Efforts to stabilize a collapsed section of a new $130-million metro tunnel in Barcelona are nearly complete. Related work on the system’s Line 5 is on hold while engineers seek ways to improve the New Austrian Tunneling method being used 30 meters deep.

Some 15,000 cu m of concrete have been poured into the newly excavated 160-m-long service tunnel, which collapsed in the Carmel area of north Barcelona late January. Soil in the collapse zone is being grouted, says a spokesman for Generalitat de Catalunya, the regional government of Catalonia.

A joint venture including Madrid-based contractor Fomento de Construcciones y Contratas (FCC) S.A., began tunneling in late 2002. Government officials say the collapse was triggered by a vertical fault rising through some 17 m of sandstone from the tunnel crown into a 15-m-deep surface clay layer. The undetected fault appeared while the contractor was excavating the lower face of the 9 x 12-m horseshoe-shaped tunnel after completing the heading.

Undetected Fault. Sinkhole caused service tunnel to cave in.

A small building fell into the resulting sinkhole, while others were undermined and needed demolishing. No one was hurt, says the government spokesman.

While the government’s project management division, Gestió d’Infraestructures S.A., reviews construction methods, work on the unaffected main extension from Horta to Vall D'Hebron has halted. The overall 2.5-kilometer extension includes a twin-track tunnel, a service tunnel and two new stations plus expansion of a third.

Elsewhere, tunneling continues on the new 42-km Line 9, due for completion in 2007. Located as deep as 60 m in variable rock, the double-deck tunnel is driven mainly by two large tunnel boring machines. A consortium including Dragados S.A., Madrid, is driving up to 10.5 km with a 12.06-m-dia earth pressure balance machine. German maker Herrenknecht A.G., says it is the world’s largest.

Another joint venture is driving 12 km in two sections with an 11.95-m-dia open-type EPB machine. The $3 billion line will run northeast through the city from El Prat International Airport.