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

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 1. SITE DESCRIPTION 1. Introduction Rio Antirrio

2. Geology  Geological conditions 1.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

2. Geology  Geological conditions 2.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.

2. Geology  Geological conditions 3.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.

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 3. The challenges

 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 4. Engineering solutions

Soil strengthened with steel inclusions 200 Hollow steel tubes 2m in diameter, m 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  Foundation 4. Engineering solutions

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  Bridge deck 4. Engineering solutions

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  Bridge deck 4. Engineering solutions

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