Investigation of The Causes of Premature Pavement Failures and Its Alternative Treatments of Bedele-Metu Road Upgrading Project

Abstract

Transportation system is one of the most important factors affecting the national and public economy/development of any country. A premature road defect is a critical situation for road sector because of the high cost for construction of new roads and maintenance of existing roads and routes. One of these roads failed before serving the design period is the Bedele - Metu road upgrading project, Lot - II (50.659 km) trunk road with 20 years design life. However, premature pavement failures have been manifested since the year 2017. The objective of this study is to assess the Causes of the premature pavement failures and also propose its alternative treatments. Hence, a desk study, field visual inspection and in-depth field and laboratory investigations have been undertaken. The thesis comprises the tasks of visual pavement condition survey, dynamic cone penetrometer test, test pitting and pavement layer profiling, materials sampling and laboratory testing have been conducted. Moreover, the past traffic data was obtained and analyzed. Following to condition survey result, ideal locations of 4 in number for dynamic cone penetrometer, 1 from failed and other 1 as control sample with a total of 16 samples were identified for essential laboratory tests. Those of samples were transported to Ethiopian Road Authority, Own Force District of Jimma laboratory center for determination of laboratory test. The road condition survey indicates the existence of different types of distresses such as: potholes/patch failure, cracking, rutting, depression/failure, raveling/fretting and others. Field and laboratory investigation have been carried out and it shown that low air voids with void in mix result in a wearing course material <3%, such as 1%, that indicates the possible factor for occurrence premature pavement deformation. Also, insufficient surfacing layer thickness, such as 11.34 mm thickness difference would be the possible causes for the formation of surface deformation and workmanship problem of the asphalt concrete works along the joint of the separate lanes are also the observed potential causes for surface defects and cracking. Accordingly, proper treatment types were suggested that tend to be enhancing the design life of the pavement. In conclusion, the individual pavement layer thickness difference from the measured to design and also their cumulative effect could be the possible causes for occurrence of premature defects such as: surface deformations. Therefore, to avoid further road damages; traffic count, more detailed analysis of traffic volume and axle load survey should be made and also further comprehensive tests on the structural capacity of the pavement would be done. Based on the result of those analyses, right remedial measures should be made urgently