The central piece of the north-south rail connection
Guadarrama Tunnel is the main job of construction on the new north/south railway link to connect the central plain and the northern half of the peninsula.
The line crosses the Guadarrama Mountains by means of a 28.2-kilometre-long double tunnel excavated from the ends inward. The job is therefore a key piece of construction for the new access by rail to northern and north-western Spain. FCC is participating in the construction of the two northern mouths of the tunnels, heading toward Segovia/Soto del Real. The most significant activities are:
- Construction of a 13,377-metre-long tunnel using a TBM (tunnel-boring machine) with telescopic double shielding, which can both excavate and set the definitive lining of 32-centimetre-thick prefabricated concrete segments in place at the same time. The excavated tunnel is circular in cross-section, 8.50 metres in diameter.
- Construction of a 15,000-metre-long parallel tunnel that is geometrically identical to the 13,377-metre-long tunnel.
- On-site segment casting with two joint facilities equipped with a concrete plant, a casting room with vibrating tables, a steam-curing tunnel and a large-capacity outdoor stockpile.
- The two tunnels are being built simultaneously, with two separate machines. The rubble is extracted on two conveyor belts that meet at a regulator hopper, from which there rolls another belt. This third belt is five kilometres long and carries the rubble to an old quarry, thus totally reducing the environmental impact of rubble disposal.
- Cross tunnels connecting the two tunnels every 250 metres.
- Underground transformer stations in side galleries every 2,250 metres.
- Installation of the railway line on concrete slabs with UIC-60 rail.
The nature of the terrain where the work is taking place is important, because the rock along the tunnel's path is extremely hard and contains different varieties of materials, an environment where TBM use is new. Generally the terrain contains granite or similar types of rock. The classification made during the course of the job is as follows:
- Grey granular orthogneiss, 41.06%
- Porphyric adamellite, 30.21%
- Episyenite and syenite, 6.95%
- Leucocratic granite, 4.57%
The geological profile is relatively homogeneous in terms of rock hardness, except for the two faults the tunnel crosses, in the valley of Valsaín (the Eresma River valley) and the valley of La Umbría (the Lozoya River valley), where fractured, loose rock was found.
The cutting edges of the drill heads have seen a great deal of wear due to the hardness and abrasiveness of the rock. The TBMs are giving excellent performance, however.
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