Deep tunnel sewer programme moves one STEP closer in Abu Dhabi

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Abu Dhabi Sewerage Services Company (ADSSC) has completed construction of its new main sewer tunnel - the primary feature of the city’s Strategic Tunnel Enhancement Programme (STEP).

STEP, started in 2008, includes a 41-kilometer long sewer tunnel and also 43 km of smaller diameter new link sewers up to 3 meters in diameter, and a large pumping station at Al Wathba Independent Sewerage Treatment Plants.

The infrastructure will triple the capacity of Abu Dhabi’s sewerage network with the aim to alleviate pressure on the existing system.

When completed, STEP will provide for an average wastewater flow of 800,000 m3/day, with an ultimate capacity of 1.7 m3/day by 2030.

In addition to increasing capacity; the gravity tunnel and the link sewers feeding into the tunnel will enable ADSSC to eventually decommission 34 existing pumping stations, in a move to save operation and maintenance costs over its 80 year life.

Consultancy CH2M HILL oversaw the delivery of the tunnel, which was built using trenchless technology. It is expected to be finished in 2015 and is set to be one of the largest and longest gravity-driven sewerage networks in the world.

Bob Marshall, programme manager of CH2M HILL STEP, said: “We used a total of eight huge tunnel boring machines to excavate the 41 km of deep tunnel so the recent breakthrough of the last TBM (tunnel boring machine) was celebrated as a significant programme milestone and one we have been working towards since 2008. With the deep tunnel complete, we can shift our attention to the network of link sewers that connect into the tunnel on both Abu Dhabi Island and the Mainland.”


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