1. E-mail: ga03ali@yahoo.com
بسم الله الرحمن الرحيم
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,
2 Engineers, Private Sector
Airports Arabia Conference Mövenpick Hotel, Kingdom of Bahrain. 5-6 May 2015

2. Recent Advances in Pavement Industry and Technology
Super pave Mix Design
Asphalt-Rubber in Hot Mix Design
Mechanistic-Empirical Design Guide for both Rigid and Flexible Pavements
Recycling of both Pavement Types
Accelerated Loading Facilities to predict performance

3. BACKGROUND Pavement Design Governing Factors: Soil Sub-grade Strength
California Bearing Ratio, CBR
Resilient Modulus, MR
Modulus of Subgrade Reaction, k
Traffic Loading
Equivalent Single Axle Load, ESAL
Axle Load Distribution, ALD

4. 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.

5. 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.

6. Premature Failure
Obeid Khatim Road after afew Months of Construction. South-Bound 2 Outer Lanes have already been Rehabilitated

7. 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

8. OBJECTIVES:
Overview of popular flexible and rigid airport pavement design methods in a relative comparative manner.
To apply procedures to conditions and data of Khartoum New International Airport for cost computations.

9. 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

10. DATA AND STATISTICS Khartoum state in Sudan: 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)

13. Applying the following Procedures:
The Current Study used 5 different methods for each of the 2 pavement types,
Applying the following Procedures:
Flexible
Rigid
AI (Analytical/ Nomograph)
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
PCA
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
FAA Method Suggested by Client and Consultant

14. Requirements for Flexible Pavement Design Methods
Aircraft Characteristics
Subgrade (CBR)
Traffic
Climate
Method X6 X
X1,2
N/A
FAA X4 AI
X6,7
X3,5
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
1Forcasted Traffic Mix Design Aircraft Concept
3Entire Traffic Mix Equivelent to DC-8
5Annual Growth Maximum Takeoff Weight
7Tire Pressure and Contact Area

15. Requirements for Rigid Pavement Design Methods
Concrete characteristics
Aircraft Characteristics
Subgrade Strength (k)
Traffic
Climate
Design Method X X6
X1,2
N/A
FAA
X6,7 X4
PCA
X3,5
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
1Forcasted Traffic Mix Design Aircraft Concept
3 Entire Traffic Mix PresentOccasional or Frequent traffic
5Annual Growth Maximum Takeoff Weight
7Tire Pressure and Contact Area

16. Air Traffic Forecast
KNIA Historical aircraft movement Data

17. Forecasted aircraft movement using time series method

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

19. 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

20. KNIA Design Traffic Mix

21. 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

22. Soil Investigation: CBR Determination
The 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 = pci

23. 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 :

24. 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

25. Comparison between the Design Methods:
Flexible Pavement:
1- Effect of Subgrade Strength:

26. 2- Comparing by Stabilized Base

27. 3- Comparing Effect of Aircraft Departures on Thickness
By FAA
By AI

28. By COMFAA
By FAARFIELD

29. By LEDFAA

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

31. 2- Comparing By Stabilized Base

32. 3- Comparing Effect of Aircraft Departures on Thickness
By PCA
By FAA

33. By COMFAA
By LEDFAA

34. By FAARFIELD

35. 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.

36. Cost Considerations
The Table and Fgure below show the cost of flexible and rigid pavements using the ODM (FAARFIELD)
flexible
rigid

38. 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.

39. Conclusions – Flexible, Continued
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.

40. Conclusions - Rigid
FAA 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.

41. Conclusions – Rigid, Continued
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.

42. 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

43. Recommendations
Modern 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.

44. 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

45. Acknowledgements
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

46. Thank you;
Questions?