Shewbridge Sess05 101309

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Shewbridge Sess05 101309

  1. 1. SIMPLIFIED APPROACH TO ASSESS LEVEE SEISMIC VULNERABILITY Presentation for SAME Conference October 2009, Sacramento, California Scott Shewbridge, Jerry Wu [1] , Sujan Punyamurthula, Juan Vargas [2] , Steve Mahnke, and Mike Inamine [3] [1] URS Corporation, 1333 Broadway, Suite 800, Oakland, CA 94612, [email_address] and Jerry_Wu@urscorp.com [2] URS Corporation, 2870 Gateway Oaks Drive, Suite 150, Sacramento, CA, [email_address] and [email_address] [3] Department of Water Resources, Division of Flood Management, 2825 Watt Avenue #100, Sacramento, CA 95821 [email_address] and [email_address]
  2. 2. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, Failure Surface-Type, K y /K max ) Charts </li></ul></ul>
  3. 3. Newmark Approach Force = Mass * Acceleration Relative Acceleration – a = a y - a f Integrate once – Relative Velocity = at Integrate twice- Relative Displacement = ½ at 2 Relative Displacement
  4. 4. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, K y /K max ) Charts </li></ul></ul>
  5. 5. Estimates of Peak Ground Acceleration (PGA)
  6. 6. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, K y /K max ) Charts </li></ul></ul>
  7. 7. Example Finite Element Model Inputs & Results Calculated Peak Horizontal Acceleration 1979 Imperial Valley Earthquake, USGS 286 Station, 135-Degree Component Scaled to 0.5g Input Motion - - - 1100 125 Elastic Base Vucetic & Dobry, PI=30 0.45 - 900 125 Pleistocene (CL) Seed-Idriss Sand (mean) 0.35 50 - 125 Holocene (Medium Dense Sand) Seed-Idriss Sand (mean) 0.35 25 - 115 Levee Fill (Silt) G/Gmax and Damping Curves Poisson’s Ratio K 2 max Vs (ft/s) Unit Weight (pcf) Material
  8. 8. Estimate of Cyclic Stress Ratio (CSR)
  9. 9. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, K y /K max ) Charts </li></ul></ul>
  10. 10. How do we evaluate K y ? Limit Equilibrium – Increase seismic coefficient until FS = 1 Infinite Slope Multi-block Wedge
  11. 11. Use Slope Stability Program UTEXAS4 is the only currently authorized computer program
  12. 12. Interpolate to Evaluate K y <ul><li>Run analysis for increasing a h (0.0, 0.05, 0.10, … up to to ½ K max ) </li></ul><ul><li>Plot results on graph </li></ul><ul><li>Interpolate to evaluate K y at FS = 1 </li></ul>K y
  13. 13. Evaluate Liquefaction Triggering Using Seed et al (2004)* Set Duration Weighting Factor = 1 All Events
  14. 14. Estimate Liquefied Soil Strengths using Seed and Harder (1990)
  15. 15. Use Undrained Residual Strength to Assess Post-Liquefaction Triggering K y Su = 250psf
  16. 16. Results Presentation <ul><li>Show </li></ul><ul><ul><li>Strengths </li></ul></ul><ul><ul><li>Analysis water conditions (“summer” “normal winter”) </li></ul></ul><ul><ul><li>Location of static critical surfaces (landside, waterside, circular, wedge) </li></ul></ul><ul><ul><li>Show location of K y failure surfaces (landside, waterside, circular, wedge - usually not the same) </li></ul></ul><ul><ul><li>Show K y graph </li></ul></ul>
  17. 17. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, K y /K max ) Charts </li></ul></ul>
  18. 18. Estimate of Site Response and 2-Dimensional Effects (K max )
  19. 19. Asymmetry/Stiffness Asymmetry may be important and can be considered. “ Stiffer” Asymmetric “ Stockton” “ Medium” Less Symmetric “ Marysville” “ Softer” Symmetric “ Sacramento”
  20. 20. Choose Model Based on Stiffness
  21. 21. Assessment of Seismic Vulnerability <ul><li>Approach </li></ul><ul><ul><li>Newmark estimation of potential deformation and assessment of post-earthquake flood protection ability </li></ul></ul><ul><li>Process </li></ul><ul><ul><li>Seismic Hazard – Urban Levee Program Probabilistic Seismic Hazard Maps </li></ul></ul><ul><ul><li>Liquefaction Triggering CSR – Urban Levee Program CSR Charts </li></ul></ul><ul><ul><li>K y – Site Specific Estimations </li></ul></ul><ul><ul><li>Earthquake Loading – Urban Levee Program K max Charts </li></ul></ul><ul><ul><li>Displacement – Urban Levee Program Displacement = f(Magnitude, K y /K max ) Charts </li></ul></ul>
  22. 22. Example Newmark Calculation Results
  23. 23. West Sacramento Stockton Marysville All scaled to be compared directly with Makdisi-Seed (1978) Interpretation of Results Displacement = f(K y /K max ? Block Type/Depth? Magnitude/Duration? Scaled PGA?) <ul><li>Makdisi-Seed (1978) </li></ul>
  24. 24. Displacement = (K y /K max )? YES K y /K max has an impact on K y /K max estimates of displacement
  25. 25. Displacement = f(Block Type / Depth)? NO Scaled PGA – 0.05 0.2 0.5 M6.5 M7.25 M8 <ul><li>Each figure shows: </li></ul><ul><li>Waterside Shallow, </li></ul><ul><li>Waterside Deep, </li></ul><ul><li>Landside Shallow, & </li></ul><ul><li>Landside Deep </li></ul><ul><li>surfaces for all 3 </li></ul><ul><li>regional models </li></ul>Magnitude Block Type and Depth have no apparent impact on K y /K max estimates of displacement
  26. 26. Displacement = f(Magnitude/Duration)? Yes for K y /K max < 0.4 Scaled PGA – 0.05 0.2 0.5 M6.5 M7.25 M8 Magnitude Magnitude / Duration has an apparent impact on K y /K max estimates of displacement
  27. 27. Displacement = f(Scaled Input PGA)? Yes, but… Scaled PGA – 0.05 0.2 0.5 M6.5 M7.25 M8 Magnitude Concern that Scaled Input PGA apparent impact on K y /K max estimates of displacement is only a numerical result Possible resolution – Spectral Matching and Arias Intensity screening
  28. 28. Use Model for Scaled Input Motion = 0.2g for Vulnerability Assessment Scaled PGA – 0.05 0.2 0.5 M6.5 M7.25 M8 Magnitude 0.2g scaled PGA model results are believed to provide a reasonable expected relationship for the study areas
  29. 29. Summary – Levee Deformation Evaluation Charts PGA = f(Return Period) CSR = f(PGA) K max = f(PGA, block depth, model stiffness) Displacement = f(K y /K max , Magnitude)
  30. 30. Freeboard Loss Assessment <ul><li>Consider compound failures each causing freeboard loss (i.e., waterside and landside both causing concurrent loss of freeboard) </li></ul><ul><li>Assume horizontal deformation causes freeboard loss at a rate of 0.7V : 1H for both circular failure surfaces and potential grabens that can form on lateral spreads </li></ul>
  31. 31. Vulnerability Assessment Compromised None Yes Unlimited (flow slide condition) Likely Compromised None Likely if existing 3’ to 10’ Possibly Compromised >1’ Possibly 1’ to 3’ Probably Uncompromised >1’ No <1’ POST SEISMIC FLOOD PROTECTION ABILITY REMAINING FREEBOARD FOR POST SEISMIC EVALUATION (2-YEAR FLOOD WATER SURFACE ELEVATION?) SIGNIFICANT DAMAGE TO INTERNAL STRUCTURES (E.G. CUTOFF WALLS AMOUNT OF DEFORMATION
  32. 32. Final Evaluation Charts PGA CSR K max Displacement
  33. 33. Questions / Discussion

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