The Major Causes of Flexible Pavement Deterioration and Propose Its Remedial Measures: A Case Study Bako to Gedo Road, Oromia Region, Ethiopia

Flexible pavement roads in Ethiopia often deteriorate in different ways, because of the harsh climatic conditions, lack of proper design and quality control, sudden increasing of traffic due to the construction of different industries, high loads and inadequate assessment for identifying causes of deteriorate before carrying out Maintenance and Rehabilitation. A possible remedial measures had been organized for every observed failure or deterioration to obtain normal pavement condition of the study area. An investigation was made by using laboratory and field test to determine the adequacy of the underlain material to serve as a subgrade, sub base course and base course for road construction based on project specifications and Ethiopian Road Authority (ERA) Specification. The investigation covered field tests to determine the in-situ condition of the road materials while laboratory tests on representative samples were extracted from site to determine the engineering properties of soil materials and to compare test results with the existing conditions of pavement layers. From the field tests and laboratory tests carried out, it is observed that the causes of flexible pavement deterioration of this road section are mainly due to the inadequacy of existing thickness of the base layer for the current traffic loading, overloading, engineering properties of the pavement layers material, poor method of construction, poor design quality and lack of side drainage. To reduce these causes, use boulder rocks at subbase course, reconstruction the base and providing proper drainage for the deteriorated sections must be required to reduce more damage of the flexible pavement the road section. Raveling, pumping, potholes, edge cracking and rutting are the most dominant type of deteriorations constituting more than 27% of the deterioration densities along Bako-Gedo road section.