The Nigerian government have consistently spent billions of Naira in rehabilitating roads which have been failing repeatedly and this has become a major concern, especially in the South-eastern region of the country. This paper established the influence of the underlying geology and soil geotechnical characteristics on the attendant road (risk) failure within a (5km) section off the Enugu – Port Harcourt Expressway and its spatial variation as well. Soil samples were collected from five (5) portions of the road where cracks were noticed while secondary data was obtained from existing literatures to explain the implication of the findings. Laboratory analysis adopted assessed four (4) five (5) major soil geotechnical properties: particle size distribution, Atterberg Limit (i.e. liquid limit, plastic limit and plasticity index), compaction test (i.e. British Light and Heavy maximum dry densites and optimum moisture contents), California Bearing Ratio (i.e. soaked and unsoaked), and Hydraulic Conductivity (K), while other parameters such as coefficients of curvature and uniformity were estimated. Principal Component Analysis was adopted to analyse the data so obtained while ANOVA test was performed to ascertain if the geotechnical properties of the different soils were significantly different. This was done using Minitab statistical package. Result obtained from the sieve analysis indicated that the soil grains all ranged from medium to coarse grains, composed of low fines, exhibit a strong uni-modal curve and are poorly graded. The result of the PCA indicated that three (3) components accounted for about 97% of the persistent road failures in the portion under investigation: Plasticity Index (50%), Maximum Dry Density (30%) and Plastic Limit (15%) were identified. Also, the result of the ANOVA test, with an R2 adjusted value of 99.16% showed that the geotechnical properties of the soils (within 2.3% of the entire expressway) were significantly different. With such results, road failure (e.g. cracks, pot holes, crevices, depressions, cut-offs etc.) is imminent and therefore calls for more critical geotechnical soil characterization for all other portions of the expressway, especially the portion within Abia State (where about 13 geologic formations have been identified). The study therefore recommended, amongst others that all relevant stakeholders discourage all practices (especially sand mining) that are capable of initiating road failures, while civil engineers should consider the varying influences of the underlying geology and the unique geotechnical characteristics of sub-grade materials before subjecting uniformly any stretch of land inthe region for road pavement construction.
Eneche et al. (Wed,) studied this question.