Technical overview
Digging the 11.8 km section will be carried out with two types of tunnel boring machine due to the different geological constraints: an earth pressure TBM and a variable density TBM. To line the walls, 5,930 rings weighing 52.78 T will be used.
The Maréchal Leclerc shafts, a major structure (2 circular shafts of 27. 60 m diameter and 36 m depth) at the intersection of avenues Maréchal Leclerc and Maréchal Koenig at Massy, will constitute the entry point of the Orly-bound tunnel boring machine and the arrival point of the tunnel boring machine from Palaiseau. Like the set of 10 circular shafts (9 to 11 m in diameter, 20 to 45 m in depth) connected to the main tunnel by a cross passage, once finished it will provide service functions (rescue, ventilation, smoke extraction, etc.).
A covered trench (200 m) and open trench (600 m) will provide the transition between the underground section of line 18 and its overground section.
For the three underground stations, Antonypole, Massy Opéra and Massy Palaiseau, diaphragm walls will be built, the excavation will be carried out underground and two layers of waling beams will support the walls.