Overcoming Multiple Caverns: Successful TBM Tunneling in Karstic Geology at Galerie des Janots

Credit/Quelle: Robbins

1 The excavation of the Galerie des Janots Tunnel in France took two years to complete due to challenges including two uncharted caverns – the largest of which measured a staggering 8 000 m³ in size

Credit/Quelle: Robbins

2 The small jobsite for the Galerie des Janots, a 2.8 km long tunnel to improve water supply in the French communities of Cassis, Roquefort-la-Bédoule, La Ciotat and Ceyreste

Credit/Quelle: Robbins

3 The weak rock and clay conditions necessitated ground support including resin-anchored bolts and rings in bad ground

Credit/Quelle: Robbins

4 Filled karst cavities with water and mud were also encountered in the first 1000 m of boring, and these often needed to be drained and then filled with foam

Credit/Quelle: Robbins

5 Crews erected a 4 m high wall of concrete so the TBM would have something to grip against, allowing them to pass by the cavern in about eight TBM strokes

Credit/Quelle: Robbins

6 At the 2157 m mark, the machine grazed the top of an unknown cavity. A Speleologist roped off and descended to map the extent of its size. The new cavern was estimated at about 22 m long, 15 m wide, and 14 m deep, or about 4500 m³ of open space

Credit/Quelle: Robbins

In April 2019, a 3.5 m diameter open-type Main Beam TBM and its crew broke through at the Galerie des Janots Tunnel in La Ciotat, France. The 2.8 km long tunnel, excavated in limestone known to have groundwater, karstic features, and voids, took two years to complete due to challenges including two uncharted caverns – the largest of which measured a staggering 8000 m³ in size (Fig 1).

Upgrading the Water Supply

Galerie des Janots is one of the 14 operations designed to save water and protect resources, which are being carried out by the Aix-Marseille-Provence metropolis, water agency Rhône Mediterranean Corsica, and the French State Government. The Janots gallery will improve access to water in the communities east of the Aix-Marseille-Provence metropolis (Cassis, Roquefort-la-Bédoule, La Ciotat and Ceyreste). The future pipeline will replace existing pipelines, currently located in a railway tunnel, that have significant safety and vulnerability deficiencies with...