1. Northumberland Strait Crossing Confederation Bridge New Brunswick, Canada Will Astley Jonathan Richards

2. Outline Introduction Geology Foundation Design Considerations Solution Construction Sequence

3. Introduction Longest bridge in Canada at 13 km – Longest bridge in the world spanning ice-covered water Crucial transport link between PEI and New Brunswick – Replaced ferry service over the strait Completed in May 1998 after 4 years of construction Total construction cost $1 bn CAN

4. Geology - History Developed in pre-glacial times Permo-carboniferous rock overlain by glacial and marine sediments Surfical deposits ranging from fine sands and silts to 1 m diameter sandstone boulders Glacial till the predominant deposit varying thickness of 0.5 – 12 m In post-glacial times there was a number of changes in sea level Between 13,000 – 7,000 B.P. Glacial rebound and sea level changes produced undulating land Estimated at around 5,000 B.P. the strait became a continuous body of water

5. Geology - Stratigraphy Extreme vertical/horizontal variations owing to the estuarine/fluvial environment of the strait Complex interlayered sequence of sandstones, mudstones, siltstones and conglomerate

6. Geology – Rock Types Glacial Till: varied grading, mixture of sand/silt, 193 kPa, φ’ = 34°, c’ = 95 kPa Sandstone: fine/medium grained, ranging from well to poorly cemented, 16 – 22 Mpa, oriented with land Mudstone: poor quality, indurated rock/hard clay, 3.5 Mpa, oriented with bedding planes Soft Mudstone: “silty clay”, friable/brittle, 43 – 280 kPa, φ’ = 15°, oriented with bedding planes

7. Foundation Design Considerations Loading – Ice, Wind, Impact Short Construction Window Overburden (up to 12m in places) Soft Mudstone Issues – Bearing Capacity / Sliding Resistance Seabed up to 40m below water surface Three main criteria – Bearing Resistance – Sliding Resistance – Settlement

8. Foundation Design Considerations Bearing Resistance – Rock Mass Rating (RMR) classification system used for jointed rock mass. Use Engineering experience, judgement, geological review, core analyses and case record studies Sliding Resistance – Need to resist lateral forces Settlement – Computer Analyses Conducted – 10mm predicted

10. Construction Sequence Dredge Overlying Material Excavate Trench Grout Bags Place Pier Tremie Concrete