'Normally you work to tolerances of 75mm on a marine piling job, ' says Edmund Nuttall project director Simon Tanner.
'But because of the environment - four knot currents and tides moving up and down at 1m per hour - we designed these works with a tolerance of 150mm.'
There is a mix of vertical and raked piles to take loads under tension and compression from ships that nudge against the piers or swing around the turning dolphin: They typically have a capacity of between 550t-600t - 'about twice what you'd normally have for a jetty, which means you need relatively few', says Posford Haskoning principal engineer Tom Rea.
Vertical piles in each bent are connected by cruciform shear connections which help spread fender loads.
Piles are between 35m and 42m long, and were placed in 17m of water from Nuttall's Marlin barge through 8m-10m of river silt into firm chalk.
'It can take half an hour to one and a half hours to position each pile, ' says Tanner.
The operator would let selfweight push the pile into the river mud. 'We'd then check its position. If it was OK, it would be driven a short way into the rock, checked again, then driven properly.'