INSTEAD OF whisking up to the door in a taxi, audiences at the new concert hall in Sondershausen, Germany have a highspeed two-minute lift ride 700m underground.
Large enough to accommodate an audience of 300, the venue has been carved out of rock salt deposits deep below the town.
After the Glucklauf salt mine opened in 1893, 2. 5Mt of salt was extracted every year to make potash. When the mine closed in 1991, 110Mt of salt had been extracted from a mining field between 700m and 1000m deep, 25km long and 6km wide.
Since then the mine has been transformed into a tourist attraction, holding sporting events such as cross country runs and, in February this year, a downhill mountain bike race.
A joint venture of German contractors Thyssen Schachtbau and TS-Bau Proterra carried out the excavation works for the concert hall. Rock mechanics experts were satisfied with the plans to excavate the 26m long, 18m wide and 10m high chamber in the stable rock salt. However, they recommended that a nonaggressive cutting action be used to form the roof and the side walls.
Work was carried out using a Voest Alpine AM50 tunnelling machine, which has a non-aggressive cutting action. High levels of workmanship had to be used to construct the walls of the hall, as these had to be at an angle of 4degrees.
Special attention was given to the complicated roof arch profile, a key area where safety and stability were paramount. Thyssen said the precision and quality required could only be achieved by using a laser surveying system. In the complicated roof sections, cutting performances were only 1. 5m 3per man shift, however in other areas performance reached 40m 3per man shift.
One of the main challenges was to create a high quality acoustic chamber. Modelling carried out before the project began to determine the best acoustic conditions showed that an arched profile and special terracing of the roof would enhance the acoustic effects.
The cavity was excavated in three drifts 3-3. 5m thick. Excavation produced a total of 4720m 3of rock salt weighing 9500t, which was removed using a loader with a bucket capacity of 1. 5m 3. Ventilation was installed in four 1m diameter boreholes, drilled from a road above the concert hall into the roof of the auditorium. Excavation work also included a foyer, cloakrooms, dining area and a bowling alley.
The concert hall was officially opened in May this year. It was jointly funded by the Federal Land of Thuringia, the Gluckauf Sondershausen Entwicklungs und