First milestone for Turin’s “Idropolitana”: TBM “Gaia” reaches the intermediate shaft

12 June 2026

A significant milestone was achieved yesterday, June 11, for one of the most important infrastructure projects in the Turin metropolitan area. One year after the start of excavation works from Parco dell’Arrivore, TBM “Gaia” has reached its first intermediate milestone, arriving at service shaft PZ030, located near the Monumental Cemetery of Turin, after excavating 2.7 km beneath the city.

The Colmeto Scarl Consortium, composed of Itinera – as lead company – and Ghella, is carrying out the construction of the Turin Mediano Collector, a strategic infrastructure designed by SMAT for the area’s hydraulic system, aimed at improving water management and mitigating the impact of extreme weather events.

The new collector extends over a total length of 14 km, of which 9.5 km are being excavated underground using a Tunnel Boring Machine, at an average depth of approximately 20 meters and more than 10 meters below the groundwater level. With the breakthrough at the intermediate shaft, the main tunnel has now reached approximately 30% completion.

TBM “Gaia”, a Hydroshield-type machine with a diameter of 4.08 meters, operates  using a mechanized excavation technique that includes the installation of precast segmental linings, each ring composed of 6 reinforced concrete segments. To date, 2,256 rings have been installed and more than 36,000 cubic meters of soil have been excavated.

Commissioned on June 3, 2025, the TBM advances at an average rate of approximately 3 cm per minute during excavation. Over the first 2.7 km, the team has encountered particularly complex geological conditions, characterized by highly heterogeneous and abrasive soils. These conditions have required more than 80 hyperbaric interventions for cutterhead maintenance, carried out at a working pressure of approximately 1.5 bar.

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