The work and the technique: Northeast Boundary Tunnel (NEBT), USA

The Northeast Boundary Tunnel, designed to last for 100 years, has a diameter of 7 metres, 4,442 rings, and was excavated at a depth of 30 metres.

Works on the tunnel were built with a TBM (Tunnel Boring Machine) named Chris. With a diameter of 7.9 metres, it was assembled in the construction site and then lowered into the shaft with four specific hydraulic jacks to raise very heavy loads (strand jacks), in a very delicate operation that required extreme precision.

The TBM Chris completed excavation operations with the breakthrough at the R Shaft shaft in April 2021.

Besides building the tunnel, the project includes building diversion systems in areas normally flooded, to lighten the existing sewage system and move the water towards the NEBT, and ventilation monitoring systems to regulate the air flow in the tunnel network, besides building sustainable infrastructure for 11 sites.

Construction site activities carried out during the emergency phase of the Covid-19 pandemic, with the adoption of extraordinary safety measures, just like in worldwide construction sites.

The project faced a series of challenges caused by the soil's geological composition, which includes heavy clay and sand clay that bring with them water with a 3-bar pressure, a complex work environment to build shafts in urban residential neighbourhoods featuring intense traffic.