Construction companies today offer many construction solutions for laying an inexpensive and at that time reliable foundation. Compromise options are usually a hybrid of two traditional methods of device support base. The pile-grillage foundation, which was originally oriented towards light wooden structures, fully applies to this concept, but as it has improved, it has also been applied to concrete structures.
Technology Overview
The house is arranged on a monolithic platform (grillage), which, in turn, is based on supporting piles. Accordingly, in the process of work, it will be necessary to create wells and carefully calculate the power structure, which will distribute the load from the building frame. This base contains and the elements of the strip foundation.
Particular attention should be paid to the trench along which the piles will be installed. The configuration of their placement can be chess, solid, single or strip. For example, a pile-grill foundation for aerated concrete is recommended to be laid in a two-lane scheme, in which the bearing supports are installed in two rows. For a bathhouse or a sennik, it is quite possible to limit ourselves to the infrequent arrangement of single piles, and industrial buildings and two-story cottages are erected on a grillage held by a dense group of supports integrated in a checkerboard pattern.
What piles are used?
All types of traditional driven and screw piles are used, but it should be borne in mind that the support must allow the possibility of immersion in a stuffed cement concrete tunnel or casing. In terms of the choice of materials, the technology of the pile-grillage foundation practically does not impose restrictions - depending on the load, wood, metal, concrete and even composites can be used. But more often, metal piles are used due to their practicality, durability and reliability.
It is important to consider further possibilities for interfacing support elements with the same grill and casing. Wire bonding, reinforcement and welding technologies may be used. It is recommended to use steel combinations for a monolithic pile-grill foundation, since on a small construction site, reinforced concrete allows you to accept large loads from the frame without additional strengthening.
Site preparation for construction
To begin with, it is worth highlighting the types of soils on which, in principle, the construction of a pile-grillage bearing base is allowed. As a rule, these are weak and unstable soils that are in a fluid-plastic state and are prone to swelling. This applies to quicksand, loam, forest and vegetation cover, the dynamics of which do not allow to arrange capital tape and monolithic structures.
How is problem soil prepared? The upper fertile layer is completely removed along with the turf and roots. Next, mark the territory on which the pile-grillage foundation with trenches will be arranged. Stakes should note the points of placement of the supporting partitions and the contours of the floors. Between them, a rope is pulled strictly in level.
Installation of bored piles
A trench is digging along the perimeter of the partitions of the future frame. In depth, it can correspond to the strip design, but in principle, the pile-grill foundation is shallow, so 50 cm will be enough. Moreover, the installation of piles will be carried out in the trench, and this will require additional space.
Bored support elements shrink to a depth of about 150-200 cm. Wells are formed by drills with a screw conveyor mechanism. At the bottom there is a 20-30 cm thick pillow based on sand and gravel. Then a reinforcing cage is installed, the walls of the well are covered with roofing material, and the casing is immersed in the niche itself. To increase the stability of the pile-grillage foundation for the house, sometimes borehole blasting techniques are also used to expand the lower part of the planting, which is subsequently poured with concrete mortar. You need to fill the entire niche of the casing.
Installation of screw piles
This technique is suitable for light and small-sized buildings - for example, aerated concrete or wooden. Supporting elements are immersed at 50-70 cm. From the point of view of the device’s technology, the manual creation of a well is the main advantage of a screw pile-grillage foundation. With your own hands, using a drill, you can drill a hole of the desired depth without connecting special equipment. To do this, insert a pile into the prepared recesses, and attach a lever to its upper part. Further, during the rotation of the support, a small well up to 100 cm will be formed. But you need to do this operation with a partner who will provide control of the verticality of the drill column.
The configuration of the arrangement of piles must be maintained horizontally - that is, the arrangement on the same line. After mounting the columns, it is also necessary to fill the niches with concrete mortar. Problems when using a screw pile-grillage foundation can occur on permafrost soil. Such soils are advantageous for their density, which increases the reliability of planting of bearing elements. However, difficulties may arise due to the fact that after the destruction of the ice structure during drilling, its subsequent restoration will violate the position of the pile relative to the vertical. Therefore, for some time after drilling, it is necessary to securely fix the piles in the cement mortar with special supports.
Device grillage and strapping
When the supports gain sufficient strength, you can proceed with the installation of the upper supporting platform. According to the previously created trench, formwork is performed, the bottom of which must be provided with a sand cushion with a thick insulator layer based on geotextiles. Then a reinforcing frame is formed of metal rods with a thickness of 8-10 mm. After that, the columns are poured under the pile-grillage foundation strictly at the level of the trench. When the screed hardens, you can disassemble the formwork and begin installing the grillage.
At this stage, different approaches can also be used, but the most reliable option will be a metal structure based on I-beams and a channel. Trimming the necessary size elements is done by a grinder at a 45-degree angle. Butt joints are fastened by double welding and additionally twisted by bolts. Such a grillage can be used for suburban residential buildings made of brick or stone, and for lightweight buildings, a design on wooden beams is also suitable.
Technology benefits
Almost all the strengths of using this type of foundation are reduced to optimizing the construction process. This is reflected in a reduction in the cost of work and materials, sometimes in the abandonment of special equipment and a reduction in the construction time. What is more important, weather conditions do not affect the construction of the pile-grillage foundation. The pros and cons in terms of technical and operational qualities also deserve attention. Of course, there is no question of a comparison in terms of strength with monolithic platforms and a tape base, but the flexibility of the design allows you to safely build a grillage on piles regardless of the characteristics of the terrain.
Technology disadvantages
As already noted, the strength of such a foundation is not the strongest side, which imposes restrictions on its use for many major buildings. In individual construction, a significant drawback of this technology is the complete exclusion of the construction of basement floors with basements. Also, despite some lightness of the workflow, the pile-grill foundation for the home requires careful calculation in the installation of load-bearing elements. Errors in this case are much more significant than with the same monolithic foundation. For example, shrinkage when the piles are not stable enough may even lead to the destruction of the building.
Conclusion
In the process of developing private house projects, architects often encounter problems combining several conflicting construction parameters. For example, the task may be to build a functional, inexpensive and reliable home with a full range of protective insulating properties of the frame. As a result, the reduction in the cost of the project leads to the rejection of a number of technological solutions used, including at the stage of foundation construction. I must say that the foundation as such to a large extent determines the future technical and operational qualities of the building.
The optimal solution in such situations is precisely the pile-grill foundation, the pros and cons of which can be adjusted during construction. For example, the lack of power of the bearing base can be made up at the stage of creating the first floor in the frame of the house. On the other hand, the functional tasks of the grillage can be strengthened - a metal platform, in particular, supplemented with insulators. At the same time, the unconditional advantages of the foundation in the form of financial savings and high construction speed will remain.