Sandvik jumbo’s on track for Rio Olympics

Published 2011-10-12 23:04:42

As part of the Mayor of Rio de Janeiro, Eduardo Paes’s transportation strategy for the 2016 Olympic Games, the Grota Funda Tunnel forms part of the first of three infrastructure schemes designed to meet the City’s Metro requirements; featuring dual lanes plus a third lane exclusively for buses.

The BRT Transoeste (Bus Rapid Transit) will benefit the local population by making journey times between Barra and Santa Cruz in the southern suburbs 150% faster at peak times.

In a contract awarded by Rio Prefeitura, main contractor Odebrecht’s contract includes constructing or upgrading 25 km of three-lane highway and a 1.1 km twin tunnel through a 250 m high peak.

The tunnel alone will considerably reduce travel times by replacing a narrow, twisting 5 km highway section of the existing Avenida das Americas around the small mountain, taking up to an hour at peak rush hours.
It forms a key element of Odebrecht’s contract and had passed the 50% excavation mark by early June thanks to good rock conditions at the City or north east portals, together with the reliability and performance of a fleet of Sandvik jumbo drill rigs and tools, according to Odebrecht Engineer, Antonio Hora.

The twin tunnels feature a 100 m2 cross section area with a 14 m width and 8 m height.  It is being excavated by drill and blast techniques using the Sandvik drill jumbo’s for drilling duties; including a 3-boom Sandvik  Axera T08 390C and a Sandvik 2-boom DT 820.

Typically the jumbo’s are drilling 165 holes at each face, depending on rock conditions, which comprise a mix of granite and gneiss –“100% of granite at one moment and then 100% gneiss the next, or a mix,” said Antonio Hora.

Meanwhile at the south western end, both portals have experienced soft soil conditions for more than 100 m.  This required excavation with front end loaders followed by shotcreting.

Currently the Sandvik jumbo’s are operational in all four adits, experiencing Class 1 rock classification in very hard granite, confirmed Engineer Hora, adding that it was taking up to 2.5 minutes to drill each 4 m long hole.

“We initially started to drill 4.5 m long holes but noted that we were only clearing 4.1 m.  However, a team of trouble shooters appointed to follow mechanical and electrical conditions inside the tunnels, proposed reducing the drilling length to 4 m.”

“This proved much more efficient clearing 3.9 m with the improved benefits suiting the drilling patterns and explosive charges,” he added.

Every 2 m a line of seven resin-type rock bolts are inserted which, once again can be increased to suit the rock conditions.

Relying on Sandvik RT 300 button bits and 4.9 m (16 ft) long R38 drifter rods, Workshop Manager, Gilberto Alves, confirmed that he was getting excellent results from the tools.

“The rods are achieving 3500 drill metres and, with regrinding every 24 drill metres (6 holes), we are achieving more than 430 drill metres with the drill bits by achieving  up to 18 regrinds on-site.

The Sandvik RT 300 button bits feature a 6 mm front flushing hole and have a 51 mm (2 inch) diameter to provide high penetration rates, straighter lines, longer bit life and reduced energy consumption.  The system has a single super grade of cemented carbide, designated XT48, and a universal face design.

A 13 hour cycle is being undertaken by Odebrecht comprising 4 hours drilling – including bolt holes; 2.5 h charging; 4 h mucking out; 1.5h shotcreting; and 1 h surveying.

“This allows us to undertake three blasts per day in the twin tunnels,” said Antonia Hora.