Abstract

In Ethiopia, the failure of roads is before the handover period. Most roads found in Ethiopia are flexible pavements. Nowadays, the failure of the surface of flexible pavement roads is common before the expected design period. For example, the Bako-Nekemte road/ has become a critical issue in our country. The most common parameters that cause stress, strain, and deflection of the roads are loads and pressures that come from vehicles. Moreover, the modulus of elasticity, Poisson’s ratio, and thickness of each layer need to be characterized. Further, the load magnitude, contact pressure (or load radius), and location are defined for each load (wheel) considered. The finite element method (FEM) is a numerical analysis technique to obtain the stress-strain and deflection of each pavement layer. The analytical method usually uses layers thickness, loads, elastic modulus, and Poisson’s ratio of the pavement materials as design parameters. The objective of this research was to study the sensitivity of the road parameters in analyzing the major causes of failure in asphalt pavement layers fatigue cracking and rutting deformation which came due to the critical tensile strains at the bottom of the asphalt layer and the critical compressive strains on the top of subgrade using the finite element method by relating the standard specification of ERA and laboratory test result. This thesis studied the analysis of stress-strain and deflection of flexible pavements using the Everstress finite element method. The Ever stress program will take into account any stress-dependent stiffness characteristics. This thesis dealt with ways to reduce deflections by varying the design configuration, such as increasing the HMA modulus, the base modulus, sub-base modulus, the subgrade modulus, and increasing the thickness of each layer. Based on the type of materials to use the value of elastic modulus and poison’s ratio are various in each layer, in layer 1 is varied from 1500 to 3500 MPa, in layer 2 is varied from 200 to 1000MPa, in layer 3 is varied from 100 to 250 MPa and in layer 4 is varied from 20MPa to 150MPa.

Abstract