Andes link a priority for Chile-Argentina-Brazil Dec 2011
Peter Kenyon, TunnelTalk
- The proposed 14km Agua Negra highway tunnel linking Argentina and Chile through the Andes has made it on to a list of South America's top priority transnational infrastructure projects for the next decade. A study by consultant CIS Associados Consultores concludes that the strategically important Agua Negra tunnel to create an all-year central South American Atlantic-Pacific road corridor is both technically and financially feasible.
Alternative Cristo Redentor tunnel is often closed in winter
- The study also states that, if offered under a concessionary arrangement, the project would return 6% annually, enough to make the it viable under Chile's public investment policy. The Governments of Argentina and Chile have signed an agreement to create a body that can move the project forward to a tender and construction phase.
- From an original five tunnel alignments (Fig 1), two options were considered, a longer 14km alignment and a 5km tunnel higher up the Andes mountain pass (Fig 2).
- The longer route is selected because the entrance portals, at 3,950m on the Argentine side and 3,750m on the Chilean side, are at sufficiently low altitude, in relation to local weather conditions, to remain open year round. This would not have been the case with the 4,500m and 4,320m portals incorporated on the shorter route.
Geotechnical studies at 4,900m
- Additionally the 14km tunnel is considered to have a lesser environmental impact, and with the portals placed close to the existing mountain road at both ends only 2.7km of interconnecting new road would need to be built, compared to 30km for the shorter tunnel option.
- Construction of the tunnel will avoid the need to use the hazardous Agua Negra border pass and save 50km of steep and winding road that can take four hours to navigate. The pass is subject to winter closures and the only other crossing is via the 3,150m altitude Cristo Redentor tunnel in Mendoza, which is also affected by winter closures that create long traffic backlogs.
- A geotechnical survey of the preferred alignment for the twin bore Agua Negra tunnel, completed by Ecominera SA and Rizzo Associates SA, has identified outcrops of Choiyoi Group rock with intrusions of rhyolite, basalt and aplite dykes, sills and veins. The site is in the Rio Colorado fault zone that is located in the Rio Colorado, a superficial high-angle reverse fault. The survey also highlights other important regional faults that directly affect the tunnel, including the Quebrada de San Lorenzo and Quebrada Amarilla faults.
- As with all high altitude tunnels, where the rarified atmosphere creates an environment where engines create higher levels of carbon dioxide, ventilation is a particular challenge. A transverse system is selected, with semi-transverse and longitudinal systems chosen for sections adjacent to the portals.
- Inclusion of the estimated US$850 million project on the South American Council on Infrastructure and Planning (Cosiplan) list does not guarantee financing, but is expected to help drive the long-running plan forward.
- During his term of office that ended in January, former Brazilian President Luiz Iancio Lula da Silva committed to help finance the work through the Brazilian national development bank. Brazil is interested also in a new Andean crossing at Agua Negra to create an all-weather central Atlantic-Pacific road corridor between Porto Allegre in Brazil and Coquimbo in Chile. This would be of major commercial benefit to Brazilian traders wanting road access to Chile's Pacific coastal ports and on to China and the Far East.
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