Even the most distant person from the topic of construction understands that the foundation of any building is the foundation, and realizes that the durability and strength of the building depends on its reliability and correct execution. When it comes to the construction of large houses and critical facilities, a pile foundation is usually chosen. It can be used on any type of soil, it provides the building with maximum reliability, and it takes less time to install such a foundation than to erect a strip or any other type of foundation. For the pile foundation, different types of piles and different ways of driving them are used. The choice depends on the type of soil, the location of other objects nearby, the nature of the structure, the length of the piles and a host of other factors. We will figure out what methods of driving piles into the ground exist, and when it is better to use this or that method.
First, a few words about the types of piles. They are stuffed and driven. The former are obtained as a result of the installation of a reinforcing cage in a previously prepared well and subsequent pouring with concrete. Driven piles are brought to the installation site ready-made; crane installations are used to transport them directly to the immersion point. When they talk about immersion, they mean driven piles.
The immersion of piles into the ground is carried out using various methods:
A combination of some of these methods allows us to speak of several mixed methods of driving piles:
- vibro shock;
- vibration pressure;
- diving with soil washout;
- diving using electroosmosis.
Let’s figure out the main subtleties of each method.
# 1. Impact method of driving piles
The impact method involves the transfer of translational energy to the pile, due to which it sinks into the soil, displacing part of it outward or compacting it. For this, complex and heavy mechanisms are used – self-propelled shock or rail installations. To move them around the construction site, a flat surface is required, so the area must first be leveled. The pile is kept in an upright position by means of piles, peculiar arrows.
In the early stages, dive slowly so that you can control the correct incline. The pile itself is affected by a rod or tubular hammer. With the same weight, a tubular hammer has 2-3 times higher impact force than a rod hammer. To prevent the piling equipment from destroying the pile, a special cap is used. The immersion continues until the pile reaches the design depth.
The main advantages of the method include:
- the ability to work on any type of soil;
- high speed and productivity of installation work;
- increasing the bearing properties of the foundation, since the piles, plunging into the soil, compact it in a zone of 2-3 diameters around them;
- work can be carried out in almost any weather.
# 2. Vibration method of driving piles
Thanks to vibration, which is transmitted to the pile by special equipment, the friction force and soil resistance are significantly reduced. That is why driving the piles to the design depth often requires much less effort than driving. We must not forget that when vibrating, just as with the impact method, the soil is compacted by about 1.5-3 pile diameters (it all depends on the type of soil), so that we can talk about the appearance of additional bearing capacities.
This method involves the use of vibrators. Such installations transmit mechanical vibrations of a certain frequency to the pile through a cap. Thanks to this effect, the soil becomes, as it were, floating, and the pile begins to sink under its own weight. If we are talking about long heavy piles, then low frequencies are used; for light small piles, high frequencies are more suitable (more than 1500 vibrations per minute).
The immersion process begins with setting the vibrator to its original position, fastening the pile and leveling it vertically. Before starting work, it is recommended to perform a test run to make sure there are no deviations from the vertical. Such equipment is expensive, and qualified specialists should operate it: the price of the vibroloader, more precisely, the cost of using it will be lower if you use rental services. In Moscow and throughout Russia, the Burovye Tekhnologii Group of Companies offers rental of such rigs: the price includes the services of an experienced operator.
The vibrational method of driving piles is recommended to be used in the following cases:
sandy and water saturation soils. Shell piles, metal sheet piles and reinforced concrete piles in this case are immersed at a speed of 3.5-7 m / min;
- on low-moisture and dense soils, the method is also applicable, but for this you will have to pre-drill a well;
- when immersed in clay and heavy loamy soils 15-30 cm before reaching the design depth, it is better to switch to the percussion method.
Please note that in dense urban areas, vibration should only be used in non-resonant modes. It is desirable that the vibration frequency be no higher than 40-50 Hz.
No. 3. Vibration shock method
As the name suggests, this method involves a combination of vibration and shock. The pile is simultaneously vibrated and bumped, which allows it to enter the soil quickly and relatively easily. This method is used on dense soils, where another method will be ineffective.
The installation, which carries out vibro-shock immersion, has two frames: on one there is an electric generator percussion apparatus, on the second there is a boom with a vibration driver. The vibratory pile driver is connected to the pile using a cap, then the pile is positioned and the mechanism is started. In a similar way, piles up to 6 m long can be driven.
No. 4. Vibrating piles
This method combines shock, vibration and indentation methods. Three forces act on the pile at once. The installation used for the work consists of an electric generator (powered by a tractor or excavator engine), a double-drum winch, a boom guide with a vibrator and blocks through which a pressing rope from the winch approaches the vibrator.
In the designated place, the vibrator lifts the pile and sets it to the point where the immersion will take place. The pile is protected by a cap. When the installation is turned on, the pile begins to sink under the influence of vibration, its own weight, the mass of the vibrator, the mass of the tractor or other equipment, and shock load. Conveniently, there is no need to prepare travel paths for installation. The method is suitable for working with piles up to 6 m long.
No. 5. Immersion of piles by indentation
The indentation method is used on especially hard and dense soils (with the exception of rocks) for driving piles of solid and tubular cross-section of small length (3-5 m). The method is based on the effect of a static load on the pile. During the work, special equipment is used, which takes up enough space, so the implementation of the method is possible only in areas where at least 500 m2 of area is available.
First, the pile is placed in a vertical position in the guide boom of the installation, and the pile shaft is fixed with clamps. The pile is deepened by a meter, after which a head holder is lowered onto its head, which will transmit pressure to the pile through a system of blocks from the base machine (excavator, tractor). This pressure causes the pile to gradually sink into the ground. If the pile cannot reach the required depth, with the help of equipment it is slightly raised, lowered again and continued pressing.
No. 6. Driving piles by screwing
The method is used for screw piles. They consist of two parts: a steel tip with adjacent blades (provides easy entry into the ground) and the pile shaft itself made of steel or reinforced concrete. Screwing is used in the construction of bridges, power lines and other objects with a large load. The optimal method is suitable for use on loose or flooded soils, can be used in any climate. Screw piles can be screwed in even in densely built areas.
Screwing takes place thanks to special equipment that is installed on the frame of the tractor. On the drive of the installation, the pile is fixed in the inventory cover (not with the help of the head). Thanks to the transmission, the torque from the equipment is transferred to the pile, it begins to rotate and sink into the ground. If the soil is too dense, it is allowed to slightly lift the pile and restart the mechanism. After the required depth is reached, the pile is expanded.
No. 7. Immersion of piles by soil erosion
The soil wash method is used on loose and loose soils (sandy and sandy loam soils) to install piles of large diameter and length. It is not allowed to use the method on subsidence soils and with the threat of subsidence of nearby buildings. The method is based on the wetting of the soil and the subsequent reduction in the friction force, due to which the pile easily enters the soil under the action of its own mass and the mass of the hammer installed on it.
Tubes are built into the tip or side walls of the pile, through which water is supplied under high pressure (about 0.5 MPa). Under the influence of water, the soil becomes softer, pliable, friable and washed out. We are familiar with this principle from the sandbox. The resistance of the soil to the pile decreases, the water also erodes the layers of soil adjacent to the walls of the pile, reducing the friction force. The water supply pipes have a diameter of 38-62 mm. Lateral flushing (provided by 2 or 4 tubes on the sides of the pile, 30-40 cm above the tip) more effectively reduces the frictional force of the pile walls compared to central flushing (provided by a single or multi-jet tip in the center of the pile).
It is clear that in this case there is no question of high bearing capacity, therefore, the washing method is often combined with the impact method. In this case, costs are reduced and the reliability of the foundation being built increases.
No. 8. Electroosmosis method when driving piles
The electroosmosis method cannot be considered independent – rather, it is a way to simplify the process of driving the pile. Well suited for dense and water-saturated clayey soils and loams. The essence of the method is to connect two piles to an electrical network. The already submerged pile plays the role of the anode, and the not driven pile plays the role of the cathode. When the current is turned on, the soil near the anode loses moisture – it passes into the zone near the cathode. As you know, it is much easier to immerse a pile in wetter soil. Immersion is carried out by shock or indentation.
After the current disappears in the network, the properties of the soil will be restored in a short time, so there is no need to worry about the bearing capacity of such a foundation.
Buranabic method of driving piles
Let’s make a reservation right away, the buranaibitive method only indirectly refers to the methods of driving piles, because in this case, the piles are created immediately on the site, but we will briefly describe it. Piles are created by constructing a reinforcement frame in a pre-prepared well, which is then poured with concrete. The well is created using a percussion or rotary drill.
Bored piles are created in one of the following ways:
casing pipes. A pipe is installed in the well, which protects the walls from collapse. Then the reinforcement cage is created and the prepared concrete is poured. The pipe itself may remain in the well or be dismantled. Naturally, these two cases require different pipes;
without casing. The concrete slurry begins to pour into the well during its drilling. It strengthens the walls and acts as a casing. Next, a reinforcement frame is placed in the concrete. For a more even distribution of concrete, use a special pipe for pouring, with a vibrator at the end.
Finally, we note that the very scheme of immersion and the subsequent location of the piles is also of great importance:
an ordinary scheme assumes an evenly distant arrangement of piles relative to each other. Suitable for sandy and gravel soils, not used on dense soils, easy to implement;
the spiral scheme assumes the location of the piles from the center of the foundation to its perimeter in a spiral. In this case, we can talk about the most uniform distribution of the load and a decrease in the likelihood of shrinkage;
the sectional scheme involves the installation of two supports in one row, the subsequent skipping of one row and the installation of two supports again. This is how the entire pile field is traversed, after which piles are installed in the skipped rows. The option is suitable for areas with dense soil.
The construction of the foundation is a very responsible process, which must be approached with an understanding of the characteristics of the soil, the specifics of the building being erected and a number of calculations. The immersion method, along with other factors, affects the reliability of the foundation, so its choice must be taken seriously.