Large diameter bored piles are excavated by auger, rock bucket, grab, chisel and/or reverse circulation drill (RCD) rig. A temporary steel casing will be installed into ground to support the unstable strata and ensure safe working conditions on ground / working platform. The casing is installed by the piling rig using oscillator, rotator or vibrator. However, carrier fluids such as bentonite or polymer may be a more effective way of stabilizing a deep pile bore than using a longer casing. The general principle is to maintain a positive hydrostatic fluid load in the bore above groundwater level, same as diaphragm wall technique.
Subsequent to the pile boring, the following processes will be followed.
- Enlarge the pile base (bell-out) by belling tool,
- Air-lifting and pile base cleaning,
- Installation of steel reinforcement,
- Concreting of the pile by tremie method. During the course, temporary casing will be removed gradually.