2. INTRODUCTION
• A Suspension bridge is a type of bridge in which the deck(load
bearing portion) is hung below the suspension cables on vertical
suspenders.
• Especially built at Deep & Narow valley.
• First modern example of this type bridge was built in the early 19th
century.
• This type of bridge has cables suspended between towers & vertical
suspender cable that carry the deck,upon which traffic crosses.
• The earliest suspension bridges were ropes slung an across a chasm,with
deck possibly at same level or hanging below the ropes.
• First iron suspensin bridge- Jacob’s Creck Bridge(1801) in Pennsylvania
• First wire cable suspension bridge-Spider Bridge(1816) at Falls Of
SCHUYLKILL
4. GEOLOGICAL SETTING
• Bedrock is
granite,shale,glacial
till,silt & mud
• Bedrock is beneath 300m
of glacial till & 200m of
silt/mud
• Ends mustn’t be
anchored in highly-
fractured shale that dips
towards the water
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
7. • Silt: fine or intermediate-sized particles from various
mineral
• Mud: silt and clay
Problems with Silt and Mud
Silt and Mud
• Mass movements can occur from saturation
• Development of quick clays (clays originating from
marine environments)
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. 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
13. 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)
14. 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
15. 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
16. 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
17. 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
18.
19. 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.
21. Bridge Maintenance
Underwater Bridge
Inspection
Fracture Critical
Inspection
Frequency of Inspection: Every Five Years Every Five Years
Primarily Looks for: Scour Visual Cracks, Rust, Weld
Termination, Arc
Strikes/Scars & Cross
Section Change
Methods/Devices: Black & White Fathometer
Color Fathometer
Dye Penetrant, Magnetic
Particle, Ultrasound
Structure Monitored: Piers Any area with non-
redundant tensile stress
Granite is 500m below surface but piles can only be driven down ?m
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
is granite overlain by 300m of glacial till and 200m of silt and mud,
Bridge ends must be anchored in highly-fractured shales that dip toward the water
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Granite is 500m below surface but piles can only be driven down ?m
Intermin- unofficial inspection done every 6 months
Damage inspections- after a collision to the bridge or major environmental changes ie floods, mass movements
Black-white fathometer: uses sound waves to detect channel depths however if the scour hole refilled it will not be able to detect it
Color Fathometer: diff colors mean diff densities this device works on refilled scour holes
