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Single pass jumbo speeds Quebec bore

WorldWatch

DEVELOPMENT OF a new rock drilling rig has allowed more efficient design of a water supply tunnel on a hydroelectric power plant in Quebec, Canada.

Use of Sandvik Tamrock Axera T12 DATA tunnelling jumbo rigs allowed Quebec contractor EBC to excavate a largely oval cross-sectioned headrace tunnel for the Toulnustouc dam.

The profile will reduce water turbulence, resulting in more pressure at the turbines and better power generation.

EBC won the e53M, two year contract from client Hydro Quebec to build 8.3km of the 9.8km drill and blast tunnel that will carry water to a generating station about 120km north of Baie Comeau.

The tunnel cross-section is big - 11m wide and 13m high. As earlier Tamrock Jumbos could only reach 12m, the tunnel would have had to be excavated in two stages, with an 8m high horizontal drilling pass and the remaining 5m by vertical drilling.

But EBC wanted to drill the tunnel in a single pass to save time and money, so Tamrock came up with the three-boomed machine. The fully automated rig is pre-programmed and uses laser guidance to drill the tunnel face, allowing all three booms to be operated by one person.

Three jumbos began work in summer 2003, two forming the main tunnel, while the third drilled an access tunnel. Progress was fast, with 600m of tunnel finished in two months. Excavation was expected to finish in February.

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