Achieving the Impossible with the Rion-Antirion Bridge — Part I
The following is the story of how a hundred year-old engineering dream was realized: a bridge crossing the Gulf of Corinth in Greece. But this would be no regular construction — it brought together an unparalleled series of environmental, physical and geographical challenges.
This would be a project involving solutions for a range of challenges, the likes of which had never been seen before. Ultimately, it would prove to be a testament to success where, according to some, failure was the only likely outcome.
Achieving the Impossible with the Rion-Antirion Bridge
“The Rion — Antirion Bridge had to overcome an exceptional combination of adverse environmental conditions.” — Institute of Civil Engineers
More than a hundred years ago, an elder statesman dreamed of a new bridge in Europe. Of a way of cutting out an arduous 240km detour by road, or a 45-minute ferry ride often subject to bad weather. And of replacing it with what would eventually be an easy five-minute drive.
Though it would be many years before this dream became reality, the challenge was set. But the sheer scale of that challenge, of the obstacles and unforeseen difficulties it presented, would only be revealed in the fullness of time.
The vision of Charilaos Trikoupis, then Greek Prime Minister, would be to cross the Gulf of Corinth, connecting Rion on one side with Antirion on the other. Opening up a whole new set of trade and travel opportunities from mainland Greece into the otherwise remote Peloponnese.
When it was eventually completed in 2004, just in time for the Greek Olympics, it would be longest bridge of its type anywhere in the world.
“Rion Bridge” by yachtvidgis
The final structure, comprised of 368 cables and 4 towers, looks deceptively simple. But beneath the surface, comes the story of one of the greatest engineering feats of our time, albeit one with many stops, starts, and dead-ends along the way. Not to mention two years of planning before building could even begin. The end result would receive awards from as many as nine different international scientific bodies — but getting there would be a herculean task.
The Rion Antirion Bridge now stretches almost 3km in length. Not only is it very long, it is almost completely earthquake proof. Which is a major consideration given that the crossing is set on an active seismic fault line. It is said to be able to resist quakes reaching up to 7.4 on the Richter scale. And this was put to the test back in 2008, when the area was hit by a tremor that caused buildings to collapse up to 25 kilometers away, killing two and injuring more. The bridge meanwhile was left unscathed, allowing emergency services to pass through as normal.
Construction of a pillar — GEFYRA — Nikos Daniilidis
But seismic activity wasn’t the only challenge the project would pose. The sea in the Gulf of Corinth is especially deep, with weak soil on the seabed. Add the strong winds the area is subject to, as well as the regular land movements at each side that could result from tectonic shifts, and it becomes an engineer’s nightmare. The effect of a collision with a large ship would also have to be factored into the structure, and reportedly this would extend to the potential impact of a 180k ton vessel travelling at 18 knots.
Beam, Arch, Suspension or Cable-stayed?
Rio Antirio Bridge: Challenging Earthquakes
The first challenge to overcome came from under the sea. When the project began, it still wasn’t clear how its foundations would be set, with it being in waters up to 65m deep. No other bridge had been built to this depth before. In short, the bridge would have to be an exceptional work of engineering. But it would also have to conform to one of four standard designs — beam, arch, suspension or cable-stayed.
While beam bridges are normally used for the longest crossings, and must be supported from below, they also block ship traffic and so didn’t fit the need. An arch bridge on the other hand would allow ships to cross, but would also be far too long. Four times longer than any arch bridge in existence, to be precise. So arches were also out. The third option, suspension bridges — where cables both stretch across and support a roadway — were dismissed as too costly. All of which meant there was really only one option, a cable-stayed bridge — meaning supported by cables hanging directly from supporting towers. Having said that, no such bridge yet built would have met the special, demanding conditions in the Gulf of Corinth.
The proposal that was eventually successful, from French firm Vinci, promised the longest suspended road span yet achieved on this type of bridge, at 2.2 meters of roadway hanging from four towers, which would have to support its entire, considerable weight. Vinci would ultimately form a consortium with local construction firms called Gefyra (appropriately enough, the Greek word for “bridge.”)
Bridge Elevation from Gefyra Construction
Laying the Foundations
In an early, major setback, Vinci discovered that the seabed beneath the crossing was made up of sand and silt for hundreds of meters down. With no solid bedrock, even at 450 meters, it looked impossible to build foundations, and Vinci’s initial design wouldn’t work.
The problem was compounded by the very real risk of earthquakes. Tremors could turn soft ground to liquid, in a process known as soil liquefaction. And as you might guess, this could have catastrophic results, as occurred around Kobe, Japan in 1995, when a major earthquake caused bridges and roads to collapse, resulting in the death of more than 6000 people.
In other situations, the sand might be drained, or the ground compacted, removing water from the area, but for obvious reasons that wasn’t an option under the sea.
The answer to this first challenge came from nature. More specifically, from a type of grass called vetiver, which is used as a hedge against erosion. Harvesting it is difficult, especially as its roots can grow up to 4 meters long. It was noted years ago that when it grew on riverbanks, it had the effect of stabilizing the ground around it.
Following the same logic, under the bridge piers, Vinci proposed installing 200 steel rods driven into the sand. Each rod would be at least 25 meters long. While they wouldn’t reach the sea above — and the bridge wouldn’t rest on them, standing more than a meter above –the rods should still prevent liquefaction. It was the first time this type of reinforcement was attempted on a bridge — and if successful, would be an elegant, groundbreaking solution.
Would this never-before-attempted solution work? To find out — along with how the engineers would deal with a whole range of other challenges — read on for part two.
Soil reinforcement — Institution of Civil Engineers
This article is part of The Paragon of Innovation series by Amdocs Delivery exploring some of the most exciting achievements and developments in technology and engineering. In each case, we look for the innovation at the heart of all such great achievements.
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