‫بسم هللا 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,
E-mail: ga03ali@yahoo.com
2 Engineers,
Private Sector
Airports Arabia Conference
Mövenpick Hotel, Kingdom of
Bahrain.
5-6 May 2015
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
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
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
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.
To determine sensitivity of the
pavement design methods to the
design parameters.
Selection of optimal
method its cost estimate
design
Study and compare using
different paving materials and
Structural
and
Economic
evaluation for KNIA pavement
design Method
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)
The Current Study used 5 different
methods for each of the 2 pavement types,
Applying the following Procedures:
Flexible
AI (Analytical/ Nomograph)
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
Rigid
PCA
FAARFIELD
LEDFAA
COMFAA
ACN/PCN
FAA Method Suggested by Client and
Consultant
Requirements for Flexible
Pavement Design Methods
Method
Aircraft
Subgrade
Characteristics
(CBR)
Climate
Traffic
FAA
N/A
X1,2
X
X6
AI
X
X4
X
N/A
FAARFIELD
N/A
X3,5
X
X6,7
LEDFAA
N/A
X3,5
X
X6,7
COMFAA
N/A
X1,2
X
X6,7
ACN/PCN
N/A
N/A
X
N/A
1Forcasted
Traffic Mix
3Entire Traffic Mix
5Annual Growth
7Tire Pressure and Contact Area
2Design
Aircraft Concept
4Equivelent to DC-8
6Maximum Takeoff Weight
Requirements for Rigid
Pavement Design Methods
Design Method
FAA
PCA
FAARFIELD
LEDFAA
COMFAA
Climat Traffi
e
c
Aircraft
Concrete
Subgrade
Characterist characteristi
Strength (k)
ics
cs
N/A
N/A
N/A
N/A
N/A
X1,2
X4
X3,5
X3,5
X1,2
X
X
X
X
X
N/A
N/A
X
X6
X6,7
X6,7
X6,7
X6,7
N/A
X
X
X
X
X
N/A
ACN/PCN
1Forcasted
Traffic Mix
3 Entire Traffic Mix
traffic
5Annual Growth
7Tire Pressure and Contact Area
2Design
Aircraft Concept
4PresentOccasional or Frequent
6Maximum Takeoff
Weight
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 fulldepth 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 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 = 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 Considerations
The 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.
Conclusions – Flexible, Continued
Based on the results from a range of subgrade 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
insensitive to stabilized base.
being
When compared using stabilized base,
LEDFAA and FAARFIELD computer programs
showed negligible average difference.
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.
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.
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.
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.
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
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
Thank you;
Questions?