SELI's double shield TBM excavating the San Just water tunnel in Barcelona is advancing fast through mix rock conditions. The 11.5km tunnel is part of the Catalonia aqueduct scheme and is being excavated by two double shield TBMs advancing from the two portals. One TBM is manufactured by SELI which is subcontracted by Spanish JV FCC/Copisa to excavate a 5,316m drive from one portal. The second machine is manufactured by Herrencknecht and is excavating the 6,192m heading from the opposite portal. Once completed, the tunnel will link two potable water distribution stations at Fontsanta and Trinitat.

SELI's €10.7 million subcontract includes supply of the 5.98m diameter double shield TBM and all its auxiliary equipment including backup, rolling stock and auxiliary equipment for excavation and lining, as well as the TBM maintenance and operation on-site with a team of specialists and operators.

	SELI's 5.98m diameter double shield TBM
Main technical specifications of SELI’s double shield TBM: Cutters 17in0 Max cutterhead thrust 11.357kN Cutterhead speed 0 to 9 rev/min Cutterhead drive power 7 motors x 250kW (1750kW)

The tunnel is lined with bolted precast segments, 25cm thick, in a 5+1 configuration, and with a final internal diameter of 5.2m.

The TBM is boring through a wide range geological formations from weak deposits under shallow cover to very hard and abrasive rock including slate, schists, porfidus, cornubiana, granodiorites, quartzites. The presence of groundwater is not expected during excavation, however, in the final 1,000m the design documents anticipate replacing the 6bar segment gaskets with those of a superior watertightness capacity of 12 bars.

After excavating an initial starter tunnel with preliminary installations, the TBM, in its final configuration, set off in February 2009. In the first two months, production rates remained in the range of 500m/month, while in April production increased to 707m and it is expected to rise further in the next months since daily advances of more than 45m/day have been achieved already.

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