Swissgrid has finished drilling work on the underground extra-high-voltage cable link tunnel between the La Bâtiaz substation and the locality of Le Verney in Martigny.
Giorgia, the mini-tunneller, was brought to the surface on 12 August 2021 at the La Bâtiaz electrical substation site. The machine will now return to the manufacturer to be reconditioned ready for use at other sites.
It took the mini-tunneller nearly nine months to drill out the tunnel with a diameter of three metres between Le Verney and the La Bâtiaz substation, at between 12 and 20 metres below ground. 507 concrete tubes were laid over a distance of 1.2 kilometres to reinforce the tunnel. During the works, Giorgia evacuated more than 24,000 tonnes of rubble, which has been recycled at the Le Verney construction site. Furthermore, the mini-tunneller had to be stopped four times over the last ten months to allow some of the tools on the drilling head to be replaced, which had been worn out during the drilling process.
Not even one worker was physically present in the tunnel during the drilling. The mini-tunneller was entirely controlled from the control station installed above ground at the Le Verney site.
Two years of work
Launched in June 2020, the construction of the La Bâtiaz – Le Verney underground cable link is currently continuing with the development of the tunnel. In the course of autumn and winter, the extra-high-voltage cables will be laid underground, in parallel with the construction of the gantry that will connect the cable link to the 380 kV Chamoson – Romanel overhead line at Le Verney. The underground cable link is scheduled to be commissioned in spring 2022.
The Nant de Drance power plant is already connected to the grid
Swissgrid is responsible for connecting the Nant de Drance power station to the electricity transmission grid. It will be one of the most powerful pumped storage power stations in Europe and produce around 2.5 billion kWh per year.
Two of the three sections of the Nant de Drance extra-high-voltage line have been in service since the end of November 2018. These consist of 6.5 kilometres of underground cable link connecting the power station to the Châtelard substation via the station's access tunnel, and 12.5 kilometres of overhead line connecting the Châtelard and La Bâtiaz substations. Pending the commissioning of the third and final section, the Nant de Drance power plant has already been connected to the power grid via a temporary solution implemented in 2019 enabling the voltage of one of the two La Bâtiaz – Le Rosel overhead lines to be increased to 380 kV.