The pile-screw foundation has already proven its advantage over other types of foundation in private construction. It lasts much longer without repair than any other support, it has a high load-bearing capacity, and can be reused. There are many other benefits. However, you will never be able to evaluate them if the installation of even one pile went wrong. There are a number of errors that periodically occur when installing screw piles if it is carried out by non-professionals and inexperienced craftsmen.
At the moment, the technology is becoming more and more popular, and an increasing number of builders are beginning to master it. And given that the technology is quite simple, it is often used by novice and self-taught builders. And in fact, you can handle the piles realistically and with your own hands, and to ensure that your foundation pleases you for many years, we will tell you how to avoid common mistakes.
Adjusting the height of screw piles and the structure on them
One of the grossest and yet most common mistakes is unscrewing piles in order to adjust the height. Such a violation leads to the formation of loose soil under the pile, in which it then sinks. The fact is that the pile is able to withstand high loads and avoid shrinkage precisely because during the screwing process the soil between the turns is not loosened, but compacted by the blades. If the work technology is followed, even loose soil eventually becomes dense and supports the pile. Accordingly, if you unscrew the pile even a little, the ground underneath it will no longer be able to withstand the weight of the structure.
Another incorrect way in which inexperienced builders try to level the height of the ground portion of the pile on a relief terrain is by screwing them to different depths. Often in such cases, the depth of the pile under the section of the building that rises above the ground is usually less than required. Note that the only acceptable way to maintain the same level of the structure is to trim the pile. By the way, the technological holes of the piles must be cut off in any case, otherwise the durability of the foundation will be greatly affected. If it turns out that the length of the pile is not enough, on the contrary, it can be increased, and then the welding seam must be painted to avoid corrosion. The welded head should also be painted.
Other errors when installing foundations on screw piles
Another, no less common mistake is not strictly vertical installation of piles. The piles themselves do not go straight into the ground, and when they encounter obstacles, they can deviate significantly from the intended trajectory. Whereas the maximum permissible angle of deviation of the pile from the vertical state is two degrees. Otherwise, the foundation on screw piles becomes unstable and unsafe. When the pile has moved to the side, it is better to agree to build it up than to leave it in this position. However, a pile that is completely screwed in at the wrong angle cannot even be extended.
Inexperienced builders can make another critical mistake during construction - installing a pile in a pre-dug hole. It should be remembered that in order for a pile to be stable, it must sink into the ground to a depth of at least 80 centimeters, and this value may increase depending on the size of the pile and the type of soil. So, a pile 2.5 meters long should sit at least 1.5 meters in the ground. When building a foundation on weak and unstable soil, such as peat, for example, the pile must completely pass through the weak area and reach dense soil. In other words, this condition can be called horizontal stability.
An error that not all builders are aware of yet is unconcrete piles with a shaft wall thickness of less than four millimeters. Such a thin pile must be filled with concrete mortar in order to acquire sufficient bending rigidity and not break under the influence of frozen soil. When the soil freezes or thaws, water can get inside the pile. Concrete helps to prevent moisture from having a destructive effect on piles, especially thin ones. At the same time, it is necessary to concrete the trunk to the very top, otherwise internal corrosion of the trunk will occur and the pile will lose its characteristics.
When done correctly, when all foundation calculations are followed, when not a single mistake is made, they can serve for over a hundred years, be a reliable support for any home and not cause any problems.
The pile-screw foundation is one of the best in the construction of not very heavy buildings, excellent for. To understand all the pros and cons of this type of foundation, let's look at it in more detail.
Screw piles are time-tested
Pouring piles with concrete
After leveling, a concrete mixture is poured inside the piles, which is designed to protect them from corrosion from the inside.
Installation of a grillage on a pile-screw foundation
At the final stage they install, i.e. the very foundation for the future home. For lighter structures, for example, houses made of timber or logs, it is possible to install a grillage made of thick timber. For houses made of bricks or blocks, it is better to make the grillage using reinforced concrete.
The pile-screw foundation will not require any time for shrinkage; you can continue immediately after installing the grillage. Now you can begin installing the frame of your house. The foundation is ready for loading and full use.
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Tensioning of the reinforcement can be done by pulling it out with concrete pressure on the clamping head during its forced compression (pressing), or by using cement that expands during hardening, or, finally, by automatically pulling out the reinforcement using the centrifugal method of manufacturing reinforced concrete pipes.
A typical example of the production of reinforced concrete elements from prestressed concrete with tensioning of reinforcement by concrete pressure is the work on the on-site production of tubular reinforced concrete piles to strengthen the foundations of a building located on the seashore.
The building was built on unstable ground and was in danger of sliding into the sea. Good solid soil was located at a depth of 20 m. It was necessary to transfer the load from the building to this layer of soil, and the possibility of driving piles was excluded for fear of increasing the rate of settlement of the building due to soil vibration and, thus, causing a disaster. It was necessary press the piles jacks into the ground and carry out work under the existing building.
Reinforced concrete cylindrical tubular piles were manufactured on site from prestressed concrete of high and quickly acquired strength. The piles had an outer diameter of 60 cm and an inner diameter of 37 cm. The reinforcement consisted of eight vertical rods with a diameter of 8 mm and a spiral steel casing with a diameter of 6 mm. The total weight of the reinforcement was 10 kg per 1 linear meter of pile.
A reinforced concrete grillage was installed between the existing foundations under the columns of the building, connecting all the bases of the foundations. With the help of special devices, the pressure from the jacks was transferred to this grillage and to the head of the pile.
Form for gradual build-up The tubular pile consisted of an outer metal cylinder 7, composed of separate sections of half-rings 40 cm high, fastened together by means of 2 clamps with screw clamps, and an inner steel pipe 3 with a rubber shell 4 attached to it, reinforced with fabric.
The space between two metal cylinders was fixed at the top by a movable flange 5 with holes for passing vertical reinforcement rods. At the lower end, the inner steel pipe was connected to another smaller steel pipe, also equipped with a rubber sheath 7. Reinforcing bars 8 passing through the movable flange were captured by clamps 9 supported on the flange.
The process of building up a tubular pile is carried out in the following order. After making a part of the pile and keeping it for the required time to acquire the proper strength, it is pressed into the ground with jacks and at the same time, as it deepens, the mounting clamps of the outer rings are released, except for the clamps of the uppermost ring. The inner steel pipe is lifted up to the height of the concreted area. The spiral reinforcement is connected to the vertical reinforcement, the rings of the outer cylinder are put in place, the vertical reinforcement rods are secured with clamps with screws, and the rods are slightly tensioned with them.
Depending on the landscape design and the complexity of the soil in a suburban building, it is often necessary to install helical piles to a depth of more than 10 meters. Russian clients often ask how this is done and how reliable the foundation structure will be with such depth.
At the technical level, it is, of course, not possible to install a ten- or even twenty-meter pile right away. And the production process does not provide for the production of piles of such length. Based on this, the piles are delivered in separate sections of 6 meters: the pile itself with a screw and, for its extension, pipes of the same diameter with a special lock. When building up, a piece of pipe with a huge diameter is welded, so that an additional pipe can be put on an already screwed-in pile.
The process itself begins with installing a pile with a screw into the ground to a certain size. It is essential to ensure that it fits in strictly at level, otherwise the extended sections of the pile will be able to seriously deviate from the specified installation characteristics. A part of the pile with a key for drilling into the ground is cut off, and the next 6 meter part is put on the pile using a lock. The toe-in piles and the key location are amazingly scalded by welding in a circle. It is very important that the welding seam is solid and strong; otherwise, when screwing in the pile, the welded part may tear off. Upon completion, the welding seam is cleaned, painted with a special anti-corrosion coating and waterproofed.
The waterproofing process is done in a couple of steps. After finishing the coloring, the joints between the pile and the extended pipe are heated with a burner. A special hydromaterial is applied to the heated area, which due to the high temperature becomes elastic and melts little, which gives it the opportunity to perfectly stick to the seam. All this is processed again with a burner, allowed to cool and screwed in. If deeper penetration of the pile is required, then do the same with the third part. Upon completion of installation, a solution of cement-sand consistency is poured into the pile, reinforcement is made, and a head of suitable diameter is put on (all in accordance with the easy installation standards).
When building piles, it is very important to take into account 5 main points:
- It is not possible to manually install a pile that lasts 10 meters or more (only a mechanized method is used)
- The pile must go strictly vertically in level
- Piles must be of good quality, in this case we recommend the development of Aster®
- The level of welding property must be at a very high level
- Waterproofing is necessary because it protects the seam from corrosion.
A very important detail in the production of piles for extension is the installation of an amplifier on the key of the pile, so that during installation its body does not break due to high loads. To do this, a piece of rod is additionally welded near the hole for installing the drill.
If all the above points are observed, a more reliable foundation simply cannot be found. Wide blades located at a depth of, say, 20 meters ensure uniform distribution of the load on the soil from the weight of the building. No one will pour a cement foundation to such a depth, and it will cost an astronomical sum. Pile-screw foundations occupy a leading position in these positions. This is not so expensive in economic terms, it does not take so long to wait (only 1-2 days) and is reliable in difficult soil conditions (high groundwater levels, elevation changes, peat).
