this also applies to shallow slab bases).

A sand base under the foundation is created only when it really protects the base. If you need to create an obstacle to water vapor, it is better to choose denser materials.

Dealt with the appointment. And then the following question arises: what kind of sand is needed for a pillow under the foundation?

Some people think that you can take any, but in fact it is not. But then what kind of sand is better?

Small does not fit - too little compression resistance contributes to greater shrinkage. Therefore, you need to choose large-fractional species, who do their job well. You can take material from the river, but then the work will be quite expensive. The career option is cheaper.

How to make a sand base?

Now let's talk about the device of such a pillow for various foundations. As with the material, many make mistakes with the layer size. There is an opinion that the higher it is, the better. In fact, the height of the sand cushion has a maximum threshold, which, like the rest of the data, depends on many factors, such as:

1. Dimensions and weight of the house.
2. Soil characteristics: freezing depth, groundwater level, etc.

For example, the thickness of the sand cushion under the foundation of the tape type should be no more than three times the width of the tape. Under the layer they make a height of 10 - 15 cm, and in columnar and pile foundations this figure is doubled; at the same time, the sandy base should be 10–20 cm wider than the pillars on all sides.

In addition to sand, you will need geofabric, which covers the layer from all sides. Geotextile under the sand cushion of the foundation is laid as a waterproofing. Sand is poured on it, leveled and rammed. You can do this with improvised means, but it is better to use the vibro technique. It is better to pour sand in layers - so it is better rammed. The base is considered ready if there are no traces of shoes on it. Next, the base is closed with waterproofing.

This is how the sand cushion device looks like - the simplest and cheapest. However, you should not choose it because of the price and the possibility of creating it yourself, because foundations often require denser foundations.

During tamping, the sand should be sprinkled with water for better compaction.

rubble

A crushed stone pillow under the foundation is also very popular. It is also simple in device, but its strength is higher than that of the previous one. If the sand is more suitable for small one-story houses, then in this case it is possible to build overall cottages.

What crushed stone is most suitable for the base? The material itself is of three types:

1. gravel.
2. Granite.
3. Limestone.

The latter is not suitable in our case, since its quality is low. L It is best to choose crushed gravel as it is cheaper and safer.

The granite version is also not harmful, although it accumulates radiation (but in a safe amount), but it has greater strength.

But such rubble is suitable for wealthy people, because it costs the most. Dealt with the view. As for the crushed stone fraction, it is recommended to use the variant of 20 - 40 mm with a strength of M 1200. It is radioactively safe and frost-resistant, which is required in this case.

The gravel cushion under the foundation is done in much the same way as described above, with the only difference being that a layer of the same sand is first poured here, which is also rammed. The crushed stone layer is also subjected to this process. However, there are exceptions: if you are building a one-story wooden house, the material can not be rammed. As a waterproofing, you can use spilled bituminous compounds, since fabric materials can easily be damaged.

Combined use

Before choosing a material, the question may arise, what is better to use for a pillow under the foundation: cheap sand or durable gravel? Most often, both types are used. As already mentioned, the bottom layer of the crushed stone base is sand. Also, in sandy counterparts, crushed stone is used for reinforcement (for example, in the construction of columnar foundations).

The device of a sand and gravel cushion for one or another foundation is not difficult. In fact, this is a “pie” of layers of sand and rubble, stacked in sequence. Particular attention should be paid to tamping, because after the laying, the base shrinks slightly. It is also necessary to take care of proper waterproofing: if the top layer is crushed stone, it can damage it.

The phased creation of a pillow for a foundation of sand and gravel looks something like this:

1. Laying the bottom of the pit / trench with a rubble (in one or two layers - depending on the load on the base).
2. Backfilling a layer of crushed stone (10 - 20 cm), and then - sand.
3. Pouring the sandy layer with water.
4. Additional pouring and watering of sand (if necessary) and so on until a continuous sandy “crust” appears.
5. Rammer.
6. Re-filling with water.

It is rational to choose a sandy - crushed stone foundation pillow for weakly bearing soils. Care must be taken to ensure that there is no clay in the sand.

Concrete

This foundation is the strongest of all. True, a concrete pad under the foundation in private construction is used less often, because of the high cost, and you can’t arrange it yourself. Otherwise, a properly created element has no flaws.

The device of a concrete foundation pad is more difficult than sand, crushed stone or ASG. The work is carried out as follows:

1. Excavation.
2. Filling, tamping and installation of a waterproofing layer.
3. Laying centimeter concrete mortar.
4. Construction.
5. Reinforcement.
6. Filling the solution with subsequent tamping.

The high cost of such a solution is due not only to the price of concrete.

During construction, professional equipment is used - for example, for pouring and ramming the material.

But, it is these foundation pillows that are the strongest.

During the drying of the concrete, it is necessary to periodically irrigate it with water. Otherwise, it may dry out.

Video

Video on how to make a pillow with your own hands.

conclusions

Now you know what a foundation foundation is for. It is she who ensures the reliability and durability of the base. Creation in most cases is also not difficult, because there is a lot of information on how to make a pillow for different types of foundation.

All of the above can be summarized in several paragraphs:

1. The answer to the question why a pillow is needed is very simple: it protects the base from moisture and movement; it is better not to neglect such an element.
2. The foundation on a sand cushion is the cheapest, but not always the most reliable.
3. A layer of sand and gravel is used most often.
4. Sand for the foundation cushion needs coarse sand, fine sand can cause problems.
5. Crushed stone is also needed in large fractions, fine screenings are used in other construction works.
6. A pillow under the foundation of the aforementioned material still requires a sand layer; what sand to use - you already know.
7. Do not think that the higher the layer, the better. The thickness of the pillow under a particular foundation depends on many factors.
8. The most durable and reliable material used in this case is concrete, although at the same time it is the most expensive. If the house is envisaged to be oversized and light, it is better to make a pillow under your foundation from sand and gravel.

Knowing all the nuances and rules, you can easily choose materials and create good protection for the base. It is then that the foundation will be able to serve for a long time and with high quality, without putting the house at risk of destruction.

In contact with

Many people know that there is a sand cushion for the foundation, but not everyone can say for sure why it is needed and how it is created. As a result, beginners in the construction business often pour sand into the trench without any understanding and, as a result, only harm the entire structure.

The cushion under the sole of the foundation can perform three functions:

How thick a pillow is needed under the foundation depends on what function it performs in this particular case.

Pillow device

The easiest way is to create a backfill that performs a leveling role. As a rule, its thickness in this case does not exceed 15-20 cm. It is enough to fill in the sand once, carefully level it, spill it with a small amount of water - moisten it and then compact it.

But such a minimum can be dispensed with either on non-rocky soils, or in the case of a deep foundation, below the level of freezing and relying on non-deformable soil layers. In other cases, you have to lay a compensating pillow. Its dimensions depend on the width of the base of the foundation. Exact data can be calculated from the table.

For example, if a foundation is laid with a base width of 60 cm, then the width of the pillow will be 60 * 2.4 = 144 cm, and the height will be 60 * 1.2 = 72 cm. A strip foundation with a tape width of more than 120 cm does not need a compensating pillow .

A compensating sand cushion is laid as follows:

Sand is considered a non-heaving material; also, due to its structure, it prevents the capillary rise of moisture from the underlying layers to concrete. But all this is typical only for sand that is not filled with water.

If a lot of moisture gets under the foundation, then it can radically change the properties of the pillow.

Therefore, in areas with a high level of groundwater or where there is a possibility of sedimentary water getting under the concrete, it is imperative to provide a system for removing moisture - drainage.

The process of laying a replacement cushion under the foundation does not fundamentally differ from a compensating one. The role of geotextiles and systems for water drainage is only increasing. In any case, the important point is the correct tamping. It is worth considering in more detail.

How to properly compact?

Clean sand practically does not shrink, but only after proper compaction. If this procedure is neglected and performed in bad faith, there is a high risk of subsidence with subsequent destruction of the foundation.

In order for everything to work out properly, you should adhere to the following rules:

It is more convenient and faster to carry out compaction work using a vibrating plate or a special construction vibrator.

In some cases, you can use road construction equipment, and sometimes it’s good to tamp by hand.

Which method to choose depends on the characteristics of the site and the possibilities.

Sand selection

Few people think about what kind of sand to choose for a pillow under the foundation. They take the one they bring. However, the properties of this material affect the properties of the bedding to no lesser extent than the correctness of its laying.

For a foundation pillow, washed quarry or river material is best suited.

The ideal choice is gravelly. Do not forget that it is allowed to use other materials that meet the requirements presented.

However, it is difficult to correctly determine the loads and properties of a particular soil at home, so the easiest way is to take the material that is guaranteed to fulfill its task.