Bearing capacity of screw piles: calculation and determination

Everyone knows that the bearing capacity of screw piles is an important indicator, through which you can determine what level of load the foundation can withstand. This takes into account the negative impact of the soil on each support separately. Screw pipes are divided into two types:

1. Hanging - have a support, which is located under the lower rings of the screw. Such supports are used in the construction of houses on soft soils. These structures are able to withstand heavy loads by the formation of frictional forces. It can appear between the screw pipes and the ground. If there are dense layers of soil on the site, there is no sense in additional installation of supports.
2. Support type - used in areas with hard ground for the construction of houses. They play the role of an intermediary in transferring the load from home to base.

Before installing such a foundation, it is necessary to find out what load capacity of screw piles is required for construction.

Nuances of installation

In most cases, the bearing capacity of a screw pile often depends on the size and diameter of the support. The screw base can be installed in two ways:

• Manual;
• With the use of special equipment.

The bearing capacity does not depend on the type of installation. Both methods of installation are performed by the principle of screwing the helical pipe into the soil structure. This action is easily performed thanks to the blades, which are located on the lower part of the support. In order not to deteriorate the bearing capacity, in some situations, the installation of the screw pile is performed differently:

• Installation of screw support in the soil, which has a solid structure, as well as in the frozen soil. Required drilling of small wells is mandatory. This action will ensure safe screwing of the screw support into the ground.
• If the flooded ground prevails on the construction site, the surface of the screw piles is additionally treated with an anti-corrosion agent. The concrete consistency must be poured into the body of the metal pipe. Due to this, the strength of the foundation material will increase, and the term of its operation will last.

If additional reinforcement is required, piles that are longer than 2 meters in length should be reinforced. Due to this, the bearing capacity of the screw piles along the entire perimeter will increase.

It is important to know that correct calculation of bearing capacity of supports can be made if the installation is carried out correctly. If even the slightest rules are violated, the strength of the entire structure will be greatly reduced. Therefore, the installation process is best entrusted to a specialist who has extensive experience with such types of foundation.

The use of a screw pile with a diameter of 133 mm

At the time of the construction of a heavy structure on a screw foundation, the question often arises: what piles diameter should be exposed and how many should be? For massive structures, it is best to use elements with a large diameter. The bearing capacity of a screw pile 133 mm with a blade diameter of 350 mm allows to withstand loads of 4 tons. With their help, you can install any type of facilities - from an apartment building to a warehouse.

Screw pillars are often used in the construction of a variety of berths and piers. For their device, piles with a pipe diameter of 133 millimeters are used. Among other things, they have a double protective coating against corrosion formations. Due to such characteristics, the foundation is firmly placed on areas with unstable soil. To determine the bearing capacity of the foundation, it is necessary to multiply the area and the value of soil resistance.

Example of determining the number of piles on a foundation

The calculation takes the structure in two floors on the foundation 6 by 6 meters and the material of the timber used. On the building site is located the soil in the form of clay. The total weight of the building with all the nuances was 59 tons. The perimeter of the building is 24 meters, there are no internal partitions. The first step is to clarify the strength of the soil according to the table. In our case this value will be 6 kg per square centimeter. The load-carrying capacity factor is 1.75 (it is needed to provide the stock if necessary). The total area of the sole is calculated. Formula:

S = (PD) x (PD): 4 = 3.14 x 352: 4 = 961.6 centimeters. This is the definition of the diameter of the blades.

The formula for computing the non-optimized carrier is:

F = S x Ro = 961.6 x 6 = 5770 kg.

Calculation of the permissible weight per pile:

N = F: yk = 5770: 1.75 = 3279, that is approximately (with rounding) 3 tons of 300 kilograms.

Determination of the carrier characteristic

If screw piles are used in foundation construction, the calculation of the bearing capacity is simply necessary. A lot of factors depend on this, including the life of the building as a whole. In order to carry out design work, you need to know the value of soil resistance, as well as the area of the blade, which is located at the ends of the screw support. But these values are not enough, you need to additionally calculate the number of supports that will be installed under the building.

In order to obtain a more accurate calculation, we should divide the carrier coefficient by the reliability index. All calculations and tests for strength fit into the project documentation. In accordance with the prepared layout of the structure, the pre-calculated number of piles is evenly distributed along the perimeter of the entire foundation.

Calculation of screw base

The main factor, which, in turn, should be identified during the calculation period, is the overall level of load on all supports. The number of piles and the distance between them is determined by the diameter of the support tube and the mass of the building. For example, the bearing capacity of screw piles 108 mm allows you to withstand a weight of 3 tons. The load on the base includes the weight of the structure along with the influence of the wind and the accumulation of snow.

The following factors influence the overall weight of the structure:

• Load overlapping;
• Weight of bearing and secondary walls;
• Roofing system;
• Household items (furniture, appliances).

Load from the roof, walls, and also overlapping must necessarily be calculated separately. For this purpose, a table is used in which the weight of each type of material is indicated.

Area of use of piles with a diameter of 89 mm

The sphere, in which the pier supports of medium diameter are most often used, is the construction of small structures. This determines the bearing capacity of screw piles of 89 mm diameter in each case separately. Weight, which can be distributed on each pile separately, is 2 tons, not more. They can be used in the construction of such objects:

• Buildings of medium size (bathhouse, dacha, garage, warehouse);
• Supports for the bases of arbors, greenhouses, cabins;
• Metal gates and fences;
• Berths and piers;
• Supports for advertising banners.

If the choice falls on piles with such a diameter, then it is necessary to focus on certain factors, such as the use and composition of the soil. This will directly depend on the reliability of the structure and the period of its operation.

Screw supports with small diameter

Before making a choice of piles, it is necessary to determine the maximum load it must endure. For example, the bearing capacity of a screw pile 57 mm in diameter makes up the permissible load fluctuation per one support from 300 to 1000 kg. Due to such a minimum weight, the price of such elements is much lower than that of piles with a large diameter. Also, the cost of installing the foundation is reduced. This is due to the fact that a small screw support can be screwed in by hand, without the use of expensive construction equipment.

Installation of the foundation is carried out in just one day, which significantly reduces the time for erecting the entire building as a whole. Also an important advantage of these screw piles is the possibility of mounting in any type of soil.

Piles with a diameter of 76 mm

Bearing capacity of screw piles 76 millimeters in diameter allows to withstand a mass of one ton. In addition to the use of various building structures in construction, these piles can be used in repair work as additional reinforcement.

Installation of piles with a diameter of 76 mm equally can be done by hand and using a construction mechanism. The cost of such a material is more expensive than that of elements with a smaller diameter, but the application possibilities are much greater. Therefore, before acquiring material, it is necessary to determine the requirements that will be presented to the supports at the time of construction.

Determination of the size of the base of the screw pile

At the time of screwing the screw piles, the soil is compacted. After installation, the pile support takes up all the load on itself. In order to determine the amount of load that a foundation consisting of screw supports can withstand, it is necessary to calculate the size of the sole area. Then, applying the formula S = πR², the complete calculation of the required index is performed.