Abstract/Summary

This research work is premised on investigating the failing state of the Sango Ota- Owode expressway with design life of 20 years when it was first opened to traffic in 1974. It was reconstructed in 1993 through 2000 when it was fully opened to traffic again. However, it has become unserviceable with several deformations and deterioration all over the entire road. Eight soil samples were collected at the chosen failed sections and five soil samples at the good section for both sub-grade and sub-base, Twenty six samples all together. The soil samples were tested to determine the Atterberg limits, particle size distribution, compaction and California bearing ratio and the results were compared with the Federal Ministry of works and housing (1994) general specification. The Optimum Moisture Content (O.M.C) test result for the sub-grade and sub-base materials shows that none of the eight samples met the required criteria as their values were greater than the maximum of 7% specified. Only three samples of locations at Km 28+100 (o-s), Km 25+069 (o-s) and Km 24+000 (o-s) with values of 8%, 7% and 8% respectively, met the soaked CBR condition of at least 7%, while only two samples of locations at Km 28+100 (o-s) and Km 24+000 (o-s) with subgrade CBR values of 16% and 17%, met the unsoaked criterion. For the sub-base, only samples of location Km 25+069 (o-s) with value of 34% met the soaked CBR value of at least 30% while samples of locations at Km 28+100 (o-s) and Km 25+069 (o-s) with unsoaked CBR values of 80% and 82% respectively, which met the minimum 80% criterion for subbase. From the above undesirable results for the geotechnical investigation, reconstruction of the pavement is recommended.