The Hercules monument in Bergpark Wilhelmshöhe in Kassel is made of tuff. Restorers repaired the damage to the monument, which has been a UNESCO World Heritage Site since June 2013. The Hercules structure in Bergpark Wilhelmshöhe in Kassel was built between 1701 and 1717 to a design by the architect Guerniero. The client was Landgrave Karl von Hessen-Kassel. The planners wanted to imitate the shape of a boulder as a natural backdrop. The building consists of an octagonal, two-storey artificial rock wall made of lapillite tuff. The filigree Belvedere storey made of ash tuff and tuff breccia rises above it in ashlar construction with a total height of 33 meters. The large arches were already lined with brickwork for structural stabilization in connection with the pyramid construction in 1714/15. The pyramid with the copper Hercules was built in a modification of the original design with a total height of over 40 meters, mainly from ash tuff.
Different restoration phases of the past centuries are visible: in the early 1950s, 1960s and 1970s, supplementary materials based on cement mortar and concrete were used, which still have a good visual quality in the surface finish of the tuff. However, they partially overlap the original surfaces. They contrast with the more heavily weathered tuff areas.
Sock anchors were used during the restoration. Sock anchors consist of a stainless steel tension rod (diameter ten to 16 millimetres), a filling pipe, a plastic vent pipe and a fabric sock made of water-permeable, tear-resistant polyester fabric with an expansion volume of around 90 percent in the longitudinal direction and around 140 percent in the transverse direction.
Read more about the restoration of the Hercules structure in Kassel in STEIN in December 2013.
Pictures: Boris Frohberg, Dr. Ulrich Huster/HAZ-Ingenieure