igs uk & university of manchester · 2/4/2019 · igs / university of manchester 4th february...
TRANSCRIPT
IGS UK & University of Manchester “GEOCELL RETAINING WALLS”
Richard Heritage
Geotechnical Engineer
ABG Geosynthetics Ltd
• What are Geocell Retaining Walls
• A Short History of Geocells
• Design • Gravity Retaining Walls
• Reinforced Retaining Walls
• Construction
• Advantages and Disadvantages
• Specification
• Case Studies
• Conclusion
OUTLINE Outline
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
OUTLINE Retaining Wall Options
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
OUTLINE Retaining Wall Options
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
Geocell wall
OUTLINE What are Geocell Retaining Walls
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Definition of geocells:
Geosynthetics made with internal structural junctions that can be
expanded on-site to form a honeycomb-like structure and filled with soil,
rock, or concrete.
• Typically made with polymers such
as HDPE or NPA membranes, or
PP/PE geotextiles.
• Backfill can be site won or imported.
• Geocell / soil combination forms a
semi-rigid block which can be
stacked up to form a gravity retaining
wall.
• Geocell provides confinement.
• Broadly two types: Gravity and MSE
OUTLINE What are Geocell Retaining Walls
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Definition of geocells:
Geosynthetics made with internal structural junctions that can be
expanded on-site to form a honeycomb-like structure and filled with soil,
rock, or concrete.
• Typically made with polymers such
as HDPE or NPA membranes, or
PP/PE geotextiles.
• Backfill can be site won or imported.
• Geocell / soil combination forms a
semi-rigid block which can be
stacked up to form a gravity retaining
wall.
• Sometimes combined with a geogrid
reinforced soil block to create a
Mechanically Stabilised Earth (MSE)
wall.
OUTLINE A Short History of Geocells
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Invented in late 1970’s with
the US Army Corps of
Engineers.
• Primarily used to create
stabilised sand roads.
• Rapid construction of fortified
walls with Operation Desert
Storm in the 1990s.
U.S. Army Corps of Engineers testing geocell roads at Camp Blanding in 1982
OUTLINE Design – Gravity Walls
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Option 1: Coulomb earth pressure theory (Standard gravity wall design methods to check for overturning, bearing,
etc. CIRIA C516 “Modular gravity retaining walls – design guidance”)
• Option 2: Limit equilibrium method for slopes (Method of slices e.g. Morgenstern & Price using slope stability software.
Model geocell-reinforced soils as having an ‘apparent cohesion’ cr)
• Special considerations: - Interface friction between geocell webs
- Flexible footing
- Consistent soil type
- Soil compaction
OUTLINE Design – Gravity Walls
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Option 1: Coulomb earth pressure theory (Standard gravity wall design methods to check for overturning, bearing,
etc. CIRIA C516 “Modular gravity retaining walls – design guidance”)
• Option 2: Limit equilibrium method for slopes (Method of slices e.g. Morgenstern & Price using slope stability software.
Model geocell-reinforced soils as having an ‘apparent cohesion’ cr)
• Special considerations: - Interface friction between geocell webs
- Flexible footing
- Consistent soil type
- Soil compaction
• Standard reinforced
earth design techniques
(BS8006 Section 7:
Reinforced slopes)
• Geocells form a facing
for the wall.
• Geocell / geogrid sliding
resistance.
• Facing may need
protection against UV.
• Soft facing.
OUTLINE Design – MSE Walls
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
GEOGRID
GEOCELL PANELS
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
• Placing geogrid
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
• Placing geogrid
• Compaction methods
(topsoil vs. general fill)
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
• Placing geogrid
• Compaction methods
(topsoil vs. general fill)
• Aligned front face cells
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
• Placing geogrid
• Compaction methods
(topsoil vs. general fill)
• Aligned front face cells
• Curves
OUTLINE Construction
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Foundation
• Expanding cells
• Connecting adjacent
panels
• Backfilling
• Placing geogrid
• Compaction methods
(topsoil vs. general fill)
• Aligned front face cells
• Curves
• Corners
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
DISADVANTAGES
• Soft facing
• Typical maximum slope 70°
• UV resistance and ESCR
• Susceptible to vandalism (repairable?)
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
MSE wall with Geocell (Webwall) vs Gabion Baskets facing elements. Based on ‘Axis Business Park’ case study from WRAP (2010)
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft Facing
Savings based on cost of exporting waste and imported material costs only.
MSE wall with Geocell (Webwall) vs Gabion Baskets facing elements. Based on ‘Axis Business Park’ case study from WRAP (2010)
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
ADVANTAGES
• Green finish
• Flexible (curves, corners etc.)
• Re-use of site won material
• Reduced Carbon footprint
• Ease and speed of construction
• Cost savings
• Soft facing
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
DISADVANTAGES
• Soft facing
• Typical maximum slope 70°
• UV resistance and ESCR
• Susceptible to vandalism
GEOGRID
GEOCELL PANELS
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
DISADVANTAGES
• Soft facing
• Typical maximum slope 70°
• UV resistance and ESCR
• Susceptible to vandalism
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
DISADVANTAGES
• Soft facing
• Typical maximum slope 70°
• UV resistance and ESCR
• Susceptible to vandalism
OUTLINE Advantages and Disadvantages
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
DISADVANTAGES
• Soft facing
• Typical maximum slope 70°
• UV resistance and ESCR
• Susceptible to vandalism (only front face, repairable)
OUTLINE Specification
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
What to look out for in
datasheets
• Tensile strength/
stiffness of strip and
joints.
• Creep.
• UV & Oxidation
resistance.
• Environmental Stress
Crack Resistance
(ESCR).
OUTLINE Specification - Strength/Stiffness
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Both polymer strips and
joints should be tested
• Strips: Strip tensile
strength, ISO 10319:
2015 (wide width)
• Joints: Strength of
internal structural
junctions. Geocells, ISO
13426-1:2003
OUTLINE Specification - Creep
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Standard Test Method:
Tensile, Compressive,
and Flextural Creep and
Creep-Rupture of
Plastics, ASTM D 2990
• Accelerated Test
Method: SIM (Stepped
Isothermal Method)
Testing, ASTM D 6992.
OUTLINE Specification - UV & Oxidation
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Accelerated Test
Method: Photochemical
(UV) & Oxidation
Resistance (HPOIT),
ASTM D 5885.
• Addition of antioxidant
stabilisers (AO)
intercepts the oxidation
reaction of polymers.
• Result must be greater
than 400 minutes.
OUTLINE Specification - ESCR
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Environmental Stress
Crack Resistance.
• Occurs only in HDPE
under tension e.g. front
face of Geocell
Retaining Wall.
• Brittle failure following
exposure to oxidation.
OUTLINE Specification - ESCR
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Test Method: Single
Point Notched Constant
Tension Load Test
ASTM D 5397.
• Result must be greater
than 500 hours.
OUTLINE Case Studies
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Clitheroe Embankment Retention
• Istanbul Seismic Resistant 15m High Wall
• Colchester Attenuation Pond
• Swansea Sea Wall
• Saundersfoot Roadside Wall
• Kentucky Flood Defence
OUTLINE Case Studies - Clitheroe
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Road underslip on a key
tourist route in an AONB.
- Limited access.
- Excavated soils
unsuitable as fill material.
- Green finish required.
OUTLINE Case Studies - Clitheroe
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells.
- Light weight fill
(expanded clay beads).
- Minimal machinery
required to achieve
speedy installation.
OUTLINE Case Studies - Clitheroe
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells.
- Light weight fill
(expanded clay beads).
- Minimal machinery
required to achieve
speedy installation.
- Drainage constructed
through the wall.
OUTLINE Case Studies - Clitheroe
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells!
- Light weight fill
(expanded clay beads).
- Minimal machinery
required to achieve
speedy installation.
- Drainage constructed
through the wall.
- Green finish.
OUTLINE Case Studies – Istanbul
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Luxury residential /
commercial complex on a
hill.
- 15m high retaining wall
- Earthquake resistance
OUTLINE Case Studies – Istanbul
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- NPA Geocells.
- MSE wall.
- Local granular infill
material used.
OUTLINE Case Studies – Istanbul
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- NPA Geocells.
- MSE wall.
- Local granular infill
material used.
- System acts as unified
drainage system with no
build up of hydrostatic
pressures.
- Colour blends into
landscape.
OUTLINE Case Studies – Saundersfoot
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Narrow roadside area
below a historic church.
- Footpath at the top.
- Green finish required.
- Simple and speedy
construction.
OUTLINE Case Studies – Saundersfoot
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells.
- Re-use of site soils.
- Rapid construction.
- Use of small machinery
in a tight space.
OUTLINE Case Studies – Saundersfoot
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells!
- Re-use of site soils.
- Rapid construction.
- Use of small machinery
in a tight space.
- Handrail in cells at top
Green finish.
OUTLINE Case Studies – Swansea
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Resisting frequent water
inundation (high tides and
flooding).
- Prevent erosion from
wave action and storm
surges.
- Withstand corrosive
effects of seawater.
- Muddy clay soft
subgrade.
OUTLINE Case Studies – Swansea
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- NPA Geocells.
- MSE wall.
- Concrete infill to resist
erosion forces.
- Dutch toe at base.
OUTLINE Case Studies – Swansea
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- NPA Geocells.
- MSE wall.
- Concrete infill to resist
erosion forces.
- Dutch toe at base.
OUTLINE Case Studies – Colchester
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Attenuation pond for a
housing development.
- Retaining walls to
steepen the sides and
maximise land take.
- Re-use challenging site
soils to minimise costs.
- Green finish required.
OUTLINE Case Studies – Colchester
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells.
- MSE wall.
- Curvilinear face.
- Re-use of site soils.
OUTLINE Case Studies – Colchester
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- HDPE Geocells.
- MSE wall.
- Curvilinear face.
- Re-use of site soils.
- Erosion resistant green
face.
OUTLINE Case Studies – Kentucky
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Challenge
- Record river surge in
Smithland, Kentucky.
- US Army Corps of
Engineers requested
emergency installation of
geocell retaining walls for
flood defence.
OUTLINE Case Studies – Kentucky
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- PP/PE geotextile
Geocells.
- Installation frame used
for increased construction
speed.
- In 34 hours 1 mile of
geocells were installed by
local, untrained
workforce.
OUTLINE Case Studies – Kentucky
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• The Solution
- PP/PE non-woven
geotextile Geocells.
- Additional 1.1m of
height added to levee
flood protection height.
- Outperforms sand bags
due to: faster installation
(and removal), less water
seepage, higher
endurance.
OUTLINE Conclusion
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS
• Geocell retaining walls have been used since 1990s
• Standard design methods
• Significant advantages (Green finish, flexible, re-use of site won material, reduced Carbon
footprint, ease and speed of construction, cost savings, soft facing)
• What to look out for in datasheets (Tensile strength and stiffness, creep, UV oxidation resistance, ESCR)
• Geocell retaining walls can be used almost
anywhere!
OUTLINE Acknowledgments
IGS / UNIVERSITY OF MANCHESTER 4TH FEBRUARY 2019 – GEOCELL RETAINING WALLS