When construction is planned on a site with clay soil, it must be borne in mind that its level may differ in winter and summer, it may settle or, conversely, swell. The fact is that when freezing, it increases in volume. Heaving creates water in its composition. Loams, gravel and sandy soils, consisting of small and dusty grains of sand, 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, large gaps appear. In addition, windows and doors stop opening and can collapse over time. To avoid such troubles, they arrange a pillow under the foundation.
Types of bedding
Cushion for the foundation of a structure is an important structural element in the construction of a building. Its application is necessaryfor 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.
The pillow under the foundation is its basis, counteracts the force of heaving, helps eliminate the negative impact of seasonal fluctuations in the ground level, prevents displacement and rupture of the foundation, the occurrence of cracks on the walls and their destruction.
Depending on the types of buildings under construction, pillows under their bases can be from:
- sand;
- rubble;
- concrete.
Each of these materials has certain properties and characteristics that must be considered when building a foundation. In addition, the choice directly depends on the level of groundwater. After all, it is water, as was said, that is the cause of the heaving of the soil.
Soil type and sand layer quality
The main function of the sand base is to smooth out seasonal fluctuations in the level of the soil, which have an uneven load on the foundation of the building. Different types of soil have different bearing capacity. Dry sandy soils can form a solid foundation for buildings. It's also the most economical option.
Sand cushion prevents heat loss through the foundation. But! Sand must be chosen correctly. Fine holds water well, so only 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 falling asleep insteadit is the foundation for the foundation (in this case, a layer of sand), and tamped well.
Choosing the thickness and width of the pillow
Based on the strength of the structure's pressure on the ground, 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 in the range of 20-60 cm. If the building is light, of a frame type, with walls made of timber or a log cabin, then a sand cushion under the foundation is arranged to a shallow depth of 30-40 cm. For the construction of a brick house, the pillow is made thicker. Especially if it's 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 to a width of 50-60 cm. If you plan to organize wall drainage, then you should add the distance intended for laying drainage pipes. It depends on their diameter. Accordingly, the sand cushion will become wider by this amount.
Pillow under foundation
Consider the case when coarse and medium sand is used with mandatory moistening and layer-by-layer compaction:
- Dig a trench according to the calculated dimensions. Its walls must be lined with a geotextile film so as not to clog the sand and prevent the pillow from silting.
- For high-quality compaction of sand, it is poured with water. Whenheaving soil (when clay, silt, peat are present), it must be protected from swelling. Therefore, the sand is not moistened directly in the trench, but separately, before laying.
- By filling the trench, the sand is carefully leveled from above and compacted tightly.
Now you can start building the foundation.
Mixed bedding
When placing 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, the builders recommend organizing backfilling by mixing coarse sand with crushed stone. Such a pillow can withstand the weight of a medium-sized wooden house or frame without tamping. In addition, it gives a completely imperceptible shrinkage at the end of the installation. If a large heavy house is planned, then it is still better to compact the foundation pillow well.
Gravel bedding
Such a pillow for the foundation of a building is much stronger than sand bedding. It is based on gravel. But first, a layer of coarse sand is prepared. How to make a pillow under the foundation using gravel:
- Sand is laid in a layer of about 10-15 centimeters, and then leveled and compacted.
- 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.
- Add more gravel to the same thickness. They ram again. The topmost layer of gravel goes to the zero level mark. It is from her that the very foundation of the structure begins.
According to the regulations, the gravel pillow is made widerfoundation by about 30-40 cm. This type of bedding for the foundation is great for any type of country house, regardless of size or number of storeys.
Concrete pillow
Such a foundation for the foundation of a house has high strength. True, its significant drawback 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. Crushed stone should be well compacted using a vibrating plate.
- After that, formwork should be erected around the entire perimeter of the foundation cushion. 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 uppermost level of the base should go to the mark, from which the foundation itself is then erected.
- Reinforcement of the pillow 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 mix. The appropriate brand of concrete is chosen based on the pressure that the future construction will exert.
- To compact fresh concrete, the resulting foundation pad should be compacted. A construction tool can help with this - a deep vibrator.
Of course, thisa pillow made of concrete will be very strong and durable. It can be applied even to the heaviest houses with several floors.
Bedding for the base of the strip foundation
For massive buildings made of brick or concrete, a buried 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 resist ground vibrations is the construction of 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 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. When the soil is heaving, the thickness increases to 0.8 m. Do not forget that the width of the bedding increases - 10-15 cm are added to the foundation on both sides.
When erecting a strip foundation, not only sand, but also crushed stone can serve as a pillow under it. Lay it in the same order as described above. Reinforcement is used to strengthen the foundation. Creating a pillow is one of the main processes in the construction of buildings and structures.
Careful observance of technology is a guarantee of no damage and destruction for many years.
