ABSTRACT

A 12% inclined and 2.8 km long tunnel was made for the execution of the new TERNA S.p.A. 380kV power line connecting Sicily and Calabria. It finished in a vertical 300 m deep shaft with a 7 m excavation diameter. The tunnel was made with a double-shield 4.1 m diameter TBM. It passed through a large part of the Calabro Arch’s crystalline-metamorphic base. This rock mass presents variations and fault areas with extremely high grades of broken rock, with very low GSI (Geological Strength Index) values. It also presents a granulometry similar to a sand-consistency, sometimes similar to a clay-consistency, with a significant quantity of water. These fault areas gave huge problems during the tunnel excavation, with very low progress areas and three “geological events” which caused TBM stops. The three TBM interruptions required the improving of the rock mass property by the use of mono and bi-component resins. These interventions allow the excavation of small tunnels to “unlock” the TBM.