The first-ever TBM-driven tunnel in Paraguay, the Itay sewerage tunnel, is set for completion by the beginning of this month, bringing the project in ahead of schedule and within budget.
Breakthrough of the 2.4m diameter UNIDEUTSCH EPBM on the 3km long, 1.6m i.d sewer tunnel drive in Paraguay’s capital, Asuncion, was achieved at the end of June 2000. Final tunnel and shaft finishing was under completion as T&TI went to press.
Constructed by Argentinian contractor Benito Roggio e Hijos and designed by British consultant, Halcrow, the tunnelling has not been without setbacks. Tunnelling started in August 1998, but soon ran into problems requiring extensive modification to the TBM. A Halcrow spokesman was unable to clarify the nature of the technical difficulties with the machine, but told T&TI a lack of local experience with the technical aspects of the TBM further added to the project re-start schedule, resulting in a nine-month delay. The completion date was subsequently revised to November 11th 2000.
Upon restarting, the TBM achieved records of 743, 2m i.d. precast concrete rings in one month. The lining consists of five segments and a key, each 0.61m long with hydrophilic gaskets for waterproofing. Secondary lining is provided by cast in-situ 180mm thick mass concrete, cast in 10m lengths using a collapsible steel shutter with concrete pumped from the surface.
The scheme necessitated a detailed settlement analysis as it passes under the ‘Beverly Hills’ of Asuncion, through densely- compacted sands with a 30m maximum depth to invert.
The overall scheme involves a new treatment plant, a river outfall and 450km of collector sewers. and is supervised by a consortium of Halcrow and local firm INAREC. Funding is via the World Bank, the European Investment Bank and the Paraguayan Government. Client, CORPOSANA, the state- owned water corporation estimates the cost of tunnelling on the scheme to be at 1997 prices, US$17m.
Upon completion, the scheme will provide a sewerage collection and primary treatment for 25% of the population of Asuncion.
