Fifth and Last TBM Launch at PajaresThe fifth of the five TBMs needed to dig the 2 x 24.7 km Pajares tunnel commenced on 10th July, 2006 from the Asturias side. That TBM has been produced at the workshop of Asturian company Duro Felguera by consortium Mitsubishi-Duro Felguera, with Robbins design, and has been ordered to excavate the west tunnel on lot 4, 10.3 km in length, to connect Telledo (Asturias) with Viadangos (Leon). The machine is a 10 m-diameter single shield TBM, which weighs 1,900 tons approximately, whereof 1,200 tons for the TBM alone and 700 tons for the back-up. It is 110 m long. Click here and here. Visit www.gdfsa.com Lot 1The first TBM at work on the Leon side, a Herrenknecht machine, started on 13th July, 2005 in La Pola de Gordon. As of 10th July, 2006 it had excavated 5,233 metres. Wirth Group's NFM Technologies TBM, which commenced tunnelling on 20th September, 2005 had driven 5,313 metres. Each TBM of lot 1 has therefore built more than 50% of each of the 10.3 km tunnels. Click here and here. Visit www.herrenknecht.com and www.nfm-technologies.comLot 2In the middle section of the project (lot 2), from Folledo to Viadangos, the second Herrenknecht TBM had progressed at that time 1,672 metres in the 5.5 km access gallery to the main tunnels. In addition to the access gallery, the TBM will bore two portions of the main tunnels (west and east), each spanning 3.9 km. The TBM stood still from 25th April to 4th July (read E-News Weekly 22/2006). Crews had no choice but to stop work after a permanent groundwater ingress was detected while the machine had drilled 1,522 metres and was working in a Barrios quartzite formation.That water hampered the proper assembly of the rings because it circulated around the outer diameter of the segments, i.e. between the rings and the ground. That situation caused a "leaching" phenomenon of both the mortar, which serves to bond the floor segment, and the compensation grout injected to solidify the gravels that fill the voids behind the extrados. In other words, the humidity that circulated between the rock and the segmental rings after their assembly made impossible the setting of the mortar between both surfaces.The solution adopted by engineers aimed at improving the mortar composition injected to fill the voids. The new mortar features a raft of characteristics that favour its fast setting before being affected by the existing ground humidity. During tests, workers advanced up to 1,638 metres.Also, water collection "containers" have been created ahead of the shield so that water can then be pumped outside before it reaches the segment erection area and leaches materials. Click here. Lot 3The third of the four lots of the Pajares tunnel project, between Viadangos and Telledo (10.3 km), is where the second Wirth-NFM Technologies TBM is working. The machine had built 48 metres until 25th April when, on that section as well, it was inevitable to halt tunnelling (read E-News Weekly 22/2006). The first 26 metres had been bored from the portal using drill and blast excavation. The TBM had to stop due to the poor geotechnical quality of the ground through which it was excavating, namely Carboniferous weathered lutites, which caused overbreak (excavation of more material than that is theoretically supposed to be excavated), with the danger of appearance of a crater in the middle of the ground.In that case, the adecuate consolidation and stabilization works of the ground above the TBM were carried out. To do so, tunnellers drilled from outside the tunnel a heavy pipe roof made of 41 steel forepoles driven in a more sound terrain composed of lutites. The goal of that measure was to create a separation between the terrain surrounding the TBM and the more superficial ground. Visit www.wirth-europe.com From inside the tunnel, another protective pipe roof was installed using fiber glass dowels with the objective of reinforcing the ground ahead of the face, in the upper part, which is always the one most likely to be affected by overbreak. Click here.Lot 4The fourth lot, the west tunnel on section Viadangos-Telledo, is the one that has seen the last TBM launch in Ubiñas massif. The machine will have to cut its way through the rock to join the tunnel driven by the TBM on lot 2 (see map). Prior to tunnelling and to avoid ground instability problems like those encountered in the tunnel of lot 3, bored at a distance of 50 metres, technicians decided to carry out various ground treatment operations. Protective measures consisted in building an umbrella vault of 41 steel pipes, 25 m of length and spaced out every 40 cm, formed by 89 mm-diameter 9 mm-thick steel rods. These roof pipes have been filled with mortar to form a kind of reinforced canopy in the upper part of the terrain to be excavated by the TBM.Outside the tunnel, a "reaction structure" has been assembled. It is a 900-tonne rigid steel gantry, shored up, on which the TBM can push to install the concrete ring. ConclusionIn all, the length excavated as of 10th July totalled 12.3 kilometres, virtually all of it from the Leon portals. When they enter in service, the Pajares tunnel will be Europe's fifth longest and the world's eighth longest tunnel. The twin bores will cross the natural barrier represented throughout history by the Pajares Pass, thus providing a high speed link between Madrid, Castilla & Leon and Asturias. The scheduled date for completion of construction is 2009. Read E-News Weekly 5/2006. Click es/55. Visit www.adif.es 31-32/06.