01. What does a tunnel boring machine do?
It’s been a long time since we used pickaxes and explosives to dig tunnels. The tools of times past have been replaced by mechanised drilling techniques, which are carried out by drilling and tunnel boring machines.
Tunnel boring machines are increasingly effective: the latest generation of boring machines, called Earth Pressure Balance (EBP), can operate in both soft and even waterlogged earth, or in the hardest rock. This is the case for the two tunnel boring machines that are in place for the M14 extension. They function just as well in the limestone of Saint-Ouen as in the sands of Beauchamps… But they can also dig through marls and pebbles, as well as the groundwater table.
By using a tunnel boring machine in an urban setting, we avoid encumbering the street surface area and generating the nuisances this type of construction work can cause for residential life. Tunnel boring is a real alternative to open-cut digging methods.
02. A veritable underground factory!
Extremely powerful, the tunnel boring machine simultaneously digs underground, supplies support for the section being crossed (to ensure the structure’s stability), and builds the tunnel itself.
In front is the cutting wheel, which is protected by a shield. It digs through the dirt while relying on the parts of the tunnel already in place to support itself. A conveyor system evacuates the debris. An erector installs the arches (cut stone wedges that are used to build the arch), which form the tunnel’s finished interior surface.
The second part of the tunnel boring machine, the back-up train, is behind. It is used to evacuate debris and move the arches into place.
03. Magaly and Solenne, the M14 tunnel boring machines
On the M14, tunnel boring machines operate 24 hours a day, 5 to 7 days a week.
The first tunnel boring machine to have been set up for the M14 line extension is named Magaly. Inaugurated on 9 September 2015, her mission is to dig a deep circular tunnel, 7.75 metres in diameter and 3.6 km long, to accommodate two tracks. The tunnel begins at Rue de Londres in the 8th arrondissement of Paris and will end at Rue Pierre Dreyfus in Clichy.
Installed at the future Pont Cardinet station, Magaly has already finished digging the first segment, direction Gare Saint-Lazare. The machine was then dismantled and reinstalled at Pont Cardinet, to tunnel its way to the Clichy – Saint-Ouen station in Clichy-la-Garenne. Digging on the second segment began in summer 2016.
Since late 2015, a second tunnel boring machine named Solenne has been digging the tunnel segment between Saint-Ouen and Saint-Denis. The 1.7 km tunnel will run from the entrance of the future Clichy − Saint-Ouen station in Saint-Ouen, to rue Marcel Cachin in Saint-Denis. Solenne will also construct the 501-metre tunnel that links to the maintenance and garage site to be located in the new Docks de Saint-Ouen district.
The M14 extension from Saint-Lazare to Mairie de Saint-Ouen is the first step in the Grand Paris Express automatic metro. The main purpose of the M14 is to reduce saturation on the M13, with four new stations (Pont Cardinet, Porte de Clichy, Clichy Saint-Ouen and Mairie de Saint-Ouen) serving the fast-growing metropolitan districts northwest of Paris.