ANALYSIS OF SOIL SUBGRADE STRENGTH PARAMETERS FOR FLEXIBLE PAVEMENT DESIGN CASE STUDY: FROM ARBAMINCH GAMO ROUNDABOUT TO NECH SAR CAMPUS ROADWAY

Abstract

In determining a cost-effective solution for the provision of low-volume roads, it would be important to determine the nature and strength of the subgrade soil. The problem of this research is how to build roadways that are less susceptible to potholes. Besides, what is the relationship between the strength of subgrade soil and road defects? This research aimed to evaluate soil subgrade strength parameters for flexible pavement design for the roadway of Arbaminch Gamo Roundabout to Nech Sar Campus. The methodology contained visual inspection, sampling of the soil, and measuring potholes at a field. Generally, there were 12 samples collected from the study area and laboratory tests were performed at Arbaminch University Geotechnical Laboratory. The tests carried out include CBR, soil classification, particle size distribution, moisture content determination, specific gravity, Atterberg’s limit, and compaction tests. The result indicated that the specific gravity of the samples lies between 2.61-2.85. Based on USCS, most of the road's soil has fine-grained soils with much silt content. The CBR value of some samples based on the laboratory test results showed poor subgrade strength. From a technical and economic perspective, it would be inappropriate to lay pavement layers on soils with poor bearing capacity. A mathematical model was developed to show the relationships between the subgrade strength, road failures, and selected soil parameters. Improved relation was obtained when multiple linear regressions Analysis (MLRA) were used by regression between the CBR with MDD and OMC. Hence, it is concluded that there was a strong relationship between the CBR with MDD and OMC