Bowbridge pile drilling - It Takes Three
by: David M.
We had ten 3.9m piles to go in on the ‘water side’ of the landing stage west of Bowbridge Lock. Only one of them hit an underwater obstacle, easily cleared, but every one of them got down to a hard layer, and went to refusal with between 0.5m and 1.2m to go. We left them at height to aid construction and mooring. However, the factory work to pre-drill holes for the steel cross-pieces and timber frames had to be re-done, as the original holes were left up in the air.
Access to the closed (landward) side was not possible (too deep for waders) so the piles had to be drilled from the open side, not far above water level. From our hi-tech flotation platform, it took one volunteer to hold the weight of the mag drill on a rope, the second to position the drill and operate the controls, and the third to apply the pressure, with the drill enclosed mainly within the pile.
Bolting the cross-pieces on was relatively straightforward, with some underwater spannering, and the five frames were lowered down, drilled and bolted together, and bolted to the steel, in a choreographed display of highly coordinated activity as darkness loomed.
A new day, and we found that cutting the remaining pile lengths off when in situ, from the moving raft or a temporary surface on the frames, was a bit trickier than doing it on the bench at Brimscombe. The Armco was hung over the side and bolted on, and the main surface panels laid for fixing in the next session. They soon got a coating of autumn leaves, which reminds me, the hydro generator screen at Dudbridge will need clearing again. Stu took three wheelbarrow loads of leaves out yesterday, there’ll be plenty more to do tomorrow. But that’s another story.