Northumberland Strait Crossing Confederation Bridge

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Northumberland Strait CrossingConfederation
Bridge

• New Brunswick, Canada
• Will Astley
• Jonathan Richards

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Outline

• Introduction
• Geology
• Foundation Design Considerations
• Solution
• Construction Sequence

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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

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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

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Geology - Stratigraphy

• Extreme vertical/horizontal variations owing to
  the estuarine/fluvial environment of the strait
• Complex interlayered sequence of sandstones,
  mudstones, siltstones and conglomerate

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Geology Rock Types

• Glacial Till varied grading, mixture of
  sand/silt, 193 kPa, f 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, f 15, oriented with bedding planes

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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

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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

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Construction Sequence

• Dredge Overlying Material
• Excavate Trench
• Grout Bags
• Place Pier
• Tremie Concrete

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