Piles aren't just piles!!

My first job was as a trainee mechanical engineer at BHP (a short lived career) and ever since I think I’ve been a frustrated engineer at heart. My daily visits to the NCV site always throw up new things at which I can to marvel. The piling technique being used for the NCV has been chosen due to the very sandy ground on site. The Continuous Flight Auger (CFA) piles (also known as Groutcrete piles) are a non-displacement pile used where fast vibration free installation is required in difficult ground conditions. The drilling process is unaffected by ground water or collapsing soil conditions. The company completing the work is Advanced Foundation Solutions.

The pile is formed by first drilling into the ground with a continuous flight auger. Cement-sand grout or concrete is then injected under pressure through the auger's hollow stem as it is being withdrawn. On completion of this operation, a reinforcing cage is pushed into the fluid column of grout or concrete. Equipment is available to install piles up to 32 metres long but the NCV piles are generally about 10 metres in length. The diagram below shows the key stages in the process, including drilling, pumping the concrete into the hole as the augur is extracted and insertion of the steel reinforcing. For the more technically minded check out this link.



The building requires 170 of these piles and a skilled operating team can complete 10-15 per day when things go well. The first week of drilling had some dramas with teething problems getting the concrete mix right and the machine set. A major breakdown meant that the machine needed to be replaced and a full day was lost. The operators are confident that they can make up for the lost time. Our sandy soil has helped with no time lost this week due to rain. Lipman hopes to see Stage 1 of the piling completed by the end of next week with a second stage of piling slightly later for the non-basement section of the building. The picture below shows the AFP drill on the NCV site drilling on the Anzac Parade side of the building.

Piles aren't just piles!!