Läntigen cavern project
Underground Mining Special projects
Jäger Bau was commissioned by Läntigen Stein AG with the development of a subterranean rock extraction project at the Vierwaldstättersee. The development was to be accessible from the lake and take place at water level, as the later quarrying or removal of the chippings (siliceous limestone) was to take place by boat.
The difficult features of this project were not just its accessibility issues and the waterfront location, but also the extreme proximity to major transport routes. Access was created immediately under the N4 national trunk road (Axenstrasse) and the two SBB tunnels, Ölberg and Fronalp, which are main links to the Gotthard. The access road crosses both above and below these routes at a distance of just a few metres, which is why the blasting technique used and the excavations were subjected to rigorous conditions and an elaborate monitoring procedure.
The contract included the provision of access to the subsequent mining areas, as well as reversing tunnels, branches, various niches for the subsequent tunnelling technology and storage facilities and a safety tunnel as an escape route above ground.
In total, around 42,000 m3 of rock were excavated during 16 months of construction from August 2012. The order volume amounted to CHF 7.5 million.
The order was expanded and prolonged until the summer of 2014 to allow for the removal of a 19,000 m3 of rock.