Line 18 is located south-west of Paris, between the Orly airport station and Versailles Chantiers. The work involves the construction of an automatic driverless metro line. In particular, the works of this lot concern the construction of the ramps and the viaduct of the aerial section of line 18 of the Grand Paris Express between the open trench of Palaiseau and the open trench of Magny-les-Hameaux excluded. It is a 6.2 km viaduct, an East ramp of 150 m and a ground section of 600 m. Line 18 has the distinction of not being connected to another line of the Grand Paris Express (15, 16, 17), but it is connected to line 14 RATP at Orly station. CIPA has been entrusted with the realisation of all the shafts in the lot by the consortium of which Vinci Construction is the principal member. These are 9 shafts, 7 of which have an internal diameter equal to 4.04 m and 2 with a diameter equal to 5.44 m, with a depth of 18 and 24 metres respectively, with the exception of a single shaft of 14 m. The first preparatory activity for the excavation of the shaft is the construction of the reinforced concrete crowning beam, the reinforcement of which includes the first steel rib. The excavation is carried out for steps that can vary from 0.80 to 1 m and the lining involves the use of a circular steel rib and the projection of fibreglass concrete, made by hand by the operator via wet. The stratigraphy characterizing the excavation of the shaft consists of silts and clays in the first meters up to half the depth and sands with intercalations of stoneware in the remaining part up to the bottom of the excavation ; to achieve which the concrete lean will be realized.