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Hydraulics Engineering

 

Strategies for Developing a Plan of Action

Lesson from: 135048 Countermeasure Design for Bridge Scour and Stream Instability


Slide 2

Learning Objectives

  • Describe the purpose of a Plan of Action (POA) for a scour critical bridge
  • Identify strategies for developing a Plan of Action (POA)


Slide 3

Plan of Action (POA)


Notes

Technical Advisory provides guidance on:

  • Developing and implementing a scour evaluation for designing new bridges
  • Evaluating existing bridges for scour vulnerability
  • Using scour countermeasures
  • Improving the state-of-practice for estimating scour at bridges


Slide 4

Highlights of Changes to Item 113


  • Description changed to emphasize that:
    • Rating factor of 2 or below requires revising Item 60 and other affected items (load ratings and superstructure rating)
    • Plan of Action should be developed for each scour critical bridge
    • Coding is based on an engineering evaluation, which includes consideration of NBIS field inspection findings

Notes

NBI Coding Guide Item 113

  • Item 113 now refers to HEC-18 and 23 for guidance on scour and countermeasures


Slide 5

Scour Critical Bridge

  • A Scour Critical bridge is one with foundation elements that are determined to be unstable for the calculated and/or observed stream stability/ scour conditions

Notes

NBI Coding Guide Item 113

Scour Critical Ratings
Code Description
3 Assessed or calculated condition
2 Comparison of calculated and observed condition
1 Comparison of calculated and observed; failure is imminent
0 Bridge failed and is closed

Slide 6

Code 8

  • Expanded guidance for a bridge foundation determined to be stable:
    • Assessment - bridge foundations on rock formations determined to resist scour within the service life of the bridge
    • Calculations
    • Installation of properly designed countermeasures

Notes

NBI Coding Guide Item 113 Use of Countermeasures

  • Determination of stability can be based on installation of properly designed countermeasures

Examples: Calculated Scour Depth (Left: Spread footing (not founded in rock)
Right: Pile footing)
Action Needed
A. Above top of footing Spread (not founded in rock) and Pile footing showing scour depth above top of footing None - indicate rating of 8 for this item
B. Within limits of footing or piles Spread (not founded in rock) and Pile footing showing scour depth within limits of footing or piles Conduct foundation structural analysis
C. Below pile tips or spread footing base Spread (not founded in rock) and pile footing showing scour depth below pile tips or spread footing base Provide for monitoring and scour countermeasures as necessary

+++++++ = calculated scour depth


Slide 7

Code 7

  • Countermeasures installed to mitigate an existing scour problem and to reduce the risk of bridge failure during a flood event
  • Instructions in a Plan of Action have been implemented to reduce the risk to users from a bridge failure during or immediately after a flood event

Notes

  • Countermeasures can be used to reduce the risk from scour
  • Monitoring can be considered a countermeasure when developing a Plan of Action


Slide 8

Code 5

  • Foundation determined to be stable for the assessed or calculated scour condition
  • Scour within the limits of footings or piles based on an assessment, calculation, or installation of properly designed countermeasures

Notes

  • Code 6 - Scour calculation/evaluation has not been made
  • Can consider installation of properly designed countermeasures in a Code 5 rating
  • Example B
  • Code 4 - Foundation stable. Field review indicates action required to protect exposed foundations


Slide 9

Goal of POA

  • Provide guidance for Inspectors and engineers that can be implemented before, during, and after flood events to protect the traveling public


Slide 10

Elements of POA

  • Management strategies
  • Inspection strategies
  • Closure instructions
  • Countermeasure alternatives and schedule
  • Other information


Slide 11

Management Strategies

  • Location and identification of bridge
  • Type of foundation and foundation material
  • Source of scour critical rating
  • Importance of roadway to the transportation network
  • Programmed for replacement (may suggest a risk-based analysis)

Notes

Evaluating importance of the roadway could include:

  • ADT
  • Access Route to Emergency Facilities
  • Evacuation Route
  • Detour


Slide 12

Inspection Strategies

  • Type and frequency of inspection
  • Need for continuous monitoring
    • When to start
    • When to stop
  • What constitutes a scour critical condition
  • Instructions for action when the scour critical condition is reached

Notes

  • Normal frequency is 2 years for superstructure and visual or probing underwater where applicable
  • 5 years for general underwater inspection


Slide 13

Guidance for Inspectors

  • Discharge measurement
  • Stage measurement
  • High water marks
  • Flood watch


Slide 14

Closure Instructions

  • Can be load restrictions, lane closure or complete bridge closure
  • Criteria for closure should be established by Scour Team
  • Identify authority for closing and reopening a bridge
    • Communication and coordination

Notes

  • Criteria for closure includes:
    • Observed scour
    • Movement of riprap
    • Monitoring bed movement
    • Water level
    • Discharge
    • Rainfall
    • Flood forecasting
    • Debris buildup
  • Communication and coordination instructions for closing and reopening a bridge must be included


Slide 15

Detours

  • Availability and description of alternative routes
  • Scour vulnerability of bridges along detour route


Slide 16

Countermeasure Alternatives

  • Alternatives considered
    • More intense monitoring can be one of the alternatives
  • Preferred alternative
  • Engineering feasibility
  • Schedule for timely design and construction

Notes

  • The HEC-23 Countermeasures Matrix is designed to assist in selecting countermeasure alternatives


Slide 17

Other Information

  • Author and sign-off on POA
  • Media alert instructions
  • Sources of emergency repair materials
  • Detour instructions

Notes

  • Communications with the media
  • Who is authorized to make statements?
  • What information should be provided?


Slide 18

Generic POA

  • Bridge Identification:
    Location of Bridge:
    Year Built:
    Replacement Plans (if scheduled):
    Foundation Type:
    Foundation Soils Types:
  • ADT:
    Service to Emergency Facilities or Evacuation (Y/N):
  • Sources of scour critical rating (Assessment, Analysis, and/or Observation):
  • Comments about rating (e.g., analysis did not account for erosion resistant material; emergency riprap placed after last flood, etc.):
  • Inspection and Monitoring:
    • Increase inspection frequency:
    • Types (Probing, diving, inspection of banklines):
    • Special Inspection Criteria (after bankfull events, during major events):
  • Monitoring Type (Fixed instrumentation, Portable instrumentation):
  • Criteria for monitoring:
  • Closure Plans (Limit loads; Lane closure; Full closure):
  • Criteria for Closure (Discharge; Floodwater Elevation; Flood Forecast; Scour Soundings):
  • Authorization for Closure (Bridge Maintenance engineer; Inspector; Police; Statewide Bridge Closure Procedure):
  • Detour Route:
  • Criteria for reopening bridge:
  • Countermeasures considered:
      (1) ___________________________________; Cost: $ ________________________
      (2)____________________________________; Cost: $ ________________________
      (3)____________________________________; Cost: $ ________________________
  • Countermeasure Recommended:
    Status:
  • Author(s) of POA:
    Date:
  • Concurrences on POA: _______________________,
    __________________________,
    __________________________________


Slide 19

POA Examples

  • Oregon DOT
  • Florida DOT


Slide 20

Oregon DOT Plan of Action


Click to view Oregon DOT's POA


Slide 21

SR 44 Bridge over St. John's River - POA Example

  • Bridge #: 110063
  • Location: SR 44 Bridge over St. John's River
  • Foundation: Pile
  • Scour Mode: Riverline
  • Status
    • Phase I: Data Collection and Qualitative Analysis => Final
    • Phase II: Hydrologic Assessment for Scour Analysis => Final
    • Phase III: Geotechnical and Structural Scour Assessment => Final
    • Phase IV: Recommended Plan of Action => Final
  • Scour Rating 3 => Critical

Slides 22-23

Photo of SR 44 Bridge over St. John's River looking downstream

Photo of SR 44 Bridge over St. John's River


Slide 24

SR 44 Bridge over St. John's River - POA Example

POA Summary

  • To mitigate active scour, riprap was recently installed from Bent 5 to the west side of bascule Pier 1
  • Riprap in conjunction with a monitoring program will reduce the risk from scour
  • If monitoring finds significant degradation below the elevation of the riprap-lined channel, a structural countermeasure may be warranted


Slide 25

SR 44 Bridge over St. John's River - POA Example

Countermeasure Alternatives

Alternatives Cost
1. Permanent Monitoring Program / Portable Instrument $313 per monitoring event
2. Permanent Monitoring Program / Fixed Instrument $18,500
3. Install Crutch Bents Not feasible, riprap in vicinity


Slide 26

SR 44 Bridge over St. John's River - POA Example

  • Plan Developer
    • XYZ Engineering, A. Smith, P.E., 01/30/98
  • Consultant Recommendation
    • Alternative #1
  • Action taken by FDOT
    • Routine monitoring/riprap already in place
  • Work Program
    • 238328 (2-98); Project file 8


Slide 27

SR 44 Bridge over St. John's River - POA Example

Closure Plan

  • If a scour condition develops, it may be necessary to close the bridge
  • If bridge closure necessary, immediately implement District bridge closure plan for state bridges


Slide 28

Learning Objectives

  • Describe the purpose of a Plan of Action (POA) for a scour critical bridge
  • Identify strategies for developing a Plan of Action (POA)

Related Features

Contact:

Dave Henderson
Office of Bridges and Structures
202-493-0520
dave.henderson@dot.gov


Cynthia Nurmi
Resource Center (Atlanta)
404-562-3908
cynthia.nurmi@dot.gov


Joe Krolak
Office of Bridges and Structures
202-366-4611
joe.krolak@dot.gov

 
Updated: 04/07/2011
 

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United States Department of Transportation - Federal Highway Administration