Evaluation of Flexible Pavement Performance under Traffic Load Using MechanisticEmpirical Design Approach.

Abstract

The development of countries all over the world is dependent to a large extent on the quality of its road transportation system. Particularly, in Ethiopia road is extensively used infrastructure for access to rural and urban areas. Because of this, a huge amount of money is being invested in road sector development. However, conditions of some roads are largely deteriorated and in poor condition. Empirical design method, which is used in Ethiopia now days, could not provide immediate evaluation of the ever increasing traffic in volume, load magnitude and axle configuration. It has been proposed that mechanistic design method offers this advantage over empirical one. However, it is a realization that Ethiopia is left behind to use Mechanistic-Empirical design approach. Therefore, it is obvious from the above that the need of this approach, despite its problems, is unquestionable. The aim of this research was to evaluate flexible pavement performance under traffic load and development of a new framework for flexible pavement design with Mechanistic-Empirical Method. To access the effects of physical factors such as vehicular load, material properties and environment on pavement responses, phenomena such as stress, strain and deflection, and performance was one of the aims of the paper. At the meantime ERA design method was reviewed. A pavement structure designed using ERA manual is analyzed and evaluated using Mechanistic-Empirical approach. In this study KENLAYER, a Mechanistic-Empirical flexible pavement ML program has been used and ABAQUS, a 3D FEM program, has also used for load configurations that could not be modeled in KENLAYER. In this research, an effort was made to review various research results and use them in the structural design method development to flexible pavement design which is mechanistic Empirical. Austroads criteria and shell 95% distress models have been used in this research for fatigue cracking and rutting respectively. According to the analysis, Allowable repetition of standard axle loads for rutting increases by 113% over the range of 1500-3500mpa AC modulus. However, allowable repetition of standard axle loads for fatigue cracking increases only by 64% over the same range of AC modulus. Only 12.69 % increase in allowable repetition of ESA for poisson’s ratio in a range of 0.15-0.4 recorded. According to this research, among all catalogue structures analyzed here, 54% performs below the design ESA of which 80% are due to fatigue cracking. This implies that Allowable Load Repetitions and in turn performance period predicted by KENLAYER is less from the number of standard design Load Repetitions expected by the ERA method. Therefore, it is necessary for Ethiopia to adapt mechanistic empirical design approach. Accordingly, an effort has been made to develop a new framework for design of flexible pavements. Finally, A new flexible pavement design tool was developed which is mechanistic Empirical based. The basis of the method is the KENLAYER computer program for the linear elastic stress analysis of the structure. The developed method treats the pavement structure as system of pavement layers and designing it accordingly