Durability of screw pile foundation

Modern manufacturers claim a 75-100 year service life for screw piles solely for advertising purposes. Such a marketing move ensures an increase in sales. However, 95% of companies that produce SVS, SVL piles and other modifications will not undertake the design of a brick building on a pile-screw foundation. This is due to both low qualifications of employees and unsatisfactory quality of products.

Low quality screw pile.

How long can a pile foundation last?

Based on the material used, screw piles are divided into several types:

• metal rods with a blade;
• reinforced concrete screw-in pillars.

Power elements of the first type are made of steel pipes of a complicated configuration with a helical blade.

The initial data for calculating the service life of such supports are the following parameters:

• steel quality;
• pipe wall thickness;
• blade thickness;
• type of anti-corrosion coating.

As a rule, for private construction, piles with a pipe thickness of at least 4 mm and blades of 5 mm are used. During a year of operation, 0.02–0.03 mm of the metal surface is destroyed under the influence of corrosion processes.

This factor is also taken into account by manufacturers who advertise data on the service life of screw piles. Consumers can trust suppliers who sell power elements with a service life of 50–80 years. In practice, additional measures are implemented that increase the wear resistance of the pile foundation, extending its service life by 15 to 30 years.

Reinforced concrete structures are free from the main drawback of metal rods - susceptibility to corrosion processes, so manufacturers of supporting elements can confidently declare their service life to be 100 years.

Production of screw piles in St. Petersburg

At our own production complex, experienced employees improve pile manufacturing technologies and carefully monitor all stages of their production. So that we can safely say that a foundation on screw piles, subject to all production and construction technologies, is one of the most durable, practical and reliable structures.

You can get professional advice from our specialists and place an order by phone.

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Durability according to GOST

According to current standards (SNiP 2.02.03-85), the operational life of screw steel piles varies between 60–120 years under the conditions that:

• pipe thickness not less than 6 mm;
• metal abrasion rate – up to 5mm per 100 years;
• development of corrosion – up to 0.5 mm in one year.

The declared service life of reinforced concrete screw supports is from 100 years. Requirements for the operation of a pile foundation are described in SP 24.13330.2011.

Taurus-Piles

1. The service life of screw piles in soil can range from 60 to 120 years. According to GOST 9.602-2005 “UNDERGROUND STRUCTURES General requirements for protection against corrosion”, the rate of electrochemical corrosion of metal in soils ranges from 0.02 mm per year to 0.05 mm per year. The thickness of the wall and screw of the pile are 5 and 6 mm, respectively. The decay rate of the pipe wall will be: 5mm/0.05=100 years. The piles are covered with a two-component polymer coating. The service life of the coating, depending on the aggressiveness of the environment, ranges from 7 to 15 years.

2. What is the difference between piles with a cast screw tip and welded ones? The difference between these tips is small. Cast tips are made of ordinary steel 35L. Their main difference is that the helical line is not welded to the pile cone, but is cast along with it. BUT few manufacturers say that the cast tip is welded to the pipe. There is no way to avoid the weld seam. The main disadvantage of cast tips is that it is not possible to control the quality of casting without ultrasonic equipment. The metal of the tip may contain dangerous cracks, pores, and cavities, which reduce the strength and durability of the pile several times. Welded tips undergo visual inspection. You can personally verify the quality of welded joints in our production. And lastly: Piles with a cast tip are 25% more expensive than welded ones.

3. What is the difference between painted and galvanized screw piles? The main difference is the resistance to metal corrosion. Paints and varnishes are designed for 7-15 years, depending on the aggressiveness of the environment. While the protection using the hot-dip galvanizing method creates a layer of zinc of 200 microns (0.2 mm) on the surface of the pile. Zinc is applied by immersing piles in baths of molten liquid metal. Zinc, unlike paint, is applied outside and inside the pile. A wired barrier is created over the entire area of ​​the pile. Also, the zinc coating is not subject to abrasion when screwing. The decay period of zinc protection is 40-50 years, depending on the aggressiveness of the soil. Although the cost of hot-dip galvanizing is 25% higher than that of paint and varnish treatment, you can confidently guarantee that the foundation on galvanized piles will also serve your grandchildren.

4. How to seal the base between the logs and the ground?

Option 1: Weld a 40x20 profile pipe horizontally to the piles in increments of 30-40 cm. Asbestos-cement sheets 12-20 mm thick are mounted to the pipe. Insulation or plaster is applied to the sheets. Perhaps sheets with insulation and stone on top. 2 The shallow tape is poured. The space between the house and the soil is filled with brickwork. Even by covering the foundation with a plinth, you leave a ventilated space under the house. The wood of your house will not rot and smolder in the damp space of the basement, as is the case with strip foundations.

5. Determine the type of soil yourself.

Determining soil moisture is also possible using a visual method.

If a drilled hole in the ground remains dry over time, then the soil can be considered dry. And if water begins to accumulate at the bottom of the well, this indicates a high level of groundwater and high moisture saturation of the soil.

Frost heaving of soils is a physically inevitable process that occurs when the water contained in the soil turns into ice. The volume of ice is 9% greater than the volume of water with the same mass. Therefore, in winter, pressure arises in the moistened soil from ice expanding in the pores of the soil, which, for natural reasons, cannot move the lower layers of the soil. Therefore, during expansion, the soil moves upward along with the foundation located in it. As a rule, soil freezing does not occur evenly over the area of ​​the foundation. Accordingly, the forces lifting the foundation in its different parts differ in magnitude, which leads to the appearance of cracks in it and the load-bearing walls. In the spring, accordingly, the ice melts, and the soil returns to its original place, but the incorrectly designed foundation does not. Shallow strip foundations and bored piles are most susceptible to this type of problem. As is already clear from the name, a shallow strip foundation has a laying depth less than the freezing depth and its use on heaving soils is fraught with failure. Also, this type of foundation is not recommended for use in soils with high groundwater levels. Bored piles are installed below the freezing depth and swelling of the soil under their base does not occur. However, bored piles have a large area of ​​rough lateral surface. Often frozen soil, which has good adhesion to the side surface, rises (swells) along with the bored pile, and the void formed under the base of the pile is filled with time by unfrozen soil. And after every winter, the owners discover that the house is growing, cracks in the door and window jambs and other troubles.

Screw piles are completely free of these disadvantages. When installing a screw foundation at a depth below the freezing point, no matter how heaving the soil is, there will be no problems with the foundation. The side surface of the screw pile has a small area and a smooth surface, and the screw, like an anchor, reliably holds it in the ground.

PS: the world experience of using screw piles goes back almost 200 years. But there will always be “literate people with experience” who can easily question these achievements. In modern design and construction, the “classical” concrete foundation still prevails. While carrying out concrete work in winter is associated with additional costs and greater risks. And we have winter for almost 6 months a year. The construction of buildings on a foundation made of screw piles eliminates the notorious “seasonality” in construction. Thus, those construction companies that use pile-screw foundations have year-round production capacity and no problems with personnel throughout the year.

Why don't developers trust pile foundations?

Despite the widespread use of pile foundations, some developers are cautious about their durability. The fact is that when calculating the number of support elements, as well as their parameters, the principles and formulas set out in SP 24.13330.2011 are used.

The calculation methodology described in the documentation is based on simplified models of interaction between soil and foundation. Thus, the design does not take into account the presence of stray currents, as well as the aggressiveness of the soil and groundwater. Negative factors include the heterogeneity of the soil composition on the site. The listed aspects together reduce the operational life of the foundation for decades.

Experts advise choosing a supplier of screw piles from companies with a proven reputation, since some unscrupulous manufacturers use low-quality steel and skimp on the thickness of the anti-corrosion coating.

Test screwing is a must!

Even despite the positive results of geodetic exploration, a trial screwing of 1-2 piles is necessary, since there may be hard rock in the deep layers of the soil, which will make installation of the piles impossible. You need to understand that with trial screwing, the cost of work will increase by 10% or more. But this should not be neglected under any circumstances. Moreover, refuse the services of a contractor who undertakes to build a foundation without trial screwing.

As for the widespread opinion that a screw foundation does not need to be maintained, this is also somewhat untrue. Experts insist that at least a year must pass before the earth shrinks and the foundation is consolidated.

What can reduce durability?

Factors that have a direct impact on the service life of a pile foundation:

1. Mobility of land masses. On sites with unstable soil, horizontal and buoyant forces act on the piles, which lead to deformation of the pipes and, as a result, a decrease in wear resistance.
2. Seasonal temperature changes . Metal tends to contract and expand under the influence of low and high temperatures. As a result, cracks appear in the coating, where moisture penetrates, causing corrosion. If there are large temperature differences in the region where the foundation is being built, it is economically feasible to purchase piles and high-strength alloy steel.
3. Agrotechnical soil erosion . The negative effect is especially pronounced in areas with hilly terrain. The action of the factor leads to local cracking of the metal surface. The presence of small stones in the soil that scratch the outer coating increases the rate of destruction.
4. Chemical corrosion . In soil with a high acidity level, rust formation occurs faster. The problem is solved by sandblasting the rod before immersing it in the soil.
5. Exposure of metal to an electrically conductive environment . Currents wandering in the soil increase the rate of metal oxidation. Foundations next to which cables or industrial facilities are laid underground are more susceptible to negative effects.
6. Failure to comply with transportation and storage rules, as well as violation of installation technology. The listed aspects lead to damage to the surface of the piles and thereby reduce the degree of protection from many external factors.

The service life of reinforced concrete screw piles depends, first of all, on the quality of the concrete used, as well as compliance with production technology. Such a foundation will last more than a hundred years if the permissible loads are correctly calculated and the alignment of the load-bearing elements at the same level is observed during the process of screwing into the ground.

Recommendations from professionals

Each developer, before starting the construction of a foundation structure, must thoroughly study the technological process, as well as obtain advice from professionals:

1. You should not skimp on the quality of the metal pipe. The thicker its walls are, the more reliable and durable the entire foundation structure will be.
2. The process of deepening metal supports into the soil must be carried out in strict compliance with technology.
3. For proper operation of the foundation, it is necessary to fill the support cavities with concrete after installation.

If a developer plans to purchase pipes from a company that guarantees their service life for 100-150 years, then he should turn to another supplier. He should remember that without special protection, a metal support can stand in the ground for no more than 30 years. It is possible to significantly increase the useful life of piles only with comprehensive protection, which includes both internal and external metal processing.

How to extend operation?

To extend the service life of a pile foundation, owners should pay special attention to the quality of structural elements, as well as carry out a number of additional measures during installation work:

1. 
   Selecting piles from high strength steel . If a geological analysis of the soil shows that the site has very aggressive soil, then it makes sense to choose pipes with a wall thickness of at least 5 mm. An increase in the indicator by even 1 mm will increase the service life of the foundation by several decades.

2. Power elements made of alloy steel . This material compares favorably with its performance characteristics compared to conventional metal. The high cost of such piles is offset by the increased period of operation of the foundation.
3. Coating with an additional layer of anti-corrosion protection. Despite the declared quality and wear resistance of supports treated with hot-dip galvanizing, this protection option does not work well in the event of destruction occurring directly in the ground. To protect the foundation from electromechanical and chemical corrosion, experts advise covering the metal with an elastic layer of material based on epoxy resins, polyurethane, etc.
4. Concreting screw piles. This is the simplest and most effective method of increasing the service life of supports. Concrete poured into the internal cavity of the pipe displaces all oxygen, eliminating the risk of oxidation and, as a result, destruction of the pile from the inside.

How to increase the service life of a foundation on screw piles?

There are several ways to cheaply extend the service life of a pile-screw foundation. Before installation, pipes are processed from the outside and inside, thereby increasing safety factors. Lack of exposure to oxygen reduces the rate of corrosion by 40%.

To extend durability, pipes are processed using three technologies.

Galvanizing

Metal that is coated with cold zinc or processed using hot-dip galvanizing technology has excellent anti-corrosion properties.

The latter option significantly improves quality, but the price will also be higher. When performing turnkey work, it is recommended to coat the pipes with cold zinc. This will reduce the cost and at the same time increase durability to 80-90 years.

Epoxy and polyurethane resins

This type of coating is used by professional construction companies. Pipes treated with a resin composition are characterized by a high level of adhesion and strength. Additional protection is provided by the formation of additional molecular bonds that minimize the effects of chemical corrosion.

Concreting

To prevent the destruction of the steel base from the inside, it is recommended to fill the pipe cavity with concrete. This method prevents the penetration of moisture and effectively increases the load-bearing properties of the supports. Filling should occur evenly so that the composition does not cause excess stress.