Where does it all begin?
Installation of any piles begins a marking of the construction site, the selection of types of piles and their length to the depth of driving (it should be noted, many construction piles technically impossible to increase, while others one`s can build up without limits, if you allow the wallet ), the choice of installation method, then piles are sunk into the ground and mounting the crane (strapping piles), builders choose the method of installation, then the piles piles are installed into the ground and the last step is making the rostrum (strapping of the piles).
Construction piles installation methods
The difference of the construction pile`s installation is about the method of diving the pile into the ground mainly. The type of pile strictly determines this method. In terms of the applicated force, piles are driven into the ground, screwed in, poured through holes with cement mortar, vibro-loaded, statically pressed in, etc. The requirement to drive the column to a level below the frost point makes manual labor impractical, and in some cases it is impossible. Although, pile driving into the ground is carried out by hand (more precisely, by feet) in some countries with low labor costs, but we will not consider it in detail, except to attach a visual picture. (Fig. 1).
We hope you do not have to use this method. In the vast majority of cases, a variety of special machines and special tools are used to install construction piles.
Pile driving by the hammer
The hammering method is used for construction concrete piles reinforced with steel rods (reinforced concrete piles). The idea of the method: the pile is driven into the ground under the action of a directed dynamic force, which is formed by a powerful hammer. It is executed by heavy and powerful pile driving machines on a tracked or wheeled base. In terms of working medium, these machines are subdivided into a diesel, steam or hydraulic hammer equipment. Note that nowadays, hydraulic impact mechanisms are used more often, due to the advantages in efficiency and low noise load. The pile itself is actuated by a rod or tube hammer. At first the pile is driven slowly (using 50% of the pile driver’s power) to control the angle of the column, accelerating from about 2/3-1/2 of piles above the surface of the ground and bringing the use of the pile driver’s power to 100%. It should be noted that a tube hammer has two to three times the impact force than a rod hammer.
The main advantage of the hammer method is the easy operation and the ability to work on any ground. A special pile head protects the construction pile from impact damage. The pile drivers are expensive to operate, so it is not always justified in terms of the economy of the low-rise and landscape construction. In addition, it would be nice to remember about the vibration load of the soil at the time of pile driving. The vibration load can cause damage to adjacent buildings (especially old buildings).
The drilling method
Drilling dry method is used for bored piles on soils with low water saturation. For this purpose, a special bored piles driver is placed in the marked site and the borehole is drilled to the length of the support. The pipe is slowly inserted into the resulting borehole in the ground, then the next pipe put up, so joining pipes piece by piece to the required casing length. All soil is extracted from the pipe cavity. The cavity of the casing pipe is filled concrete mortar not more than 1 m, tamp the concrete mixture. Then lift the pipe, pour the concrete mixture again, tamp it down and repeat until the level of concrete at the bottom of the pipe is 40 cm. At 1.5-2 m from the surface of the ground, the pile is reinforced with steel rods, leaving over the surface of the column for the future binding of the piles with a rostrum. If the borehole drilling inspection reveals quick sands or layers of soils with high moisture content, the bored pile cannot be constructed using the dry boring method. It must be applied additional moisture-protecting techniques, such as the casing boring method. In this case, the casing pipe is not removed from the ground, being an additional protection against soil washout from the bored pile.
Another method is drilling method using the concreted clay mud. This clay is supplied under pressure to the borehole through the hollow rod of the bored pile driver simultaneously it is drilled the borehole. During the process the clay mud meets the resistance of the ground, so the clay mud begins to rise back under pressure, briefly sealing the walls of the borehole with clay (it creates a “clay pipe”), resulting in no need to leave the pipe in the borehole.
The advantages of the drilling method are the variability of use on different soils (you can install piles nearby a river, an azure, a pond, by the sea) and the ability to withstand heavy weight of the bored pile. The disadvantages of the drilling method are the high consumption of concrete, the use of expensive equipment, the high complexity of calculations and the technology.
The vibrational method
The vibrational method of pile driving is successfully used with water-saturated soils for large pile shafts (up to 3 tons). Vibratory pile driving significantly reduces the friction force between the pile`s surface and the ground, in addition, it further compacts the ground around the pile, so the pile is more stable. Usually this method is used for reinforced concrete piles and concrete piles. Pile drivers machines with attachments of low-frequency, medium-frequency or high-frequency vibroloaders are used for this method of installation.
The vibroloader consists three main components: an electric drive to operate the hammer, a vibrator with non-centered multidirectional unbalances (unbalances make vibration reactions during movement) and a rigid cap that is fixed on the head of the reinforced concrete pile (this cap connects it to the vibroloader).
There are two types of vibroloaders: the first kind is rigid vibroloader – in this case, the vibrator is attached to the electric drive, which has a high wear resistance of the vibrator; the second kind is an electric drive is installed on springs to the vibrator platform, which reduces the vibration damage and increases the life of the equipment. The vibration driving method doesn`t let to increase the length of the pile due to frequency fluctuations in the pile driving process, because it can deform or break the weld and make the pile unusable. Builders prefer the vibration driving method for working with hollow shell piles, including hollow steel pipes ( the smaller the horizontal section of the pile base, the faster and more efficient the vibro pile driving).
The obvious advantages of the method are low noise, no destructive effect on adjacent buildings, and the high installation speed. The disadvantage of the method is the low efficiency of working with clay soils, the impossibility of using composite reinforced concrete piles, the need for leader drilling on dense soils using the impact method at the final stage.
Static pressing-in of construction piles
Static pressing-in of piles – it is the pressure on a head of the pile by the constant vertical dynamic force. This method can be applied to all reinforced concrete piles and metal sheet piles (square section, hollow round piles and shell piles). Installation is carried out using pile-pressing drivers. The equipment consists a support frame on which a pile clamp is attached. Hydraulic cylinders connect the clamp and frame. Hydraulic pumps are mounted on the frame. They provide the pressure to the pile for driving into the borehole. Anchor loads are mounted on the pile-pressing drivers for providing the enough mass of driver to overcome the resistance we have during driving. The equipment is mounted on the chassis (the chassis is arranged on the principle of a walking chassis) to move on the platform.
This method is good for the conditions of infill development (the construction of multi-storey buildings, industrial premises, etc.) due to low noise, no destructive impact on the environment, no precipitation of the foundation, precise pile driving depth (it is possible to estimate the load-bearing capacity of the pile by the final compression force), low crush risk compared to the pile driving by the hammer, the possibility of installing prefabricated metal-free joint piles (they are assembled from several sections, the length can be anything). Some construction piles, such as pyramidal ones with variable cross-section length, cannot be install by any method other than static pressing-in.
The obvious disadvantage is a high-cost pile-pressing driver, it can be up to 400 tonnes (4-5 laden railway wagons), and it is oversized, so it`s great difficult to move between different building plots, and, consequently, you have high transport costs. The pile-pressing driver is transported in a disassembled state and it increases the period of the installation the pile foundation.
The screw-pile method
The installation of screw piles is a relatively new technology for the installation of a pile foundation. Screw piles are rapidly gaining popularity, supplanting the classic methods of building foundations. The installation of metal screw piles is carried out by a manual hydraulic tool as Manual ground screw driver (fig. 6) or by a light self-propelled driver like Self-Propelled ground screw machine (fig. 7). The Manual ground screw driver consists 3 main parts:
- hydraulic power pack – energy source pack
- Hydraulic drive head – actuator for rotation (screwing) the pile
- High-pressure hoses with quick couplers – hoses supply to the hydraulic drive head a working fluid (special hydraulic oil) from the hydraulic power pack to set the head in motion.
Self-Propelled ground screw machine is the equipment of a hydraulic ground screw driver on the chassis with a control panel. It allows you to have maximum mechanization of manual labor. Both machines are relatively easy to control the vertical level of the screw pile in the ground, and both of them have a mechanism for reversing the pile if necessary, for example, adjusting the marking of the pile foundation, or dismantling and moving the temporary structure to another place. You can install the screw quickly, not more than during 5-20 minutes, depending on its size.
The installation technology is simple and beautiful. The first of all you need to mark the screw pile field for the future foundation (the site does not require leveling). The next step is making a small pit of 15-20 cm, in which the pile will be placed (for dense soils only, it isn`t necessary for others soils). Then the pile is screwed to a preset depth or to the ground until it stops. After the installation the builder makes the bond of screwed piles, so the foundation of screw piles is finished.
Conclusion
In each case it is necessary to choose the method that is most suitable for your construction. Screw piles have one drawback – a load bearing capacity of the piles themselves is no more than two floors of a private house. But just imagine how many construction projects are in the category of low-rise construction!
Private houses, bungalows, gazebos, greenhouses, solar panels, outbuildings, terraces, fences and temporary fences, road signs, piers and pontoons and more. In addition, the installation of screw piles is simple execution, low labor intensity, low cost of the machines for screwing piles, low noise, gentle attitude to nature, the ability to work in closed conditions, impressive installation speed and the possibility of foundation organization on any unstable soils (peat, marshy, etc.) as well as on sites with complex terrain. Undoubtedly, the installation of screw piles is a successful solution for the private building, low-rise and landscape construction.
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