One of the important issues at the design stage of the house is the calculation of the foundation. The durability and reliability of the construction will depend on how well it is made. When calculating it, the type of construction, the material of the future home, soil features, climatic conditions are taken into account.
The most reliable way is to entrust the calculation of the foundation (for a house with three floors) to the design company. However, if the construction is planned no higher than two floors, then it is completely possible to make the project yourself.
How to choose the foundation for the house?
There are several types of foundations that are used in private construction. They depend on what material the house will be made of, as well as on the type of soil in the area. The material of the structure determines its weight. The larger it is, the stronger the foundation should be.
In addition to the weight of the house, the bearing capacity of the soil is a decisive factor. The higher its density, the greater the load it can carry without deformation. Therefore, the determination of the type of soil will help to correctly approach the choice of construction and foundation material. Soil properties such as graininess, mobility, and moisture are also taken into account.
The third factor affecting the type of foundation will be climatic conditions. They are associated with seasonal loads of snow on the roof, which increase the mass of the house, as well as the depth of freezing. It depends on the latter which design, as well as the amount of penetration should be applied.
How does the foundation depend on the soil?
Before starting the calculation of the foundation of the house, a soil study is carried out. Its purpose is to determine the maximum load that can be applied to a unit area. The degree of heaving is also considered. This indicator indicates how much the foundation will be pushed out of the ground as the soil freezes. Also - the higher this indicator, the longer the shrinkage will take place. Some types of foundations can not be used on moving soils. Wrong choice will lead to the destruction of the house.
Soil types
The following types of soils are available:
- Rocky and rocky soil. These varieties are the most durable. They are able to withstand any load with minimal shrinkage and are not subject to heaving due to the lack of water in them. Ideal for laying any type of foundation.
- Cartilaginous soils. They consist of a combination of sandstone, stones and clay. Water also does not linger in this type of soil, therefore, heaving does not occur in winter.
- Sandy soil. Well suited for construction. They do not accumulate excess moisture in themselves, but they freeze in winter to a depth of 1 meter, depending on the region.
- Clay. Accumulates moisture and is poorly released from it. Therefore, it greatly freezes in the winter. When calculating the cost of the foundation, you need to lay the additional costs of a sand cushion under the base. Excess water will be discharged through it. If this is not done, then the bottom of the foundation will become wet, and when freezing, the concrete will begin to collapse. Clay soil freezing reaches 1.5 meters.
- Loam and sandy loam. This is a kind of mixture of sand and clay. Depending on the ratio of clay to sand, the soil can both retain moisture inside and pass it through itself. Therefore, how strong the hell will be in this case, you need to look at the ratio, as well as how cold winters are in this climate zone.
- Peatlands and marshy soils. The calculation of foundations for this category begins with a mandatory geodetic survey. Such soils are characterized by close occurrence of water and have a low bearing capacity. In addition, they are heterogeneous, which increases construction risks. During the construction of the foundation , a lot of additional work is carried out in the form of soil compaction with the partial replacement of peat with sand filling, the arrangement of drainage slots. The most justified on such soils is the construction of monolithic tile, as well as pile foundations.
Pile foundations
This variety of foundations is used for various purposes. Piles are used for the construction of light frame houses. There is no big load on the foundation, therefore, along the perimeter of the future home and on the site of wall partitions, poles are screwed into the ground, which will serve as the basis.
Another option in which piles are used is construction on moving soils. For example, in swampy soils. It uses reinforced concrete piles, which are driven into the ground by the method of clogging or vibration dipping to more stable and durable layers.
How to calculate the pile foundation?
When calculating the pile foundation, the cross section of the piles, the step between them, and their length are determined. Of these three components, only a section is known in advance. The remaining indicators are calculated based on the following parameters:
- Load on grillage. This parameter includes the total weight of all possible loads, including the weight of the house, furniture, equipment, snow load, living people.
- The load on a separate pile. It will depend on the bearing capacity of one element without its destruction.
The weight that will fall on one element of the pile foundation can be found by the formula:
P = (0.7 • R • S) + (u • 0.8 • fin • li), where:
- P - permissible load, which will fall on one pile;
- R is the strength of the soil, which is determined after a geodetic study;
- S is the cross-sectional area of that part of the pile, which it rests on the ground;
- u is the perimeter of the pile itself (found by the formula for the circumference);
- fin is the friction force that arises from the side of the pile walls (taken from tabular data);
- li is the thickness of the soil layer onto which the pile will be twisted (selected from the table, depending on the bearing capacity of the soil);
- 0.8 is a coefficient.
After the possible load on one pile is calculated, knowing the total value of the weight of the house, you can determine the required number of piles and the step between them: l = P / Q, where Q is the weight of the structure per meter of foundation.
How to determine the weight of the house?
Before making the calculation of the foundation of any type, the total weight of the house is determined. Knowing its design and the materials of which it consists, it is possible to calculate the mass using the following table.
Element of structure and material of manufacture | Specific Weight (kg / sq.m) |
1 brick thick brick wall | 684 |
1.5 brick thick brick wall | 918 |
Wooden wall 200 mm | 100 |
Wooden wall 300 mm | 150 |
Wall of a frame house with a thickness of insulation up to 150 mm | 30-50 |
Plasterboard walls 80mm | 27,2 |
Walls of insulated drywall 80 mm | 33,4 |
Wooden ceiling with insulation | 100-150 |
Reinforced concrete floors with a thickness of 220 mm | 500 |
Roofing cake coated with the following materials | Specific Weight (kg / sq.m) |
Decking and metal tile | 60 |
Shingles | 70 |
Ceramic tile | 120 |
Loads of equipment, furniture and people | 150 |
Snow load | Depends on the geometry of the roof, material, region. |
Column concrete foundation
The main material for the construction of the foundation is concrete. It allows you to make the foundation in the form of pillars cast in the ground. Before pouring, a hole is drilled in the ground. Then, a frame made of steel reinforcement is installed in it and poured with concrete. Above ground level, formwork of the required height is made. Several similar pillars are installed under the building in increments of 1.5–2 meters. Such a foundation is used on stable soils that are not prone to heaving.
Strip foundation
This variety is in turn divided into deep and shallow foundation. The difference between them is that the first is used for houses of large weight, as well as in cold regions, where there is a large depth of freezing of the soil. A shallow version can be used for low-rise buildings, as well as on high strength soils. It is not recommended to use on sandstones and loams. It may crack due to uneven shrinkage. The calculation of the strip foundation is carried out depending on its occurrence. Shallow is at a depth of 0.5-0.7 meters. The deep-seated tape is below the freezing depth.
Monolithic foundation
This foundation is made in the form of a solid plate, which is cast on top of a sand cushion. Such a variety may be the only construction option on unstable soils. In addition, the monolith is not subject to heaving. The only thing to observe is the perfectly leveled surface onto which the sand base is poured. If this is not done, then over time the pillow along with the house will begin to slide down.
Calculation of the foundation of the house: step by step instructions
First you need to find out what parameters need to be calculated. Firstly, it is the width (for the strip foundation), the number of piles (for the pile foundation). Secondly, the amount of concrete required for pouring.
For example, we take the calculation of the strip foundation and determine: will the planned width of the tape allow the weight of the house to be supported? To do this, you need:
- Find the perimeter of the foundation. Fold all sides of the house and add the length of the internal load-bearing walls.
- We make the calculation of concrete on the foundation: multiply the resulting value by the width and height. So we find the necessary volume.
- We multiply the volume by 2500 (specific gravity of concrete). The result is the weight of the concrete structure.
- We perform the calculation of reinforcement for the foundation and add the result to the previous one.
- The weight of the house is added to the obtained value, then the result is divided by the area of the foundation. So is the pressure that the building will exert per unit area.
- Then, according to the table with the characteristics, it is checked whether your soil type can withstand such a load. If not, the width increases and the foundation calculation is done again.
After determining the required volume of concrete, the cost of work and materials is calculated. The calculation of the cost of the foundation depends on the market price of the concrete grade that is required for the construction, on the required amount of reinforcement, as well as transportation costs for the delivery of materials to the construction site.
How much reinforcement is needed for the foundation
Concrete structures significantly increase their bending strength if a metal frame is used inside. Depending on the type of foundation, rods of different diameters are used. When calculating the reinforcement for the foundation, the weight of the house is taken into account. Dense soils reduce the deformation of concrete under the weight of the structure, which affects the reduction in the number of reinforcement.
For strip foundations, rods with a diameter of 10–16 mm are used. They are laid in the formwork with a step of 10-15 cm and are connected to each other by transverse rods, which are fastened with knitting wire. Since the foundation experiences a transverse load, the main impact falls on the longitudinal bars of the reinforcement. In this regard, transverse reinforcement can be used with a smaller diameter.
For monolithic tile foundations, thin reinforcement of 10 mm or reinforcing mesh is used. If the plate is run on unstable soil or the weight of the house is large, then the diameter of the rods increases. The caracas is made in the form of a grid with a pitch of 20 cm. If high strength of the plate is not required, then reinforcing bars can be replaced with a grid.