Line C Extension of Prague Metro Makes HeadwayThe extension of Line C in Prague from Ladvi to Letnany (4,602 m, whereof 2,360 m in mined tunnels, with stops in Strizkov, Prosek and Letnany) is built by Skanska, Metrostav and Subterra. The section between Letnany and Prosek stations (1,350 m, of which 1,285 m were driven to the profile of a two-track tunnel) holed through on 2nd November, 2005. At that date, the work yet to be completed at the tunnels included pouring concrete to produce the final lining, laying the rail tracks and installing internal equipment (cables, etc.). The tunnel sections (not including the station lengths) from Ladvi to Strizkov (975 m) and from Letnany to Prosek (1,350 m) are now fully completed. The project owner is Dopravni podnik h.l.m. Prahy. The work supervision company is IDS. Visit www.skanska.cz, www.metrostav.cz, www.subterra.cz and www.dp-praha.cz/cz/index.htm and www.ids-praha.czTunnelling between Prosek and Letnany stations was launched on 11th November, 2004 and progressed in two directions from the Klicov access shaft towards Letnany and Prosek. A 500 m double-track tunnel, with a cross-section area of 63-97 sq m, and a 2 x 65 m single-track tunnel, featuring a cross-section area of 35 sq m, were driven towards Letnany. A 785 m 63-75 sq m double-track tunnel was bored towards Prosek. Excavation as per NATM was carried out towards Letnany by means of drilling and blasting using two Atlas Copco drill rigs (one L2C and one 352) and towards Prosek using two Liebherr mechanical excavators (one 932 and one 934). The tunnel excavators progressed through glauconitic sandstones, shale and clayey rock under the Klicov and Prosek housing developments. The advance rates were as follows: daily average of four metres, best day of 6.6 metres and best month of 128 metres. Visit www.atlascopco.com and www.liebherr.comThe primary support consisted of 20 cm-thick shotcrete SC 25, with Sika's Sigunit L53 AFW accelerator, reinforced with welded mesh and steel arches. Also, anchoring elements have been employed (SN, IBO, HTEX, Boltex and GRP). Arcelor fibres were implemented only at the experimental section toward Letnany. The use of reinforcement fibres in shotcreting was a premiere for Metrostav. Three shotcreting machines were used (one Aliva PM500, one Meyco Potenza and one Aliva PM300). The secondary support consisted of a protective geotextile, a 3 mm-thick PVC waterproofing membrane and 40 cm-thick concrete reinforced with welded mesh and steel arches. The concrete was cast in two steps (invert first and then vault). Visit www.sika.com and www.meyco-equipment.ch Two 1,400 mm-diameter Korfmann fans ventilated the jobsite. For mucking-out, wheeled loaders have been used (one Volvo and four Komatsu). Visit www.korfmann.com, www.volvo.com and www.komatsueurope.comThe final stages of work involved relatively shallow locations under housing developments situated in Prosek. At some points the tunnel roof is no more than just 10 metres under the surface. Thanks to the adoption of NATM, which subdivides the excavation in several sequences, subsidence at the surface was never more than 2 cm.Section Ladvi-Strizkov (975 m) is characterised by inner and outer excavation areas of 60-77 sq m. It is the same type of tunnel as Prosek-Letnany. Tunnelling proceeded using a tunnel excavator ITC Schaeff 312 and a rotary head Eickhoff 380. The geology consisted of Cretaceous quartziferous sandstone with an overlying layer of glauconitic sandstone (1 to 2 m of thickness). Visit www.tunnel-mucking.net and www.eickhoff-bochum.deFor support, the same technology and materials were employed as on tunnel section Prosek-Letnany. Tunnelling was completed in December 2005. The building consortium is using a formwork carriage, which fills the interior formworks of the 10 m-long sections with 100 to 130 cu m concrete each. The concrete is initially delivered from above ground with a Putzmeister BSA 1408 E through an approximately 30 m-long drop line to tunnel level and then 250 m horizontally to another electrically driven relay pump. This pump is a Putzmeister BSA 1405 E, which, depending on the progress of the inner form, pumps the concrete (C30) up to 250 m into the formwork carriage. Visit www.putzmeister.deAll the stations have been built using the cut-and-cover method. Concrete construction is finished at all stations. Equipment (sanitary, technologies, paving, electric lines, etc.) is being installed. Track laying will commence in September. Trains should run on the new subway section, also known as IVC2, as of April or May 2008. Click cz/12. 30/06.