Karayolu üstyapısında güvenilirlik analizi için Monte Carlo simülasyon yöntemi kullanılarak mekanistik-ampirik tasarım yöntemlerinin karşılaştırılması
Comparison of mechanistic-empirical design methods using the Monte Carlo simulation method for reliability analysis in highway pavement
Yazar: BARIŞ ÇAKMAK
Danışman: DOÇ. DR. MURAT ERGÜN
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / İnşaat Mühendisliği Ana Bilim Dalı / Ulaştırma Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Mühendislik Bilimleri = Engineering Sciences ; Ulaşım = Transportation ; İnşaat Mühendisliği = Civil Engineering

Özet:
Karayolu üstyapısı, yol güzergahındaki iklim koşulları, malzeme türleri ve ekonomik 
koşullara bağlı olarak rijit ve esnek kaplamalar olmak üzere iki tipte inşa edilmektedir. 
Esnek üstyapılar; bitümlü yüzey tabakası, temel tabakası ve alttemel tabakalarından 
oluşmaktadır. 
Esnek üstyapı tasarımı; üstyapı tabaka kalınlıklarının hesaplanması ve tabakaları 
oluşturan agrega ve bitüm gibi malzeme özelliklerinin belirlenmesini içermektedir. 
Tasarımı etkileyen en önemli faktör yola etkiyen trafik yükleridir. Üstyapı tasarımında 
genel olarak analitik yöntemler, ampirik yöntemler ve mekanistik-ampirik (M-A) 
yöntemler kullanılmaktadır.
Ülkemizde esnek üstyapı tasarımı, Karayolları Genel Müdürlüğünün yayımladığı, 
AASHTO 93 tasarım yöntemi esas alınarak hazırlanan Esnek Üstyapılar 
Projelendirme Rehberi ile yapılmaktadır. AASHTO 93 üstyapı tasarım yöntemi 
ampirik bir yöntemdir. Son yıllarda hem analitik hem de ampirik yaklaşıma uyum 
sağlayabilen mekanistik-ampirik tasarım yöntemleri birçok ülkede kullanılmaktadır.
Üstyapı tasarımı açısından güvenilirlik, kaplamanın hizmet ömrü boyunca maruz 
kalacağı trafik yükü ve çevresel koşullar altında yeterli performans gösterme 
olasılığıdır. Güvenilirlik analizi için bir simülasyon metodu olan Monte Carlo yöntemi 
kullanılmıştır. Bu yöntemde tasarım parametreleri; dağılım türü, ortalama ve standart 
sapma değerleri kullanılarak simüle edilmektedir. Parametrelerin istenen olasılık 
dağılımı rastgele sayı üretimi yoluyla yapay olarak elde edilmektedir. Tasarım 
parametreleri kullanılarak oluşturulan kesitlerin mekanik tepkileri KENLAYER 
yazılımı ile belirlenmiştir. Mekanik tepkileri yol ömürlerine dönüştürmek için ampirik 
transfer denklemleri kullanılmıştır. Hesaplanan yol ömürleri ve yola etkiyen trafik 
yükleri ile kesitlerin güvenilirlik değerleri bulunmuştur.
Bu tez çalışmasının amacı Esnek Üstyapılar Projelendirme Rehberi'nde önerilen 
üstyapı tabaka kalınlıkları ve üstyapı tasarım parametrelerinin Monte Carlo 
simülasyon yöntemi ile simüle edilerek mekanistik-ampirik tasarım yöntemleri 
açısından güvenilirliğinin araştırılması ve karşılaştırılmasının yapılmasıdır. 
Bu tez altı ana bölümden oluşmaktadır.
Birinci bölümde, ulaşım, ulaştırma ve karayolu üstyapısı ile ilgili genel bilgiler 
verilmiş ve tezin amacı açıklanmıştır.
İkinci bölümde, karayolu esnek üstyapısı ve üstyapıyı oluşturan tabakalar hakkında 
ayrıntılı bilgiler verilmiştir. Esnek üstyapı tasarım yöntemleri; analitik, ampirik ve 
mekanistik-ampirik olmak üzere üç başlık altında toplanmıştır.
Üçüncü bölümde, Monte Carlo simülasyon yöntemi kullanılarak yapılan güvenilirlik 
analizinin esnek üstyapı tasarımına uyarlanması açıklanmıştır.
Dördüncü bölümde, tasarım parametrelerinin seçimi anlatılmış ve güvenilirlik analizi 
sürecinin adımları sıralanmıştır.
Beşinci bölümde, yapılan analizler sonucunda elde edilen sonuçlar; grafikler, 
çizelgeler ve şekiller yardımıyla gösterilmiştir. M-A yöntemlerin benzerlikleri ve 
farklılıkları ortaya koyulmuştur.
Altıncı bölümde, sonuçlar irdelenmiştir. AASHTO 93 ile uyum sağlayan M-A 
yöntemler açıklanmış ve öneriler sunulmuştur.

Abstract:
Highway pavements are constructed in two types, rigid and flexible pavements, 
depending on the climatic conditions, material types, and economic conditions on the 
road. In Turkey, flexible pavements are more commonly used than rigid and composite 
pavements.
Flexible pavements consist of a bituminous surface layer, base and sub-base layers 
built on the subgrade. Bituminous layers are the top layers of the pavement that are 
directly exposed to traffic loads. While bituminous layers exhibit viscoelastic 
properties, base and subbase layers are composed of granular materials.
Flexible pavement design is defined as the calculation of the required pavement layer 
thicknesses so that the pavement can serve safely without being exposed to large 
deformations under traffic loads and environmental conditions throughout its design 
life. The most important factor affecting the design is the traffic loads on the road. In 
the design of flexible pavements, analytical methods, empirical methods, and 
mechanistic-empirical methods are commonly utilized.
Analytical methods enable the calculation of layer thicknesses using theoretical 
analysis programs. The Shell flexible pavement design method is the most widely 
recognized analytical method.
Empirical methods, which are conventional design methods, rely on the results of 
experiments and are dependent on the conditions under which the experiments are 
conducted. Over the years, widely utilized empirical design methods include 
California Transport Rate, Rode Note 29, and AASHTO.
The AASHTO 93 method, a regression-based empirical approach for designing 
flexible pavement, is used in Turkey. The Highways Flexible Pavement Design Guide 
prepared by the Turkey General Directorate of Highways presents Tables 12.1, 12.2, 
and 12.3 for specifying flexible pavement thicknesses based on specific reliability 
values and traffic loads throughout the pavement's service life.
Mechanistic-empirical methods combine situations that cannot be modeled with 
analytical methods with empirical correlations and performance observations. 
Mechanistic-empirical methods offer both an analytical and empirical approach to 
design. The mechanical aspect of mechanistic-empirical design methods involves 
calculating the mechanical responses (stress, strain, and displacement) that may occur 
in the pavement based on traffic loads, material properties, and environmental 
conditions. The empirical part of the method is to convert response values into service 
life by using empirical transfer equations obtained from road tests and laboratory 
experiments. Asphalt Institute (AI), Shell, US Army Corps of Engineers (USACE), 
Belgian Road Research Center (BRRC), Transport and Road Research Laboratory (TRRL), Federal Highway Administration (FHWA), Illinois Department of 
Transportation (ILLINOIS), Austin Research Engineers (ARE) and MechanisticEmpirical Pavement Design Guide (MEPDG) are the mechanistic-empirical methods.
The reliability of a designed pavement is the possibility of showing adequate 
performance during its service life under the traffic load and environmental conditions. 
Reliability in terms of pavement design is expressed as the probability that the number 
of standard axle load wheels allowed is greater than the number of standard axle load 
wheels applied. There are three basic reliability analysis methods: First Order Second 
Moment (FOSM) Methods, Point Estimation Methods, and Simulation Methods. 
Simulation methods include Monte Carlo simulation. The Monte Carlo simulation 
method is used to reveal the relationships between certain parameters and variables. 
In this method, a given model is simulated many times by generating random numbers. 
It allows the comparison of design methods by generating random data sets with 
known distribution properties and design parameters.
The aim of this study is to investigate and compare the reliability of the proposed 
pavement layer thicknesses and pavement design parameters in terms of mechanisticempirical design methods by simulating them with the Monte Carlo simulation 
method. The design parameters to be used in mechanistic-empiricial methods are 
selected as layer thicknesses, elasticity modulus, poisson's ratios, and tire contact 
pressure. 
In this thesis study, a traditional pavement section consisting of a bituminous hot 
mixture surface layer, base, and sub-base layers was selected. KENPAVE software 
was used to determine the mechanical responses of the design section under load in 
mechanistic-empiricial design methods. KENPAVE is software used for the analysis 
and design of both rigid and flexible pavements. It has two parts: KENSLAB and 
KENLAYER. The KENSLAB section is used for the design of rigid pavements, while 
the KENLAYER section is used for the design of flexible pavements. KENLAYER is 
used to find values such as displacement and strain of linear elastic, non-linear elastic, 
and viscoelastic defined layers under various axle loads.
In the reliability analysis, firstly, different variations of the parameters, whose mean 
and standard deviations were determined, were calculated using the Monte Carlo 
simulation method per the probability distributions. The mechanical responses of the 
sections created using these parameters were determined with the KENLAYER 
software. Transfer equations were used to transform mechanical responses into road 
life values. Reliability values of the sections were found using the calculated road lives 
and traffic values. Reliability analysis was conducted based on the safety margin (S). 
The safety margin is calculated as the difference between the number of allowed 
standard axle repetitions (N) and the number of applied standard axle load repetitions 
(n). While "N" values are the road lives found by mechanistic-empiricial design 
methods, "n" values are the T8.2 standard axle load. In the reliability coefficient adapted 
to the normal distribution, values below 0 indicate the possibility of deterioration, and 
values above 0 indicate the safe area.
The thesis consists of six main chapters.
The first chapter is the introduction. In this chapter, general information about 
transportation, and highway pavement is given and the aim of the thesis is explained.
In the second chapter, detailed information about highway flexible pavement and its 
constituent layers is given. Flexible pavement layers are explained with figures. 
Flexible pavement design methods are categorized under three headings: analytical, 
empirical, and mechanistic-empirical. The steps used in pavement design methods are 
explained with formulas.
In the third chapter, the concepts of reliability and reliability analysis are explained. 
The methods used in reliability analysis are listed. The method of adapting the 
reliability analysis using the Monte Carlo simulation method to pavement design is 
given.
In the fourth chapter, the steps of the design parameters selection and reliability 
analysis process are explained. 
In the fifth chapter, the results of the analysis are presented with graphs, charts, and 
figures. The similarities and differences of the mechanistic-empirical methods are 
presented.
In the sixth chapter, the results are discussed. Mechanistic-empirical methods 
complying with AASHTO 93 are explained and recommendations are presented. 
Reliability and compatibility comparison of the AASHTO 93 method, which is used 
for flexible pavement design in the Highways Flexible Pavement Design Guide 
prepared by the Turkey General Directorate of Highways, with the mechanisticempirical design methods was carried out. 8 fatigue and 5 rutting based mechanisticempirical methods were analyzed. According to the results obtained from this thesis, 
the following evaluations were made:
It is seen that the rutting dependent reliability of the design sections is higher than the 
fatigue dependent reliability. It is concluded that the AASHTO 93 pavement design 
method used in our country produces sections that are more resistant to rutting failure 
type. It was observed that the rutting reliability was more consistent with the Shell and 
USACE methods.
It is seen that the Shell mechanistic-empirical design method achieves good 
compatibility levels in both fatigue and rutting failure analyses. It is seen that ARE 
method is more reliable for fatigue failure and USACE method is more reliable for 
rutting failure.
Compliance tables that can determine the level of reliability of a section in 
mechanistic-empirical design methods according to different load, climate and soil 
conditions are thought to provide great convenience to designers.
In future studies, the sensitivity of design parameters to affect the reliability of 
mechanistic-empirical design methods can be measured for both types of failure. By 
determining the parameter that is more sensitive to variability, the relevant design 
section can be strengthened or if the section is too strong, the pavement thickness can 
be reduced to be economical.