On 08.10.2013 boring of the 41 km-long Abu Dhabi deep sewer tunnel was completed at internal diameters up to 5.5 m. The final section to be completed was the 4.7 km from the Officers’ Club area to the Abu Dhabi National Exhibitions Centre. The 90 m-long, 450 t TBM mined at a depth of 32 m through dolomitic siltstone, clay, mudstone and gypsum without any surface accidents. The second longest gravity-driven tunnel in the world, STEP now stretches from Al Mushrif to Al Wathba.The construction is one of several phases in the USD1.46bn STEP project, which will also include 43 km of sewerage links varying in diameter from 800 mm to 3 m.There is a main pumping station at the end of the tunnel, which has a capacity of 30 cu m/sec and an expected capacity of 1.7 million cu m of sewage by 2030. Work continues on the remaining parts of the projects, including the main pumping station and the sewerage links.Last January, 2013 Impregilo completed the 25 km tunnel for T-02 and T-03 contracts using five TBMs. The project will be completed in 2015. Click here, here and here for further information and ae/16 for tunnelbuilder archive. 45/13.