La Cabrera Tunnel lies on the section of the Madrid/Cuenca/Valencia, Siete Aguas/Buñol high-speed railway line. It connects the Utiel plain, Requena and La Hoya de Buñol, coping with a severe difference in altitude and one of the major obstacles facing the line on its arrival in Valencia, the Sierra de La Cabrera mountain range. This route was designed for a projected speed of 350 km/h.
The Siete Aguas/Buñol section is located in a mountainous, ravine-filled area that has had its own influence on the layout. With a length of 11.2 kilometres and an altitude difference of 245 metres, the section crosses the Hondo de Massegar ravine over a 224-metre-long viaduct of the same name. It enters the Siete Aguas artificial tunnel (420 metres) running parallel to the A-3 dual carriageway and enters La Cabrera Tunnel, which goes through the mountain range whence it gets its name. The tunnel is 7,157 metres long and has dual tubes. At the exit in Buñol, the section connects with the viaduct over the Rambla del Gallo (50 metres) and enters the 1,916-metre-long Buñol Tunnel. This tunnel is made up of two sections, a 1,390-metre-long excavated section and a 526-metre-long cut-and-cover section. Lastly, the line crosses the municipality of Siete Aguas and Buñol and comes to rest at an embankment that connects to the next section (Buñol/Cheste) on its way to Valencia. The tunnels account for 85% of the total length of the section's route.
La Cabrera Tunnel, the longest of the tunnels on the 914-kilometre-long high-speed line, is made up of two circular tubes having an inner diameter of 8.75 metres. It has been dug through carbonate rock (limestone, dolomite and marlaceous lime) and built employing different procedures, conventional methods (new full-section Austrian method on the Madrid side) and a tunnel-boring machine (on the Valencia side), depending on the geological characteristics of the terrain and external conditioning factors. In addition, the dual tubes are interconnected by galleries every 400 metres.
The tunnel-boring machine used to dig out the tunnel, the Herrenknecht AG S-373 UNAX, was a double-shielded TBM and facilitated progress on the work. Made in Germany and assembled right at the tunnel mouth, this magnificent machine gave a record performance excavating tube 1 of La Cabrera Tunnel. The TBM is 204 metres long and weighs 2,700 tons. Its optimum boring capacity is 1.60 metres every 25 minutes. In two months it broke the world record for daily boring distance five times in La Cabrera Tunnel: 83.2 metres excavated and 52 rings set in place in a single day. The tunnel length excavated up to 1 December 2007 was 4,400 metres.