Holdfast Training Services Trial Blog

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This slide show lays out the basic process to piling at Paradise.

Piling began in Paradise three weeks ago. The piles are 1200mm bored RC piles working in end bearing. Each pile requires a rock socket length of approximately 6D.

Despite the management issues with the demolition subcontractor being currently 9 weeks behind schedule and still on site, the piling has been going well. The target has been to complete 2.5 piles per day and the pilers are currently hitting around 3 per day.

The estimation that the piling is working on is that of the rock head level (m AOD of the incredibly weak and completely underwhelmingly named “Bromsgrove Sandstone”). The rock head level is required 10 days before the piles are installed and this has been assumed based on previous construction drawings that show the underside of foundation levels. This level effects the overall length of the pile and more importantly the length of the steel reinforcement cages, hence the lead time.

The issue I had yesterday on site was an obstruction encountered below the presumed rock head level. This obstruction appeared to be a concrete slab, possibly blinding, at about 5.5m below piling mat, the rock head should be 4.25m below. A quick inspection of the piling hole identified the sandstone was collapsing above the obstruction and water was trickling in to the base.

The piling designer was contacted and assured everyone that the rock socket length could still be achieved by increasing the depth of the pile, but not the length of the cage, so the bottom 1.25m would have no structural steel. (Revision – due to additional length in the cages the actual length without steel is only 600mm). This pile will be recorded as a non-conformity by the piling sub-contractor and I will advise that further testing be carried out on this pile.

This pile is located in the core of the structure and as such I am now concerned that the surrounding piles will also have a rock head level lower than expected. When we do the surrounding piles (Approx 3 days after that pile in question – Monday) I will be able to get a better idea of what the obstruction is.