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To cope with the increasing traffic pressure and to provide better access to the (planned) residential area, the N206 ir. G. Tjalmaweg between Leiden and Katwijk will be widened and renewed. A number of engineering structures will also be added. Boskalis Netherlands is responsible for the design and realization of the new Tjalmaweg, including ten years of maintenance. Together with Geri de Bijl, project director at Boskalis Netherlands, we take a look at the technically very challenging project.
As part of the RijnlandRoute, the N206 ir. G. Tjalmaweg is an important traffic artery for the region and especially for the access to Katwijk. "The existing single-lane road no longer met the increased traffic intensity and noise standards. That is why the province of South Holland put a deepening and doubling of the number of lanes out to tender in 2019. Boskalis became the contractor with the best EMVI score, in which especially the landscape integration, the environment-oriented execution and the sustainable construction method received high marks," says De Bijl. "Above the sunken position we are building two flyovers. There is also an express bicycle path and a green park strip in the so-called Park Zone. In addition, we are building a new bridge next to the existing Torenvliet bridge and the old bridge over the Oude Rijn will be completely upgraded. With which also here the traffic passage will be significantly improved to 2×2 lanes, including a bicycle and footpath."
Boskalis Netherlands has divided the project into four subprojects. "Part 1 involves upgrading the existing Torenvlietburg and building a new bridge next to it," explains De Bijl. "We are currently in the process of building the new bridge, which is similar in construction to the existing Torenvliet Bridge, but will be constructed with a fixed bridge deck. Around the construction vacation this year, traffic will be directed over the new bridge and we will upgrade the existing bridge to the new standards, with the biggest change being that the fall will give way to a fixed bridge deck. According to schedule, traffic will be able to use both bridges in the first quarter of 2023."
Subproject 2 included all preparatory work to create the sunken location. De Bijl: "For example, we put in the necessary pre-loading, but also made all the arrangements needed to divert the existing traffic to the temporary N206. Including the relocation of cables and pipes, complete culverts, traffic circles for accessing the residential area and the construction of the temporary provincial road itself. In this phase, the Achterweg viaduct was also demolished and in its place a 60-meter temporary bicycle/pedestrian bridge was built over both the temporary road and the road under construction. The conversion to the temporary N206 went extremely well and we opened a month ahead of schedule, at the beginning of August last year."
The most far-reaching phase is subproject 3 involving the deepening of the new Tjalma Road, a phase that is currently underway. "We have divided the deepening into thirteen compartments in which nineteen activities will be carried out one after the other in a train. In doing so, we are working from east (Leiden) to west (Katwijk)," De Bijl explained the phasing. "The sunken location is 1,900 meters long, 30 to 50 meters wide and lies up to 7 meters below N.A.P. Instead of realizing a traditional concrete basin, we are using a foil construction that we are putting in a dry basin. To realize this dry tub, we press sheet pile walls into the ground and apply a temporary injection layer to a depth of 17 meters below ground level.
A proven methodology, but one that has not previously been applied on this scale in the Netherlands. By also using existing and recycled raw materials as much as possible, we are able to realize a very sustainable construction, with a very favorable MKI value."
Boskalis Netherlands expects traffic to be able to use the sunken location by mid-2023. After that, the surrounding road network will be upgraded and the Park Zone will be constructed (subproject 4). Local residents will then experience virtually no inconvenience from this busy thoroughfare. Moreover, with the Park Zone they will get a very beautiful natural strip in return, equipped with all kinds of facilities.
historical anecdotes such as the ancient Limes Road from the time of the Romans.
Before that happens, there are still some things to be done. "It really is a battle against the water here in some places," De Bijl notes. "The disturbances in the subsoil are very large. In two compartments we even had to completely adjust the working method because of the high pressure of water from underlying layers, which disturbs the gel injection layer. This created bubbles in the tub. The good thing is that the chosen phasing of work in compartments does give us the flexibility to come up with appropriate solutions during execution."
So the new Tjalma Road is technically a very challenging project. "The complex interfaces in a very limited space requirement make it quite challenging here, not to mention the scale of the soil injection, the high level of finishing with conservation of flora and fauna, and attention to the environment. By informing stakeholders on a periodic basis, we reduce the surprise effect and experience a lot of goodwill from the environment." Completion of the new N206 ir. G. Tjalmaweg is scheduled for 2023. "For Boskalis Netherlands, this is a wonderful project with many challenges and on which we enjoy working. Everyone who visits the project experiences the passion and pride with which we get this job done together!"
The RijnlandRoute is a new road link between Katwijk, via the A44, and the A4 near Leiden. It will include a new road with a bored tunnel, the N434, and parts of the N206 in Leiden and Katwijk will be modified and renewed. The province of South Holland is the client of the RijnlandRoute. The N206 ir. G. Tjalmaweg is one of the three project sections of the RijnlandRoute. www.rijnlandroute.nl
