Scour Memo Part A Hydraulics Bill P Schmidt, PE Senior Hydraulics Engineer, INDOT

1. Scour Memo Part A Hydraulics Bill P Schmidt, PE Senior Hydraulics Engineer, INDOT wpschmidt@indot.in.gov 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 • 1997-2002: 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 • 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 does scour analysis and creates a scour report • 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 www.in.gov/indot/3595.htm 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 • 256-36-03370, 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 • 10-15-2018, 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 203-3.05 • 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 • Choose Part B for determination • 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 Scourcritical

20. SCOUR DETERMINATION 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 Scourcritical

21. SCOUR DETERMINATION • Other or Unknown Cases • 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. Scour Memo Part B & C The Rest of the Story Ed Spahr, PE Bridge Design Team Lead, INDOT espahr@indot.in.gov 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

26. Part B – Not Scour Critical • Grey area for hydraulics • Part C Not Required • Typically Site Based • Minimal Scour • Lousy Soils • Foundation on Rock

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

28. Part B – Scour Critical (Contingent Determination) • Part C Analysis Required • Beneficial for: • Environmentally Sensitive Areas • Larger Costs • Known Erodible Layer

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

30. Part C – Additional Analysis • Requires Structural Analysis of Unbraced Length • Verify Capacity of embedded pile with Geotechnical

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

32. Use with New Construction? Design for scour required on new piers per AASHTO 2.6.4.4.2 So countermeasures are not allowed in place of appropriately designed substructure And countermeasures not required for appropriately designed substructure

33. Considerations Not Worth It? • 2ndoverlay 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