MS GEOTECHNICAL ENGINEERING

SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING

Term Paper Report

On

Course Code:

Course Title:

Date:

Submitted By:

Zahra Bashir Malik

00000171792

Nabeela Maheen

00000118852

Submitted To:

Dr. Kamran Ahmed

Design of Flexible Pavement Using Asphalt Institute Method and AASHTO

Empirical Method

CE860

Pavement Design & Analysis

16 -Jan -2017

i

TABLE OF CONTENTS

Table of Contents ………………………….. ………………………….. ………………………….. ……………………….. i

List of Tables ………………………….. ………………………….. ………………………….. ………………………….. .. ii

List of Figures ………………………….. ………………………….. ………………………….. ………………………….. . ii

1. INTRODUCTION ………………………….. ………………………….. ………………………….. ……………… 1

2. OBJECTIVES ………………………….. ………………………….. ………………………….. ……………………. 1

3. CALCULATION OF EASL ………………………….. ………………………….. ………………………….. … 1

3.1. Average Annual Daily Traffic (AADT) ………………………….. ………………………….. ……. 2

3.2. % Truck (T) ………………………….. ………………………….. ………………………….. ……………… 2

3.3. Truck Factor (TF) ………………………….. ………………………….. ………………………….. ……… 3

3.4. Growth Factor (GY) ………………………….. ………………………….. ………………………….. ….. 3

3.5. Directional Distributio n Factor (D) ………………………….. ………………………….. ………….. 4

3.6. Lane Distribution Factor (L) ………………………….. ………………………….. ……………………. 4

3.7. Calculation of EASL ………………………….. ………………………….. ………………………….. …. 4

4. PAVEMENT DESIGN ………………………….. ………………………….. ………………………….. ……….. 5

4.1. Pavement Design by Asphalt Institute Method ………………………….. ………………………….. 5

4.1.1. Traffic Characteristics ………………………….. ………………………….. ………………………….. .. 5

4.1.2. Subgrade engineering properties ………………………….. ………………………….. …………… 5

4.1.3. Subbase and base engineering properties ………………………….. ………………………….. ….. 5

4.1.4. Determine Min. Thickness Requirements ………………………….. ………………………….. . 6

4.1.5 . Thickness of HMA layer ………………………….. ………………………….. ……………………… 6

4.1.6. Planned Stage Construction ………………………….. ………………………….. …………………. 7

4.2. Pavement Design by AASHTO Method ………………………….. ………………………….. ………. 8

4.2.1. Pavement Performance ………………………….. ………………………….. ……………………….. 8

4.2.2. Traffic ………………………….. ………………………….. ………………………….. ………………….. 8

4.2.3. Roadbed Soils (subgrade material) ………………………….. ………………………….. ……….. 8

4.2.4. Materials of Construction ………………………….. ………………………….. ……………………. 8

4.2.5. Drainage ………………………….. ………………………….. ………………………….. ……………… 10

4.2.6. Reliability ………………………….. ………………………….. ………………………….. ……………. 11

4.2.7. Calculation of Thicknesses of layers ………………………….. ………………………….. …… 11

5. COMPA RISON ………………………….. ………………………….. ………………………….. ……………….. 13

6. CONCLUSION ………………………….. ………………………….. ………………………….. ………………… 13

7. REFRENCES ………………………….. ………………………….. ………………………….. …………………… 13

ii

LIST OF TABLES

Table -1 Estimated Section Wise AADT (Year 2019) ………………………….. ………………………….. …. 2

Table -2 Calculat ion of Percentage Truck (T) ………………………….. ………………………….. …………….. 2

Table – 3 Axle Load Study on National Highway, NTRC, 1995 and NHA ………………………….. …. 3

Table – 4 Calculation of Growth Factor from Expected Growth Rates ………………………….. ……….. 3

Table – 5 Percentage of Total truck Traffic in Design Lane ………………………….. ………………………. 4

Table – 6 Lane Distribution Factor ………………………….. ………………………….. ………………………….. … 4

Table – 7 Calculation of EASL for 2019 -2024 ………………………….. ………………………….. ……………. 4

Table – 8 Calculation of EASL for 2024 -2039 ………………………….. ………………………….. ……………. 5

Table – 9 Quality Requirements for Untreated Aggregate Base and Sub -bases ………………………… 6

Table – 10 Minimum Thickness of Asphalt C oncrete or Untreated Base ………………………….. …….. 6

Table – 11 Definition of Drainage Quality ………………………….. ………………………….. ………………… 10

Table – 12 Recommended m i Values ………………………….. ………………………….. ……………………….. 10

Table – 13 Suggested Levels of Reliability for Various Functional Classifications …………………. 11

Table – 14 AASHTO Recommended Minimum Thickness of Highway Layers ……………………… 12

LIST OF FIGURES

Figure 1: Flow Chart for Calculation of EASL ………………………….. ………………………….. ………….. 1

Figure 2: Flow Chart of Design Procedure for Aspha lt Institute Method ………………………….. …… 5

Figure 3: Design charts for HMA with 8 inches Untreated Aggregate Base ………………………….. .. 6

Figure 4: Determination of thickness of Asphalt layer for Planned Stage Construction ……………. 7

Figure 5: Flow Chart for AASHTO Empirical Method ………………………….. ………………………….. .. 8

Figure 6: Variation in Granular Subbase Layer Coefficient, a 3, with various Subbase Strength

Parameters ………………………….. ………………………….. ………………………….. ………………………….. ……. 9

Figure 7: Variation in Granular Base Layer Coefficient, a 2, with various Base Strength

Parameters. ………………………….. ………………………….. ………………………….. ………………………….. …… 9

Figure 8: Charts for Estimating Structural Layer Coefficient of Dense -Graded/Asphalt Concrete

Based on the Elastic (Resilient) Modulus ………………………….. ………………………….. ………………… 10

Figure 9: Determination of Structural Number from R, S O, W 18, M R and ?PSI …………………….. 11

1

1. INTRODUCTION

On a proposed highway, a flexible pavement is designed by using estimated traffic data from two

methods, i.e. Asphalt Institute Method (AI) and AASHTO Empirical Method . An estimated

traffic and growth rate s were provided.

2. OBJECTIVES

The objectives of this report are:

? Calculation of EASLs

? Design of Flexible Pavement by AI Method

? Design of Flexible Pavement by AASHTO Empirical Method

? Comparison of results obtained from AI and AASHTO methods.

3. CALCULATION OF EASL

For Calculation of EASLs the following formula is used;

Figure 1: Flow Chart for Calculation of EASL

Caculation of EASL

Average

Daily Traffic

ADT

% Truck

T

Truck Factor

TF

Growth

Factor

G

Design Period

Y

Directional

Distribution

Factor

D

Lane

Distribution

Factor

L 365? ? ? ? ? ? ? ? L D Y G TF T ADT ESAL

2

3.1. Average Annual Daily Traffic (A ADT)

Average annual daily traffic was given and provided in Table -1.

Table -1 Estimated Section Wise AADT (Year 2019)

3.2. % Truck (T)

Percentage of Trucks for each section is calculated and shown in Table -2

Table -2 Calculation of Percentage Truck (T)

Se ction Car Hiace Large

Buse s

2-Axle

Truck

3-Axle

Truck

4-Axle

Truck

>5-Axle

Truck

1 23,129 975 266 2,277 895 404 1,033

2 16,876 1,041 217 2,208 708 386 944

3 12,765 978 200 1,550 902 386 858

4 10,937 1,165 163 1,893 858 394 620

5 18,325 1,085 157 1,927 728 518 726

6 20,431 1,015 223 2,608 973 449 944

7 16,254 1,443 255 2,470 1,367 459 923

sum= 1481 14,933 6431 2996 6,048 Se ction Car Hiace Large

Buse s

2-Axle

Truck

3-Axle

Truck

4-Axle

Truck

>5-Axle

Truck

1 23,129 975 266 2,277 895 404 1,033

2 16,876 1,041 217 2,208 708 386 944

3 12,765 978 200 1,550 902 386 858

4 10,937 1,165 163 1,893 858 394 620

5 18,325 1,085 157 1,927 728 518 726

6 20,431 1,015 223 2,608 973 449 944

7 16,254 1,443 255 2,470 1,367 459 923

sum= 1481 14,933 6431 2996 6,048

Total Sum of passes = 31,889

% Truck = 4.644 46.828 20.167 9.395 18.966

3

3.3. Truck Factor (TF)

TF are determined from Table -3 NTRC , 1995.

Table – 3 Axle Load Study on National Highway, NTRC, 1995 and NHA

3.4. Growth Factor (GY)

The estimated growth rate s were provided and are mentioned in Table -4. Growth factors against

each vehicle typ e is calculated and shown as under.

Table – 4 Calculation of Growth Factor from Expected Growth Rates

Growth rates of first 10 design years will be used for calculating EASLs.

S. No Ve hicle Type Growth

Rate (1+r)^n Growth Factor

(1+r)^n-1/r

Growth

Rate (1+r)^n Growth Factor

(1+r)^n-1/r

1 Passenger Cars, Jeep/ 4WD 5 1.277 5.54 4.5 1.936 20.8

2 Hiace/Mini Bus 4 1.217 5.425 3.5 1.676 19.315

3 Large Buses 4 1.217 5.425 3.5 1.676 19.315

4 2 – Axle Rigid Truck 4.5 1.247 5.489 4 1.801 20.025

5 3 – Axle Rigid Truck 4.5 1.247 5.489 4 1.801 20.025

6 4 – Axle Articulated Truck 4.5 1.247 5.489 4 1.801 20.025

7 5 – Axle Articulated Truck 4.5 1.247 5.489 4 1.801 20.025

8 6 – Axle Articulated Truck 4.5 1.247 5.489 4 1.801 20.025

2019 – 2024 2024 – 2039

4

3.5. Directional Distribution Factor (D)

Assuming 3 lanes in each direction. The number of traffic l anes in two directions will be 6 and

directional distribution factor will be 0. 40. Table -5 provides directional distribution.

Table – 5 Percentage of Total truck Traffic in Design Lane

3.6. Lane Distribution Factor (L )

Assuming 3 lanes in each direction. The lane distribution factor will be 0. 6. Table -6 provides

Lane distribution factor against no. of lanes in each direction.

Table – 6 Lane Distribution Factor

3.7. Calculation of EASL

Following Tables 7, and 8 shows calculations of EASLs for 5 and 15 years of design life.

Table – 7 Calculation of EASL for 2019 -2024

Ve hicle Type AADT T

(%age ) TF GY D L EASL

Large Buse s 1481 4.644 0.939 5.425 0.4 0.6 30691.4

2-Axle Truck 14,933 46.828 4.67 5.489 0.4 0.6 1.6E+07

3-Axle Truck 6431 20.167 8.84 5.489 0.4 0.6 5512764

4-Axle Truck 2996 9.395 10.35 5.489 0.4 0.6 1400800

>5-Axle Truck 6,048 18.966 10.9 5.489 0.4 0.6 6011895

2.9E+07

5

Table – 8 Calculation of EASL for 2024 -2039

Design EASL s are 2.9 x 10 7.

4. PAVEMENT DESIGN

4.1. Pavement Design by Asphalt Institute Method

A flow chart of the design procedure for AI method is shown is Figure 2 as under

Figure 2: Flow Chart of Design Procedure for Asphalt Institute Method

4.1.1. Traffic Characteristics

Calculated EASLs = 29 x10 6

4.1.2. Subgrade engineering properties

Assuming CBR of Sub grade = 6

M r = 1500 x 6 = 9,0 00 psi

4.1.3. Subbase and base engineering properties

Certain requirements are needed for subbase and base materials , which are given in Table -14 .

AI Method

Traffic characteristics

EASL

Subgrade engineering

properties

Mr

Subbase and base

engineering

properties

Determine Min.

Thickness

Requirements

Feasibility of

Planning stage

construction Ve hicle Type AADT T

(%age ) TF GY D L EASL

Large Buse s 1481 4.644 0.939 19.315 0.4 0.6 109272.7

2-Axle Truck 14,933 46.828 4.67 20.025 0.4 0.6 57285695

3-Axle Truck 6431 20.167 8.84 20.025 0.4 0.6 20111696

4-Axle Truck 2996 9.395 10.35 20.025 0.4 0.6 5110408

>5-Axle Truck 6,048 18.966 10.9 20.025 0.4 0.6 21932627

1.05E+08

6

Table – 9 Quality Requirements for Untreated Aggregate Base and Sub -bases

4.1.4. Determine Min. Thickness Requirements

From Table -15, minimum thickness of Asphalt Concrete over untreated aggregate base is

determined its value is 5 inches which is satisfied .

Table – 10 Minimum Thickness of Asphalt Concrete or Untreated Base

4.1.5. Thickness of HMA layer

From Figure 3, the thickness of HMA with 8 inches untreated aggregate base is = 1 4 inches

Figure 3: Design charts for HMA with 8 inches Untreated Aggregate Base

Total thickness of pavement by AI method = 1 4 + 8 = 22 inches

7

4.1.6. Planned Stage Construction

Planned Stage Construction involves successive application of HMA layers according to a

predetermined time schedule. Assuming Damage ratio of 60%;

n1= 2.9×10 7 & D r = 0.6

N1 = n 1/D r = 2.9×10 7/ 0.6 = 4.8×10 7

From design Chart with N 1 & M r; h1=15.8 i n. (use 16 in.)

n2 = 1.05×10 7 & 1 -Dr = 0.40

N2 = n 2/ (1 -Dr) = 1.05×10 7 / 0.4 = 2.61×10 7

From design chart with N 2 & M r; h2 =1 4 in.

Overlay thickness h s = h 2 –h1 = 1 6 – 14 = 2.0 in.

Figure 4: Determination of thickness of Asphalt layer for Planned Stage Construction

8

4.2. Pavement Design by AASHTO Method

Figure 5: Flow Chart for AASHTO Empirical Method

4.2.1. Pavement Performance

Serviceabili ty Performance: Measured by PSI ( Present Serviceability Index ) with scale 0 to 5.

The PSI initial value that was measured at AASHTO test road about 4.2 for flexible pavement

while 2.5 is taken as terminal value.

Pi = 4.2 , Pt = 2.5

?PSI = 4. 2 – 2.5 = 1.7

4.2.2. Traffic

Calculated EASLs = 29 x10 6

4.2.3. Roadbed Soils (subgrade material)

During struc tural design, only M r values are used. The f ollowing conversion formula is used f or

CBR .

M r = 1500 x 6 = 9 ,000 psi

4.2.4. Materials of Construction

M r of AC at 68 oF = 450,000 psi

CBR value of base = 100, M r = 31 ,000 psi (25,000 psi – 75,000 psi )

CBR value of sub base = 22, M r = 13,500 psi (5,000 psi – 50,000 psi )

AASHTO Method

Pavement

performance

Serviceability

?PSI

Traffic

EASL

Roadbed soils

(subgrade

material)

Mr

Materials of

construction

a3, a2, a1

Drainage

mi

Reliability

ZR x S o

9

4.2.4.1. For Subbase, a 3

Figure 6: Variation in Granular Subbase Layer Coefficient, a 3, with various Subbase Strength Parameters

From Figure 6 , a3 = 0.1 (CBR = 22, sub base)

4.2.4.2. Base course, a 2

Figure 7: Variation in Granular Base Layer Coefficient, a 2, with various Base Strength Parameters .

From figure 7, a2 = 0.14 (CBR = 100, Base)

10

4.2.4.3. AC surface, a 1

Figure 8: Charts for Estimating Structural Layer Coefficient of Dense -Graded/Asphalt Concrete Based

on the Elastic (Resilient) Modulus

From figure 8, a1 = 0.44 ( Mr = 450 ,000 psi, AC )

4.2.5. Drainage

A week for water to be drain with in moisture level = 30%

Table – 11 Definition of Drainage Quality

From Table -11 the drainage quality is assumed as „Fair?.

Table – 12 Recommended m i Values

For “Fair” and 30% exposure, then mi is 0.80.

11

4.2.6. Reliability

Table – 13 Suggested Levels of Reliability for Various Functional Classifications

From Table -13, for urban highway interstate and other freeways have reliability of 80 -99%.

Reliability level (R ) = 99%

So for flexible pavement i s 0.4 -0.5. Taking S o = 0.4 9

4.2.7. Calculation of Thicknesses of layers

Figure 9: Determination of Structural Number from R, S O, W 18, M R and ?PSI

a1 = 0.44, a2 = 0.14 , a3 = 0.1

By using Figure 9, SN 3 = 7.3 (M r= 9 ,000 psi)

SN 2 = 6.2 (M r = 13 ,500 psi)

SN 1 = 4 .8 (M r = 31 ,000 psi)

12

a

SN 1*= a1 D1* =0.44 x 11 = 4.84

2

0. 4 x 0. x 4 . 2

0. x 0. x 4 . 2

Asphalt concrete surface = 11 ”

Granular base = 1 2.5 ”

Su b base = 1 7″

Total Thickness of Pavement = 40.5 ”

Table – 14 AASHTO Recommended Minimum Thickness of Highway Layers

13

5. COMPARISON

AI Method AASHTO Method

Structural Design

Total thickness of Pavement 22 inch 40.5 inch

Thickness of Asphalt Wearing course 14 inch 11 inch

Thickness of Aggregate Base course 8 inch 12.5 inch

Thickness of Subbase 17 inch

CBR and M r

Asphalt Concrete at 68 OF M r = 450,000 psi

Base Course Min CBR = 20 CBR = 100, M r = 31,000 psi

Subbase Min CBR = 80 CBR = 22, M r = 13,500 psi

Subgrade CBR = 6, M r = 9,000 psi CBR = 6, M r = 9,000 psi

Cost (depends on Asphalt layer)

Higher than other Lower than other

6. CONCLUSION

It is concluded that AASHTO Empirical method is more realistic than AI method, because it

comprises of variety of parameters for pavement designing.

7. REFRENCES

i. TRC tudy, “Axle Load tudies on ational Highways”, ational Transport Research

Centre, Government of Pakistan, 1995.

ii. Pavement Analysis and Design, Second Edition, Yang H . Huang, University of Kentucky .