Page 7 - TunnelTalk Annual Review 2012

Extreme excavations planned for
It is planned as one of the largest and most challenging projects ever: a privately- funded US$3.5 billion, 52.5km TBM twin-tube rail tunnel between Argentina and Chile, through the mighty Andes. Under the leadership of the Argentine investment company Corporación América, the international consortium is advancing the project towards an international request for qualifiers to take part in one of the boldest infrastructure projects in South America.
Figures show that some 83% of 45 million tonnes of cargo that travels annually between the South American east and west coasts at the latitude that connects Buenos Aires and Santiago, goes by ship. Two-thirds of the rest, some 4.9 million tonne each year, crosses the Andes via the Cristo Redentor Pass, a steep mountain road with an altitude of 3,200m that includes a 3km-long tunnel.
“It is the best option by land, but this has become a major bottleneck,” said Corporación América Project Director Nicolás Posse. “The route is also closed 45 to 60 days per year by heavy snowfall.” The road, with its 26 hairpin bends and steep inclines, cannot be widened.
There was a fragile passenger railroad that crossed the Andes around the desired latitude of the planned new Bioceánico Aconcagua route, but the Ferrocarril Trasandino Central was closed in the early 1980s and it is not considered feasible to upgrade and reopen it as a cargo railway.
In the meantime, trade between South America and emerging Asian countries, including China and India, is increasing rapidly. Corporación América projects that by 2040, 70 million tonne per year will be transported to opposite sides of the South American continent. An improved land connection between Argentina and Chile seems inevitable. In 2008, Corporación America proposed an all-weather freight railway line to the Governments of both Argentina and Chile.
The Bioceánico Aconcagua has a total track length of 205km and includes a 52.5km-long twin-tube bored base tunnel. It connects directly on both sides of the Andes with the existing rail and highway infrastructure. When complete, the first tube of the proposed truck-on-train freight forwarding system would transport 24 million tonne of cargo/year, increasing
Andes rail link
Armand van Wijck, TunnelTalk
Fig 1. Alignment of the 52km trans-Andean link; Fig 2. Alignment under Cristo Redentor; Figs 3 and 4. Construction and operating data of the new link
to 77 million tonne/year when both tubes are in operation.
Some 14 alignments of varying length and gradients have been studied, including one that featured a ‘helter-skelter’ declining circular tunnel design to ease the gradient over a short distance. In addition to the main base tunnel a further 20km of underground alignments, split into 33 different tunnels, are incorporated into the project’s overall design.
Project goals
The selected alignment is named after the peak of Aconcagua, which, at 6,960m, is the highest mountain in the Western Hemisphere. The tunnel itself will be excavated just south of the mountain, beneath the Cristo Redentor Pass (Fig 1).
According to Corporación América, which consists of Empresas Navieras SA from Chile, Mitsubishi Corporation of Japan, Geodata, Italy, and Contreras Hermanos of Argentina, the proposed rail line would reduce travel times through the Andes from 12hr to 4hr, saving tens to several hundreds of dollars for each tonne of cargo.
The Governments of Argentina and Chile formed a bi-national commission to evaluate the project, call for an international tender, and regulate the future concession.
A preliminary environmental impact assessment has been completed and after submitting its recommendation to the Governments of both Chile and Argentina, the commission will call for expressions of interest and release an international tender for the concession. “By the end of 2013 we hope to start first excavations,” said Posse.
It is a huge task ahead. The region’s geology consists of a number of major fault zones, with overburdens rising in places to more than 1,600m. “We have to deal with several possible hazards, including volcanic intrusions, slaking and high-temperature thermal waters,” said Posse. Designers have modelled the tunnel and its surroundings in 30 homogeneous segments. For each reach they have determined the associated risks and possible solutions.
Double shield TBMs with a precast segmental lining are anticipated as the methods of choice.
“I visited the Gotthard Base Tunnel project in Europe myself,” said Posse. “We have a more aggressive approach in mind, using four 10m diameter TBMs for each 8.5m i.d. tube to help speed delivery of the project. Two TBMs will start boring steep access adits to the main tunnel alignment at about 17.5km from the tunnel portals. At the same time, a third TBM will start from
From left: Existing high altitude Cristo Redentor crossing; Trucks will board trains at transportation hubs
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