An unprecedented operation on the Grand Paris Express, the digging of this gallery, which will serve as an emergency access when the metro is commissioned, is carried out using traditional hyperbaric method. A technique retained on the one hand, because of the particular location of the site - in the immediate vicinity of two SNCF rail bridges, a residential building and a sand chamber of the environmental and of the sanitation (DSEA) services departments on the other hand, given the geology - the ground is composed of Beauchamp sand in the upper part and Marne and gravel in the lower part, all in the presence of water.
To excavate this 23 m² section over 11 meters long, a hyperbaric SAS was designed and divided into three chambers :
- a staff access room of 6 m²,
- a material room of 31 m²,
- a working chamber of 35 m² before digging.
The pressure generated in the working chamber - 2.05 bar - keeps the gallery dry and secures the ground to avoid any risk of settlement.
High safety procedures and a specific work organization, due to hyperbaric regulations in force since 2019, have been put in place, allowing the smooth running of the activity for hyperbarists who work in 3 shifts 24 hours a day from Monday to Thursday and from 6 am to 10 pm on Friday.
On September 2, the first metal hanger was successfully installed and the excavation should be completed in early October.
Photos Credit: Hervé Piraud