The document summarizes the geological setting and engineering challenges for constructing a suspension bridge where the bedrock is granite located beneath 300m of glacial till and 200m of unconsolidated silt and mud, with the ends anchored in highly fractured shale that dips toward the water. Some of the challenges discussed include water ingress through fractures in the shale increasing weathering, slope failures due to clay expansion in the shale, and rapid scouring of the shale. The document outlines solutions such as anchoring directly into bedrock instead of shale, using concrete slabs with rock bolts over fractured shale areas, and locating anchor placements in zones with minor shale fractures. Bridge maintenance procedures are also briefly discussed.

1. Suspension Bridge Sadia Khan Terryn Kuzyk Brogan Gordon-Cooper Paul Coutts

2. PresentationOutline Introduction Geological Setting Bridge Components Engineering Solutions Maintenance Conclusion Tacoma Narrows Bridge

3. Introduction Structure Suspension Bridge GeologicalSetting Bedrock is granite Bedrock is beneath 300m of glacial till & 200m of silt/mud Ends must be anchored in highly-fractured shale that dips towards the water

4. Geological Settings Shale Glacial Till Granite Bedrock Unconsolidated Silt and Mud

5. Shale Lithified Mud Highly Bedded & Fissile Weak Rock Fractured Shale is Permeable & Susceptible to Fluid Migration

6. Problems with Fractured Shale Water can creep through the cracks increasing weathering of the rock Clay within the shale can expand and contract resulting in slope failure Shale rapidly scours Excavation causes stress release Since it dips towards the water, hydrostatic pressure develops forcing bedding planes apart

8. Glacial Till Poorly sorted Primarily angular in nature Contains almost all rock sizes Result of glacial movement

9. Problems with Glacial Till Unsorted sediment introduces risk of hitting large boulders, which can interfere with construction Mass movements can occur when overriding silt and mud layer starts to slide

10. Granite Bedrock Extrusive igneous rock consisting of mostly quartz, orthoclase and biotite Relatively hard rock therefore ideal for placing foundation of structures 500m below surface (our geological location)

11. Problems with Granite Bedrock Depth may not be feasible for constructing anchors and piers Excavating hard rocks such as granite may abrade expensive machinery

12. Suspension Bridge Components Main Cables Hangers Deck Piers Anchors

13. Engineering Solutions Outline Problems Solutions

14. Solutions for Anchoring into Fractured Shale Anchor directly into granite bedrock instead of fractured shale Locate anchor in areas with minor fractures in shale Place concrete slab over fractured shale Use rock bolts to restrain fractured rock

15. Anchoring into Granite Bedrock Granite is an ideal rock to anchor into due to its high compressive strength and lack of bedding Unreasonable solution due to its location at 500m depth and highly costly (35%-50% increase in cost) Project descriptions specifies anchoring into fractured shale

16. Locating Ideal Placement Fractures in Shale are of interest to the oil and gas industry Vertical Drilling is commonly used but many bore holes maybe required Horizontal drilling is a relatively new method and it can cover a larger area Horizontal drilling is more expensive Drilling and closing the bore hole maybe difficult and time consuming

17. Locating Ideal Placement Fracture zones compared to host rock have: Lower resistivity (higher conductivity) Lower seismic velocity Cause scattering of seismic and Ground Penetrating Radar (GPR) waves Topographic depressions due to fracturing and weathering

18. Placement of Concrete Slap Over Shale Ends of the main cables need to be hooked into the concrete slab which will carry all of the loading from the bridge Need to ensure shale is consolidated under the concrete slab Concrete slap cannot be placed parallel to the shale bedding Concrete slab cannot be placed parallel to the dipping angle of shale Rock bolts and tendons used to keep shale intact

19. Placement of Concrete Slap Over Shale Post-tensioned Concrete will be used Concrete slab will withstand the tension from the cables and the compressive loads from the weight of the anchor Expansion and contraction from underlying rock are supported by the concrete without significant flexure

20. Anchors of the Golden Gate The Golden Gate is also anchored into shale using a concrete slab Over one million tons of concrete was used to build the anchors that hold the cables in place

21. Scour is one of the top three causes of bridge failure. Approximately 60% of bridge failures are caused by scour at the abutments and the piers.

22. Problems with Fractured Shale

23. Bridge Maintenance Initial Inspection Intermin Inspection Damage (Emergency) Inspections Underwater Bridge Inspection Fracture Critical Inspection

24. Bridge Maintenance