Transportation Research Board 2002 Annual Meeting Presentations from Workshop on Plan of Action for Scour Critical Bridges

PowerPoint Version (0.8 mb)

Slide 1

Approach to Developing a Plan of Action for Scour Critical Bridges

Presented at TRB annual meeting January 16, 2002

by:
J. Sterling Jones
Jorge E. Pagán Ortiz

Slide 2

A Plan of Action (POA) should be Developed
for Each Existing Bridge Found to be Scour Critical

Per FHWA guidance contained in Technical Advisory T 5140.23, "Evaluating Scour at Bridges" dated October 28, 1991

Slide 3

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.

Includes the following categories from the NBI Coding Guide item 113:

Slide 4

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 5

Elements of the POA

• Management Strategies
• Inspection Strategies
• Closure Instructions
• Countermeasure Alternatives and Schedule
• Other Information

Slide 6

Management Strategies

• Location of Bridge
• Bridge Identification
• Type of Foundation and Foundation Material
• Source of Scour Critical Rating
• Importance of Roadway to the Transportation Network
  • ADT, Access Route to Emergency Facilities, Evacuation Route, Detour
  
  
• Programmed for Replacement (may suggest a risk- based analysis)

Slide 7

Inspection Strategies

• Type and Frequency of Inspection
  • Normal frequency is 2 years for superstructure and visual or probing underwater where applicable.
  • 5 years for general underwater 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

Slide 8

Closure Instructions

• Can be Load Restrictions, Lane Closure or Complete Bridge Closure
• Criteria for Closure should be Established by Scour Team based on one or more of:
  • Observed scour, movement of riprap, monitoring bed movement, water level, discharge, rainfall, flood forecasting, debris build-ups
  
  
• Identify Authority for Closing and Reopening a Bridge
  • Communication and coordination
  
  

Slide 9

Countermeasure Alternatives

• Alternatives Considered
  • More intense monitoring can be one of the alternatives
  
  
• Preferred Alternative
• Engineering Feasibility
• Schedule for Timely Design and Construction

Slide 10

Other Information

• Author and sign-off on POA
• Media Alert Instructions
• Sources of Emergency Repair Materials
• Detour Instructions

Slide 11

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 12

POA Examples from DOT's

• Oregon
  • Dave Bryson
  
  
• Florida
  • Rick Renna
  • Seta Koroitamudu
  
  
• Maryland
  • Andy Kosicki
  • Stan Davis
  
  

Slide 13

Slide 14

Slide 15

I-84 Bridges over the Snake River near Ontario, Oregon

Slide 16

Oregon Snake River

• Determined to be Scour Critical, Code 3. Scour has been observed to shale layer.
• Foundation material is Shale that is continuously wet.
• Annual Underwater Inspection; Murky Water; All Inspection by Feel.
• Re-Evaluation by Annandale procedure might elevate Item 113 to Code 5.

Slide 17

SR 44 Bridge over St. John's River
District 5, Florida

Slide 18

SR 44 Bridge over St. John's River
District 5, Florida

Slide 19 - 23

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

• Bridge Number: 110063
• Location:          SR 44 over St. John's River
• Foundation:      Pile
• Scour Mode:    Riverine
• Status:
     -Phase I: Data Collection and Qualitative Analysis          --> Final
     -Phase II: Hydrologic Assessment for Scour Analysis     --> Final
     -Phase III: Geotechnical & Structural Scour Assessment --> Final
     -Phase IV: Recommended Plan of Action                       --> Final
• Scour Rating: 3 --> Critical
• POA Summary
  • To mitigate active scour, riprap was recently installed from Bent 5 to the West Side of bascule Pier 1.
  • Although a temporary scour countermeasure, the riprap in conjunction with a monitoring program may be an effective permanent scour countermeasure.
  • Should the monitoring program find significant degradation below the elevation of the riprap lined channel, a structural based countermeasure may be warranted.
  
  
• 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

• Closure Plan
  • If a scour condition develops, it may be necessary to close the bridge.
  • If bridge closures, immediate implement District 5 bridge closure plan for state bridges.
  
  
• Plan Developer
  • Ayres Associates, Brian A. Acken, 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
  
  

Return to top