Resort to a small diameter exploratory drift before widening to full face excavation as a survey and experimental method of advance in particularly uncertain ground has been known to tunnelling specialists for some time. By fully exploiting the availability of modern boring machinery capable of driving tunnels in heterogeneous ground Rocksoil S.p.A. has incorporated the pilot tunnel as a truly integral part of tunnel design in the ADECO-RS approach.
One particular feature of the "RS Method" is the use of T.B.M.'s as huge penetrometers which measure machine parameters (thrust, advance velocity, absorbed power, etc.) for the purpose of determining the specific energy employed per cubic metre of material excavated and this is in turn correlates with the strength of the rock mass.
More than one hundred kilometres of tunnel have been driven to date using this new system of designing and constructing tunnels, in full respect of forecast construction times and costs. It has certainly passed the baptism stage.