As the main problem of choosing the type of foundation during the construction of facilities for various purposes, soil indicators, or rather its ability to expand, are made. These soils include: fine and silty sands, loams, sandy loam and clay soils.
They increase in volume during freezing, which causes the rise of layers of the earth at a depth of freezing of the soil. If buoyant loads are not balanced by the load from the building or in a constructive way, then point deformations will lead to the destruction of the building.
This problem is most often solved by the construction of a bearing underground part at or below the freezing depth of the soil. However, for light buildings, this option is not an option, since the lateral surface of the recessed bases contributes to the increase in tangential forces from heaving. Even if you choose the most expensive option for the foundation, it will not guarantee one hundred percent quality, so today houses are increasingly being erected on shallow grounds.
Device features
The use of shallow foundations provides for their location at a depth of 40 to 90 cm. This saves construction and labor resources. Such bases do not include a large amount of concrete and a thick layer of rubble. The cost of erecting a foundation of this type is reduced by 3 times.
The shallow foundation construction consists of:
- a cutoff;
- soles;
- the sides.
The first node is the top that takes over the load. Bottom is the sole, it transfers the load. The vertical parts of the base are the sides that form the foundation wall.
Such designs are used:
- in the construction of wooden houses;
- for small brick buildings;
- when laying houses from light materials in low-rise construction;
- with low groundwater passage;
- when building a house with a small basement.
The main varieties of shallow foundation
When considering the types of shallow foundations, you should pay attention to the most common of them, namely - tape. It is popular among individual developers who will commission work on their own. Tape bases for wooden and heavier stone structures are used.
This design is a continuous strip of concrete, which is evenly loaded with walls. To date, several varieties of tape shallow foundation are known. He can be:
- reinforced concrete;
- block with the lower or upper arrangement of reinforcement;
- monolithic;
- national teams;
- Capless with two reinforcing belts.
Sometimes reinforced concrete block tape foundations of shallow laying have a reinforcing belt not only from below, but also from above. When prefabricated monolithic structures are being erected, they are supplied with reinforcement outlets. Among the types of foundation for shallow laying, a columnar base should be distinguished, which can be used in the construction of the following houses:
- brick;
- lumber;
- wooden;
- stone.
This design consists of pillars installed at every corner of the house, as well as in those places where the outer and inner walls are connected. The distance between the supports should not be more than 2 m.
A foundation pit is prepared to arrange a shallow foundation of a columnar type, the depth of which is about 1 m. Reinforced concrete rings are laid in it, which are compacted with sand and covered with concrete slabs. They are installed grillage.
Description of slab and monolithic foundations
The slab foundation is a reinforced concrete structure, the thickness of which is equal to the limit of 20 to 30 cm. A building is being erected from above. This design is similar to tape. The main difference is the rigid reinforcement of the entire plane, while the plate absorbs any load during soil movement.
The shallow foundation may be monolithic. It is the most reliable and can be used on any type of soil. As an exception, plots with slopes appear. The disadvantage of this reason is the high cost of labor and funds, as well as the laborious preparatory process.
Settlement
Calculation of the foundation of shallow laying is necessary in order to determine the geometric dimensions and choose the type of base. In the process, you must find out what is the pressure of the building on the soil, determine the strength of the frame of the structure and calculate the strength of the soil pressure during frost heaving. The load from the building is the sum of all the loads. In a simplified calculation, this is the mass of a building distributed per square meter of the bottom plane.
To calculate the mass of the building, you should use a project that mentions the size of the building and its features. It is determined taking into account the winter snow load. To do this, calculate the mass of the structural parts of the building, add them and divide by the area of the base of the foundation.
Calculation Recommendations
For a certain type of soil, the specific design resistance R 0 is determined, and then it is compared with the specific load N. If the first value is less than the second, then the dimensions and shape of the foundation should be reviewed. It is made with a wider sole or expanded from the bottom, increasing the width.
After calculating the shallow foundation for a brick one-story house with dimensions of 10 x 8 m, you will receive: N = 23 t / m 2 . In this case, when building the walls, a solid red brick was used, the width of which is 0.4 m.
The floor is reinforced concrete, and the ceiling is wooden. The roof structure is gable, it has a coating in the form of corrugated board. Construction is underway on heavy loamy soil in the Moscow region.
Design work procedure
During design work, the first step is to evaluate the soil. In this case, it is important to find out at what depth and with what concentration the soil water lies. The following geological changes may affect soil deformation:
- floods;
- landslides;
- earthquakes.
When changing seasons, the soil can undergo a transformation. At the first stage of studying the characteristics of the site, it is necessary to find out the chemical composition of the soil. Next, the design of the building is studied. Foundation design is related to the form and type of construction. You must find out the layout, size of the building and the number of floors, this includes underground.
The form of operation and structural stability will influence the choice of the type of shallow foundation . The design of shallow foundations involves the calculation of loads. In this case, the coefficient and the level of load on the base, which are calculated separately for each structural element, are taken into account. These data are summarized in a common indicator.
It is important to determine the rough dimensions of the foundation. Intermediate dimensions as well as technical specifications are calculated. Data for this must be taken, referring to the geology of the soil, the purpose of construction and the method of future construction.
The next step will be to optimize the size of the foundation for shrinkage. At this stage, it is necessary to carry out calculations for the parameters and dimensions of the building, taking into account the actual loads. Now you can find out the degree of settlement of the shallow foundation. The data obtained are compared with the norms of possible structural deformation.
If necessary, changes are made to the size and shape of the building. This data may be adjusted. As one of the last stages are verification calculations. In this case, the strength of the base and the stability of the building are determined. Changes may be made to the design that are justified in terms of the likelihood of deformations. After the final calculations for the design, schemes and drawings are developed with the necessary data.
The main varieties of shallow strip foundation
If there is continental soil on the territory, which was formed during natural tamping, then on such soil it is best to erect a strip foundation. It is suitable for buildings made of the following materials:
- concrete small blocks;
- samana;
- a brick.
The main advantage is the simplicity of design. Shallow foundation tape can be classified by material. The construction can be carried out from:
- brick;
- concrete;
- concrete;
- buta.
For the erection of the latter type of foundation, rubble stones are laid using cement mortar. Such bases are the most labor intensive and have the largest mass. The traditional height of the rubble base varies from 55 to 65 cm.
The scope of use are cabins and small country houses. For a concrete base strip, mortars of lime and cement or only cement are used. The mass is poured onto the base of rubble stones, bricks, gravel or rubble.
Strip foundation device
The shallow foundation strip is built on the prepared site. It is leveled and cleaned of vegetation. The territory is marked. Attention should be paid to the internal and external corners. According to the marking, digging a pit is carried out. The bottom of the future foundation is leveled. The depth of the structure can vary from 30 to 120 cm.
If necessary, fasteners are installed on the side walls. These elements are:
- mortgage bonds;
- sheet pile;
- in the form of a pillow.
Using Mounts
Mortgage fasteners are vertical racks that are used to fix the foundation walls. Racks can be made of wooden boards or beams. Mortgages are used when arranging pits with inclined walls. Of the tongue-and-groove bundles, the fastening of the same name is made, which can be made of metal, wood or reinforced concrete.
The tongue-and-groove fastening has found its distribution in those territories where the soil is located above the bottom of the pit. At the next stage of the work, the bottom of the pit is covered with a sand cushion. If the soil is sandy, then it is poured with a layer of concrete up to 150 mm thick. The material is sealed using equipment.
Formwork installation
Now you can proceed with the installation of wooden formwork. To improve the hardening of concrete, a film can be laid or waterproofed with resin. The foundations of shallow laying of the tape type are reinforced with rods with a cross section of 1 cm. Elements are laid from one corner to another. Joints are connected by clamps.
With additional reinforcement of corners, rods are used, which allows to increase the strength of the foundation. If the base is brick or rubble, then an additional layer of backfill should be laid.
Pouring
Another step will be the filling of the formwork. For this, concrete of the M200 brand is used. Filling should be carried out in several approaches, forming layers up to 20 cm for better solidification. Before pouring the foundation of shallow laying, the inner surface of the formwork must be moistened with water so that moisture from concrete is not absorbed into the boards.
Features of the device shallow shallow foundation
Before proceeding with the construction of the slab foundation, it is necessary to prepare the base. It is leveled, marking is carried out in the territory. Then remove the topsoil and build a drainage if the soil is wet. To do this, dig trenches and install plastic pipes, which are covered with geotextile on top.
Thermal insulation and filling
The foundation is recommended to be insulated. You can use polystyrene for this, which is stacked on all sides of the structure. At the next stage, a pillow of sand or gravel is laid. It is well compacted and watered with water for greater compaction. The thickness of the pillow can reach 20 cm. Styrofoam is placed on top of it. If the slab is planned to be built in place, then the formwork should be installed. For this, a beam is usually used, the width of which will be equal to the width of the formwork. Its elements are fixed, closed with a waterproofing film, and then the interior is filled with concrete.