Pile foundation: calculation of the number of piles, bearing capacity and load

Tags:Design, With your own hands

Often there are situations when a strip or slab foundation is not suitable for the conditions of a particular land plot. The reasons may be different: too complex relief surface, weak bearing properties of the soil or a significant level of freezing. These and other factors make the construction of the base of the building overly complicated and its cost can exceed the cost of building the entire house. In this seemingly hopeless situation, experts recommend using a pile foundation. Calculation of the number of piles, their bearing capacity, the dimensions of the pillars, their depth and location - all this must be found out in advance.for the arrangement of the pile structure. You can make these calculations yourself, using the information, algorithms and recommendations that are offered in our material.

Pile foundation: calculating the number of piles

The pile structure will allow you to install a house on a site with any relief

The content of the article [Hide]

1 Screw pile foundations technology and their advantages
2 Varieties and features of the pile grillage
3 How to choose the right screw piles and calculation of permissible loads
4 Permissible loads on screw piles, taking into account the characteristics of the site
5 Bearing capacity calculator for pile supports
6 The simplest calculation of the pile foundation, without formulas and complex schemes
7 Load calculator for the whole structure

Screw pile foundations technology and their advantages

Basis of the device

A pile-screw base is a set of metal supports installed in the soil. On the surface, they are fastened into a single whole with the help of a grillage. Each pile has specially shaped blades. They help the support easily enter the soil and, in addition, simultaneously compress the soil and provide a solid foundation that resists increased stress.

The structure of the pile allows it to easily pass all levels of weak and unstable soil to dense layers. The support is deepened so that it is not afraid of surface deformations from getting wet and freezing.As a result, we get an exceptionally solid foundation of the house, which does not depend on the vagaries of the weather, terrain and soil structure.Inside, the metal support is poured with concrete mixture.

No additional reinforcement required, no metal inside the support to prevent internal corrosion damage

On the upper part, the pillars are cut along a single horizontal level. A metal mounting platform is attached to the cut point, on which the grillage will subsequently be fixed.

Scope of application

Such foundations are suitable not only for the home. Pile foundations are used for baths, carports, garages, construction of the foundation for the oven. This prefabricated base is used in the construction of lightweight structures: for gazebos and for fences... Piles can be safely used for the construction of premises with high humidity, for example, for a greenhouse. Such a base has proven itself well for sliding gates.At the same time, such structures are so reliable that they are used for metal overpasses of road bridges.

You can imagine what kind of loads such foundations can withstand if they are installed during the construction of bridges along which road and rail transport moves.

Advantages and disadvantages of a pile foundation

pros	Description
The cost	It cannot be said without accurate calculations that a pile foundation will cost much less than a strip or slab foundation. But any specialist in construction can confidently testify that the screws will cost at least twenty percent cheaper than a columnar base and two times cheaper than a full-fledged tape base. These significant savings can significantly impact construction costs.
Easy to install	To install the pile foundation, no special equipment is required. The screws can be screwed in by hand, requiring only three people.
Work speed	Installation of the foundation by professional workers takes only a couple of days. And pouring the strip base with digging a trench, installing the formwork and pouring it will take at least seven days. After the strip foundation should gain strength and settle for another month. And on piles you can build immediately after their installation.
Possibility of installation on sloping areas	It does not matter to the screw base whether there is a slope on the site and how many degrees it is. Even a difference of eight meters is not an obstacle to building a house.
Absence of excavated soil at the construction site	The installation site of the pile foundation does not change - there will be no piles of excavated earth and spilled concrete. Spot installation will keep the landscape of the site intact.
The ability to carry out work at any time of the year	If the construction of a strip foundation in winter requires a special heating technique and the use of additives that prevent concrete from freezing, then the piles can be screwed in at any air temperature without losing the bearing qualities of the structure.
Warm floor	The good thermal insulation properties of the air in combination with the pile base make the floors in the building under construction warm.
Possibility of extension	Adding piles to an existing foundation is easy. While the extension of the strip foundation will require significant effort and expense.
Easy to repair	If necessary, it is possible to replace a single damaged pile even after the completion of construction work.
Moisture does not reach walls	It doesn't matter what the house will be built from: from foam blocks or wood - its walls will be reliably protected from soil moisture. It will not penetrate the dotted base.

Minuses	Description
Weight limitation of structures	Such foundations are mainly suitable for lightweight structures: frame and wooden houses. Heavy brick walls can be overwhelming, especially if the load is calculated incorrectly.
Restriction by soil type	Screw supports cannot be installed in places where stony soil predominates.
Difficulties in arranging a basement	To organize the basement, you have to tinker. Usually it is done separately from the house, leaving only the passage in the area of the supports.
High requirements for the quality of the material	Unfortunately, it is not uncommon for unscrupulous manufacturers to let their customers down, saving on anti-corrosion treatment or metal thickness. As a result, the support quickly breaks down and bursts.

What you need to know when deciding to build a pile foundation

This type of foundation is impractical to use if dense layers of soil lie at a depth of more than six meters. In this case, the slab construction will be cheaper.
The screws should only be purchased from reputable manufacturers. Saving on material can be a waste of repairs.

The task of screwing in the supports will be greatly simplified by a special installation. She will do all the work in a matter of hours and with high quality

In the process of designing a foundation, one should take into account not only the size of the supports, but also all the parameters of the building and the characteristics of the soil on the site.
It is important to pay attention to the quality of metal protection against corrosion. The durability of the entire foundation depends on it. With proper processing, the foundation will last at least half a century.

Advice! You can independently analyze the soil on the site if you dig a hole at least two meters deep. Such research should be carried out aside from the future foundation.

Do not use supports for grounding power supply at home... In the event of a short circuit, the current passing through the metal of the support will provoke the development of rust in the welding areas.

Varieties and features of the pile grillage

In the construction of private houses, a pile-grillage foundation is mainly used. This foundation allows you to significantly save on construction and further reduce operating costs.

High-quality base strapping increases the reliability of the entire structure

If a residential building needs to be installed on loose soil, construction experts recommend using a screw-pile foundation.

The foundation strapping is divided into three types:

Suspended. This type of foundation is ten to fifteen centimeters above the ground. Hanging piles are especially in demand in subsiding soils. Buildings of lightweight material are built on such a foundation: frame and panel houses. This type of grillage needs additional insulation of the free space between the ground and the floor.

Suspended foundation

Ground and slab-pile. It is placed at soil level or at the level of gravel backfill and is often fixed by pouring ground slabs. Suitable for stable ground.

Ground pile foundation

Recessed or piled tape. Will cost more than other options and is suitable for loose soil. The depth should take into account the level of freezing.

Pile-strip foundation

Grillages can also be conditionally divided into three main types.

A type	Picture	Features:
Wood		It is used in the construction of houses made of wood and frame-panel structures. To distribute the load evenly, a large section strapping bar is used. This structural element is part of prefabricated houses.
Metal		A metal channel or beam is used to bundle the piles into a single whole. It is a stronger and more durable base than wood. It can be used as a frame for a pile-slab foundation. The floors of the first floor are laid directly on such a base.
Concrete		This type of grillage is rarely used. It combines all the positive qualities of pile and concrete foundations. This construction does not bend even under heavy brick and block walls.
Bush		This type of grillage is a "bundle" of piles located at several anchor points.The screws are installed close to each other and fastened together. Such a cluster arrangement allows for a good distribution of point pressure and is used under columns or other similar objects (power lines, towers, masts).

Bored grillage and shallow piles evenly distribute the weight of the building not only on the piles, but also on the soil itself

Shallow bored grillages-piles evenly distribute the weight of the building not only on the piles, but also on the soil itself

Note! To determine the optimal size of the supports and their depth, the information obtained from static sounding is used. During this study, the probe is immersed in the ground at a speed of about one and a half meters per minute. During the immersion, the equipment determines the degree of friction and resistance of the soil, the possible deviation of the drill from the given direction. The obtained data are necessary to determine the bearing capacity of the supports. The cost of such work starts from 1200 rubles per running meter.

How to choose the right screw piles and calculation of permissible loads

Screw piles: standard sizes and basic principles of selection

Screw piles vary in pipe diameter. Depending on this indicator, the purpose of the support is determined:

for individual housing construction - diameters 10.8; 13.3; 15.9; 21.9; 32.5 cm;
for small light structures (baths, gazebos, pavilions) - 8.9; 10.8; 13.3 cm;
for fences, advertising signs - 5.7; 7.6 cm;
for terraces, piers, walkways - 8.9; 10.8; 13.3; 15.9; 21.9; 32.5 cm.

Welding or Casting?

The poles are available in two types - they can be welded or cast. The production of these elements is different, consider the basic principles:

Welded ones consist of a pipe with a pointed end, to which the blades are welded. On the bottom, the welded screw elements are made of thick steel. In the production of such supports, it is important that the welded elements have clear geometric shapes. The slightest violation will lead to deviation of the pile from the vertical. In addition, in the presence of dense soil in the area, the weld on the screw may burst during the installation of the pole. As a result, the support will rotate and lose its load-bearing functions. It is not uncommon for welding to fail after the installation of the pole, several years after the start of operation of the foundation. A support without stabilizing vanes can sink under the wall mass.

Welded screw

Cast lugs are attached to the piles with a lock connection. They do not suffer from corrosion, therefore it is precisely such supports that are recommended for use in areas with a high level of groundwater occurrence. Cast steel screws have strong blades with precise dimensions, they are more resistant to loads and difficult soils. They can even be used in soils with fine stone filling. A properly installed cast pile will last a hundred years.

Cast screw

Note! The price for cast piles is higher than for welded ones. For example, a pile of the most popular diameter of 10.8 cm and a length of three meters will cost as follows: SVS-108 (welded) -1.8 thousand rubles, SVLN-108 (Cast) - 2.5 thousand rubles.

Before you buy the poles, check the quality of the product carefully. In the construction market, you can run into fakes that look like cast ones, but are actually made by welding and using used or defective materials. To ensure the quality of the product, ask the sellers for quality certificates. Do not be too lazy to check the pile wall thickness - it should be 4 mm for a high-quality support. The fake will have less. Look inside the tube with a flashlight - traces of use may be visible to the naked eye.

Number of blades

Piles can have a different number of blades. Supports should be sized according to the expected load.

A type	Picture	Appointment
Screw pile (screw)		Suitable for lightweight structures such as podiums or decking, for use in rocky soil
Single-blade support		Suitable for most foundations for different purposes
Two-blade pile		It is used for the construction of objects subject to wind loads (fences, billboards, awnings).

Note! The number of mounting holes is usually the same for all supports. They come in one standard size. Under the order for installation using special equipment, supports with nozzles for yamobur are selected.

Coating

What else should you pay attention to when choosing a support? It turns out that piles differ in the type of coverage:

two-component paint coating. This is an epoxy enamel. This paint was developed by manufacturers specifically for processing ground supports. It adheres firmly to the metal surface and is resistant to friction while screwing in the pile;
cold zinc. It is played by a thin zinc film with good adhesive properties. It is a good protection against corrosion, but zinc has little resistance to mechanical damage. Epoxy enamel is used to protect the zinc coating. This double processing guarantees the safety of the support;
hot zinc. The processing technology is the same as for galvanized buckets. Layer thickness - up to one hundred and twenty microns. It is a strong, durable and reliable coating. It will become practically eternal if it is additionally treated with epoxy enamel;

Zinc coating is the most resistant

heat shrinkable material. This is a new word in the protection of metal in conditions that provoke corrosive damage. The principle of processing is extremely simple, have you ever used shrink stickers on Easter eggs? And everything is very similar here. A tube of polymer material is put on the pile and then the pile is heated with a building hair dryer. The polymer tightly wraps around the support and after that nothing is scary: neither frost, nor moisture. A millimeter layer of polyolefin will not only reliably protect the support, but will facilitate its easy screwing.

Permissible loads on screw piles, taking into account the characteristics of the site

We examined in detail the types and sizes of piles, it is time to talk about their bearing capacity. How many supports will be required for a reliable foundation of your structure depends on this indicator.

The bearing capacity of piles depends not only on their size, but also on the characteristics of the soil.When designing the foundation, it is necessary to carefully examine the site and take into account the peculiarities of the local climate.

The stability of the pile foundation is achieved through the active resistance of the supports to the action of the compressive and buoyant forces of the soil

Advice! To increase the strength of the structure, the piles are installed in two-meter increments. With this arrangement, the foundation beam can have a relatively small cross-section.

Approximate parameters of the bearing capacity of the pile in different soils:

Soil type	Support load
Solid clay	4 - 6.2 tons
Soft clay	3.7 - 6 tons
Silty sandy soils	4 - 6 tons
Medium sands	9-11 tons
Loam	4.5 - 7 tons

One of the basic building rules is not to bring the load on the foundation to the maximum. To determine the behavior of the future foundation during operation, a test is carried out with a reference pile with a diameter of 114 millimeters. This composite support is driven into the ground and subjected to various types of loads: pulling, indentation, displacement. Using this method, data on soil resistance is obtained and the dimensions of the supports and their depth are determined.

All studies are carried out using special equipment that records changes in the state of the reference element

The load-bearing capacity can be calculated using the proven formula:

W = O / k, Where

W Is an indicator of the permissible load on the support;

O - calculation of the permissible load taking into account the size of the support and the characteristics of the soil;

k - coefficient of the operational reserve of the foundation.

First, let's calculate the value ABOUT... The following formula is required:

O = S x Ro, Where

S Is the cross-section of the support blade;

Ro - soil resistance at a depth to which the screw part of the pile will sink.

Find the last value can be for this or other tables containing general information on the characteristics of the soil in your area.

Soil characteristics table

Returning to the value of k will explain that it has records of 1.2 to 1.7. In this case, 1.2 - the lowest figure, characteristic of the most stable ground.

Advice! The most complete picture of the condition of the soil in the area and the exact calculation of the foundation can be obtained only by turning to the professionals, exploring the ground with the help of special equipment. Based on the limit states of the reference devices, they will determine the permissible horizontal load on the future foundation and make recommendations on the level of deepening of the supports.

Bearing capacity calculator for pile supports

We offer you to simplify the calculations use the online calculator bearing capacity of piles. This program is designed taking into account the requirements of SNIP and SP for pile foundations.

Specify the requested parameters and click "CALCULATE the bearing capacity of a screw pile"

Pile size

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Soil quality is determined:

- conducting professional geological surveys

- installation of a reference pile

- based on personally conducted research

CALCULATION RESULTS

Permissible load on the pile, taking into account the required safety margin

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The above method, as in the formula of which we spoke earlier, based on the size of the trunk and the support screws, installation depth and composition of the soil at the site.

Geometric data of supports is available to everyone, but data on soil properties can only be obtained as a result of professional research. If there is no such information, the program can calculate according to the average indicators included in the snippet. This option will help to get approximate calculation of data for the design to be used with caution, putting margin.

It can be used for calculations of special programs - SCAD or Lear. Members forumhouse note that the lyre more simple and intuitive interface, and Scud have the necessary calculations for sections of the designer. Furthermore, scad 21 is the possibility of visual imaging calculation results. In any case, and she and the other programs are available and understandable only to professionals. Not having the basic knowledge, the rookie is unlikely to deal with all the necessary to work with the program parameters.

Lira program interface

So, for self-calculations, we suggest you use the example of a calculator from this material.Having calculated the bearing capacity of each support, you can easily calculate the cost of the entire foundation.

Related article:

DIY foundation on screw piles. Any more or less competent builder is quite capable of making such a structure. Its advantages and disadvantages, installation and finishing features are all about this in our material.

The simplest calculation of the pile foundation, without formulas and complex schemes

Once identified all the features of the soil on the site and calculated the carrying capacity of screw piles for the foundation, one can start planning the foundations for a house.

We offer little benefit calculation for individual construction:

Select the diameter of the piles for construction. It does not require any complex calculations.It is enough to know that for one-story frame and wooden houses there are enough supports with diameters of 89 millimeters, and for structures made of foam concrete, piles with diameters of 108 millimeters will be required.
At some distance from the construction site, at the highest point of the site, dig a meter-deep hole. If clay or compressed sand is found at its bottom, choose supports with a height of two and a half meters. If soil moisture or peat is found, continue with a garden drill until you reach the clay.

Calculate the depth of the pillars by the size of the pit

Study the relief of the site for the foundation. All elevation differences should be taken into account. Pole sizes in low-lying areas should be larger. That is, the calculated length plus the height of the drop. And lay another half meter on "every fireman." It is easier to cut off the excess than to re-install the support.
To calculate the number of piles, you don't have to go deep into complicated mathematical formulas. For light frame-panel houses, the step between the supports is three meters, for foam concrete buildings - two. Draw a foundation plan on the grid and count how many posts you need to install. For optimal distribution of the load, they should be placed in the corners and at the intersections of the walls. Fill the remaining openings with support points with a step corresponding to the material of the house.

Important! Provide additional supports at the locations of the stove and fireplace. If a veranda or terrace is added to the house, this should also be reflected in the plan for the future foundation.

Using this simple guide, it is not difficult to correctly plan a pile structure for a simple structure.

Returning to the topic of how to calculate the load on the foundation, we can recommend another version of the online calculator. It will help determine the total load on the entire foundation structure.

Load calculator for the whole structure

So, the following program will help to calculate the total load on the base of the building, taking into account all important factors: the dimensions of the internal and external walls, the mass of the floors, the features of the rafter system and the roof covering. These indicators are important for determining the type and strength of the foundation. Even after rough calculations, you will see how different the results will be for a frame house and, for example, a foam concrete structure.

Specify the requested parameters and click "CALCULATE the total load on the pile foundation"

HOUSE WALLS

The area of the walls is indicated in total, if desired, it is possible minus the window and door openings (you can enter two options, for example, for load-bearing and internal walls. If the option is not used, leave the default area value - 0)

Walls, type 1

Wall area, m2

Walls type 2

Wall area, m2

Overlap

If there is an opening in the floor, for example, for an interfloor staircase, then it should be excluded from the total area (two options are available, for example, for an interfloor and attic floor. If this option is not used, leave the default area value - 0)

Overlap, type 1 (interfloor)

Overlap area, m2

Slab, type 2 (attic)

Overlap area, m2

RAILING SYSTEM AND ROOFING

When choosing the type of roof, the average weight of the rafter system with the crate will also be automatically taken into account. At the same time, an approximate value of snow load will be added to the weight of the roof, depending on the region of construction and the steepness of the slopes

Total roof area, m2

Specify the angle of the roof slope

- up to 25 degrees

- from 26 to 59 degrees

- from 60 degrees and steeper

GRILLAGE

If a wooden beam is used for tying the piles, then it can be taken into account in the area of the walls - there will be no big mistake. A grillage made of rolled metal or reinforced concrete is better taken into account additionally.

To take into account the grillage in the calculation?

- no, it is taken into account in the construction of the walls

- yes, add the weight of the grillage to the calculation

Grillage length (taking into account the outer perimeter and internal lintels), m

CALCULATION RESULTS

Total consolidated load on the foundation

Where to send the result?

Leave it empty if sending results is unnecessary

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Let's look at everything in order:

Component	Description
Walls	It is necessary to indicate the dimensions of the building structure, number of storeys and the material from which they will be made. You can subtract windows and doorways from the total area. If this is not done, an additional margin of safety will be included in the calculations.
Overlapping	Choose from four types of slabs. The program will calculate the load taking into account the mass of all floors based on average values for timber, hollow, metal or reinforced concrete structures.
Roof	From the proposed options, you should choose your type of roof and indicate the materials that you plan to use. As a result, you will get a lot of roofing with a rafter structure. The angles of the roof slopes and the indication of the region are required to calculate the possible loads from precipitation.
Foundation	The calculator will offer to select the type of foundation and indicate its basic material. By default, it is taken into account that supports are provided under all, including internal walls. The weight of the grillage is also taken into account. The wooden grillage will be taken into account within the total area of the walls, but if you plan to use metal or concrete for strapping the pile foundation, indicate this in the program.
Finishing	Interior and exterior finishes also exert stress on the base. It should indicate what materials are planned to be used for these purposes. Recall that under the columns, if there are any in your house, it is necessary to provide additional sets of several piles placed by the cluster method.
Other loads	The weight of furniture, people, snow load - all these additional parameters will be included in the calculation.

The final result will be in tons. Final calculations can be made without special tools. In the first calculator, you got the size of the load on one pile, taking into account the characteristics of the soil. In the second, the total mass of the structure. It remains to divide the second result by the first and get the required number of piles.

Important! Do not forget to provide for the placement of additional piles at all points of intersection and conjugation of the enclosing structures.

And at the end of the topic about the pile foundation, some more useful information:

Screw piles are used not only for the construction of new objects, but also for the restoration of old ones. Reinforcing existing foundations with drill injection piles does not require capital intervention. Thus, it is possible to significantly strengthen the foundation of even multi-storey structures.
When installing a pile foundation with a concrete grillage, do not forget about high-quality concrete reinforcement.

Video tips for proper planning of the pile foundation