1 SG-1: Lateral Spreading – Observations and Analysis Raghudeep B., and S. Thevanayagam, UB Aug. 07, 2007, 2-4 pm; UB-VTC SG-1: Lateral Spreading – Observations and Analysis Raghudeep B., and S. Thevanayagam, UB Aug. 07, 2007, 2-4 pm; UB-VTC 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, 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 oInitiation of spreading – hypothesis oNewmark analysis - Sliding oSome thoughts  Comparisons of LG-0 and SG-1 oHighlights – Similarities & Differences (flat versus sloping ground)  Thoughts on lateral spreading

3 Review of Test SG-1

4 Inclined Box (2 o ) 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 Acceleration Response Base Input Motion

8 Excess Pore Pressure Response

9 Displacements (Potentiometers)

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

11 Acceleration & PWP Response Ring Accelerations Top Middle Bottom

12 Lateral Spreading Observations & Animation

13 Velocity 0 – 7ft

14 Velocity (Contd.) 10 – 13ft

15 Velocity (Contd.) 10 – 17ft

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 Spreading Initiation 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 Newmark Rigid Sliding Displacement Analysis Rigid Block a 1 (t) a 2 (t) a i (t) a n (t) a n-1 (t) a avg (t) Yield Acceleration Yield Acceleration obtained from the available shear strength data which in turn is obtained from the pore pressure data.  = 22 o is assumed. Double-integration of relative acceleration to obtain displacement. Original Laminar Box

28 Newmark Displacements (without dilation)  = 22 o

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

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 Ground LG-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 Negligible r u during 5s (ND) Faster pwp 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 (  = 22 o ) which causes rapid build up of strain. This Fig. clearly explains why soil in SG1 degraded faster than in LG0

37 Cyclic Shear Strains Significantly cyclic in nature Monotonic Strains dominate

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

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

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 high r u ~  Sloping Ground Soil Strains low r u (~ )

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