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slide1
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)
outline
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
review of test sg 11
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
test sg 1 configuration
Test SG-1 Configuration

Top View

Side View

shear strains potentiometer
Top Rings

Spread Initiation

Bottom Rings

Delayed Initiation of Spread

Shear Strains (potentiometer)
acceleration pwp response
Acceleration & PWP Response

Top

Ring Accelerations

Middle

Bottom

velocity observations
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
deduced shear stresses
Deduced Shear Stresses

Top Rings

Bottom Rings

newmark rigid sliding displacement analysis
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.
newmark displacements with dilation
f

Strain

Newmark Displacements (with dilation)

f = 26o

Lower Displacements

lateral spreading thoughts
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)
level ground vs sloping ground
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

lg0 vs sg1 accelerations
LG0 Vs SG1: Accelerations

Quick degradation of accelerations in SG-1 due to fast pwp

development due to initial static shear

pore pressure ratios
Pore Pressure Ratios

Faster pwp during 5s (ND)

Negligible ru during 5s (ND)

a closer look at previous slide
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

shear stresses
Shear Stresses

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

stress strain behavior
Stress-Strain Behavior

Large Deformations, primarily initiated

by graviational static shear

Small Deformations

comments on lg 0 vs sg 1
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)
conclusions
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
ad