1. Senior Hydraulics Engineer, INDOT
Scour Memo Part A
Hydraulics
Bill P Schmidt, PE
Senior Hydraulics Engineer, INDOT
November 15, 2018

2. TOPICS Quick History Scour Data Scour Determination
Scour Memo Parts B & C

3. QUICK HISTORY
1988: FHWA issues technical advisory requiring bridges to be rated on scour vulnerability
1988: Hydraulic scour analysis begins on some new bridge replacements (geotech determined scour before 1988)
1991: INDOT updates IDM to begin designing new bridges to resist scour (per HEC 18 methods)
1998 to present: New bridges constructed are considered scour safe by foundation design, no further analysis required or by riprap protection based on standard drawings (for three & four-sided structures)

4. QUICK HISTORY Bridge Rehab Scour History
1997: INDOT Scour Committee divides all bridges in to High, Medium, and Low Risk Categories
: High risk bridges given priority for scour evaluation/monitoring
1999: INDOT & FHWA agreement requires all bridges to be evaluated for scour when rehabbed
1999: Hydraulics & Bridge Rehab send out two design memoranda detailing need for scour design during rehab
1999 to present: The memos are still in effect

5. QUICK HISTORY Exemptions for Bridge Rehab Scour
Bridges constructed from 1998 to present
Previous scour analysis already performed
Check BIAS
Contact INDOT Hydraulics
Bridge maintenance projects – such as painting
Thin Deck Overlays (Polymeric only)
Entire foundation embedded in competent (non-scouring) rock
Model may still be required to get the bridge velocity for sizing riprap for abutment protection
However, bridge would be stated as “not scour critical”
Documentation required in the scour report

6. QUICK HISTORY Scour Memo Goals Old Method New Method
Designer to fill out scour memo instead of INDOT Reviewer
INDOT Bridge to make final scour determination instead of Hydraulics
Hydraulics will still produce scour analysis and results and make obvious determinations
Old Method
Consultant does scour analysis and creates a scour report
INDOT fills out scour memo and signs and stamps it
New Method
Consultant fills out scour memo and signs and stamps it
INDOT reviews scour memo and signs it
Scour Memo sent to INDOT bridge section for evaluation if needed

7. QUICK HISTORY Scour Memo INDOT has created a new scour memo template
Available on INDOT Hydraulics Webpage in the “Submitting Documents” section
Scour Memo Instructions also found on the INDOT Hydraulics Webpage
Scour Memo now involves three parts (A, B, and C)
Part A - Hydraulics Scour Data (provided by Consultant Hydraulics Engineer)
Part B – Bridge Scour Critical Determination (provided by INDOT Bridge Design)
Part C – Bridge Scour Critical Determination (provided by Bridge Engineer of Record)

8. SCOUR DATA Filename Example: prelim ScourMemo 256-36-03370 10-15-2018
Start with “prelim”, this will be removed later by INDOT when finalized
Note: The submitted memo should be considered final by the designer
ScourMemo is one word
, the bridge structure number, rehab letter not needed
Since only one scour memo per bridge
It may be necessary to designate direction such as west bound (WBL) or east bound (EBL), if a scour memo will exist for each
, date in mm-dd-yyyy format
The scour memo should be submitted as a word document

9. SCOUR DATA
Title Information
Information available in SPMS

10. SCOUR DATA Designer and Reviewer
Consultant Engineer will sign and stamp
INDOT Hydraulic Engineer will sign when Part A is finalized

11. SCOUR DATA Scour Data Data comes from HEC-RAS model
Definitions found in INDOT Design Manual
Only 100-year storm event needed for bridge rehabilitation projects
Modify flow rate for roadway overtopping
Include more scour data if needed or desired

12. SCOUR DATA Bridge Foundation Data
State the source of the data (pile driving records, existing plans, quantities, etc)
Include the pile driving records and/or existing bridge plans with submittal as separate file
State pile material if information is available
Include any other explanations of data or reasons for incompletion
Be consistent with datum (assumed NAVD88 unless stated otherwise)
Data is needed by INDOT Bridge for scour evaluation purposes

13. SCOUR DATA Bridge Foundation Data Bottom of Footing Elevation
Should be located on the existing bridge plans
Low Pile Elevation
This is the pile tip elevation of the shortest pile for each pier or bent
Preferred hierarchy of source
Pile Driving Records
Elevations identified on the existing bridge plans
Elevations estimated from quantities on the bridge plans
Choose Part B for determination
Unknown or no information available
The source of the low pile elevation must be identified in the scour memo
If no piles, then this will be N/A

14. SCOUR DATA Bridge Foundation Data Q100 Low Scour Elevation
Use value determined from scour data section of the memo
Exposed Pile length
The difference between the bottom of footing elevation and the low scour elevation
Length of Pile Still Buried
The difference between the low scour elevation and the pile tip elevation

15. SCOUR DATA Bridge Foundation Data
D50 of soil used in scour analysis (mm)
From soil borings or soils report (use smallest particle within scour range)
If not known use 0.01 mm to be conservative
# of Rows of Piles
Should be determined from the existing plans or pile driving records

16. SCOUR DATA Narrative Leave first paragraph as it is
Add any additional information to explain scour results
Add qualitative information
Document unknown information or estimated information
Provide scour countermeasures even if it is unknown whether the bridge will be scour critical

17. SCOUR DATA Scour Countermeasures Based on IDM Figures 203-2D &
IDM Figure 203-3B

18. SCOUR DETERMINATION Options
Idea is for INDOT Bridge (structural) to determine whether a bridge is scour critical instead of Hydraulics
Hydraulic Engineers will make determination when obvious
Foundation configuration (piles, no piles, etc.), along with low scour elevation is used to determine scour recommendation by hydraulics

19. SCOUR DETERMINATION Bridge with piers on footings with no piles
Not scour critical – top of footing is not exposed at low scour elevation
Scour critical – low scour elevation is below bottom of footing
Scour Status pending Part B – low scour elevation is along the footing
Low scour
elevation
Not scour critical
Top of Footing
Part B
determination
FOOTING
Bottom of Footing
Scour critical

20. SCOUR DETERMINATION Bridge with piers on piles
Low scour
elevation
Bridge with piers on piles
Not scour critical – piles are not exposed at low scour elevation
Scour critical – low scour elevation is below pile tip elevation
Scour Status pending Part B – piles are exposed at low scour elevation
Do not use “10 foot of pile is still embedded” rule
PIER
Not scour critical
Bottom of Pile Cap or Footing
Part B
determination
PILE
Pile Tip
Scour critical

21. SCOUR DETERMINATION Other or Unknown Cases Justification/Comments
Choose Scour Status Pending Part B
Justification/Comments
State the reason why a particular Part A Scour Status was selected
Example: Scour critical due the low scour elevation being lower than the pile tips
Give any additional information that might be useful for INDOT Bridge to make a determination
Example: Riprap already in place
Provide as a separate files: the existing bridge plans and pile driving records if available
The existing bridge plans
Pile driving records if available
Inspection Reports if applicable

22. SCOUR MEMO Resubmittal
If minor changes are needed to the hydraulic memo after review, INDOT Hydraulics will contact the consultant engineer and inform them of the items that will be changed in the scour memo by the INDOT Hydraulic Engineer
Some examples: Misspelled word, minor language change, minor data change, all data correct but determination needs to be changed
If major changes or multiple minor changes are necessary, the INDOT Hydraulic Engineer may require a resubmittal for the consultant to make the necessary changes to the scour memo

23. QUESTIONS
On To Scour Memo PART B & C

24. Bridge Design Team Lead, INDOT
Scour Memo Part B & C
The Rest of the Story
Ed Spahr, PE
Bridge Design Team Lead, INDOT
November 15, 2018

25. Revised Scour Memo - Part B
Determination made by INDOT Bridge Design
Signed off by INDOT Bridge Design Director
Decision made for individual projects based on scope of the project
Switch from overlay to super replacement may change need for mitigation
Options:
Not Scour Critical
Scour Critical with three possible outcomes
Final Determination
Contingent Determination – Analysis Required
Contingent Determination – Adequate Existing Countermeasures
*Leaves door open for further analysis on rehabs
*Can go through effort to justify decision
*See memo 18-14

26. Part B – Not Scour Critical
Grey area for hydraulics
Part C Not Required
Typically Site Based
Minimal Scour
Lousy Soils
Foundation on Rock
*Easiest option: Designer does nothing
*Include documentation in Design Comp file and/or Correspondence file

27. Part B – Scour Critical (Final Determination)
Like the good ol’ days -> Just do it
Part C Not Required
Use with Lower Environmental Impacts and Construction Costs
*Determined Scour Critical
*Option 1 – Final Determination
*Also easy access = just go ahead and do it

28. Part B – Scour Critical (Contingent Determination)
Part C Analysis Required
Beneficial for:
Environmentally Sensitive Areas
Larger Costs
Known Erodible Layer
*Option 2 – Contingent Determination
*EoR may choose to install countermeasures and not do analysis
-Documented In Part C comments
*Can use even without restrictions

29. Part B – Scour Critical (Contingent Determination)
Part C Not Required
Verify Installed Countermeasures:
Properly Sized in Existing Plans
Appears Stable
No History of District Maintenance
Check Previous Inspection Reports
*Option 3 – Contingent Determination / Sufficient Countermeasures in place
*2nd easiest option: Just Document it
*Bridge considered Not Scour Critical by means of existing countermeasures
*No Part C Analysis
*Include documentation in Part C: Justification, ie Plans, Pictures, Conversation Record
*If no existing plans circle back with Hydraulics and Bridge Design

30. Part C – Additional Analysis
Requires Structural Analysis of Unbraced Length
Verify Capacity of embedded pile with Geotechnical
*Small Fraction will likely go to Part C
*EoR may choose to install countermeasures and not do analysis -Documented In Part C comments
*Must consider all applicable loads and load cases (thermal & long. Etc.)
*Special attention should be given to changes in bearing types

31. Part C – Additional Analysis
Direction agreed upon by Designer, INDOT PM and District BAE prior to Additional analysis
Options:
Scour Critical – must install countermeasures
Not Scour Critical
No countermeasures required
Document accordingly
See previous presentation on evaluating unbraced pile length
Calculations verified by INDOT Bridge Reviewer
Signed off by INDOT Engineer of Record and documentation submitted to INDOT for review
Goes back to Hydraulics by (Hydraulics will upload the final memo to ERMS)

32. Use with New Construction?
Design for scour required on new piers per AASHTO
So countermeasures are not allowed in place of appropriately designed substructure
And countermeasures not required for appropriately designed substructure
*Sent back to Hydraulics after each step
*New bridge designed for Q500 (AASHTO )
*Rehab has likely seen Q500 or risk of Q500 in service life is way down therefore no mention of Q500 in rehab scour memo

33. Considerations Not Worth It?
2nd overlay with crazy MOT – may be worth replacing the bridge
Very deep water – good place to consider economic feasibility
Or Just It?
Dry land – not worth spending the time to analyze