The basis of any structure is the foundation, which performs the function of holding the rather big weight of the building. It must be resistant to high humidity, temperature fluctuations, precipitation and soil flowability.
In this article we will consider the installation of the foundation on screw piles, the types and features of its construction.
A screw pile is a steel pipe consisting of a pointed tip with spiral blades that screw them into the soil on the principle of a self-tapping screw. With the help of these blades, the pressure of the pile on the soil is reduced, which prevents it from being squeezed out by the heaving of the frozen soil.
The tip or auger is the main element of the pile and the determinant of its reliability.
The force of frost heaving acts on the lateral surfaces of the foundation immersed in the soil. This power is very great.
Note: The magnitude of the force of frost heaving of the soil on the side surface of the concrete base, depending on the type of soil, can be from 7 to 11 tons per square meter.
So, for example, the force of pushing out heaving soil onto a driven concrete pile with a section of 200 * 200 mm is up to nine tons.
The weight of a low-rise building cannot compensate for these forces. There were cases when the pillar of the bored pile was damaged and pulled away from the heel.
The pile, which has a diameter of 108 mm, has a small surface on the sides and the ground does not freeze up to the metal post as to the reinforced concrete. Therefore, piles are the most stable when exposed to heaving of the soil. The blades provide reliable support for light structures.
There are 4 common forms of pile columns:
The following types of piles are distinguished, depending on the manufacture of tips: welded and cast. The welded ends are welded to the post. This method, due to its simplicity, is used both in large factories and in small industries, which cannot but affect their different quality. They are used on low-density soils - clay, loamy, sandy loam.
Important: When the blades collide when screwing in with hard rocks or tree roots, the propeller may deform.
Casting consists of pouring a solid structure. Their quality is much higher than welded ones. The standard pile blade size for individual residential buildings is 30 cm.The steel used to form the blades can be up to one centimeter thick. The core of the structure is made of steel pillars with a wall thickness of at least 0.
4 cm and a diameter of 5 to 15 cm. Cast piles differ from welded piles in the accuracy of positioning the rod when screwing in. They do not have the peculiarity of skewing during the process of deepening, and when they encounter an obstacle, their tip is not damaged.
Piles with galvanized tips are preferable, due to which they are not subject to corrosive formations from the influence of groundwater. In terms of service life, they exceed ferrous metal piles treated with anti-corrosion agents.
After direct installation, any piles are equipped with steel caps, which are used as a support platform for the location of the base strap.
Note: Heads are a cut cylinder with a square pad on top. Free-standing piles are combined into one structure with strapping. This system is called the grillage.
To avoid shrinkage of the supporting elements, in front of the foundation device it is necessary to make calculations in the following sequence:
Selection of the pile by diameter is performed according to the bearing capacity and weight of the proposed building. When building residential buildings, they mainly use pillars with diameters from eighty-nine to one hundred and eight millimeters. Piles 89 mm (maximum load more than five tons) are used for light frame structures. And piles 108 mm are suitable for a house made of profiled timber.
The length of the piles is selected depending on the relief differences and the level of soil freezing.
For flat terrain, piles from three to three and a half meters are used.
Note: When constructing one base on a different-level relief, it is possible to use pillars of different sizes.
To calculate the required number of supports for a given foundation, you need to divide the mass of the structure by the maximum load of 1 trunk. The piles are installed at intervals of 2.5 to 3 m.
The disadvantages of such a foundation include large shrinkage, weakness to corrosive formations and the fact that there is no possibility of a basement.
Currently, the pile foundation is becoming more and more popular, because it can be installed on problem soils. Also, another indicator is the relatively low cost of both the material itself and the installation.
The entire process of the device can be divided into stages:
Important: The location of the pile blades is done in the deep layers of the earth to reduce the risk of base shrinkage.
It is necessary to analyze the relief features of the area on which the piles will be erected. Such a foundation differs from other types in that it does not need to level the surface on the site. The evenness of the heads is achieved by using piles of different lengths.
It includes calculations:
Piles are installed along the planned walls at intervals of 3 m. The tip type is also selected depending on the soil. The size of the rod is selected based on the load, the location of the freezing layer, the heaving of the soil.
Also, the preparatory work will include the delivery of material and equipment to the construction site, the marking of the site, and the necessary communications.
The device of the piles is made according to a previously developed plan, in which the specific screw-in places and to what depth are indicated. First, small depressions from 15 to 20 cm are made, into which piles are then screwed in a strictly perpendicular position. This can be done by hand or with a special technique.
Important: Throughout the entire process, it is necessary to check the verticality of the pillars with a level, because it will be very difficult to correct the errors at the end.
The error is allowed no more than two degrees. Once all the piles are screwed in, trim the tops of the trunks one level at a time. This is done with a special truck crane with a svayorez or an ordinary grinder.
Concreting of pillars. After screwing, a sand-cement mixture is poured into the hole of each pile.
This promotes air displacement and provides protection against corrosion. Metal heads are welded to the piles;
The strapping of piles protruding less than 60 cm from the ground is optional. If more, then a channel is welded to the pile heads. The strapping is performed along the outer and inner contours. The grillage is the basis for the further construction of the walls of the building.
Anti-corrosion treatment. To do this, all welds are cleaned, after which they are covered with a protective agent.
Pile foundations have been used for more than two hundred years for the construction of lighthouses, moorings, lighting masts. The oldest pier served for more than 1.5 centuries.
In our country, the military used piles to quickly set up and dismantle the foundation when changing positions. In Russia, pile foundations for residential construction have been used for no more than 15 years. Over the years, there have been no comments on corrosion. There is not a single case of breakage of pile foundations due to corrosive formations. There are several isolated cases when there was a shrinkage of the base due to installation violations, as well as tearing off of the blade due to poor-quality welding of materials.
When using cast piles, this issue is not relevant.
There are claims that with precise production, high-quality assembly and anti-corrosion actions, piles can serve for more than a hundred years. However, one hundred percent is unknown in the same way as in the construction of other types of foundations.
As a rule, siding and decorative panels are used for finishing pile foundations.
Important: When carrying out decorative plating of the base, it is necessary to leave a gap from the ground.
This is necessary so that it would not be damaged during the heaving of the soil.
The gap will not be conspicuous, since it will be constantly covered by grass or snow. If there is such a need to close it, you can use a metal mesh. As a rule, a gap of five to seven centimeters is sufficient, but these figures are relative. Everything will depend on the characteristics of the soil on your site, because the heaving of the soil does not occur evenly.
Therefore, the soil should be analyzed from all sides of the base. This can be done as follows:
Note: When making measurements, take into account the fact that winters are different. So in case of a harsh winter, the gap is made with a small plus.
You can take measures to lower the level of heaving of the soil and the gap will not be needed.
To do this, drainage is performed, the soil is replaced with sand and the soil is insulated along the perimeter of the foundation.
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