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.
The construction of artificial tunnels to cross lengths of a route in which there is insufficient overburden for bored tunnel advance inevitably involve deep incisions into the slopes to be crossed with consequent problems of safety and environmental impact.
Rocksoil S.p.A. researched and developed the use of special "artificial overburdens" of improved ground created over the crowns of tunnels before excavation. They can then be bore tunnel driven thereby by-passing all the problems connected with traditional methods of constructing artificial tunnels.
This new method has been used for the construction of approximately 1.5 km of tunnels on the new Milan to Naples and Bologna to Florence High Speed railway lines. It was found extremely practical and safe, not to mention economical and environmentally sound.
Full face mechanical precutting and ground improvement of the advance core using fibre glass structures are both construction technologies developed by Rocksoil S.p.A. between 1986 and 1988. They have both solved once and for all the problem of tunnelling in ground with a clayey matrix of very poor geomechanical quality susceptible to chemical and physical weathering.
The large number of tunnels which had previously posed serious problems to designers and constructors and that have now been completed with success, demonstrate just how effective these new technologies are. Used together they have resulted in constant and safe tunnelling with excellent advance rates (2.75 m./day full face) even in situations of extreme instability which would otherwise not have allowed any advance.
Each year the American technical journal, Engineering News-Record published by McGraw-Hill, nominates a man of the year in the construction field. In 1990, Prof. Pietro Lunardi was included as one of those who had contributed with his ideas to the achievement of significant progress in the construction field, "he invented the 'Cellular arch technique' to excavate wide span underground caverns in cohesion-less ground".
This original construction system can be employed to drive bored tunnels with very shallow overburdens up to a diameter of 60 m. in very poor ground without causing surface subsidence.
One significant application of this system was for the construction of the Venezia Station on the Milan Urban Link Line. A cavern 30 m. in diameter and 270 m. in length was bore tunnel excavated right in the centre of the city with an overburden of only 4 metres and under the water table.
Rocksoil S.p.A. researched and developed horizontal jet-grouting systems to improve ground during tunnel advance in ground with poor cohesion, together with similar systems applied vertically for foundation shafts and tunnel portals in unstable slopes, in the second half of the 1980's.
They are currently deemed irreplaceable for working in ground subject to difficult stress-strain conditions if subsidence and undesirable deformation phenomena are not to be triggered.
Special features of these systems include the ability to schedule operations and operational safety.
