Greater Paris: 30 meters underground, the tunnel boring machine "Rita" is ready to begin its ascent.

Christened on Monday evening, with a female first name according to custom - in homage to Saint Barbara, patron saint of miners -, this immense 95-meter-long drilling train will set off at the end of May to connect Bobigny to Bondy, one of the segments of the future line 15 East.

Around the enormous machine, at the bottom of the pit, workers are busy: no less than 25 of them, in teams of 3/8, will accompany its progress 24 hours a day.

As the tunnel boring machine descends into its shaft, shuttle vehicles will be deployed to transport the workers back to their starting point. The machine will also carry restrooms and even a cafeteria for those who will be traveling with it for several kilometers through the tunnel.

Local officials and site managers came to unveil the name of the machine, a necessary ceremony before the start of its slow underground journey over 5,2 km.

Custom-built in Germany by the Herrenknecht group and transported in December to this "Normandie-Niémen" site, between Drancy and Bobigny, "Rita" is the 35th tunnel boring machine put into service since the start of the pharaonic construction of the Grand Paris Express lines, around 2015. It was named after an engineer from the Corea works group.

Two and a half years of digging

The works on the four new metro lines (15, 16, 17 and 18) will be completed in 2031, having used a total of 42 tunnel boring machines - all German except for two Chinese - to dig 180 km of tunnel out of the 200 km route.

Arriving in pieces, the tunnel boring machine was assembled at the bottom of the shaft, starting with its large drilling wheel, a kind of giant flat screw 10 meters in diameter, then its entire rear axle.

When Rita "leaves," as they say on the construction site, there will be no deafening noise or shaking ground: so deep underground, a pedestrian on the surface won't notice a thing. Unlike the Paris metro, which is sometimes only 3 or 4 meters below our feet, explains Gaëtan Chelles, project director for Corea, a consortium led by Eiffage.

The tunnel boring machine will start by the end of May at a rate of 12 meters per day and will excavate for two and a half years, reaching its final destination in Bondy in October 2028, according to the Société des Grands Projets, the project owner. Section 15 East will include 12 stations, including Bobigny-Picasso, which will connect to line 5 of the Paris metro.

Although the southern section of line 15, already excavated, will be put into service as early as April 2027, the eastern (from Saint-Denis-Pleyel to Champigny-sur-Marne) and western (from Pont de Sèvres to Saint-Denis-Pleyel) sections will not open until 2031. Line 15, the keystone of the project, will then make a large loop around Paris.

This Normandie-Niémen site will also see the arrival in 2027 of the tunnel boring machine Marine (named after a collaborator of the Société des grands projets), coming from Aubervilliers, after two years of drilling.

For the mayor of Bobigny, Abdel Sadi, "line 15 will revolutionize our territory" because "the city has the chance to host three stations on this line".

"It took a lot of fighting and a lot of mobilization to secure its route and these stations," recalled Stéphane Troussel, president of the Seine-Saint-Denis department.

Seine-Saint-Denis will host 22 stations of the Grand Paris Express, he recalled, which will allow easier access to employment, culture, other transport lines, housing opportunities as well as considerably shorter transport times.

"From Bobigny to Pleyel in 8 minutes, from Bobigny to Aubervilliers town hall in 8 minutes. That shows how much it will change people's daily lives and the attractiveness of the area," he concluded.