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Slide rules Northern Greece is full of gorges slicing across Egnatia Odos' alignment.

'This project is a constant battle with the elements,' says Brown & Root design manager Iain Ure. 'We're finding landslips 0.5km long. Sometimes you ask: are we in the right valley?' Brown & Root project director Rod Capper agrees: 'People have encountered these problems before, but here the whole geomorphology is bad.'

In the Pindus mountains acute instability has resulted in large scale realignment of the highway. Appalling landslides caused one contractor to abandon work. The section is being redesigned to incorporate a 3km cut and cover tunnel.

On another section, two well-advanced adjoining sections allowed little or no flexibility of alignment. The 6km section grinds up a valley side at maximum 5% gradient and crosses the tail end of a landslide that would have been hugely expensive to stabilise. Design manager for the section Giles Wilkinson describes it as 'scree slopes, loose rock, hanging boulders the size of a house, cavities filled with clay and sediment'.

To traverse the aggressive hillside a design involving tunnels and four bridges was evolved.

However, investigative drilling by contractor Krystallopigi-Psilorachi joint venture discovered a stratum of clay below the rock in which the structures were to be footed. The original design was therefore unworkable.

Geological expertise was drafted in to find an alternative, shorter but steeper alignment 150m further up the hillside. The design, currently being produced, will eliminate the bridges with two deep cut and cover tunnels, 430m and 900m long. Gradient now exceeds the normal highway maximum of 5%, but the section is unbuildable otherwise, says Wilkinson.

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