igs uk & university of manchester · 2/4/2019 · igs / university of manchester 4th february...

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

Geocell wall

OUTLINE What are 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

• Geocell provides confinement.

• Broadly two types: Gravity and MSE

OUTLINE What are 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

• Sometimes combined with a geogrid

reinforced soil block to create a

Mechanically Stabilised Earth (MSE)

OUTLINE A Short History of Geocells

• 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

• 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

• 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

GEOGRID

GEOCELL PANELS

OUTLINE Construction

• Foundation

• Expanding cells

• Foundation

• Expanding cells

• Connecting adjacent

panels

• Foundation

• Expanding cells

panels

• Backfilling

• Foundation

• Expanding cells

panels

• Backfilling

• Placing geogrid

• Foundation

• Expanding cells

panels

• Backfilling

• Placing geogrid

• Compaction methods

(topsoil vs. general fill)

• Foundation

• Expanding cells

panels

• Backfilling

• Placing geogrid

• Aligned front face cells

• Foundation

• Expanding cells

panels

• Backfilling

• Placing geogrid

• Curves

• Foundation

• Expanding cells

panels

• Backfilling

• Placing geogrid

• Curves

• Corners

OUTLINE Advantages and Disadvantages

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?)

ADVANTAGES

• Green finish

• Cost savings

• Soft Facing

ADVANTAGES

• Green finish

• Cost savings

• Soft Facing

ADVANTAGES

• Green finish

• Cost savings

• Soft Facing

ADVANTAGES

• Green finish

• Cost savings

• Soft Facing

MSE wall with Geocell (Webwall) vs Gabion Baskets facing elements. Based on ‘Axis Business Park’ case study from WRAP (2010)

ADVANTAGES

• Green finish

• Cost savings

• Soft Facing

ADVANTAGES

• Green finish

• 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)

ADVANTAGES

• Green finish

• Cost savings

• Soft facing

DISADVANTAGES

• Soft facing

• Susceptible to vandalism

GEOGRID

GEOCELL PANELS

DISADVANTAGES

• Soft facing

DISADVANTAGES

• Soft facing

DISADVANTAGES

• Soft facing

• Susceptible to vandalism (only front face, repairable)

OUTLINE Specification

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

• 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

• 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

• 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

• 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

• Test Method: Single

Point Notched Constant

Tension Load Test

ASTM D 5397.

• Result must be greater

than 500 hours.

OUTLINE Case Studies

• 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

• The Challenge

- Road underslip on a key

tourist route in an AONB.

- Limited access.

- Excavated soils

unsuitable as fill material.

- Green finish required.

• The Solution

- HDPE Geocells.

- Light weight fill

(expanded clay beads).

- Minimal machinery

required to achieve

speedy installation.

• The Solution

- HDPE Geocells.

- Light weight fill

- Minimal machinery

required to achieve

- Drainage constructed

through the wall.

• The Solution

- HDPE Geocells!

- Light weight fill

- Minimal machinery

required to achieve

- Drainage constructed

through the wall.

- Green finish.

OUTLINE Case Studies – Istanbul

• The Challenge

- Luxury residential /

commercial complex on a

- 15m high retaining wall

- Earthquake resistance

• The Solution

- NPA Geocells.

- MSE wall.

- Local granular infill

material used.

• 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

• The Challenge

- Narrow roadside area

below a historic church.

- Footpath at the top.

- Simple and speedy

construction.

• The Solution

- HDPE Geocells.

- Re-use of site soils.

- Rapid construction.

- Use of small machinery

in a tight space.

• The Solution

- HDPE Geocells!

- Rapid construction.

- Use of small machinery

in a tight space.

- Handrail in cells at top

Green finish.

OUTLINE Case Studies – Swansea

• 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.

• The Solution

- NPA Geocells.

- MSE wall.

- Concrete infill to resist

erosion forces.

- Dutch toe at base.

• The Solution

- NPA Geocells.

- MSE wall.

- Concrete infill to resist

erosion forces.

- Dutch toe at base.

OUTLINE Case Studies – Colchester

• 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.

• The Solution

- HDPE Geocells.

- MSE wall.

- Curvilinear face.

• The Solution

- HDPE Geocells.

- MSE wall.

- Curvilinear face.

- Erosion resistant green

OUTLINE Case Studies – Kentucky

• The Challenge

- Record river surge in

Smithland, Kentucky.

- US Army Corps of

Engineers requested

emergency installation of

geocell retaining walls for

flood defence.

• 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.

• 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

• 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 uk & university of manchester · 2/4/2019 · igs / university of manchester 4th february...

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