Design of Geosynthetics for Paved Roads

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Design of Geosynthetics for Paved Roads

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

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Outline of Presentation

• Introduction
• Base Reinforcement Design
• Evaluation of Base Reinforcement
• Drainage Design

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Introduction
4
Pavement Components
AC (Asphalt Concrete) or PCC (Portland Cement
Concrete
Base
Subbase
Subgrade
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Base Reinforcement

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

Courtesy of Reck
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Current and New Types of Geogrid
New
Current
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Triangular A Stable Structure
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Triangular A Stable Structure
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Triangular Better for Confinement
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Base Reinforcement Mechanisms
Perkins (1999)
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Drainage
Shukla (2002)
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Base Reinforcement Design
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Design Procedures
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AASHTO Design Procedures
AASHTO Guide for Design of Pavement Structures
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ESAL Provided by Flexible Pavement
log10(W18) ZR S0 9.36 log10(SN1) - 0.20
?PSI
log10
4.2 1.5
2.32 log10(MR) 8.07

1094
0.40
(SN 1)5.19
W18 predicted number of 18-kip ESAL
ZR standard normal deviate
S0 combined standard error of traffic
prediction and performance prediction or
overall std. deviation
?PSI difference between the initial design
serviceability index, p0, and the
terminal serviceability index, pt
MR resilient modulus
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Design Chart for Flexible Pavements
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Standard Normal Deviate
Reliability, R()
Standard normal deviate, ZR
50
0.000
60
-0.253
70
-0.524
75
-0.674
-0.841
80
-1.037
85
-1.282
90
-1.405
92
-1.555
94
-1.751
96
-2.054
98
-2.327
99
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Suggested Levels of Reliability, R
Recommended level of reliability
Functional classification
Urban
Rural
Interstate and other freeways
85-99.9
80-99.9
80-99
Principal arterials
75-95
80-95
75-95
Collectors
50-80
50-80
Local
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Overall Standard Deviation, S0
0.30 - 0.40 Rigid pavement
0.40 - 0.50 Flexible pavement
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Structural Number (AASHTO 1993)
SN a1D1 a2m2D2 a3m3D3
ai ith layer coefficient
Di ith layer thickness (inches)
mi ith layer drainage coefficient
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Layer Coefficients
Average values of layer coefficients for
materials used in the AASHTO Road Test
Asphalt concrete surface course
0.44
Crushed stone base course
0.14
Sandy gravel subbase
0.11
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Layer Coefficient of Dense-Graded Asphalt Concrete
______________________________________________ Ela
stic modulus, EAC (psi)
Structural layer coefficient, a1, for of asphalt
concrete (at 68oF) asphalt concrete
surface course ___________________________________
____________________ 110,000 0.20 150,000
0.25 200,000
0.30 250,000 0.34 300,000 0.37 35
0,000 0.39 400,000 0.42 450,000 0.45
______________________________________________
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Layer Coefficient of Granular Base
___________________________________________
Granular base CBR () Structural layer
coefficient, a2 __________________________________
__________________ 20 0.07 30 0.09 35
0.10 45 0.11 55 0.12 70 0.13 100 0
.14 ___________________________________________
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Layer Coefficient of Granular Subbase
_____________________________________________
Granular subbase CBR () Structural layer
coefficient, a3 __________________________________
____________________ 10 0.08 25 0.10 3
0 0.11 40 0.12 70 0.13 100 0.14
__________________________________________________
____
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Recommendation for Drainage Factor (AASHTO 1993)
time pavement is exposed to moisture levels
approaching saturation
Quality of Drainage
lt 1
1 to 5
5 to 25
gt 25
Excellent
1.40-1.35
1.35-1.30
1.30-1.20
1.20
Good
1.35-1.25
1.25-1.15
1.15-1.00
1.00
Fair
1.25-1.15
1.15-1.05
1.00-0.80
0.80
Poor
1.15-1.05
1.05-0.80
0.80-0.60
0.60
Very poor
1.05-0.95
0.95-0.75
0.75-0.40
0.40
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Drainage Quality
_____________________________________________ Qual
ity of Drainage Water Removed Within ____________
_________________________________ Excellent 2
hours Good 1 day Fair 1 week Poor 1
month Very poor (water will
not drain) _________________________________
____________ Note the drainage conditions at the
AASHO Road Test are considered to be fair
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Empirical Correlation between MR and CBR
MR (psi) 1,500 x CBR
For fine-grained soil with a soaked CBR of 10 or
less
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Minimum Thickness
______________________________________________ Tra
ffic, ESALs Asphalt Concrete Aggregate Base
(mm) (mm) __________________
_____________________________________ Less than
50,000 25 (or suraface treatment) 100 50,001-
150,000 50 100 150,001-500,000
63 100 500,001-2,000,000
75 150 2,000,001-7,000,000
87 150 Greater than 7,000,000
100 150 _______________________________________
________________ Note Individual design agencies
may modify the above minimum thickness for their
own use.
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Traffic Benefit Ratio Using Geosynthetics
Traffic benefit ratio (TBR) is defined as
the ratio of the number of cycles necessary to
reach A given rut depth for a test section
containing Reinforcement divided by the number
of cycles necessary to reach this same rut depth
for an unreinforced section with the same
section thickness and subgrade properties
TBR 1.5 to 10 for geotextiles
TBR 1.5 to 70 for geogrids
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Determination of TRB
Shukla (2002)
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Extension of Pavement Life
Extended pavement life can be estimated by
W18 (reinforced) TBR W18 (unreinforced)
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Layer Coefficient Ratio
Layer coefficient ratio (LCR) is defined as
A modifier applied to the layer coefficient of
the aggregate
SN a1D1 LCR a2m2D2 a3m3D3
LCR is determined from lab and field tests
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Layer Coefficient Ratio
Tenax
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Design for Base Reinforcement
Option 1
Extension of performance period
Option 2
Reduction of base course
Option 3
Extension of performance period reduction of
base course
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Design for Extension of Performance Period
Design with a TBR
W18R TBR W18
Design with a LCR
SNR a1D1 LCR a2m2D2 a3m3D3
W18R
SNR
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Design for Reduction of Base Thickness with a TBR
Step 1
(W18)R W18/TBR
Step 2
(W18)R
SNR
SNR - a1 D1
Step 3
D2(R)
a2 m2
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Design for Reduction of Base Thickness with a LCR
Step 1
W18
SN
SN - a1 D1
Step 2
D2(R)
LCR a2 m2
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Army Corps Field Study (Webster, 1992)
25mm AC
30,000 lb single tire load
300mm base
460mm base
BX1200
Subgrade CBR 3
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Army Corps Field Study (Webster, 1992)
500
CBR 3
Unreinforced
400
Reinforced
Unreinforced
300
Depth (mm)
200
Reinforced
CBR 8
100
0
100
1,000
10,000
100,000
Passes
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Geogrid Properties Affecting Base Reinforcement
Geogrid item
Property
Better Performance
Thicker Stiffer Square or rectangular
Thickness Stiffness Shape
Rib
0.75 - 1.5in. Round or square Stiffer
Size Shape Rigidity
Aperture
Junction
Strength
Adequate strength
Secant modulus Stability
Adequate strength
Grid
A good index
(Webster, 1992)
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University of Alaska Study (Kinney)
Section 1 BX1200
Section 2 BX1100
Section 3 Control
Section 4 2 BX1100
South End
North End
2.4m
0.9m
Plan View
0
125
Depth of Base (mm)
250
375
500
0
7.3
10.7
14.0m
0.6
3.9
Section View
Base
50mm AC
Clay (CBR1.9)
1.2m
Concrete floor
Sand gravel
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Traffic Benefit Ratio (Kinney)
25mm rut depth
12
10
8
BX1200
6
Traffic Benefit Ratio
4
2
BX1100
0
300
150
200
250
275
225
175
Base Thickness (mm)
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Evaluation of Base Reinforcement
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Current Test Methods
Y Yes, N No, and P possible
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Concepts for New Method

• Geosynthetic interacting with base course
  material
• Suitable for geosynthetics
• Simulate localized deformations
• Under repeated wheel loads
• Proved test method for asphalt mixture
• Machine available in many state DOTs in the U.S.
• Easy, quick, and cost effective

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Testing Machine
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Placement of Geogrid
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Placement of Aggregate above Geogrid
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(No Transcript)
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Loaded Wheel Test
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Rutting after Testing
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(No Transcript)
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Manual Measurement
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Test Conditions
Wheel load 89 or 355N, hose pressure 138 or
552kPa Hose dia. 19mm, rut width 25mm
Base material Kansas river sand or AB-3
aggregate (Dr 70)
Depth of reinforcement at depth of 25mm or 13mm
Surcharge 0 or 2.9kPa
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Base Materials
Kansas River Sand sub-round, poorly-graded AB-3
Aggregate Angular, well-graded
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Geosynthetic Specimens
HP370 (GT1)
BX1100 (GG1)
BX1200 (GG2)
BX1500 (GG3)
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Properties of Geosynthetics
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Surcharge (2.9kPa)
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Repeatability of Test Results
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Effect of Base Material
Unreinforced
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Effect of Surcharge
GG2
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Effect of Geosynthetic Type
Kansas River sand
AB-3 aggregate
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Traffic Benefit Ratio
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Calculated TBR Values
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Discrete Element Modeling
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Tensile Stress and Deformation
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Drainage Design
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Sources of Water
Pavement infiltration
Seepage from higher ground
Vapor movements
Capillary action
Rising water table
Water table
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Drainable Pavement Systems
Asphalt or PCC pavement
Permeable base
Subgrade
Edgedrain pipe
Geotextile
Aggregate separator layer
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Drainable Pavement Systems
FHWA(1987) recommend a minimum k of 300m/day
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Drainage Quality
_____________________________________________ Qual
ity of Drainage Water Removed Within ____________
_________________________________ Excellent 2
hours Good 1 day Fair 1 week Poor 1
month Very poor (water will
not drain) _________________________________
____________ Note the drainage conditions at the
AASHO Road Test are considered to be fair
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Geocomposite Drainage of Base
Asphalt Pavement
Base aggregate
Subgrade
Geocomposite drainage net
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Geocomposite Drainage of Base
Geocomposite drainage net
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Geocomposite Drainage of Surface Asphalt or
Concrete Pavement
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Geocomposite Drainage of Subgrade
Asphalt or PCC pavement
Base aggregate
Frost susceptible soil
Subgrade
Geocomposite drainage net
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Time to 50 Drain
The time to drain is determined by
t T50 x m x 24
t time to drain in hours
T50 time factor, determined from the
relationship with Sl
Sl (LR SR)/H
LR drain distance
SR resultant slope
H drainage layer thickness
m N0LR2/(kH)N0LR2/?
N0 effective porosity of the drainage layer
? transmissivity of the drainage layer
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Recommended Time to Drain
1 hour for the highest class roads with the
greatest amount of traffic 2 hours for
most other high use roadways 1 day for
secondary roads
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Time Factor for 50 Drainage
Slope Factor S1
Time Factor T50
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Effective Porosity of Geosynthetics

• The ratio of the volume of drained water to the
  total
• volume of the sample

For example Effective porosity of Tendrain
100-2 0.69 Porosity of the material 0.74
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Geocomposite Directly underneath Pavement
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Geocomposite Directly underneath Base Course
Asphalt or PCC pavement
Base aggregate
Subgrade
Geocomposite
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Geotextile Filtration Design
Proper geotextile should be selected outside the
geonet to allow the flow of water into the
geonet and prevent soil from washing into the
system