Construction of the Deurganckdoksluis, a massive lock in the Port of Antwerp, is civil engineering on a grand scale. It is impossible to stand beside the lock’s massive, 28m tall concrete walls without being blown away by the scale of it.
The project will provide vital new access to Antwerp port’s western quays. The existing lock that provides access to the port’s expanding west side is not working as it should. And rather than faff about repairing or upgrading it, the port’s owners are cracking on with a €382M (£323M) replacement, using a derelict strip of land between the main navigational channel and quay complex.
In deciding to press ahead with the project, the dual client of Port of Antwerp and Belgium’s Department of Mobility and Public Works, has unleashed a monster: 4.7M.m3 of material is to be excavated and 795,000m3 of concrete is to be poured in creating the 500m long, 68m wide and 28m deep structure. At each end, two massive, 70m long steel gates are to be installed along with two almost 100m long bascule bridges.
The lock has also to be connected to the navigation channel and quays by more excavation. All that in a 53 month construction programme.
Stepping up to take on the monster is THV Waaslandsluis, a contracting joint venture of Jan De Nul, Bam and Herbosch Kiere.
And it is under no illusions about the challenge it faces to do that volume of work in the time allotted.
“We started construction on 24 October 2011 and the end date is 24 March 2016 - that’s a 53 month construction programme with a fixed end date to build the biggest lock in the world,” says Bam project leader Guido Franx.
Temporary and enabling works are a significant part of the scheme, amounting to almost 10% of the £229M total construction cost. They are led by THV’S temporary works leader Robbrecht Cassiman.
Right at the start, work involved construction of a temporary bridge to take a road away from the site, a concrete batching plant and a 200m long sheet-piled quay wall to receive materials. The team even had to move two navigation light towers.
The batching plant in particular is a serious bit of kit, with a minimum output of 200m3/h through batches of either 4m3 or 5m3. Typically, the plant churns out 250m3/h over an eight hour period.
But by far the most challenging part of the enabling works was installation of a 2.8km long, 30m deep cement/bentonite wall, forming a ring around the site to prevent groundwater ingress during excavation. Lengths of up to 30m of the wall were completed per day.
Once the cement/bentonite wall was complete, the site was dewatered with 70 wells and four vertical drains. Meanwhile, 53 logging points outside the cement/bentonite shield constantly log levels to ensure the groundwater outside the site is unaffected.
And so to construction proper. First, excavation of the 4.7M.m3 of sand and silt. A sizeable 2.8M.m3 was considered of such poor quality that it was dumped straight into an abandoned dock handily positioned adjacent to the site. That work is done. The rest, decent quality sand, is being excavated and stockpiled on site to be used as backfill, and that work is ongoing. Indeed, the site today is awash with dumper trucks and dozers as excavation continues alongside construction of the permanent works.
To keep on top of the tight schedule, THV has carried out excavation in two shifts, moving 20,000m3 of material per day using a fleet of 20 dumpers, four bulldozers and three cranes. A fuel truck was also needed to supply the 17,000l of fuel used by these machines each day.
As soon as the excavations hit base level, 17.8m below mean sea level, work on the permanent works begins, starting with sheet piling. “The ground is like quicksand,” explains Cassiman. “So the dock walls are stabilised with sheet piles. We will have to install 9,000t of sheet piles to ensure the stability of the construction.”
The sheet piles will support the toe and heel of each wall, which is L-shaped, slightly inclined and tapers from bottom to top. Ultimately, each wall will be supported on the land side by backfilling onto the wall’s concrete base. They will also be tied into the 1.3m thick concrete base slab.
Twenty to 25 sheet piles are installed per day and once in place reinforcement bars are welded to the sheet piles to ensure a good connection is made to the base slab when the concrete is poured.
And that’s the big job. It’s hard to picture how much concrete goes in to a lock of this size but fortunately Franx has a handy comparison.
“It’s one football pitch, 35 storeys high,” he says, before adding: “And at 55,000t the reinforcement weighs the same as seven and a half Eiffel Towers.” In monetary terms its perhaps even starker: £118M - more than half of the construction cost - is in the concreting.
A typical 20m long wall unit is poured in five stages - two stages for the up to 5m deep foundation piece and then three phases, each a climb of around 8m, for the wall itself, which tapers from 5m thick at the base to 2.5m thick at the top.
The two foundation phases take eight days, with the rest taking three to four days each. Generally, it is one day to set the formwork, one day to install the reinforcement, and one day to do the concreting. “And they are long days,” says Franx.
A bespoke travelling formwork system has been developed for the job, supplied by Doka to an in-house design. Each piece weighs 50t and travels on rails.
Concrete is poured in 1m deep layers, using a low heat mix to minimise cracking. Reinforcement is mostly prefabricated and lifted in by tower crane. And the tower cranes have another, unusual, use. “To vibrate the concrete we use the tower cranes,” says Cassiman. “It’s like fishing, what we are doing,” he says, referencing the motion of the tower cranes as they dip the vibrating hoses in and out of the concrete mix.
There’s more to it than just building the walls though. Some fairly serious recesses have also to be accommodated. There are four recesses for the two pairs of sliding lock gates - each end has two gates to allow for one to be out of action for maintenance. There are two more recesses for the bascule bridges’ counterweights, a pair of tunnels to channel water into and out of the lock, and a chamber running the length of the lock to trap and remove silt being dragged through it.
Many of these structures - housed on the east side of the dock - are under construction now, while excavation of the west side of the lock continues. It truly is a site where all stages of a mammoth construction project are laid bare before you.
“To do this size of works in 53 months, we have to work simultaneously,” says Cassiman. And right now all is going seamlessly. As Cassiman says, gazing down from ground level into the bear pit: “It’s great that the formwork system I designed is working perfectly.”
What is not going quite so perfectly is the construction of the mammoth steel lock gates, the design of which the client has yet to sign off. It’s perhaps understandable that this aspect of the project gets due care and attention as, after all, it is what it is all about.
But for Franx’s team, the real issue will be getting them in place. It’s a real crux point of the project, with the gates planned to be floated in to place once the lock is complete, its approaches dredged, and then the lock itself opened up to the elements.
Incredibly it has been worked out that there will be just 100mm of clearance as the 70m long gates are positioned. “There is going to be a bit of manoeuvring to fit them in and it is very tight,” notes Cassiman.