STUDY OF THE SUBGRADE FAILURE ON THE HIGHWAY PAVEMENT ALONG ENUGU-ONITSHA EXPRESSWAY AT GARIKI LIVESTOCK MARKET AMANSEA

Abstract

This research addresses a comparative study and examination of the subgrade failure on the Highway along Enugu-Onitsha Expressway at Gariki Livestock Market Anambra. A highway pavement is composed of a system of overlaid strata of chosen processed materials that is positioned on the in-situ soil, termed the subgrade. The load-bearing capacity of a pavement depends chiefly on the subgrade features especially its strength. The major importance of this study is the resolution of the environmental impacts due to the pavement failure such as soil erosion and extreme traffic conjestion. In this project, three locations were selected for sampling of the soil. Particle size distribution test was carried out on the soil samples to give an insight on the nature of the soil. Atterberg limit test was carried out to determine the plasticity of the soil from the clay content. The compaction test and the California Bearing Ratio (CBR) test was also carried out to determine the maximum dry density and load-bearing capacity of the subgrade soil. The sieve analysis test classified the soil as a poorly graded subgrade soil with a uniformity coefficient of 3.29 and a coefficient of curvature of 0.94. The Atterberg limit test which gave the plasticity index of 7.65% indicated the soil is of a moderate clay content and will therefore exhibit some plastic behaviour. With ranges between 2008–2041(kg/m3 ) of MDD and a range between 7.8% - 10.2% of OMC, the compaction test indicated that the soil can be effectively compacted to achieve a desirable density to enhance the strength and stability of the subgrade soil. The CBR test with an average value of 10% indicated a relatively low strength and load-bearing capacity of the subgrade soil. The results reveal the high degree of distress on the subgrade exposing some defects on the pavement like edge cracks and portholes. It was recommended that further investigation is required to give more insight into the soils behaviour and in adverse case additional measures such as soil stabilization, geosynthetic reinforcement or subgrade modification technique should be considered to improve the soils load-bearing capacity