A design and build contract to construct 113m of new quay wall, which will be used to enable the mooring of Service Operation Vessels associated with Dogger Bank Windfarm. The new quay wall consists of a driven steel pile combi wall, tied back to the land via tie bars and anchor piles. Working with consultant GHD, the design was developed in accordance with challenging ground conditions, arising from unknown historic structures, with the site formerly used for shipbuilding and offshore oil/ gas module fabrication.
An initial earthworks programme was undertaken to remove ground obstructions across the site footprint, which involved excavating to a depth of 9m to accommodate anchor piles. Ground obstructions encountered included foundations, crane tracks and 3no. disused slipways. Installed using a 250t Crawler Crane, the anchorage system includes a total of 12no. 1422mm, and 16no. 914mm diameter tubular piles.
In order to construct the combi wall, a temporary piling gate was used to pitch the piles into position. The new combi wall consists of 24no. 1067mm, and 15no. 1422mm diameter tubular piles. Accompanying sheet piles measuring 18m and 20m long were also installed to complete the combi wall arrangement. Using a 250t and 400t Crawler Crane, piles were driven to refusal using a combination of vibro and impact hammers. Where tubular piles couldn’t reach the specified toe level, pile top drilling and the installation of ground spigots was required for stability purposes. Following construction of the combi wall, a total of 36no. tie bars were installed and tensioned.
A total of 20no. precast concrete units weighing up to 17 tonnes each were manufactured on site to form the required capping beam for the quay wall. Associated work elements included additional reinforcement and in-situ concrete pours. Following construction of the capping beam, ducting, services and drainage were installed at the rear of the quay. This allowed for construction of an 18m wide ground slab with a bearing capacity of 10t/m². Quayside furniture was then installed in the form of fenders, ladders, grab chains and mooring bollards. To protect the face of the quay wall from future corrosion, a new cathodic protection system has also been installed.