Impregilo seals sewage tunnel deal

Impregilo has won a US$ 243 million contract to build the first 15 km section of a 40 km-long sewage tunnel in Abu Dhabi.

The tunnel will collect waste water on Abu Dhabi Island and mainland and carry it to the treatment plant in Al-Wathba.

The project forms part of the Strategic Tunnel Enhancement Programme (STEP) which is being developed by the Abu Dhabi Sewerage Services Company (ADSSC).

Impregilo will build the 6.3 m diameter tunnel between Mussafah and Mafraq with six, 40 to 50 m deep access shafts.

In a statement Impregilo said STEP is a technically complex project.

"It will involve simultaneous use of three earth pressure balance and tunnel boring machines to excavate and at the same time case the tunnel with precast concrete sections.

"This is the first time this advanced mechanised excavation technology has been used in Abu Dhabi," the company added.

The hydraulic tunnel and the access shafts will be lined with a special membrane to keep the concrete sections fully protected against the aggressive environment, for a minimum of 100 years.

CH2M Hill, an international project management and engineering company, has been appointed programme manager.

Work on the tunnel is expected to start at the end of the year and will be completed in the second half of 2013.