Kandt and BAM Infra Civiel join forces for Trekvliet bridge The Hague

Under the Trekvliet bridge in The Hague a new underpass will be created especially for cyclists and pedestrians. This will eliminate a dangerous intersection and create a safe connection towards the city center. But building under a busy traffic artery is no easy task. 

Such a large-scale infrastructure project requires smart choices and close cooperation. The construction team, with BAM Infra Civiel as the main contractor and the municipality of The Hague as the client, together with specialist partners, is committed to a short, intensive closure of the Mercuriusweg. "That 9-day road closure is the moment when everything comes together," says Bastiaan Verheul, head of the business office at Kandt Aannemings- en Funderingsbedrijf.

Collaboration from design

The project was put on the market two years ago as a construction team. The Municipality of The Hague expressly sought a contractor who would contribute ideas on feasibility and nuisance limitation from the outset. BAM Infra Civiel was commissioned to work with the municipality to develop the design further. Foundation specialist Kandt BV contributed its expertise as early as the design phase.

"Mercury Road is an important entrance to the city," Verheul says. "The original design provided for a lengthy phasing with significant traffic disruption: twice half a road closure for an extended period of time. BAM proposed one complete closure of nine days, during which the underpass at the junction with Mercuriusweg could be realized. After that, the road could be reopened immediately. That was smarter, safer and with considerably less inconvenience. That's how BAM won the contract, and we joined the construction team as a foundation partner to develop the plan further and make it feasible."

Wide range of foundation work

For Kandt, it meant a wide range of work. "We provided some 250 meters of definitive and 100 meters of temporary sheet piling," says Verheul. "We applied fluidization to reduce vibration nuisance to the surroundings. In such a built-up urban environment, this is crucial. A special feature was the temporary sheet pile wall 17 meters from the existing quay. This surface was backfilled with sand, creating space to drive in the pre-built deck during the closure."

In addition, Kandt installed 60 permanent and 20 temporary LeKa piles. "Thanks to design optimizations, the number of piles is limited, which is more sustainable. The temporary piles were drilled at the pre-construction site and will be drilled out after the bridge deck is driven in and reused in another project later this year." Kandt is also removing 65 old piles under the existing wharf that run right through the new bike path alignment. "BAM is demolishing that old quay section, we are clearing it for the new underpass and the bike path alignment. They are precast concrete piles 18 meters long, under bracing of 3:1 and 4:1. Pulling them requires craftsmanship."

Smart solutions for complex conditions

The complexity was mainly in the existing environment. "The new dam wall route crosses existing grout anchors in several places. At the clash points, we drilled through the anchors at a depth of 7 meters using a special technique to make room for the new route. That requires precise preparation and execution." Traffic stops were applied when working within falling range of traffic. "That is essential for the safety of our people and road users."

The underpass and part of the quay renovation covered a total of one year of construction time. Almost all foundation work, such as installing sheet piling, LeKa piles, grout anchors and pulling piles, took place on regular working days. Only the section crossing Mercury Road was carried out during the 9-day road closure.

Overkill and construction team collaboration

Another challenge was protecting underground cables and pipes from overburden. "Together with BAM, we designed and built overpasses to allow traffic on Mercury Road to flow for as long as possible while protecting the infrastructure. You work out that kind of solution together in the construction team step by step."

Verheul emphasizes the importance of that construction team approach. "It's not just about executing what's on paper, but about identifying and resolving risks together. We were in one team with BAM and the municipality from the beginning to prepare everything in detail. During those nine days everything has to fit together seamlessly: we install the sheet pile walls, piles and road anchors, halfway through BAM drives in the bridge deck. Then the route is completed and asphalted so that traffic can drive again."

The value of preparation

"To make sure everything was all right in those nine days, everything was planned in detail for months. Despite the many disciplines, it is set up in such a way that everyone says: it is feasible. But that is only possible if you work together in a construction team, tackle risks in advance and incorporate solutions integrally into the design. That's where we as specialists add value: making sure it can actually be done later as conceived."