Basic requirements for the installation of screw piles
For the stability and durability of the foundation on screw piles pay attention to:
– Quality of screw piles
– Precise calculation of the foundation (number and type of piles, distance between piles, depth of screwing)
– Correct installation of screw pile
During the installation of screw pile pay attention to:
– Keep vertical screwing of piles (strictly!).
– Sufficient depth of immersion (in the classical method – up to the base ground)
– Formation of the final foundation plane (strict plane horizon)
– Pouring concrete into the screw pile barrel
– Anti-corrosion treatment of the pile part protruding above ground (usually using bitumen)
– Correct welding of the screw pile heads (smooth solid seam)
In reality, in the process of installation there may be errors, which we will now list and which you should avoid.
1. Vertical control of the screw pile installation
The screw pile is always mounted strictly vertically, regardless of the type of soil, the pile etc. Strict vertical ensures maximum design capacity and maximum rigidity. The maximum deviation from the vertical should not be more than 2 degrees. Otherwise, the foundation will not last long enough and effectively.
The vertical control of piles is carried out using of two levels that are attached to the pile pipe by magnets. If screwing is done manually, you need at least four people, one of whom constantly monitors the level visually and if necessary reports deviation from the vertical. If special machine for screw pile installation is used, which quickly twists piles (2-7 minutes depending on the size of the pile and the type of soil), then you should screw the pile without using the limit revolutions (especially for piles of small diameters) so as not to miss the moment of deviation of the screw pile from the vertical.
Meanwhile, pay attention, deviation of the pile more than 2 degrees from the vertical is a fatal mistake. In this position the pile can not be left! The big mistake will be the complete to turn back the pile and to screw it again into the same place! It would seem that the pile will now be mounted vertically, it is true. But in this case, its bearing capacity will be significantly reduced. When you screw a pile, its blade is compacting the ground, which contributes to the achievement of its calculated bearing capacity. If the pile is screwed out, the ground will open up and the repeated screwing will not be able to seal it sufficiently, even if the final depth is sufficient.
Thus, any screwing out of the pile and its repeated screwing into those hole of ground weakens the bearing capacity of the entire foundation. If the verticality is disturbed, it is recommended either to install an additional screw pile next to the pile or, much more economically, to screw out the pile completely and screw it nearly (manually doing this is very difficult, but we are ready to offer you the reverse movement of our equipment for screw pile installing, which allows you to screw out piles during a few minutes).
2. Screwing piles and soil density
It is important to secure the pile in the ground. The main forces acting on the pile are the elastic force of the soil (it affects the outer walls of the pipe), and the resistance force of the soils to the plane of the blade pile during vertical load. In this regard, the screwing of the pile into the ground achieves maximum results if the ground is in its original state. You can not open the soil before screwing the pile in any case! The maximum that is allowed is to create small depressions for a more accurate and easy entry of the pile into the ground, with a depth of not more than 30-40 cm.
It is considered a significant error to screw piles into pre-drilled holes in the ground. Screwing piles into such pre-prepared holes significantly reduces the load-bearing capacity of the entire foundation, although it facilitates the installation process.
3. Errors in formation of flat horizontal surface of foundation
The foundation plane for tying up piling construction is prepared by cutting the screw piles to the similar height relative to the horizon. Obviously, this method involves excessive material consumption – part of the pipe goes into waste. Often the developer is tempted to somehow avoid unnecessary expenses. For example, in uneven terrain, piles are screwed to different depths.
This is a serious mistake!
The fact is that the calculation of the foundation provides for the achievement of blades of screw piles of a certain depth. It is at the calculated depth of the ground the soil is sufficiently compacted, and the load capacity of the screw pile is maximum. For example, it is believed that the mean depth of the piles should be at least 1.5-2.5 metres, depending on the characteristics of the soil itself. This is especially true for foundations for massive structures. The fact is that the calculation of the foundation provides for the achievement of blades of screw piles of a certain depth. It is at the calculated depth of the ground is sufficiently compacted, and the load capacity of the pile is maximum. For example, it is assumed that pile immersion should be at least 1.5 to 2.5 metres on average, depending on the characteristics of the soil itself. This is especially true for foundations for massive structures.
If some of the piles are not screwed in sufficient depth, the foundation will be less stable than expected.
If the screw pile is not properly cut, it negatively affects the future foundation. In order to save money, builders sometimes allow themselves not to cut through areas with mounting holes. This is a gross mistake! The presence of holes in the pipe body significantly reduces its rigidity and, accordingly, the load-bearing capacity of the pile.
4. Pouring concrete into the screw pile barrel
Pouring concrete into the pipe screw pile plays a significant role, as it provides:
– bending pipe rigidity
– Inside pipe body corrosion protection
Sometimes, when installing piles, the developer ignores this stage because the concreting process takes considerable time. Some builders use substandard or substandard concrete, or pour the concrete negligently, not to the edge of the pipe, etc.
As a result, the pipe does not have the necessary rigidity, especially if pipes with a wall up to 4 mm are used. In addition, it quickly rusts from the inside, which significantly reduces the durability of the foundation.
5. Anti-corrosion treatment of protruding screw pile parts
The part of the screw pile above the ground, especially at the point of contact with the ground, is exposed to aggressive external factors. Intense pockets of corrosion develop here. Protection for the open part of the screw pile is a layer of anti-corrosion material, for example, bitumen mastic.
The process of applying mastic is associated with inconvenience due to the high labour intensity, and, it happens, builders don`t make it. This is a gross violation that will significantly reduce the life of the foundation.
6. Improper installation of screw pile heads
It is important to install the screw pile heads correctly! Correct installation of screw pile heads will form a flat ground for the foundation binding.
Errors of installing headers:
– The heads are significantly larger than the diameter of the screw pile pipe (the pile head should be 1.3-1.8 times larger than the pipe diameter)
– Low-quality welding of heads to the pipe body (welding seam holes, insufficient seam thickness)
– Warping of screw pile heads in the foundation plane
Any disruption of the installation of screw pile heads will cause unnecessary stresses on the foundation binding, reducing the life of the foundation.
Conclusion: These 6 mistakes can be avoided by strictly following the instructions for the installation of screw piles and a reliable foundation on screw piles will please you for a long time!
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