The document discusses local scour as a critical issue affecting bridge piers, with an emphasis on the mechanisms of scour and its implications for bridge integrity. It outlines various types of scour, specifically local scour caused by water flow around bridge structures, and describes multiple scour protection methods such as armoring and flow-altering countermeasures. The document highlights case studies and specific techniques, including ring columns and collars, to mitigate the effects of scour and enhance the durability of bridges.

1. LOCAL SCOUR PROTECTION
METHODS IN BRIDGE PIER
Guided by Presented by
Paul Jose Muhammed Rafi M A
Roll no:19
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2. OVERVIEW
• Introduction
• Scour mechanism
• Scour protection methods
• Case study 1
• Case study 2
• Conclusion
• References
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3. Introduction
• Scour is a common soil- structure interaction problem.
• It is the removal of sediments such as sand and rocks from
abutments.
• Scour can be defined as the excavation and removal of
material from bed and banks of streams as a result of erosive
action of flawing water.
• Bridges play an important role in transportation.
• Due to the increase in traffic volume more bridges have been
built across rivers and canals.
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4. Contd..
• Scour caused by swiftly moving water ,can scoop out scour
holes and affects the integrity of the structure.
• Its has been estimated that 60% of bridge failures result from
scour.
• Bridge failure leads to disorder in transportation systems and
may cause loss of life and properties.
• So scouring consideration in the design of bridges is an
important issue.
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5. Failure of bridge due to scour-Sava bridge, Zagreb
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6. Malahide viaduct, Dublin
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7. Contd.
• There are mainly three main types of scour.
• General scour
• Contraction scour
• Local scour
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8. General scour
• Occurs naturally in river channels.
• This includes the aggradation and degradation of river bed
occurs as the result of changes in the hydraulic parameters
such as changes in flow rate or changes in the quantity of
sediment in the channel.
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9. Contraction scour
• It occurs as a result of the reduction in channel’s cross
sectional area that arises due to the construction of structures
such as bridge piers and abutments.
• It manifests itself as an increase in flow velocity and resulting
bed shear stresses.
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10. Local scour
• It occurs around individual bridge piers and abutments.
• Local scouring around the bridge pier occurs because of flow
separation and developing several vortexes around bridge
piers.
• Due to the flow and action of vortexes scour hole created
around bridge pier.
• Such scour hole cause failure of the bridge especially during
the river floods.
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11. Local scour mechanism
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12. Contd.
• The flow pattern and mechanisms of scouring are very
complicated and the complexity of flow increases with the
development of scour hole.
• The basic mechanism causing local scour at piers is the down
flow at the upstream face of the pier and the formation of
horseshoe vortex (HSV) at the base of the pier.
• Down flow is believed to be the primary cause.
• HSV developed due to the separation of flow at the edge of
the scour hole upstream role rolls to form a helical flow.
• HSV is the consequence of scour , not the primary cause of
scour.
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13. Contd.
• HSV pushes the down flow inside the scour hole closer to the
pier.
• Separation of the flow at the sides of the pier also creates the
wake vortices.
• These are unstable and shed alternatively from each side of
the pier.
• They act as a little tornados lifting the sediment from the bed
and form a scour hole downstream of the pier.
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14. Scour protection methods
• In order to protect bridge piers from scouring, engineers have
designed and used different types of countermeasures.
• They are mainly divided into two .
• Armoring and flow altering countermeasures.
• Armoring includes usage of riprap stones, tetrapods , reno-
mattresses etc.
• Flow altering countermeasures includes sacrificial piles ,
collars etc.
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15. Contd.
• Ring columns as pier scour countermeasures.
• Scour reduction using collars.
• Scour reduction using simultaneous use of cable and collar.
• Protection using tetrahedral frames.
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16. Ring columns as pier scour
countermeasures
• This method presents the use of intact used tires in a stream
channel.
• The proposed protection structure comprises flexible rubber
rings formed into cylinders in groups of interlocking columns
placed upstream of the pier .
• This will shelter the bridge pier and minimizes the flow
impact.
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17. Schematic diagram of different ring columns
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18. Configuration of ring columns and bridge pier
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19. Contd.
• The were interlaced, generating irregularly shaped protective
structure.
• The impact of water flowing around the protective structure
gets reduced due to frictional forces generated by the
irregular surface of ring columns.
• Due to permeability of the ring layers, down flow strength
gets reduced.
• Ring column structures absorbs flow energy due to the flexible
rubber composition.
• As water approaches towards the pier, an ill defined flow field
is formed, neutralizing upward and downward kinetic energy
and minimizing particle entertainment in water ,thereby
reducing scouring of the river bed near bridge pier. 19

20. Flow around the ring columns and pier
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21. Flow inside the ring columns
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22. Contd.
• Because the rings are hollow ,some water seeps through the
gaps of rings and flow strength gets reduced.
• Causes sediment deposition behind the ring columns .
• Scour holes around bridge piers were filled with sediment ,
thereby reducing depth of bridge pier scour.
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23. Scour reduction using collars
• The basic mechanism causing local scour at piers is the down
flow at the upstream face of the pier and the formation of
horseshoe vortex (HSV) at the base of the pier.
• Down flow is believed to be the primary cause.
• Collars are mainly used to reduce the effect of down flow.
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24. flow mechanism
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25. • A collar at any level above the bed divides the flow into two
regions above and below the collar.
• This countermeasure acts as an obstacle against the down
flow due to which the down flow loses its strength on
impingement at the bed.
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26. Contd.
• For the region below the collar, down flow and HSV strength
are reduced.
• The efficiency of the collar increases at the lower elevations
since low flow can penetrate below it.
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