Comparative Analysis Of Airport Pavement Design Methods: Case Study

for Khartoum New International Airport

Prof Galal Ali – PhD, 1, Abdalla Khairy2, Tarig Mohamed2 and Ashraf Ahmed2

1Professor and Consultant Engineer, Sudan University of Science & Technology,

E-mail: ga03ali@yahoo.com

2 Engineers, Private Sector

الله بسمالرحيم الرحمن

Airports Arabia Conference Mövenpick Hotel, Kingdom of

Bahrain.5-6 May 2015

Super pave Mix DesignAsphalt-Rubber in Hot Mix Design Mechanistic-Empirical Design Guide for

both Rigid and Flexible PavementsRecycling of both Pavement Types Accelerated Loading Facilities to

predict performance

Recent Advances in Pavement Industry and Technology

BACKGROUND

• Traffic Loading• Equivalent Single Axle Load, ESAL• Axle Load Distribution, ALD

Pavement Design Governing Factors:

• Soil Sub-grade Strength California Bearing Ratio, CBR Resilient Modulus, MR

Modulus of Subgrade Reaction, k

Search for applicability, adoption and use of latest mechanistic asphalt and concrete airport pavement design methods, particularly in developing countries including the rich developing Gulf States.

Required: improvements in terms of reduced life-cycle cost, shorter construction period, less disruption to residents and business, as well as safe and manageable field activities.

Pavement poor performance with premature failure in many cases, specially flexible pavements, a major concern with frequent and extensive occurrence making them unmanageable.

Doubts and misinterpretation regarding their economics under various conditions when selecting a pavement type, particularly those countries predominantly use flexible pavements.

Premature Failure

Such preference mainly relies on cost factor

Two most crucial parameters that govern design of asphalt and Concrete Airport pavements are design traffic (million ESAL.) and soil subgrade strength in terms of CBR, Resilient modulus, MR and modulus of subgrade reaction, k

To apply procedures to conditions and data of Khartoum New International Airport for cost computations.

Overview of popular flexible and rigid airport pavement design methods in a relative comparative manner.

OBJECTIVES:

To determine sensitivity of the pavement design methods to the design parameters.

Selection of optimal design method its cost estimate

Study and compare using different paving materials and

Structural and Economic evaluation for KNIA pavement design Method

Population 8 X 106;

Current international airport & domestic one

The most Common pavement type and design method: flexible pavement designed by FAA semi-empirical method using CBR for soil subgrade strength, and the number of flight traffic operations

KNIA Site Visit with Client (next slide)

DATA AND STATISTICS

Khartoum state in Sudan:

The Current Study used 5 different methods for each of the 2 pavement types,

Flexible Rigid

PCAFAARFIELDLEDFAACOMFAAACN/PCN

AI (Analytical/ Nomograph)

FAARFIELDLEDFAACOMFAAACN/PCN

Applying the following Procedures:

FAA Method Suggested by Client and Consultant

1Forcasted Traffic Mix 2Design Aircraft Concept 3Entire Traffic Mix 4Equivelent to DC-85Annual Growth 6Maximum Takeoff Weight7Tire Pressure and Contact Area

Requirements for Flexible Pavement Design Methods

Aircraft Characteristics

Subgrade (CBR)

Traffic Climate Method

X6 X X1,2 N/A FAAN/A X X4 X AIX6,7

X X3,5 N/A FAARFIELDX6,7

X X3,5 N/A LEDFAAX6,7

X X1,2 N/A COMFAAN/A X N/A N/A ACN/PCN

Requirements for Rigid Pavement Design Methods

Concrete characteristi

cs

Aircraft Characteristi

cs

Subgrade Strength (k)

Traffic

Climate

Design Method

X X6 X X1,2 N/A FAAX X6,7 X X4 N/A PCAX X6,7 X X3,5 N/A FAARFIELDX X6,7 X X3,5 N/A LEDFAAX X6,7 X X1,2 N/A COMFAA

N/A N/A

X N/A N/A

ACN/PCN

1Forcasted Traffic Mix 2Design Aircraft Concept 3 Entire Traffic Mix 4PresentOccasional or Frequent traffic5Annual Growth 6Maximum Takeoff Weight7Tire Pressure and Contact Area

Air Traffic Forecast

KNIA Historical aircraft movement Data

•Forecasted aircraft movement using time series method

KNIA Projected Flight Operations

KNIA Traffic Forecast Analysis (KTFA)The results of forecasting show annual increase for aircraft operations by 2031 to reach 48.827 and 184,973 for international & domestic, respectively. . 1

KTFA-Continued

To reach the movement of aircraft to the limit we need the proportion of annual increase for the movement of internal and external proportion of the increase expected it to serve that number of foreign trips is 3.5% for the Movement in 2011, the proportion of increase of the movement are up to 8.5% of the movement in 201

KNIA Design Traffic Mix

Determination of Mean Annual Air Temperature (MAAT)

Temperature has great influence on the stress-strain characteristics of full-depth asphalt pavement and surface layer; thicknesses are increased as the average annual air temperature gets warmer. The table below shows the Mean Monthly Average Temperatures From Table below MAAT = 37 C

Soil Investigation: CBR DeterminationThe area has rocky land characterized by high consistently and twice the capacity. All tests conducted by KNIA Unity Engineers indicated that the ground possed good natural resistance where they determined design CBR to be equal to 10 % suitable for use in the structural design of the Airport pavement.

modulus of sub-grade (k):The k value was found using the equation above. With CBR =10, then k = 141.3 pci

Summary of Airport Pavement Design

Using the required traffic data, conducting analysis of the design variables for KNIA and applying the various design methods resulted in a range of designs providing entirely different thicknesses. The design values are compared with the value suggested for KNIA . Summary:KNIA Structural Flexible Pavement Design :

Summary: KNIA Structural Rigid Pavement Design

The results for flexible and rigid structural pavement designs show that FAA used for KNIA uneconomic over design compared with any of the methods adopted here. The difference was more pronounced for flexible pavement. Further study was undertaken to select the optimum method for each of flexible and rigid pavement

Comparison between the Design Methods:

Flexible Pavement:

1- Effect of Subgrade Strength:

2- Comparing by Stabilized Base

3- Comparing Effect of Aircraft Departures on Thickness

By FAA

By AI

By COMFAA

By FAARFIELD

By LEDFAA

Comparing Rigid Pavement Design Methods 1- Comparing by Modulus of Sub-Grade

Reaction

2- Comparing By Stabilized Base

3- Comparing Effect of Aircraft Departures on Thickness

By PCA

By FAA

By COMFAA

By LEDFAA

By FAARFIELD

Optimal Design Method (ODM)

The study and analysis of 858 design results showed that the FAARFIELD is the best option available to design thus far with coefficient of determination not less than 0.995, It also followed a new methodology in the design (CDF) by using entire traffic mix for the design, It also can give the design life accurately for forecasted traffic mix, it also can give full depth design, As the results show it has the high sensitivity of the various paving materials and With all of this it give economically design.

Cost ConsiderationsThe Table and Fgure below show the cost of flexible and rigid pavements using the ODM (FAARFIELD)

flexible rigid

Conclusions - Flexible Regarding pavement thickness design for

KNIA case study, FAARFILED computer program was found to be the best option for airport pavement Structural design.

The FAA design method does not yield reliable results for low subgrade strength, while becomes uneconomical design at higher subgrade strength .

The structural design of airport pavements by LEDFAA & FAARFIELD computer program provide the most acceptable results.

Based on the results from a range of sub-grade strength values, the Asphalt Institute (AI) method gives lower thickness than other methods while not including most of new generation aircraft, as well as not accounting for the Stabilized-base option.

COMFAA program exhibited being insensitive to stabilized base.

When compared using stabilized base, LEDFAA and FAARFIELD computer programs showed negligible average difference.

Conclusions – Flexible, Continued

Conclusions - RigidFAA method was found to be insensitive to

stabilized-base material providing same slab thickness. On the other hand, LEDFAA and FAARFIELD showed high sensitivity to varying base material.

FAA method resulted in average thickness difference ranging between 9 and 3 inches compared with PCA, LEDFAA, COMFAA and FAARFIELD, respectively confirming the method is relatively not effective.

The PCA method gives design for the surface layer only, while base and subbase thicknesses are assumed.

For KNIA pavement thickness design, the same first conclusion for Flexible pavement applies, that is FAARFILED is the best option

The PCA method showed a differing trend, giving larger thicknesses than FAA values for medium and high subgrade strength, and small thicknesses than FAA method for low strength.

Conclusions – Rigid, Continued

The pavement structure appeared to be more sensitive to departure levels than any other parameter.

Results showed that FAARFIELD computer program give accurate results with coefficient of determination not less than 0.995.

Conclusions Rigid, Continued

RecommendationsModern technology advances need to be adopted

in order to keep design development up-to-date. Conduct specialized research to develop new

design variables to improve design methods. Introduce new forecasting techniques for aircraft

traffic growth rates. Adhere to using entire traffic mix for airfield

design rather than relying on design aircraft.Replace semi-empirical design charts, typical of

FAA method, by mechanistic design procedures.Using stabilized base instead of crushed aggregate

is preferred for airports weighing weight more than 100 kips to.

Recommendations Continued

FAAFAIELD design method is Recommend for adoption by Sudan Civil Aviation

Due to lack of experience and qualified staff, it is recommended to establish research institutes specialized in airport engineering.

As was justified technically & economically in earlier studies on highway pavements, use of rigid pavement should be encouraged.

The AI method is stressful mathematically in the design where it can be dispensed with FAARFIELD for full depth design

Eng Muram Mohamed, Lecturer at University of Science and Technology;

Eng Mohamed H Ismael

Project Implementation Unit, Air Traffic Control and Aviation Security Departments of Khartoum New International Airport

Acknowledgements

Thank you;Questions?