The Kalkberg (limestone mountain) is mainly composed of anhydrite. Under the influence of humidity, dew, and rainfall, this turns to gypsum and increases volume. This process, known as gypsification, creates shell-like «bulges» up to several meters thick which protrude from faults running parallel to the slope.
Since 2007, in the Limestone Stadium of Bad Segberg, rock faces were cleared to protect performers and spectators from rockfall. Unfortunately, this caused considerable damage to the stage and scenery. There was also a persistent risk that «bulges» over 100 m² and several meters thick would come loose and crash down without warning.
Extensive tests and calculations were carried out before the protective work began. Trial anchors were installed to select the most suitable grouting mortar.
The SPIDER® rock protection system was dimensioned with SPIDER ONLINE-TOOL software by the Technical University Freiberg.
Around the stage, the appearance of the rock face could not be altered. No nets could be hung in this area. Rock nails with countersunk heads were used instead.
Installation of the SPIDER® rock protection system took place in 2009 and 2010 on several rock faces (e.g., near the cave exit and above the spectators' area). In some cases, this occurred while events were in progress, in the theater. The rock face heights are between 20 and 30 meters which posed an additional challenge to the contractor, due to limited accessibility. A mobile crane with an attached drilling platform was used for some of the drilling work.