Calculation of pile field on screw piles online. Screw pile foundation calculator, online calculation. Total weight of reinforcement

On the pages of our portal, options for constructing strip, slab, and column foundations are discussed in detail. However, often circumstances develop in such a way that none of the above schemes can be implemented in practice for one reason or another. Difficult terrain at the construction site, insufficient bearing capacity of the surface layers of the soil or a very large depth of its winter freezing, the presence of high water - any of these features can either make it impossible to use the most widely used technologies, or extremely complicate the design of the foundation, which, naturally, is accompanied by a sharp rise in cost the total cost of its construction. The best option may be a pile-type foundation.

Any building foundation requires preliminary design. And if a pile foundation was chosen for construction, calculation of the number of piles and their location become key planning parameters. Of course, it would always be better to entrust design and survey work to professionals. However, such calculations, albeit in a somewhat simplified form, can be carried out on your own. This will help, for example, in the construction of utility buildings, as well as for a preliminary assessment of the scale of work when planning the construction of a country house.

Most often in the practice of private construction, screw-pile foundations are used, and recently the use of bored concrete piles - the so-called TISE technology - has become widespread. Although the principle for calculating the number of supports for a building under construction is approximately the same, there are still significant differences, so these two types of foundations will be considered separately. Today it’s the pile-screw’s turn.

A pile-screw foundation is a set of metal piles buried (screwed) into the ground to the calculated depth, which are connected from above into a single structure by a common grillage. The piles are equipped with blades, which become not only a “tool” for screwing a metal support into the thickness of the soil - due to their area, the blades compact the rock below them during excavation and become a reliable support that can withstand considerable loads.

This technology allows you to go through the surface layers of soil, unstable soil, so that, in the end, the pile “finds” stable rock at a depth, usually below the freezing level, in order to minimize the influence of frost heaving forces. Not only do the blades of the pile rest on compacted soil, but they also successfully resist the forces that pull the pile upward. Thus, with proper calculation and installation, the building receives a stable foundation in conditions where other types of foundations would be useless or extremely complex and expensive.

The internal cavity of the pipe-pile is most often filled with concrete along its entire height (without additional reinforcement) - this makes it possible to protect the walls from internal corrosion. The installed piles from above are cut to a level at one level in the horizontal plane, caps with mounting platforms are welded to them, on which a grillage is placed, which then becomes the basis for the further construction of external walls and internal capital lintels.

The grillage can be mounted from various materials:

Illustration	Specification	Area of use
	1 – pile body (metal pipe); 2 – blade part; 3 – concrete filling of the pile; 4 – head with mounting platform; 5 – I-beam.
	6 – grillage made of channel.	Frame, block or brick walls, houses made of logs or timber, buildings made of metal sandwich panels.
	7 – strapping made of wooden beams (or lower crown); 8 – mechanical fastening of the strapping bars (corner); 9 – pin connection of strapping bars.	Frame houses, walls made of logs or timber, light outbuildings.
	10 – monolithic concrete grillage (in some cases – even a slab); 11 – connecting embedded reinforcing structure.	Houses made of brick, aerated concrete blocks, walls made of metal sandwich panels, frame, logs or timber.

This design ensures uniform distribution of loads across all supports and predetermines the main dignity pile-screw foundation:

Minimum construction time - in terms of this parameter, pile-screw foundations probably have no equal. With coordinated actions by the team, and unless, of course, the soil “brings surprises” such as an impassable rock ridge at depth, work on constructing a full-fledged foundation for building a house can literally take a day or two. The waiting period for full maturation characteristic of most other foundations is completely eliminated.

Very often, the construction of a pile foundation can be carried out independently, without resorting to the services of special equipment, which significantly reduces the overall cost of construction.

True, if financial opportunity allows, and there is a desire to save yourself from difficult manual labor, you can also use the services of a special installation for screwing in such piles. The work will go even faster and better.

Prices for screw piles

screw piles

The construction of a pile foundation is possible on almost all types of soil, including swampy and peat areas - the main thing is that the blade part reaches dense rock at a depth located below the freezing level. In this situation, frost swelling forces are unable to have any significant effect on the stability of the structure.
A pile-screw foundation is one of the most successful solutions when it is necessary to build on a site with rugged terrain. Although the screw part of all piles should be located at the same level horizontally, their upper part can be easily trimmed at the level, also bringing it into a single plane before tying it with a grillage.

When using high-quality piles that have anti-corrosion treatment, such a foundation should last at least 50 years.

However, foundations of this type also have certain flaws :

There are certain difficulties in installing close to newly erected buildings, for example, during the construction of an extension. The problem is solved by using special equipment.
Existing limitations on the load-bearing capacity of screw piles. However, this drawback is not significant when conducting private construction - the built-in capabilities of piles, with their correct selection, are usually quite sufficient.
It is not possible to equip a full-fledged basement or basement.
Finally, the most important drawback is the effect of corrosion on metal piles, which can significantly reduce their service life. Of course, conscientious manufacturers provide possible measures to reduce such impacts - galvanized pipes and special polymer coatings are used. However, it is difficult to completely eliminate the influence of corrosion. In addition, it can be enhanced by the unfavorable chemical composition of the soil, the high probability of stray currents due to the proximity of the house to electrical substations, mines, high-voltage power lines or cell towers, and the railway.

In addition, some owners unknowingly “plant a bomb” with their own hands by connecting a circuit to the screwed-in piles. There are no words for how grounding this circuit is quite functional. But this is the trouble - in any emergency situation with electrical appliances, the current will flow through the pile, sharply activating corrosion processes, especially in the areas of welds.

However, let's return to the topic of our publication. With high-quality installation of screw piles, their correct placement and tying, the load from the building should be distributed evenly over all points of support. This means that to determine the number of piles it is necessary to have two fundamental parameters - the bearing capacity of the support and the total load that will be created on the foundation. Moreover, not only the mass of the building itself must be taken into account, but also operational and other external loads.

First, let's look at piles - the varieties produced and the permissible loads on them.

Screw piles and calculation of permissible loads on them

Main standard sizes of screw foundation piles

Screw piles are now widely available for sale. There are several standard sizes, usually used in individual construction. They differ in the diameter of the trunk (pipe) and blades, and therefore in their load-bearing capabilities. In addition, piles of any standard size are available in a fairly wide range of lengths, usually from 1650 to 7000 mm, which allows you to choose the right size depending on the features of the planned construction.

The table below shows the main parameters of piles of the SVS model range - with welded blades of the screw part. These models are the most common and affordable. As a guide, average prices for piles 2500 mm long will be given.

Illustration	Brief description and purpose of the model	Approximate price level (length 2500 mm)
	SVS-57. The pile does not have a high load-bearing capacity - the permissible load is up to 800 kg. The standard area of application is lightweight fences that do not have windage, that is, made from chain-link mesh. Most often, 4-meter products are used, based on 2 meters of depth and another 2 meters for the height of the fence.	1300 rub. + 100 rub. for every additional 500 mm of length. Head OVS-57/200/200 – 260 RUR/piece.
	SBC-76 can withstand loads of up to 3000 kg, and therefore can be used for the construction of fences and enclosures of the “blind” type, that is, those with windage (from corrugated sheets, metal or wooden picket fences, slate sheets, polycarbonate, etc.) If necessary, they allow you to create an additional strip foundation for the fence between the supports. The most commonly used size is 4000 mm.	1450 rub. + 100 rub. for every additional 500 mm of length. Head OVS-76/200/200 – 300 RUR/piece.
	SVS-89 with a permissible load of up to 4÷5 tons. Typical areas of application are the construction of gazebos, outbuildings, and garages. Perfect for adding a veranda to the house. Used as additional support, for example, when installing a stove or fireplace in the house.	1500 rub. Head OVS-89/200/200 – 300 RUR/piece.
	SVS-108 can already be used in the construction of residential buildings - houses made of timber, log cabins or frame structures. The permissible load on the support can range from 5 to 9 tons. Excellent for construction on marshy and peaty soils.	1700 rub. Head OVS-108/200/200 – 300 RUR/piece.
	SBC-133 is capable of withstanding loads reaching up to 10÷14 tons. Such piles are used for the construction of foundations for the construction of fairly heavy houses made of bricks or aerated concrete blocks. It is permissible to use a monolithic grillage and even pour the floor slab of the first floor.	2250 rub. OVS-133/300/300 – 350 RUR/piece

Now here is a very important note. All the models presented above can be called a “budget option” - they are made using the technology of welding blades to the pipe body, and this is their main drawback.

Even a slight deviation in geometry when welding the blades can have the undesirable effect of deflecting the pile from the vertical when it is screwed into the ground. In addition, under extreme stresses that the blade necessarily experiences when screwing in, ruptures of the weld often occur - the pile simply begins to rotate in place, and there is no talk of any load-bearing capacity. Moreover, in the practice of using such foundations, there are cases when, under the consolidated influence of the corrosion already mentioned above and external mechanical load, the joint broke off along the seam after several years of operation. At the same time, the pile also significantly loses its load-bearing capacity, an additional load falls on the adjacent supports, and subsidence of this part of the foundation with deformation of the grillage, and therefore the walls of the house, cannot be ruled out.

If we approach the matter with all seriousness, and even more so in the case of constructing not an outbuilding or a fence, but a full-fledged residential building, the optimal solution would be to use piles with a cast screw tip. Made from steel ST-25 or ST-35 by precision casting in a vacuum environment, the tips have a precise spiral geometry, a thicker blade that will not be affected by extreme loads, and the absence of welds sharply reduces vulnerability to corrosion. The resistance of such tips to deforming loads allows you to screw in piles even in soils with small stones. With favorable physical and chemical characteristics of the soil and subject to proper installation, a foundation with such supports can last up to 100 years.

True, you will have to pay a slightly larger amount for this. Thus, the cost of one SVLN-108/300/2500 pile (abbreviation LN - cast tip) is already approximately 2600 rubles, and SVLN-133/350/2500 is 3350 rubles, that is, on average, a third more expensive than welded ones.

When choosing any screw piles, you must pay special attention to the quality of workmanship. The trouble is that there are many semi-handicraft manufacturers working in this area, whose products do not stand up to any criticism. This applies to pipes, to the steel used to weld the blades, to the quality of the welds, to the correct geometry of the propeller, and to the anti-corrosion coating of the piles. By the way, cunning “leftists” have even mastered the production of pseudo-cast tips, which in appearance may differ little from the real ones. So be extremely careful and never hesitate to request certification documentation, which must accompany any shipment of “legal” products. When it comes to building a foundation, you can’t rely on chance; mistakes can cost a lot.

The variety of screw piles is not limited to the above models - the most common and widely used options in private construction were simply demonstrated. And besides this, specialized piles are produced for rocky soils, which are shaped more like a self-tapping spiral, for permafrost - with an additional drill bit, and others. For particularly critical buildings with high specific pressure on the supports, screw piles with two rows of blades spaced apart along the height of the column are used. This allows you to compensate for horizontal soil movements, eliminate distortion when screwing in, and increase the load-bearing capacity of the pile. True, for the installation of more complex varieties, as a rule, it is no longer possible to do without special equipment.

Permissible loads on screw piles

After you have become acquainted with the characteristics of the piles, you can move on to considering an important question - what load-bearing capacity they will have, that is, what permissible load can be planned on them.

This parameter directly depends on criteria such as the standard size of the pile and the characteristics of the predominant load-bearing soil layer. If with the first indicator everything is relatively clear, since the piles are maintained in standard geometric dimensions, then with the second it is already more complicated. And this difficulty mainly lies in the fact that independently assessing the characteristics of the soil is not an easy task, and sometimes it is not at all solvable without the involvement of specialists.

So, the formula for the bearing capacity of a screw pile can be expressed as follows:

W=Q/k

W– in fact, the bearing capacity of the pile itself, that is, the operational load that the support is guaranteed to withstand.

Q– the calculated value of the bearing capacity of the pile, based on its dimensional parameters and the characteristics of the load-bearing soil layer.

k– the so-called “reliability factor”, which takes into account the required operational reserve of bearing capacity and depends on the quality of preliminary soil studies and, to a certain extent, on the total number of piles.

It would seem that the calculated value of the permissible load is also easy to determine. The following formula is used for this:

Q =S ×Ro

S – cross-sectional area of the supporting part of the pile, that is, its blade (in vertical projection).

Ro – calculated soil resistance at the depth level of the screw part of the pile.

Soil resistance is a tabular value that is easy to find. Some values for the most common soils on which the construction of a pile-screw foundation is practiced, provided that the screw part of the pile lies at a depth of 1500 mm and below, are given in the following table:

Type of soil at the level of the screw part of the pile	Soil features	Soil resistance at a depth of 1500 mm and below, kg/cm²
Sandy soil	Large fraction, from 2.5 to 5 mm	15,0
	Medium fraction, from 1.5 to 2.5 mm	15,0
	Fine fraction, from 1.0 to 1.5 mm	8,0
	Dust fraction, less than 1.0 mm	5,0
Sandy loams and loams	Semi-solid state	5,5
	Resistant	4,5
	Soft-plastic	3,5
Clays	Semi-solid state	6,0
	Resistant	5,0
	Soft-plastic	4,0
Loess	Soft-plastic	1,0

The plasticity of clay, loam or sandy loam can be determined by simply squeezing a soil sample in the palm of your hand - whether the lump will retain its given shape or crumble when touched. It is also not difficult to determine the sand fraction. Loess layers (porous rock with a characteristic fawn or beige color) are extremely rare, and their bearing capacity is extremely low.

However, that's not all. Let's return to the correction "reliability factor". It can take a value from 1.2 to 1.7. Not only does this already establish the operational reserve of the bearing capacity of the pile, but such an amendment will also take into account the accuracy of determining the soil structure. Let's explain in more detail.

The most correct decision when designing a foundation is a professional analysis of the condition of the soil at the construction site. To do this, wells are drilled in several places and samples are taken for organoleptic and laboratory analyses. Based on the results of the study, a conclusion is drawn up about the picture of the location of soils and aquifers, after which recommendations are developed for the use of one type or another. With this approach, the minimum reliability coefficient can be taken: k = 1.2.

Alas, such measures are rarely resorted to when performing “small-format” private construction, simply because of the high cost of these services: such a professional analysis may require an additional several tens of thousands of rubles.

Prices for foam blocks

foam block

The second method, which, however, will also require the involvement of specialists with the appropriate equipment, is screwing in a so-called reference well.

At the site for future construction, a pile of the selected standard size is screwed in. After its screw part passes the level of soil freezing, they begin to monitor the torque applied to the support. This makes it possible to determine with a high degree of accuracy the location of soil layers with maximum bearing capacity.

The cost of such services is no longer so high - only a few thousand rubles, so this approach is most often used in private residential construction. The degree of reliability of the obtained parameters is quite high, so the reliability coefficient is also assumed not to be particularly large: k = 1.25.

Finally, many developers, at their own peril and risk, determine the condition of the soil on their own by digging pits or drilling wells to the expected depth of the screw part of the pile, observing the structure of the soil in dug wells, cellars, etc.

Due to the fact that this approach is not highly accurate, the maximum reliability coefficient for calculations is taken into account. k = 1.45 ÷ 1.7. So, for saving in one thing (refusing the services of specialists), you may have to pay for an increase in the total number of piles. Something to think about...

Total load generated by the building and final calculation of the number of screw piles

Now it is necessary to calculate what load will fall on the pile foundation from the building planned to be erected on its basis. To do this, the weight of all building structures is calculated: external and internal main walls, internal partitions, floors - first floor and attic, rafter system and roofing. Operating loads are also taken into account - the mass of people living in the house, pieces of furniture and other interior items, large household appliances and equipment, etc.

You can “burrow into the tables” with the parameters of the main building materials and carry out this calculation yourself. We propose to do it even simpler - use the capabilities of the calculator located below, which, without claiming engineering accuracy, will still give results within a completely acceptable range of errors, which will be sufficient to determine the required number of piles for a screw foundation.

Calculator for calculating the load from a building planned for construction on a pile-screw foundation

A few necessary explanations for the calculation:

The wall material can be selected from the drop-down list. The area of the walls is calculated independently, using the “outlines” of the house or utility structure planned for construction. If desired, you can exclude window and door openings from the area, but sometimes this is neglected, especially since in this way an additional safety margin for the foundation is ultimately laid.

Having trouble calculating areas? We can help!

Even long-familiar geometric formulas sometimes get forgotten, and some complex configurations of rooms, walls or roofs sometimes baffle. An article on our portal will come to the rescue, specially dedicated and supplemented with convenient calculators to facilitate calculations.

The area will also be needed to determine the mass of the floors. The average operating loads on the floors are immediately entered into the calculation program.

The slope angle of the roof slopes is necessary to determine the amount of snow load. For the same purposes, you will need to determine the zone of your region of residence using a schematic map and indicate it in the corresponding field of the calculator - this will take into account the average snow load.

Finally, it makes sense to take into account the mass of the grillage connecting the piles.

If it is made with timber, then it won’t be a big mistake to simply include it in the wall area, and in this case, simply leave the default “0” on the “grillage length” slider.
But if heavy materials are used - rolled steel or reinforced concrete, then the increase in load can be serious. Therefore, it is necessary to indicate the total length of the grillages, including the outer perimeter and, if any, the planned internal lintels for the installation of capital partitions. Then the material of manufacture is indicated, and its specific gravity is already entered into the calculation program.

The final value will be given in kilograms and tons.

It has long been no secret that the correct choice of foundation for a house and the quality of construction determine the service life and convenience of living in it. It is necessary to calculate screw piles for the foundation at the project development stage, since without this information it is not possible to prepare an estimate or purchase tools and materials.

Design Features

Metal foundations, due to their versatility, have earned wide use among developers.

What are the features of piles?

Design. This is a welded pipe with a sharp end, on which screw-shaped blades are welded - a fixing element that does not allow the pile to move from its seat when the soil swells, stably holding the entire building.
carried out with precise control of the verticality of the pipe, done mechanically or manually. The main requirement is that drilling occurs to a stable soil layer. The piles are screwed in regardless of the time of year and precipitation.

Indicators influencing the calculation

Calculation of screw piles for the foundation will require determining the total load on the foundation of the house, which consists of:

The masses of the building installed on the foundation. When designing a house, mass is a calculated indicator; it is determined by the materials included in the structure.
Additional load, including snow, furniture, equipment and people. Information for this must be taken from the approved regulatory documents SNIP No. 2.01.07-85. The payload in the form of people and furniture is assumed to be on average 150 kg per m 2.
Soil density. To determine this, it is necessary to carry out engineering and geodetic research, since without this work the object will not pass the state examination. The calculation is carried out in accordance with SNIP No. 2.02.03-85.
For private construction of houses up to 3 floors, you can carry out research on your own.

After calculating the rated loads, it is necessary to take into account a safety factor of 1.2.

Types of piles

It is impossible to calculate a foundation made of screw piles for a house without first selecting their type. Each standard size is calculated for a specific type of object being built.

Dependence of pile diameter on type of load

Pipe diameter, mm	Purpose
		Under support pillars of various types of fencing.
		For light country houses.
		Heavy fences, one-story frame houses, gazebos, verandas.
		Buildings of 2 floors are frame type, as well as wooden buildings made of timber.
		Under medium-heavy houses made of foam blocks.
		For heavy brick structures and two- and three-story houses.
		Rarely used for residential buildings, more for industrial facilities.

The choice of length depends on:

Horizontal level of the construction site: if there are significant differences in height, then a choice of piles of different lengths is possible.
The nature of the soil. Reliable installation involves screwing to stable soil and below the soil freezing level by 25÷40 cm. In this case, the pile part should go into the ground no higher than 1500 mm.

Standardized length:

Short: 1.65÷2.5 m.
Long: up to 11.5 m (500 mm increments).

Calculation of the number of screw piles for the foundation: stages

You will need:

A plan of the site to the scale on which it is necessary to plot the planned foundation with center lines.
Tie to the communication lines: sewer pipe from the plumbing rooms and from the kitchen, drawing the diameters.
Results of engineering-geological research.

Location:

Single - point supports for light structures or country houses.
Tape - sequential arrangement with a certain step.
Custom - for heavy houses with many partitions and under each support in a frame building.

The calculation of screw piles for the foundation is carried out taking into account the layout features:

The distance between support points must be at least 2500 mm.
The pile should be installed in places of peak loads, which are concentrated at the center of the intersection of perpendicular lines, namely:

In the corners of the building.
At the junctions of load-bearing walls and partitions.
Intermediate supports must be installed evenly, including along the diagonals of the main cells of the building.
The size of piles and blades is determined depending on the type of load and soil characteristics.

Influence of soil on the calculation

Whatever screw piles are selected for loading is impossible without determining the bearing capacity of the soil. Thus, the soil does not always have the necessary composition to support a building without subsidence.

Important! The selected pile should not exceed the soil load capacity.

To determine, the composition of the soil is first determined and then compared with the characteristics given in the table.

Load value kg/m2 carried by different types of soil

Soil type		Soil resistance kg/cm 2 for a pile lowered by 2m (SNIP 2.02.03-85)
Soil type


	Small, wet
	Small, wet


Loams
Loams

In order to calculate screw piles for the foundation, it is necessary to determine the type of soil:

Coarse sand: 2.5÷5 mm one grain of sand, up to 2 mm - medium. Does not change its size.
Sandy loam is obtained by mixing sand with a small percentage (10%) of clay rock.
If the clay content is up to 30%, the result will be loam. When wet, the mixture does not spread and can be rolled into a ball, but cracks appear when pressed.
If a lump of wet soil does not crack under pressure, but is crushed plastically, the clay composition is above 30%.

Note! The higher the clay content, the higher the swelling of the soil.

Peat is a soft and airy composition that does not imply bearing loads.

The proximity of groundwater and the degree of moisture resistance is determined by drilling a well to the depth of lowering the pile. If water has formed in a standing pit, then there is a moisture-saturated soil with a close location of the aquifer.

Screw piles for foundations: customer reviews

One of the main tasks that arises during the design of the construction of a future building is calculating the load of the main structure on the foundation. The choice of foundation type and its configuration depends on the results obtained. This article is devoted to the features of the pile foundation of a house and its advantages. The conditions under which pile construction is most advantageous will be discussed, and examples will be shown of how to calculate the number of piles based on potential foundation loads and soil characteristics.

What is a pile foundation and what does it consist of?

The basis for this type of foundation is hollow steel piles, evenly distributed around the perimeter of the future load-bearing walls of the house. The outer surface is covered with a protective anti-corrosion layer based on zinc or polymer material, and the inner surface is protected with concrete poured into the installed pile. The upper part of the foundation piles is connected by welding to the cap, which in turn will support the grillage - a structure that combines individual piles into a single base. Most often, concrete, steel channels and I-beams are used to make a grillage, less often - wooden beams.

Unlike a strip or monolithic foundation, which is also loaded along the entire perimeter of the building, installation does not require a significant amount of excavation work. It is recommended to use a foundation on piles in the following cases:

The soils located under the construction site are characterized by instability, high humidity, and shrinkage under the influence of seasonal factors;
Construction is carried out in an area with complex terrain, where it is extremely difficult or impossible to install conventional foundations;
The climatic conditions in the area, as well as the groundwater level, according to the current SNiP rules, force the construction of a massive concrete foundation, which requires significant financial investments;
When constructing a frame building, as a rule, a pile foundation is used.

Types of foundation piles

There are two main categories that differ in the way they resist settlement of pile foundations: rack-mounted and suspended. The stability of a friction pile is ensured by the frictional force between the outer surface and the surrounding soil after immersion. Rack-mounted ones are equipped with a stop near their bases, which holds the structure based on the dense layers of soil underneath it. The blades of the screw piles also serve as a support, additionally compacting the soil during installation.

Separation of piles according to construction method:

Driven type

As the name suggests, these piles are driven into the ground using special mechanisms (construction pneumatic hammers). Their peculiarity is the fact that when driving, the force acting on it is taken from the calculation of the pile foundation. Thus, it is immersed to a depth at which there is a fairly strong layer of soil capable of supporting the estimated weight of the house. This type is considered very stable; when driven, the soil around it and under it is further compacted. Installation of driven piles is practically not used in the construction of small houses and private cottages, as it requires the use of complex special equipment.

Screw

The products consist of a steel pipe and blades welded at the bottom, or it is a one-piece construction (which is preferable in terms of durability). The blades facilitate penetration into the ground when it is twisted, and after installation they support the load on the pile foundation and prevent it from turning. At the top of the product there are special holes with which the pile is screwed into the ground. Moreover, this process can be carried out manually, controlling the vertical position during operation. The internal volume is filled with concrete to increase mass and protect against corrosion.

Bored

The procedure for installing bored piles does not provide for the use of ready-made metal structures. The role of the pile in this case is played by concrete poured into a pre-drilled well. If the soil is not dense enough, formwork will also be required. This method is quite easy to use and suitable for individual construction. The only caveat: the calculated load on the pile may be too high for the soil layer chosen as the base.

In further examples of the article, illustrating how to accurately calculate a pile foundation, the maximum load parameters of screw piles will be used. The following table briefly lists the most common brands of these products.

Details about the pile foundation with grillage

On the one hand, the grillage serves as a connecting element for individual piles, on the other hand, it is the basis for the rest of the building structure. The grillage and conditional foundation piles are combined in pairs (tape type of bundle) or all the heads are combined (tile type). A grillage for a home can be made from the following materials:

Reinforced concrete. The concrete strip is laid on the pile heads located at ground level. During design, the locations for laying shallow trenches running deep into the grillage are also indicated.
Concrete grillage of suspended type. A similar method in which a gap is left between the soil and the grillage. This gap allows you to compensate for possible ground vibrations (within normal limits).
Grillage made of reinforced concrete. The basis is an I-beam and a channel (for installation under load-bearing walls, SNiP recommends) channel 30.
Wooden beams. Lately they have hardly been used.

How to calculate the number of piles for a foundation

Correct calculation of the number of piles used requires preliminary geodetic survey. First of all, it is necessary to calculate the level of soil freezing in winter, taking into account that this indicator differs in different regions. To install the pile firmly, its lower end must be below this level.

It is also necessary to find out the degree of density of the soil layers. The higher the density, the shallower the depth of the pile should be laid at the design stage. For example, for semi-rocky and large-block rocks it will be minimal (but not less than 0.5 meters), and for sandy and clayey soils it will have to go as deep as possible.

To calculate the number and type of piles used, many parameters must be taken into account. To simplify the task, you can use a special online calculator, but for a general understanding of the process, it is better to go through all the stages of the calculation yourself.

1. Calculation of the potential ultimate load on piles

Before you start calculating the number of piles for the foundation, you should find out the bearing capacity of an individual pile. The general form of the formula is as follows:

In this case, W is the desired actual load-bearing force, Q is the calculated value of the load-bearing force, calculated for an individual pile based on the material, dimensions and characteristics of the soil; k is an additional “reliability factor” that expands the operational reserve of the foundation.

2. Calculation of the design load on piles

Where S is equal to the cross-sectional area of the pile blades, and Ro is an indicator of soil resistance at the depth of the blades. Soil resistance can be taken from the prepared table:

As for the “reliability coefficient” of a conditional foundation, its value can vary between 1.2-1.7. It is logical that the lower the coefficient, the lower the cost of the foundation at the design stage, since the use of a large number of piles will not be required to achieve a given value of the bearing force. To reduce the coefficient, a high-quality and reliable analysis of the soil at the construction site should be carried out, involving specialists.

And also for these purposes, the technique of screwing in a reference well is used. Its use is often required to calculate the settlement of pile foundations on industrial construction sites and during the construction of multi-apartment buildings, as required by SNiP. But if desired, a reference well can also be drilled during individual construction.

3. Calculation of the load from the building structure

At the final stage of designing a pile foundation, the number of piles is calculated. To do this, you will need to summarize all the structural elements of the building: from the main walls and ceilings, to the rafter system and roof. It is quite difficult to accurately calculate all components, so we recommend using one of the specialized calculators. And also operational loads are entered into the calculation calculator, including interior items, furniture, household appliances and even people living in the house.

4. Calculation of the required number of piles

Before calculating the number of piles involved, we need to obtain two values at the previous stages: the total mass of the building (M) and the load-bearing capacity of the pile (W) multiplied by the “reliability factor”. The value of the bearing capacity can be taken from Table 1. So, if the mass is 58 tons, and the adjusted bearing capacity of the SVS-108 pile is 3.9 tons, then:

As the calculation example showed, for a house weighing 58 tons, 15 piles of the SBC-180 grade will be required. It should be noted that this value is approximate and does not take into account the rules for the exact distribution of piles according to SNiP:

The first should be installed at the intersection points of load-bearing structures;
The rest are mounted evenly between the designated corners;
The minimum distance between individual piles is 3 meters;

As a rule, during the design process it turns out that to comply with the above rules, a little more piles will be required than the calculations showed.

5. Installation depth of piles and distance between them

The basic value of the installation depth of the pile is calculated based on the depth of soil freezing in a particular region, plus 25 centimeters. And also before calculating the pile foundation, you need to find out:

Pile strength level by material and design;
Bearing capacity of the soil;
Calculate the settlement of the pile foundation that occurs over time under the load of the building;
Additional parameters (temperature conditions throughout the year, precipitation volume, wind loads, etc.).

Conclusion

With the help of a pile foundation, you can quickly and for little money build a solid foundation for a residential or non-residential building. In some cases, this is the only option, since such a foundation is not afraid of ground settlements and can be easily erected on difficult terrain. In addition, compared to a traditional strip or monolithic foundation, installation of a pile foundation does not require a large amount of excavation work. If the pile foundation is correctly calculated, it will last for decades without losing functionality.

Almost any calculation of a pile foundation comes down to determining their diameter, length, number and pitch, as well as breaking down their position on the plan, both around the perimeter and inside the house. In this article we will look at how, if necessary, you can independently make a simplified calculation of this type of foundation using screw and bored piles.

Calculation of a pile-screw foundation

In a pile-screw foundation, metal screw piles of different diameters and lengths are used as load-bearing elements. In order to calculate a pile-screw foundation, specialists use complex calculations that take into account all the loads that act on such a foundation and the bearing capacity of the soil at the construction site. But, you can also make a simplified calculation, which is based on experience in constructing foundations of this type.

Selecting the optimal diameter of screw piles

Screw piles, which are used to construct the foundation for a house and outbuildings, can have a diameter of 57, 76, 89 and 108 mm. The diameter of the piles is selected depending on the foundation for which building or structure they are going to build and its weight:

– screw piles with a diameter of 57 mm are most often used for constructing fences with low weight, for example, made of mesh;
– piles with a diameter of 76 mm with a load-bearing capacity of up to 3000 kg, usually chosen for light outbuildings or medium-heavy fences (wooden or corrugated sheet);
– piles with a diameter of 89 mm and a bearing capacity of 3000-5000 kg, as a rule, are used for constructing foundations for light one-story houses (frame, panel), various extensions and outbuildings, as well as for heavy fences;
– piles with a diameter of 108 mm with a load-bearing capacity of 5000-7000 kg are used to construct foundations for one- and two-story houses with low weight (frame, timber, logs, foam blocks or aerated concrete).

Calculation of the length of screw piles

One of the important points in calculating a pile-screw foundation is the correct determination of the length of the piles. Because if they are not long enough, the house or other structures may sag under their own weight during their operation.

The length of the piles must be selected depending on two factors: soil density and elevation differences at the future construction site.

Soil density

In order to reliably know the characteristics of the soil on the site, it is best to use geological research data. If geological studies of soil characteristics have not been carried out on the site, then a simplified method for determining its density can be used. Using a shovel, dig a small pit, 0.5-1 m deep, at the lowest elevation of the site.

If dense rocks lie under the soil layer, such as dense clay or sand, then in this case it is advisable to choose screw piles 2.5 m long. If under the top layer there are low-density rocks: peat, quicksand or groundwater, then it is necessary to use a garden Using a drill, deepen the hole to the level of dense rocks and, based on the length of the drill, calculate the required length of the piles.

Height difference on the site

To select the length of the piles, in addition to taking into account the density of the soil, it is also necessary to take into account the height difference on the site. If there is a difference in heights on the site, then if piles with a length of 2.5 m or more are selected based on the density of the rocks, then they will be suitable for the top row. The piles that will be located in lower places should be longer by the difference in the elevations of the points at which they will be installed. The height difference can be determined using a level or water level, plumb line and tape measure.

It is advisable, if the height difference is more than 0.5 m, to add 0.5 m to each resulting pile length, because it often happens in practice that when installing piles in low places, 10-20 cm of their height is missing.

Simplified calculation of the required number of piles

The required number of piles depends on the size and weight of the structure that will be supported by the pile foundation. On average, the distances between piles can be as follows:

– for wooden houses (frame, frame-panel, timber or logs) – the distance should be no more than 3 m;
– for houses made of aerated concrete, foam concrete, foam or cinder blocks – no more than 2 m;
– for light fences – 3-3.5;
– no more than 3 m (in the presence of a large wind load – no more than 2.5 m).

Take or draw up a plan (diagram) of the future foundation or first floor of the house;
First you need to place the piles in all corners of the building;
After this, it is necessary to place the piles at the joints of the external and internal walls (load-bearing partitions);
Between the already located piles, it is necessary to mark the position of the piles under the external and internal walls in such a way that the distance between them is no more than that previously determined, depending on the type and weight of the house;
The rest of the internal space must be filled with piles so that the distance between the nearest piles is no more than the calculated one (2 or 3 m);
At the future location of the stove or fireplace, at least two piles must be provided (depending on the size of the heating device);
If the house has a terrace, porch, or extension, it is necessary to mark the installation locations for the piles according to the same principle;
Now that the locations of all the piles are indicated, all that remains is to calculate their total number.

Calculation of the bearing capacity of bored piles

Sometimes, when constructing a pile foundation for a house or outbuildings, instead of screw ones, bored concrete or rubble concrete piles are used, which are made by concreting wells prepared for them. The installation depth of such piles is selected depending on the characteristics of the soil on the site and the depth of freezing in the construction area and should be at least 0.5 m greater than the latter (0.2 m for the sand and gravel cushion, 0.3 m for the pile itself).

The number and cross-section of bored piles are determined in accordance with the calculation of the bearing capacity of such a foundation and the weight of the structure that will support this foundation. The bearing capacity of a foundation made of bored piles, in turn, is determined based on the resistance of both the foundation material and the soil (base and side surface). For a bored pile 1.5 - 3 m long, the load-bearing capacity can be calculated using the formula:

P – bearing capacity of the pile;
0.7 - coefficient of soil homogeneity;
Rн - standard soil resistance under the lower end of the pile (accepted from tables depending on the type and characteristics of the soil);
F – pile support area, m2;
0.8- coefficient working conditions
U – perimeter of the bored pile, m;
fin – standard soil resistance of the lateral surface of the pile, t/m2 (determined from tables);
li is the height of the load-bearing soil layer that is in contact with the side surface of the pile, m.

We do not provide tabular values of the standard soil resistance here, but, if desired, they can be easily found on the Internet.

In practice, bored piles are most often made with a diameter of 200-250 mm and placed in increments of 2-2.5 m.

Calculation of pile foundation grillage

A grillage is a horizontal reinforced concrete foundation beam or slab, which is constructed to evenly distribute the load from the weight of the house onto all piles. Therefore, pile-grillage foundations are constructed both during the construction of houses made of aerated concrete or foam blocks, and wooden ones. Tape grillages can be prefabricated or in the form of a monolithic strip. Both must be made of concrete grade no lower than 150.

In order to arrange a grillage on piles, it is necessary to calculate its required dimensions. There are special calculations for this, but we will not introduce them in this article. The recommended minimum dimensions of the strip grillage for a pile foundation are: height – 30 cm, width – 40 cm.

To ensure sufficient rigidity of the grillage, it is reinforced with steel reinforcement with a diameter of 10-12 mm in the longitudinal and transverse direction, tied together using a knitting wire in the form of an armor belt. There must be a distance of at least 2.5 cm between the reinforcement and the edge of the grillage to completely cover it with concrete and protect it from corrosion.

The connection between the grillage and the piles can be rigid or freely supported. In the first case, the grillage reinforcement is connected to the outlets of the pile reinforcement, in the second, the grillage rests freely on the upper base of the piles.

Simplified calculation of a pile foundation

How to make a simplified calculation of a pile foundation made of screw or bored piles and calculation of the grillage for them.

Calculation of a pile foundation is a very important stage in creating a project for a future house. If you make even the slightest mistake, the service life of the building will be reduced by twenty years at best. Under the least favorable circumstances, a disaster can occur during construction.

If the building area contains unstable soils with high humidity, or any complex terrain, then the only optimal solution would be a competent one. The main advantage of this design is the extremely high reliability of fastening even in relatively weak soils due to the fact that the supports are immersed to a sufficiently large depth. Such structures are much more reliable and durable, and their implementation does not require such a large amount of concrete, but you must understand that the process of their calculation and construction is quite labor-intensive.

There are more than enough reasons for calculating a pile foundation. Firstly, a properly modeled structure is highly stable. Secondly, driving piles is much cheaper than erecting a strip or tiled structure. Thirdly, with low bearing capacity of the soil, a pile foundation is the only possible option.

If the site has a low load-bearing capacity, then having made the correct calculation of the pile foundation, you will not have to dig deep trenches to make a reliable foundation. Screw piles are used for this. But the calculation formulas when using such materials become significantly more complicated.

Types of foundations with grillage

The grillage is the upper part of the foundation, with the help of which the pile heads are combined into one whole, and it is the grillage that represents the support for the future building. The combination of the grillage and piles is carried out using specialized welding or by standard concrete pouring.

According to the method of installation, grillages can be divided into several categories:

Tape - only adjacent piles are combined;
Tiled - each individual head is connected.

By type of materials:

Made of concrete with reinforcement. Piles are installed under the load-bearing walls, and shallow trenches are dug to the depth and width of the grillage;
Suspended concrete. It is similar to the previous option, however, the peculiarity of such a foundation is that the concrete strip does not come into contact with the ground, and the construction of a compensation gap makes it possible to prevent the rupture of the supports when significant ground vibration occurs;
Reinforced concrete. The manufacture of such a foundation involves the use of an I-beam or a wide metal channel, while a 30 channel is mounted under the load-bearing walls, while the remaining supports are connected using a 15-20 channel;
Made of wood. An extremely rare option that has hardly been used recently;
Combined. Not only metal load-bearing elements are used here, but also concrete.

What are screw piles

To correctly calculate a pile foundation, you need to learn as much as possible about the base material. This will allow you to draw up a project as accurately as possible, based on the characteristics of the pile structures, as well as their properties.

All piles are connected on top by a grillage. It can be made from either wooden or metal beams. You can also take a solid reinforced concrete slab. But this will greatly add weight to the main structure.

Pile structures for foundation calculations can be made either independently or ordered at the factory. When manufactured directly at the construction site, their base is best made flat.

To make a correct calculation of a pile foundation, knowing only the area of the structure is not enough. It is necessary to take into account the friction force that occurs between the side surface of the rod and the ground.

Previously, screw piles were often used by military engineers in the construction of fortifications. This was due to the fact that they allow the structure to withstand increased loads in extreme conditions.

Attention ! Pile structures are still indispensable when creating bridges and crossings.

The main part of the pile is the trunk. Its diameter is from 80 to 130 mm. The end is shaped like a sharp cone. A blade is welded onto it. This allows you to screw pile structures into the ground as quickly and efficiently as possible.

Some piles come without a head. In this case, there is a hole at the end of the barrel. A lever is inserted into it, which allows you to rotate the pile at the desired speed. This feature makes it possible to lengthen the barrel if necessary. This option is extremely necessary when work is carried out on unstable soils.

The advantages of pile structures include:

Safe installation technology, which allows you to build the foundation of a house in the shortest possible time.
Possibility of use on any soil. The only exception is rock formations.
When the piles are screwed in, no impact load is generated. Thanks to this feature, pile foundations can be built even in densely built areas, without fear for the safety of nearby houses.
As soon as the screw elements are installed, you can immediately install the grillages. Of course, this feature is taken into account in the calculations.
Calculation of a pile foundation can be done for both hilly terrain and uneven areas.
Installation is carried out in almost any weather conditions. It doesn't matter how many degrees outside the window. This will not affect the quality of the foundation in any way.
Possibility of redevelopment. No other type of foundation provides as much scope for design changes as a pile foundation. If necessary, the steel bolt can be unscrewed and screwed into another location.

Knowing the advantages and features of a pile foundation, you can make the most accurate calculations, taking into account all the design features.

We calculate the distance between the piles and the depth of their installation

The calculation of a pile-screw foundation with a grillage includes a large number of aspects, but first of all, the depth of the piles is determined, which depends on the type and complexity of the soil. First of all, you need to determine the standard freezing depth of the soil in your region of residence, and then measure below 20-25 cm - this will be the depth of the piles.

After the survey work has been carried out, it will be necessary to determine the level of groundwater, as well as the possibility of its fluctuation in different seasons and the qualitative characteristics of the soil on the site. It is best if a qualified specialist is involved in the design of the pile foundation, as well as its arrangement.

When calculating the number of screw piles for the foundation in each individual case, the following characteristics should be taken into account:

How durable is the material and grillage used;
What is the load-bearing capacity of the soil, also taking into account compaction during the installation of the support;
If there are significant differences in relief, then in this case the bearing capacity of the base of the support is also determined and taken into account;
How much will the piles shrink under the influence of vertical load;
What weight does the structure with internal contents have?
What seasonal, dynamic and wind loads are present?

In addition, it is imperative to take into account the settlement of the pile foundation. The pile foundation must be made in accordance with the working plan, so it is best if a professional architect is involved in its creation.

Important ! Calculation, as well as subsequent design of the pile foundation, is carried out only after all survey work on the territory, carried out by a qualified specialist, has been completed.

Data for computational formulas in this case will be selected depending on the quality of the soil and its type. It is worth noting that the calculation of a pile foundation based on shrinkage and deformation necessitates the highest possible accuracy of output indicators.

How to lay a foundation based on calculations

To make correct calculations, it is necessary to carry out geodetic surveys at the construction site. First of all, under soft soils, it is necessary to determine the depth of the layer that can support the weight of the building.

Important ! It is necessary to make calculations in such a way that the pile structures go deeper into the load-bearing layer by at least half a meter.

To find out to what depth the piles need to be screwed in, preliminary drilling is carried out. This allows you to determine where groundwater lies. You also need to consider how much the ground freezes in winter.

The entire construction process is divided into the following stages:

First, marking and alignment are done. The places where the main piles will be installed are determined. After this, you can install secondary elements. The distance between them should be in the range of two to three meters. There should be steel bolts under all the walls of the house.
Screwing begins with corner piles. A crowbar is passed into the upper hole of the steel bolt. To lengthen the lever, metal pipes are put on the crowbar. When screwing in, the deviation from the vertical cannot exceed two degrees. The angle of inclination during operation is controlled by a magnetic level.
The calculation of a pile foundation on corner piles is done using a hose level. Then marks are applied. They define the horizontal plane and the lower edge of the grillage.
The remaining piles are screwed in.
The screwing depth should be such that there is 20 cm from the top to the ground.
The non-load-bearing surface is cut to the designated levels.
The cement mortar is mixed. One part cement to four parts sand. The piles are filled with it.

Correctly carried out calculations at the level of planning a pile foundation make it possible to create a strong and reliable structure.

Examples of calculations

Calculating the strength of one element allows you to determine how many piles will be needed for the foundation in general. As a constant, let’s take the distance between the pillars to be two meters. Moreover, according to modern architectural trends, the supports must have a common grillage.

Example one

The diameter of one metal bolt is 30 centimeters. The estimated weight of the building is one hundred tons. In the formula for calculating a pile foundation, the bearing capacity of the soil plays a special role. Let’s take the most commonly found figure of four kilograms per square centimeter.

Important ! The load should not exceed the bearing capacity of the soil.

The indicator of the force that will act on each pile in the foundation is designated as Fst. The parameter is calculated using the following formula:

Let's clarify the values of all variables:

π is a constant quantity, an infinite number, which for simplicity of mathematical calculations is usually denoted as 3.14.
d is the diameter of the metal bolt (30 cm).
R - radius

Let's put everything into one formula:

Fsv=(πd2/4)·R =707.7·4=2826 kg.

This is exactly the weight that one foundation pile can support in this soil. Based on these data, we will continue the calculation.

The total weight of the building is exactly 100 tons. This figure was taken for ease of calculation. Before further calculation of the pile foundation, it is necessary to bring the indicators to one metric system. Let's convert tons to kilograms and get the value N (number of supports).

N= 100000/2826=35.4.

Of course, no one will install thirty-five and a half supports. Therefore, we round up. It turns out that in order to build a house weighing one hundred tons on soils with a bearing capacity of 4 kg/m2, at least 36 supports are needed.

Example two

To understand the algorithm for calculating a pile foundation, let’s fix the material and slightly change the basic indicators. Let's expand the base to 50 centimeters. This will increase the practicality of the entire structure. We will leave the remaining indicators unchanged.

Fst=1962.5·4=7850 kg

Let's calculate the pile foundation and get 13 supports. As you can see, expanding the base allows you to significantly save on the number of piles, achieving good structural stability indicators.

Example three

The calculation of a pile foundation, an example of which you will see below, can be used both for light country houses and for massive cottages, it’s just that in the first case standard screw piles are used, while when building cottages you will need to use massive bored piles that can withstand quite serious loads.

To simplify the example, the calculation of the pile foundation is carried out using screw supports. It is worth noting that for such small-sized piles, the calculation process does not take into account lateral friction, which is determined during the construction of heavy buildings that have a significant impact on the piles.

In this case, we will consider a detailed calculation of the total number of piles, as well as the step of their installation for a one-story house, the size of which is 7x7 m:

Initially, the total mass of consumables is determined. Let's assume that the total weight of the roof, timber and cladding will be 27526 kg, taking into account the snow load;
The payload size is 7x7x150=7350;
The snow load is 7x7x180=8820;
Thus, the approximate mass of the load on the foundation will be 27526 + 7350 + 8820 = 43696 kg;
Now the resulting weight will need to be multiplied by the reliability factor 43696x1.1=48065.6 kg;
Let's say it is planned to install screw supports, the size of which is 86x250x2500. In order to calculate their number, it will be necessary to distribute the resulting amount of the total load over the load that is applied to each pile. 48065.6/2000=24.03, round the resulting number to 24, and get the exact number of piles we need;
In order to install 24 supports, you will need to use an installation step of 1.2 meters. To form the floor joists, you will need to use two additional piles, which will already be located directly inside the house.

Thus, using the above technology, you can calculate the number of piles you need for any house, regardless of its features.

In the video below you can see how specialists calculate a pile foundation:

Results

A pile foundation is an economical and quick way to create a base for a building. It allows you to work in any weather conditions, and also makes it possible to erect buildings even on the most problematic soils.

Calculation of a pile foundation allows you to determine in advance how many piles are needed for a house of a certain mass. Using the formulas described in the article, calculations can be carried out quickly and accurately.