Technology for diving piles

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Technology for diving piles

Kakharov Z.V.

Islomov A.S.

Abstract

this article presents various methods of piling, using undercutting, as well as various combinations of these methods.

Keywords: pile devices, impact method, vibration method, indentation method, screwing method.

Depending on the characteristics of the soil, there are a number of methods for piling, including impact, vibration, indentation, screwing, using undercutting, as well as various combinations of these methods.

The impact method is based on the use of impact energy (impact impact), under the influence of which the pile with its lower pointed part is introduced into the ground. As it sinks, it shifts soil particles to the sides, partially down or up. As a result of immersion, the pile displaces a volume of soil that is almost equal to the volume of its immersed part. A smaller part of this soil is on the day surface, a large part is mixed with the surrounding soil and significantly compacts the soil base. The zone of noticeable soil compaction around the pile is 2...3 pile diameters.

The impact load on the pile head is created by special mechanisms:

steam-air hammers, which are driven by the force of compressed air or steam directly acting on the impact part of the hammer;

diesel hammers, the operation of which is based on the transfer of energy from the combustion gases of the impact part of the hammer;

vibratory hammers - transmission of oscillatory movements of the working body to the pile (use of vibration);

vibrohammers - a combination of vibration and impact on the pile.

Diesel hammers, in comparison with steam-air hammers, are characterized by higher productivity, ease of operation, autonomy of action and lower cost. Autonomy is ensured by lifting due to the power stroke of a two-stroke diesel engine.

The main advantage of a tubular-type diesel hammer over a rod-type hammer is that, with the same mass of the impact part, they have a significantly greater (2 ... 3 times) impact energy.

Vibratory pile drivers and vibratory hammers are more commonly used for driving large-diameter tubular shell piles, driving into the ground, and extracting sheet piles. The working cycle of hammers of all types consists of two cycles: an idle stroke, during which the impact part rises to a certain height, and a working stroke, during which the impact part moves down at high speed until it hits the pile. In a number of pile hammers, the working stroke occurs only under the action of the mass of the shock part; such hammers are called single-action hammers.

To lift and install the pile in a predetermined position and to drive piles with the transfer of force from the pile hammer in a strictly vertical position, special devices are used - copra.

The main working part of the copra is its boom, along which a hammer is installed before diving, lowered and raised as the pile is driven. Inclined piles are driven into the ground by pile drivers with an inclined boom. Headframes are rail-mounted (universal, metal tower-type headframes) and self-propelled - based on cranes, tractors, excavators and vehicles with an arrow 9 ... 18 m long.

Universal headframes have a significant own weight up to 20t. The installation and dismantling of such pile drivers, the installation of crane runways for them are rather labor-intensive processes, therefore universal pile drivers are used for driving piles with a length of more than 12 m with a large amount of pile work at the facility.

Pile driving consists of three main repetitive operations:

moving and installing a pile driver at the place of pile driving;

lifting and placing the pile in position for driving;

pile driving.

The pile driving process includes placing the pile in the design position, putting on the cap, lowering the hammer and the first blows on the pile from a height of 0.2 ...0.4m. From each impact, the pile sinks to a certain depth, which decreases as the pile deepens. In the future, there comes a moment when the depth of pile driving is almost imperceptible. In practice, the pile sinks into the ground by the same small amount, called failure.

Failure - the depth of immersion - piles for a certain number of blows of a conventional single-action hammer or per unit of time for double-action hammers. The failure rate is the average of 10 or a series of strikes per unit time.

Pledge - a series of blows performed to measure the average failure value: for steam-air hammers in a pledge 20 ... 30 blows; for diesel hammers in pledge 10 strokes; for double-acting diesel hammers, failure is determined in 1 min. blockages.

Pile driving by vibration is carried out using vibration mechanisms that exert dynamic effects on the pile, which make it possible to overcome the friction resistance on the side surfaces of the pile, the frontal resistance of the soil that occurs under the pile tip, and plunge the pile to the design depth.

The vibration indentation method is based on a combination of vibration or vibro-impact impact on the pile and static weight. The vibropressure unit consists of two frames. On the rear frame there is an electric generator powered by a tractor engine and a double-drum winch, on the front frame there is a guide boom with a vibratory driver and blocks through which the pressing rope from the winch passes to the vibrator. In the working position, the vibratory driver, located above the place of immersion of the pile, lifts the pile and sets it together with the fixed head at the place of its driving. When the vibrator and winch are turned on, the pile is loaded due to its own weight, the mass of the vibratory driver and part of the tractor mass, transferred by the pressing rope through the vibrator to the pile. At the same time, the pile is subjected to vibration created by a low-frequency loader with a sprung plate.

Pile driving by indentation is used for short piles of solid and tubular section (3...5m). Static indentation is carried out in the following sequence: the pile is installed in a vertical position in the guide boom of the unit. Next, the head of the pile is lowered and the head is fixed, which transfers pressure from the base machine (tractor, excavator) through the system of blocks and tackles directly to the pile, which, thanks to this pressure, gradually sinks into the ground. After the pile reaches the design mark, the dive is stopped, the cap is removed, the unit moves to a new position.

Driving piles by screwing is based on driving steel and reinforced concrete piles with a steel tip using mobile units mounted on the basis of cars or other selfpropelled vehicles. The method is most often used in the construction of foundations for masts of power lines, radio communications and other structures, where the bearing capacity of screw piles and their pull-out resistance can be used to a sufficient extent.

Pile driving by washing the soil is used in non-cohesive and slightly cohesive soils - sandy and sandy loam. It is advisable to use flushing for piles of large cross-section and great length, but it is unacceptable for hanging piles. The method consists in the fact that under the action of water flowing under pressure at the tip of the pile from one or more pipes fixed on the pile, the soil is loosened and partially washed out.

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