"Dragon's Rock" at Königswinter: Scaffolding for rock protection

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The Drachenfels in the Siebengebirge rises with 321 m height over the Rhine valley between Königswinter and Bad Honnef. Its trachyte rock was a much-used building stone down the Rhine, especially in the Middle Ages, for example in the construction of Cologne Cathedral. For decades, the legendary Drachenfels has been a popular excursion destination in the Rhineland and a highly frequented tourist attraction.

The friable rock of the rock massif, however, causes problems again and again. In some places, deep cracks were found in the rock face. That's why the so-called Eselsweg, a winding hiking trail that leads up to the Drachenfels ruins from Königswinter, had to be closed at the beginning of 2017 due to a high risk of rockfall.

Extensive rock stabilization work is currently being carried out to secure the Drachenfels for the next decades.

The company Bonner Gerüstbau Karl Breit NL of Teupe & Söhne Gerüstbau GmbH was commissioned by the Bau- und Liegenschaftsbetrieb NRW Cologne with the scaffolding for the implementation of the securing measures. Extensive working scaffolds are needed to restore the static load-bearing system of the rock anchors and to assess the condition of the rock, as well as to close the crevices that have appeared on the Drachenfels. Due to the difficult topography, safe accesses as stairway towers to the areas to be worked on must also be created.

The scaffold foundation was built on the fissured and uneven bedrock. For the scaffold footprint of the working scaffold, the ground had to be leveled and straightened first. Complex load-distributing measures were required to ensure safe load transfer. This is done using lattice girders, hand shafts, auxiliary foundations, etc. Horizontal anchoring is provided by dowel anchors (7.5 kN) with multiple setting depths into the load-bearing subsoil. The scaffold structure had to be erected in such a way that all rock faces could be worked. A total of about 120 tons of scaffolding material was used. 

Since both the access road and the restaurant operation are located in the immediate vicinity of the construction project, all material transports during the entire construction period are only possible outside visiting hours. In addition, the construction site is located in the Siebengebirge nature reserve, so that a sensitive approach to nature and the environment is required. The complex material transports to the Drachenfels will be carried out by means of telescopic forklifts and the use of special trucks via the Eselsweg, which is closed to the public.

The scope of work for Bonner Gerüstbau includes all services including detailed design, construction, erection and dismantling of the scaffolding and stairway towers, including technical processing and preparation of working drawings in the company's own technical office.

The rock support work has been underway since May 2017 and is expected to be completed in 2018.

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