Engineering Geological Assessment of Road Foundation Soils in Owerri, Imo State

Repeated failure of road pavements in Owerri, the capital of Imo State in South East Nigeria, has drawn attention to the need for systematic engineering geological characterisation of subgrade and foundation soils before road construction. This study conducts an engineering geological assessment of soils along three selected road alignments in Owerri, evaluating their geotechnical properties and suitability as pavement subgrade materials. Disturbed and undisturbed soil samples were retrieved from trial pits at depths of up to 1.5 metres at regular intervals. Standard laboratory tests including particle size analysis, Atterberg limits, compaction characteristics, and California Bearing Ratio were conducted in compliance with BS 1377 standards. Natural moisture content and specific gravity determinations supplemented the index property dataset. Classification of soils followed the Unified Soil Classification System. Vertical electrical sounding profiles were acquired alongside the sampled sections to delineate subsurface variability not captured by trial pits alone. The study identifies zones of expansive clay and high plasticity index soils likely to contribute to pavement distress during wet season saturation. Recommendations are made for subgrade stabilisation using lime or cement admixtures where warranted by the results. Findings are communicated to the Imo State Ministry of Works and are intended to inform cost-effective road design standards for similar lateritic terrain. Keywords: engineering geology, road foundation, CBR, soil classification, Owerri.