September 7, 2016 - The construction of the Abu Dhabi Deep Sewer Tunnel, one of the deepest gravity tunnels in the world, as explored in a documentary by National Geographic.

Shown on September 5th at a premier event in the auditorium of the Emirates Palace in Abu Dhabi, "Megastructures: Abu Dhabi Super Tunnel" describes in detail the Strategic Tunnel Enhancement Programme (STEP), which was completed in 2014.

STEP oversaw the construction of a tunnel about 40 kilometres long in order to collect the waste waters of the island and mainland of Abu Dhabi by means of gravity, and direct them to a treatment plant in Al Wathba.

Salini Impregilo took part in the project, working on two of the three lots (T-02 and T-03) awarded to contractors. It drilled a tunnel of 25 kilometres with an excavation diameter of about seven metres, and 10 access shafts with depths varying between 40 and 80 metres. The Group used sophisticated, mechanised excavation technology never previously deployed in Abu Dhabi.

The project was particularly complex from a technical and organisational point of view because it involved the simultaneous use of five Tunnel Boring Machines (TBMs) at earth pressure. As they excavated, the TBMs simultaneously coated the tunnel with prefabricated concrete.

Both the hydraulic tunnel as well as the access shafts were covered with a special membrane to protect the concrete structures from the aggressive environment, enabling them to endure for at least 100 years.

Once again, a special documentary gives testimony to the kind of projects pursued by the Group throughout the world: grand, distinctive and technologically advanced.