PAVEMENT FAILURE ALONG OTA-LAFENWA- ITELE HIGHWAY, SOUTHWESTERN NIGERIA

Abstract

Ota-Lafenwa-Itele highway has experienced severe failure of various forms over the years. Being an interstate road that link some Nigerian border communities in Ogun State to Lagos, the effect of the failure has significant negative impact on socio-economic growth. In order to assess the causes of the road failure and proffer preventive measures for future reconstruction of the road, geotechnical engineering properties of the subsoil and visual pavement condition were evaluated. Twenty five disturbed and nine undisturbed soil samples were collected from nine test pits at depths of 1.5 m to 2 m. The soil tests carried out on the disturbed samples were Atterberg limits, linear shrinkage, grain size, hydrometer, standard compaction, California Bearing Ratio (CBR), consolidation and triaxial tests. Those carried out on undisturbed samples were natural moisture content, bulk density, dry density and specific gravity tests. The study area is underlain by Coastal Plain Sand (CPS) formation, a Tertiary age sediment of the uppermost Dahomey Basin. Pavement failures observed are rutting, potholes, corrugation, side drain, edge collapse. The natural moisture content values obtained ranged from 9.98 to 16.89%, specific gravity ranged from 2.65 to 2.71, liquid limit values ranged from 26.7 to 58.18%, plastic limit values varied from 13 to 40.1%, while linear shrinkage ranged from 3.6 to 14.8, plastic index ranged from 11.35 to 28.43, swell index values ranged from 0.1765 to 0.67621, liquidity index varied from -1.0532 to -0.0004, activity index varied from 0.39 to 0.69. Dominant subgrade soil types are CH,CL,MH and ML groups based on USCS classification system and A-7 soil group based on the AASHTO classification system. Grain size analysis shows that gravel fraction ranged from 0.1 to 2.4%, sand fraction ranged from 20.6 to 52.8%, silt fraction ranged from 13.8 to 29%. The MDD ranged from 1350 to 1672kg/m3 and the OMC ranged from 13.4 to

25.5%. unsoaked CBR values ranged from 19 to 44% and soaked CBR ranged from 4 to 13%, coefficient of consolidation ranged from 0.0067 to 0.4236m3/yr, final void ratio ranged from 0.407 to 0.878, the rate of settlement ranged from 0.6024 to 1.1622mm/yr, angle of internal friction ranged from 35.40 to 39.30, cohesion ranged from 43.5 to 150.1kPa, shear strength ranged from 101.1 to 202.5kPa. The negative and weak correlation between CBR and clay content (r=-0.10), CBR and swell index (r=-0.08), CBR and plastic index (r = - 0.11) suggest that the clayey, plastic and swelling property of the soils has less effect on their bearing capacities. The correlation between CBR and coefficient of consolidation (r = + 0.52), CBR and MDD (r=+0.33) implied that increase in MDD values and consolidation characteristics increases the CBR values. The correlations between MDD and Settlement (r =-0.47), MDD and void ratio (r =-0.65) indicate that the soil’s improvement through compaction has strong effect on compressibility. The weak correlation between MDD and shear strength (r = +0.15) implied that the shear strength has less effect on the MDD. Dominance of low CBR, low MDD, high linear shrinkage, and A-7 soil group expectedly contributed to the road failure. Total overhaul of the road, treatment of the subgrade soil, replacement of the base course material and construction of drainage are recommended for the highway.