Nowadays, the increasing need and demand of transferring a series of infrastructures to the underground has brought about an impressive rise in the numbers of tunnels to be constructed, regardless of the nature of the soil to be penetrated. The excavation of tunnels in loose soils, in presence of unstable formations or in presence of soils prone to landslide, requires the use of preventive consolidation of the arch and, if needed, of the walls and invert before the final lining is completed.

This has created a scenario of constant developing of technologies and machinery able to tackle any kind of situations.

The final aim is to reach the tunnel stability before the excavation through soil consolidation, avoiding expensive temporary supporting devices.

The Trevi Group has designed and successfully applied a tunnel consolidation technology known as RPUM (Reinforced Protective Umbrella System). The method finds its way in those tunnels with an unstable or short term stable core face condition. The technology envisages in the installation of a series of sub-horizontal elements aiming at consolidating the soil beyond the face of the tunnel before carrying out safely and speedily the excavation under the protection of the arch-like shell by using specially designed forepiling machinery.

The technological development has therefore pursued two major ways:

• The study and design of the right equipment able to efficiently operate in confined spaces, to be quickly set up in the required drilling position and finally able to execute longer and longer sub-horizontal consolidation in one single stage, thus dramatically reducing the cycle time.

• Design of the most suitable consolidation grout treatment for stabilizing the excavation and featured by mechanical strength to allow for the excavation and to reduce the number of supporting ribs to be installed.