The programme includes a new deep gravity sewer tunnel 45 km in length taking the main sewer flows from Abu Dhabi to a new treatment works outside the city and a series of link sewers connecting into the deep tunnel.
The tunnel varies in diameter from 4.5 m to 5.5 m and is to be constructed with seven Earth Pressure Balance (EPB) TBMs which are launched and operated from seven deep shafts.
COWI is carrying out the detailed design of one of the major contracts that comprises of 15 km of deep tunnel, six deep shafts that vary from 50 m to 60 m in depth and all ancillary works, (the STEP T-02 contract).
Environmental challenges
The design of the permanent concrete works is challenging as the site has very severe environmental conditions including high levels of chloride and sulphate in the groundwater. The chloride levels are considerably higher than seawater thus giving a major challenge for the durability design.
In order to deal with this severe environment, COWI’s leading edge durability design solutions have been used which has enabled the concrete mixes to be designed to meet the 80 year lifetime required of the structures.
