Rotary Bored Piles
Rotary bored piles are often larger diameter than conventional continuous flight auger (CFA) piles. They are used to support greater loads, overcome underground obstructions and to penetrate ground too hard to bore using continuous flight auger techniques. Rotary pile installation can also be used to create piles with a cut-off level beneath the platform level. Because the rotary bored technique enables the reinforcement to be added into the open bore rather than into the ready poured concrete, as in CFA, it has the distinct advantage of allowing the cage to be the full depth of the pile.
Depending on the rig, the installation of piles over 40m deep and up to 2.5m diameter is possible. This is a straightforward method of piling and is advantageous when compared to CFA, as the size and depth range is greater and a number of piles can be drilled in advance of concreting. A further advantage of rotary or open hole piling is that with special tools the base of the hole can be reamed out to create a bell shape to increase the bearing area of the pile.
Rotary piling is often used in places such as factories and town centres where it can often be difficult to ensure a consistent and timely supply of concrete.
Bored Displacement Piles
A continuous displacement pile is a bored pile which displaces the soil through which it is constructed. It therefore creates no appreciable arisings ensuring that there is minimal spoil to remove from site.
This type of pile can be used for all foundation applications where bearing piles are required for buildings or structures. It can also be used where there is a retaining requirement. The ability to form bored piles without producing any spoil makes this kind of pile particularly advantageous on contaminated sites. The technique produces minimal vibration and noise. In most ground conditions, this pile is an ideal alternative to CFA (continuous flight auger). Enhanced load carrying capacity may be achieved compared with CFA piles of similar dimensions, due to compaction of the soil during boring. In some ground conditions improvements of up to 30% have been demonstrated with a consequential shortening of the pile and reduction in cost.