The whole truth about screw piles or how not to be fooled

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Do you need a reliable, cheap foundation, and under the pressure of advertising, you are inclined to use screw piles? Do not hurry. Perhaps, after reading this article, you will change your mind about this type of supports, or at least get the necessary information to help you navigate when buying them..

The whole truth about screw piles or how not to be fooled

Today, when the construction market is full of various new or well-forgotten old materials, when craftsmen do not have time to master more and more new technologies, it is very difficult for an ordinary developer who does not have engineering and construction education to evaluate the construction innovations offered by advertising. Arguments and searches for truth are sometimes conducted even at the professorial level. One of such controversial technologies turned out to be well-spreaded screw piles..

The whole truth about screw piles or how not to be fooled

Low cost, quick installation and unpretentiousness (at least at first glance) in use made screw supports super popular, and, as a result, well bought. And if we add here the fact that the average developer knows practically nothing about the requirements put forward for such piles, but is always greedy for cheapness, then there is nothing to be surprised at the situation that has developed today – screw piles began to be produced at every second metal warehouse. At the same time, the quality of the manufactured product defies criticism..

The whole truth about screw piles or how not to be fooled

The situation with the aircraft is similar to that of foam concrete. When “garage” production completely discredited the generally good material.

Let’s try to figure out what a screw pile is, where it should be rationally used, what it should be and compare it with what a modern manufacturer offers and recommends to us..

Screw pile

The screw pile is a steel structure consisting of a barrel and a screw tip. The essence of the idea of ​​using such a support is that, with the help of rotary forces, the pile is screwed into the soil thickness until it reaches dense incompressible layers. And it is there that it is fixed with blades. In this case, the pile rests on the ground not only with the diametrical area of ​​its trunk (as a rule, it is insignificant), but also with the entire surface of the blades.

The whole truth about screw piles or how not to be fooled

The advantages of such a support are obvious:

  1. No vibration, no noise like driven piles.
  2. Quick and easy installation without the involvement of drilling equipment (compare with bored piles).
  3. The ability to use on difficult soils, where it is simply impossible to lay the tape.
  4. And finally, according to manufacturers, cheapness .

Screw pile in the USSR. History of the 108/300 format

Now let’s turn to history. Screw supports were well studied back in the USSR. No matter how today they belittled the achievements of the past, Soviet engineers did everything thoroughly, in all their calculations there was a necessary margin of safety. The products have been designed to perform their engineering tasks as efficiently as possible, rather than simply being financially attractive to the customer. For such things as the quality of building materials and the rationality of the use of building technologies, the state kept strict control.

The whole truth about screw piles or how not to be fooled

Let’s see “Piles and pile foundations. Reference book “1977. On pages 29-30 it is well described what a screw pile should be:” The trunk of a metal screw pile is made of steel pipes with a wall thickness of 10-14 mm (usually from seamless hot-rolled pipes in accordance with GOST 8732-70) … “.

Optimum screw pile sizes:

Name of quantity Size, m
Pile length 8
Blade diameter D 0.4-1.2
Barrel diameter d 0.22D-0.35D
Propeller pitch a 0.15D-0.3D
Shoe tip height h 1.5D-2.5D

We can agree that the foundation on such supports will be reliable enough even for capital construction. But will it be cheap? Based on the price of the materials used – definitely not, which means that the attractiveness of such a little-known technology for an ordinary developer will be minimal.

What happened. The pile-screw foundation had a number of conditions necessary for its popularization (simplicity and speed of installation, the ability to work at negative temperatures, solving the problem of difficult soils and reliefs), but the price of the finished product crossed out all hopes for conquering the construction market.

The whole truth about screw piles or how not to be fooled

The solution logically followed from the problem. The price of the pile must be reduced, and this can be done only by reducing the cost of the raw materials.

The businessmen had to once again turn to Soviet scientific luminaries, in particular, to Viktor Nikolaevich Zheleznyakov. To reduce the cost of the screw support, the entire anti-corrosion margin of safety was removed from it, and up to 6-10 mm of metal was allocated for this, and it was replaced with a cheaper anti-corrosion layer. The diameter of the blades was also minimized, and as a result, the diameter of the pile shaft itself (if we look at the table, it should be 0.22–0.35 of the blade diameter). This is how the modern 108/300 format appeared with a pile wall thickness of 4 mm..

The whole truth about screw piles or how not to be fooled

Theoretically, such a support could be used in non-capital construction, with a guaranteed service life, again, subject to correct use, about 50 years. Agree, it’s also very good. Especially when you consider that the price of such a pile has decreased 2–3 times to an acceptable 1000–1300 rubles per linear meter. Why is it so? Yes, because the price for the installation of the main competitor, the bored pile, ranges from 1,500 to 3,000 rubles. per running meter, and this despite the fact that this type of support is well tested by time and is capital.

The whole truth about screw piles or how not to be fooled

But let’s return again to modern domestic (in the West, such standards are simply unacceptable) screw supports. Even in the 108/300/4 format, they should look good in construction, where the service life of the wall material is less than 50 years. That is, for frame-panel construction, as well as the construction of wooden houses, a screw pile is ideal.

How to choose a screw pile

But buying even such an economical format developed by Zheleznyakov in proper quality is quite problematic. This is due to the fact that there are too many low-quality, low-quality handicraft products in the modern construction market..

There is no ready-made recipe for how not to be fooled in such cases; only a few practical advice can be given. What should be especially paid attention to and what should in no case be believed.

The whole truth about screw piles or how not to be fooled

Manufacturer

First of all, you should pay attention to the manufacturer himself. The production of high-quality screw piles is a rather complicated technical process that requires the manufacturer to have a good material base. In other words, if you came and saw some seedy metal base where these piles are sculpted right in front of your eyes (or around the corner), then this is clearly not the manufacturer that can provide quality products..

Anti-corrosion coating

By reducing the pile wall thickness to a minimum of 4 mm, the manufacturer committed himself to providing a reliable anti-corrosion layer. It’s just not always easy to check how reliable it is..

The whole truth about screw piles or how not to be fooled

First, we will screen out the “canard” about galvanizing piles by thermal diffusion. In theory, it is very reliable and very high quality, in practice it is very expensive. And if we take into account the fact that installations capable of covering a pile with zinc can be counted across the country on the fingers of one hand, then there is a completely logical suspicion that the manufacturer is simply trying to deceive you.

In practice, cheaper anti-corrosion coatings are used. Not necessarily substandard (although most often they are), but more economically viable.

The whole truth about screw piles or how not to be fooled

You can check their quality in the following way. Try to take an ordinary stone and with a sharp edge scratch the pile offered to you for purchase. At the same time, do not pay attention to the seller’s complaints that, they say, you spoil an expensive product.

When screwing the support into the ground, the walls and blades of the pile are subjected to significant frictional forces, which are many times greater than the forces that you can apply when trying to scratch the pile by hand. That is, if the pile is not scratched, it is not necessarily of high quality, but if the anti-corrosion layer is damaged, then buying such a product is definitely not worth it.

The whole truth about screw piles or how not to be fooled

Weld seam

Corrosion of the welded seam, and especially of the metal near it, is several times higher than that of conventional solid iron. Therefore, for high-quality screw piles, the number of welds should be minimized..

Let us turn again to the Soviet reference manual of 1977: “… Usually from seamless hot-rolled …”, “Screw blades are made of cast steel …”. Please note that Soviet specialists are trying to minimize the number of welded seams in this way. So the buyer should strive to buy piles with a minimum amount of welding..

The whole truth about screw piles or how not to be fooled

We will not say anything about the quality of these very seams, since it is hardly possible to test it in practice, just keep track of their number.

Specifications

The manufacturer has already reduced the pile wall thickness to the minimum allowable 4 mm. It should be remembered that there is simply nowhere less for residential construction. So it is simply impossible to buy piles with a smaller wall thickness or blades. Invisible to the eye 0.5 mm – these are additional years of life for your support.

Price

Don’t expect high quality from cheap products. When buying a screw support, it should be remembered that its production is a rather complicated technical process, which means it costs money. The competitive market regulates the price very well, so that the product usually costs exactly as much as it actually costs.

The whole truth about screw piles or how not to be fooled

Typical mistakes

But even the best screw pile, made in accordance with all norms and standards, cannot protect the buyer from improper or irrational use..

So the rules for operating screw piles are violated all the time. Installers are guided not by international or at least domestic standards, but by the advice of incompetent sellers and managers.

Let’s consider just some common mistakes and false statements of PR specialists.

1. The quality of the soil does not affect the construction of the foundation from screw piles.

Fundamentally wrong statement. We turn to the already known reference manual. Page 30: “Screw piles can be laid in any soil that allows screwing, except for clayey soils with a fluid consistency, as well as silts and peat soils …”. Add here an excerpt from ICC AC358 Acceptance Criteria For Helical Foundation Systems and Devices, US standards, (and there the state maintains strict control over the quality of housing construction), which in turn are based on international standards.

The whole truth about screw piles or how not to be fooled

According to American standards, screw supports are also strictly forbidden to be used:

  1. In soils with electrical conductivity < 1000 Ohm • cm.
  2. In soils with pH < 5.5.
  3. In soils with a high organic content.
  4. In soils with sulfation >1000 ppm.

And also on landfills, soils containing mine landslides, and those soils that cannot provide lateral support to the screw support.

As you can see, there is a fairly serious list of soils where screw supports simply cannot be used. So, it is unacceptable to establish such a foundation without a serious geological study, no matter what the manufacturers say..

The whole truth about screw piles or how not to be fooled

2. The indisputable advantage of screw piles is their high seismic resistance..

Another erroneous statement of PR people. If we turn again to the same ICC AC358, or rather to paragraph 1.2.1, we will see that the use of screw supports is limited to seismic zones A, B and C. In other words, they can be used only in seismically safe areas, and this despite the fact that in the USA, according to their standards, screw piles with a wall thinner than 9.5 mm simply cannot be found. There is no need to talk about our “cigarettes” at all.

3. We can often see a reliable grillage rigidly welded to screw piles. At first glance, everything is correct and logical. But this is only at first glance. If we turn again to foreign standards, we can read approximately the following: “Aircraft should not have any galvanic connection with other steel building elements.”.

The whole truth about screw piles or how not to be fooled

This is done in order to protect such a foundation from corrosion, multiplied by electric currents. Especially awful against this background looks the grounding, which the enterprising “kulibins” throw directly on the steel support.

4. Other common installation errors include uncontrolled and unreasonable deepening of the aircraft.. The client bought two-meter piles, the installers drilled them and that’s it. Forgetting that the depth of the screw pile must be controlled not only by geological survey data, but also by the torque required to drive the pile. The bearing capacity of the foundation directly depends on the latter..

The whole truth about screw piles or how not to be fooled

And finally, I would like to say: the pile-screw foundation is not a panacea for all problems, it is, if done correctly, a rather expensive structure that needs to be used only in those rare cases when there really is no other choice, and an accurate engineering calculation offers the SVF as the only sensible solution.

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