Switzerland's intent to force road vehicles onto the railroads will relegate the 1913 Lötschberg Alpine rail tunnel, built with pneumatic drills and hand shovels, to a secondary role. Crews building the 34.8-kilometer route that will supersede it now utilize jumbos and tunnel boring machines. But uncertain, variable geology that led to numerous fatalities on the old tunnel still taunts crews on the new one today.
Geotechnical surveys had predicted the existence of rubble-filled pockets, or karsts, that could drain rivers up to 2 km above into the tunnel. "What we didn't know was whether the karsts actually existed," says Peter Hufschmied, a director with the project's co-designer Emch+ Berger A.G., Bern. Having taken two months this spring to cross just 25 m of karstic rock, engineers are now prepared for a potentially slow slog through the remaining 3 km of similar ground. But so far, progress has been good.
Tunneling bids fell within a few percentage points of the total $2.2-billion budget, and have deviated little the last two years. The project so far is on schedule and budget, says Peter Teuscher, director of BLS AlpTransit A.G. (BLSA), Thun, the sponsor. As tunneling approaches 60% completion, BLSA is reviewing bids for railroad equipment.
|DANGEROUS DEPTHS Jumbos and TBM's drill into uncertain ground conditions in same area as original 1913 tunnel. (Photo courtesy of BLSA)|
DANGEROUS DEPTHS. Jumbos and TBM's drill into uncertain ground conditions in same area as original 1913 tunnel. (Photo courtesy of BLSA) The new tunnel received voter support in plebiscites during the 1990s as part of a policy to promote railroad investments to mitigate environmental impacts of growing transit truck traffic. Crossing the Bernese Alps, the Lötschberg will smooth the route from Italy to France. Also launched as part of that strategy was the 57-km Gotthard tunnel, located about 100 km further east to serve German-Italian connections.
Excessive costs predicted for the tunnel projects forced planners to shelve some of the other Gotthard-related tunnels, says Teuscher. Tunneling, now beginning on Gotthard itself, is due to end in around 12 years. But the location of the north portal has yet be to determined. On the twin-tube Lötschberg, only part of the west bore is under construction. Much of that bore will be left unequipped for now.
Connecting Frutigen to Raron, the Lötschberg includes twin bores, except for the northern few kilometers of the west tube. To function initially with a single track, the Lötschberg will use a trial tunnel built five years ago 80 m to one side as the escape route in that stretch. Elsewhere, escape passages will link the two main tubes every 330 m.
At BLSA, Teuscher heads 26 people, relying on outside firms to design, manage and supervise work. Designers even provide templates for treating different ground conditions, such as specifying rock-bolt lengths, says Hufschmied. His firm is handling all design, along with Ingenieurunternehmung Bern A.G. preparing. Lötschberg's route came from a "spaghetti plan" of options, says Hufschmied. Selection criteria included picking a route of known geology. Some 20 deep cores formed the basis of the designers' knowledge, helping to calibrate a "general geological understanding [that] is based on an extrapolation from the surface, adjusted by data from the (1913) tunnel," he adds.
Anticipating difficult conditions in the north, engineers ordered construction of the 9.6-km-long trial tunnel to probe the rock. With its data, the north drive from the Mitholz access tunnel poses few uncertainties. But in the lesser- known twin south drives, engineers suspect the existence of karsts with water pressurized up to 75 bars. To find them, work halts every three to four weeks for drillers to probe 250 m ahead.
The SATCO joint venture has the biggest share of drilling and blasting. Led by Austria's Strabag A.G., Vienna, and including Paris-based Vinci Group, Stockholm-based Skanska International and two local firms, SATCO signed a roughly $360-million contract in early 2000 for the northern tubes.
Drill/blast is used for all current tunneling from a point about 10 km from the south portals. With its use of bolts, mesh and sprayed concrete in amounts depending on conditions, the technique would be recognized as the New Austrian Tunneling Method. But the Swiss engineers eschew that term. Tunnels due to carry traffic in this phase will be concrete-lined, and the rest will be left with a sprayed covering.
In 72 months, SATCO must drive about 8 km of a single tube north of the Mitholz access to Frutigen. To the south, it will build two 8.7-km tubes until it meets the oncoming joint venture's drill/blast teams. Led by Paris-based Bouygues S.A., that joint venture is driving Lötschberg's central tubes from the Ferden access. Click here to view map
Working three daily shifts, SATCO is advancing each face at an average of 10 m per day, says project manager Wolfgang Lehner. He is pleased with that rate, considering his teams must travel 2 km underground just to reach the tunnel. "We have chosen sophisticated equipment to provide high productivity," says Lehner. Hanging the entire jumbo backup from the tunnel roof is the most obvious innovation. "We thought it was necessary to get something like a TBM backup working in drill and blast to minimize handling time with the installations," he explains.
Most backup equipment follows the faces hanging from the ceiling. High-level conveyors remove spoil without disruption of activities below. Dump trucks take rock from the faces some 60 m back to a mobile crusher feeding the conveyors. The conveyors are emptied into a holding cavern leading to other removal conveyors, in order to isolate rock disposal from surface snags.
|KICKING OFF Northern portal excavation has just began. |
(Photo by Peter Reina for ENR)
TUNNEL DUO. Tunnel boring machines are used only for some 18 km of tubes at the south end. Two machines are driving the eastern main tube from Raron and part of the west drive from the side at Steg. But the MaTrans joint venture in that area decided drill/blast would cost less than using a TBM for the short 4.9 km of the west tube. Led by the Swiss Marti Tunnelbau A.G., Bern, MaTrans includes London-based Balfour Beatty Group Ltd.; Germany's Walter Group, Augsburg; and A. Porr A.G., Vienna.
Offered as two contracts, MaTrans first won the Steg section in November 1999. It then secured a combined deal worth about $335 million, including the Raron tunnel, six months later. "A soon as the group got a letter of intent for Steg, our strategy was clearly to go for Raron as well, with a variation for the whole project," says project manager François Bertholet.
Using two 9.4-m-dia Herrenknecht TBMs, MaTrans set off from the Steg portal in October 2000, and its Raron machine followed the next July, say Bertholet. For a 150-m stretch of the Raron tube a half kilometer from the portal, MaTrans used drill/blast in Trias rock, which was too weak for TBMs, says Rolf Dubach, the drill/blast manager. Crews dug from the west tube to gain access.
TBM progress reached a record 41.8 m in one 18-hour stretch this June, but the average is closer to 17.5 m, says Bertholet. But abrasive, blocky rock has held back the Steg machine by some six weeks.
At the north end, local contractors are building cut-and-cover sections ramping to the surface. One of them has begun excavating a 100-m section of tunnel to meet the SATCO crews. Its workers are drilling a canopy of steel tubes to support the tunnel roof as they dig short sections beneath.
Excavation, accounting for more than 40% of the total cost, is going well enough for an anticipated completion date of 2007. Commercial operations could begin that December, in line with general timetable changes. But if good progress continues, trains could start the December before. Asked which date is more likely, Teuscher is guarded. "Ask me at the end of 2004," he says.