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Bridges Round up

Bridges Round up

DMJM + Harris and Caltrans have received the Consulting Engineers and Land Surveyors of California Honor Award for the design and construction of the Rock Creek bridge, linking Mendocino and Humbolt Counties in California.

The bridge spans a deep Vshaped chasm, surrounded by forest, in a highly seismic area.

Refurbishment of the original bridge was impractical, and the project team opted on a slantleg structure carrying a curving box girder deck.

Unconventional foundation techniques were called for to cope with the difficult site conditions. Pier shafts - shafts tunnelled deep into the canyon walls at a perpendicular angle - were chosen for two reasons.

First they provide an elegant method to support the bridge structure, and secondly they also serve to stabilise the existing slopes because of the force exerted on the canyon walls.

However, the steepness of the canyon walls and the distances beneath the bridge made bringing in heavy equipment impossible. So, stepping back in history, the shafts were dug by hand, which proved to be the most effective and economic method.

The unusual design meant that unique seismic codes had to be agreed. But the bridge was completed successfully, on time and to budget.

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