The contract to build the 15.2km long Cuncas 1 water supply tunnel in Brazil will be let by the end of this year by the Brazilian Ministério da Integração Nacional (the Ministry of National Integration). The tunnel, with an estimated cost of US$32M, will be the first of ten totalling 50km let on the São Francisco water diversion project, and is likely to be tendered as a unit price contract.
The “Projeto de Transposição de Águas do Rio São Francisco para o Nordeste Setentrional”, has been designed to bring water into Brazil’s driest north east areas via 680km of canal. The 3m-6m wide canal will be lined with a geomembrane and 500mm thick plastic fibre reinforced concrete slabs.
The 10 tunnels along the route will range in diameter from 7m-10m, and, with the exception of the power intake tunnels, will be unlined except for a concreted invert.
The Cuncas 1 tunnel will be a 9.3m wide horseshoe shape constructed through a complex geology including hard massive sandstones, jointed phyllites, jointed mica schists and hard massive sandstones. As with the other tunnels, lining will be restricted to a concrete invert. The original design was developed in 2001 and the entire tunnel was expected to be built using drill and blast from four faces with a 772-day completion schedule. However, due to an acceleration of the first phase completion to mid 2006, the possible use of TBMs has been brought onto the design board. A final decision regarding the construction method should be made in the first half of 2004.
The diversion canal will carry up to 99m3/s of water from the São Francisco River to the four states of Pernambuco, Rio Grande do Norte, Paraíba and Ceará. Eleven pumping stations and seven power plants will also be built along the canal route.
