CFA (Continuous Flight Auger)
Continuous flight auger (CFA) piling is the technique in which piles are drilled and concreted in a single continuous operation hence allowing much quicker installation times than simply bored piles.
First, the steel cage is placed, followed by the pouring of wet concrete. This enables the pile to resist a range of structural loads. This technique is suitable for construction in most types of strata like sand, gravel, silt, clay, and soft rocks.
CSP (Cased Secant Piling)
The cased Secant Piling (CSP) system utilized the much cost affect continuous flight auger technique with heavy-duty casings that are otherwise linked to traditional methods like rotary bored piling methods. This method is more commonly employed for secant piles.
Similar to CFA, it can be almost employed in any type of soil condition.
LDA (Large Diameter Auger)
Large Diameter Bored piling technology employs powerful hydraulic rigs to construct large diameter piles. They use interchangeable attachments like augers, core barrels, and buckets.
This type of construction technology is also suitable for various types of soil conditions and can be applied to both types of piles: contiguous or secant.
Steps of construction
Following steps are usually followed in each technique listed above to make contiguous bored piles. Note that these steps are for the construction of a single pile. They are repeated again and again to construct more piles.
Positioning: First of all, wooden pegs are used to locate the center position of each pile to be bored. The gap between the two piles is also outlined at this stage.
Case Installation: The next step is the installation of the case using a Vibro-hammer, that drives a casing into the ground. It leaves about 1-meter length of the casing for protruding above the ground.
Augering of borehole: A drilling tool name Auger cuts and removes the earth inside the casing for forming a borehole. The case supports the soil surrounding the borehole. In cases, when the casing is not long enough to support the borehole, bentonite slurry can also be used as support against the soil.
Installing steel cage: After the hole is made, a crane lift the steep cage and place it down the borehole.
Pouring concrete: After placing the steel cage concrete is poured down the hole to form a pore pile.
Casing Extraction: The last step is removing the casing from the ground, which is done using a Vibro-hammer.
There are three most commonly used construction techniques for Contiguous bore piles:
- CFA (Continuous Flight Auger)
- CSP (Cased Secant Piling)
- LDA (Large Diameter Auger)