Planning for the construction of two 4.5 m internal diameter cross harbour tunnels under the entrance to Durban Harbour is well advanced, with invitations to contractors to prequalify for the job about to be issued by Ethekwini Water & Sanitation, the client.The first tunnel, about 530 m long, will carry services (sewage mains, 33 kV cables, etc.). It has to be commissioned by mid-2006 to allow the existing utility tunnel (an immersed tube, constructed some 50 years ago) to be demolished to make way for the widening and deepening of Durban Harbour by the National Ports Authority.The second tunnel (provisional at this stage) is intended to serve as a people mover tunnel between new tourist and residential developments on the north and south sides of the harbour. It will be between 750 m and 1,000 m long depending on final design, and coupled to long cut-and-cover moving walkway (or light rail) declines, and/or lift shafts.Both tunnels are foreseen to be driven at a maximum depth of about 35 m below sea level, primarily through marine sediments (dense, fine-to-medium sands and silty clays, with some soft clayey sandstone on the south bank for the last 150 m or so) using a slurry-type or EPB pressurised face TBM, with a precast concrete segmental lining, 4.5 m ID. No secondary lining is envisaged. The project will also include the construction of terminal structures and temporary and permanent access shafts, varying from 10 m to 20 m deep according to the grade of the north and south bank declines, which are envisaged to vary between 12% and 20% depending upon the capability of the TBM and associated segment and muck transport systems. Equipping of the new utility tunnel and demolition of the old one (after decommissioning and stripping out) also form part of the project.Interested contractors may get more information from consulting firm Goba Moahloli Keeve Steyn (GMKS), who prepared prequalification documents, tel. +27 312071525, fax +27 312071080, e-mail jamesm@gmks.co.zaPrequalification documents may be obtained as from 10th August, 2004 from Ethekwini Water & Sanitation, 3 Prior Road, Durban, Kwazulu-Natal, South Africa. Contact Ian Duncum, tel. +27 313024645, fax +27313024549, e-mail iandu@dmws.durban.gov.zaNon-compulsory project briefing to be held on site at the Durban harbour entrance on 16th August, 2004. Documentation return date is 7th September, 2004. Formal tender documents will be issued to prequalified consortia at the end of October. Work is expected to start in January 2005. 31-32/04.