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Albula granite

Albula granite -

The Albula granite is the longest rock formation to be penetrated and proved itself already at the construction of the first tunnel to be of hard and compact consistency with some parts including quartz crystal. Often the solid rock could be left without the internal fitting-out with concrete.

Location

 

 

1,260 – 5,605 m from Preda Tunnel entrance onwards, interspersed with individual fault-zone types

 

 

 

 

Length

 

 

4,345 m

 

 

 

 

Characteristics

 

 

The term “Albula granite” covers various types of rock; from granites and granodiorites to diorites and gabbros. Only granodiorites, diorites and gabbros, along with one granitaplit, were identified among the samples examined. Albula granite is typically characterised by its light to pronounced greenish tinge.

 

 

 

 

Faults

 

 

Albula granite can display various faults, ranging from re-crystallised cataclastic to tectonic breccia types of rock.

 

 

 

 

Hazards

 

 

Undamaged Albula granite does not tend to cause rockfalls, and does not supposed any special difficulty for tunnelling. However, fault zones containing other types of rock – such as cataclastic or tectonic breccia – are susceptible to such falls.
Mylonite

Mylonite

Those rocks are a matter of relatively large Mylonite which origin cannot be declared anymore.
At the construction of the first Tunnel the Mylonite was perceived as being stable and unproblematic, although it was containing large amounts of water in the first 15 m.

The mountain

The mountain

To select the accurate and suitable construction methods it is important to know the geological and hydro-geological conditions of the area. Detailed investigations were carried out in order to determine the layer sequence of the different types of rock. This involved an examination of historical documents, along with the carrying-out of additional, new analyses.