The experience and suggestions of a design engineer who is a genuine expert in tunnel construction are essential to those who construct tunnel boring machines (TBMs), as they compete with each other to produce increasingly more flexible and efficient shields and cutters. To achieve this Rocksoil S.p.A. has always co-operated with major producers of machines who have asked for opinions and suggestions.

A new generation of shielded TBMs has been born from the close co-operation between Rocksoil and Herrenknecht. They allow the rock mass to be surveyed continuously in real time and ground improvement to be performed in advance where necessary.

Advanced study and experimentation in the field performed by Rocksoil on prefabricated concrete segment linings are of great importance in this respect for recent developments in mechanised excavation and Rocksoil is the firmly acknowledged world leader in this field with the development of the “Universal Ring” and special concretes and additives.

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.

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.

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.

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.

Extrusion tests performed in triaxial cells were researched and developed by Rocksoil S.p.A. to study the probable deformation response of a tunnel to be constructed under difficult stress-strain conditions.
A test sample from rock or soil is inserted into the cell and the original stress state of the ground is recreated.

By maintaining the stress state around the sample constant and progressively decreasing the state of stress inside the extrusion chamber, the change in the stresses induced by tunnel advance is simulated and an estimate of extrusion at the face as a function of time or of internal pressure is obtained.

From an analysis of the extrusion curves obtained with this method, it is possible to make reliable predictions of the stress-strain behaviour of a tunnel during excavation and to design conservation procedures that may be indispensable to the success of the tunnel.