A single double-shielded Herrenknecht TBM in Spain has completed the twin tubes of the Cabrera railway tunnel near Valencia five full months ahead of schedule. Advance rates of up to 106m/day cut construction of the 6km long twin-tube tunnel by a quarter with the civil structures ready to be fitted out with the railway technology in only 14 months.

Breakthrough after a rapid run

Tunneling on the two, almost 6km long railway tunnels started on July 27, 2007, three and a half months after acceptance of the TBM at Herrenknecht's factory in Schwanau. Excavation of the first tunnel tube confirmed that the S-373 TBM was well designed for the geology encountered as daily performance rates topped 83.2m. In November 2007, a total 1,600m of 9.69m diameter tunnel was advanced towards completing the first 6km tube six months after launch.

After work started on the second tube on May 5, 2008, the team achieved weekly performances of more than 400m on several occasions. On average, the machine excavated 284m of tunnel per week and laid 178 lining segments. The second 9.69m diameter TBM S-373 achieved breakthrough on September 25, 2008.

At the time, Herrenknecht branch manger Juan Arroyo forecast that: “If everything continuous to run smoothly, we can finish work in December 2008." His estimate was over by three months.

For excavation of the second tube, the site was equipped logistically for tunnelling performances to outmatch those achieved in the first tube. The lining segments were produced around the clock and production of the annular mortar was extended so that double the amount of material was available all the time.

Double shield non-stop tunnelling
As the 9.69m diameter machine advanced through the rock, the lateral grippers applied counter force against the tunnel walls while allowing, at the same time, construction of the 1.6m wide rings of the one-pass precast concrete lining weighing up to 8.8 tonnes in the tail shield.

Herrenknecht branch managers in Spain, Francisco Avila Aranda and Juan Arroyo, said several factors explained the speedy progress of tunnelling activities including the experienced site team of the contractors FCC Construcción S.A. and Construcciones Sanchez Dominguez-Sando S.A.; the logistics system, which was planned in great detail; and the tunnel machine, which was adapted precisely to the hard limestone geology.

TBM S-373 ready to work at Cabrera

Consultant and tunnelling experts including Dr Ingeniero de Caminos, Canales y Puertos Don Felipe Mendaña have said that the right machine type was chosen for the geology, which made it to work in the simultaneous excavation and ring-build double shield mode for almost 100% of the time. “Furthermore, the construction site team was excellently trained and coordinated by the construction company, and this, in conjunction with perfect logistic systems contributed to this extraordinary performance."

The La Cabrera tunnel crosses beneath the Sierra de La Cabrera and overcomes a difference in height of about 170m with a gradient of up to almost 3% between the western and eastern portal. As part of the extension of the high speed railway network between Madrid and Valencia, the tunnel forms the core part of the 11.2km long ‘Siete Aguas-Buñol’ section. The plan is to put the tunnel into operation at the end of 2010, after installation of the necessary railway systems.

Herrenknecht