Airlifting is normally carried out prior to concreting to remove debris and clean the base of pile bores. It essentially acts as an airlift pump by using compressed air. The setup of a typical airlifting operation is as follows: a hollow tube is placed centrally inside the pile bore and a side tube is connected to the end of the tube near pile bottom for the passage of compressed air inside the tube.
The upper end of the tube is linked to a discharge tank for the circulation of pumped fluid from pile base.
The efficiency of airlifting operation is dependent on the performance of air compressor. During airlifting, compressed air is piped down the tube and it returns up to the discharge tank carrying it with the fluid. It functions by imparting energy to the fluid and forces the fluid to move vertically upwards. The injected air mixes with the fluid, resulting in the formation of lower unit weight of the combined mixture when compared with surrounding fluid. This hydrostatic pressure forces the fluid/air mixture up to the discharge tanks.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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If any of the pilers have experiance in air lifting; whether the debris from pile base can be sucked out using air lifting when pile bore is not filled with fluid. there is only a few meters of ground water present in a 30m deep pile.