Evaluation of Flexible Pavement Deflections with Respect to Pavement Depths Using Software (A Case Study Jimma to Seka Road)

Tarekegn Kumela

doi:10.11648/j.ajce.20180605.11

Abstract

Road building in Ethiopia is increasingly in demand to meet medium and long terms development programs. Roads are constructed radiating from the capital city of the country in all direction. The objective of this research study is to evaluate the flexible pavement deflections with respect to pavement depth using Software along Jimma to Seka road segment and compare the laboratory results with the Ethiopian Road Authority (ERA) standards. Ever Stress Software (ESS) is a numerical analysis technique to obtain the deflection of pavement layers. The methodology of this research was finding the sensitivity of the road parameters (dimension, layers thickness, elastic modulus, Poisson’s ratio, loads and pressures) in reducing the major causes of failure in asphalt pavement fatigue cracking and rutting due to vertical surface deflections, the critical tensile strains at the bottom of the asphalt layer and the critical compressive strains on the top of subgrade. The analytical method used was the elastic modulus and Poisson’s ratio of the pavement materials as design parameters after CBR results of each layers was obtained. The expected outputs have shown that the displacement or deflection (uz) was as high as 0.38mm in the asphalt surface and gradually decreased as the pavement thickness increased. Large values of deflections indicates an over stressed condition which results in the pavement surface to crack and distortion as a results of fatigue or accumulated plastic deformation. Therefore, the relative deflection of pavement layer decreases as the pavement depth increases.

Highlights

Flexible pavements with asphalt concrete (AC) surface courses are used all around the world
The thickness of the flexible asphalt concrete (AC) layer, base and sub base course layers were taken as 50 mm, 200mm and 250 mm, respectively
The primary purpose of determining the deflection is to check the structural adequacy of the existing pavement as along the study area

Summary

Introduction

Flexible pavements with asphalt concrete (AC) surface courses are used all around the world. Asphalt concrete in the surface layer is a viscous material with its behavior depending on time and temperature. As the demand for applied wheel loads and number of load applications increases, it becomes very important to properly characterize the behavior of unbound granular material and subgrade soil layers as the foundations of the layered pavement structure. The major causes of failure in asphalt pavement are fatigue cracking caused by excessive vertical compressive and horizontal tensile strain at the top subgrade and bottom of asphalt layer due to repeated traffic loading and rutting deformation, caused by densification and shear deformation of sub grade. Excess vertical surface deflections in flexible pavements have always been major concern and used as a criterion of pavement design [1]

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Conclusion