Cast-in-situ Bored Piles
This type of pile installation is used to replace soil removed by drilling rather than occupying the space of displaced soil as in driven piles. Thus, it mostly relies on end-bearing capacity of the earth layer at the drilled depth. Bored piles provide the largest pile dimensions and hence the highest load bearing capacities.
One method of installation is to drill a shaft using a continuous auger with a hollow stem at its center, which is later used to grout the drilled shaft. This method is known as Continuous Flight Auger (see following section).
Another technique is to drill the shaft, insert the reinforcement steel cage (if required) and then pour concrete under pressure to fill the entire shaft space. The shaft is drilled using an auger in dry land conditions and a drilling bucket in wet land conditions.
When shaft wall support is required, the drilling process takes place inside a steel casing or with the aid of drilling slurry such as Bentonite.
Temporary Steel Casing Support
Steel drill casing is driven into the ground using a vibratory hammer. Steel cage reinforcement is placed within the borehole and concrete is poured into the shaft under high pressure. The temporary casing is then gradually extracted from the ground and load is transferred to the formed concrete pile shaft. In permanent casing foundation piles the casing is not extracted.
Bentonite Polymer Slurry Method
Drilling mud or slurry such as bentonite and polymer are used for drilling support where the bore hole is unstable. A positive head of bentonite suspension above the water table is maintained during the drilling process, providing continual support to the borehole walls. Fluid concrete displaces the bentonite which is collected, cleaned and can be recycled.
Continuous Flight Auger (CFA) piles
This method combines all major piling operations in a single process, providing a highly productive, cost-effective solution that facilitates fast, noise and vibration-free piling installation. A continuous flight auger with a hollow stem at its centre is used for the drilling process. After reaching the desired depth, concrete is pumped through the hollow stem blowing off the expendable cap.
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