Geotechnical Studies of the Sub-grade Material beneath Akure-Ijare Highway, Ondo State, Southwestern Nigeria

Abstract

In order to solve the incessant road failures along Akure-Ijare Highway in Ondo State Nigeria, geotechnical investigation was carried on the subgrade material to know its competence/load bearing capacity for the reconstruction of the road along the failed segments. The failed segments were extended at both ends into classified stable segments. The geotechnical investigation involved natural moisture content test, grain size analyses, specific gravity test, linear shrinkage test, Atterberg's Limits, Compaction test and California Bearing Ratio (CBR) determination. The natural moisture content of soils from the classified stable segments is 4.0 % while that of failed segments ranges from 3.0 % to 5.0 %. The percentage of fines, specific gravity, Liquid Limits, Plastic Limits, Plasticity index, Linear shrinkage and CBR of the soils taken from classified stable segments are 46 - 48.3 %, 2.67 - 2.68, 32 - 33 %, 22 - 23 %, 10 - 11 %, 2 - 12 %, 46 - 70 % respectively, while that of failed segments are 27 - 58%, 2.65 - 2.73, 22 - 54 %, 17 - 29 %,  5 - 25 %, 6 - 7 %, 26 - 57 % respectively. All the soil samples from both classified stable and the failed segments have high Maximum Dry Density at low Optimum Moisture Content. The significant overlap in the geotechnical properties of the soils in the classified stable segments and failed segments of the road suggests that the cause(s) of road pavement failure along the studied highway may be due to factors other than or complementary to geotechnical factors.