Impregilo has been awarded the third and final lot on Abu Dhabi’s 40km underground Strategic Tunnel Enhancement Programme (STEP). Worth US$200M, the contract includes the construction of 10km of 7m diameter water tunnel. In September 2009, the Italian contractor was also assigned the US$243M contract to build the first 15km of tunnel on the mega project put out to international tender by the Abu Dhabi Sewerage Services Company (ADSSC).
In addition to the tunnel, which will collect waste water and convey it to a treatment plant in Al Wathba, the project involves the construction of four access shafts to depths of between 60 – 80m, as well as the links to the main tunnel. The work will be completed in just over three years.
The project presents significant technical and logistical complexities, involving the simultaneous use of two EPBMs in pressures up to 8 bar, whilst lining the tunnel with prefabricated concrete elements.
This is the first time mechanised boring technology has been used in Abu Dhabi. 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.