Soletanche Bachy France completes drilling and deep grouting works on the Lyon-Turin worksite

The entire project, entrusted to the LYTO consortium (VINCI Construction Grands Projets, Dodin Campenon Bernard, Campenon Bernard Centre Est, and WeBuild) and Bergteamet two years ago, involves the construction of:

• Four vertical ventilation shafts 5.2m in diameter, 500m deep, using the raise-boring method (Raise-boring is a mechanical excavation method starting at the foot of future shafts. It involves drilling a pilot hole from top to bottom, then boring from bottom to top, removing rubble from the bottom (via the existing cavern),
• underground galleries and 7 caverns measuring up to 22 m high and 23 m wide (digging using conventional methods with explosives).

It is to the consortium Soletanche Bachy France (as lead company) and Botte Fondations, mobilised since September 2021, that the works of very deep drilling and grouting (135m) work has been entrusted.

Technically, it should be noted that the tunnel is partly ventilated by four shafts in the commune of Avrieux at 1,305m altitude. Excavation of these 500m-deep shafts, using the raise-boring technique requires consolidating and sealing the rock for the first 135m.

In order to implement the best possible soil treatment, several drilling and grouting test plots were carried out. It should be noted that this type of work is very unusual, with major technical requirements including the vertical nature of the boreholes and the grouting of several grouts with variable viscosity.

The first rock-treatment phase between 0m and 70m has been completed and the deep grouting (70m to 135m) are now in progress. This operation, requiring three drilling workshops in three positions, will take several more months to complete and to secure the execution of the work of raise-boring.

For our teams, this is a complex project with many technical and environmental requirements. In fact, before the beginning of the works, an acoustic and thermal shed has been set up to protect the environment from noise pollution and allow the teams to work sheltered from the region’s harsh weather.

The project was also subject to a major environmental requirement in terms of water treatment, with water having to be recycled rather than discharged into the natural environment. To do this, Soletanche Bachy set up a worksite water treatment plant which operates according to the following principle:

• Water collection via channels built into the slabs
• Provisional storage
• Flocculation system (physico-chemical process by which matter suspended in a liquid gathers to form larger particles, facilitating filtration)
• Settling in big bags to filter and recover the water
• pH treatment by CO2 grouting
• Storage
• Reuse of water, mainly for drilling in Hi’Drill® (different coloured flexible pipes are used to differentiate that water from mains water)

This facility, developed in partnership with TELSTAR, had already proven itself on works package T3A as part of the Grand Paris Express project.