TWO HERRENKNECHT Double Shield TBMs are on their way from Germany to Valencia in eastern Spain to begin work on the Jucar-Vinalopo Water Transfer project.
Once finshed, the 67km long Jucar-Vinalopo Channel will annually transfer about 80M. m 3 of drinking water from the Jucar Basin west of Valencia to the dry Mediterranean coastal regions around the tourist centres of Murcia, Alicante and Benidorm.
The scheme is one of the largest under the Spanish government's programme to improve the national water supply system.
Rivers in the Jucar Basin supply drinking water to the local region, which also has abundant groundwater resources. The area is one of the few in Spain where water reserves exceed local demand.
Construction firms Nesco and OHL/UTE Cuesta Vinalopo will use the Herrenknecht 2950 hard rock machines, with an outer diameter of 3,370mm, to install 23.3km of new pipeline through dolomite, limestone, siltstone and marl. Tunnelling is in four sections, ranging from 4km to 7.3km long.
The double shield system allows the 170m long machines to be operated in conventional or continuous mode depending on ground conditions.
In solid rock, the machines can install rings continuously behind them as they bore, resulting in higher production rates. But when entering and passing through fault zones, the operating mode is changed to conventional shield drive, providing maximum safety for operators, the machines and the tunnel.
The large cutters fitted to the TBMs - 432mm - help them cope with the hard rock conditions, minimising the number of cutter changes needed on the long drives.
The machines were handed over to the construction team at Herrenknecht's factory in February and are now being broken down for transport to site in Ayora, Valencia, where they will start tunnelling this spring.