ENEL awarded the construction of the headrace tunnel for the Crevola Toce III hydropower scheme to a joint venture led by SELI (82%), with Monti (14%) and Giacomini Comm. Alberto (4%) as other partners. Visit www.montispa.it, www.agifin.com/giacominispa/index_giacominispa.html and www.selitunnel.com or www.selitecnologie.comThe length of the headrace tunnel is 9,128 m. Its cross-section is 13.85 sq m, the outer diameter is 4,200 mm and the inner diameter equals 3,900 mm. A TBM will bore 8,589 metres while 565 metres will be drilled and blasted.From the geological point of view, the area of the headrace tunnel entirely involves litotypes belonging to lower Pennidic Units and among these the bedrock through which the tunnel will be excavated is composed of Valgrande gneiss (fine grain granitic gneiss), a series of Teggiolo metasediments (carbonatic rocks of the Mesozoic age comprising marble, dolomites and micaschists) intercalated between the Valgrande gneiss and the Antigorio gneiss (ortogneiss), metasediments of the Baceno syncline, a carbonatic sequence interbedded between the Baceno micaschists and the Antigorio gneiss, consisting of dolomitic marble and/or micaschists, calcareous clayey schists, dolomitic marble and anhydrite, and Baceno micaschists and micaschists. The tunnel path runs mainly through the Antigorio gneiss, but the detailed analysis of the preliminary studies identified a series of geomechanical issues that the tunnelling will face through the metasediments, approximately at chainage 6,500 and stretching for a length of 350 to 500 metres. The metasediments comprises the following lithology: marble and averagely to highly fractured calcareous clayey schists, massively to averagely fractured anhydrites, locally with micaceous contents, and dolomitic sediments completely wheatered with characteristics of soil.The TBM and the back-up have been completely designed by SELI and will be constructed in SELI's facilities in Aprilia. The basic concept is to produce a compact TBM system easy to transport, assemble and operate and capable of reducing the construction costs while keeping the typical productivity and versatility of double schield TBMs. It is a notable technical innovation especially studied for multiple use in small diameter tunnels, for small to medium lengths. The TBM System DSU Compact will be outfitted to install traditional supports: rock bolts, welded mesh, steel arches, shotcrete, fibre-glass rods and steel bars, as required by the geological conditions. The rock will be run out on a conveyor belt to the mouth of the tunnel.Tunnelling is programmed to begin on 16th June, 2008 and to end on 15th September, 2010. 06/08.