design of flexible pavement using AASHTO

1. “Design of Flexible Pavement Using AASHTO"
By: Eng. Mohamed Mohamed El-Shafie Shams
Construction Engineering Department, Egyptian Russian University
Submitted to
Menoufia University
Faculty of Engineering – Shebin El-Koom
Civil Engineering Department
Dr. Mohamed Adel
Professor of Highway Engineering
Faculty of Engineering- Shebin El-Koom
Menoufia, Egypt
‫المنـــوفية‬ ‫جــــامـــعة‬
‫الهندس‬ ‫كلية‬
‫ــــــ‬
‫الكوم‬ ‫بشبين‬ ‫ة‬
‫المدنية‬ ‫الهندسة‬ ‫قسم‬

2. ‫باستخدام‬ ‫المرن‬ ‫الرصف‬ ‫تصميم‬
‫األشتو‬
Design of Flexible Pavement Using AASHTO
•
‫سمك‬ ‫حساب‬ ‫يعني‬ ‫المرن‬ ‫الرصف‬ ‫تصميم‬
‫كل‬
‫الرصف‬ ‫طبقات‬ ‫من‬ ‫طبقة‬
•
‫اليجاد‬
d1
‫و‬
d2
‫و‬
d3
‫االنشائي‬ ‫الرقم‬ ‫معرفة‬ ‫أوال‬ ‫يجب‬
Structure Number (SN)
‫طبقة‬ ‫لكل‬
•
‫االنشائي‬ ‫الرقم‬ ‫قيمة‬ ‫نحدد‬
Structure Number (SN)
‫خالل‬ ‫من‬ ‫طبقة‬ ‫لكل‬
Chart
:
‫الـ‬ ‫ندخل‬
Chart
‫بـ‬
5 inputs
‫هم‬
:
4. Mr (Modulus of Resilience) ‫طبقة‬ ‫لكل‬ ‫المرونة‬ ‫معامل‬
MrSubgrade – MrSubbase – MrBase
5. ∆PSI (Pavement serviceability index) ‫الرصف‬ ‫كفائة‬ ‫مؤشر‬
1. % R (Reliability) ‫الثقة‬ ‫درجة‬
2. So (Standard Deviation) ‫المعياري‬ ‫االنحراف‬
3. ESAL (Equivalent Single Axial Load)
AASHTO : American Association of State Highway and Transportation Officials

3. ‫تكون‬ ‫غالبا‬
Given
‫األتي‬ ‫الجدول‬ ‫من‬ ‫ايجادها‬ ‫يتم‬ ‫او‬
‫تكون‬ ‫غالبا‬
Given
‫األتي‬ ‫الجدول‬ ‫من‬ ‫ايجادها‬ ‫يتم‬ ‫او‬
1. % R (Reliability ‫درجة‬
‫الثقة‬ )
•
‫للتصميم‬ ‫تجميعها‬ ‫تم‬ ‫التي‬ ‫والبيانات‬ ‫النتائج‬ ‫في‬ ‫الثقة‬ ‫درجة‬ ‫هي‬
•
‫فرضها‬ ‫يتم‬ ‫بيانات‬ ‫اي‬ ‫يذكر‬ ‫لم‬ ‫اذا‬
%
95
Functional Classification Urban Rural
Freeways 85-99.9 80-99.9
Arterial 80 – 99 75 – 95
Collectors 80 – 95 75 – 95
Local 50 – 80 50 – 80
2. So (Standard Deviation ‫االنحراف‬
‫المعياري‬ )
•
‫المرور‬ ‫واحمال‬ ‫المواد‬ ‫خصائص‬ ‫مثل‬ ‫التصميم‬ ‫مدخالت‬ ‫قيم‬ ‫في‬ ‫الموجودة‬ ‫التباين‬ ‫درجة‬ ‫هي‬
Design condition Standard Deviation
Variation in pavement performance prediction without traffic error 0.35
Total variation in pavement performance prediction and in traffic estimation 0.45
•
‫فرضها‬ ‫يتم‬ ‫بيانات‬ ‫اي‬ ‫يذكر‬ ‫لم‬ ‫اذا‬
So = 0.45

4. AADT = Annual Average daily traffic G.F = growth factor = [(1+r)n – 1]/r , r is decimal rate
T = Truck percent L.F = Lane factor
T.F = Truck Factor value of all trucks [Σ(L.E.F × No of Axles)]/No of Trucks
(w tons/8.2 tons)4 ……..for single axle
Load Equivalency Factor (L.E.F) (w tons/15.1 tons)4 ……..for tandem axles
(w tons/21.8 tons)4 ……..for tridem axles
3. ESAL (Equivalent Single Axle Load)
•
‫للطريق‬ ‫التصميمية‬ ‫الفترة‬ ‫خالل‬ ‫التصميمية‬ ‫الحارة‬ ‫فى‬ ‫المارة‬ ‫القياسية‬ ‫المحاور‬ ‫تكرار‬ ‫مرات‬ ‫عدد‬
4. Mr (Modulus of Resilience ‫المرونة‬ ‫معامل‬ )
MrSubgrade (lb/in2) = 1500 CBR for CBRSubgrade ≤ 10%
MrSubgrade (lb/in2) = 2550 CBR0.64 for CBRSubgrade > 10%
MrSubbase , MrBase : Given or from Chart 1 & Chart 2 Using CBRsubbase and CBRbase
‫يكون‬
Given
‫األتية‬ ‫المعادلة‬ ‫من‬ ‫يحسب‬ ‫او‬
:
ESAL (W18)=365 × AADT × G.F × % T x L.F x T.F

5. ‫رقم‬ ‫شكل‬
1
‫رقم‬ ‫شكل‬
2
a
2
a
3
5. ∆PSI (Pavement serviceability index ‫الرصف‬ ‫كفائة‬ ‫مؤشر‬ )
•
‫من‬ ‫تتراوح‬ ‫قيمتة‬ ‫الطريق‬ ‫عمر‬ ‫خالل‬ ‫الرصف‬ ‫كفائة‬ ‫عن‬ ‫يعبر‬ ‫مؤشر‬
(
0
‫الي‬
5
)
.
PSI= 0 Very Rough (Poor) Pavement ‫الرصف‬ ‫سئ‬ ‫طريق‬
PSI= 5 Very Smooth (Good) Pavement ‫طريق‬
‫الرصف‬ ‫جيد‬

6. Pi = Initial serviceability index ‫االبتدائية‬ ‫الرصف‬ ‫كفائة‬
Pi = 4.2 to 4.5 ‫مباشرة‬ ‫الطريق‬ ‫تنفيذ‬ ‫بعد‬
Pt = Terminal serviceability index ‫النهائية‬ ‫الرصف‬ ‫كفائة‬
‫للطريق‬ ‫التصميمي‬ ‫العمر‬ ‫انتهاء‬ ‫بعد‬
3 for major road
Pt = 2.5 for collector road
2 for local road
∆PSI = Pi - Pt
‫فرض‬ ‫يتم‬ ‫بيانات‬ ‫اي‬ ‫يذكر‬ ‫لم‬ ‫اذا‬
PSI = 2
∆
‫على‬ ‫للحصول‬ ‫الـمنحني‬ ‫استخدام‬ ‫كيفية‬
Structure Number (SN)
‫بهم‬ ‫ندخل‬ ‫الخمسة‬ ‫المدخالت‬ ‫حساب‬ ‫بعد‬
AASHTO Chart
‫علي‬ ‫للحصول‬
Structure Number
‫طبق‬ ‫بكل‬ ‫الخاص‬
‫ة‬
.1
‫قيمة‬ ‫نوقع‬
Reliability
‫محور‬ ‫علي‬
Reliability
(
‫نقطة‬
1
)
.
.2
‫قيمة‬ ‫نوقع‬
So
‫محور‬ ‫علي‬
Standard Deviation
(
‫نقطة‬
2
)
.
.3
‫النقطة‬ ‫نصل‬
1
‫بنقطة‬
2
‫في‬ ‫التالي‬ ‫المحور‬ ‫يقطع‬ ‫حتى‬ ‫استقامتة‬ ‫على‬ ‫ونمده‬ ‫مستقيم‬ ‫بخط‬
(
‫نقطة‬
3
)
.4
‫قيمة‬ ‫نوقع‬
ESAL
‫علي‬
‫محور‬
ESAL
(
‫نقطة‬
4
)
.
.5
‫النقطة‬ ‫نصل‬
3
‫بنقطة‬
4
‫في‬ ‫التالي‬ ‫المحور‬ ‫يقطع‬ ‫حتى‬ ‫استقامتة‬ ‫على‬ ‫ونمده‬ ‫مستقيم‬ ‫بخط‬
(
‫نقطة‬
5
)
.
.6
‫نوقع‬
‫قيم‬
Mr
‫لطبقات‬
(
Subgrade , Subbase, Base
)
‫محور‬ ‫على‬
Mr
(
‫نقط‬
6
8,7,
‫الترتيب‬ ‫علي‬
)
.
.7
‫نقطة‬ ‫من‬ ‫مستقيمة‬ ‫خطوط‬ ‫ثالث‬ ‫نمد‬
5
‫بالنقط‬ ‫تمر‬
6
8,7,
‫وممتدة‬
‫على‬
‫استقامتها‬
‫حتى‬
‫منهم‬ ‫كل‬ ‫يقطع‬
‫المحور‬
‫التالي‬
(
‫نقط‬
9
,
10
,
11
‫علي‬
‫الترتيب‬
)
.

7. .8
‫منحني‬ ‫نحدد‬
PSI
∆
‫النقط‬ ‫من‬ ‫مستقيم‬ ‫خط‬ ‫بعمل‬ ‫نقوم‬ ‫ثم‬
9
‫و‬
10
‫و‬
11
‫الـ‬ ‫قيم‬ ‫على‬ ‫فنحصل‬ ‫نقطة‬ ‫فى‬ ‫المنحني‬ ‫ويقطع‬ ‫حدة‬ ‫علي‬ ‫كل‬
Structure Number
‫المقابلة‬
‫والخاصة‬
‫طبقة‬ ‫بكل‬
(
SNSubgrade , SNSubbase, SNBase
)
‫التالي‬ ‫شكل‬ ‫فى‬ ‫موضح‬ ‫هو‬ ‫كما‬
.

8. SN for any layer = ( ∑ a d m ) for all layers above
1. SNbase = a1 d1
2. SNsubbase = a1 d1 + a2 d2 m2
3. SNsubgrade = a1 d1 + a2 d2 m2 + a3 d3 m3
• a1 : Structural coefficient for w.s layer
• a2 : Structural coefficient for Base layer
from Chart 2 Using CBRbase
• a3 : Structural coefficient for Subbase layer
from Chart 1 Using CBRsubbase
• m1 : ‫للماء‬ ‫منفذ‬ ‫غير‬ ‫االسفلت‬ ‫الن‬ ‫يوجد‬ ‫ال‬
• m2 : drainage factor for Base layer
• m3 : drainage factor for Subbase layer
Mrw.s = 450,000
a1 = 0.44
Get a2
Get a3

9. ‫على‬ ‫الحصول‬
m2 , m3
•
‫الماء‬ ‫من‬ ‫للتخلص‬ ‫الطبقة‬ ‫تحتاجة‬ ‫الذي‬ ‫الزمن‬ ‫بمعلومية‬ ‫التالى‬ ‫الجدول‬ ‫ندخل‬
(water removed within)
‫المقابلة‬ ‫الصرف‬ ‫كفائة‬ ‫على‬ ‫نحصل‬ ‫ثم‬
Quality of drainage
.
‫من‬ ‫كال‬ ‫بمعلومية‬ ‫التالي‬ ‫الجدول‬ ‫ندخل‬ ‫ثم‬
Quality of drainage
‫بالمياة‬ ‫التشبع‬ ‫زمن‬ ‫نسبة‬ ‫و‬
‫قيمة‬ ‫على‬ ‫لنحصل‬
m2 , m3
.
Quality of drainage water removed within
Excellent 2 hours
Good 1 day
Fair 1 weeks
Poor 1 month
Very poor Water will not drain
Quality of
drainage
Percentage of time pavement structure is exposed to moisture
levels approaching saturation
Less than
1%
1 – 5 % 5 – 25 %
Greater than
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. 5 – 1.05 1.00 – 0.80 0.80
Poor 1. 5 – 1.05 1. 05 – 0.80 0.80 – 0.06 0.60
Very poor 1. 05 – 0.95 0.95 – 0.75 0.75 – 0.40 0.40
‫الطبقات‬ ‫سمك‬ ‫حساب‬
.1
‫األسفلت‬ ‫طبقة‬ ‫سمك‬ ‫حساب‬
(d1) W.S
SNbase = a1 d1 get d1
‫قيمة‬ ‫نقارن‬ ‫ثم‬ ‫بالزيادة‬ ‫بوصة‬ ‫نصف‬ ‫ألقرب‬ ‫الناتج‬ ‫نقرب‬
d1
‫بالـ‬
dmin
‫الجدول‬ ‫في‬ ‫الموضحة‬
‫االكبر‬ ‫القيمة‬ ‫ونأخذ‬
Example

10. .2
‫األساس‬ ‫طبقة‬ ‫سمك‬ ‫حساب‬
(d2)
SNsubbase = a1 d1 + a2 d2 m2 get d2
‫قيمة‬ ‫نقارن‬ ‫ثم‬ ‫بالزيادة‬ ‫بوصة‬ ‫نصف‬ ‫ألقرب‬ ‫الناتج‬ ‫نقرب‬
d2
‫بالـ‬
dmin
‫الموضحة‬
‫و‬ ‫الجدول‬ ‫في‬
‫االكبر‬ ‫القيمة‬ ‫نأخذ‬
.3
‫األساس‬ ‫طبقة‬ ‫سمك‬ ‫حساب‬
(d3)
SNsubgrade = a1 d1 + a2 d2 m2 + a3 d3 m3 get d3
‫قيمة‬ ‫نقارن‬ ‫ثم‬ ‫بالزيادة‬ ‫بوصة‬ ‫نصف‬ ‫ألقرب‬ ‫الناتج‬ ‫نقرب‬
d2
‫بالـ‬
dmin
‫الجدول‬ ‫في‬ ‫الموضحة‬
‫ونأخذ‬
‫االكبر‬ ‫القيمة‬

11. 11
Example (1):
Design a flexible pavement by AASHTO method and draw typical cross section of the flexible pavement for rural highway has
following data:
- Elastic modulus of Asphalt is 450000 Ib/in2, Mr of base = 31000 Psi, Mr of subbase = 13500 Psi.
- CBR of base = 100, CBR of sub base = 22, CBR of subgrade = 6, water removed within one week, percentage of time pavement
structure is exposed to moisture levels = 30 %, reliability = 95 %, Standard deviation = 0.45, initial serviceability = 4.2, terminal
serviceability = 2.5 and ESAL = 2 m.
Sol.
R = 95 % , S = 0.45 , ESAL = 2 * 106 ,
Pi = 4.2 , Pt = 2.5
∆PSI = Pi – Pt = 4.2 – 2.5 = 1.7
For CBRSubgrade = 6 ≤ 10% MrSubgrade (lb/in2) = 1500 CBR =1500 * 6 = 9000 Psi
MrAsphalt = 450,000 From chart 1 a1 = 0.44
Mrbase = 31,000 Psi
Mrsubbase = 13500 Psi
From chart 2 a2 = 0.14
From chart 3 a3 = 0.1
water removed within one week From table : Quality of drainage is Fair

12. Chart 3 Chart 2 Chart 1
Quality of drainage is Fair
moisture levels = 30 %
m2= m3 = 0.8
From table
• SNb = 2.5 SNbase = a1 d1
2.5 = 0.44 * d1 d1 = 5.68 ≈ 6 In
ESAL = 2 * 106 From table d1 > dmin = 3 In
SN
S.g
=
4
Using AAHTO chart to get SN:
d1 = 6 In

13. 13
• SNS.b = 3.5 SNsubbase = a1 d1 + a2 d2 m2
3.5 = ( 0.44 * 6 ) + ( 0.14 * d2 * 0.8 ) d2 = 7.68 ≈ 8 In
ESAL = 2 * 106 From table d1 > dmin = 6 In
• SNS.g = 4 SNsubgrade = a1 d1 + a2 d2 m2 + a3 d3 m3
4 = ( 0.44 * 6 ) + ( 0.14 * 8 *0.8) + ( 0.1 * d3 * 0.8 ) d3 = 5.8 ≈ 6 In
d2 = 8 In
d3 = 6 In

14. 14
1. Get ESAL :
Example (2):
Existing 2-lane highway pavement serviceability index 4.2 consisting of 4 in asphalt concrete surface with Mr = 400000 Psi
constructed above base layer 11 in with CBR = 55 % resting on subgrade has CBR = 6 %, the current AADT is 2000 vpd with
annual growth rate = 5 %, truck percent = 20 % and truck factor = 0.8. Find the life time of the pavement to reach terminal
serviceability index = 2.2 ( R = 80 %, S = 0.4, m2 = 1, a1 = 0.42, a2 = 0.12)
Sol.
m2 = 1, a1 = 0.42, a2 = 0.12, Pi = 4.2 , Pt = 2.2
∆PSI = Pi – Pt = 4.2 – 2.2 = 2
For CBRSubgrade = 6 ≤ 10% MrSubgrade (lb/in2) = 1500 CBR =1500 * 6 = 9000 Psi
• SNsubgrade= a1 d1 + a2 d2 m2 • SNsubgrade= 0.42 * 4 + 0.12 * 11 * 1 = 3
Using AAHTO chart to get ESAL:
R = 80 % , S = 0.4, Mrsubgrade = 9000 Psi, ∆PSI = 2, SNsubgrade = 3

15. 15
ESAL = 365 × AADT × G.F × % T x L.F x T.F
• AADT = 2000 vph, % T = 20 %
• T,F = 0.8, growth rate ( r ) = 5 %
• Lane factor (L.F) From table
2-lane highway L.F = 0.5
1.5 *106 = 365 × 2000 × G.F × 0. 2 x 0.5 x 0.8
G.F = 25. 68 =
[ 𝟏+𝒓 𝒏
−𝟏]
𝒓
=
[ 𝟏+𝟎.𝟎𝟓 𝒏
−𝟏]
𝟎.𝟎𝟓
2.28 = 𝟏. 𝟎𝟓 𝒏
𝟏. 𝟎𝟓 16.9 = 𝟏. 𝟎𝟓 𝒏
𝒏 = 𝟏𝟔. 𝟗 𝒚𝒆𝒂𝒓𝒔
• life time of the pavement

16. 16
Example (3):
The traffic on design lane 4 – lane rural highway consists of 40 % trucks and T.F = 0.45.
Design a flexible pavement by Aashto method and draw typical cross section of the flexible pavement for highway has the
following data :
- AADT on design lane during the first year is 1000, design life = 20 years, growth rate = 4 %.
- Elastic modulus of asphalt is 450000 ib/in2.
- CBR of base = 70, CBR of subbase = 22, CBR of subgrade = 7, water removed within one week, percentage of time pavement
structure is exposed to moisture level = 20 %, reliability = 95 %, standard deviation = 0.45, initial serviceability = 4.2,
terminal serviceability = 2.5.