The foundation of any building is the foundation. Construction work begins with it. The strip foundation has found wide application in the construction of private houses and industrial buildings. It is let down under structures with heavy walls or ceilings. The depth of the laying of the strip foundation is calculated in advance, before the start of the main construction. It depends on a number of conditions.
Depth determination
The depth of the foundation tape is the distance from the bottom point of the foundation surface to the surface of the earth. The section is a trapezoid or rectangle. This value is calculated. To calculate it, certain knowledge is required - engineering, geological. High-quality and reliable project of the future building, taking into account all the nuances, can only be done by a specialist.
What depth of laying the strip foundation is required in each particular case can be accurately determined by a number of indicators. For all types of substrates, no matter what material it is made of, they are always taken into account.
Depends on the depth of the laying of the strip foundation. The main provisions that are taken into account when designing:
- type and characteristics of soil;
- base load (construction weight);
- soil freezing depth;
- heaving, or the property of the soil to change its volume indicators depending on the ambient temperature;
- structural features (basement, number of floors);
- groundwater level indicators.
Classification by type
A strip foundation is a continuous strip of durable material (mainly reinforced concrete) running along the perimeter of the entire structure. Lay it under all internal and external capital walls. They do this in such a way that the base of the foundation is at least 10 cm wider than the walls themselves.
They are of two types: monolithic and prefabricated, but both are called "strip foundation". Depth is calculated for both species. Monolithic require more time for installation, but they can protect the basement well from moisture and simulate any configuration of the foundation. For the manufacture of this design using concrete.
To equip a prefabricated tape base, reinforced concrete or concrete blocks of standard sizes are taken. The depth of the lower layer of blocks should be at least 15 centimeters below the depth of freezing of the soil. Such a foundation is being built:
- for subsequent construction of walls of stone, concrete or brick with a density above 1300 kg / m 3 ;
- for the construction of heavy structures and powerful reinforced concrete floors on it;
- if the walls of the precast foundation are used for a basement or basement;
- if the foundation is laid in heterogeneous soil.
Depth classification
There are foundations and the depth of the foundation:
- Shallow is used under light houses on loosely soiled soils. The depth of the laying of the strip foundation of this type ranges from 50 to 70 centimeters.
- In-ground is used in the construction of houses on several floors, with heavy walls or with a basement on heaving soil. Such a foundation is laid to a depth of 20 cm to 30 centimeters below the level of soil freezing. This type of foundation is certainly more reliable and does not undergo deformation. Accordingly, its service life is much longer than that of a shallow base.
Properly calculated depth of the foundation will allow it to last up to 70 years without any repair. Above the surface of the earth, the base should rise no less than 30 centimeters. This part can be made of brick, stone or concrete blocks.
Advantages and disadvantages
Each type of strip foundation has some advantages:
- durable;
- reliable;
- any configuration is possible.
- easy to assemble;
- reduce the time of manufacture of the base.
The disadvantages of all types of strip foundations are:
- a large amount of time for the production of all necessary work;
- the complexity of the process;
- require significant investment.
The base of reinforced concrete blocks is less practical. It is mainly suitable for buildings of simple shapes (with a complex configuration of the structure it will be necessary to cut blocks) and can pass water at joints.
Whatever type of strip foundation is used for the construction of the building, it requires careful calculation of the depth of arrangement of the foundation.
Soil dependency
The type of soil layer is of great importance in calculating the depth of the foundation. This indicator is related to the level of groundwater , how the strip foundation will be arranged depends on their ratio. Depth of laying varies depending on the composition of the soil itself. This relationship can be seen in the table:
Groundwater depth during freezing | Depth of laying for buildings in 2 floors | Priming |
Irrelevant | Regardless of freezing ground | Rock, large, clastic |
Irrelevant | Regardless of the level of freezing of the soil, but not less than 50 cm | Large and medium sands |
More than 200 cm below freezing | More than 200 cm below freezing | Fine, dusty sands |
Exceeding the calculation of the depth of freezing by less than 200 cm | Not less than 70 cm | Sandy loam |
Less than the estimated freezing limit | Not less than the estimated level of freezing | Loamy and clayey soils |
Soil freezing
An important indicator that determines what the depth of the laying of the strip foundation is needed is the freezing of the soil. Due to such a physical phenomenon as an increase in the volume of moisture during cooling, the depth of freezing should be known exactly. In winter, the moisture contained in the soil freezes, begins to increase in volume. The soil “hesitates” and pushes to the surface any structure immersed in it.
It is impossible to neglect this phenomenon. The power of freezing water is too great (remember how easy the ice breaks pipes). This movement of soil can lead to destruction of the base.
Moreover, the quality of the soil itself also matters, as evidenced by the data given in the table.
Estimated values of soil freezing of semi-solid and hard rock (with slightly pronounced heaving) | Depth of Least Foundation | Estimated value of soil freezing (conditionally not heaving) |
from 250 cm to 350 cm | 150 cm | |
from 150 cm to 250 cm | 100 cm | more than 300 cm |
no more than 150 cm | 75 cm | no more than 300 cm |
no more than 100 cm | 50 cm | no more than 200 cm |
With a high heaving index of the soil, the strip foundation must be necessarily monolithic. The depth of freezing depends on the climatic conditions of the area, its geographical location. For each individual terrain, it is necessary to carry out calculations of the depth of the foundation based on the average annual temperature indicators.
Neglect of this rule can lead to deformation of the walls and destruction of the building as a whole.
Ground water
Practice shows that the indication of the level of standing (annual average) of groundwater can seriously adjust the calculation of the height of the foundation of the strip foundation. If in winter groundwater does not rise above 2 meters to the level of (extreme) freezing of the soil, then the level of freezing of the soil is neglected.
Otherwise, the foundation is always laid lower than the level of freezing of the soil, by 20-30 centimeters. Due to the proximity of water, the soil will be moist and at low temperatures (frost) will become very agitated.
Depth under the house
The foundation under the house, apart from all other conditions, must take into account the structure of the building itself. If it has a basement, then the depth of the laying of the strip foundation under the house is arranged 40 centimeters lower than the level of the basement floor. In this case, the level of freezing of the soil (in this case, the sole of the base should be lower), as well as the level of standing of groundwater (the base of the base should be higher), must be taken into account.
On a suitable ground and without a basement, a foundation is built at a depth much less - up to 70 centimeters. In moist soils, the minimum depth is 120 centimeters.
Outbuildings
Detached buildings on a suburban area require no less attention than a residential building. When erecting small and light buildings, the depth of laying the strip foundation is also important. For a bath, it can be made to a depth of 50 to 70 centimeters. This is enough to support the weight of a wooden building.
For reliable operation of utility rooms, not only the weight of the structure is taken into account. Take into account all other indicators that affect the calculation of the depth of the foundation of the strip foundation.
Similar calculations for the arrangement of the foundation are recommended for other household structures: a barn, a workshop, a garage, a chicken coop or a barn for keeping animals.
Depth and types of laying under a brick fence
The depth of the laying of the strip foundation under the brick fence should correspond to the weight of the proposed fence. If construction is supposed to be entirely made of brick, then the calculation of the very depth of the foundation is carried out in the same way as under the construction of a conventional building.
A completely brick fence - the pleasure is very expensive. Most often, pillars are made of brick, and a cheaper fence is installed between them. There are two options for arranging the foundation for this type of fence :
- tape around the perimeter;
- columnar - only under brick pillars.
The column foundation also requires compliance with certain rules, all recommendations regarding heaving soil are applicable to it, its depth should be below the freezing point of the soil.
Modern technologies
Modern technologies and the quality of the material (reinforced concrete) allow even shallow foundations to be applied even on problem soils. This significantly reduces both the time of construction of buildings and their cost (the foundation of the structure can cost 25% of the cost of a house).
Subject to certain rules, a shallow strip foundation can be laid at a depth of only 50 cm, even on heaving soils. Mandatory conditions are:
- the use of reinforced concrete for a monolithic base of the M200 or M300 brand;
- in the trench, under the foundation tape, heat insulation (expanded polystyrene plates) is necessarily laid and non-fluffy materials are poured;
- tamping and leveling the drainage cushion of sand and gravel with a thickness of at least 2 cm;
- the lateral area of the base is waterproofed and insulated (with polystyrene plates);
- the cavities are covered with any non-porous material (a mixture of gravel and sand, sand, gravel).
Such technologies are widely and successfully used in the construction of buildings in the United States and some European countries. Many years of experience confirm the possibility of significant savings in construction work when laying the foundation.