Spain suffers from a shortage of water. To improve the supply of fresh water in Madrid, another one of the numerous reservoirs in the mountains around the metropolis – in the form of the Valmayor reservoir – was to be linked to the water supply network. The geology was demanding in the extreme. After all, the TBM here impacted onto granite – a tough and brittle assignment with intervening instable conditions.
Herrenknecht supplied a Double Shield TBM to operate both without and with segmental lining, should the need arise. To this end, the machine was specially designed so that – for tunnel supporting purposes – both roof bolts and ring beam segments could be placed into position. Where the rock was at times stable, then ring beam segments and roof bolts were there to strengthen the granite rock. In instable sections with brittle rock, the tunnel was lined with lining segments. Tunnel breakthrough was achieved in April 2008.