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Performance of Improved Ground

Performance of Improved Ground. Elizabeth A. Hausler and Nicholas Sitar. Acknowledgements. U.S.- Japan Cooperative Research Program for Urban Earthquake Disaster Mitigation, NSF, Award No. CMS-0070278 Earthquake Engineering Research Centers Program, NSF, Award No. EEC-9701568

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Performance of Improved Ground

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  1. Performance of Improved Ground Elizabeth A. Hausler and Nicholas Sitar

  2. Acknowledgements • U.S.- Japan Cooperative Research Program for Urban Earthquake Disaster Mitigation, NSF, Award No. CMS-0070278 • Earthquake Engineering Research Centers Program, NSF, Award No. EEC-9701568 • Public Works Research Institute, Japan • Port and Airport Research Institute, Japan • University of California, Davis Center for Geotechnical Modeling • Hayward Baker

  3. 1964 Niigata Earthquake Case History Unimproved, up to 50 cm settlement (Watanabe, 1966) Improved with vibroflotation, 2-3cm settlement (Fudo Corp., 1964)

  4. 1995 Kobe Earthquake Case History Portopialand, Port Island, improved with vibro-rod (Fudo Corp., 1995) Unimproved area 

  5. 2001 Nisqually Earthquake Case History Home Depot, improved with VR stone columns  Unimproved

  6. Field Case Histories by Earthquake Hausler, E.A. and Sitar, N., (2001). “Performance of Soil Improvement Techniques in Earthquakes”, Fourth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, Paper 10.15, March 26 - 31.www.ce.berkeley.edu/~hausler/casehistories.html

  7. Field Case Histories by Method

  8. Results of Case History Analysis • Field case histories indicate that sites with ground improvement experience less ground deformation than adjacent, unimproved areas • 10 % of the case histories received inadequate performance designation, most commonly because there was a significant lateral spreading hazard present or the improvement was not deep enough • Most field case histories, however, lack sufficient quantitative information on building settlement, vertical ground strain, and degree, depth, and lateral extent of ground improvement

  9. B Lc Nonliquefiable Soil Improved Soil Liquefiable Soil Zc B Lc Nonliquefiable Soil Improved Soil Liquefiable Soil Zc How Deep? How Wide? ? ? ? ? Zc H ? ? ? ? H

  10. Approach • Compile field case histories of sites with liquefaction mitigation that have been shaken by an earthquake • Review available design guidelines for remediation zone geometry • Review previous physical model studies with ground improvement • Perform centrifuge-based shaking table tests to study the influence of remediation zone geometry on performance of a structure on embedded shallow foundation • Develop the design guidelineusing case histories and physical model studies

  11. Experience and Guidelines -- Depth • In U.S., common to determine depth using SPT, CPT, or Vs measurements in deterministic simplified liquefaction triggering analysis (Seed and Idriss, 1971, Youd and Idriss, 1997, Cetin, 2000); sometimes, assessment of potential settlement using Ishihara and Yoshimine (1992) or Tokimatsu and Seed (1987), or more detailed site response analysis is done • In Japan, similar procedures, emphasis on lab testing, Road and Bridge Code specifies maximum 20m depth for liquefaction hazard evaluation • Field case histories:45% of cases with sufficient data were improved through the full potentially liquefiable thickness

  12. Experience and Guidelines – Lateral Extent • Lateral extent should be equal to improved depth (Mitchell, case histories) • Lateral extent should include the zone that influences the stability of the structure (Iai, laboratory tests and numerical modeling) or is affected by seepage • Lateral extent equal to 2/3 liquefiable thickness, but at least 5m and no greater than 10m (Japanese Fire Code) • Field case histories: 20% (5 of 25) of cases with sufficient data were improved laterally to a distance equal to the improved depth

  13. Tests at PWRI – Field Scale Prototype 8m x 18m, 96 kPa 18m Dr = 6m=30%H 14m=70%H 85% 20m=100%H 20m .3H Dr = 35% Keisa 16m 132m Kobe Port Island 83m depth record, NS 6.6m radius centrifuge rigid model container scaled to 0.16g, 0.37g PGA spinning @ 60g

  14. Tests at UC Davis – Field Scale Prototype 8m x 8m, 96 kPa 32m 16m 6m=30%H 14m=70%H Dr = 20m=100%H 85% 20m .3H 16m Dr = 30% Nevada Sand 132m Kobe Port Island 83m depth record, NS 9.1m radius centrifuge flexible shear beam scaled to 0.16g, 0.75g PGA spinning @ 40g model container

  15. Parameters varied • Depth of improvement (100%H, 70%H, 30%H, 0%H) • Lateral extent of improvement relative to depth of improvement • Static stress condition (2D vs. 3D) • Soil (Nevada, Keisa) • Relative density of liquefiable soil (Dr,initial = 30%, 35%, 50%) • PGA, frequency, and energy content of the input motion (scaled Kobe Port Island 83m depth wave, changed centrifuge shakers)

  16. Normalized Settlement vs. Improved Depth PWRI 0.16g UCD 0.16g

  17. Normalized Settlement vs. Improved Depth Liu + Dobry 0.2g PWRI 0.16g UCD 0.16g

  18. Normalized Settlement vs. Improved Depth PWRI 0.37g Liu + Dobry 0.2g PWRI 0.16g UCD 0.16g

  19. PWRI02 Large Event Movie 4m 30%H 8m 70%H 12m 16m Dr = .7H 85% 20m .3H

  20. Normalized Settlement vs. Improved Depth PWRI 0.37g Liu + Dobry 0.2g PWRI 0.16g UCD 0.16g

  21. Normalized Settlement vs. Improved Depth UCD 0.75g PWRI 0.37g Liu + Dobry 0.2g PWRI 0.16g UCD 0.16g

  22. Below the 70% Improved Depth Block16 to 20m BGS, Initial Dr = 30%

  23. Normalized Settlement vs. Improved Depth UCD 0.75g PWRI 0.37g Liu + Dobry 0.2g PWRI 0.16g UCD 0.16g

  24. Tokachi Port Movie 4m 30%H 8m 70%H 12m 16m Dr = .7H 85% 20m .3H

  25. Normalized Settlement vs. Improved Depth UCD 0.75g PWRI 0.37g Liu + Dobry 0.2g Tokachi Port Blast PWRI 0.16g UCD 0.16g

  26. Normalized Settlement vs. Improved Depth UCD 0.75g, 0.63g, Dr=50% UCD 0.75g PWRI 0.37g Liu + Dobry 0.2g Tokachi Port Blast PWRI 0.16g UCD 0.16g

  27. Most Influential Factors • Initial relative density of liquefiable soil • Energy/intensity of the input motion • Confining stress (structure) • Confining stress (depth of soil) • Confining stress (layering of improved and unimproved ground)

  28. Vertical Strain by Layer 85% .3H .3H

  29. By Layer Comparison with Empirical Relation Shamoto, Zhang, Tokimatsu based on emin, einitial, maximum shear strain PWRI data UCD data

  30. Lessons Learned – Low Levels of Shaking • Vertical ground strain decreases with increasing improved zone depth • Settlement is not totally eliminated with improvement through full liquefiable thickness

  31. Lessons Learned – High Levels of Shaking • Vertical ground strain DOES NOT NECESSARILY decrease with increasing improved zone depth • Settlement is still significant with improvement through full liquefiable thickness; differential settlement possible • Acceleration measured on the structure is highest for the case with the improvement through the full liquefiable thickness

  32. Modeling Underway… Corinne Cipière, UC Berkeley Using FLIP (Port and Airport Research Institute)

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