GEOTECHNICAL INVESTIGATION OF SUBGRADE SECTION OF FAILED HIGHWAY IN PARTS OF AKURE AND OKITIPUPA, SOUTHWESTERN NIGERIA

ABSTRACT

Pavement failure has constituted the major problem in Nigeria highways especially on Akure-Ado, Akure-Owo and Ore- Okitipupa highways in parts of Akure and Okitipupa, South Western Nigeria. Extensive field and laboratory investigations revealed that the pavement failure is a function of poor geotechnical behavior of the underlying soils. Tests carried out on the disturbed samples collected from the failed sections of the roads show that the mea values of soils’ natural moisture =17.49%, liquid limit =39.18%, plastic limit =10.42%, linear shrinkage=8.29% and the specific gravity=2.62. Mean values of the particle size analysis show that gravel fraction=4.82%, sand fraction =49.45% and the fine fraction=44.78%. D₁₀, D₃₀ and D₆₀ range from 0.0029 to 0.0095, 0.0028 to 0.28 and 0.028 to 0.89 respectively. The mean dry density is 1.68kg/m3 while the mean optimum moisture content is 17.13%. California Bearing Ratio (CBR) value mean for the unsoaked sample is 56.8% while that of the soaked sample is 21.68%. Particle size analysis shows that the presence of excess fines value of 44.78% in the pavement construction materials across the study areas, contributed to the failure of the highway pavements; the soils classified as SC, CL and CH. The low CBR value is also a noted cause of the highway failure because of the significant reduction in the strength of the materials. Generally, the soils are poor engineering materials for pavement construction.