Impregilo wins US$ 200 million Abu Dhabi tunnel contract

Impregilo has secured a US$ 200 million contract to build an extra 10 km of hydraulic tunnel for Abu Dhabi Sewerage Services Company (ADSSC).

The Italian construction group is already building the first 15 km of the tunnel - a ground-breaking project in the region known as the Strategic Tunnel Enhancement Programme (STEP), which aims to overhaul existing waste water systems.

On top of its initial contract for the tunnel, the new extension takes the total value of Impregilo's STEP contracts to US$ 443 million.

ADSSC has tendered three contracts for STEP - a deep gravity sewer tunnel that will be 42 km long overall and will run from the northern part of Abu Dhabi Island to a treatment plant in Al Wathba on the mainland.

ADSSC aims for the three tunnel sections to be completed by 2012, replacing some of the existing pumping stations in Abu Dhabi and decreasing the pressure on the existing system.

In addition to the new length of tunnel, Impregilo's contract involves construction of four access shafts to depths of between 60 and 80 m, as well as links to the main tunnel.

"The project presents significant technical and organisational complexities," Impregilo said.

"It involves simultaneous use of two earth pressure balance tunnel boring machines for pressures up to 8 bars, to bore and simultaneously line the tunnel with prefabricated concrete elements".

The company explained that both the hydraulic tunnel and the access shafts will be lined with a special membrane to ensure the concrete structures are fully protected from the aggressive environment for a minimum term of one hundred years.

It is the first time mechanised boring technology has been used in Abu Dhabi, Impregilo said, adding that the work will be completed in "just over three years".

Impregilo has constructed six desalination plants in Abu Dhabi since 1987.