Benson Cove

Strengthening the quay wall required casting an added thickness of concrete against the existing structure, over its full height.

The main challenge was to design formwork that could be completely submerged by the tide and remain loaded throughout the pour, with the end of the pour timed to coincide with high tide.

Custom formwork panels — Design of 3.2 m steel panels with stiffened facing plate, sized for a concrete pressure of 48 kPa and lowered by crane from the top of the quay to close against the existing wall.

Placing method in submerged conditions — Pouring through successive ports from the base of the formwork, fluid concrete height limited to 2 m and a maximum differential of 610 mm between the port and the concrete front, with the sequence set by the tidal cycle.

Rock anchors — Sizing of anchors in friable rock and design of a dedicated bearing plate for the pull-out test confirming their capacity before loading.

Execution support — Successive drawing issues, coordination of panel shop drawings and technical responses to the contractor during construction.

Submerged formwork cannot be corrected mid-pour. Panel geometry, port positions and the placing sequence were therefore settled together, against the tidal range, so that the temporary works would be right on the first attempt.

This is exactly the kind of constraint that defines temporary works engineering: there is no margin for correction, so it is taken at the design stage.

Thanks to Constructions Bé-con and the teams involved.