Bilbao Metro Line 3 Txurdinaga-Casco Viejo alignmentFrom the beginning of the stretch (km 3+400 to km.4+350) the design consists of a double-track tunnel 950 m long of 58 m2 in cross section. In the km 4+350, the line is divided into two independent single-track tunnels, north and south branches. Both lead to Casco Viejo station, which is the final point of the projected works. The Zurbaranbarri station (km3+825 to km 3+935) is accomodated into a cavern of 190 sq m cross section and 110 m length. In addition to the principal tunnel and the station, the construction project includes the access to the station, two construction galleries and one elevator; ventilation facilities: three emergency ventilations and a EBA (under platform air extraction well) and an emergency exit/ventilation in Etxebarria park.The excavation of the tunnel will be by roadheader in two phases (top heading and bench) with NATM.The initial lining is made of a layer of shotcrete applied to the excavation surface, reinforced with bolts and steel rib supports as required. The final lining consists of a 30 cm-wide ring of cast-in-place concrete, which will be reinforced in the vicinity of the emergency ventilation facilities.In between the initial shotcrete layer and the final cast concrete lining, an impermeable membrane will be placed to ensure that the tunnel is watertight.The section of the Zurbaranbarri station will be excavated by roadheader in several sequential excavation phases. The initial lining design will depend on the rock quality found during the development of the excavation works. Subsequently, reinforced concrete is placed as a final lining and finished with prefabricated concrete plates.In February, 2010 the JV Comsa/Cycasa/Nortunel started with two Sandvik MT520 roadheaders on excavation of the ventilation tunnel and access ramp for the 2.6 km Etxebarri-Txurdinaga section, following on with the tunnel toward Zurbaranbarri-Txurdinaga. Environmental considerations restricted the hours of operation to daytime hours only, therefore reducing the daily advance rate to 3.5-4.5 m. The roadheader was also used to excavate the western running tunnel. The machine is equipped with a Geodata automatic profile control and guidance system, allowing the site engineers to program the desired tunnel profile into it's control system. The roadheader cutter boom automatically cuts the selected profile to great accuracy, minimizing overbreak and reducing costs for support concretA further two ICUTROC-equipped Sandvik MT720 tunnelling roadheaders are involved in the running tunnel excavation. Click es/107 and es/114 for more on the Line 3 project and here for the MT520 technical details and here.Visit www.ets-rfv.euskadi.net and www.metrobilbao.es. 39/10.