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```					 MINISTRY OF SCIENCE AND TECHNOLOGY
YANGON TECHNOLOGICAL UNIVERSITY
DEPARTMENT OF CIVIL ENGINEERING

CE 3017 Highway and Traffic Engineering

PRESENTER
DAW KYAING
LECTURER
DEPARTMENT OF CIVIL ENGINEERING
WEST YANGON TECHNOLOGICAL UNIVERSITY
Flexible Pavement Design

AASHTO Design Method

(American Association of State Highway
and Transportation Officials)
Design Considerations

Pavement Performance
Traffic
Materials of Construction
Environment
Drainage
Reliability
Pavement Performance
 Structural Performance
 Related to physical condition (cracking,
faulting, revealing
 Functional Performance
 How effectively the pavement serves the
user (riding comfort)
 Pavement Performance (Serviceability
Performance) PSI  0 to 5
 Based on roughness & distress (cracking,
patching, rut)
Two Serviceability Indices

1. initial serviceability index (pi)
2. terminal serviceability index (pt)

1. Initial serviceability index (pi)
 Serviceability index immediately after the
construction of the pavement
 pi = 4.2 (4.5 for good condition)
(based on existing condition)
2. terminal serviceable index (pt)
    Based on class of highway

    Pt = 2.5 or 3 (for major highway)

    Pt= 2.0     (for lower class highway)

    Pt = 1.5    (for economic constraints
performance period may
be reduced)
Traffic

in terms of

Equivalent 18000 lb Single Axial Load
(ESALs)
for CBR of 10 or less
Mr (lb/in2) = 1500 CBR

for R of 20 or less
Mr (lb/in2) = 1000+ 555xR value
Mr = Resilient modulus
Material of Construction
     Quality of Material 
In terms of
Layer Coefficient , a

Sub base Construction Material                  a3 (from Fig. 20.15)

Base Course Construction Material               a2 (from Fig. 20.16)

Surface Course Construction Material            a1 (from Fig. 20.17)
(hot plant mix of AC & dense-graded agg. with max. size 1”)
Environment
•   Temperature
•   Rainfall
 Drainage
 Drainage Factor, mi
 Based on
1) % of time during which pavement
str. nearly saturated &
2) Quality of Drainage
Table 20.14
Definition of Drainage Quality

Quality of Drainage      Water Removed within

Excellent                2 hours
Good                     1 day
Fair                     1 week
Poor                     1 month
Very Poor                water will not drain
Table 20.15
Recommended mi Values
% of time pavement str. Is exposed to moisture
levels approaching saturation
Quality of drainage   less than 1%     1-5%        5-25%       greater than 25%

Fair           1.25-1.15       1.15-1.05   1.0-0.8          0.80
Reliability (R %)
 Depends on highway class & Region (T20.16)
 ESAL based on assume growth rate
 i.e may not be accurate
• Other method do not consider this uncertainty
• AASHTO consider reliability factor possible
uncertainties in traffic condition performance
prediction
 50 % Reliability design performance success is
50 %
 Variation in traffic forecast
Standard Deviation , So
Flexible pavement                             0.4-0.5
Rigid Pavement                                0.3-0.4

Table 20.16
Suggested levels of reliability for various functional
classification
Recommended Level of Reliability
Functional Classification             Urban              Rural
Interstate and other freeways         85-99.9            80-99.9
Table 20.17
Standard Normal Deviation (ZR) Values Corresponding to
Selected Levels of Reliability

Reliability (R%)    standard Normal Deviation ,ZR

99                  -2.327
Structural Design

SN = a1D1+a2D2m2+a3D3m3

D1,D2,D3 = actual thickness in inches of surface, base,
& sub base course
Example 20.8

Given
 Flexible Pavement
 Urban Interstate Highway
 ESAL = 2 x106
 a week for water to be drain with in moisture level
= 30%
 Mr of AC at 68 F                = 45000psi
 CBR value of base = 100,     Mr = 31000psi
 CBR value of sub base = 22, Mr = 13500psi
 CBR of Sub grade = 6
Solution
Reliability (R) = 99% (Table 20.16)
Standard Deviation (So) = 0.49 (0.4 - 05)
Pi = 4.5
Pt = 2.5
∆ PSI = 4.5-2.5 = 2.0
a1 = 0.44 (Mr = 45000psi, AC)         Fig. 20.17
a2 = 0.14 (CBR = 100,Base)            Fig. 20.16
a3 = 0.1 (CBR = 22, sub base)         Fig. 20.15
By using Figure 20.20,
SN3 = 4.4 (Mr= 9000 psi)
SN2 = 3.8 (Mr = 13500 psi)
SN1 = 2.6 (Mr = 31000 psi)
D1 = SN1/a1 =2.6/0.44 = 5.9”          (use 6”)
D1* = 6”
SN1*= a1 D1* =0.44 x 6 = 2.64
D2*≥ (SN2-SN1*)/(a2m2)≥(3.8-2.64)/(0.14x0.8)
≥10.36’’               (Use 12’’)
SN2*= 0.14x0.8x12+2.64=1.34+2.64 =3.98
D3* =(SN3-SN2*)/(a3m3)=4.4-(2.64+1.34)/(0.1x0.8)
= 5.25 ’’             (Use 6’’)
SN3*=2.64+1.34+6x0.8x0.1 = 4.46
Asphalt concrete surface = 6”
Granular base            = 12”
Sub base                 = 6”
THE END

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