Inventing a multifaceted system for dyke reinforcement

Renewed Afsluitdijk

In 2017 Rijkswaterstaat put out to tender a design for a thorough renovation of the Afsluitdijk. The crowning achievement of the Zuiderzee Works needed to be made capable of withstanding the fiercer storms and higher waves that climate change brings with it.

In collaboration with Royal HaskoningDHV, Vista landscape architects and Corneel (VolkerWessels and Boskalis), ZJA presented a design for the reinforcement of this national monument.The view of the architects at ZJA was that the assignment was far more than a matter of civil engineering. The design needed to do justice to the cultural-historical monument that the Afsluitdijk undoubtedly is. Moreover, in ecological terms the Afsluitdijk accommodates great resources on the edge of the Waddenzee, which is a World Heritage site.

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What makes the Afsluitdijk special?

In the early decades of the twentieth century, the Afsluitdijk was tremendously innovative. The dyke that dams off what was until then the Zuider 19 Zee is not straight, it bends with the sea currents at the places where the sluice complexes are located. The dyke is so long that it curves to take
account of the curvature of the earth. The dyke and its stone base are the epitome of the dyke-building craft, and their gradients are adjusted to the currents, waves and undulations of the sea. The visionary qualities of its hydraulic engineering alone make the Afsluitdijk a national cultural-historical monument. It is a strong but clever and slim dyke that fits into the Dutch man-made landscape.

Stronger does not always mean higher

It proved impossible to avoid raising the height of the dyke to make it able to absorb the greater forces of more extreme wave action. There was also a need for features that would break up the higher waves in the event of a monster storm. But how could this be done without negatively affecting the character of the Afsluitdijk?

In the design by ZJA, Royal HaskoningDHV, Vista and Corneel, two inventions in the field of hydraulic engineering are central, and they ensure that the green, slim appearance of the dyke can be preserved as far as possible.

The first can be found at the bottom of the incline. Along with Dirk Jan Peters of Royal HaskoningDHV, ZJA developed a system of interlocking warped concrete columns, intended to replace the basalt blocks. The columns lock together in such a way as to create a network that can absorb the suction forces better than separate blocks of basalt. The harder a retreating wave sucks, the more tightly the columns are pulled against each other. The forces are absorbed as they would be by an arch.

 

Moreover, the warped shape of the columns means that 20% of the outer surface of the dyke is made up of hollow spaces, which further stifles the force of the incoming waves. This makes the new dyke considerably stronger, while reducing the amount of material needed by 30%. The cavities between the columns provide space for plants and insects, which in turn attract birds. Dirk Jan Peters, Royal HaskoningDHV and ZJA took out a patent on this system in 2020.

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This series shows the development of the warped oval columns into the ultimate ring shape on the uppermost slope. In the end we used the columns only on the lowest part of the incline for strength (they absorb the impact of a wave and the suction effect that follows) and the rings on the uppermost part, for roughness to limit the uprush and overspill once the wave has been broken.

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