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  1. SG-1: Lateral Spreading – Observations and AnalysisRaghudeep B., and S. Thevanayagam, UBAug. 07, 2007, 2-4 pm; UB-VTCPI: R. Dobry, co-PI’s: A. Elgamal, S. Thevanayagam, T. Abdoun, M. ZeghalUB-NEES Lab: A. Reinhorn, M. Pitman, J. Hanley, SEESL-StaffTulane: Usama El ShamyStudents & Staff: UB (N. Ecemis, B. Raghudeep) and RPI (J. Ubilla, M. Gonzalez, V. Bennett, C. Medina, Hassan, Inthuorn)

  2. Outline • Review of Test SG-1 • Lateral Spreading Observations & Animation • Reanalysis of Lateral Spreading • Initiation of spreading – hypothesis • Newmark analysis - Sliding • Some thoughts • Comparisons of LG-0 and SG-1 • Highlights – Similarities & Differences (flat versus sloping ground) • Thoughts on lateral spreading

  3. Review of Test SG-1

  4. Review of Test SG-1 • Inclined Box (2o) • Hydraulic Fill (Dr~50~55%) • 18 ft Deep Saturated Sand • Dense Instrumentation • Design Base Motion (5s/10s/10s/10s) • Uninterrupted Base Motion (5s ~0.01g/3s ~0.05g) • Soil Liquefied • Large lateral spreading observed

  5. Test SG-1 Configuration Top View Side View

  6. Input Base Motion 2 Hz

  7. Base Input Motion Acceleration Response

  8. Excess Pore Pressure Response

  9. Displacements (Potentiometers)

  10. Top Rings Spread Initiation Bottom Rings Delayed Initiation of Spread Shear Strains (potentiometer)

  11. Acceleration & PWP Response Top Ring Accelerations Middle Bottom

  12. Lateral Spreading Observations & Animation

  13. 0 – 7ft Velocity

  14. 10 – 13ft Velocity (Contd.)

  15. 10 – 17ft Velocity (Contd.)

  16. Velocity: Observations • Spreading Initiation • Top 0 – 7ft ~ 19.5s • Middle 7 – 10ft ~ 20s • Bottom 10 – 17ft ~ 20.5s • Each spread – 1 cycle apart & coincides with peaks. • Parting velocity begins when the base turns ‘up-slope’ & when soil could not follow the base • Bottom soil shows Newmark type response

  17. Visualization SG1 (17.5~21.5s, x10)Pore Pressure Shear Strain

  18. Reanalysis of Lateral SpreadingInitiation of Spreading - Hypothesis

  19. Strain Profile

  20. Velocity Profile

  21. Deduced Shear Stresses Top Rings Bottom Rings

  22. Strength Degradation & Dynamic Induced Stresses: Animation

  23. Strength Degradation & Dynamic Induced Stresses

  24. Strength Degradation: Animation

  25. Strength Degradation: Animation

  26. Strength Degradation

  27. Original Laminar Box a1(t) Rigid Block a2(t) aavg(t) Yield Acceleration ai(t) an-1(t) an(t) Newmark Rigid Sliding Displacement Analysis • Yield Acceleration obtained from the available shear strength data which in turn is obtained from the pore pressure data. • f = 22o is assumed. • Double-integration of relative acceleration to obtain displacement.

  28. Newmark Displacements (without dilation) f = 22o

  29. f Strain Newmark Displacements (with dilation) f = 26o Lower Displacements

  30. Lateral Spreading - Thoughts • Tentatively Newmark model agrees with initiation of sliding • But over-predicts magnitude of spread • Perhaps, dilation contributes to smaller spread than Newmark (w/o dilation) • Tentatively, Newmark spreading decreases with inclusion of dilation (increase of frictional angle)

  31. Level Ground versus Sloping GroundLG-0 Vs SG-1

  32. Level Ground Vs Sloping Ground • LG-0: No static shear • SG-1: Non-Zero Static Shear Influence of initial static shear on pwp development and shear strains – Discussed next

  33. LG0 Vs SG1: Accelerations Quick degradation of accelerations in SG-1 due to fast pwp development due to initial static shear

  34. Displacements

  35. Pore Pressure Ratios Faster pwp during 5s (ND) Negligible ru during 5s (ND)

  36. A closer look at previous slide • At depth ~ 6.3ft, in LG0, the stress oscillates about zero shear stress. • In SG1, due to the static shear stress (sloping ground), the stress path is shifted up closer to the failure envelope (f = 22o) which causes rapid build up of strain. This Fig. clearly explains why soil in SG1 degraded faster than in LG0

  37. Significantly cyclic in nature Cyclic Shear Strains Monotonic Strains dominate

  38. Shear Stresses Propagation of shear stresses in SG-1 diminishes with faster soil degradation

  39. Stress-Strain Behavior Large Deformations, primarily initiated by graviational static shear Small Deformations

  40. Comments on LG-0 Vs SG-1 • Initial Static shear stress plays an important role • Soil degraded faster in SG-1 compared to LG-0 • Mostly Cyclic Strains in LG-0; Monotonic strains dominate in SG-1 • Level Ground Soil Strains accumulate @ high ru ~ 0.9-1.0. • Sloping Ground Soil Strains accumulate @ low ru (~ 0.6-0.7)

  41. Conclusions • Unique & High Quality Large scale Lateral Spreading Data is now available to study mechanism of lateral spreading • Lateral Spreading begins before full liquefaction and spreads downward with soil degradation • Newmark Sliding Block Approximation, coupled with strength degradation, appears to be a likely tool for lateral spreading analysis • Dilation during lateral spreading may be a constraint against build up of spreading • Initial static shear appears a distinct component in build up of pwp, strength degradation during shaking, and initiation of large lateral spreading

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