Inadequate design of two immense gate caissons for the world’s largest ship lock, located in the Netherlands, will cost its design-build construction team $65 million to fix and will complicate the work. The construction contract is valued at $590 million.

Rob van Wingerden, CEO of project co-contractor Royal BAM Group N.V., Bunnik, says the design-build team must stiffen the deep concrete boxes, which are 80 m long, 55 m wide and 29 m deep.

Having an open side and top, the caissons would in fact be prone to twisting forces when sunk into place later in the project.

The caissons are being built at the North Sea coastal site of IJmuiden, roughly 25 km west of Amsterdam. When complete, one caisson will be placed to house a sliding gate at each entrance of the lock, whose dimensions are 500 m long, 70 m wide and 18 m deep. 

BAM is in an equal joint venture with Royal VolkerWessesl N.V., Rotterdam, and serves as the lock’s design-builder under a 26-year public-private partnership contract with the infrastructure authority Rijkswaterstaat. Including maintenance, the deal is valued at $710 million.

Caissons
Image: Courtesy of BAM

Reporting the financial loss on Dec. 6, van Wingerden said that the big caissons had been regarded during bidding and early design as stiff, closed boxes. However, having an open side and top, the caissons would in fact be prone to twisting forces when sunk into place later in the project. 

When the contractor identified the problem early this year, “we thought everything would need to be a bit thicker,” said van Wingerden. But the full implications only became known as construction began. 

The redesign involved the introduction of stiffening cross walls and heavier reinforcement. “Constructability became...very difficult. It requires much more planning, specialist equipment and personnel,” said van Wingerden.

Starting construction in early 2016, the contractor has now completed about 30% of the work. The caissons under the new schedule are due to be placed in early 2019, when the work was supposed to be completed. Now the work won't be finished until the 2020.

“It’s not a good story,” said van Wingerden. “But it's a one-off.”