Pavement Design

Pavement Design
Guest Lecturer
Dr. Sirous Alavi, P.E.
SIERRA TRANSPORTATION ENGINEERS, INC.
1005 Terminal Way, Suite 125
Reno, Nevada 89502
Topics
„
Introduction
– Design Factors
– Pavement Types
„
Fundamentals of Pavement Design
– AASHTO
– Asphalt Institute
FUNDEMENTALS
Types of Design
State-of-Practice State-of-the-Art
Empirical
MechanisticMechanistic
Empirical
1
FUNDEMENTALS
Mechanistic-Empirical
(M-E) Design
„
Primary advantage is the consideration of
the state of stress
HMA
Base
Subbase
Subgrade Soil
FUNDEMENTALS
Mechanistic-Empirical
(M-E) Design
„
Establishes connection between distress
and distress mechanism
FUNDEMENTALS
Mechanistic-Empirical
(M-E) Design
Accounts for new materials, traffic loads,
and construction procedures
„ All design features affecting pavement
performance considered
„ Relies more on fundamental engineering
mechanics
„ Primary focus on pavement performance
„
2
FUNDEMENTALS
Mechanistic-Empirical
(M-E) Design
„
„
1993 AASHTO Guide
Design Variables
–
–
–
–
–
–
Time
Traffic
Reliability
Environment
Serviceability
Structural Number
FUNDEMENTALS
Mechanistic-Empirical
(M-E) Design
FUNDEMENTALS
AASHTO Design
„ Time
Constraints
– Performance Period
„ Refers
to the time that an initial pavement
structure will last before rehab
– Analysis Period
„ Refers
to the period of time that any
design strategy must cover
3
FUNDEMENTALS
AASHTO Design
„
Traffic
– Equivalent Single Axle Load (ESAL)
„ Converts
wheel loads of various
magnitudes and repetitions to an
equivalent number of "standard" or
"equivalent" loads based on the amount
of damage they do to the pavement
FUNDEMENTALS
AASHTO Design
„
Equivalent Axle Load Factor (EALF)
– Damage per pass to a pavement by the axle
in question relative to the damage per pass
of a standard axle load
– Depends of type of pavements, thickness or
structural capacity and terminal conditions
FUNDEMENTALS
EALF Table for Flexible Pavement,
Single Axle & pt of 2.5
Pavement Structural Number (SN)
Axle
Load
(kips)
2
4
6
8
10
12
14
16
1
2
3
4
5
6
0.004
0.003
0.011
0.032
0.078
0.168
0.328
0.591
0.004
0.004
0.017
0.047
0.102
0.198
0.358
0.613
0.003
0.004
0.017
0.051
0.118
0.229
0.399
0.646
0.002
0.003
0.013
0.041
0.102
0.213
0.388
0.645
0.002
0.002
0.010
0.034
0.088
0.189
0.360
0.623
0.002
0.002
0.009
0.031
0.080
0.176
0.342
0.606
4
FUNDEMENTALS
AASHTO Design
„
m
„
i =1
„
ESAL = ∑ Fi ni
m = number of axle
load groups
Fi = the EALF for the
ith axle load group
ni = number of
passes of the ith axle
load group
FUNDEMENTALS
200X AASHTO Design Guide
„
„
„
No more ESALs
Traffic input
– Vehicle type (number of axles)
– Axle weight
Quantity and quality of raw traffic data
similar to that used to compute ESALS
– Consistent with FHWA Traffic Monitoring
Guide
FUNDEMENTALS
Traffic Hierarchical Input Levels
Input
Level
Input Values
Knowledge of
Parameters
1
Site specific WIM & AVC
Good
2
3
Regional Default WIM &
AVC, Vehicle Counts
National Default WIM &
AVC, Vehicle Counts
Modest
Poor
5
200X AASHTO Design Guide
Load Spectra
– Axle weight frequencies for each
common axle combination (e.g.
single axle, tandem axle, tridem
axle, quad axle).
800
700
600
Number of Axles
FUNDEMENTALS
„
500
400
300
200
100
0
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
55000
60000
65000
70000
75000
80000
Axle Load (lbs)
FUNDEMENTALS
AASHTO Design
„
Reliability - Incorporating some degree of certainty
into the design process to ensure that various design
alternatives will last the Analysis Period
Recommended Level of Reliability
Functional
Classificaiton
Urban
Rural
Interstate
Arterials
Collectors
Local
85 - 99.9
80 - 99
80 - 95
50 - 80
80 - 99.9
75 - 95
75 - 95
50 - 80
FUNDEMENTALS
AASHTO Design
„ Environmental
– Temperature
„ Stresses
induced by thermal action
„ Changes in creep properties
„ Effect of freezing and thawing of subgrade
– Rainfall
„ Penetration
of surface water into underlying
materials
6
FUNDEMENTALS
AASHTO Design
„ Serviceability
– Initial serviceability index is function of
pavement type and construction quality
– Terminal serviceability index is lowest
index that will be tolerated before
rehab, resurfacing, or reconstruction
SURFACE (AC)
AASHTO Design
BASE
FUNDEMENTALS
SUBBASE (OPTIONAL)
„
Structural Number
SUBGRADE
– mi = drainage coefficient for layer i
– a1, a2, a3 = layer coefficient representative of
surface, base, and subbase course, respectively
– D1, D2, D3 = thickness representative of surface,
base, and subbase course, respectively
SN = a1D1 + a2 D2 m2 + a3 D3 m3
FUNDEMENTALS
AASHTO Design Example
„ Ridgeview
Dr. Rehabilitation
– 20-year flexible pavement analysis
period
– Low volume road with limited growth
potential
7
NAM
ED
M
PLU
VIEW
COPPER
POINT
R IDGE
AS
FUNDEMENTALS
C OPP
ER PO
INT
COPPER POINT
GREEN RANCH
V
GE
IE
W
D
ME
TA
ADO W HEIG
IN VIS
WINDY M
MOU
N TA
NS
CR
EE
HTS
GREEN RA
NCH
RID
NA
UN
RIDGEVIEW
UM
PL
W
VIE
GE
AS
RID
COPPER
„ Traffic
– 72-hour vehicle counts were conducted
directionally at three locations within the
project boundaries using machine traffic
counters
– Manual classification counts were conducted
at the machine count locations to “calibrate”
the machine count data and categorize into
the FHWA 13 vehicle classification scheme
Vehicle Classification
FUNDEMENTALS
AASHTO Design Example
8
Adjusted Traffic Volumes and Vehicle Classification Year 2005 Through 2010
Road Segment:
Ridgeview Drive @ Plumas Street
Class 1
EB
Class 2
%
Volume
WB
Volume
Class 3
Class 4
Class 5
Class 6
0.15
Class 9
Total
43.64
54.11
0.35
1.60
0.15
100
1132.30
1404.00
9.10
41.60
3.90
3.90
2594.8
43.29
54.11
0.70
1.60
0.15
0.15
100
1123.20
1404.00
18.20
41.60
3.90
3.90
2594.8
%
5189.6
Road Segment:
Class 1
FUNDEMENTALS
Total ADT
Ridgeview Drive @ Mountain Vista Way
EB
Class 2
%
43.44
Volume
WB
Class 3
823.65
54.11
1026.00
Class 4
Class 5
0.45
1.60
8.55
30.40
Class 6
0.20
Class 9
Total
0.20
100
3.80
3.80
%
42.94
54.11
0.95
1.60
0.20
0.20
100
Volume
814.15
1026.00
18.05
30.40
3.80
3.80
1896.2
1896.2
3792.4
Total ADT
Adjusted Traffic Volumes and Vehicle Classification Year 2011 Through 2025
Road Segment:
Ridgeview Drive @ Plumas Street
Class 1
EB
%
Volume
WB
%
Volume
Class 2
Class 3
Class 4
Class 5
43.94
54.11
0.35
1.60
1140.10
1404.00
9.10
41.60
43.59
54.11
0.70
1.60
1131.00
1404.00
18.20
41.60
Class 6
Class 9
0.00
0.00
0.00
0.00
Total
100
2594.8
100
2594.8
5189.6
Road Segment:
Total ADT
Ridgeview Drive @ Mountain Vista Way
Class 1
EB
WB
Class 2
Class 3
Class 4
Class 5
%
43.84
54.11
0.45
1.60
Volume
831.25
1026.00
8.55
30.40
%
43.34
54.11
0.95
1.60
Volume
821.75
1026.00
18.05
30.40
Class 6
Class 9
0.00
0.00
0.00
0.00
Total
100
1896.2
100
1896.2
3792.4
Total ADT
AASHTO Design Example
FUNDEMENTALS
Compute ESALs using EALFs from
AASHTO Tables in Appendix D
„ Assumptions
„
– Typical axle weights for each vehicle class
– SN of 3.0
– pt of 2.5
WB Daily ESALs
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
WB Yearly ESALs
Cumulative ESALs
Plumas
Mountain Vista
Plumas
Mountain Vista
Plumas
Mountain Vista
90
90
90
90
90
90
75
75
75
75
75
75
75
75
75
75
75
75
75
75
75
81
81
81
81
81
81
66
66
66
66
66
66
66
66
66
66
66
66
66
66
66
33,031
33,031
33,031
33,031
33,031
33,031
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
27,362
29,487
29,487
29,487
29,487
29,487
29,487
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
23,963
33,031
66,062
99,093
132,124
165,155
198,187
225,548
252,910
280,271
307,633
334,994
362,356
389,717
417,079
444,441
471,802
499,164
526,525
553,887
581,248
608,610
29,487
58,973
88,460
117,947
147,433
176,920
200,882
224,845
248,807
272,770
296,732
320,695
344,657
368,620
392,582
416,545
440,507
464,470
488,432
512,395
536,357
9
FUNDEMENTALS
AASHTO Design Example
„
Materials
– R-value data was collected at five sample
locations (8, 7, 10, 20, 8)
– Resilient Modulus (MR) relationship
R-value ≤ 20 MR = 1000 + 555 x R-value (psi)
Parameter
Design Life, years
Traffic (ESALs), W18
Reliability, R (%)
Average
20
610,000
80%
Standard Deviation (New Construction), So
0.45
Subgrade R-value
10.60
Subgrade Resilient Modulus, MR (ksi)
6.9
Initial Serviceability, P0
4.2
Terminal Serviceability, Pt
2.5
Modulus of Elasticity for New AC (ksi)
350
Layer Coefficient for New Plant Mix Surface (AC), a1
0.39
Layer Coefficient for Gravel Base, a2
0.14
Layer Coefficient for Subbase (Borrow), a3
0.08
Drainage Coefficient for AC layer, m1
1.0
Drainage Coefficient for Base layer, m2
1.1
Drainage Coefficient for SB layer, m3
1.1
SN ≈ 3.1
10
AASHTO Design
SURFACE (AC)
BASE
FUNDEMENTALS
SUBGRADE
„
Assume D values for surface and base
– Asphalt is 4 inches
– Base is 10 inches
„
Calculate SN - Is it acceptable?
SN = a1D1 + a2 D2 m2
SN = 0.39 × 4.0 in + 0.14 × 10 in × 1.1
SN = 3.1
Topics
„
Introduction
– Design Factors
– Pavement Types
„
Fundamentals of Pavement Design
– AASHTO
– Asphalt Institute
FUNDEMENTALS
Asphalt Institute (AI)
Design
„
Determine minimum thickness of asphalt
layer that will adequately withstand the
stresses that develop for two strain
criteria
– Vertical compressive strain at surface of
subgrade
– Horizontal tensile strain at bottom of asphalt
layer
11
Asphalt Institute (AI)
Design
FUNDEMENTALS
Wheel
load
P0
P1
P1
SUBGRADE
Stress distribution
within different
layers of the
pavement structure
General form of
stress reduction
Asphalt Institute (AI)
Design
FUNDEMENTALS
Wheel
load
SUBGRADE
Tension
Compression
FUNDEMENTALS
Asphalt Institute (AI)
Design
„
20%
Fatigue
Design Criteria
– Fatigue
„ Nf
= allowable number of load repetitions
= dynamic modulus
„ ∈t = horizontal tensile strain at the bottom of the
asphalt layer
„ Assumes asphalt volume of 11% and air void
volume of 5%
„ |E*|
Nf = 0.0796(∈t)-3.291 |E*|-0.854
12
FUNDEMENTALS
Asphalt Institute (AI)
Design
„
0.5
inch
Design Criteria
– Permanent Deformation
„ Nd
= allowable number of load repetitions
= vertical compressive strain on the surface
of the subgrade
„ ∈c
Nd = 1.365 x 10-9 (∈c)-4.477
FUNDEMENTALS
Asphalt Institute (AI)
Design
„
Five main steps
1.
2.
3.
4.
Select or determine input data
Select surface and base materials
Determine minimum thickness required
Evaluate feasibility of staged construction
and prepare plan, if necessary
5. Carry out economic analyses
NAM
ED
M
PLU
VIEW
COPPER
POINT
R IDGE
AS
C OPP
ER PO
INT
IE
W
TA
ADO W HEIG
IN VIS
WINDY M
MOU
N TA
NS
CR
EE
HTS
GREEN RA
NCH
V
GE
D
ME
RIDGEVIEW
COPPER POINT
GREEN RANCH
RID
NA
UN
FUNDEMENTALS
UM
PL
W
VIE
GE
AS
RID
COPPER
13
FUNDEMENTALS
Asphalt Institute (AI) Design
Example
Gross
„
Select or
determine input
data
– Traffic
Characteristics
– ESALs similar to
AASHTO
WB Daily ESALs
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Axle
Load
(kips)
1
2
4
6
8
10
12
14
16
WB Yearly ESALs
Single Tandem Tridem
Axles
Axles
Axles
0.00002
0.00018
0.00209 0.0003
0.01043 0.001 0.00030
0.0343 0.003
0.001
0.0877 0.007
0.002
0.189
0.014
0.003
0.360
0.027
0.006
0.623
0.047
0.011
Cumulative ESALs
Plumas 2
Plumas 2
Plumas 2
118
118
118
118
118
118
72
72
72
72
72
72
72
72
72
72
72
72
72
72
72
43,110
43,110
43,110
43,110
43,110
43,110
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
26,197
43,110
86,221
129,331
172,441
215,552
258,662
284,859
311,057
337,254
363,451
389,649
415,846
442,043
468,241
494,438
520,635
546,833
573,030
599,227
625,425
651,622
FUNDEMENTALS
Asphalt Institute (AI)
Design Example
„ Select
or determine input data
– R-value data was collected at five sample
locations (8, 7, 10, 20, 8)
– Resilient Modulus (MR) relationship
MR = 1155 + 555 x R-value (psi)
14
FUNDEMENTALS
Asphalt Institute (AI)
Design Example
„ Select
surface and base materials
– Asphalt concrete surface or emulsified
asphalt surface
– Asphalt concrete base, emulsified
asphalt base, or untreated aggregate
base
FUNDEMENTALS
Asphalt Institute (AI)
Design Example
„
Determine minimum thickness required
– Obtained by computer program
– Entering the appropriate table or chart
„ Assume
10 inch untreated aggregate base
MR of 7 psi
„ Design ESAL of 655,000
„ Subgrade
6.5 inch
15
FUNDEMENTALS
Asphalt Institute (AI)
Design Example
„ Evaluate
feasibility of staged
construction and prepare plan, if
necessary
– Used when adequate funds are not
available to construct the pavement to
the “required” depth
FUNDEMENTALS
Asphalt Institute (AI)
Design Example
„ Carry
out economic analyses
– Evaluate alternative designs based on
the type of pavement, type of materials
used, whether or not staged
construction is used, etc.
FUNDEMENTALS
Questions
16