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.



From Preda entrance 1,236.5 m (after Raibler cellular limestone) and 3,912.5 m (in Albula granite)




54 m and 66 m




Mylonite consists of finely flaked layers of silicate, embedded in a matrix of superfine-grained quartz and calcite, with veins of calcite running through it.




It is physically damaged (but re-crystallised) fault-zone rock, with a hard, relatively compact consistency.




Rockfalls are not likely, given its structure, and this material does not suppose any particular difficulty for tunnelling. Historical reports suggest that major ingress of water can be expected along the first 15 metres (from the Preda end).

Loose rock

Loose rock

The Loos rock includes the Base moraine and the waterborne rock debris, which is located at both tunnel entrances in Preda and Spinas. In the historical report the base moraine is described as being solid, dry and unproblematic. Whereas the waterborne rock debris was discovered as non-cohesive and yielding material.

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 This involved an examination of historical documents, along with the carrying-out of additional, new analyses.