If you managed to buy a wonderful plot at a surprisingly low price, do not rush to rejoice - it is quite possible that the groundwater on the purchased plot comes close to the surface or you got heaving soil. These factors can cause your foundation to cost a lot more money than expected. In addition, you also need to choose the right type of foundation so that uneven settlement of the house does not occur in the spring.
What is a pile-screw foundation?
The best option in such cases is a foundation on screw piles, suitable for any terrain and for any “problematic” soils.
Pile screw foundations have been successfully used in construction since 1850, when the first lighthouse on stilts was built in the United States. The fact that the lighthouse still stands today confirms the high strength of the screw foundation and explains why this technology has gained such popularity throughout the world in a relatively short time.
Installation of foundations on screw piles is possible on any terrain
The peculiarity of a screw pile is that this steel pipe has a pointed tip with a thread and blades or a combined thread for screwing into the ground. The most expensive are screw piles equipped with blades, but they compact the soil better due to their design. There is no specific standard for screw piles. They are solid and hollow, of various diameters and lengths, with a cap at the top of the pipe of a rectangular, round or U-shape.
Video about foundations on screw piles
Installation of a foundation on screw piles is possible on any terrain: on uneven or flooded areas, on slopes, on peat soils, on well-groomed lawns without the risk of harming the lawn, near large trees. Thus, there is no need to carry out any preliminary work to clear the site and level it, and there is no need to disturb the natural topography.
Advantages of a screw foundation :
- there is no need for excavation work;
- there is no need to provide access roads for equipment;
- installation can be carried out in winter;
- three people are enough to build the foundation;
- all work on laying the foundation takes from one to three days;
- You can always easily add a new structure to a house built on stilts.
All foundation work takes from one to three days
Piles can be screwed into the ground, either using special equipment or manually - the pillars themselves make their way in the soil to a given depth. If necessary, the screw foundation can be quickly dismantled (if you do not fill the hollow pillars with concrete) and moved to another location. Thanks to the listed advantages, foundations on screw piles invariably receive the best reviews and are successfully used in industrial and private construction.
How to deal with a screw foundation on your own
Screw piles for the foundation must cut into solid layers of soil that lie below the level where the soil freezes; in this case, the pillars will not be subject to the force of soil heaving. To correctly determine at what depth a stable layer of soil is located, it is best to contact a specialist. In addition, to correctly calculate the future foundation, you will need to take into account the weight of the future structure, seasonal fluctuations in groundwater, soil type, wind load and climatic features of your region. Finding out all this on your own is not so easy.
The number of piles is determined depending on the dimensions of the building under construction. The pillars will need to be evenly distributed under the base of the building with the same spacing, not forgetting about the nodes of the internal walls and the corners. The length of the ground part is usually about half a meter; the visible part of the piles can be hidden behind a false base or left open.
The number of piles is determined depending on the dimensions of the building under construction
The construction of a screw foundation is carried out as follows:
- markings are applied to the site with pegs exactly in the places where the piles will be located;
- the piles are twisted manually using a special rod, and their level position is checked using a level;
- the installed piles are leveled to the same level with a laser level, the longest pillars are trimmed with a grinder;
- Concrete is poured into the cavity of the pipes to protect the internal surfaces of the piles from corrosion;
- It is recommended to coat the outside of the ground parts of the pillars with an anti-corrosion compound;
- A metal frame is welded to the supports and painted in two layers of protective paint.
Video about screw foundation
Insulation of the foundation on screw piles is not required, since this type of foundation is ventilated. High supports protect the house from the cold that comes from the ground. You can insulate the grillage, but keep in mind that improper thermal insulation will lead to dampness, which will negatively affect the entire structure. To make your house warmer, it is better to pay attention to insulating the floor rather than the screw foundation.
If you come across reviews about a pile screw foundation that are not very positive, this means that some mistakes were made during the construction of the foundation (holes were dug for the pillars, the position of the pile was not controlled when screwed, the pipes were not protected from corrosion, etc.) . But even if, due to improper installation, the building sank a little, you can always repair the foundation with screw piles, replacing the sagging pillars with new ones. The ability to quickly repair is another great advantage of a screw foundation.
Making screw piles is difficult, but it is possible. Therefore, we will take the liberty of describing this technology. And the advice of FORUMHOUSE users will help us with this.
Let's consider the manufacturing process of the main elements indicated in the drawing.
Trunk
The base (trunk) is a hollow metal pipe.
In all cases, barrels are recommended to be made of steel with a strength of at least St. 20 according to GOST 8732-74 (for ordinary structural steels). If stronger alloy steels are used, then GOST 19281 is suitable (but at home you can limit yourself to the first option).
The first thing the creator needs to do is determine the length of its trunk. Using various “tricks” he will have to find out at what depth of the construction site the hard soil is located. The most correct (but expensive) solution would be to contact a geological exploration service. But among the sociable neighbors you may find a person who has a reasonable idea of the state of the underground layers.
The length of the pipe should exceed the depth of the load-bearing layer by approximately 300...500 mm (if the pile protrudes higher from the ground, this distance may be greater). People with practical experience recommend making the length of the piles with a margin, so that later they do not have to be increased.
BSergeyM User FORUMHOUSE
We screwed 17 pieces (house 9 by 8). Site on a slope. I trimmed some of the piles, extended some and filled them with concrete.
In order to determine the diameter of the pipe, you can refer to SNiP 2.02.03-85 (with its tables and formulas). But those who are not practically familiar with the design of building structures are guided by less sophisticated calculations:
- Pipe with a diameter of 47 to 76 mm is used in the construction of light fences and all kinds of fortifications
- Piles with a diameter of 89 mm are used in the construction of courtyard buildings (gazebos, bathhouses, etc.), as well as in the construction of brick fences
- For the construction of frame houses and log buildings, options with a diameter of 108 mm are used.
At home, it is not recommended to make DIY screw piles with a diameter exceeding 108 mm (which can withstand high loads). They will require a reinforced blade, and it will be very difficult to ensure such a product with high quality if manufactured independently.
Alexey Oreshkov User FORUMHOUSE
The larger the diameter, the more difficult it is to make the screw, that is, the blade itself to bend.
The minimum thickness of the barrel walls should be 4 mm. Its calculation is simple - the thicker the better. But when choosing the wall thickness, you should remember that the pile cone will have to be bent with a hammer.
Alexey Oreshkov
I made screw piles myself, it’s really possible to do it yourself. Pipe – 68x4 mm, screw – diameter 168 mm, screw thickness – 5 mm, pitch on the screw – 50 mm, tetrahedral tip length – 150 mm. Everything is cooked very well using a semi-automatic machine.
DIY screw piles. Cone
As can be seen in the drawing, the cone is the tip of the pile. Its length is equal to 1.5 to 2 pipe diameters. This is the standard, but some make the length a little longer to make the cone sharper and the pile to go into the ground easier.
At home, the cone is made tetrahedral or hexagonal. To do this, special sectors are cut out at the edge of the barrel, which are bent with a hammer into a cone and scalded by welding.
Bone FORUMHOUSE user
I made a template from thick paper, after dividing the circumference of the pipe into equal parts. Then I marked the pipe with a marker and made cuts with a grinder. The result is the so-called crown. The thickness of the pipe allows it to be easily bent with a hammer. At first it turned out very clumsily, but by welding all the defects were eliminated, and the tip turned out to be completely sealed, which made it possible to fill the pipe with concrete immediately after twisting.
This is what it looks like in the photo:
Do-it-yourself screw pile, manufacturing.
As you can see, the barrel was marked using a paper pattern. It's quite simple to produce. To do this, the diameter of the pipe circumference must be divided by the number of sectors. The found value is the distance between the top points of neighboring sectors. It is easy to transfer the data onto a paper drawing and get a ready-made template. Further actions consist of cutting out the “crown”, bending the petals and welding the resulting joints.
Before bending the cone petals, small slits should be made at the base of the crown. Then it will be easier to form the tip.
Construction of screw piles. Blade
The blade is the main working part. It should be made from sheet steel 5 mm thick. Many people prefer to do this. Someone manages to make a blade 6 mm thick, but bending such a part correctly is much more difficult. The blade material is carbon steel of ordinary quality (GOST 380-71). It is optimal to use the grade 3 (it is used even in the industrial production of piles).
Now it's time to talk about the shape of the blade. Creating its geometry is the most critical stage of work. And if you make a mistake, the pile simply will not screw into the ground.
First, let's determine the internal and external diameters of the blade blank. The outer diameter of the blade (pile width) is directly dependent on the diameter of the pile shaft. Take a look at the table.
The internal diameter of the blade corresponds to the diameter of the pipe. Only the dimensions of the workpiece (taking into account the fact that it will bend to form the pitch of the screw) are slightly different from the diameter we already know. A simple solution for determining the dimensions of the workpiece is offered to us by the user of the FORUMHOUSE portal.
Ergali User FORUMHOUSE
Take a pipe and measure the screw pitch on it. After this, measure the length of the turn on the pipe, divide by Pi and get the internal diameter of the workpiece. You add the width of the blade to the inner radius of the workpiece and get the outer radius of the workpiece.
Now a little about how to determine the propeller pitch. Typically the propeller pitch is 0.2…0.4 from the outer diameter of the blade. If the propeller pitch is smaller, then small solid inclusions in the ground will get stuck between the blades, interfering with the progress of the pile. If this figure is higher, you will have to make more effort to screw it into the ground.
Which specific step to use depends on the type of soil into which the piles are to be screwed. It’s easier to focus on the characteristics of the soil: the harder the soil in your area, the smaller the propeller pitch should be. On sandy soil (predominant in the east of Moscow), we take the maximum step.
Once all the dimensions have been determined, you can begin marking the steel sheet and cutting out the workpiece. To cut out the contour of the workpiece, we will need a plasma cutting machine with sufficient power, and we should make sure that it is available in advance.
At the next stage, the cut blank is bent in accordance with the selected screw pitch. At home, this can be done using an ordinary vice and available tools.
User FORUMHOUSE BSergeyM offers its own version of the blade extension device.
Screw piles: manufacturing.
Please note that the bend on the cutting edge of the blade is quite small. This is how it is always done. Such a bend is enough for the pile, like a self-tapping screw, to go into the ground.
On the part of the blade that will go first into the ground, it is necessary to make a cut at 45°. This will help the pile to easily bypass solid mechanical inclusions located in the ground.
At the next stage, the finished part is welded to the pile shaft. The seam is laid at the top and bottom of the blade. The blade must be welded perpendicularly. Otherwise, the pile will loosen the soil while screwing in, destroying and weakening its structure. And on weakened soil, the pile will not be able to cope with the loads placed on it.
The foundation on screw piles is a load-bearing structure that supports the weight of the structure. Pile foundations are widely used in the construction of multi-story buildings and private housing construction. The design is characterized by low financial costs, ease of installation, reliability and versatility. The installation of a pile foundation for a summer house or cottage can be done independently, having certain knowledge and a simple set of tools.
The main difference between a pile foundation and a slab or monolithic foundation is the absence of excavation work. This is especially important if it is impossible for earthmoving equipment to arrive to construct a pit. Also, the advantages of a screw base include:
- Possibility of erecting a structure on soft soil (loams, loess, quicksand, sandstones, etc.). When using screw piles, the load will be taken not by the upper, but by the lower, stronger layers of the soil.
- Warm floors in the house. Thanks to the non-continuous structure of the pile foundation, an air gap is formed between the soil and the base of the house, which is an excellent heat insulator.
- Device on an inclined area. If there is a complex terrain with different heights and differences in the area, a screw foundation can be used without expensive landscaping work.
- Simplicity and high speed of installation. You can make a pile-screw foundation with your own hands without using construction equipment. You can install a screw base for your home all year round at any temperature.
- Low cost. Screw piles are many times cheaper than pouring a monolithic or laying a slab base. On average, the price of a pile foundation is 50-60% lower than a monolithic foundation of similar area.
- Maintainability. If a screw pile becomes deformed or breaks, it can be easily replaced.
- Does not attract moisture. Due to the fact that a small area of the foundation is in contact with the ground, moisture and groundwater do not enter the house. The basement and basement, built on a pile foundation, are always dry and warm.
Despite the advantages, it is worth noting that in many cases the construction of a screw foundation is impractical due to the following disadvantages:
- Requires careful engineering calculations.
- Not suitable for heavy monolithic structures.
- Not applicable on rocky soils.
- Metal screw piles are susceptible to corrosion.
- Not used for rocky soils.
- Expensive and complex basement design.
It will not work to use a pile foundation as basement walls.
The walls can be made of bricks or blocks, but this will lead to a significant increase in construction costs. This is why 90% of houses on screw piles do not have additional usable space in the form of a ground floor and basement.
Calculation of a pile-screw foundation
The calculation of a screw foundation is carried out in order to obtain:
- diameter of pile supports;
- length of screw piles;
- distance between supports;
- number of piles.
The calculation is carried out on the basis of SNiP 2.02.03-85 and SP 50-102-2003 standards. For multi-storey buildings and large-scale objects, the calculation of the pile foundation is carried out using special computer programs. When building a private house, you can perform the calculations yourself, without resorting to the services of design organizations.
Screw piles are standardized products manufactured in accordance with GOST of the following diameters:
- 57 mm - suitable for small and light structures: fencing, outbuildings;
- 76 mm - used for structures whose weight does not exceed 3 tons;
- 89 mm - used for the construction of country houses, bathhouses, verandas weighing no more than 5 tons;
- 108 mm - suitable for houses made of gas and foam blocks, wood, frame-panel buildings.
Expert opinion
Sergey Fedorov
Ask a question to an expertWhen constructing 2-3-storey houses, reliable piles with a diameter of 108 mm are almost always used.
Determination of the length of screw piles.
The length of screw products is determined on the basis of hydrogeological surveys at the site where construction is taking place. If the project for your future home does not contain a geological survey section, then you can use publicly available maps for your area.
If the top layer of soil is represented by weak soils or quicksand, then the piles must go deep to hard rock, which means that when calculating the length it is necessary to take into account the thickness of the weak layer.
For each type of soil, the length of the screw piles is determined according to the SNiP tables, taking into account the density of the soil and the region of construction:
The grillage device is the simplest and most popular reinforcement for a screw foundation. In most cases, a grillage is sufficient to ensure the reliability of the structure, but if the house is being built on soft soils or is heavy, then additional reinforcement is required.
For pile-screw foundations of private houses, there are the following ways to strengthen the foundation:
- Tying a screw foundation with metal pipes. For strengthening, profiled pipes 30x60 are used. Pipes sequentially connect all the supports of the pile base along the perimeter and inside it. The pipes are connected to each other by welding. This type of harness is optimal on unstable and floating soils.
- Strengthening the pile foundation with metal structures. The strengthening technology is based on the use of products such as channel 16, 20 and 22 or angle. Metal products are welded to the top chord of the piles instead of the head. The result is a strong metal frame on which the house will rest. The method is suitable for swampy areas and peat bogs.
- Additional soil reinforcement. In the process of installing a pile-screw foundation, the integrity of the soil is compromised; it may sag or become looser. To strengthen the soil, compaction, cementation, and resinization are used.
Arrangement and insulation of the basement
A full-fledged base with usable space will not be possible when installing a screw foundation. Therefore, when talking about a plinth, builders mean a false plinth, which gives the building a complete aesthetic appearance. The finishing of the false base must meet the following requirements:
- be moisture and frost resistant;
- have minimal thermal conductivity;
- be resistant to mold, insects, rodents.
The choice of finish for the base depends only on the preferences and financial capabilities of the owner. You can cover the base with facing bricks, tiles, artificial and natural stone. You can use ordinary reinforced concrete slabs followed by plastering or painting. For wooden and timber houses, an excellent option is to cover the base with clapboard.
To preserve heat and create a comfortable microclimate in the house, it is recommended to insulate the base and grillage. Insulation can be carried out inside or outside, depending on what material was chosen for finishing. Lightweight insulation materials with high thermal insulation parameters are used as thermal insulation:
- extruded polystyrene foam (penoplex);
- liquid sprayed polyurethane foam;
- ordinary polystyrene foam in PSB-S 35 slabs.
Insulation work begins with covering the grillage and base with waterproofing. As a waterproofing material, special membranes or cheap and easy-to-install roofing felt are used. Covering the grillage with insulation in the form of slabs is done using fastening dowels and nails. If polyurethane foam was chosen as insulation, then it is sprayed in a layer of 3-5 cm. The thermal insulation must be sealed with sheathing made of boards or laminated chipboard panels.
Expert opinion
Sergey Fedorov
Professional builder. 18 years of experience
Ask a question to an expertIs it necessary to insulate metal screw piles? Builders answer this question in the negative. Insulation of piles in this case is not only economically unprofitable and troublesome, but also leads to a decrease in the service life of the foundation due to increased corrosion.
Blind area for pile-screw foundation
It is necessary to make a blind area for a screw foundation. It is better to begin its arrangement during the construction of the basement. The blind area performs important functions:
- prevents precipitation from entering the space between the floor of the house and the ground;
- is additional thermal insulation for the first floor;
- gives the building an aesthetic appearance;
- serves as a sidewalk.
The design of the blind area is simple, you can quickly do it yourself as follows:
- A trench 20-30 cm wide and deep is dug along the perimeter of the base of the house.
- A 10 cm thick layer of clay is poured onto the bottom of the trench.
- Ruberoid or other insulating material is lined.
- Gravel or coarse sand - 10 cm - is poured onto the roofing material.
- Boards 3 cm thick are installed along the perimeter, edge up.
- On the opposite side of the boards, formwork is arranged so that a slope of 5 degrees is formed.
- The trench is filled with concrete.
- After the concrete has hardened, the seams between the boards are filled with fine sand.
The top covering of the blind area is made of tiles, stone or any other moisture-resistant materials to the taste of the owner. If a house is being built on an area with a high level of groundwater, then drainage is necessary to drain the liquid. Drainage pipes made of ceramic or PVC are laid below the edge of the blind area in a pre-dug trench on a gravel-sand cushion 20-30 cm thick. Water through the drainage pipes will be drained into a well, artificial reservoir or sewer system on the site.
Service life of a pile-screw foundation
A foundation on screw piles without reinforcement lasts an average of 25-30 years. After this period, the piles begin to collapse, and the base requires dismantling and replacement. When using galvanized piles and under favorable operating conditions, the piles can last up to 40 years. Factors that shorten the service life of a screw foundation are:
- high concentration of groundwater on the site;
- reduced soil acidity;
- temperature fluctuations in the region;
- presence of stones in the soil;
- poor-quality installation, violation of technology when screwing in piles;
- increasing the load, for example, building another floor, terrace, etc.
In order for the foundation on screw piles to last as long as possible, it is recommended to inspect it every 2-3 years and replace or repair deformed piles or grillage elements.
The pile-screw foundation is one of the best in the construction of not very heavy buildings, excellent for. To understand all the pros and cons of this type of foundation, let's look at it in more detail.
Screw piles are time-tested
Pouring piles with concrete
After leveling, a concrete mixture is poured inside the piles, which is designed to protect them from corrosion from the inside.
Installation of a grillage on a pile-screw foundation
At the final stage they install, i.e. the very foundation for the future home. For lighter structures, for example, houses made of timber or logs, installation from thick timber is possible. For houses made of bricks or blocks, it is better to make the grillage using reinforced concrete.
The pile-screw foundation will not require any time for shrinkage; you can continue immediately after installing the grillage. Now you can begin installing the frame of your house. The foundation is ready for loading and full use.
Where to buy piles and what is the price?
So, one of the best options for creating a foundation yourself is a screw foundation, which is also one of the simplest, but is not inferior in quality.
In order to create a foundation on screw piles with your own hands, you don’t even need to carry out any preparatory work or prepare the site. This technology was developed specifically for areas where installing a full-fledged foundation is not possible or simply not profitable.
This may be a mountainous or forest area, where tree roots can prevent the creation of a hole, for example, under a strip foundation. The simplicity of the technology allows you to install a screw foundation with your own hands without the help of professional construction companies and at the same time understanding it is not difficult.
Site marking
Now let's move on to the process of creating a screw foundation with your own hands. First, you need to mark the required area of the territory where the screw piles will be installed. To do this, you need to take measurements, but remember that it is extremely important to create exactly even angles, because otherwise the foundation pillars will not meet and the work will be done in vain. After the area has been marked, it is necessary to mark the locations of future foundation pillars.
At this point, the entire preparatory process is completed and no additional work is required.
Installation of screw piles
Let's move on to installing the screw posts themselves. In appearance, this is an ordinary metal pole at the end of which a screw blade is installed, which allows the pole to be securely fixed in the ground and the installation process is quite simple (you just need to screw the pole into the ground).
The upper end is specially adapted for twisting and has a hole into which even an ordinary crowbar can be freely placed (it can be used to install a pile).
It is extremely important to install the pile exactly vertically, so screwing it in yourself can be a very difficult undertaking or not at all possible. This task will require a minimum of 2 people.
In addition, at least one more person must monitor the work and correct the pile if it tilts. The length of the pile can be from 1.65 to 9 meters (choose depending on the characteristics of the soil). You need to tighten the screw pile by approximately 1.5 m (the depth of soil freezing for central Russia), if the screw pile is 2.5 m long.
All that remains to be done to create a screw foundation with your own hands is to fill the piles with concrete, weld the cap and install a grillage (the upper part of the pile foundation that unites and connects the pile system).