New Albula Tunnel II - Lot 105, Consolidation Raibler Cornieule
The 5‘864 m long Albula Tunnel (I) is situated on the railway line Chur-Thusis-St. Moritz and was put into operation in 1903.
The new Albula Tunnel II is being constructed parallel to the existing Albula Tunnel with an axial distance of 30 m. When constructing the first Albula Tunnel I, the aquiferous zone of the so-called Raibler-Formation (cell dolomite rock) already revealed to be a geologically difficult zone. In 2013, starting from a specially excavated cavern connected to the existing tunnel, exploration drillings have been done in the whole Raibler-Formation zone in order to develop a more accurate geological model.
The cavern, situated in the axis of the Albula Tunnel II, is only accessible through a cross passage from the Albula Tunnel I. Following the drillings results, the Raibler-Formation can be subdivided in three different geological sectors. The sector denominated III is a fault zone of silty fine sand (swimming Raibler-Formation) with a water pressure of approximately 5 bar.
For safety reason the sector III will be excavated with the freezing method. Before starting the excavation, the ice casing will have to be built. This will perform a temporary support against rock and groundwater pressure and furthermore ensure the sector’s impermeability during construction time. Apart from the drillings for the construction of the ice casing, control drillings to monitor the ice casing’s impermeability and injection and drainage drillings to reduce the amount of water, will be necessary. The ice casing will be retained until the termination of the excavation and inner lining in sector III.
Rhaetian Railway - Chur
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Special studies; Construction supervision