Pile foundations are deeper frameworks that are used where the site is somewhat weak and has shallow bearing stratification making it necessary to pass load to a more profound stratum either by means of friction or end bearing principles. Foundations protect structures by shifting the weight to the rock or soil layers having adequate bearing ability and right establishment properties. There are a wide variety of foundation types available that are fitting for diverse applications.
The pile foundation techniques and the deployment procedures are the factors that are just as crucial as the designing process. The Pile foundation installation methods include:
- Pile hammer
- Boring by a mechanical drill
Experienced and competent Piling Contractors in London advice to choose the tools and construction equipment very carefully to prevent any damage to the piles in the designing phase
Displacement pile driving methods
- Dropping weight
Non-Displacement pile driving methods
- Continuous Flight Auger (CFA)
Drop Hammer Method of Pile Driving
A hammer of roughly the mass of a pile is lifted in a guide to an appropriate elevation and released to hit the top end of the pile. This is a basic form of hammer used in tandem with light blocks and sample piling, where bringing a steam boiler or compressor to a construction site could be an expensive affair to drive a fairly restricted number of piles.
There are two major types of drop hammers:
- Single-acting steam or compressed-air pile hammers
- Double-acting pile hammers
A single-acting team or compressed-air in the shape of a cylinder contains a huge mass, which disengages the piston rod. The steam is cut off at the peak of the motion, or at a lower height which the Piling Contractors can easily regulate, and the cylinder drops freely on the pile head.
The hammers of double-acting piles can be powered by steam or compressed air. With this sort of hammer, a piling framework is not needed and can instead be connected by leg-guides to the top of the pile-driven by a wooden frame. When employed with a pile framing, rear guides are bolted to the hammer to interlock with heads, and only short leg-guides are utilized to block the hammer from shifting to the position relative to the top of the pile. Double-acting hammers are primarily employed for sheet pile driving.
Pile Driving by Vibration
Typically, vibratory hammers are either electrically driven or hydraulically operated and comprise of coaxial contra-rotating unconventional parts within a covering attached to the head of the pile.
The amplitude of the fluctuation on the sides of the pile is enough to break down the surface friction. Piling Contractors recommend the land bearing sandy or gravelly soil as the best candidate for deploying vibrational pile driving methods.
Water jetting can be used to assist the infiltration of piles into sediment or gravel-filled soil. The method has, however, very limited success against stiff clays or any land that contains a lot of coarse gravel, cobbles, or pebbles.
Auger (CFA)Here, the machinery consists of a mobile foundation carrier configured with a hollow-stemmed flight drill that is shuffled in the soil to the needed piling depth. Concrete is poured through the flight auger to build the pile, as it is removed from the ground.
The auger is equipped with a shielding cover at the exit on the foot of the central conduit and is wheeled to the ground by the top-mounted rotatory hydraulic motor operating on a mast-mounted carrier.
Highly functional concrete is injected through the void stem of the auger; upon hitting the required depth, the protective lid gets automatically disengaged under pressure from the filling concrete. While pivoting the drill in the corresponding direction as during the boring stage, the soil is ousted vertically. Finally, the auger is removed, and the pile is formed by packing with concrete.
Skilled contractors opine that it is necessary to align with the movement of the auger and concrete pouring motion to prevent the breakdown of the sides of the concrete hole, especially during the lower drill flight, which might lead to voids in concrete, stuffed with soil.
The method is particularly effective on wet and soft soils and allows the installation of a number of bored piles of varying diameters which can infiltrate a myriad of ground conditions.
Underreaming is a unique feature of auger bored piles which is sometimes used by offering an expanded base to leverage the load-carrying capacity of appropriate strata. In order to use this technique, the soil must be able to stand upright in the open and on its own— Rigid and harder clays, such as the ones found in London are the best candidates.
The Underreaming device is mounted inside the straight section of a pile shaft in its locked state and then enlarged at the bottom of the pile to create the under ream.