1. Structural Engineering and Earthquake Simulation Laboratory SG-1: Lateral Spreading – Observations & Analysis Raghudeep B. & Thevanayagam S. 20 Aug 2007: 9-9:30 AM, NEESR-Workshop PI: R. Dobry, co-PI’s: A. Elgamal, S. Thevanayagam, T. Abdoun, M. Zeghal UB-NEES Lab: A. Reinhorn, M. Pitman, J. Hanley, SEESL-Staff Tulane:Usama El Shamy Students & Staff: UB (N. Ecemis, Raghudeep B.) and RPI (J. Ubilla, M. Gonzalez, V. Bennett, C. Medina, Hassan, Inthuorn)

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

3. Structural Engineering and Earthquake Simulation Laboratory 3 Review of SG-1 Test

4. Structural Engineering and Earthquake Simulation Laboratory 4 Review of Test SG-1 Inclined Box (2 o ) Hydraulic Fill (Dr = 45~55%) 5.58m [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. Structural Engineering and Earthquake Simulation Laboratory 5 SG-1 Test Configuration Top View Side View

6. Structural Engineering and Earthquake Simulation Laboratory 6 Input Base Motion 2 Hz

7. Structural Engineering and Earthquake Simulation Laboratory 7 Base Accelerations Base Input Motion

8. Structural Engineering and Earthquake Simulation Laboratory 8 Excess Pore Pressure Response

9. Structural Engineering and Earthquake Simulation Laboratory 9 Displacement Response

10. Structural Engineering and Earthquake Simulation Laboratory 10 Shear Strain [Potentiometers]

11. Structural Engineering and Earthquake Simulation Laboratory 11 Accelerations & PWP Response Ring Accelerations Top Middle To ND Shaking

12. Structural Engineering and Earthquake Simulation Laboratory 12 Lateral Spreading Mechanism

13. Structural Engineering and Earthquake Simulation Laboratory 13 Shear Stresses Top Rings Bottom Rings

14. Structural Engineering and Earthquake Simulation Laboratory 14 Factors Conducive for Lateral Spreading: LG-0 versus SG-1 SG-1 Shear Strain 00 Cyclic Flow Failure Strain Accumulation Monotonic Strength Envelope Shear Stress Shear Strain LG-0 Monotonic Strength Envelope Small Strain Accumulation No Static Shear Very little Strain Accumulation No Flow observed Failure termed as Liquefaction Non-zero Static Shear Strain Accumulation until  curve hits the strength envelope Large Flow thereafter and  curve follows the envelope Failure termed as Flow Failure Lateral spreading begins when cyclic shear stress meets monotonic failure envelope

15. Structural Engineering and Earthquake Simulation Laboratory 15 Triaxial Test Data Triaxial Test Data (no initial shear, Theva 2003) e=0.779 (Moist tamping) e = 0.778 (MT) e=0.804 (MT) Is this what is seen in SG-1? Is hydraulic fill creating meta-stable structure more prone to collapse? Is collapse potential higher if static shear is present (i.e occurs at higher densities)?

16. Structural Engineering and Earthquake Simulation Laboratory 16 Lateral Spread Mechanism [Contd.] Lateral spreading begins when cyclic shear stress meets monotonic failure envelope. Soil is not necessarily at liquefied state when lateral spread begins. Ultimate  int Monotonic Strength Envelope Flow Begins !!!

17. Structural Engineering and Earthquake Simulation Laboratory 17 Strain Accumulations - ND Phase LG-0 SG-1 Little Strain Accumulations in 0-5s More Strain Accumulations in 0-5s

18. Structural Engineering and Earthquake Simulation Laboratory 18 Strain Accumulations – ND & Strong Shaking Phase Small Deformations Large Deformations, primarily initiated by gravitational static shear

19. Structural Engineering and Earthquake Simulation Laboratory 19 Comments on LG-0 Vs SG-1  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 r u ~ 0.9-1.0.  Sloping Ground Soil Strains accumulate @ low r u (~ 0.6-0.7). Initial Static shear has a significant influence in initiating large strains.  Cyclic shear in SG-1 degrades the soil sufficiently to a point where the cyclic shear stress meets undrained strength envelope, lateral spreading begins?  Identify lateral spread initiation points from stress-strain curves deduced from acceleration data (next)  Then perform Newmark analysis modified to account for strength degradation

20. Structural Engineering and Earthquake Simulation Laboratory 20 Soil Response @ 1.3m - Animation

21. Structural Engineering and Earthquake Simulation Laboratory 21 1.3m Soil Response & Spreading Initiation

22. Structural Engineering and Earthquake Simulation Laboratory 22 Soil Response & Spreading Initiation 0.78m

23. Structural Engineering and Earthquake Simulation Laboratory 23 1.94m Soil Response & Spreading Initiation

24. Structural Engineering and Earthquake Simulation Laboratory 24 2.71m Soil Response & Spreading Initiation

25. Structural Engineering and Earthquake Simulation Laboratory 25 3.37m Soil Response & Spreading Initiation

26. Structural Engineering and Earthquake Simulation Laboratory 26 Soil Response @ 4m - Animation

27. Structural Engineering and Earthquake Simulation Laboratory 27 4m Soil Response & Spreading Initiation

28. Structural Engineering and Earthquake Simulation Laboratory 28 4.65m Soil Response & Spreading Initiation

29. Structural Engineering and Earthquake Simulation Laboratory 29 5.17m Soil Response & Spreading Initiation

30. Structural Engineering and Earthquake Simulation Laboratory 30 Mobilized Strength & Friction Angle during Spreading Strain-dependent strength and Friction Soil strength equal to the existing stress, from the spread initiation point onwards Friction angle increases with strain, during spreading tan   f()f() (1- r u )  ’ v0 =

31. Structural Engineering and Earthquake Simulation Laboratory 31 Mobilized Friction Angle [during sliding]  Top Rings

32. Structural Engineering and Earthquake Simulation Laboratory 32 Mobilized Friction Angle [during sliding]  Bottom Rings

33. Structural Engineering and Earthquake Simulation Laboratory 33 Mobilized Friction Angle [during sliding]  Top Rings

34. Structural Engineering and Earthquake Simulation Laboratory 34 Mobilized Friction Angle [during sliding]  Bottom Rings

35. Structural Engineering and Earthquake Simulation Laboratory 35 Modified Newmark Rigid Sliding Block Analysis Coupled with Strength Degradation and variable yield acceleration

36. Structural Engineering and Earthquake Simulation Laboratory 36 Model Description Original Laminar Box Rings Soil a 1 (t) a 2 (t) a i (t) a n (t) a n-1 (t) Rigid Block a avg (t) Weight of Rings, including the unfilled incorporated Weight of each ring 11% of the weight of saturated soil filled in one ring Horizontal Ground surface considered Acceleration of the rigid block = Average of accelerometers present above the sliding surface Yield Acceleration

37. Structural Engineering and Earthquake Simulation Laboratory 37 Other Assumptions Strength & Yield Acceleration varying with strain (& time) Yield Acceleration obtained from shear strength during sliding a yield = (  f A-Wsin  )/M  f (  ) = (1-r u )  ’ v0 tan    f (  ) = shear strength during sliding   = Friction angle varying with Strain (& time) A = Area of Laminar Box (12.75 m 2 ), M = mass of the rigid block

38. Structural Engineering and Earthquake Simulation Laboratory 38 Newmark Displacements [Top Rings] Excellent Agreement with Shape Array Data

39. Structural Engineering and Earthquake Simulation Laboratory 39 Newmark Displacements [Bottom Rings]

40. Structural Engineering and Earthquake Simulation Laboratory 40 Threshold Flow Slide Strains & Times Top Rings slide at 19.29s Bottom Rings at 20.2s Initiation 2 (Red) Threshold Strains between 0.4 to 0.65%

41. Structural Engineering and Earthquake Simulation Laboratory 41 Excess Pore Pressure Response Soil is NOT at liquefied state when lateral spread begins at 19.3 and 20.2 s.

42. Structural Engineering and Earthquake Simulation Laboratory 42 Flow Slide Threshold Strengths ≈ Constant !!!

43. Structural Engineering and Earthquake Simulation Laboratory 43 Threshold Strengths Undrained Shear strength approaching initial static shear stress !!!

44. Structural Engineering and Earthquake Simulation Laboratory 44 Some Variations in Initiation Point (More to come later) Shear Strain Shear Stress Shear Strain Shear Stress Higher Amplitude Shear Strain Shear Stress Steady State Strength ≠ Initial Static Shear Shear Strain Shear Stress Peak Strength ≈ Initial Static Shear

45. Structural Engineering and Earthquake Simulation Laboratory 45 Factors Conducive for Lateral Spreading SG-1 Shear Strain 00 Cyclic Flow Failure Strain Accumulation Monotonic Strength Envelope Shear Stress Shear Strain LG-0 Monotonic Strength Envelope Small Strain Accumulation No Static Shear Very little Strain Accumulation No Flow observed Failure termed as Liquefaction Non-zero Static Shear Strain Accumulation until  curve hits the strength envelope Large Flow thereafter and  curve follows the envelope Failure termed as Flow Failure

46. Structural Engineering and Earthquake Simulation Laboratory 46 Triaxial Test Data Triaxial Test Data (no initial shear, Theva 2003) e=0.779 (Moist tamping) e = 0.778 (MT) e=0.804 (MT) Is this what is seen in SG-1? Is hydraulic fill creating meta-stable structure more prone to collapse? Is collapse potential higher if static shear is present (i.e occurs at higher densities)?

47. Structural Engineering and Earthquake Simulation Laboratory 47 Conclusions Soil does not have to fully liquefy for lateral spreading to begin. But soil must be degraded to a ‘threshold’ strength for lateral spreading to begin. Lateral spread likely begins when the soil is sufficiently degraded and the cyclic  curve hits monotonic strength envelope Threshold spreading point depends on initial static shear, cyclic shear amplitude, pore pressure generation and associated degradation of soil strength. Once lateral spreading begins, little or no cyclic component exist. ‘Effective’ soil friction angle during spreading increases. Modified Newmark Analysis, coupled with strength degradation, traces the measured lateral displacements well. Undrained strength ratio at threshold lateral spreading falls in a narrow range of about 0.08 Does hydraulic fill method create soil structure prone to collapse?