“In winter it is hot and in summer it is cool.
It has advantages to work in a tunnel boring machine ”, smiles Amara Achemouk, works supervisor of the Vincent group, on the site of the extension of line 14 towards Orly.
At the beginning of March, the Allison tunnel boring machine finished digging the tunnel for the southern extension of line 14 between Orly (Val-de-Marne) and Maison-Blanche (Paris 13th arrondissement).
The opportunity to visit the 1,500 tonne factory machine, which had to be dismantled quickly.
Because on closer inspection, these machines are real technological feats and are worth the detour.
But before entering the site, you must bring a mini GPS beacon.
This makes it possible to locate people in the event of a problem.
The tone is set.
Once equipped, you can descend to a depth of 30 meters via the entrance shaft located in Villejuif (Val-de-Marne).
After 4.8 km is the Maison-Blanche station (Paris XIIIe), currently on line 7 and soon also on line 14.
The tunnel boring machine must dig nearly 5 km of underground galleries to accommodate the extension of line 14 between Paris and Orly./LP/JV
This is where Allison has been installed to be able to dig from July 2019 in the basements in the direction of Paris.
At the entrance of the tunnel that she has pierced between Villejuif and Maison-Blanche (Paris 13th century), a statuette of Sainte-Barbe, the patron saint of minors, sits discreetly.
As with each construction of galleries, shafts, caves or tunnels, in order to protect workers from possible accidents.
Sainte-Barbe, the patron saint of mining, was installed at the entrance to the tunnel. / LP / JV
The "minibus" has already left.
We have to wait for him.
“On foot, it's a long time.
In a vehicle alone, it now takes about fifteen minutes to reach the tunnel boring machine, ”explains Marie Coblard, from the Elios group, the prime contractor.
In fact of minibus, it is a vehicle without window provided with seats on shock absorbers.
And we quickly understand why, when the vehicle starts the bumpy part and it is no longer possible to hold a conversation.
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“The machine never stops.
Every day, three teams of twenty workers take turns in the tunnel boring machine, ”explains Nicolas Bonfils, owner of the southern extension of line 14 at the RATP, once lowered.
The companions, as they are called here, stay underground for eight hours, continuously.
Allison was able to move 12 meters per day on average.
With peaks at 35 meters.
To reach the tunnel boring machine, the workers borrow a minibus, without windows, with seats on shock absorbers./LP/JV
You have to continue on foot, on a temporary scrap span.
We finally arrive at the tunnel boring machine from the rear.
Or rather to a set of several platforms connected by mazes of stairs, in a tangle of cables, pipes of all kinds and thousands of visible metal parts.
“It's a real mobile factory,” smiles Marie Coblard, from the Elios group, the project manager.
"A tunnel boring machine makes it possible both to dig the tunnel, to lay the segments
(the wall of the tunnel, editor's note)
and to evacuate the cuttings", explains Nicolas Bonfils.
At the back of the tunnel boring machine, a set of several platforms linked by maze of stairs, in a tangle of cables, pipes of all kinds and thousands of visible metal parts. / LP / JV
Then, you have to continue 100 meters, without forgetting to lower your head, to arrive at the front of the tunnel boring machine.
“There, the cutting wheel while turning, digs the ground, a bit like a mixer,” continues Nicolas Bonfils.
On the way, we discover a water point there to wash our hands, there the toilets: “Yes, when we mount the tunnel boring machine, we also need a network of wastewater and drinking water”, underlines Amara. , showing the pipes that run along the tunnel.
In height, a treadmill of twice 4.8 km is at a standstill.
It was he who evacuated the spoil dug by the tunnel boring machine, a mixture of clay and limestone called the "sailor".
No less than 260,000 cubic meters have been extracted.
In the process of dismantling, it should leave for line 18. “Anything we can recycle, we try to do it”, assure the guides.
A little further, a door opens onto the driver's cabin.
“It is the pilot who directs the machine, according to the advancement instructions.
But also according to what he smells.
»Then, another staircase leads to the canteen: a room offering two microwaves and refrigerators in which the workers can put the dish they have brought back.
"It would take too long to get out of the tunnel boring machine every noon", continues Nicolas Bonfils.
In the canteen, a few tables and microwaves, to allow the workers to eat. / LP / JV
Then, after an office in a row appears the survival box.
The companions must take refuge there in case of problem.
“The voussoirs are so solid that there is no risk of collapse,” says Amara.
The biggest danger is fire.
"Behind the sealed door during the digging phase, two rows of 20 survival seats house water and dry cakes:" There is also oxygen and enough to last 24 hours.
"
The survival cabin allows workers to take shelter in the event of an incident.
 / LP / JV
Assembled in four and a half months, the tunnel boring machine will be dismantled in three to make room for the laying of railway equipment.
Throughout Ile-de-France, 18 tunnel boring machines are still digging.
One for Eole, the western extension of the RER, one on the Rosny side on line 11, and 16 for the Grand Paris Express.
The commissioning of line 14 at Orly is scheduled for spring or summer 2024. Right in time for the Olympic Games.
One million travelers are expected.