Geosynthetic Reinforcement Technologies and Recent Developments

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Geosynthetic Reinforcement Technologies and
Recent Developments
Jie Han, Ph.D., PE Associate Professor
The University of Kansas, USA
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Outline of Presentation

• Introduction
• Reinforcement Mechanisms
• Reinforcement for Earth Retaining
• Reinforcement for Foundation Support
• Concluding Remarks

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Introduction
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Ancient Reinforcement Technology
Han Great Wall
Courtesy of Xue
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Modern Reinforcement Technology
In the 1960s, noted engineer and architect, Henri
Vidal introduced reinforced earth technology
Source Reinforced Earth Company
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Geosynthetic Reinforcement
Woven Geotextile
GSI
New Geogrid
Geocell
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Evolution of Geosynthetic Reinforcement

• 1926 Woven cotton textiles were used in test
  sections in highways in South Carolina, USA
• 1977 International Conference on the use of
  fabrics in geotechnics - Paris, France. The words
  "geotextiles" and "geomembranes" were coined by
  Dr. J.P. Giroud.
• 1980 The first book on Geosynthetics by Koerner
  Welsh
• 1983 The International Geotextile Society (IGS)
  was founded in Paris, France
• 1986 Giroud, J.P., From geotextiles to
  geosynthetics a revolution in geotechnical
  engineering, Proceeding III International
  Conference on Geotextiles, Vienna, Austria
• Two Terzaghi Lectures Koerner (2000) and Giroud
  (2008)

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Reinforcement Mechanisms
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Reinforcement Mechanisms

• Provide (tensile) strength necessary for soil
• Increase shear (interlocking or confinement)
  resistance
• Mechanisms anchorage (tensile resistance),
  lateral
• and vertical confinement

Vertical Confinement (Tensioned Membrane)
Lateral Confinement
Anchorage
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Confinement and Interlocking
Interlocking
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Particle Movement Under Wheel Loading
Geogrid Reinforcement
No Reinforcement
Courtesy of Kinney
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Effect of Confinement - Strength
Tensile force
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Effect of Confinement - Modulus
Applied Pressure
E1
1
Vertical Displacement
3D reinforcement
Unreinforced
2D reinforcement
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Original Research by US Army Corps of Engineers
- 1979
Beach Landing Tests - Virginia, USA - 1984
Wheels Sink into Sand
Support of Wheels on Geoweb Confined Sand
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Vertical Stress Distribution in Two-Layer System
a
h1r
E1
E2
z/a
Burmister (1958)
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Benefits of Geosynthetic Reinforcement

• Increase bearing capacity
• Increase factor of safety of slope stability
• Increase stiffness of soil
• Reduce differential settlement
• Reduce permanent deformation under dynamic
• loading
• Minimize/slow down deterioration of base course

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General Applications
Slopes
Earth retaining
Walls
Reinforcement
Embankments Foundations Roads Railroads Landfills
Foundation support
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Reinforcement for Earth Retaining
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Case History - Recreational Water Park

• Design Requirements
• Create artificial mountain 21m (70 ft) high
• Highly irregular surface shape
• Slopes from 3H1V to 0.35H1V
• Compressible foundation soils

Orlando, FL
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Facing Details
Orlando, FL
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Placement of Geogrid in Slope
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Complete Product

• Lessons Learned
• Fast track construction
• Flexible facing
• Onsite or low quality fill
• Natural vegetation
• Economic

Orlando, FL
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Failure Modes of Reinforced Slopes
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Search for Minimum Factor of Safety
Method 1
FS
Exit points
FS
Start points
Method 2
Critical surface
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FS Safety Map
Courtesy of Leshchinsky
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Surficial Failure

• Shallow failure surface up to 1.2m (4ft)
• Failure mechanisms
• Poor compaction
• Low overburden stress
• Loss of cohesion
• Saturation
• Seepage force

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Surficial Slope Stability
z
Saturated
Primary reinforcement
H
ß
Secondary reinforcement
Tg summation of geosynthetic resisting force
(controlled by pullout or rupture)
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Full-Height Panel Wall System
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Modular Block Wall System
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Failure Modes of Retaining Walls
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External and Internal Stability
External stability
S1/2hs
q gS
hs
z
qr gz
H
Internal stability
pa1KagH
pa2KagS
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Water-induced Wail Failure
Courtesy of Leshchinsky
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Geogrid-Reinforced Wall along JR Kobe Line (1992)
Courtesy of Leshchinsky
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Geogrid-Reinforced Wall along JR Kobe Line (1995)
Courtesy of Leshchinsky
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Case Study Limited Space MSE Walls
(Courtesy of Daryl Wurster)
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(Courtesy of Daryl Wurster)
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(Courtesy of Daryl Wurster)
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(Courtesy of Daryl Wurster)
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Modified Coefficient of Lateral Earth Pressure,
Ka
? 36o, m ?
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Case Study Tiered Wall
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Exterior/Interior Wall Cracks
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Limit Equilibrium and Numerical Analyses
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Tiered Wall Lessons Learned

• Limit equilibrium and numerical analyses
• yield nearly identical Factor of Safety (FoS)
• FoS 1.20 (with c), FoS 1.05 (without c).
• Cohesion should not be considered for a
• long-term stability
• FoS gt 1.3 is enough for slope stability but
• FoS gt 1.5 is required to support sensitive
• structures

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Case Study Piles in MSE Wall
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Wall and Pile Construction
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Geogrid and Fill
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Single Pile Test
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Group Pile Test
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Facing Deflection Horizontal Profile
Single Pile Test
Group Pile Test
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Wall after Testing
Group after test at noon
Group after test
Group after test afternoon
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Reinforcement for Foundation Support
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Failure Modes of Basal Reinforcement
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Geosynthetic-Reinforced Pile/Column-Supported
Embankments
Geosynthetic-reinforced fill platform
Ds?0
Geosynthetics
Embankment
Ds0
Small size Pile caps
Piles or columns
Firm soil or bedrock
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Type of Columns
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Piles and Caps
Geosynthetics
Courtesy of Chris Dumas
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Applications of Pile-supported Embankments
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Displacement Vector DEM Study
Soil Arching
Tensioned membrane
Unreinforced embankment
Reinforced embankment
Bhandari and Han (2008)
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Current Design Method
Step 1
Soil arching
Pressure on geosynthetic
Step 2
Membrane or Beam theory
Tension in geosynthetic
Step 3
Slope stability
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Field Performance
Courtesy of Huesker
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Physical Model Simulation
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Design Issues

• Percent coverage of pile or cap 10 to 20
• Pile type rigid pile is better
• End-bearing condition preferred
• Critical height (1.0 to 1.5) clear space of
  piles
• Soil resistance a significant effect
• Strain in geosynthetics 2 to 6 (design) and 0
  to 3
• (measured)
• Settlement more effective for differential
  settlement
• and no reliable and simple method available

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Subgrade Improvement for Unpaved Roads
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Base Reinforcement for Paved Roads

• Prevent lateral spreading of base aggregate
• Increase confinement
• Reduce plastic deformation - rutting

Courtesy of Reck
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Failure of Base Courses
Unreinforced
Horizontal confinement
Vertical confinement
Geocell-Reinforced
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Bearing Capacities for Unreinforced and
Reinforced Cases
p0?c
pu(?2)c
p
p
p
Base
Base
Elastic limit
Subgrade
Subgrade
Ultimate bearing capacity
s
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Failure of Subgrade
Tire
Initial distribution
Distribution at failure
Distribution after N passes
Giroud and Han (2004)
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Cyclic Plate Loading Test
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Testing of Geocell-reinforced Bases
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Moving Wheel Testing
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Cumulative Plastic Deformation
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Base Thickness - Reinforced
Giroud and Han (2004)
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Landfill Slope Stability
Geogrid
Geomembrane
Courtesy of Giroud
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Courtesy of Giroud
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Landfill Liner Support
Geogrid
Void
Geosyntec
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Concluding Remarks

• Geosynthetic reinforcement has been successfully
  
• used for many different applications
• Geosynthetic reinforcement can provide tensile,
  shear,
• and confinement resistance
• Reinforced slope is flexible at different slope
  angles
• but surficial slope stability is a major
  concern
• FoS gt 1.3 is enough for slope stability but FoS
  gt 1.5 is
• required to support sensitive structures
• Geosynthetic-reinforced wall has a superior
  seismic
• resistance
• Reinforced wall can effectively carry lateral
  load from pile
• Geosynthetic can reduce plastic deformation
  under
• traffic loading

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Thank You!