The project involved the construction of two out of three lots of the STEP Programme (Strategic Tunnel Enhancement Programme), featuring the construction of a tunnel approximately 40 km long which is designed to collect the wastewaters of the island and mainland of Abu Dhabi by means of gravity and direct them to the treatment plant located in Al Wathba.

The works consisted of the construction of 25 km of the tunnel with an excavation diameter of approximately 7 metres and 10 access shafts with depths varying between 40 and 80 metres.

The project, which is particularly complex from a technical and organisational point of view, involved the simultaneous use of five TBMs (Tunnel Boring Machines) at earth pressure, capable of excavating and at the same time coating the tunnel with prefabricated concrete.
It is the first time that this sophisticated, mechanised excavation technology has been used in Abu Dhabi.
Both the hydraulic tunnel and the access shafts are covered with a special membrane which will guarantee the concrete structures total protection from the aggressive ambient and will last at least one hundred years.

The upgrading of the sewer system to meet the demands of future generations was an ambitious project, allowing for the treatment of an average wastewater flow of 800,000 m3 per day. 

Client: Abu Dhabi Sewerage Services Company (ADSSC) Abu Dhabi Water & Electricity Authority (ADWEA)