High above Hohenlimburg, a district of Hagen in Germany’s Ruhr region, the Old Synagogue built in 1870 sits on a narrow hillside terrace that leaves little room for error. The building now serves as a museum and event venue, and two retaining walls help secure the slope and adjacent embankments, where the incline reaches up to 40 degrees.
Time and weather have taken a toll on the historic masonry. A structural inspection found one retaining wall had begun to lean, raising concerns about stability. Part of the wall has already collapsed, and large bulk bags are being used as temporary stabilization while a permanent fix is built.
Wirtschaftsbetrieb Hagen AöR commissioned Spesa Spezialbau und Sanierung GmbH to fully dismantle both retaining walls, stabilize the hillside, and then reconstruct the historic masonry to meet heritage preservation guidelines. A materials assessment determined deterioration was extensive enough that full demolition and rebuild was the only viable path.
Site logistics are a big part of the challenge. One wall supports a terrain break and nearby slope and has partially failed. The second wall runs close to the synagogue’s southeast annex, where the bulk bags between wall and building limit access and must be removed in stages as stability is maintained.
Spesa is carefully removing the existing natural stone first so it can be stored, prepared, and reinstalled later. After demolition, the slope will be secured with a shotcrete shell installed using drilling and excavator rigs. The plan calls for about 75 metric tons of shotcrete across roughly 150 square meters, reinforced with 110 anchors. Only after that load-bearing slope stabilization system is complete will crews rebuild the wall facing using the original natural stone, with missing pieces matched using comparable locally sourced stone.
The gap between the shotcrete shell and the natural stone masonry will then be filled in layers with single-grain concrete to control pressure on the new wall and the drainage layer behind it. Spesa notes the rebuilt natural stone wall is not intended to carry the slope loads. It supports its own weight and the drainage pressure.
Work began in February and is expected to wrap up in July 2026.
Read the full, original article from geplus.co.uk (subscription required at source) here.