Wirth TBM Breaks Through Canale Viola TunnelA Wirth TBM model SM 360 E/TS broke through last 27th November the 18,770 m-long Canale Viola tunnel in Valtellina valley in Sondrio province, Lombardy (Italy). The tunnel is part of the Premadio II hydro power plant expansion programme designed to enhance the capacity and bring production from 150 to 235 MW. The tunnel replaces an open air water duct and collects waters from Val Lia allowing to keep the Cancano Dam at a maximum capacity of 123 million cubic metres. The machine started tunnelling in May 1999. The contracting JV reached the Foscagno intake structure in April 2002, which then represented a completed length of 6,350 m. Read E-News Weekly 26/2002. Breaking through into the Viola Dam took place in January, 2003, completing 12,478 m of tunnel. Read E-News Weekly 5/2003.The TBM is a telescopic shield with a 1,120 kW installed power, 14 rpm and a 1,600 kN breakout torque. The telescope supplies a thrust of 12,560 kN at 400 bar with seven cylinders. The diameter of the TBM cutter head is 3.66 m. The tunnel features a 3.02 m inner diameter. The lining rings consist of five concrete segments. Progress reached a daily average of 25-30 m, with best day in May 2002 (51 m) and a record month in October 2003 (928 m). Geology was predominantly composed of limestone, marls and phyllite.The Premadio II plant also required the construction of 830 m-long 3.9 m-diameter penstock tunnel and a 800 sq m, 30 m-wide x 30 m-high cavern. Read E-News Weekly 15/2002. Visit www.wirth-europe.com, www.aem.it and www.selitunnel.com 03/04.