Rion-Antirion Bridge, Greece.

1. Rion-Antirion Bridge, Greece. Presented by James Mitchell, Dan Bundy and Hung Nguyen

2. 1. Introduction 1. SITE DESCRIPTION • Spans 2880m across Gulf of Corinth • Links town of Rion to mainland Greece • Previous crossings by boat took 45 minutes, reduced to 5 • Completed August 2004, 4 months ahead of schedule • Second longest cable stayed deck in the world • Cost €630 million Antirrio Rio

3. 2. Geology • Geological conditions • Subsoil • Steep slopes on each side and long plateau seabed 65m below water surface. • Site investigations found no bedrock at depths of 100m • The weak alluvial deposits of interbeded granular and cohesive layers continue down to a predicted 1000m. • Interspersed with liquefiable sand pockets

4. 2. Geology • Geological conditions • Tectonic movement • The Corinth Rift is caused by a geological feature known as a ‘Graben’ • The rift is relatively young at 2-5 million years old • North and south sides separating due to tectonic forces by up to ~15 millimetres per year • Uplifting of its southern shore approximately 1mm per year.

5. 2. Geology • Geological conditions • Seismic activity • This area is one of the most seismic regions in Europe. • Seismicity lies between antithetic faults, the Alepohori fault dipping north and the Kaparelli fault dipping south • The circle symbols on the map represent historical earthquakes with a magnitude greater than 5.5 Richter.

6. 3. The challenges • An exceptional combination of geological conditions present many challenges in the engineering of The Rion Antirion Bridge: • Creating stable foundations on porous granular soils in deep seabed • Reduced effective strength • Tectonic movement • Possible seismic activity • Isolation of bridge deck to seismic energy- reduce sway • Reduce dynamic response under wind loading • Liquefaction of soil • Movement of foundations • Expansion of rift • Elongation of bridge deck

7. 4. Engineering solutions • Possible Solutions • Could not tunnel due to seismic activity • Bridge only option • Minimum number of seabed supports desired • Two choices: • Suspension • Cable Stayed • Antirion side of gulf possessed slope stability problem • Could not install large ground anchors needed for suspension bridge • Cable stayed bridge only option

8. 4. Engineering solutions • Foundation • Soil strengthened with steel inclusions • 200 Hollow steel tubes 2m in diameter, 25-30m long driven into soil beneath each pier • Covered by 3m thick gravel layer to reduce shear force transfer to substructure • 90m diameter footings rest on top • No connection between footings and gravel • Pylons are able to lift or slide up to 2m in an earthquake

9. 4. Engineering solutions • Bridge deck • Bridge deck is fully suspended by the cables • Isolated as much as possible from piers to reduce seismic impacts • Longitudinally, expansion joints allow adjustment to thermal and seismic movements • Deck can withstand movements of 2m between each set of piers • Fuse restraints installed on pylons, as gulf expands load cell monitors identify change in load and dampers can be extended • Allow for 2-5m expansion over 125 years

10. 4. Engineering solutions • Bridge deck • 4 Dampers and a fuse restraint at each pylon isolate bridge deck in transverse direction • 10500kN fuse restraint keeps deck rigid during high winds • Fails under seismic events allowing bridge to swing with 3500kN dampers • This is the only connection between pylons and bridge deck • Deck designed to move 2m in all directions

11. 5. Construction methods • Construction of the foundation footings in a dry dock. • In parallel, driving steel inclusions is carried out to strengthen soil. • Towing and mooring of these footings to a wet dock site. • Immersion of the foundations at final position. • Erection of the prefabricated bridge deck  using the balanced free-cantilever technique