I must admit to a few days of squeaky-bum time prior to piling last month, but as it turned out it was painless (apart the kick in the budget). Don't know anything about screw piles (we had end-driven case piles), but here's what I learnt:
- quotes varied by as much as 50%
- big piling rig equals big mobilisation cost and big vibrations, but a quicker job.
- quoted pile depth is a best guess based on soil survey and local knowledge. Make sure you compare like for like regarding depth, and on-costs per extra metre to achieve a set.
- don't forget the Party Wall Act if you're close to neighbours (piling within 6 metres)
- if you have close neighbours, you probably need to give your piling method some thought with respect to Jct 21.2.1 insurance, but that's a whole new headache...
- piling was cheap compared to the ring beam; get a cost breakdown for each element
We had 24 x 10m piles put in by a local (regional) contractor with a small rig (£200 mobilisation fee), in just over a week without pi$$ing the neighbours off. He was the only quote that offered a refund if a set was achieved at less than quoted depth, and we got nearly £500 back (plus £25 beer money from weighing in the cut-off steel casing he left behind!?).