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Incorporation of Environmental Factors in Flexible Pavement Design
Presented at theSoutheastern Pavement Management and Design
ConferenceNashville, TNJune 25, 2002
ByEric C. Drumm
The University of Tennessee
• Eric C. Drumm, University of Tennessee
• Ronald E. Yoder, University of Tennessee
• N. Randy Rainwater, University of Tennessee
• Roger W. Meier, The University of Memphis
Investigators
University of Tennessee
• Gang Zuo, University of Tennessee• Wesley Wright, University of Tennessee• P. Chris Marshall, The University of Memphis
Contributors
Acknowledgments• This work was performed as part of a
research contract supported by the Tennessee Department of Transportation, Nashville, TN. – Harris Scott– Jim Maxwell– Bill Trolinger– Len Oliver– Mike Presley
Introduction• Mechanics-based approach to flexible
pavement design – resilient modulus (Mr) used to define behavior
of each layer in pavement system– Mr is a function of stress level, loading
history, temperature, etc..• Mr of subgrade soil dependent upon
environmental factors– changes in moisture conditions– freeze/thaw state
• High or maximum value– the “best case” properties
may not be safe or reliable• Low or minimum value
– the “worst case” properties may not be economical
• Mean value– “average” properties may
not reflect the relative duration of the seasons during which the “best case” and “worst case” properties occur timetimetimetime
MMMMrrrr
What value(s) of Mr to use for design?
Introduction
Introduction• Laboratory studies investigated variation
of subgrade resilient modulus due to changes in – water content – degree of saturation– matric potential
• But, there is a little data on the seasonal variations of the moisture conditions
AASHTO Guide (1993)• Suggests a procedure to incorporate the
seasonal variation of subgrade Mr in the design process to determine MR– (MR = effective roadbed resilient modulus)
• MR is the single value of subgrade resilient modulus which reflects the cumulative damage from the entire year
• unfortunately, knowledge of the seasonal variation of modulus is required
Introduction
Objectives of Research
• Measure seasonal variations of water content and temperature in pavement systems
• Measure the effects of those variations on pavement structural capacity
• Develop methods to incorporate those effects into existing pavement design procedures used by TDOT
Objective 1
Measure seasonal variations of water content and temperature
inside pavement systems
University of Tennessee
Instrumented Pavement SitesTennessee Department
of Transportation
SUMNER COUNTY
215 mmAsphalt
255 mm Gravel
150 mm LSS
BLOUNT COUNTY
215 mmAsphalt
255 mm Gravel
OVERTON COUNTY
255 mmAsphalt
255 mm Gravel
Pavement SectionsMcNAIRY COUNTY
335 mmAsphalt
255 mm Gravel
LSS = Lime Stabilized Subgrade
Schematic of instrumentation system (section)Schematic of instrumentation system (section)Schematic of instrumentation system (section)Schematic of instrumentation system (section)
Pavement Instrumentation
roadwayroadwayroadwayroadwayshouldershouldershouldershoulder
Data Data Data Data collection collection collection collection vaultvaultvaultvault
Instruments under Instruments under Instruments under Instruments under outer wheel pathouter wheel pathouter wheel pathouter wheel path
Temporary trench for Temporary trench for Temporary trench for Temporary trench for instrument installationinstrument installationinstrument installationinstrument installation
Instrumentation installed under outer wheel path from trench in shoulder
• Time Domain Reflectometry (TDR)– Used to measure water content– Probes have 5 segments– Probes are 5 feet long
Pavement Instrumentation
Buried TDR Probes
Installing TDR ProbesPavement Instrumentation
Pavement Instrumentation
Asphalt Treated Base
Asphalt Treated Base
Surface LayerBinder Layer
Asphalt Concrete
Stone Base
Soil Subgrade
Pavement Edge
TDR Probes
AggregateUnderdrain
Paved Shoulder
TDR Probes
Pavement Instrumentation• Pan Lysimeters
– Measure infiltration through AC layers
– Some located in the wheel path
– Others located under a pavement joint
Pavement Instrumentation
Asphalt Treated Base
Asphalt Treated Base
Surface LayerBinder Layer
Asphalt Concrete
Stone Base
Soil Subgrade
Pavement Edge
TDR Probes
AggregateUnderdrainPan Lysimeter
Paved Shoulder
Pavement Instrumentation
• Thermistors– Measure pavement temperature
Installing Thermistors
– 1” below surface– 1” above stone base– AC mid-height– In soil subgrade
• Weather Station– Air temperature– Solar radiation– Rainfall– Relative humidity– Wind speed
Pavement Instrumentation
Pavement Instrumentation
Cable Trench
Pavement Instrumentation
UndergroundVault
• Data collected once each minute
• Hourly averages are stored on data logger
• Data sent to UT by cell phone once a day
Underground Instrumentation Panel
Pavement Instrumentation
Pavement Instrumentation
Field Verification Tests
Drilling & sampling pavement and subgrade
Field Verification Tests
Pan lysimeter flush test
Material Characterization
• Index tests– Atterberg limits,
Proctor tests, etc.• Resilient modulus tests
– AASHTO Standard Test Method
• Resilient modulus – AASHTO T 307-99 Determining
the Resilient Modulus of Soils and Aggregate Materials
Material Characterization
020406080
100120140160180200
0 10 20 30 40 50 60 70Deviator Stress (kPa)
Res
ilien
t Mod
ulus
(MPa
)
Material Characterization
IncreasingConfiningPressure
Observations: Pavement Temperature
10
15
20
25
30
35
40
10/01/00 10/06/00 10/11/00 10/16/00 10/21/00 10/26/00 10/31/00
Mid
-Dep
th T
empe
ratu
re o
f AC
Lay
er (o C
)
Hourly Temperature
Daily Average
-10
0
10
20
30
40
50
1-Jul-97 1-Jul-98 1-Jul-99 1-Jul-00 1-Jul-01 1-Jul-02Date
Tem
pera
ture
(C)
0.0
0.5
1.0
1.5
2.0
Sola
r Rad
iatio
n (J
/hr)
Top Middle Bottom Air Solar Radiation
Observations: Pavement Temperature
0
10
20
30
40
50
1-Jun-97 1-Jun-98 1-Jun-99 1-Jun-00 1-Jun-01 1-Jun-02Date
Tem
pera
ture
(C
)
Regression Model Measured Data
Observations: Pavement Temperature
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Oct
-97
Nov
-97
Dec
-97
Jan-
98Fe
b-98
Mar
-98
Apr
-98
May
-98
Jun-
98Ju
l-98
Aug
-98
Sep-
98O
ct-9
8
Nov
-98
Dec
-98
Jan-
99Fe
b-99
Mar
-99
Apr
-99
May
-99
Jun-
99
Infil
tratio
n (m
m/m
2 )
McNairy County before binder and surface courses added
Observations: Infiltration
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Oct
-97
Nov
-97
Dec
-97
Jan-
98Fe
b-98
Mar
-98
Apr
-98
May
-98
Jun-
98Ju
l-98
Aug
-98
Sep-
98O
ct-9
8
Nov
-98
Dec
-98
Jan-
99Fe
b-99
Mar
-99
Apr
-99
May
-99
Jun-
99
Infil
tratio
n (m
m/m
2 ) Predicted
Measured
McNairy County before binder and surface courses added
Observations: Infiltration
• Since binder and surface course was placed, infiltration of water has essentially ceased (only small measurable amounts of infiltration).
• Function of lysimeters verified by field flush tests
• Will infiltration increase as pavement ages?
Observations: Infiltration
Observations: Subgrade Water Content
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0 200 400 600 800 1000 1200 1400 1600Time Since 01/01/1997 (Day)
Vol
umet
ric W
ater
Con
tent
0102030405060708090100110120
Tem
pera
ture
(o C) o
r Rai
nfal
l (m
m)
TDR Probe (0.15 m below the Top of the Subgrade)TDR Probe (0.45 m below the Top of the Subgrade)RainfallTemp. 3
Days Since January 1,1997
TDR Probe 0.15 m below top of subgradeTDR Probe 0.45 m below top of subgradeRainfallSoil Temperature
Objective 2
Measure the effects of moisture and temperature variations on pavement structural capacity
Pavement Response• Measured with
Falling WeightDeflectometer
FWD
Pavement Response
Courtesy of Dynatest, Inc.
Pavement Response
ET / E20 = 3.31e-0.060T
0.0
0.5
1.0
1.5
2.0
2.5
0 10 20 30 40 50
Measured Mid-Depth AC Temperature, T (C)
Mo
du
lar
Rat
io, E
T / E
20
Present Study
Pavement Response
ET / E20 = 3.31e-0.060T
ET / E20 = 3.55e-0.063T
0.0
0.5
1.0
1.5
2.0
2.5
0 10 20 30 40 50
Measured Mid-Depth AC Temperature, T (C)
Mo
du
lar
Rat
io, E
T / E
20
Kim et al.
Present Study
Pavement Response
0
5
10
15
20
25
30
0 100 200 300Day of Year
Su
bg
rad
e M
od
ulu
s (k
si)
0.3
0.4
0.5
0.6
0.7
0.8
Vo
lum
etri
c W
ater
Co
nte
nt
Pavement Response
0
5
10
15
20
25
30
0 50 100 150 200 250 300 350Day of Year
Su
bg
rad
e M
od
ulu
s (k
si)
7000-lb Wheel Load10000-lb Wheel Load13000-lb Wheel Load
020406080
100120140160180200
0 10 20 30 40 50 60 70Deviator Stress (kPa)
Res
ilien
t Mod
ulus
(MPa
)
Material Characterization
IncreasingConfiningPressure
0 12 24 36 48 60 72
17294153657789
Radial Offset (in)
Dep
th (i
n)
Summer
0-0.5 0.5-1 1-1.5 1.5-22-2.5 2.5-3 3-3.5 3.5-4
0 12 24 36 48 60 72
17294153657789
Radial Offset (in)
Dep
th (i
n)
Winter
Pavement Response
Objective 3
Develop methods to incorporate environmental effects into TDOT
pavement design procedures
Temperature Averaging
• AC stiffness varies with temperature
• AC stiffness affects the stiffness of underlying stress-dependent materials
• Pavement life estimates are based on the pavement stiffness and so can vary widely depending on AC temperature used in the analysis
Temperature Averaging: Monthly Data
0%
5%
10%
15%
20%
0 5 10 15 20 25 30 35 40 45 50Temperature (C)
Freq
uenc
y
Temperature Averaging: Monthly and Daily Data
0%
5%
10%
15%
20%
0 5 10 15 20 25 30 35 40 45 50Temperature (C)
Freq
uenc
y
DailyMonthly
Temperature Averaging: Monthly, Daily, & Hourly Data
0%
5%
10%
15%
20%
0 5 10 15 20 25 30 35 40 45 50Temperature (C)
Freq
uenc
y
HourlyDailyMonthly
• What is the effect of the temperature averaging interval on computed design life?
• What is the effect of assuming a uniform distribution of traffic throughout the day?
Temperature Averaging
Temperature AveragingEffect of Traffic Distribution
0%1%2%3%4%5%6%7%8%
1 3 5 7 9 11 13 15 17 19 21 23Hour of the Day
Perc
enta
ge o
f Dai
ly T
rips Tractor-Trailer
Trip Distribution
Temperature Averaging
Monthly Average Temps
DailyAverage Temps
Hourly Average Temps
9%Stiff
10%Medium
10%Soft
11%Very soft
Pavement Life OverestimationUsing Uniform Traffic and ...Subgrade
Stiffness
Temperature Averaging
Monthly Average Temps
DailyAverage Temps
Hourly Average Temps
39%9%Stiff
47%10%Medium
54%10%Soft
58%11%Very soft
Pavement Life OverestimationUsing Uniform Traffic and ...Subgrade
Stiffness
Temperature Averaging
Monthly Average Temps
DailyAverage Temps
Hourly Average Temps
52%39%9%Stiff
62%47%10%Medium
71%54%10%Soft
76%58%11%Very soft
Pavement Life OverestimationUsing Uniform Traffic and ...Subgrade
Stiffness
Temperature Averaging
0.E+00
2.E+06
4.E+06
6.E+06
8.E+06
1.E+07
1.E+07
1.E+07
Very Soft Soft Medium Stiff
Subgrade Soil Type
ESA
Ls
Hourly (Nonuniform Traffic)
Hourly (Uniform Traffic)
Daily (Uniform Traffic)
Monthly (Uniform Traffic)
• To obtain the most reliable estimates of design life, use hourly temperature data whenever possible.
• If hourly truck traffic distribution is known, reliability can be increased even more.
Temperature Averaging
Summary and Conclusions
Summary
• Four years of data at 4 sites in TN– Climatic data– Pavement temperature– Base and subgrade moisture– Infiltration– Layer moduli
• This is a rare and valuable dataset
Conclusions
• TDOT surface courses are relatively impermeable (at least early on)
• TDOT designs limit the stresses in subgrade
• Water content of subgrade may not change much seasonally (at least in fill sections)
Conclusions
• FWD is sensitive enough to pick up stress-dependence of subgrade soils
• Using monthly average temperatures to estimate asphalt modulus can lead to under-designed pavements
Issues to Address
Issues to Address
• As instrumented pavements age, how will they respond to wheel loads?– AC properties will certainly change– Infiltration will probably increase– Drainage layers may stop working– Water content may change long-term
Issues to Address
• Do “cut” sections respond the same as “fill” sections now and over time– Measure FWD response in cut areas at
the same time as in fill areas– Measure water content (by sampling) and
compare to TDR data in fill sections
Questions?