INVESTIGATING CAUSES OF FLEXIBLE PAVEMENT FAILURE: A CASE STUDY OF THE BAKO TO NEKEMTE ROAD, OROMIA, ETHIOPIA

Most of the roads constructed in Ethiopia fail prematurely before serving design life due to various causes arising from many factors. One that failed reaching its lifetime is Bako Nekemte Trunk Road. This road was and opened traffic 2013. The pavement estimated at 20 years. However; failures have manifested since 2014 after it for traffic. main objective this research investigate cause failure flexible on segment. To achieve objective, study followed by experimental type purposive sampling method. Also, field observation condition survey methods data collection were used. asphalt, base course, subgrade, sub-base layer material sampled segment are used study. Different such as rutting, pothole, alligator cracking, raveling, edge depression, corrugation observed along section. For estimations index, divided into five different sections based distress densities, which measured during survey. From those sections, four selected determination Pavement Condition Index (PCI). Using systematic random 159 sample units evaluated Rating (PCR) result shows 1.89% excellent, 8.18% very good, 20.13% 31.45% fair, 18.87 % poor, 18.24% 1.26% failed. Based PCI value, samples taken surface (1), poor (2), none distressed area (1) comparison purposes. quality tests like Atterberg limit, wash gradation, soil classification, compaction test, California Bearing Ratio (CBR), Los Angeles Abrasion (LAA), Flakiness ( FI), Aggregate Crushing Value (ACV), Ten percent fines value (TFV), bitumen content, gradation asphalt carried out. results these compared with ERA specifications identify probable failure. found case was: insufficient absence side drainage structure, loading, course material, subgrade soil. also recommended urgently needed routine maintenance a treatment option reduce further deterioration extend service time.