EVALUATION OF SUB-GRADE INFLUENCE IN RIGID PAVEMENT: A CASE STUDY IN THE SECTION OF THE RING ROAD FROM KALITY TO HANA MARIAM

Most part of Ethiopia covered by black cotton soil. Roads that are constructed in such soils usually face failures; as their performance highly affected by the soil’s weak strength and moisture sensitivity. This research is inspiring to define the influence of such soils in a rigid pavement of a ring road section between Kality ring road to Hana Mariam, in Addis Ababa. The subgrade soil in the studied road section has seriously affected the pavement repeatedly and forced to make regular maintenance as well as design shift with different structural arrangements. Finally, Addis Ababa City Road Authority had changed the road pavement from flexible to rigid giving solution. However, the newly constructed rigid pavement faced different pavement distress such as; corner break, joint seal damage, cracking, lane-to-shoulder separation and improper drainage condition. The pavement distresses categorized as low to high level of severity, the corner break damage has low level of severity the extent varies between 3m to 4m in length and an average width between 10cm to 15cm. the joint seal damage has low level of severity in transverse expansion joint and construction joints. The cracking categorized as transverse, longitudinal and alligator cracking has medium and low level of severity. In defining the subgrade soil’s influence in to the rigid pavement, field mapping of the pavement distress conditions, characterizing the subgrade soil’s engineering properties through test pitting, soil sampling and laboratory testing were conducted. Accordingly, the laboratory test results of sieve analysis, CBR value, Atterberg Limits of subgrade soils and fill material samples shows that the material has poor quality to a make a reliable subgrade soil, according to AASHTO soil classification system and ERA manual. Thus, the rigid pavement distress is mainly associated the poor subgrade condition. Generally, this research discuss on significance maintenance option of rigid pavement, consider extensively different factors to analysis road distress, compare contribution of problem causes and required laboratory tests are included