- Pile wall thickness: every millimeter counts
- Steel quality, adhesion
- Protective coating thickness
- Blade thickness
- Blade geometry
- Pile behavior during erection and dismantling
- Let’s sum up
The pile-screw foundation is gaining more and more popularity in the construction of private houses. And as the well-known economic law says, demand creates supply, which means that the market offers more and more choice. We procured screw piles from various manufacturers and arranged testing for them.
In appearance, all products are the same – steel pipes with blades at the end, coated with paint on the outside. Let’s try to figure out if they differ in quality. We did not warn manufacturers about the tests of their products.
We purchased piles from the following manufacturers:
- “Screw pile factory” (sample No. 1).
- “Pile Structures Plant” (sample No. 2).
- “SvayBur” (sample No. 3).
- HelixPRO (sample no. 4).
- “Kalita” (sample No. 5).
- KKZM (sample No. 6).
Let’s define the parameters by which we will evaluate the presented samples:
- Wall thickness.
- Steel quality, coating adhesion.
- Protective coating thickness.
- Quality of welds.
- Behavior during assembly and disassembly.
And so, about everything in order.
Pile wall thickness: every millimeter counts
Let’s start by checking the thickness of the pile barrel metal. The thicker the support, the longer it will last. After all, rust will take longer to “eat” steel. Let’s see some calculations. According to the Eurocode, the corrosion rate for technogenic soils is from 0.015 mm to 0.030 mm per year, and the average value is 0.0225 mm per year. According to the manufacturers, all but one of the samples presented in the test have a wall thickness of 4 mm. This is the normal wall thickness for piles with a diameter of 108 mm. Accordingly, to find out how many years the supports will rust by half, you need to divide 2 mm by 0.0225 mm and we get 89 years. And this is without taking into account anti-corrosion protection. Not bad!
We make a real measurement of the wall of each pile using an electronic thickness gauge. Results in the photo.
Sample No. 1 – 3.6 mm:
Sample No. 2 – 4.1 mm:
Sample No. 3 – 3.6 mm:
Sample No. 4 – 4.3 mm:
Sample No. 5 – 3.3 mm:
Sample No. 6 – 4.1 mm:
So, the first and third samples are thinner than the declared one by 0.4 mm. The second, fourth and sixth samples are thicker than the face value, which is good. The fifth sample, with a declared metal thickness of 3.5 mm, falls short of 0.2 mm. The next step is to check the quality of steel.
Steel quality, adhesion
To reduce the cost of screw piles, manufacturers can use rusted or used pipe. Of course, for buyers the final prices turn out to be more attractive, but the quality of the foundation installed on such supports does not guarantee the durability of use. Let’s start checking samples.
Sample No. 1:
A pipe with traces of rust under an anti-corrosion coating was used. The pipe may have been in use or stored outdoors for a long time.
Sample # 2:
Don’t find fault with the sample. The coating on the pipe holds well, the adhesion is normal.
Sample No. 3:
The sample deserves attention not only because of the steel, but also because of its good adhesion. It takes considerable effort to remove the protective layer. By the way, the steel is fresh.
Sample No. 4:
Fourth sample. Under the anticorrosive layer – galvanized. Double protection of metal against corrosion.
Sample No. 5:
Sample No. 6:
The fifth and sixth samples are hot-dip galvanized to ensure the use of fresh steel.
Protective coating thickness
Let’s move on to measuring the thickness of the protective coating layer. This indicator directly affects the durability of screw piles. Technologists recommend applying anticorrosive in two layers of 20 microns, respectively, the minimum readings of the tested samples should be at least 40 microns.
Sample No. 1 – 0.062 mm.
Sample No. 2 – 0.017 mm.
Sample No. 3 – 0.031 mm.
Sample No. 4 – 0.129 mm.
Sample No. 5 – 0.090 mm.
Sample No. 6 – 0.069 mm.
In addition to the pipe, the blade also determines the quality of the pile. Let’s start by checking the blade thickness. This indicator should be equal to 5 mm *.
Sample No. 1 – 5.0 mm.
Sample No. 2 – 5.0 mm.
Sample No. 3 – 4.9 mm.
Sample No. 4 – 5.3–5.4 mm.
Sample No. 5 – 2.6 mm.
Sample No. 6 – 5.8 mm.
The manufacturer determined the thickness to be 2 mm, the device showed 2.6 mm.
* – At number 5 we have a sample of a multi-turn pile, the blade thickness of which is thinner, due to the greater number of turns. To the credit of the manufacturer, the blade thickness is more than the declared nominal 2 mm.
The diameter of the helical blade is responsible for the bearing capacity of the entire foundation. For all samples (except for the fifth), the diameter should be 30 cm.For a multi-turn pile – 10 cm.
Sample No. 1 – 28 cm.
Sample No. 2 – 29 cm.
Sample No. 3 – 29.5 cm.
Sample No. 4 – 30 cm.
Sample No. 5 – 9 cm.
Sample No. 6 – 30 cm.
Some piles are smaller than stated. But taking into account the slight deviation from the norm, we can say that the samples passed this test.
Also pay attention to the geometrical position of the blade, which affects the speed and ease of installation..
While waiting for installation, it is easy to guess that pile number 5 will outperform its competitors in terms of installation speed, but lose in terms of “bearing capacity”. This is due to the small diameter and number of turns of the blade.
The screw piles selected for the test have welded ends. Therefore, an equally important quality criterion is the seam.
There are several types of welding that are used in the production of screw piles – automatic, semi-automatic and manual. The difference lies in the process of wire feeding and the quality of its attachment to the metal of the blade and barrel.
The only pile where the blade is automatically welded is pile number 5.
For all other samples, manufacturers used semi-automatic welding..
Pile behavior during erection and dismantling
Now we have moved on to the most interesting part of our testing – editing. What happens if you install the screw piles to the working depth and unscrew it back? let’s get a look.
It is worth noting that the protective coating on the edge of the blade has worn off all piles. However, this is not unusual, since the blade makes several revolutions in the ground. This is one of the reasons why it is made thicker than the pile shaft..
The galvanized piles remained unchanged. Only in sample No. 5 the blade turn was bent.
In general, there have been no significant changes.
Let’s sum up
J sample No. 1 lost to competitors in terms of metal thickness. Also note the existing rust on the pile shaft..
Sample No. 2 has too thin a layer of protective coating, but nevertheless, the installation in frozen soil went with a bang.
Sample No. 3 was distinguished by the adhesion of the protective coating to the pipe surface. Nevertheless, the protective layer is thin, and also the thickness of the metal does not reach the nominal value.
Sample No. 4 boasts galvanized finish. But small scratches during installation still remain.
Sample No. 5 is a multi-turn pile, it is installed easier than the others, but it loses a lot in bearing capacity. One of the blades bent during installation.
Sample No. 6 – galvanized pile, during the tests of which no minuses were found.
Let’s summarize the results in a table:
Sample No. Manufacturer Pile length Barrel diameter Pile thickness declared Pile thickness measured Blade thickness Blade diameter stated Blade diameter measured Zn Anticorrosive thickness Cost, rub. 1 “Screw pile factory” 150 cm 108 mm 4 mm 3.6 mm 5 mm 30 cm 28 cm – 0.062 mm 1200 2 “Pile Structures Plant” 165 cm 108 mm 4 mm 4.1 mm 5 mm 30 cm 29 cm – 0.017 mm 1200 3 “SvayBur” 150 cm 108 mm 4 mm 3.6 mm 4.9 mm 30 cm 29.5 cm – 0.031 mm 1150 4 HelixPro 150 cm 108 mm 4 mm 4.3 mm 5.4 mm 30 cm 30 cm + 0.129 mm 1300 five “Kalita” 150 cm 114 mm 3.5mm 3.3 mm 2.6 mm 10 cm 9 cm + 0.090 mm 4200 6 KKZM 150 cm 108 mm 4 mm 4.1 mm 5.8 mm 30 cm 30 cm + 0.069 mm 1850