Berding Beton supplied “Verkalit”-system for dike rehabilitation on Borkum

For many centuries, dikes have protected land and people from the elemental forces of the sea. Effective protective measures have thus always had an important significance, which has increased again against the backdrop of global climate change. This is because people living on the coast or on an island will be particularly affected by the consequences of global warming in the future. These include a massive rise in sea levels and an increase in extreme weather events with storms and flooding.

During the dike rehabilitation on the German island of Borkum, all these considerations were incorporated into the planning of the repair. Extensive construction work was carried out on the „black dike“ as a storm surge protection measure. This is part of a flood protection system in the area of the former Borkum naval facility from the Bundesanstalt für Immobilienaufgaben (BImA), which was acquired by the city of Borkum. The name came about because the dike was covered with asphalt. For the rehabilitation of the approx. 40,000 m² revetment area of the dike, those responsible now relied on the innovative Verkalit system from Berding Beton.

Optimum resistance

Verkalit stones are characterized by optimum resistance, especially to high loads such as wave impact, ice drift or flotsam. They have been specially developed to prevent erosion of embankments and thus jeopardize the stability of flood protection structures. Their high stability results, among other things, from a groove-spring system that provides force transmission between the installed Verkalit stones. The functionality of this groove-spring system has not only been proven by numerous practical references, but has also been scientifically investigated in large-scale tests in the wave channel of the Forschungszentrum Küste in Hanover. It has been demonstrated, for example, that a tensile force of typically 40 kN is required to detach a single stone from the system, and that the stability index of the Verkalit revetment system is > 7. In other words, the detachment of a block and thus the destruction of the revetment is not possible without high mechanical force application.

An important prerequisite is that the installation is carried out professionally. Here, too, users benefit from the advantages of the system. Verkalit blocks can be installed economically with the help of professional laying equipment with high laying performance. The brick geometry allows direct connection of the laying units to each other without additional work. Many special features had to be taken into account during the construction project, such as dike drainage using Verkalit filter stones (5,000 m²) or the integration of more than 50 bench seat elements. In addition, 4,500 linear meters of dike closure blocks as well as 2,000 linear meters of tie bars and 27,000 m² of Verkalit blocks were supplied by Berding Beton. Even the delivery to the construction site on the island required a logistical masterstroke. The goods were loaded onto ships via a port in Wilhelmshaven and transferred to a storage area on Borkum via a port rented locally.

Good walkability without tripping hazards

4,000 m² of Verkalit facing bricks were also used. The compatibility of all products, which can be selected individually according to need, is one of the great advantages of the Verkalit system. There are no weak points, as the elements are connected throughout with the sophisticated tongue-and-groove system in a friction-locked manner. This means that - as in the construction project on Borkum - even seating elements on the dike can be integrated into the system. The Verkalit facing bricks used, in turn, enable good walkability and thus tourist use of the dike crest. Particularly noteworthy here is the small joint width of the facing bricks, which ensures safe walking without tripping hazards. This is an important aspect for anyone walking on the dike with a walker or baby carriage. A particularly appealing design was implemented by using a gray-black color mixture.

In addition, 1,000 m² of Verkalit stones were installed to act as „breakwaters“ and absorb the energy generated by the waves. These stones with a thickness of 30 cm can easily be combined with the other stone thicknesses used in the revetment (12, 15, 18 and 25 cm). Likewise, the filter stones at the bottom of the dike fit perfectly into the Verkalit system. Due to their water permeability, they ensure that water absorbed by the dike can flow away again without damage and without causing erosion. This drainage of the dike is very important to prevent water from accumulating in the dike body and to maintain the stability of the dike.

Good teamwork is the key to success

Berding Beton realized the order in good cooperation with the company Strabag (Aurich) and the building material supplier Luths (Wilhelmshaven). Strabag subcontracted the laying of the stones to Weseloh from Hamburg. The cooperation also worked smoothly with the client and the responsible engineering office, as Berding Beton Sales Manager Jens Felten states: „In this construction project, the good teamwork of all colleagues was the key to success. Together we achieved our goal - the repair of the dike and the flood protection walls and thus the restoration of the necessary technical flood protection.“ The project involved high demands on planning and implementation. The decision in favor of the Verkalit system was exactly right, Jens Felten is certain: „No other technical product of ours has been tested so enduringly and extensively for the area of application. And it is a unique composite system that convinces with its sophisticated technology instead of mass!“

After the end of the rehabilitation measure, the Verkalit system not only impresses with the fact that it has a high resistance to weather-related influences such as wave impact or water pressure thanks to its full-surface composite effect. The vertical bond with tongue and groove acts like a ball bearing so that the revetment can absorb settlements or elevations of the dike. At the same time, damage to the dike, such as cavities, can be detected and repaired more quickly than with conventional set stone revetments. And there is another significant advantage over other systems: Once installed, Verkalit does not require any subsequent maintenance, such as re-splitting of the joints.