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.



Tunnel entrances




104.5 m base moraine and 114.5 m rock debris near Spinas / for a few metres near Preda


Special Features


The mountain water level is reached approx. 60 metres from the Spinas entrance.


Base moraine


Historical reports describe these deposits left by earlier glaciers as being solid and dry. We now know however, thanks to exploratory drilling, that there is a possibility of encountering both non-solid material and the ingress of water.


Waterbone rock debris


This debris is not at all solid, and tends to cause major rockfalls. The ingress of water is also to be expected. Waterborne debris may include large blocks of granite, which can complicate precise excavation on a slope.

Where does the water come from?

Where does the water come from?

Preventing the drying-up of mountain springs and streams is a great concern of the Rhaetian Railway. It is therefore important to understand how the interdependence of springs and bodies of surface water is linked to prevailing hydro-geological conditions inside the mountains.

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 This involved an examination of historical documents, along with the carrying-out of additional, new analyses.