In Lyon, Gantelet-Galaberthier has dug a tunnel 5 metres under the water table and 8 metres under natural ground level, using a standard sheltered technique with jet grouting in the soil mass.
The Lyon subsidiary set itself the impressive challenge of creating the final section of these sewer mains along 180m! This is the first time a gallery has been dug using traditional methods in the alluvium of the Saône river.
To achieve this, a technique had to be devised in order to create a waterproof underground mass, from surface level, around the future location of the gallery, enabling miners to dig and reinforce the facility safely.
In order to avoid the driving of sheet piles in this district in the 9th arrondissement, Métropole de Lyon initially opted for the jet-grouting technique along a 15m test phase.
This technique treats the soil mass by high-pressure injection of cement-based slurry, resulting in an in-situ mixture of soil and cement. A sufficiently tight grid of these columns of jet grouting ensures both waterproofing of the mass and a ground texture which is not too resistant to manual digging.
This innovative solution was definitively approved by the customer after this test phase. Works are thus continuing with:
- The creation of two masses via jet-grouting columns, including within the access shaft area
- The creation of 2 access shafts
- Manual digging of the 2m-wide by 3m-high tunnel
- Extraction of the rubble from the cutting face
- Standard shoring with sheet metal and arches
In the second phase:
- The implementation of frames for the definitive reinforcement of the facility
- The installation of the tunnel formwork
- Concreting of the 130-long by 180-high collector.
Congratulations to the teams on the ground who worked so hard to deliver a compliant structure for December 2020.