Wai-Fah Chen.The Civil Engineering Handbook
Подождите немного. Документ загружается.
62-70 The Civil Engineering Handbook, Second Edition
which the overlay is placed directly on the existing pavement without the application of a bonding or
unbonding medium.
Design of Unbonded Overlay
The procedure selects an overlay thickness that, under the action of an 18-kip (80-kN) single-axle load,
would have an edge stress in the overlay equal to or less than the corresponding edge stress in an adequately
FIGURE 62.46 Chart for determining temperature correction factor F. (Source: Asphalt Institute. 1983a. Asphalt
Overlays for Highway and Street Rehabilitation. Manual Series MS-17. With permission.)
FIGURE 62.47 Estimation of pavement temperature. (Source: Asphalt Institute. 1983a. Asphalt Overlays for Highway
and Street Rehabilitation. Manual Series MS-17. With permission.)
UNTREATED GRANULAR
BASE THICKNESS
DEFLECTION ADJUSTMENT FACTORS FOR
BENKELMAN BEAM TESTING
TEMPERATURE ADJUSTMENT FACTOR (F)
MEAN PAVEMENT TEMPERATURE
30
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4
0¢¢ 3¢¢ 25¢¢
25¢¢
40
50
60
70
80
90
100
110
120
0¢¢
3¢¢
6¢¢
12¢¢
19¢¢
TEMPERATURE AT DEPTH, ∞F
TEMPERATURE AT DEPTH, ∞C
-10
-10 0 10 20 30 40 50 60 70 80 90 100 110 120
PAVEMENT SURFACE TEMPERATURE PLUS 5-DAY MEAN AIR TEMPERATURE, ∞C
PAVEMENT SURFACE TEMPERATURE PLUS 5-DAY MEAN AIR TEMPERATURE, ∞F
0
10
20
30
40
50
60
70
020406080100 120 140 160 180 200
DEPTH IN PAVEMENT 25mm (1 in.)
50mm (2 in.)
150mm
(6 in.)
200mm
(8 in.)
300mm
(12 in.)
100mm (4 in.)
220 240 260
160
140
120
100
80
60
40
20
Highway and Airport Pavement Design 62-71
designed new pavement under the same load. Design charts in Fig. 62.50 are provided for the following
three cases:
Case 1. Existing pavement exhibiting a large amount of midslab and corner cracking; poor load transfer
at cracks and joints.
Case 2. Existing pavement exhibiting a small amount of midslab and corner cracking; reasonably good
load transfer across cracks and joints; localized repair performed to correct distressed slabs.
Case 3. Existing pavement exhibiting a small amount of midslab cracking; good load transfer across
cracks and joints; loss of support corrected by undersealing.
The design charts were obtained from computer analysis of pavements assuming modulus of elasticity
of 5 ¥ 10
6
psi (35 GPa) for overlays and 3 ¥ 10
6
and 4 ¥ 10
6
psi (21 and 28 GPa) for existing pavements.
If a tied shoulder is provided, the thickness of the overlay may be reduced by 1 in. (25 mm) subject to
the minimum thickness requirement of 6 in. (150 mm).
Example 62.27
Design a concrete overlay for an existing 10-in.-thick concrete pavement if the required new single-slab
thickness is 10 in.
For case 1, T
OL
= 9 in., from Fig. 62.50(a). For case 2, T
OL
= 6 in., from Fig. 62.50(b). For case 3, where
T
OL
< 6 in., from Fig. 62.50(c), use minimum 6 in.
Design of Bonded Overlay
The same structural equivalency concept as for unbonded overlay is adopted in the design for bonded
overlay, except that the comparison is now made between the stress-to-strength ratios of the new and
the overlaid pavements. The design chart (Fig. 62.51) has three curves for three different ranges of moduli
of rupture S
c
of the existing concrete. S
c
may be estimated from the effective splitting tensile strength f
te
as follows:
FIGURE 62.48 Design chart for overlay thickness. (Source: Asphalt Institute. 1983a. Asphalt Overlays for Highway
and Street Rehabilitation. Manual Series MS-17. With permission.)
10,000,000
ESAL
5,000,000
2,000,000
1,000,000
500,000
200,000
100,000
50,000
20,000
10,000
5,000
16
14
12
10
8
6
4
2
0
024681012141618
Representative Rebound Deflection (0.01 in.)
Overlay Thickness (in.)
20,000,000
50,000,000
62-72 The Civil Engineering Handbook, Second Edition
(62.41)
(62.42)
where f
t
is the average value of splitting tensile strength of cored specimens determined according to
ASTM Test Method C496, s is the standard deviation of splitting tensile strength, and A is a regression
constant ranging from 1.35 to 1.55. An A value of 1.45 is suggested in the absence of local information.
One core should be taken every 300 to 500 ft (91 to 152 m) at midslab and about 2 ft (0.6 m) from the
edge of the outside lane. The 0.9 factor in Eq. (62.42) relates the strength of the concrete specimens to
that near or at the edge.
Example 62.28
A 9-in.-thick concrete pavement is to be strengthened to match the capacity of a new 10-in.-thick concrete
pavement. What is the required thickness of bonded overlay if the existing concrete has a flexural strength
of 450 psi?
Using curve 3 of Fig. 62.51, the thickness of existing pavement plus overlay = 11.5 in. Overlay thickness
= 11.5 – 9 = 2.5 in.
FAA Design Procedure for Flexible Overlay on Flexible Airport Pavement
The design method of FAA [1978] is similar in the equivalent thickness concept to the PCA method that
adopts the component analysis. The FAA equivalency factors are shown in Table 62.13. A high-quality
material may be converted to a lower-quality material — for example, surfacing to base and base to
FIGURE 62.49 Thickness of asphalt overlay on concrete pavement. (Source: Asphalt Institute. 1983a. Asphalt Over-
lays for Highway and Street Rehabilitation. Manual Series MS-17, p. 79. With permission.)
TEMPERATURE DIFFERENTIAL
∑
(∞F)
TEMPERATURE DIFFERENTIAL (∞C)
Slab
Length
(Ft)
10
or Less
15
30
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
115mm
(4.5 in.)
125mm
(5 in.)
150mm
(6 in.)
20
25
30
35
40
45
50
60
Slab
Length
(m)
3
4.5
6
7.5
9
10.5
12
13.5
15
18
17
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
200mm
(8 in.)
175mm
(7 in.)
150mm
(6 in.)
140mm
(5.5 in.)
115mm
(4.5 in.)
100mm
(4 in.)
40
22
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
125mm
(5 in.)
150mm
(6 in.)
175mm
(7 in.)
190mm
(7.5 in.)
215mm
(8.5 in.)
Use
Alternative
2 or 3
50
28
100mm
(4 in.)
100mm
(4 in.)
100mm
(4 in.)
125mm
(5 in.)
150mm
(6 in.)
225mm
(9 in.)
200mm
(8 in.)
175mm
(7 in.)
Use
Alternative
2 or 3
Use
Alternative
2 or 3
60
33
100mm
(4 in.)
100mm
(4 in.)
125mm
(5 in.)
150mm
(6 in.)
175mm
(7 in.)
215mm
(8.5 in.)
Use
Alternative
2 or 3
Use
Alternative
2 or 3
Use
Alternative
2 or 3
Use
Alternative
2 or 3
70
39
100mm
(4 in.)
100mm
(4 in.)
140mm
(5.5 in.)
175mm
(7 in.)
200mm
(8 in.)
Use
Alternative
2 or 3
Use
Alternative
2 or 3
Use
Alternative
2 or 3
Use
Alternative
2 or 3
Use
Alternative
2 or 3
80
44
f
te
f
t
1.65s–=
S
c
0.9Af
te
=
Highway and Airport Pavement Design 62-73
FIGURE 62.50 PCA design charts for unbonded overlays. (Source: Ta yabji, S.D. and Okamoto, P.A., Proceedings 3rd
Int. Conf. on Concrete Pavement Design and Rehabilitation, Purdue University, April 23–25, 1985, pp. 367–379. With
permission.)
89101112 13 14
k = 100—300 pci
Overlay
Thickness (in.)
Case 2
Base
Line
456
Existing Pavement Thickness (in.)
New Full-Depth Slab Thickness (in.)
( b ) Case 2
78910
6
7
8
9
10
11
12
Overlay
Existing
89101112 13 14
k = 100—300 pci
Overlay
Thickness (in.)
Case 1
Base
Line
456
Existing Pavement Thickness (in.)
New Full-Depth Slab Thickness (in.)
( a ) Case 1
78910
6
7
8
9
10
11
12
Overlay
Existing
Existing Pavement Thickness (in.)
New Full-Depth Slab Thickness (in.)
891011
12
13 14
45678910
(c) Case 3
Case 3
Overlay
Thickness (in.)
7
6
8
9
10
11
Base
Line
k = 100—300 pci
Overlay
Existing
62-74 The Civil Engineering Handbook, Second Edition
subbase. A material may not be converted to a higher-quality material. The overlay thickness is equal to
the difference between the total equivalent layer thicknesses of the existing pavement and the correspond-
ing required layer thickness of a new pavement. The minimum overlay thickness allowed is 3 in. (75 mm).
Example 62.29
An existing asphalt concrete airport pavement has 4-in. bituminous surface course, 7-in. base course,
and 14-in. subbase. The CBR of the subgrade is 8 and that of the subbase is 12. Provide an overlay to
strengthen the pavement for 6000 annual departures of a design aircraft (dual-wheel landing gear) with
maximum weight of 100,000 lb.
From Fig. 62.17, a new pavement requires 30 in. total thickness based on subgrade CBR of 8 and a
thickness of 17 in. above subbase, based on subbase CBR of 12. Using 4 in. of asphalt concrete surface
course, the base layer is (17 – 4) = 13 in. The deficiency of thickness of the existing pavement is all in
the base layer. Assuming that the existing asphalt concrete surface course can be converted to base at an
equivalency ratio of 1.4 to 1 (see Table 62.13), the thickness of asphalt base required = (13 – 7)/1.4 =
4.3 in. An additional 0.3 in. of asphalt concrete base is needed. The total thickness of overlay = (4 in. of
new surface course) + 0.3 = 4.3 in. Use a 4.5-in. overlay.
FAA Design Procedure for Flexible Overlay on Concrete Airport Pavement
The equation for computing bituminous overlay thickness T is
(62.43)
where F =factor to be obtained from Fig. 62.52
h = single thickness of rigid pavement required for design condition, in inches (use the exact
value without rounding off )
FIGURE 62.51 PCA design charts for bonded overlays. (Source: Tayabji, S.D. and Okamoto, P.A., Proceedings 3rd
Int. Conf. on Concrete Pavement Design and Rehabilitation, Purdue University, April 23–25, 1985, pp. 367–379. With
permission.)
89101112 13 14
89101112 13 14
123
Full Depth Stab Thickness, In
Total Thickness of Existing Pavement and Resurfacing. in.
Base Line
Curve No.
1
2
3
Existing Pavement
Flexural Strength, psi
526 to 575
476 to 525
426 to 475
Resurfacing
Existing Pavement
T inches()2.5 F( h C
b
h
e
)–=
Highway and Airport Pavement Design 62-75
C
b
=condition factor for base pavement, 0.75 £ C
b
£ 1.0
h
e
= thickness of existing rigid pavement, in inches
The F factor is related to the degree of cracking that will occur in the base pavement. It has a value
less than one, indicating that the entire single concrete slab thickness is not needed because a bituminous
overlay pavement is allowed to crack and deflect more than a conventional rigid pavement. C
b
is an
assessment of the structural integrity of the existing pavement. C
b
is 1.0 when the existing slabs contain
nominal initial cracking and 0.75 when the slabs contain multiple cracking.
Example 62.30
An existing 10-in. concrete pavement has a condition factor C
b
of 0.8. The subgrade k is 200 pci. Provide
a bituminous overlay to strengthen the pavement to be equivalent to a single rigid pavement thickness
of 12 in. for a design traffic of 3000 annual departures.
From Fig. 62.52, F = 0.92. By Eq. (62.43), overlay thickness t = 2.5{(0.92 ¥ 12) – (0.8 ¥ 10)} = 7.6 in.
Use an 8-in.-thick overlay.
FAA Design Procedure for Concrete Overlay on Concrete Airport Pavement
The design of concrete overlay requires an assessment of the structural integrity of the existing pavement
and the thickness of a new concrete pavement on the existing subgrade. The design equations are
(62.44)
(62.45)
(62.46)
where C
r
= 1.0 for existing pavement in good condition — some minor cracking evident but no
structural defects
C
r
= 0.75 for existing pavement containing initial corner cracks due to loading but no progres-
sive cracking or joint faulting
C
r
= 0.35 for existing pavement in poor structural condition — badly cracked or crushed and
faulted joints.
FIGURE 62.52 Graph for determination of F factor. (Source: Federal Aviation Administration. 1978. Airport Pave-
ment Design and Evaluation. Advisory Circular AC No. 150/5320-6C, p. 105. With permission.)
F - FACTOR
MODULUS OF SUBGRADE REACTION
0.6
0.7
0.8
0.9
1.0
0 100 200
pci
300 400
25000
15000
6000
3000
[100][75][50]
MN
/
m
3
[25][0]
1
2
0
0
A
N
N
U
A
L
D
E
P
A
R
T
U
R
E
S
Unbonded overlay Th
2
C
r
h
e
2
–()
12§
=
Partially bonded overlay Th
1.4
C
r
h
e
1.4
–()
11.4§
=
Bonded overlay Thh
e
–=
62-76 The Civil Engineering Handbook, Second Edition
The variables h and h
e
are the thicknesses of new and existing pavements, respectively. The use of
partially bonded overlay — which is constructed directly on an existing pavement without debonding
medium (such as a bituminous leveling course) — is not recommended for an existing pavement with
C
r
less than 0.75. Bonded overlays should be used only when the existing rigid pavement is in good
condition. The minimum bonded overlay thickness is 3 in. For partially and unbonded overlays, the
minimum thickness is 5 in.
Example 62.31
An existing 10-in.-thick concrete airport pavement with C
r
= 1.0 is to be strengthened to match the
capacity of a new 12-in. rigid pavement. Determine the required thickness of bonded, partially bonded,
and unbonded overlays.
Unbonded overlay. T = = 6.6 in. Use 7 in.
Partially bonded overlay. T = = 4.1 in. Use 5 in. (min).
Bonded overlay. T = 12 – 10 = 2 in. Use 3 in. (min).
Defining Terms
Asphalt pavement (asphalt concrete pavement, bituminous pavement) — The most common
form of flexible pavement in which the surface course is constructed of asphaltic (or bituminous)
mixtures.
Base course — The layer of selected material in a pavement structure placed between a subbase and a
surface course.
Concrete pavement — The most common form of rigid pavement, in which the top slab is constructed
of portland cement concrete.
Flexible pavement — A pavement structure that does not distribute traffic load to the subgrade by
means of slab action but mainly through spreading of the load by providing sufficient thickness
of the pavement structure.
Overlay — A new surface layer laid on an existing pavement to improve the latter’s load-carrying
capacity.
Pavement structure — A structure consisting of one or more layers of selected materials constructed
on prepared subgrade to designed strength and thickness(es) for the purpose of supporting
traffic.
Rigid pavement — A pavement structure that distributes traffic loads to the subgrade by means of slab
action through its top layer of high-bending resistance.
Subbase — The layer of selected material in a pavement structure placed between the subgrade and the
base or surface course.
Subgrade — The top surface of graded foundation soil, on which the pavement structure is constructed.
Surface course — The top layer of a pavement structure placed on the base course, the top surface of
which is in direct contact with traffic loads.
References
AASHTO. 1972. AASHTO Interim Guide for Design of Pavement Structures. American Association of State
Highway and Transportation Officials, Washington, D.C.
AASHTO. 1989. Standard Specifications for Transportation Materials and Methods of Sampling and Testing.
Part I and II. American Association of State Highway and Transportation Officials, Washington,
D.C.
AASHTO. 1993. AASHTO Guides for Design of Pavement Structures. American Association of State
Highway and Transportation Officials, Washington, D.C.
ACI. 1977. Building Code Requirements for Reinforced Concrete. American Concrete Institute, Detroit, MI.
12
2
10
2
–
12
1.4
10
1.4
–
1.4
Highway and Airport Pavement Design 62-77
Asphalt Institute. 1983a. Asphalt Overlays for Highway and Street Rehabilitation. Manual Series No. 17.
Lexington, KY.
Asphalt Institute. 1983b. Asphalt Technology and Construction Practices. Educational Series ES-I, 2nd ed.
Lexington, KY.
Asphalt Institute. 1991. Thickness Design — Asphalt Pavements for Highways & Streets. Manual Series No. 1.
Lexington, KY.
ASTM. 1992. Annual Books of ASTM Standards. American Society for Testing and Materials, Philadelphia,
PA.
Boussinesq, J. 1885. Application des Potentiels a l’etude de l’equilibre et du Mouvement des Solids Elastiques.
Gauthier-Villars, Paris.
FAA. 1978. Airport Pavement Design and Evaluation. Advisory Circular AC No. 150/5320-6C. Federal
Aviation Administration.
Fwa, T.F., and Li, S. 1994. Estimation of lane distribution of truck traffic for pavement design. Paper
accepted for publication. Journal of Transportation Engineering.
Fwa, T.F., Shi, X.P., and Tan, S.A. 1993. Load-Induced Stresses and Deflections in Concrete Pavement —
Analysis by Rectangular Thick-Plate Model. CTR Technical Report CTR-93-5. Centre for Transpor-
tation Research, Faculty of Engineering, National University of Singapore.
Fwa, T.F., and Sinha, K.C. 1985. A Routine Maintenance and Pavement Performance Relationship Model
for Highways. Joint Highway Research Project Report JHRP-85-11. Purdue University, West Lafay-
ette, IN.
Highway Research Board. 1962. The AASHO Road Test, Report 5 — Pavement Research. HRB Special
Report 61E. Washington, D.C.
PCA. 1984. Thickness Design for Concrete Highway and Street Pavements. Portland Cement Association,
Skokie, IL.
Shi, S.P., Tan, S.A., and Fwa, T.F. 1994. Rectangular plate with free edges on a Pasternak foundation.
Journal of Engineering Mechanics. 120(5):971–988.
Tayabji, S.D. and Okamoto, P.A. 1985. Thickness design of concrete resurfacing. Proc. 3rd Int. Conf. on
Concrete Pavement Design and Rehabilitation, April 23–25, Purdue University, West Lafayette, IN,
pp. 367–379.
Van Til, C.J., McCullough, B.F., Vallerga, B.A., and Hicks, R.G. 1972. Evaluation of AASHO Interim Guides
for Design of Pavement Structures. NCHRP Report 128. Highway Research Board, Washington, D.C.
Westergaard, H.M. 1926. Stresses in concrete pavements computed by theoretical analysis. Public Roads.
7(2):25–35.
Westergaard, H.M. 1933. Analytical tools for judging results of structural tests of concrete pavements.
Public Roads. 14(10).
Westergaard, H.M. 1948. New formulas for stresses in concrete pavements of airfield. ASCE Transactions.
Vol. 113.
Yo der, E.J., and Witczak, M.W. 1975. Principles of Pavement Design, 2nd ed. John Wiley & Sons, New York.
Further Information
A widely quoted reference to the basics of practical design of highway and airport pavements is Principles
of Pavement Design, by E.J. Yoder and M.W. Witczak. Although the described design methods by various
agencies are outdated, the book is still a valuable reference on the requirements of pavement construction
and design.
Detailed descriptions of pavement design methods, pavement material, and construction requirements
by various organizations are available in their respective publications. The Asphalt Institute publishes a
manual series addressing bituminous pavement-related topics — including thickness design, pavement
rehabilitation and maintenance, pavement drainage, hot-mix design, and paving technology. Additional
information concerning topics related to portland cement concrete pavement is found in publications
by the Portland Cement Association and American Concrete Institute.
62-78 The Civil Engineering Handbook, Second Edition
The latest developments in various aspects of pavement design are reported in a number of technical
journals in the field. The most important are the Journal of Transportation Engineering, published
bimonthly by the American Society of Civil Engineers, and Transportation Research Records, published
by the Transportation Research Board. There are about 40 issues of Transportation Research Records
published each year, each collecting a group of technical papers addressing a specialized area of trans-
portation engineering.
There are several major conferences that focus on highway and airport pavements. The International
Conference on Structural Design of Asphalt Pavements has been held once every five years since 1962.
The seventh conference, in 1992, was named International Conference on Asphalt Pavements: Design,
Construction and Performance to reflect the added scope of the conference. The proceedings of the
conferences document advances in areas of asphalt pavement technology. Another conference, the Inter-
national Conference on Concrete Pavement Design and Rehabilitation, focuses on the development of
concrete pavement technology. It has been organized once every four years since 1977 by Purdue Uni-
versity. There is also the International Conference on the Bearing Capacity of Roads and Airfields, held
at intervals of four years since 1982. Other related publications are the Proceedings of the World Road
Congress, published by the Permanent International Association of Road Congress, and the Proceedings
of the Road Congress of the International Road Federation.
© 2003 by CRC Press LLC
63
Geometric Design
63.1 Introduction
Design Process
63.2 Fundamentals of Geometric Design
Highway Types • Design Controls • Sight Distance • Simple
Highway Curves
63.3 Basic Design Applications
Horizontal Alignment • Vertical Alignment • Cross Section
Elements • Intersections • Esthetic and General Considerations
• Design Aids
63.4 Special Design Applications
Complex Highway Curves • Three-Dimensional Alignments •
RRR Projects
63.5 Emerging Design Concepts
Design Consistency • Design Flexibility • Safety Audits • Human
Perception • Smart Design
63.6 Economic Evaluation
63.7 Summary: Key Ingredients
63.1 Introduction
Geometric design of highways refers to the design of the visible dimensions of such features as horizontal
and vertical alignments, cross sections, intersections, and bicycle and pedestrian facilities. The main
objective of geometric design is to produce a highway with safe, efficient, and economic traffic operations
while maintaining esthetic and environmental quality. Geometric design is influenced by the vehicle,
driver, and traffic characteristics. The temporal changes of these characteristics make geometric design
a dynamic field where design guidelines are periodically updated to provide more satisfactory design.
Policies on highway geometric design in the United States are developed by the American Association
of State Highway and Transportation Officials (AASHTO). These policies represent design guidelines
agreed to by the state highway and transportation departments and the Federal Highway Administration
(FHWA). Guidelines for highway geometric design are presented in
A Policy on Geometric Design of
Highways and Streets
[AASHTO, 2001], which is based on many years of experience and research. Repeated
citation to AASHTO throughout this chapter refers to this policy. In Canada, geometric design guidelines
are presented in the
Geometric Design Guide for Canadian Roads
[TAC, 1999], which is published by the
Tr ansportation Association of Canada (TAC).
This chapter discusses the fundamentals of highway geometric design and their applications and is
divided into four main sections: fundamentals of geometric design, basic design applications, special
design applications, and emerging design concepts. It draws information mostly from the AASHTO policy
and TAC guide and provides supplementary information on more recent developments. Since geometric
design is a major component in both the preliminary location study and the final design of a proposed
highway, it is useful to describe first the highway design process.
Said M. Easa
Ryerson Polytechnic University