Design/build-team approach opens the way to test innovations

Opened in 1977, the Kiltunnel is one of the oldest underwater tunnels in the Netherlands. It is also an important traffic artery, connecting the city of Dordrecht with the Hoeksche Waard region of the province of Zuid-Holland. With over four million road and “slow traffic lane” (cyclists, etc.) users per year, it is also one of the busiest. In 2021 and 2022, this tunnel underwent major maintenance as well as a “sustainability makeover”, carried out by the sKILs consortium (Mourik Infra and SWARCO Mobility Nederland). Thanks to the design/build-team approach, we were involved in the project right from the design phase. Though our guiding principles were safety, accessibility and user comfort, this maintenance project also became a real testing ground for innovations in the area of sustainability.

The ambition: safer and more sustainable than ever

The reason for the major maintenance was the condition of a number of technical systems for the tunnel and the traffic moving through it, which, after years of reliable service, were ready for replacement. Tunnel operator Wegschap Tunnel Dordtse Kil wanted to take this opportunity to make the tunnel, including the toll plaza, ready for the future while improving road safety. This meant, for example, carrying out concrete rehabilitation, applying a new coating in the tunnel, repaving the road surface, improving safety in and around the tunnel and on access roads, constructing an extra toll lane in both directions, installing modern technology, and building a brand new toll office.

​​We implemented more than 15 innovative measures in areas like cutting emissions, using green energy, greening buildings, and using circular materials and a materials passport. Extra attention was also paid to the health and well-being of employees. To give an example of the sustainability measures, the office roof has 384 solar panels. The white bitumen roofing with CO2-absorbing mineral granules that reflect the light increase the efficiency of the solar panels and the PV installation. Another is the particulate filtration system with ionizer at the entrances to the tunnel, which capture exhaust gases and non-exhaust emissions (road surface wear, tire wear, etc.), cutting emissions by 50%.​ 

The challenge: complexity and short lead times

The diversity of work was enormous, involving construction, traffic engineering, civil engineering, infrastructure, and installations. There were also a number of technical tours de force, such as the toll gate technology, energy saving measures and technical systems in the tunnels. And all of this in a tunnel that had to remain open to traffic. We carried out all the work in two periods of eight weeks each, with two partial weekend closures for the north and south sides of the tunnel respectively. It was a spectacular event when, after months of preparation, the footbridges were hoisted 9 meters above the road surface. One weekend, two gigantic sections (each 27 meters long and weighing 45 metric tons), an enormous crane, an audience: it was truly the “crowning achievement”.

This “maintenance round” was actually a complete upgrade of one of the most important traffic connections in the Netherlands. Despite a tight schedule, Covid-19 and shortage of materials due to the war in Ukraine, we managed to complete this upgrade within the agreed time. And the results are nothing short of spectacular. The lifespan of the tunnel has been substantially extended and safety has improved enormously – for road users on the access roads, in the tunnel, at the toll plaza, for people on the escalators, and for the staff working at the tunnel. The Kiltunnel now has more capacity and better flow, achieved by being widened to two times five lanes, the construction of a new, advanced toll plaza, and more. Maintenance and management costs have been reduced and the tunnel is more sustainable than ever, with a drastic reduction in emissions.