At what distance should the screw piles be installed?

Determining the distance between piles when erecting a foundation for a private house requires adherence to a method that takes into account many factors. They include parameters that describe both the properties of the piles themselves and the specifics of the soil and weather conditions of the area. But the main point is the total load that the structure has on the foundation.

There are methods for the typical placement of piles, as well as rules indicating the most loaded sections of the building. To determine the exact placement of the piles, it is necessary to calculate their number and, following the instructions, place the supports in the foundation plan.

To determine the exact distance between screw piles when building a frame or timber house, it is necessary to perform some calculations. Usually this distance ranges from 1 to 3 meters. When constructing temporary or small non-essential buildings, it is calculated by eye, which is not allowed when designing permanent buildings.

When finding the exact distance between the piles, the length of the grillage beams is taken into account, because with their two ends they must abut against the heads of the screwed-in supports. This rule applies to both frame and log houses, but it does not matter if the grillage is cast from concrete. In this case, the beams are simply not used in it.

When using slabs as a foundation material, the interval between screw piles is determined by the design documentation, taking into account their weight and structural features. In this case, the calculations become more complicated, but the principles for placing the support beams remain the same - the piles must be installed under the load-bearing walls, at the entrance portal, under the columns, etc.

The correct placement of piles is the basis of the integrity and durability of the foundation and the entire structure. When placing supports, according to the load applied, it is possible to avoid critical zones that threaten the subsidence of piles and individual parts of the house. If the building has complex contours, the placement of supports requires special attention.

For this purpose, several basic techniques have been developed.

• Single placement. Piles are installed under the supports of frame structures, at the corner joints of the walls and under all load-bearing elements. Moreover, their interval cannot be more than 3 meters.
• Tape placement. The piles are located under the load-bearing walls, with the difference from the single type in that the interval of their location is noticeably reduced and often amounts to only half a meter. This technique is used when it is necessary to withstand a large load (for example, a heavy 2 or 3-storey house).
• Bush placement. This type is required to support heavy single or group structures. There is no specific step for this type, since often the piles are placed close to each other in a chaotic manner corresponding to the load applied. Their placement directly depends on the calculation of pressure zones. The only condition is that the elements must be present along the entire perimeter and area of ​​the slab foundation, for which they are supports.
• Solid placement or pile field. Supports are installed everywhere under the slab foundation area, the step is about 1 meter.This technique is used for massive structures or on soils with weak bearing capacity.

Certain essential criteria must be considered when calculating the pile spacing. This will avoid placing the elements too close, wasting money, and not placing them too far, exposing the foundation and the entire house to the danger of subsidence.

In the calculations of professional builders, the following points are taken into account:

• the mass of the structure (frame, roof, decoration, etc.);
• the mass of internal content (equipment, furniture, things and residents);
• dynamic factors (wind load, weight of snow on the roof in winter);
• bearing capacity of the soil;
• technical parameters of screw piles;
• safety factor.

To determine the payload when calculating the pile spacing, the corresponding SNiP is used. For example, for a one-story residential building, the load is set at 150 kg per 1 sq. m. area. Wind and snow load indicators are reference and are set for each region depending on local weather conditions. The safety factor is on average from 1.1 to 1.25.

Before planning the location of the piles, it is necessary to calculate their number. It is determined based on the total support load. The total weight is divided by the bearing capacity of one pile, resulting in the exact number of supports. Further, they are placed at equal intervals along the perimeter of the building and under the supporting structures.

The second option is the placement of piles, planned based on the determination of the load per 1 running meter of the grillage. To calculate it, it is necessary to divide the total load of the building by the total length of all load-bearing walls, and then divide by the load-bearing capacity of the selected type of piles. The result is an indicator that determines the required number of supports to maintain 1 meter of the grillage. After that, the required pile spacing is determined, sufficient to support the foundation. This method is used for more massive buildings and is rarely used for low-rise frame houses.

To determine the approximate bearing capacity of a specific type of pile, you need to look at the table with the corresponding indicators. More accurate information used in the final calculations is indicated by the manufacturer in the specification for a specific product. It should be borne in mind that the minimum distance at which piles for a house and a terrace are screwed in is 108 cm.

To support the structure and ensure an even load, the supports should be located according to the established order in the places with the greatest load.

The following zones can be distinguished:

• in the corners of the facade walls;
• at the points of intersection of load-bearing walls and interior partitions;
• near the entrance opening;
• on the inner area with an interval of no more than 2 meters;
• under a stove or fireplace (from 2 piles or more);
• under the load-bearing wall, on which an additional structure such as a balcony or a mezzanine is located, which locally increases the load on the wall.

After finding the exact number of piles, the stage of the schematic arrangement of the supports in the foundation plan begins. In this case, the above rules for their placement under load-bearing elements and at critical points of the structure must be taken into account. The remainder should be evenly spaced between the key supports. This is how the step in the placement of screw piles is determined.

Consider the features of the calculation using the example of a square-shaped house with a perimeter of 8x8.

Other structural features include:

• frame type, slate roof, porch;
• the dimensions of the foundation are 8x8, the height of the building is 3 meters;
• the house has 3 rooms formed by the intersection of a solid wall 8 meters long and a partition 4 meters long;
• the frame is made of timber 150x150, grillage - 200x200;
• the walls are covered with sandwich panels.

Calculating the area of ​​the walls:

• outdoor - 8 * 3 * 4 = 96 sq. m;
• internal - 8 * 3 + 4 * 3 = 36 sq. m.

Calculation of the mass of the walls using tabular values ​​for the mass of 1 sq. m:

• external (load bearing) - 50 * 96 = 4800 kg;
• partitions - 30 * 36 = 1080 kg;
• total mass - 4800 + 1080 = 5880 kg.

Calculation of the mass of basement and attic floors using tabular values ​​for a mass of 1 sq. m:

• basement - 8 * 8 * 150 = 9600 kg;
• attic - 8 * 8 * 100 = 6400 kg;
• total weight - 9600 + 6400 = 16000 kg.

To determine the mass of the additional load (internal filling of the house: finishing materials, things, equipment), a tabular value of 350kg / 1kv is used. m. When calculating the load for a two-story house, the weight of the additional load is multiplied by 2.

8 * 8 * 350 = 22400 kg.

Calculation of the total load on the foundation:

16000 + 22400 = 38400 kg.

Calculation of the number of piles according to the formula K = P * k / S, where:

"P" - total load;

"K" - coefficient of reliability (in the example - 1.4);

"S" is the maximum load on 1 pile (this value is based on the specifics of the pile, in the example it is a support with a diameter of 300 mm).

Soil resistance is determined by the specifics of the area on which the house is being built. In the example, this is soil with an average density of 3 kg. / cubic meter see, weak freezing of 1 meter and deep groundwater.

38400*1.4/2600=20.6

The above example shows a possible calculation. It does not take into account the specific specifics of an individual structure, which may affect the final number of piles and their placement in the foundation plan.

One of the main points is finishing materials and other filling of the house, which makes up about half of the load. The table value is based on the average weight of the materials. If solid cladding is used, such as slabs of granite or marble, stone or brick masonry, etc., the total load may change significantly. In such circumstances, an accurate calculation of the weight of all elements related to the additional load is indispensable.

For pile foundations and the recommended distance between piles, see this video.