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Rio prepares for international games Oct 2011
Peter Kenyon, TunnelTalk
A major World Cup and Summer Olympic Games infrastructure project in Brazil has come a step closer following breakthrough at the Grota Funda tunnel in Rio de Janeiro.

Twin-tube Grota Funda highway portals

Contractor Odebrecht completed excavation of the 1.1km twin-bore tunnels that form a critical element of a wider 25km three-lane highway bus rapid Transit Transoueste project for Rio Prefeitura.
The scheme is one of three major transportation projects designed to meet Rio de Janeiro's metropolitan transportation requirements in time for the football World Cup in 2014 and the 2016 Olympic and Paralympic Games.
The BRL 692.1 million (US$ 393 million) project is part of Rio de Janeiro Mayor Eduardo Paes's infrastructure strategy and will benefit the community by making journey times between Barra and Santa Cruz in the southern suburbs 150% faster at peak times.
The tunnel alone will save drivers an estimated 40 minutes at rush hour by replacing a dangerous and narrow 5km section of the existing Avenida das Americas, which currently winds its way around a small 250m high peak. Two of the lanes on the completed highway will be for cars, with a third lane reserved for buses only.

Aerial view of the Recreio dos Bandeirantes portals

The twin tunnel tubes feature a 100m2 cross-section area of 14m wide x 8m high. It was excavated using drill+blast through Pedro Branca solid rock consisting of volcanic diabase dikes. The first blast was carried out at a special ceremony on September 15, 2010. In all 400 tonne of explosives were used.
Sandvik drill jumbos were used for drilling, that typically involved 165 holes at each face, depending on rock conditions which comprised a mixture of granite and gneiss.
Odebrecht Engineer Antonio Hora observed: "It was 100% granite at one moment and then 100% gneiss the next, or a mix."
At the south-western portals soft soil conditions for more than 100m were excavated using front end loaders and supported with shotcrete.

Drill+blast breakthrough

Excavation teams experienced Class 1 rock classification in very hard granite according to Hora. He said it took up to two and a half minutes to drill each 4m long hole.
"We initially started to drill 4.5m long holes but noted that we were only clearing 4.1m. However a team of trouble-shooters appointed to follow mechanical and electrical conditions in the headings proposed reducing the drilling length to 4m," explained Hora.
"This proved much more efficient clearing 3.9m with the improved benefits suiting the drilling patterns and explosive charges," he added.
Workshop manager Gilberto Alves explained that Sandvik RT 300 button bits and 4.9m long R38 drifter rods were used.
"The rods achieved 3,500 drill metres and, with regrinding every 24 drill metres [6 holes] we achieved more than 430 drill metres with the drill bits getting up to 18 regrinds on site."

A Sandvik jumbo drill rig (left) and laying the charges (right)

Excavation followed a 13-hour cycle comprising 4 hours drilling (including bolt holes), 2.5 hours charging, 4 hours mucking out, 1.5 hours shotcreting and 1 hour surveying. This allowed for three blasts a day in the twin bore tunnels.
Fitting out, paving, ventilation and fire safety installation work is continuing.

           

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