How does it work?
If we would like to answer this amazing question, it will be better to remind the original mission of construction piles and some conditions to apply them. Construction piles are used to transfer the existing loads from the surface layers of the weak soil to the underlying layers of the soil with higher strength values. Thus, buildings to be constructed on piles (house, gazebo, pier, etc.) are supported on the strong lower layers of soil, so the building contractor can get a low-cost and quick solution of the construction of the strong foundation already at the design stage, and, certainly, this solution consider different problems complex topography of the construction area and problems of the density of surface soils. For this reason, pile foundations are usually used in the case of deep soils with sufficient load-bearing capacity and/or if it is economically inexpedient to use more expensive types of foundations. All types of construction piles are very good for difficult terrains and weak soils, but some of them is the best solution for prefabricated buildings, low-rise construction, landscape design and others.
Classification
Construction piles and pile foundations are classified according to different characteristics. There are short and long piles according to their length. The shorter the pile, the stiffer the support. The variety of piles by sectional shape is limited only by the possibilities of geometry: round, pyramidal, solid, hollow, T-beam, and others. There are «pile stands» (supported by the strong rocky lower layers of soil) and «hanging piles» (supported by the side surface of the pile on the ground through frictional force) according to their work. By design, piles can be solid or composite. According to the method of installation of piles in the ground builders distinguish driven, bored, screw piles and piles-shell. In addition, piles are made of different types of materials – metal piles, reinforced concrete, soil concrete and even … wood. Let’s consider the main ones.
Timber piles
Timber piles are used infrequently nowadays, and usually they are made of softwood (pines, spruces). The first wooden piles were discovered by archaeologists in Switzerland and date back to the Bronze and Stone Ages. The method of installation is very ancient. The hammering method consists of driving a pile into a prepared guide hole in the ground using a coping machine or hammers. During driving, the builder must control the vertical level of the wooden pile. The main advantage of the wooden pile is the low weight, this pillar does not upload the soil, and its carrying capacity is comparable to metal and reinforced concrete piles (adjusted for the rigidity of wood), which also greatly reduces the complexity of installing the pile foundation.
Besides, the wooden pile is an environmentally friendly technology. Sometimes short wooden piles are used to organize grazing pens for livestock or as garden stakes, for the arrangement of decorative fences, for the creation of foundations for farm buildings. The timber pile can be increased if necessary, the final length of the pile depends on the construction budget only. The big disadvantage of such piles is their short service life. Wood is not resistant to rot, it can be destroyed by insects, it is thinning under the influence of sunlight.
Wooden piles are treated with special compounds, often creosote, to extend life, but the treatment is still not a panacea against rot, although it will provide additional operation of the pile for a couple of decades. It should be noted that sometimes builders suggest using larch and oak wood to increase strength, which, however, makes piles unreasonably expensive.
Reinforced concrete piles
Reinforced concrete piles, of course, are clearly a fresher solution than using wooden piles. These piles were first widely used by the French engineer François Gennebique in more than 300 projects in France in the late 19th century. The advantages of reinforced concrete piles are their high bearing capacity and strength (load up to 60 tons, you can put a three-story stone house without the slightest risk of collapse), and the best moisture resistance compared to other types of piles used in a low-rise construction, because the concrete is very slowly destroyed in the soil. A reinforced concrete pile will remain in the ground under load for a hundred and fifty years without any destruction. Such piles are usually installed by driving, vibrating or static method with the use of highly expensive specialized construction equipment – piling machines, vibrating pile drivers, hydraulic static pile drivers. At the same time, the disadvantages of this type of piles include, above all, the high cost of construction of foundations for low-rise construction and, even more so, for the construction of elements of landscape design (arbors, arches, etc.) or household structures (greenhouses, solar panels, fences, etc.). In addition, this type of piles cannot be increased. The builder gets a difficult to solve the problem if it needs to lengthen the pile to achieve a strong point in the lower layers of the soil (the lower soil horizon is most often is uneven). The same problem could appear in the case of a construction site with steep drops in the terrain.
Jet grouting
Jet grouting columns creates without excavation by diving the hollow-bore drill to a specified depth (drilling a leader borehole) through the soils with supplying of water-cement mortar. The mortar mixes with the soil, hardens and forms a jet grouting column. The jet grouting process builds Soil Concrete panels, full or partial piles with designed strength.
This relatively new technology has appeared Japan, Italy, England in the 1960s. Aqueous cementation is most commonly used in the construction of underground structures in order to strengthen the structure of soils and, ultimately, to stabilize the liquid soils. Soil concrete piles are often used to strengthen existing foundations of old buildings either. The advantages of soil concrete piles compared to other types of piles are precisely the collaboration with surrounding soils: these piles reinforce the surrounding soil, they have unique stability due to the high degree of adhesion of the column to the ground, this technology can work with any types of soils, including the permafrost. There are also some disadvantages of the jet grouting. These are the requirement for a highly specialized powerful and very expensive equipment for installation. Besides, it is guaranteed watering of the surrounding soil with a subsequent rise of groundwater while drilling and supplying the water-cement mortar. During washing of borehole builders have some problems of the soil-cement slurry on the surface. Such a picture will not add to the aesthetics of the environment and will require additional labor if you’re going to use surface soils in the future improvement of the site or it will be necessary to replace surface soils completely. For this reason jet grouting are practically not used in low-rise and landscape construction.
Screw piles
Today metal piles are usually represented by screw piles. Now screw metal piles are becoming the gold standard for foundation technologies in low-rise building and landscape construction. Foundation on screw metal piles is a concise and beautiful idea, it has entered into our lives not so long ago, but carries out a victorious march, easily to oust nearest competitors. Screw pile – it is high strength, reliability, ease and speed of the installation, it`s a high cost-effectiveness in comparison with all other types of modern foundations in the construction of private houses and buildings. Screw piles are necessarily coating by powder paints or they are galvanized, such coverage protects against the metal corrosion in the any adverse (acidic or alkaline) soils. Screw metal pile is a lightweight design. It does not require to use the powerful and energy-consuming equipment for installation, it is sufficient to use a hydraulic handled tool or a small-sized self-propelled machine for screwing piles, that a couple of people can managed without any problem. Such piles are installed by the equipment quickly and properly (for example, the screw pile foundation for a small, elegant gazebo will take you no more than an hour), and importantly, it will be without damage to your lawn or the flower garden in the nearly.
For some time ago it was thought that rocky ground was a direct obstacle to the use of screw piles. However, technology does not stand still. Now engineers have developed some ways to drive screw piles even into difficult rocky soils. Screw piles are not recommended for installation in areas of high seismic activity, despite the fact that recent tests show the stability of the screw pile in an earthquake on the intensity scale of 7 points. While the population increase it is likely that the screw piles will develop more and more regions of our planet due to the growing demand for quickly built and inexpensive houses.
Conclusion
Foundation piles are a diverse construction technology that is rapidly developing in many different directions and gaining popularity due to the versatility of the solutions offered. To summarize, it is easy to see, each type of pile has its own advantages and disadvantages, which mean nothing in some conditions and which stand out brightly in others. Proper assessment of the construction site, soils, topography, as well as the goals and objectives of the construction, will help you to choose the correct piles to organize a strong, stable and durable foundation.