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The long hop

Greece's spectacular Egnatia highway is now over half complete, reports Adrian Greeman.

If you want bridge construction then Greece has it - in spades.

Not only has the country just inaugurated one of Europe's biggest and most spectacular crossings, the Rion-Antirion, over the mouth of the Gulf of Corinth. In the north it is working on more than 600 bridges, with at least 40 major structures more than 200m long, and a couple just topping 1,000m.

These form part of the ongoing Egnatia highway project, an even bigger and more difficult challenge than the just-in-time infrastructure for the Olympics. Begun in the mid-1990s, the dual two-lane highway is now more than half complete with most of its eastern section, from Thessaloniki to the Turkish border, carrying traffic.

One critical eastern link remains to be done, says Guy Hindley, project director for KBR (formerly Brown & Root), which has been working with Greek client Egnatia Odos since 1996. This stretches across the environmentally sensitive Nestos Delta wetlands; it will feature one of the largest bridges with 20 spans carrying the road for 945m.

Although parts of the road have opened in the west, where most of the project focus has now moved, conditions here are much more difficult than in the east. The route to the Adriatic port of Igoumenitsa rises through complex mountain terrain, including the Pindos mountains - 'the Grecian Alps'.

The highway must leap from tunnel to tunnel here via some high and often dramatic bridges, across tumbling valleys with limited access and often difficult slip-prone ground for foundations.

The region has a mixed and tortured geology, considered the among the most complex in Europe. It is additionally the most seismically active.

All the bridges are in concrete and built using relatively well tested techniques including incremental launching, travelling formwork systems and balanced cantilever. Bridges with shorter spans up to about 40m length use precast beams and cast insitu top slabs.

'Some of these, such as the Votonosi, push the balanced cantilever technique close to its limit, ' says Mike Agius, project manager for the 110km long western section. Total length of the twin bridges at Votonosi is 478m with just two piers for each of the separate carriageways.

Kristallopigi bridge, just 16 km from Igoumenitsa, sweeps the road in an elegant curve across a flat valley before it starts a climb into the Pindos mountains. The just-finished twin 13.5m wide decks are curved on a 450m radius, the inner measuring 638m long and the outer 848m.

They were cast insitu, with a moving scaffold used to make the 2.7m deep post-tensioned box girders. Designer was Athens based firm Denco. The bridge links to an unbuilt motorway section across a large and difficult mountainside landslip. Therefore a section of so-called 'operational Egnatia' link road - upgraded national highway - will carry traffic at present. Contractor was Michaniki/Atti Kat The Michaniki/J&P Avax/Athina/Mochlos JV has been working on the 481m long Megalorema bridge, which continues the road just beyond the connecting Votonosi tunnel.

The first of two incrementally launched decks is complete with the steel nose section recently moved over to begin the second; a work shelter which allows winter working in the often bitterly cold mountains will follow. Rock sockets were used for foundations although some piling was also done; box section piers carry the deck over a 30m deep valley. A push launch system for the deck sufficed for seven of the mainly 45m spans but was supplemented with winch pulling for a remaining four, to overcome friction effects. Designer is T Tsiknias & Associates In the Pindos mountains the high links between tunnels include the dramatic Votonosi bridge, one of several which have given Greek contractors valuable experience in large scale balanced cantilever work. Huge 20m deep rock sockets - 'more like tunnels than piles', says Agius - carry four hollow section box piers, 5m by 8m and rising up to 40m high. With the deck box depth reaching 12m, height for the bridge is 52m.

Central span of the twin deck bridge is an impressive 230m, cast in 3m to 5m long sections using four sets of Norwegian NRS travelling formwork. A special cantilever truss was used to infill the 25m connecting to the tunnel entrance at the eastern end, explains principal structural engineer Kamran Kashani from the Egnatia Odos regional office.

Contractor Megalorema is currently finishing the stitch infill between the cantilevers for the main span. Designer is Domi.

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