During the construction of a building, it is important to correctly select the types of main supporting structures. This will reduce the complexity of the work, financial costs and construction time. One of the types of construction that can simplify the process of building a building is a shallow strip foundation. During its construction, you need to take into account a large number of nuances, but with technology and proper selection, you can significantly save.
Application area
This type of tape has a fairly limited area of use. Do not dig deep into the foundations if:
- it is planned to build a building from light materials (wood, aerated concrete);
- the site has a high level of groundwater;
- the characteristics of the base soil are quite good, the soil has high strength characteristics.
When building a frame house or a house from aerated concrete, a shallow strip foundation is the best option. It will reduce the amount of earthwork and increase the speed of construction. It is possible to make such a design without carrying out additional measures to remove water from the site with the location of groundwater at a distance of 1 meter or more from the surface of the earth. For a recessed tape, this value is much higher (50 cm more than the sole).
The shallow strip foundation is suitable for conditionally non-porous soils and non-porous soils, which include:
- rock formations;
- coarse-grained bases (including with dusty filling);
- large and medium gravelly sands;
- clay soils of solid consistency with natural moisture.
It is possible to determine the composition of the soil on the site using a pit hole or the manual drilling method. In determining the type of soil will help GOST "Soils. Classification".
Types of foundation
The shallow foundation has two classifications. The first depends on the manufacturing method:
- monolithic;
- made.
A shallow tape foundation is best done using monolithic technology, because in this case you will not have to worry about ensuring the joint operation of the tape. During the construction of a prefabricated structure for a house made of aerated concrete, it will be necessary to additionally provide for a monolithic belt, so that monolithic work cannot be avoided in any case.
Depending on the type of section emit:
- rectangular;
- t-shaped.
Rectangular foundations have a lower bearing capacity, therefore they are more often used for the construction of frame houses. For the construction of a house from heavier aerated concrete, it will be correct to make a choice in favor of a T-shaped section.
This type differs from the rectangular one by the presence of a broadened base, which allows to significantly increase its bearing capacity even with a shallow depth of laying. The shallow foundation in this case consists of a tape located horizontally (cushion) and a vertical part.
Foundation depth
In order to correctly design the support for the building, it is necessary to choose the depth of laying. For this type of tape, it will be practically higher than the depth of soil freezing over almost the entire territory of the country, which increases the risk of structural damage due to frost heaving.
Frosty heaving is a phenomenon when water in the soil freezes and increases in volume. In this case, the foundation tape is deformed and subjected to additional loads. The design begins to go cracks. That is why it was said above that a shallow foundation is mainly used for non-porous soils.
The depth of laying is determined depending on the freezing, which is calculated according to SN "Foundations and Foundations" or is according to the tables. Minimum Depth:
- when freezing to a depth of less than 2 m - 50 cm;
- when freezing less than 3m - 75cm;
- when freezing more than 3 m - 100 cm.
It is also important to consider the location of groundwater. If the water is closer than 2 measures from the estimated elevation of the sole, and on the soils in the area are clay, loam, sandy loam, fine or dusty sands, it will be correct to opt for a buried foundation with a drainage system.
Regulatory documents also prescribe the choice of the depth of foundation of a house from aerated concrete not less than ½ of freezing for clay and loam with a deep arrangement of water.
This is caused by increased heaving of this type of soil.
Security methods
Before you build a shallow strip foundation with your own hands, you need to familiarize yourself with the technology of protecting it from negative external influences. Frosty heaving is caused by two factors:
- high humidity;
- low temperatures.
To avoid this phenomenon, measures are taken to protect against these negative influences:
- Thermal insulation of a house from aerated concrete at the entire height of the laying. It is carried out using extruded polystyrene foam. Proper use of this particular material, the use of foam or mineral wool is highly not recommended.
- Additional insulation of the foundation due to the warm blind area of the house. It can be made of concrete or asphalt concrete. By laying a heat-insulating layer under the material. As a heater, extruded polystyrene foam or expanded clay gravel is used. The thickness of polystyrene for most regions will be 100-150 mm, the thickness of the expanded clay layer is taken in the region of 30-50 cm.
- Vertical waterproofing. The layer is provided for insulation. It is made of bituminous rolled materials or mastic.
- Water drainage from the foundation. To do this, you need a device for stormwater (from rainwater) and drainage (from underground moisture). Drainage pipes are placed 30-50 cm below the sole of the tape and at a distance of not more than 1 m.
- Sand preparation device 30-50 cm thick. Coarse or medium sand is non-porous material. Replacing part of the soil with it allows you to increase the reliability of the base.
The implementation of all these measures will reduce the likelihood of structural damage to the house from aerated concrete by frost heaving in the winter.
Manufacturing technology
It is not much different from performing work on a buried tape. The shallow strip foundation is constructed in the following order:
- Marking of the terrain is carried out and a trench or foundation pit of the required size is excavated.
- Sand preparation is arranged (mentioned earlier). When laying, it is necessary to provide layer-by-layer compaction of the layer (by vibration, spilling or weights).
- Formwork is installed. For the type of foundation under consideration, the most optimal option is foam. After pouring, no additional insulation work is required. Can be used as a formwork board.
- Reinforcement of the structure. For private houses, reinforcement can be performed without preliminary calculations. Reinforcement in construction is of three types: longitudinal working, constructive horizontal, constructive vertical. Structural reinforcement plays the role of a link between the working rods. The minimum diameter of the rods is 8 mm. Working reinforcement with a diameter of 12-16 mm is laid in two rows: upper and lower. The total cross section of the working rods of the house of aerated concrete or wood should be equal to approximately 0.1% of the cross section of the foundation.
- Pouring concrete mixture. It is carried out in one step. If absolutely necessary, you can do it in layers, but this is undesirable. For foundation work, concrete B15-B25 is used depending on the load.
- Vibrating concrete for compaction.
- Set concrete strength and care for it.
- Formwork removal (if necessary).
- Waterproofing the foundation.
- Warming (if necessary).
- Backfilling.
- Blind device.
To make a reliable foundation, it is necessary to carefully consider each stage of the work: correctly select the laying depth, reinforcement, concrete grade, and carry out all necessary protective measures.