Large-scale refurbishment makes the highest demands on complex scaffold anchoring systems
The Kerspe Dam in Kierspe, Germany, built in 1909-1912, is one of the larger of its kind with a surface area of 1.5 million m². It has a capacity of 15.5 million cubic meters and supplies the german regions of Remscheid, Wuppertal and Wipperfürth with drinking water. In addition to drinking water production, energy is generated at the Kerspe dam with the help of a small hydroelectric power plant. Unfortunately, the dam is not freely accessible to recreationists, as the entire water surface is completely fenced off. Thus, it is considered one of the best-kept dams in Germany.
Since spring 2021, the dam, which belongs to the class of gravity dams, has been undergoing extensive renovation on the valley side and has been provided with an elaborate scaffolding structure for this purpose. The water-side cut-off wall had already been rehabilitated in 1992-1995. In the course of this work, the spillway area, including the bridge above it, was demolished and replaced by a concrete structure. Its face surfaces were then clad with a composite masonry made of graywacke stones. The valley side of the dam was only partially repaired. A complete renovation according to today's knowledge, as it is currently carried out, did not take place at that time. This is now to be carried out between March 2021 and the end of October 2022.
Stump-Franki Spezialtiefbau GmbH, the masonry rehabilitation/structural safety department from Chemnitz, was commissioned with the rehabilitation. The latter in turn awarded the contract for the working scaffold to BSB Bau- und Spezialgerüstbau GmbH, West Branch, from Kaarst. BSB belongs to the Building Partners Group, one of the largest scaffolders and construction logistics companies in Germany, based in Wandlitz near Berlin.
For BSB, whose name says it all - "Special Scaffolding" - and which already has a long list of references for important projects, the contract for scaffolding the core barrier wall is once again a special challenge. After all, a barrier wall arched in two directions and 34 meters high is not part of the day-to-day business of a scaffolding company, but falls into the category of special scaffolding. And BSB is a master of this, as they proved once again on this project.
An area of around 4,800 m² was scaffolded with Rux-Super 65/100 facade scaffolding. It was important to adapt to the shape of the barrier wall, which meant that the facade scaffolding had to be offset upwards at the angle of the wall. And this entailed much more effort for anchoring the scaffold structure than is the case with a smooth facade. BSB solved this technically challenging problem by drilling 700 mm deep holes into which threaded rods from the HILTI HIT RE 500 system were inserted. A total of 834 boreholes were made and the same number of threaded rods were set. Since some of the drill holes were made in critical material (graywacke), each individual scaffold anchorage was tested with pull-out equipment and verified for 1.5 times the design force, including the corresponding documentation.
A centrally located service scaffold was erected to ensure trouble-free transport of tools and materials to the individual scaffold levels. This was equipped with a 500 kg construction hoist and a stair tower for safe and convenient scaffold access. As large parts of this service scaffold were free-standing, BSB had to create a special solution for the anchoring by bracing the scaffold in the area of the stair tower every 4 meters with steel cables and lattice girders on both sides. And the entire construction still had to withstand a special force of nature. Because during the flood of the century in July 2022, water had to be drained from the dam to prevent it from overflowing. Thousands of liters of water poured over the scaffold structure, but it survived everything unscathed.
The foundation of the scaffold also posed special challenges, especially in the area of the stilling basin. With the help of a 15 m long bridge made of HEB 300 girders supported in the dam wall and on the wall of the stilling basin, a stable foundation structure was created to safely erect the scaffold, the stair tower and the personnel and material elevator.
Safety is a top priority for this project, which has been structurally approved by the engineering firm Trabert + Partner. Once a week, a site inspection is carried out with the participation of the district government of Cologne (Department of Dams, Occupational Health and Safety) and the Bau-Berufsgenossenschaft Dortmund. Such a technical feature also generates increased attention.