The construction of the foundation costs about 15 – 20% of the estimated cost of the house. It is extremely difficult and expensive to repair an incorrectly made foundation: the costs can reach up to 50% of the money spent on construction. So, compliance with the technology of its construction and the correct choice of the type of foundation is an extremely responsible matter.
Consider the most popular types of foundations currently in construction, their design features, advantages and disadvantages.
Strip foundation.
This type of foundation is performed in the form of tapes deepened by the calculated value into the ground. The foundation is arranged along the perimeter of the house and takes the load from the main load-bearing elements of the house. The tapes redistribute the load from the structure to the “foundation slabs” (distribution pads). This makes it possible to do without special preparatory work and allows you to distribute the load from the walls and columns over a large area of \u200b\u200bground.
The strip foundation is used in houses with load-bearing multi-layer walls or with walls made of brick and reinforced concrete floors in one- and two-story construction of houses with and without a basement. The pressure under the base of the foundation is from 10 t/m2.
Strip foundations have many positive features: high bearing capacity, ease of implementation, the ability to use them as basement walls.
The main disadvantage is that during construction it is necessary to use special construction equipment (dump truck, crane, concrete mixer) to deliver material to the facility and perform installation work.
Pillar foundation.
This type of foundation is an ordinary pillar, which was immersed to the required depth or a special concrete solution was poured into a drilled well. In the upper part, the foundation pillars are connected with special reinforced concrete beams (rand beams).
Column-type foundations can be used for the construction of small cottage-type houses up to 2 floors, built from light materials or wood, with a total volumetric weight not exceeding 1000 kg / m3.
Also, this type of foundation is used in the construction of frame objects and small country houses.
Mandatory condition: soils should not be subjected to temperature deformations.
A positive feature of this type of foundation is its low cost: by reducing the cost of materials and labor, it reduces the cost by 30-40%.
The negative features of the columnar foundation are the problematic reduction of the basement or basement and low strength characteristics.
Tiled foundation.
This is a deep reinforced concrete slab laid on the ground with reinforcements with a diameter of 12 to 25 mm. The thickness of the slab, which is made of VZ25 class concrete, varies from 30 cm to 1 meter. To level the soil, layers of sand or low-power concrete of class B7.5 are placed under the slab. The tiled view of the foundation allows you to redistribute the load over the entire area of \u200b\u200bthe slab and perceive both horizontal and vertical deformations.
If the house has a large length or complex shape, the foundation monolith is cut into separate parts of a small size, creating expansion joints: with them, the parts of the slab will work as a whole, but if the slab is uneven, firstly, there will be no cracks and, secondly , its bearing capacity will not decrease.
The tiled foundation is used on weak soils: quicksand, water-saturated sands, bulk soils, with uneven soil compressibility, etc. It is also typical for the construction of houses above 2 floors with a load under the base of the foundation of more than 20-25 t / m2.
The advantage of such a foundation is that the structure will rest on a single solid slab: this practically eliminates the possibility of deformations and cracks.
Minus one, but significant: the tiled foundation is the most expensive: the cost of materials and installation is very significant.
Weld foundation.
Foundations of this type are made of individual piles or their groups: on top they are united by a concrete or reinforced concrete slab or beam (grillage). Piled foundations are used in cases where it is necessary to transfer significant loads to weak soil or, having passed through weak soil, to support it on a stronger one. It is also advisable to use a pile foundation if weak soils lie at a considerable depth: subsiding soils (capable of significantly subsiding under the influence of the building’s own weight or external loads), loose and sandy, water-saturated sands.
Piles are used mainly for large massive houses with a load on the foundation cut in the range of 15 – 25 t / m2. In private construction, they are used in the form of reinforced concrete or wooden piles of short length – in cases where it is not possible to use another type of foundation. The pile foundation is quite expensive, as it becomes necessary to attract special equipment for transporting and installing piles. A positive feature is the low material consumption and the volume of earthworks.
When laying the foundation, you should not:
abuse piles, because if there is a strong base-soil with a large design resistance, it is better to save time and money by using a conventional strip foundation;
use strip and column foundations in areas that are washed away, on silty, subsiding soils: in such cases it is better to go through the soils with piles and rely on a stronger foundation. On difficult soils, tiled foundations can be used: then the load will be distributed over its entire plane, and the house will stand as if on a large and strong pillow.
So, the tiled foundation is expensive, but it allows you to reduce the cost of replacing or improving the foundation.
The main factors for the correct selection of the type of foundation. (in order of importance)
Engineering and geological situation
To find out which one you have on the site, you need to order special studies. Geologists drill wells, take soil samples, or draw up a report based on the results of previous studies.
These studies objectively show the thickness of the soil layers, the proximity of groundwater and the possibility of their rise in spring, the qualitative characteristics of the soil, its subsidence, and the seismic activity of the construction area. At this stage, it is better not to save money: choose good, well-known specialists in this field with extensive experience in carrying out similar work.
Foundation load. The engineer collects the load on the foundation by calculating the sum of the weight of all structures and payload (people, furniture, equipment) that the foundation should “bear”. The greater the weight, the greater the area of \u200b\u200bthe foundation should be.
However, a very large foundation will make your construction more expensive. Here the main task of the design engineer is to make the most efficient use of the material, the design of the foundation, as well as the characteristics of the soil.
Foundation laying depth and groundwater level
Load from houses that stand nearby
The soil under the erected building can be deformed by other structures: then, by building a house nearby, you increase this load.
Possibility of technogenic accidents During accidents of water communications, a huge outflow of water occurs: it goes underground and changes the structure of the soils that lie under the base of the foundation. This may be the reason for its additional subsidence.
Poor performance of work and the choice of low-quality construction materials
Be careful when choosing a construction team: use the recommendations of friends, as well as design bureaus with which your builders have already worked. Use the materials included in the project, and in case of their replacement, be sure to consult with the designer. We hope that our small recommendations on the right choice of foundation will help you make the right choice, lay a strong and reliable foundation for your home.