The 6.7km long, 9.9m diameter twin Bolaños rail tunnels have been completely bored on the Madrid-Galicia High-Speed Line for client in Spain.
A Herrenknecht S-511 single shield TBM has been used to construct the two tunnels through ground conditions consisting of shales, quartzite, phyllite and sandstones. Advance rates on bore 1 reached 19.4m per day and took 11.5 months to finish, whilst bore 2 achieved 24.32m per day with a construction period of 9.5 months.
The tunnel was lined using precast segments 370mm thick and 1,600mm long. The full line is expected to be opened in 2018.
When TBM is used for excavating tunnel with rock, it is suitable for boring long tunnel in good stability, deep depth and high strength rock stratum. While the basic question is how to break rocks to keep high efficiency and project smoothly.
When TBM is used for excavating soft stratum, it is suitable for boring finite length tunnel in soft stratum below underground water with finite pressure. While the basic questions are to control cavity, stability of excavation surface and settlement of ground surface.
Rock bolts（
pernos de roca） in tunnel combine drilling, grouting and anchoring together, can be used in narrow spaces. Through full slurry bonding to surrounding rocks, rock bolts can prevent deformation and even collapse.
