Sketch of the constituent elements of a pile foundation with a grillage

Pile-grillage foundations are deservedly popular among those private developers who want to build a high-quality foundation in the shortest possible time on a landscape with a complex structure. After all, the grillage can be shallow or shallow, and this is a significant cost savings for its construction.

But, there is a problem of correctly calculating the required number of load-bearing structures, their type and installation step, so before construction you need to do a complete collection of information.

Also, first the foundation is designed taking into account the characteristics of the future building, because the final cost of building the house depends on how many piles are installed, and only then the pile foundation is calculated.

What information should you collect first?

1. Obtain detailed information about the condition of soils, the height of water horizons and the degree of mobility of individual layers.
2. Develop a project for the future house, taking into account the building materials used, and additionally allow for errors in furniture and other materials.
3. Calculate how much weight of all building materials is needed to build a house.
4. Determine the depth of strong rock layers and the degree of their heaving.
5. Select the optimal type of piles and grillage characteristics.
6. Calculate the permissible load per unit area of ​​soil, as well as the permissible number of load-bearing structures.

As a rule, the design of such foundations involves collecting all the information about the future building and construction site. These are complex engineering calculations that should be done by a professional builder with experience in this field.

Also, given the open area between the house and the ground, the tilt of the structure under the influence of wind is inevitable, and it must be taken into account.

When calculating such foundations, it is also sometimes taken into account how much and what kind of waterproofing materials are needed to protect the foundation. The design and calculation of this foundation consists of several key stages:

• selection of the optimal diameter of the piles used;
• calculation of the maximum permissible length of the structure;
• calculation of the minimum amount of materials on which the grillage will be located;
• calculation of the bearing capacity of bored piles as an alternative to factory ones;
• calculation and selection of grillage.

At the design stage, you need to immediately decide what type of structure will be used. After all, the maximum possible number of structures, their permissible diameter and construction technology depend on their characteristics.

Selecting the optimal diameter of the structure

It is clear that each type is designed for its own permissible load, so in some cases professionals calculate the diameter themselves and adjust it to factory standards. So, now on the building materials market you can order structures with a diameter of 57, 76, 89 and 108 mm. They are selected according to certain rules:

1. The diameter of 57 mm is designed for a small load, therefore it is often used for the construction of foundations for fences, sheds, and other outbuildings of small mass.
2. The diameter of 76 mm is designed for a maximum load of up to 3 tons, therefore it is used for the construction of light outbuildings.
3. The diameter of 89 mm already has a greater load-bearing capacity, withstands a load of up to 5 tons per unit, therefore it is optimal for the construction of residential one-story frame buildings.

But a diameter of 108 mm is already capable of supporting frame residential buildings with several floors. They just need to be built from relatively light building materials, because the permissible load on one pile is up to 7 tons.

Choosing the optimal length

When designing pile foundations, it must be remembered that the length of the load-bearing elements must be sufficient to reach the depth of soil freezing and rest against strong layers of soil. After all, if errors are made in the design, then subsidence of a separate corner of the house occurs with its further destruction. Therefore, the length of the structure is selected taking into account some important factors

Soil density

If the soils are loose and cannot withstand heavy loads, then the piles are lowered to the depth of freezing or reaching strong soils. At the construction site, it is necessary to conduct detailed geodetic studies and collect data on the condition of the soil and groundwater level. This is done using the deep core method or manually using a shovel.

If there are strong soils such as clay or sand underneath the layer, then you need to use piles up to 2.5 meters long. If there are low-density rocks under a layer of fertile soil, then using a garden drill, a well is made to the level of strong rocks and the length of the load-bearing elements is calculated based on the depth of the well.

Height difference on the site

An example of calculating the height of a pile foundation with a height difference on a site

As a rule, when constructing such foundations, the site is rarely leveled on a single plane due to high financial costs.

Then they make a well in the lowest place of the future foundation and in the highest, then calculate the length of the well in both places. It is clear that the level of hard rocks will not always be the same at different elevations, so drilling is carried out in several places.

The result is a full-fledged project for choosing the optimal length of the base for a house, taking into account the type of soil and height on the site. It is prohibited to install piles of the same length in such cases, otherwise there will be a tilt towards less soil resistance.

Calculation of the required number of load-bearing structures

The choice of the optimal number of piles is made taking into account the possible roll, as well as the size and weight of the structure. Average distances can be as follows:

• for small houses (frame, wooden or log) the distance is taken to be no more than 3 meters;
• for aerated concrete, foam concrete or similar houses - no more than 2 meters;
• for fences – 3.5 meters;
• for large massive buildings made of brick, natural stone and other building materials, an additional calculation of the permissible load of the structure per unit area of ​​soil is carried out.

1. Make or draw up a house plan, preferably with a roof and load-bearing partitions.
2. Install load-bearing piles at the corners of the building and at the intersections of load-bearing walls.
3. Calculate the design mass of the building, then select the type of pile taking into account the material and diameter of the structure.
4. Design additional supports between the corner and intermediate piles, taking into account the permissible length of the structure and the weight of the building.
5. Fill the internal space with supports, taking into account the distance between them within 2-2.5 meters.

When the preliminary design for the location of the piles is ready, you can already calculate the total number of supports required.

Calculation of the bearing capacity of bored piles

Factory piles are not always justified if you take into account the financial costs of transport delivery. In such cases, bored or injection piles are often used, because they can be made directly on the construction site.

The depth of such piles depends on the depth of the strong soil layers, and their number can be significantly less than for screw piles.

The number and cross-section of such structures is determined taking into account the load-bearing capacity of each pile separately, as well as the mass of the building as a whole. The resistance of the soil itself, both horizontal and vertical, is also taken into account. For a pile 3 meters long, the load-bearing capacity can be calculated using the formula:

P = 0.7 x RнхF + 0.8 x U x fin x li, Where:

• P – bearing capacity of load-bearing elements;
• 0.7− soil coefficient;
• Rн – soil resistance under the lower end of the structure (reference materials);
• F – support area, m2;
• 0.8− working conditions coefficient
• U – perimeter in meters;
• fin – standard soil resistance of the lateral surface to load-bearing elements, t/m2 (determined from tables);
• li – height of the soil layer in the zone of contact with the foundation in meters.

Grillage calculation

The design of pile-grillage foundations involves the installation of a special pad on which load-bearing walls are already mounted. This grillage evenly distributes the load from the building onto all supports simultaneously and is designed separately.

A grillage is a concrete, reinforced concrete or prefabricated strip, rigidly connected to piles by reinforcement. It distributes the mass over all piles at the same time, so it is necessary to calculate its dimensions and dimensions.

Special calculations are used here; they can be found in specialized literature, and professional designers must do them, because the number of installed piles depends on this.

To connect the piles and provide additional rigidity, the grillage is additionally reinforced with steel rods with a diameter of 12 mm in various directions. The reinforcement must be completely hidden in concrete to prevent the spread of corrosion. You can calculate how much and what kind of reinforcement you need to use using ready-made formulas or taking into account the zonality of the grillage.

The foundation is the basis of the building, and its correct calculation is the basis for the longevity of the entire structure. In order to calculate the required number of screw piles, their width and other parameters necessary for the construction of the foundation, you need to adhere to a proven standardized methodology. It includes a set of formulas into which it is necessary to substitute geodetic data about the specifics of a particular area and tabular values ​​​​correlating with the required foundation parameters. In order to calculate the number of screw piles for the foundation in a private house, it is necessary to delve into all the features and subtleties of the calculations.

Purpose

A foundation on screw piles is an excellent solution for areas with difficult terrain, which is also moderately priced. The specificity of this technology allows the installation of supports to be carried out within 3 days and at the same time guarantees the reliability of the foundation for at least 100 years. To obtain a high-quality result, it is necessary to take into account all the factors included in the technical process: uniform load distribution, soil characteristics, soil freezing depth, the presence and specificity of groundwater, etc.

As a result of all calculations, data appears that answers questions such as:

• required height of screw piles;
• diameter of screw piles;
• depth of their installation;
• required number of screw piles;
• total cost of materials.

Calculation order

Always the first step in any work is design.

To carry out calculations, you can use the standardized methodology for screw piles described in SNiP 2.02.03–85. It is based on data from geodetic studies of a specific plot of land.

They include the following information:

• description of the terrain of the site;
• soil composition and density;
• groundwater level;
• soil freezing depth;
• seasonal precipitation level in the development region.

Using this data, the number of screw piles for the foundation (K) is calculated.

For calculations you will need the following indicators:

• total load on the foundation (P), which is the sum of the masses of all materials used;
• reliability coefficient (k), which is a correction indicator for the value of the total load on the piles;
• bearing capacity of the soil – tabular value;
• the area of ​​the pile heel, which is directly dependent on its diameter, is a tabular value;
• maximum permissible load (S), indicator for one pile - tabular value.

The reliability coefficient (k) correlates with the total number of piles and has the corresponding values:

• k=1.4, if there are from 11 to 22 piles;
• k=1.65 – from 5 to 10 pieces;
• k=1.75 – from 1 to 5 pieces.

Each pile bears a load equal to the total load divided by the number of supports. The fewer there are, the greater the load on one pile and the faster it becomes unusable, and with it the entire foundation and house.

The correct calculation is to select a number of piles that will be enough for the entire period of operation of the structure, but without excessive surpluses, which are a waste of funds.

Using the above formula and the coefficient for screw piles, the calculation of loads and further construction are not associated with any particular difficulties.

In the final calculations, it is necessary to distribute the loads under load-bearing structures and critical points with excessive pressure on the foundation, taking into account:

• type of piles (hanging or racks);
• masses;
• roll force values.

Options

When calculating a screw foundation and the loads placed on it, it is necessary to take into account the following indicators:

• the total mass of the structure (constant), measured in kilograms, is the sum of the masses of the following elements:
  • walls and partitions;
  • floors;
  • roofs;
• additional loads (temporary, variable):
  • mass of snow on the roof;
  • the mass of all items in the house: furniture, equipment, finishing materials and residents (average value 350 kg/sq. m);
• dynamic loads of a short-term nature arise from the influences of:
  • gusts of wind;
  • sedimentary processes;
  • temperature fluctuations.

Varieties

Depending on the structure (shape) of the screw pile, the specifics of its application vary.

The following common types are distinguished:

• wide-plate with a cast tip - used for small buildings with simple soil;
• multi-layer with several blades at different levels - used for increased load on difficult soil;
• with variable perimeter - narrow-profile product for specific conditions;
• narrow-plate with a cast toothed tip - used in permafrost and rocky soil conditions.

Specifications

There are several main technical characteristics of screw piles.

These include:

• barrel length and material of manufacture;
• pile diameter;
• type of blades and their method of fastening to the trunk.

Diameter

Piles are manufactured with standardized dimensions to perform the relevant tasks:

• 89 mm (blade diameter 250 mm) - with a calculated load on one support of no more than 5 tons, these are mainly frame one-story houses;
• 108 mm (blade diameter 300 mm) - with a design load on one support of no more than 7 tons: frame one- and two-story houses, timber buildings and foam block structures;
• 133 mm (blade diameter 350 mm) - with a design load on one support of no more than 10 tons: brick and aerated concrete houses using metal elements.

Length

The choice of pile length is based on soil density: the pile should rest only on solid soils.

Also, their length depends on the existing elevation differences on the site:

• loam depth less than 1 meter – pile length 2.5 meters;
• in case of loose soils or quicksand, the length of the pile is determined by the depth of immersion of the drill to hard layers;
• if the site is uneven, the difference in the length of the piles can vary from 0.5 meters or more, depending on the specific case.

Number of supports and their spacing

The tabulated values ​​for the location of supports relative to each other include the following values:

• from 2 to 2.5 meters – for houses with wooden frames and block buildings;
• 3 meters – for buildings made of timber or logs.

When arranging foundation piles to evenly distribute loads, the following rules for their placement should be taken into account:

• at every corner of the house;
• at the intersection of the load-bearing wall and the internal partition;
• near the entrance portal;
• inside the perimeter of the building at intervals of 2 meters;
• there are at least 2 piles under the fireplace;
• under a load-bearing wall, where a balcony, mezzanine or similar structure is located.

Grillage

A grillage is a foundation element necessary to uniformly distribute the load exerted by the building on the foundation. To ensure the reliability of the grillage, it is necessary to calculate a number of parameters, and the type of grillage does not matter.

Calculations include:

• foundation pushing force;
• punching force acting on each corner separately;
• bending force.

If a high grillage is used, the entire load is applied to the piles. The vertical load acts from below, and the deforming load acts from the side. Such calculations are very complex and require professional knowledge. For calculations, it is necessary to use individual construction standards.

They define the following standards:

• The supports can be connected to the grillage in two ways: rigid and free;
• the depth of insertion of the pile head into the grillage is at least 10 cm;
• the distance between the ground and the grillage is at least 20 cm;
• the thickness of the grillage cannot be less than the thickness of the walls and is at least 40 cm;
• the grillage must have a height of more than 30 cm;
• the grillage is strengthened with longitudinal and transverse reinforcement with a rod cross-section from 10 to 12 mm.

Counting example

This example serves to show in detail the application of formulas when calculating a pile-screw foundation.

The initial data for a house with a perimeter of 10x10 are:

• a house built using frame technology, the roof is covered with slate, there is a porch;
• foundation dimensions – 10x10, building height – 3 meters;
• There are two partitions installed inside, which, intersecting, divide the room into 3 rooms;
• roof slope - 60 degrees;
• the frame is made of timber with a section of 150x150;
• the grillage is made of timber with a section of 200x200;
• The walls are made of SIP panels.

• wall area:
  • load-bearing: 10*3*4= 120 sq. m;
  • partitions: 10*3+5*3= 45 sq. m;
• mass of the walls (the mass of 1 sq. m of timber wall and partition is taken from the table of average values):
  • load-bearing: 50 kg*120=6000 kg;
  • partitions: 30 kg*45=1350 kg;
  • total: 6000+1350=7350 kg;
• weight of floors per 100 sq. m.:
  • basement: 150 kg*100=15000 kg;
  • attic: 100 kg*100=10000 kg;
  • roof: 50 kg*100=5000 kg;
  • total: 15000*10000+5000=30000 kg;
• the mass of additional elements (internal content of the house, type of household appliances, finishing, number of residents, etc.), the tabular average value for 1 sq. m is taken. m at 350 kg:
  • 350*100=35000 kg;
• total weight of the building:
  • 35000+30000+7350=72350 kg;
• for example, a reliability coefficient of 1.4 is taken;
• the maximum load on the heel of a pile with a diameter of 300 mm is 2600 kg, provided that the soil resistance is 3 kg / cubic meter. cm (soil with medium density, deep water and a freezing level of no more than 1 meter);
• We calculate the number of piles using the formula K=P*k/S: K=72350*1.4/2600=39 piles.

In the process of calculating the number of piles and their distribution over the entire area of ​​the foundation, there are many small features, each of which in one way or another affects the improvement of the final result:

• when installing a foundation made of screw piles on complex unstable soil, a strapping using a metal angle or channel at the level of the base is used to strengthen the supporting structure;
• in the absence of geodetic data for calculations, it is better to use parameters corresponding to the minimum design load, that is, create a maximum safety margin;
• to improve the quality of calculations, in addition to formulas and tabular data, it is worth using a design program: it will recalculate all parameters and refute or confirm manual calculations;
• the least strong piles have trunks made of seamed pipes with welded blades;
• According to the standards, the base should not rise more than 60 cm above the ground, while the length of the pile should be from 20 to 30 cm.

The calculated number of piles is not always optimal: there may be additional circumstances that require the use of a larger number. In addition, a small margin of safety has a beneficial effect on the durability of the foundation.

When installing piles on an uneven area, it is advisable to leave a margin of about 20–50 cm in length. In the future, the excess can be cut off or pulled out. But if there is a deficiency, you will have to drive a new pile.

In this article we will tell you what mistakes can be made when independently calculating a pile foundation for low-rise construction projects and how to avoid it

Common mistakes in designing screw pile foundations

Here are the mistakes that are often found in pile foundation projects developed on our own:

• ignoring the structural features (inability to correctly determine where the main loads will be concentrated and where the secondary ones will be);
• inability to correctly calculate loads (often only the weight of the structure itself is taken into account);
• ignoring soil conditions at the construction site (degree of corrosion activity, physical characteristics of soil, etc.).

Sometimes inaccuracies in calculations arise due to incorrect consideration of the landscape of the site (it turns out that the minimum height of the base has not been met, etc.).

The result is an incorrect assessment of the load-bearing capacity of the structure and the degree of environmental influence on the foundation, which often leads to subsidence and accelerated development of corrosion and putrefactive processes.

We have developed this material so that you can independently determine the size and number of screw piles for the future foundation. On the one hand, the above calculation is conditional, since it uses average indicators that may vary depending on the type of building and the region of construction. On the other hand, it is universal, as it is based on the most standard solutions and data. But most importantly, it allows you to understand the calculation scheme itself and understand what must be taken into account at this stage.

The material is focused on the field of individual housing construction and does not take into account the design features of complex objects.

Load collection

First of all, to calculate the foundation, it is necessary to collect all the loads that will act on it. They can be permanent Pd and temporary (long-term Pl, short-term Pt, special Ps).

Constant P d – the weight of parts of structures, including load-bearing and enclosing building structures.

Long-term P l - the weight of temporary partitions, grouts and footings for equipment, the weight of stationary equipment, the liquids filling it, solids, etc.

Short-term P t - impacts from people (animals, equipment) on floors, from moving lifting and transport equipment, from vehicles and climatic conditions (snow, wind, etc.).

Special P s - seismic, explosive impact, impact from collision of vehicles with parts of the structure, impact caused by fire or deformation of the base, accompanied by a radical change in the structure of the soil.

Please note that this calculation will take into account only those types of impacts that are of fundamental importance when calculating a foundation made of screw piles.

Constant loads. How to calculate the weight of parts of a structure?

To calculate the weight of a structure, it is enough to know the specific gravity of the materials that will be used in its construction and their expected volumes. This does not require any special knowledge or skills. You can try to request the necessary data from the building materials supplier.

When performing calculations, we will use reference data with average values ​​of the specific weight of house structures (walls, floors, roofs) given in Table 1.

Specific gravity of 1 m 2 walls
Frame walls 200 mm thick with insulation
Walls made of logs and beams	70-100 kg/m2
Brick walls 150 mm thick		200-270 kg/m2
Reinforced concrete 150 mm thick		300-350 kg/m2
Specific gravity of 1 m 2 floors
Attic on wooden beams with insulation, density up to 200 kg/m 3		70-100 kg/m2
Attic on wooden beams with insulation with a density of up to 500 kg/m 3		150-200 kg/m2
Basement on wooden beams with insulation, density up to 200 kg/m 3		100-150 kg/m2
Basement on wooden beams with insulation, density up to 500 kg/m 3		200-300 kg/m2
Reinforced concrete
Specific gravity of 1 m 2 of roofing
Sheet steel roofing
Ruberoid coating
Slate roofing
Roofing made of pottery tiles

Table 1. Reference data with average values ​​of the specific weight of house structures: walls, ceilings, roof.

When performing calculations yourself, it is worth considering that, according to clause 4.2. SP 20.13330.2011, the design value of the load should be determined as the product of its standard value by the load reliability factor (γ f) for the weight of building structures corresponding to the limit state under consideration:

Table 2. Tab. 7.1 SP 20.13330.2011

Let's perform the necessary calculations using the example of a 6x9 frame-panel house with an attic.

To calculate the weight of the walls of the house, you need to calculate their perimeter. Perimeter of external walls + internal walls: P = 47 m, we will take the average height of the wallsh=4.5 m. Then the weight of the wall structure will be equal to: P xh x specific gravity of the wall material.

47 m x 4.5 m x 70 kg/m 2 = 14,805 kg = 14.8 t.

Next, let's calculate the weight of the roof. We assume that the weight of the roof (wooden rafter system covered with metal tiles) is 40 kg/m2 (total weight of metal tiles, sheathing, rafters). Then the weight of the roof will be equal to:Sroof x specific gravity 1 m 2

92 m 2 x 40 kg/m 2 = 3,680 kg = 3.7 t.

54 m 2 x 0.1 t/m 2 x 2 = 10.8 t.

After all the necessary calculations have been completed, we multiply the resulting weight of the structure by the reliability coefficient, which we talked about earlier (in the calculation for a frame-panel house, we take the coefficient equal to 1.1 - for wooden structures):

29.3 t x 1.1 = 32.2 t

Thus, the load from the building itself will be 32.2 tons. This weight is accepted conditionally, without deducting door and window openings.

Short-term loads. Loads on floors and climatic loads

From people (animals, furniture, equipment) to floors

We must not forget about the impact on floors, that is, the weight of people, animals, furniture, equipment. Since it is impossible to accurately determine the value of this indicator at the design and construction stage, the standard value of a uniformly distributed load - Pt (Table 8.3 SP 20.13330.2011), acting per 1 m 2, is added to the weight of the floor structure.

For residential buildings it is 1.5 kPa (150 kg/m 2 ). When calculating we get:

S floors x150 kg/m 2 x number of overlaps

Loads from people (animals, furniture, equipment) on floors = 54 m 2 x 150 kg/m 2 x 2 = 16,200 kg = 16.2 tons.

Snow

To calculate climatic loads (wind, snow, etc.) acting on the foundation, in accordance with clause 10 of SP 20.13330.2011, it is necessary to take into account the snow area (weight of snow cover per 1 m 2) and the structure of the building’s roof (the more it slope, the less impact).

Taking into account the construction area when calculating the snow load is of fundamental importance, since, for example, the weight of the snow cover is very different for different regions. For the central part of the Russian Federation it is 180 kgf/m2 ( where kgf is a kilogram-force equal to the force that imparts to a resting mass equal to the mass of the international prototype of the kilogram an acceleration equal to the normal acceleration of gravity), for a significant part of the Volga region - 320 kgf/m2, and for certain regions of Siberia - already 400 kgf/m2, which will affect the calculation results.

Fig 1. Map of snow areas of the Russian Federation

S roofs x Estimated weight of snow cover x coating slope coefficient (assumed equal to 0.7 - for the most typical coatings with a slope from 30° to 45°)

For Central Russia we get:

92 m 2 x 0.18 t/m 2 x 0.7 = 11.6 t

For the Volga region:

92 m 2 x 0.32 t/m 2 x 0.7 = 20.6 t

For regions of Siberia:

92 m 2 x 0.4 t/m 2 x 0.7 = 25.8 t

Wind

There is a high probability that when calculating the wind load you will get a negative value. This will mean that the weight of the above-ground structure has not increased, but, on the contrary, has decreased. Therefore, sometimes this indicator can be neglected.

But if we are talking about lightweight structures, especially those characterized by a large “windage”, the same indicator will already be of fundamental importance, since you will need to clearly understand how the pulling and horizontal effects on the piles will increase in this case.

The standard value of the wind load W n is determined by the formula:

W n =0.7 W×k (z) ×c

where W is the calculated value of wind pressure, determined from the maps of the appendix to SP 20.13330.2011 or from Figure 1 (values ​​are indicated with and without a coefficient of 0.7);

k - coefficient taking into account changes in wind pressure for height z, determined from Table 3;

c is the aerodynamic coefficient, which takes into account the change in the direction of pressure of normal forces depending on which side the slope is located in relation to the wind, on the leeward or windward side.

Figure 2. Zoning of the territory of the Russian Federation according to the calculated value of wind pressure (calculated value of wind pressure w)

Height z, m
no more than 5
Terrain types: A – open coasts of seas, lakes and reservoirs, deserts, steppes, forest-steppes, tundra; B – urban areas, forests and other areas evenly covered with obstacles more than 10 m high; B – urban areas with dense buildings with a height of more than 25 m

Table 3. Coefficient k (z) for terrain types

When there is wind on the roof slope
With the wind in the gable

Table 4. Coefficient (c) for gable roofs with wind in the slope and in the pediment

The reliability factor for wind load g t should be taken equal to 1.4.

The prevailing winds are directed towards the gable of the roof, hence the aerodynamic indicator for a roof with a slope of ά = 45 is equal to C = -1.4;The roof is located at a height of 10 meters, that is, the coefficient is 0.65 (urban areas):

Wн =0.7 x 23 kgf/m 2 ×0.65 x (-1.4) = -14.65 kgf/m 2 (the “-” sign indicates the force trying to tear the roof off the entire building).

The total force on the roof will be: 92 x (-14.65 kgf/m 2 ) = - 1,348 kgf = -1.35 t.

Load collection

Total total impact on the foundation: 32.2t + 16.2t. + 21.5 t. + (-1.35 t) = 68.55 t.

Ground conditions at the site: geotechnical surveys, express geology or test screwing?

The next stage, which is often forgotten, is determining the soil conditions of the proposed construction site.

To obtain reliable information about the bearing capacity of soils, it would be most effective to conduct control field tests of soils using a full-scale pile. At the same time, it is worth considering that they are carried out only on the basis of geotechnical survey data (EGS). That is, tests are needed to confirm conclusions drawn from the information contained in the IGI reports (detailed description of soil properties, its heaving and freezing depth, results of laboratory tests of soils, data on their physical and mechanical properties, engineering geological section, etc. .).

However, due to the high cost of these methods for assessing the bearing capacity of soils, they are practically not used in the field of low-rise construction.

Companies that build screw pile foundations offer a number of alternatives to these procedures.

Test screwing. It is not a soil research method. The results obtained will greatly depend on the time of year and the degree of moisture saturation of the soil. Consequently, if the procedure is carried out on the same area in the spring or after heavy rainfall and in the summer, that is, during the hot and dry season, the data obtained will be very different. This indicates the insufficient effectiveness of the method.

A good alternative to IGI for low-rise construction is express geology (geological and lithological surveys). It makes it possible to identify potentially dangerous geological objects and processes (watershed, suffusion, karst, etc.), timely determine complex soil conditions that require a special approach to both the design and construction of objects, and the level of their reliability (more about express Geology you can read in the article “”). Having knowledge about the properties and structure of soil allows you to choose a combination of modifications and the number of screw piles for a specific site.

In addition, express geology allows you to determine the physical characteristics of soils, which are important for selecting the configuration of the blade (not to be confused with the diameter), which affects the load-bearing capacity of the pile (more information about the need and reasons for selecting the configuration of the blade is contained in the article “”).

To confirm the results of geological and lithological surveys and compliance of the bearing capacity of soils with the requirements of design documentation, after installing screw piles, it is recommended to perform control measurements of the torque value.

Corrosive aggressiveness of soil is the most important indicator for selecting the characteristics of screw piles

It is also important to remember that during the foundation design process, not only the structural, but also the geometric parameters of the piles are assigned. Therefore, an obligatory design stage is the determination of the corrosive activity of the soil, based on the data on which the thickness of the trunk and blade, steel grade are selected, ensuring compliance of the service life of the structure with the requirements of GOST 27751-2014 “Reliability of building structures and foundations. Basic provisions".

To clarify the correct selection of parameters, it is recommended that after calculating the service life, check the residual thickness of the barrel wall for compliance with the design loads.

Base height. Is there a difference in the selection of screw piles?

Taking into account the landscape of the proposed construction site is another mandatory condition that must be met when calculating the foundation.

The presence of a height difference on the site requires not only the use of screw piles of various lengths, but also in a different combination of modifications than in the case of construction on a flat surface. This is due to an increase in horizontal impact on the foundation.

It is important to take care in advance to comply with the minimum height of the plinth (at least 500 mm). If this condition is not met during the process of tying a pile-screw foundation, due to the proximity of the structural elements to the ground, there will be a risk of the development of corrosion (when tying with a channel or I-beam) or putrefactive processes (when tying with timber or logs) processes, which will require the organization of additional measures to protect structural elements.

Determination of areas where loads accumulate. How to place piles in the foundation?

When placing piles, it is necessary to take into account the uneven distribution of the load along the base, as this will allow for a uniform distribution of the safety factor of the entire foundation and will significantly increase its service life.

Under the ridge of a house with a gable roof, the impact will be maximum, under load-bearing and non-load-bearing walls these indicators will decrease, and the piles installed to support the floor joists are designed to absorb minimal impact. That is why, in most cases, when constructing a foundation, configurations with different design parameters are used.

After determining the critical components of the structure, the location of the load-bearing and non-load-bearing walls of the building, you can proceed directly to the arrangement. There are a few basic rules to follow here.

The main thing when selecting piles is the number, diameter and configuration of the blades, since the load-bearing capacity depends on these parameters. The thickness of the barrel wall and its diameter provide rigidity and strength, while the thickness of the barrel wall is decisive.

For critical components of the structure, two-bladed screw piles with the maximum blade diameter for a specific modification are suitable. This is due to a number of reasons. Firstly, they are resistant to all types of impact. Secondly, unlike single-blade ones, designs with two blades ensure the inclusion of a near-pile soil mass into the work of the pile, which increases the load-bearing capacity.

When determining the frequency of arrangement, one should proceed from two parameters:

• places where walls intersect and foundation turns;
• grillage sagging characteristics.

A common point of view is that, regardless of the type of object (house, bathhouse, etc.), in order for the grillage not to sag, it is enough to ensure that the distance between the piles does not exceed three meters.

The sagging characteristics of the grillage are a calculated value that takes into account the load on the strapping beam from each wall and is determined individually for each specific case. Only by calculating them will you be able to select the optimal cross-section of timber for the grillage and determine the span length.

Thus, when calculating the foundation, a large number of aspects must be taken into account. The diameter and design of screw piles, their number and combination are determined individually for each object.

The popularity of pile-screw foundations for private housing construction is gaining momentum. This type of foundation is very economical, 2-2.5 times cheaper than a strip foundation. In addition, the pile foundation can be installed at any time of the year, it is durable and easy to install (installation takes no more than 1 day), and its construction does not require special equipment or knowledge. Screw foundations can be erected on peat and waterlogged soils, slopes, and areas with difficult terrain. Another undeniable advantage is that the piles can be reused, which is important for temporary structures.

Pile-screw foundation is becoming a very popular foundation for a house. It is 2.5 times cheaper than tape, it can be installed all year round, and installation does not take more than one day.

In order for a pile-screw foundation to be of high quality, it is necessary to correctly calculate it.

• type of underlying soil;
• number of screw supports;
• pile depth level;
• location of installation of each support.

In addition, it should be borne in mind that the pile, like any building material, has parameters that must be taken into account if it is necessary to calculate their quantity:

• diameter;
• length;
• load bearing capacity.

Screw piles for various types of houses.

The first parameter is important when constructing a screw foundation for heavy structures. The remaining parameters are important in order to correctly distribute the load on the soil. The length of the pile must be sufficient so that it rests on solid underlying rocks and does not fall through. Bearing capacity is responsible for the same parameter, namely the resistance of the entire foundation to loads.

To determine how many supports are needed for the foundation of a private house, you need to decide on the type of underlying soil. If it is stable, with a flat surface, then the calculation will be very simple and will not take much time. If the site has different types of soil or complex terrain, then some problems are possible during the calculation.

It should be taken into account that when constructing a pile foundation for a private house, several types of piles can be used, which will create a strong foundation for the future house. An important factor for this will be the material from which the piles are made.

Calculation of the number of piles

How to determine how many supports are needed for a quality foundation? Calculation of their quantity required to build a high-quality foundation consists of three stages.

The first step is to determine the total load. It includes several factors:

1. The weight of the future structure, including internal walls, interfloor ceilings, furniture and interior items, roof and facade decoration.
2. The calculated payload that is created when the house is used by people. It is calculated based on clause 3.11 of SNiP 2.01.07-85* “LOADS AND IMPACTS”. According to SNiP, the payload for a private house is 150 kg/m2, and for office buildings - 200 kg/m2.
3. Snow load on a house, which is the pressure of a mass of snow on the roof and foundation during seasonal accumulation. The calculation of the snow load is described in clause 5.2 of SNiP 2.01.07-85* “LOADS AND IMPACTS”. For example, for the third snow region of Russia, the calculated snow pressure is 180 kg for every m 2 of roof surface;
4. The total load from the listed factors is summed up and multiplied by a factor of 1.1-1.2 to obtain the load value for calculating the number of supports for a private house.

Schemes of pile foundations made of various materials.

The second stage of the calculation is located on the construction site. This characteristic determines the maximum load on each foundation pile. It depends not only on the soil itself, but also on the climate. When cold temperatures prevail, the depth of soil freezing is much greater than in regions with a warm climate.

Can be determined in two ways:

1. Based on geological surveys. The rules for conducting geological research and calculating the load-bearing capacity of the soil are given in clause 4.10 of SNiP 2.02.03-85 “Pile foundations”.
2. If it is impossible to carry out geological surveys, the calculations must use the minimum design load on each pile. It is determined for most types of soil and also depends on the size of the supports used.

The averages are presented in the table:

Taking into account all the listed factors, at the last stage it is calculated how many supports are needed to build a high-quality foundation.

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Features of calculating the number of piles

Scheme of a pile foundation made of prefabricated screw piles.

Given the fact that the screw piles are located at a distance of 2-3 m from each other, there is a possibility that the house may settle unevenly over time. In order to avoid such problems, it is necessary to take into account possible additional loads on the foundation from the side of the building.

If strong winds of one direction prevail in the construction area, then at least 20% must be added to the load. As practice shows, in most cases, not 20% is added, but 30-35%, in order to cover all possible inaccuracies when . Many loads do not manifest themselves after construction is completed, so it is better to play it safe.

When calculating the loads from a building on a pile-screw foundation, it is necessary to take into account the internal load-bearing walls. The best option would be to place supports more frequently in such areas. If the wall is not load-bearing, then the piles can be placed at a greater distance from each other.

If there are weak underlying soils at the construction site, it is best to use wooden floors that have less weight. The walls and roof of the house in such conditions should also be as light as possible.

It is worth taking into account the fact that while overall saving money on the construction of a screw foundation for a house, you should not skimp on the quantity and quality of screw supports, since the reliability and durability of not only the foundation, but also the entire structure depends on them.

House Bathhouse Extension Veranda Pier Hangar Household Barn

The final cost may differ slightly from the base price, as it depends on more parameters and conditions for installing a pile-screw foundation on your site.

Find out how much the future pile-screw foundation costs, calculate the exact price, taking into account the parameters of your project.
If you have any difficulties using the calculator with installation, call us, tell the employee the necessary parameters and instantly find out the cost. Find out about current discounts, promotions and make your purchase as profitable as possible.

Price turnkey, calculator calculates based on the following main critical parameters:

• type of structure
• geometric dimensions of the house, bathhouse...
• construction material
• the need to install piles

The calculator automatically selects the optimal set of piles (their number, diameter, length, spacing), depending on the characteristics of the structure being built.
If there are specific features of a particular project that are not included in the parameters of the calculator, order a calculation from a specialist; it will take a minimum of your time, but will give the most correct cost.

To name the exact amount, we use a number of important indicators that allow us to carry out all work in compliance with SNiP standards. The BalSvai store catalog is rich in a wide range of screw piles of different parameters and load-bearing capacity. Calculation of a pile foundation for a house will help determine the configuration of the pile, quantity, screw-in depth, location steps.

What is taken into account when designing

If design calculations are carried out incorrectly, the pile is often unable to withstand the pressure of the structure of the structure; this will lead to subsequent replacement/strengthening and entail unnecessary costs.

During the project development process, the following points are required:

• actual weight of the building;
• weight taking into account operational loads;
• load from snow mass and wind influences;
• the material from which the construction will be made;
• location of internal walls/partitions;
• purpose of the building;
• soil properties for building construction;
• relief of the construction site.

We produce exclusively reliable products; the company pays special attention to the quality of products. We are trying to make prices for pile-screw foundations in Moscow and the region competitively attractive, this effort gives successful results.

The BalSvai LLC company is ready for all types of cooperation on special terms, provides 15 year old guarantee for materials and installation + individual discounts for clients.

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