Geotechnical investigation of some failed sections along Osogbo-awo road, Osun-State, Southwestern Nigeria.

Abstract

This study aimed at investigating the possible causes of the persistent road failure along Osogbo – Awo road of Osun State, Southwestern Nigeria. Following a geological mapping of the study area, soil samples were collected from different locations where the road had failed severely. The samples were subjected to geotechnical analyses such as particle size analysis, natural moisture content, specific gravity, Atterberg limits, compaction and California Bearing Ratio (CBR). Results of the geological mapping revealed that the road pavement is underlain by schist with pegmatite intrusion, whose minerals have weathered into expansive clay. Laboratory analyses revealed that the soils around these area are wet, with most of them having natural moisture content of above 15%, fine content ranging from 11.2 to 86.4%, liquid limit of 32.37 to 75.0%, plastic limit of 22.71 to 56.00%, plasticity index of 9.63 to 31.13% and linear shrinkage of 1.43 – 27.86%. The soils fall within the A-2-7 to A-7-5 of the AASHTO classification scheme. The specific gravity of 2.20-2.73 showed a lower degree of laterization. The Maximum Dry Density, (MDD) ranged from 1.32– 2.15 Mg/m³ while Optimum Moisture Content, (OMC) ranged from 13.01 - 27.98%, The California Bearing Ratio, (CBR) ranged from 6.10 to 8.21 for soaked and 8.93 – 18.05 for unsoaked samples. The study concluded that the clayey nature of the road pavement subgrade and the poor geotechnical properties of the soils which were generally below the specifications of the Federal Ministry of Works and Housing could largely be responsible for the persistent road failures.

 Keywords: Geotechnical Analyses, Road Failure, Osogbo-Awo Road