Service life of screw piles under the foundation

Screw piles are increasingly used today to build the fundamental foundations of private houses and when building larger industrial facilities. Supports of this type are experiencing enormous loads and after the completion of the construction of the building continue to be exposed to the destructive effects of environmental factors. That is why many now wonder if it makes sense to use screw piles or the service life of these widely available building elements is too short?

A bit of history

Piles of screw type appeared about 200 years ago. All this time they were widely used in the construction of bridges, moorings, towers, power lines and many other serious objects. There is much evidence that the service life of screw piles can reach up to 150 years. For example, the pier has not yet collapsed, which has been standing in seawater for similar supports for more than a century and a half.

There are whole museums where visitors can personally view the tips of the very first screw piles. However, this does not mean that metal structures will last forever. Negative feedback on the life of screw piles is fully justified, since hand-made supports are really quickly destroyed. The technology of making building structures is characterized by a lot of nuances and features. If the production standards have been violated, the finished piles will not last for one third of the deadline. Therefore, it is very important to pay attention to these subtleties in the choice of structures for the foundation.

Service life according to GOST

According to state regulations, the service life of screw piles is from 60 to 120 years. The following information is also specified in the GOST:

• Electromechanical corrosion of metal in the soil develops at a rate from 0.02 to 0.05 mm per year.
• The thickness of the walls of the screw and the support itself is at least 5-6 mm.
• The walls of the pipes decay at a speed of 5 mm / 0.5 = 100 years.

In addition, the piles are covered with special polymer compositions of the two-component type, which retain their properties for 7-15 years. This allows you to extend the life of screw piles under the foundation. If these conditions were violated during the manufacturing process, the products will be less reliable and durable.

Is there any difference between cast helical and welded pile tips

There are no significant differences between such products. Cast tips are made from standard steel with the marking 35L. The main difference between these support elements is that the screw lines are not welded to the pile cones, but are immediately cast together with them. However, very few people know that in fact the cast tips are welded to the pipe. This means that when using them, it will not be possible to avoid welding seams.

If we talk about the shortcomings of casting tips, then in their production it is necessary to control the quality level of pouring. In addition, their manufacture is impossible without the use of ultrasonic equipment. The fact is that the material from which the product is made can have small cracks, pores and voids, which will significantly reduce the strength characteristics and service life of screw piles.

Welded handpieces can be checked independently, because even with a visual inspection it becomes possible to evaluate the quality of production of products. Piles with cast lines are almost 25% cheaper.

Is there any difference between painted and galvanized pile tips

The main difference is in resistance to corrosion. According to numerous reviews, the service life of screw piles treated with paintwork materials is significantly lower due to the influence of an aggressive environment. The protective coating lasts a maximum of 15 years, after which the metal products begin to quickly become covered with rust.

Piles that have undergone hot dip galvanizing do not undergo corrosion for 40-50 years. However, everything depends on the aggressiveness of the soil. Thanks to the method of hot galvanizing, a layer of thickness 0.2 mm is formed on the surface of the piles, which does not wear out for a long period of time. In addition, the protective layer of zinc will not be erased during the screwing of the support.

Also worth paying attention to the cost of products. Supports, which have passed hot-dip galvanizing, will cost 25% more expensive than products treated with paint and varnish.

What affects the decrease in longevity

The service life of the foundation on screw piles can be significantly reduced due to the following factors:

• Impact of mobile soils. Under normal conditions, the soil has a minimal effect on the screw piles. However, when it comes to extreme conditions and increased soil mobility, this can affect the performance characteristics of the supports.
• Thermal action. Due to seasonal temperature fluctuations, the metal constantly narrows and expands, its structure is broken. The bearing capacity of the supports is significantly reduced, since cracks and pores appear in the material. When using quality piles, the number of cycles of freezing and defrosting is sufficient for up to 120 years, this does not happen.
• Chemical corrosion. If the acid level is exceeded in the soil, the rust on the piles will spread much faster.
• Electromechanical corrosion. Similar damage occurs when the piles are strongly oxidized due to stray currents, which may be part of the soil. Most often electromechanical corrosion is affected by supports located not far from underground cables or various industrial facilities.

How to extend the service life of screw piles

There are several ways that will help extend the "life" of the foundation installed on the supports of this type:

1. Use piles with thickened walls. Each millimeter of metal extends the service life by about 15 years.
2. Use supports made only of alloy steel. Piles should be treated with special compounds that prevent chemical corrosion.
3. If the products are not protected against rust, it is necessary to cover them yourself with anti-corrosive compounds.
4. Carry out a concreting of the inner trunk. Thanks to this procedure, it is possible to protect the structure from moisture and increase the bearing capacity of the support.

It is not recommended to use percussion equipment during the installation of piles. This will preserve the structure of products and increase the period of their operation. If the piles were assembled in accordance with the regulations, the supports will last up to 100 years.

Advantages of screw piles

Despite the problems that may arise during the operation of this type of supports, they are still very often used for the construction of foundations and the construction of other structures. This is due to the following advantages of screw piles:

• The basis of the average size can be erected in the shortest possible time (no more than 1-2 days).
• The cost of the foundation is reduced by almost half, thanks to which the construction of the entire structure will cost much less.
• Screw piles are optimally suited for use on unstable soils.

Summing up

Knowing the truth about the service life of screw piles, you can build a durable, reliable and durable foundation for a short time. The main condition is the observance of the technological process for the manufacture of supports and the correct installation of products.