Foundation cushion

When construction is planned on a site with clay soil, it must be borne in mind that its level in winter and summer may differ, it may settle or, on the contrary, swell. The fact is that during freezing it increases in volume. The swell creates water in its composition. Loam, gravel and sandy soils consisting of fine and dusty grains can also swell during freezing. These so-called heaving soils lead to the displacement of the foundation, the destruction of the walls of the structures located on them.

Cracks appear in the brick walls, and the log house loses its geometry, and large gaps appear. In addition, windows and doors cease to open, may collapse over time. To avoid such troubles, arrange a pillow under the foundation.

Types of bedding

A pillow for the foundation of the structure is an important structural element in the construction of the building. Its use is necessary for the construction of foundations of various types and is mandatory for the construction of small houses, as well as for huge industrial buildings located on heaving soil.

A pillow under the foundation is its foundation, counteracts the heaving force, helps eliminate the negative effects of seasonal fluctuations in the soil level, prevents the foundation from shifting and tearing, cracks on the walls and their destruction.

Depending on the types of buildings being built, pillows for their bases can be from:

• sand;
• crushed stone;
• concrete.

Each of these materials has certain properties and characteristics that must be taken into account when building the foundation. In addition, the choice directly depends on the level of groundwater. After all, it was water, as was said, that caused the heaving of the soil.

Soil type and sand quality

The main function of the sand base is to smooth out seasonal fluctuations in the soil level, exerting an uneven load on the building foundation. Different types of soil have different bearing capacity. Dry sandy soils can become a solid foundation for buildings. In addition, this is the most economical option.

A sand cushion prevents heat loss through the foundation. But! Sand must be chosen correctly. Small holds water well, therefore, only the large and medium fractions are used. To do this, they dig a pit with a depth greater than the freezing level, removing the heaving soil and filling the foundation under it instead (in this case, a layer of sand) and compacting it well.

Choosing the thickness and width of the pillow

Based on the pressure force of the structure on the soil, determining the type of soil and knowing the amplitude of its seasonal fluctuations, it is possible to calculate the thickness of the sand cushion. It can be within 20-60 cm. If the building is light, frame type, with walls made of timber or a log house, then a sand pillow under the foundation is arranged to a shallow depth of 30-40 cm. A pillow is made thicker for building a house made of brick. Especially if it is a two-story building. Since in this case, the weight of the structure increases.

The width of the pillow under the foundation is determined depending on the width of the future base. To do this, add another 20-30 cm. For example, if the width of the base of the foundation is 30 cm, to arrange a pillow under the foundation, sand is laid on a width of 50-60 cm. If you plan to organize wall drainage, then add the distance intended for laying drainage pipes. It depends on their diameter. Accordingly, the sand cushion will become wider by this value.

Foundation cushion

Consider the case when sand of large and medium fractions with mandatory moisture and layer-by-layer compaction is used:

1. Dig a trench according to the calculated dimensions. Its walls need to be lined with a geotextile film, so as not to clog the sand and prevent silting of the pillow.
2. For high-quality compaction of sand, it is watered with water. In the case of heaving soil (when clay, silt, peat are present), it must be protected from swelling. Therefore, they moisturize the sand not directly in the trench, but separately, before laying.
3. Having fallen asleep with a trench, sand from above is carefully leveled and densely packed.

Now you can begin the construction of the foundation.

Mixed bedding

Arranging a pillow under the foundation, it is forbidden to use fine sand. If the soil of the site on which the building is being built is weakly bearing, builders recommend organizing the filling by mixing coarse sand with crushed stone. Such a pillow can support the weight of a wooden house or medium-sized frame without tamping. In addition, it gives a completely invisible shrinkage at the end of the installation. If a large heavy house is planned, then it’s better to compact the foundation pillow.

Gravel bedding

Such a pillow for the foundation of the structure is much stronger than sand bedding. It is based on gravel. But first prepare a layer of coarse sand. How to make a pillow under the foundation using gravel:

1. The sand is laid in a layer of about 10-15 centimeters, and then leveled and rammed.
2. Gravel is poured over a layer of sand, the thickness of which is from 20 to 25 centimeters. It is carefully leveled and rammed with a vibrating plate.
3. Add more gravel to the same thickness. Tamped again. The topmost layer of gravel reaches zero. It is with her that the foundation of the structure begins.

According to the standards, a gravel pillow is made wider than the foundation by about 30-40 cm. This type of bedding under the foundation is great for any type of country house, regardless of size or number of storeys.

Concrete pillow

Such a foundation under the foundation of the house has high strength. True, its significant disadvantage is the high price. The base in the form of a concrete pillow is arranged in a certain sequence:

• First you need to prepare the soil, which is very carefully leveled. Then a layer of rubble is laid on it. Moreover, its thickness is maintained about 10 centimeters. It is necessary to compact crushed stone well, using a vibrating plate.
• After that, formwork should be erected around the entire perimeter of the foundation pillow. It can be made from boards. At the same time, the height of the formwork is maintained equal to the thickness of the planned concrete base. The highest level of the base should go to the mark from which the foundation itself is then erected.

• Reinforcing pillows is highly desirable. This will give it greater strength, make it more resistant to destruction. Reinforcement is performed using steel rods, the diameter of which is 0.8-1.2 cm.
• The next step is to fill the formwork with concrete. A suitable brand of concrete is selected based on the pressure that the future construction will exert.
• To compact fresh concrete, the entire foundation pillow should be tamped. A construction tool - a deep vibrator can help with this.

Of course, such a pillow made of concrete will be very strong and durable. It can be used even for the heaviest houses with several floors.

Additive for the foundation of the strip foundation

For massive buildings made of brick or concrete, a recessed strip foundation is used. Its base is located on soils lying below the level of freezing. Therefore, they are resistant to frost heaving. Another way to counter ground vibrations is to build a strip foundation with shallow penetration into the ground. At the same time, the technology provides for a sand cushion under the strip foundation.

When the sand is protected from getting wet, it compensates for the movement of freezing soils. The load of the building on the foundation is distributed evenly. The thickness of the pillow with a foundation width of up to three meters is maintained up to 0.6 m. With heaving of the soil, the thickness increases to 0.8 m. Do not forget that the width of the bed increases - 10-15 cm are added to the foundation on both sides.

When erecting a strip foundation, a pillow under it can serve not only sand, but also crushed stone. Lay it in the same manner as described above. To strengthen the foundation, reinforcement is used. Creating a pillow is one of the main processes in the construction of buildings and structures.

Careful adherence to technology is a guarantee of long-term damage and destruction.