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Construction of the LINE C tunnels

The works to build Line C continue with the launch of two TBMs (S409 and S410) in Line C’s Shaft 3.3 at Via Sannio.

On 19 and 21 June 2017, the two TBMs (Tunnel Boring Machines) were lowered into the shaft. Once the back-up is assembled and all the preparatory operations are completed, they will perform the excavation for the construction of Line C’s tunnels towards Fori Imperiali. The TBMs, weighing approximately 450 tons each, were hoisted by a special crane with a 750-ton capacity, placed at the bottom of the shield introduction shaft.



TBM excavation is one of the most sophisticated technologies in the field of mechanised excavation in an urban setting. Along with excavation, the machines also make the final lining of the tunnel, which is then ready to be equipped with tracks and technological systems.

The TBMs used for the excavation of Line C’s tunnels are 6.70 m in diameter. The tunnels’ internal lining consists of precast segments in reinforced concrete, 30 cm thick, and with an internal diameter of 5.80 m. Each precast ring, 1.40 m in length, consists of 6 main segments + 1 key segment. The rings are of the “universal” type, and adapted to 19 different possible positions depending on the radius of curvature to be obtained.

The TBMs are composed of a circular cutterhead 6.70 m in diameter, equipped with steel claws and rotating discs to crush the ground, connected to the machine body (shield) and to the trailing equipment needed for it to operate (called the “back-up,” it is about 90 metres in length, and contains the services structure housing the cab, the systems’ cables, and the conveyor belt needed to extract the muck).

The TBM is controlled by electric motors placed in the rear area of the machine, and by electromechanical or hydraulic speed governor systems.

During the excavation, the ground is mixed with foams and maintained under pressure to guarantee the stability of the excavation face, in order to prevent impacts on ground level.

I numeri delle TBM

The tunnels already used

The excavation of the already-used tunnels of Line C for the Giardinetti-San Giovanni section (underground part of the section from the terminus Monte Compatri/Pantano to San Giovanni) was completed in June 2011.

The 4 TBMs used made a total advance of 19 km in the two tunnels.

Metro C S.c.p.A.’s member companies