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Overview of Geosynthetic Materials,
Their Characteristics, Applications,
and Design Considerations
Jie Han, Professor, Ph.D., PE
The University of Kansas
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Outline of Presentation
Introduction
Geosynthetic Products
Primary Functions
Material Characteristics
Applications
Design Considerations
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Geosynthetics
Geo: Earth - soil or rock
Synthetics:
Man-made products, mainly polymers
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Textural Soil Classification
Soil Name Particle Size (in.) U.S. Sieve No.
Boulders > 12
Cobbles 12 - 3
Gravel
Coarse
Fine
Sand
Coarse
Medium
Fine
Clays and silts
3 – 3/4
3/4 – 0.19
0.19 – 0.079
0.079 - 0.017
0.017 - 0.003
< 0.003
3 - 3/4 in.
3/4 in. to No. 4
No. 4 to No. 10
No. 10 to No. 40
No. 40 to No. 200
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State of Soil
Dry
Unsaturated
Saturated
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Particle Sizes
Particle Size (in.) – log Scale
Perc
en
t o
f P
assin
g (
Fin
er)
100
80
60
40
20
10 1 0.1 0.01 0.001
D10 D30 D50 D60 D85 D15
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Soil Gradation
Cu > 4 (gravel) or 6 (sand)
Others
1 < Cc < 3 Well-graded (W)
Poorly-graded (P)
Coefficient of uniformity
10
60u
D
DC
Coefficient of curvature
1060
2
30c
DD
DC
D60 D30 D10
60
30
10
% fines
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Surface Erosion Potential and
Plant Growth Capability
Rivas (2006)
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Soil Permeability
Ah
QLk
Q
h Area
A
L
Permeability
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Basics of Physics
tanW
Ff
Frictional coefficient
= frictional angle
P
W
F = P
F
W
T N
Factor of Safety
tan
tan
T
FFoS
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Soil Strength
tanA
Wcf
Shear strength
c = cohesion
= frictional angle
P
W
F = f A
A
Soil
Short term
c = 0 for uncemented sand
(air dry or saturated)
c > 0 for clay
(air dry or saturated)
Long term
c = 0 for uncemented sand
c = 0 for clay (saturated)
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Apparent Cohesion
tanA
Wcaf
Shear strength
ca = apparent cohesion
= frictional angle
Apparent cohesion
• Exist when soil is unsaturated due to capillary action
(i.e., suction), but disappear when soil is saturated or dry
• Rooted soil has apparent cohesion
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Long-term Stability of Natural Slope
01.tan
tanFS
m:1 m:1
0150 .tan
tan.FS
Seepage water
For typical soil, = 30o
2(H):1(V) slope (27o) 4(H):1(V) slope (14o) Stable
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Products of Geosynthetics
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Geosynthetic Products
Geotextile (GT)
Geogrid (GG)
Geonet (GN)
Geomembrane (GM)
Geosynthetic Clay Liner (GCL)
Geocell/geoweb (GW)
Geocomposite (GC)
Geotube (GTB)
Erosion mat (EM)
Others
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Types of Geosynthetics Used
Gabr et al. (2006)
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Type of Polymer
Polypropylene (PP)
Polyester (PET)
Polyethylene (PE)
Polyamide (nylon)
Others
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Geotextiles
Nonwoven Geotextiles: bonded or needle-punched
Woven Geotextiles
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Geogrids
Consist of apertures with ribs
UX, BX, or TX geogrid
Punched and drawn, coated woven or wielded
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Geonets
Grid-like materials, made of polyethylene (PE)
Have thickness difference in ribs
Used for in-plane drainage
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Geomembranes
PE dominates, sometimes PP or PVC
Manufactured by extrusion
Smooth or rough (textured) surfaces
Impermeable materials, mainly used as barriers
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Geosynthetic Clay Liners
Bentonite clay bonded between two geotextiles
Used as replacement for compacted clay liners or
geomembranes
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Geocomposites
Combine two or more geosynthetic products to one
product
Geotextile-geonet composites
Geotextile-geogrid composites
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Geocell or Geoweb
An expandable three-dimensional honeycomb-like
structure
Used for soil confinement
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Geotubes
Sediment-filled sleeves of geotextile with an oval
cross section
Mainly used for erosion protection along shores and
waterfronts
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Erosion Blanket or Mats
Protect ground surfaces (especially slopes) from
loss of soil due to water
Temporary erosion mats are used for flatter slopes
(<45o) and degraded after development of vegetation
(i.e., Erosion-control blanket)
Permanent erosion mats are used for steep slopes
(>45o) (i.e., Turf Reinforcement Mat)
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Functions of Geosynthetics
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Primary Functions of Geosynthetics
Separation
Filtration
Drainage
Reinforcement
Containment (barrier)
Erosion protection
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Separation Function
Keep the integrity and functioning of two
dissimilar materials intact
Prevent stone aggregate intruding into fine soil
Prevent soil fines pumping into aggregate
Courtesy of
Christopher
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Filtration Function
Allow for adequate liquid flow
Limit soil loss across the interface plane
Natural filter Geotextile filter
GRADUALLY INCREASE
PARTICLE SIZES
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Drainage Function
Large porosity or open space to allow
water quickly flow through
Nonwoven geotextile Geocomposite
Fabric
Voids
Nonwoven geotextile
Core
Geopipe
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Reinforcement Function
Provide (tensile) strength necessary for soil
Increase shear (interlocking) resistance
Increase stiffness & minimize deformation (confinement)
Interlocking Confinement
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Containment Function
Low permeable materials minimize liquid
flow
Geomembrane or GCL
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Erosion Protection Function
Avoid water drops directly hitting on soil
surface
Reduce rate of water flow
Contain and retain soil particles
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Summary of Primary
Functions of Geosynthetics
Type
NWV GT
WV GT
GG
GN
GM
GCL
GP
GTB
GC
SP RF FT DN CT
SP=Separation
RF=Reinf.
FT=Filtration
DN=Drainage
CT=Containment
EP
EP=Erosion
Protection
X X
X X
X X X X X
X X X X X
X X X
X X X
X X
X X X X X
D D D D D D
GW X X X
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Properties of Geosynthetics
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Properties of Geosynthetics
Physical properties
- Mainly for quality control and assurance
Hydraulic properties
- Important for separation, filtration,
drainage, and containment applications
Mechanical properties
- Important for reinforcement applications
and constructability
Durability properties
- Important for long-term performance
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Physical Properties
• Polymer (PE, PP, PET, etc.)
• Mass per unit area (oz/yd2 or g/m2)
•Thickness (mil = 1/1000 inch, mm)
• Roll length
• Roll width
• Roll diameter
• Specific gravity and density
• Surface characteristics
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Hydraulic Properties
• Opening characteristic (geotextile)
Apparent Opening Size (AOS)
Percent Open Area (POA)
Porosity (n)
• Permeability and permittivity
• In-plane flow capacity (transmissivity)
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Apparent Opening Size (AOS)
Test procedures
- Place geotextile sample into the sieve frame
- Start with the smallest diameter beads
- Place 50g of one size glass beads on the center of
geotextile
- Shake the sieve for 10 min.
- Weigh the glass beads that pass through the specimen
- Repeat the test using larger bead size fractions until the
weight of beads passing through the specimen to be 5%
or less
AOS or O95 = the size of the beads of which 5% or less pass
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Test for AOS
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Permittivity
t
Water flow
t
kn
= Permittivity
kn = Cross-plane permeability
oefficient
t = Thickness at a specified normal
pressure
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Transmissivity
Water flow
tk p
= Transmissivity
k = In-plane permeability coefficient
t
Normal pressure
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Allowable Flow Rate of
Geosynthetic Filter or Drainage
1 qa = qult
1
RFSCB x RFCR x RFIN x RFCC x RFBC = qult
RF
qa = allowable flow rate
Tult = ultimate flow rate
RF = overall reduction factor
RFSCB = RF for soil clogging and blinding (2 – 10)
RFCR = RF for creep reduction of void space (1 – 2)
RFIN = RF for adjacent materials intruding into void
space of geosynthetics (1 – 1.2)
RFCC = RF for chemical clogging (1 – 1.5)
RFBC = RF for biological clogging (1 – 4)
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Geotextile Clogging and Blinding
Bell and Hicks (1980) Richardson
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Mechanical Properties
• Tensile strength
Grab strength (geotextile or geomembrane)
Single rib strength (geogrid)
Narrow strip strength (geomembrane)
Wide-width strength (geotextile or geogrid)
• Junction strength (geogrid)
• Creep resistance
• Seam strength (geotextile or geomembrane)
• Tear strength (geotextile or geomembrane)
• Burst strength (geotextile or geomembrane)
• Puncture strength (geotextile or geomembrane)
• Penetration Resistance
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Tensile Strength Test
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Creep Test
Yuan Courtesy of Leshchinsky
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Creep Reduction Factors
Polyester (PET)
Creep reduction factor, RFCR Polymer Type
Polypropylene (PP)
High Density Polyethylene
(HDPE)
1.6 to 2.5
4.0 to 5.0
2.6 to 5.0
(FHWA NHI-00-043)
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Resistance Tests
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Durability Properties
• Abrasion resistance
• UV resistance
• Chemical resistance
• Biological resistance
• Temperature stability
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Sunlight (UV) Degradation
Laboratory exposure test
- Xenon-arc exposure test (ASTM D4355)
- Ultraviolet Fluorescent light test (ASTM G53
and D5208)
Time exposed (hours) Str
en
gth
re
tain
ed
(%
)
100
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Resistance of Polymers to
Specific Environment
Soil Environment
Acid Sulphate Soils
Polymer
PET PE PP
NE ? ?
Organic Soils NE NE NE
Saline Soils pH < 9 NE NE NE
Calcareous Soils ? NE NE
Modified Soils/Lime, Cement ? NE NE
Sodic Soils, pH > 9 ? NE NE
Soils with Transition Metals NE ? ?
NE = No Effect ? = Questionable, exposure test required
(FHWA NHI-00-043)
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Allowable Tensile Strength of
Geosynthetic
1 Ta = Tult
1
RFID x RFCR x RFCD x RFBD = Tult
RF
Ta = allowable tensile strength
Tult = ultimate tensile strength in lab
RFID = reduction factor for installation damage
RFCR = reduction factor for creep
RFCD = reduction factor for chemical degradation
RFBD = reduction factor for biological degradation
RF = overall reduction factor
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Installation Damage Test
Step 2:Compaction
Backfill
Foundation soil
Step 1:Place geosynthetic
and backfill
Step 5: Determine reduction
factor
Step 4: Test for tensile
strength
RF= Tcontrol /Tdamaged
Step 3:Exhume geosynthetic
sample
Geosynthetic
Courtesy of
Leshchinsky
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Installation Damage Reduction Factors
(FHWA NHI-00-043)
Geosynthetic
Reduction Factor, RFID
HDPE UX geogrid
Type 2 Backfill Type 1 Backfill
1.20 - 1.45 1.10 - 1.20
PP BX geogrid 1.20 - 1.45 1.10 - 1.20
PVC coated PET geogrid 1.30 - 1.85 1.10 - 1.30
Acrylic coated PET geogrid 1.30 - 2.05 1.20 - 1.40
Woven geotextiles (PP&PET) 1.40 - 2.20 1.10 - 1.40
Nonwoven geotextiles (PP&PET) 1.40 - 2.50 1.10 - 1.40
Slit filmwoven geotextiles (PP) 1.60 - 3.00 1.10 - 2.00
Type I backfill: Max. particle size of 102mm & D50 of 30mm
Type II backfill: Max. particle size of 20mm & D50 of 0.7mm
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Interface Shear Test
ASTM D5321
Soil
Block or soil
n
Geosynthetic
Interaction coefficient:
Ci = Interface strength
Soil strength
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Geotextile/Soil Friction Angles
Getextile
Soil Type
Nonwoven
needle-punched
Ottawa sand
( =300)
Concrete sand
( =300)
Nonwoven
heat-bonded
Woven slit-film
300 260 250
260 - -
260 - -
240 240 230
Martin et al. (1984)
Mica schist
sand ( =260)
Woven
monofilament
Ci = Interface strength
Soil strength =
tan (24o)
tan (30o) = 0.8
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Geosynthetic Applications
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Soft Soil
Stabilization
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Erosion Control
• Erosion Mat or Blanket
• Enhance seed
germination and erosion resistance
• UV protected
Village at Westlake - Austin, TX
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Stream/River Bank Protection
FHWA NHI-07-092
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Geocell for Low-water Crossing
Clarkin et al. (2006)
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Geocell for Channel Protection
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Geotubes for Erosion Control
Geotubes
Water
Soil
Wave
Fill entry
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Geotube Applications
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Marine Mattress for Coastal Revetment
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Rubber Dam by Geotube
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Canal Liner
Soil Geomembrane
or GCL
Anchor trench
Concrete or soil Water
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Geosynthetic-Reinforced Slope
Foundation soil
Drainage
composites
Retained soil Geosynthetics
Geopipe
Reinforced fill
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Mechanically Stabilized Earth (MSE) Wall
Foundation soil
Drainage
composite
Retained soil
Geosynthetics
Geopipe
Reinforced fill
Block Gabion
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Design Considerations
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Channel Design Criteria
• Based on peak flow capacity
• Consider site conditions
• Design channel lining to ensure the stability
Vegetation
Riprap
Geosynthetic liner
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Design Methods
• Maximum permissible velocity method
Predicted mean velocity < maximum
permissible velocity
• Tractive force (shear stress) method
Predicted shear stress < maximum
allowable shear stress
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Maximum
Permissible
Mean
Channel
Velocity
USACE (1991)
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Max. Design Velocity and Flow
Duration for Erosion Resistance
Hewlett et al. (1987)
Theisen (1992),
Clarkin et al. (2006)
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Required
Size of
Riprap
Stone
FHWA (1967)
BA
NK
SL
OP
E IN
CL
INA
TIO
N
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Predicted and Maximum Allowable
Shear Stresses
= w d s
w = unit weight of water, d = depth of flow
s = channel slope
Shear Stress
General Guide for Maximum Allowable Shear Stress (psf)
Vegetation (unreinforced) 3
Erosion control blanket 3
Rip-rap (18” stone) 6
Rip-rap (24” stone) 8
Typical turf reinforcement mat 8
Articulating concrete block 15
Fabric-formed concrete 20
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Bio-stabilization
tan
tan.
sinH
cFS 50
2
2
Example:
ca = 50 psf, H = 2 ft, = 120 pcf, = 30o
FS = 1.0
= 40o (1:1 slope, no-seepage condition)
= 27o (2:1 slope, seepage condition)
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Toe Protection or Support
WA
Active wedge
Passive wedge
WP
R
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Anchorage Requirements
in Erosion Control Applications
ARMY TM 5-818-8 (1995)
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Pin Spacing Requirements
in Erosion Control Applications
ARMY TM 5-818-8 (1995)
Steel securing pins: 8/16 in. (diameter), 18 in. (long), fitted
with a 1.5-inch metal washer
Longer pins are advisable for use in loose soils
Slope Pin Spacing (ft)
Steeper than 3(H) : 1(V) 2
3(H) : 1(V) to 4(H) : 1(V) 3
Flatter than 4(H) : 1(V) 5
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Why is Anchorage Needed Sometimes ?
tan
tanC
tan
tanFoS i
Typical Ci = 0.6 to 0.8
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Typical Geosynthetic Layout for
Reinforced Slope
FHWA NHI-07-092
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Face Options for Reinforced Slopes
Collin (1996)
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Slope Stability Analysis
Courtesy of Leshchinsky From ReSSA Software
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MSE Wall vs. Reinforced Slope
Increase Space
• Slope: Face
inclination < 700
• Solution driven by
many factors
Space
Cost
Vegetation
Backfill
Vertical Height (m)
Cast-in-
Place Wall
Precast
Concrete
MSE Wall
Reinforced
Slope
System Es
tim
ate
d C
on
str
uc
tio
n C
os
t
($ V
ert
ica
l m
2 o
f F
ac
e)
500
400
300
200
100
3 6 9 12
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MSE Wall Design
(a) Sliding (b) Overturning
(d) Global failure
x
P
(c) Bearing
(e) Pullout
P
(f) Rupture
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Backfill Requirements for MSE Wall
Sieve size % passing
4 in. 100 – 75
No. 4 100 – 20
No. 40 0 – 60
No. 200 0 - 35
Plasticity Index (PI) of fine fraction < 20
National Concrete Masonry Association
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MSE Wall Drainage Design
Low permeable soil
Drainage material
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Design Procedure for Geotextile Filter
beneath Hard Armor
Step 1: Evaluate critical nature of site conditions
Step 2: Obtain soil samples from site and test
Step 3: Evaluate armor material and placement
Step 4: Determine anticipated reversing flow through system
Step 5: Determine geotextile requirements
A. Retention (i.e., AOS)
B. Permeability/permittivity (kgeotextile > ksoil or 10 ksoil)
C. Clogging (i.e., O95, porosity, POA)
D. Survivability (i.e., geotextile class)
Step 6: Estimate costs
Step 7: Prepare specification
Step 8: Obtain samples of geotextile before acceptance
Step 9: Monitor installation and performance
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FHWA Filter Design Procedure
RETENTION CRITERIA
Steady State Flow
Sands, Gravelly sand, Silty Sands & Clayey
Sands (< 50% passing No.200 sieve)
Silts and Clays
(> 50% passing No.200 sieve)
For
CU≤2 or CU≥8
B=1
For
2 ≤ CU ≤ 4
B=0.5 CU
For
4 < CU < 8
B=8 / CU
Wovens
B=1 &
O95 ≤ D85
Nonwovens
B=1.8 &
O95 ≤ 1.8 D85
Unstable Soils Dynamic Flow
O95 ≤ 0.5 D85
Performance Tests
to select Suitable
Geotextile
D95 ≤ B D85 O95 ≤ 0.3 mm
For less critical applications and less severe
conditions: kgeotextile ≥ ksoil
For critical applications and severe conditions:
kgeotextile ≥ 10 ksoil
% Passing #200 sieve: < 15% 15% to 50% >50%
Permittivity Required: Ψ ≥ 0.5 sec-1 Ψ ≥ 0.2 sec-1 Ψ ≥ 0.1 sec-1
qrequired = qgeotextile (Ag/At)
CLOGGING RESISTANCE
For less critical applications and less severe conditions: For critical applications and severe conditions:
For CU >3
O95≥3D15
For CU ≤ 3 Use
maximum O95 from
Retention Criteria
Optional Qualifiers for gap-graded or silty soils
For Nonwovens: n ≥ 50%
For woven monofilament and silt films: POA ≥ 4%
and
Perform filtration test
with on-site soils and
hydraulic conditions
SURVIVABILITY and ENDURANCE CRITERIA
PERMEABILITY/PERMITTIVITY
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Classifications of Geotextiles in
AASHTO M288-96 Specifications
Class 1:
For severe or harsh survivability conditions where
there is a greater potential for geotextile damage
Class 2:
For typical survivability conditions; this is the
default classification to be used in the absence of
site specific information
Class 3:
For mild survivability conditions
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Geotextile Strength Property Requirements
for Permanent Erosion Control
AASHTO (2006)
Grab strength lb 315 200 250 157
Sewn seam strength lb 280 180 220 140
Tear strength lb 110 80 90 56
Puncture strength lb 620 433 495 309
Ultraviolet stability 50% retained strength after 500 hours of exposure
Geotextile Class
Class 1 Class 2
Units Elongation (%)
< 50 > 50 <50 >50
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Design of Geotube
Input:
Pressure head, b1
Circumference, S
Output:
Tube heights, H, H’ Tube width, B, B’
Geotextile strength, T
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Next Presentation: Case Studies
• Simple Slope with Temporary Toe Protection
• Reinforced Vegetation with Temp. Toe Protection
• Reinforced Slope with Permanent Toe Protection
• Hard Armor Structures
• Retaining Structures
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Questions?