Bored Mini Piles
Drilled mini piling has been more common within the last 10 years due to developments in plant and methods of providing small diameter piles.
Relatively high capacity piling using this equipment is possible with the safe working load of 900 KN realistic if rockhead is at a reasonable depth.
Bearing is achieved by drilling into the rock forming a socket which can be several metres long.
This type of pile is also an anchor resisting uplift should this be required where excessive loading to cantilever caps is generated.
Brown Field Areas
This system of casing and drill stem advancement using a down the hole hammer is effective in drilling through obstructions which is an advantage in brown field areas where all materials may be present.
Air powered rotary percussion methods provide sockets in the rock.
This method of drilling can be adapted to draw down a casing with the drill head creating a pile stem through the overburden.
Proprietary systems such as Atlas Cop C5 Odex piles or Symmetric piles can be produced.
As the pile is permanently cased to rock and no reduction in stem diameter is possible. Piles are tremie grouted to ensure a maximum bond to the rock.
The principles of BS 8081 (Ground Anchorage Design) are generally used to establish length of socket required.
Restricted Access Conditions
This type of Mini Piling is best used in restricted access conditions where a smaller rig is able to install piles in low headroom.
A smaller version of CFA (Continuous Flight Auger) Piling can also be undertaken where friction is generated along the full length of the pile.
A lower displacement water flush is now available using 'wassara' casing system and water hammer for works near particularly sensitive structures.