3. Description of conventional methods

3.1 Basic method

As mentioned in the previous paragraph, "conventional" (or "traditional") tunnelling techniques involve building the tunnel using a sequential process, as opposed to mechanized methods, in which tunnelling is carried out using a tunnel boring machine (see chapter 4).

With conventional methods, the methods of cutting and lining the tunnel are strictly related to the geological conditions encountered and, in particular, differ according to whether the surrounding medium is competent rock, degraded rock or soil. The type of rock also dictates the length of the excavation pass, and thus the "unsupported" length between the working face and the last lining profile in place (if any).