Characteristics of Tropical Residual Soils for Multipurpose Structural Applications in Edo State, Nigeria

Abstract

Tropical residual soils constitute the predominant natural foundation and construction materials in many tropical regions of the world, particularly in Nigeria, where they are widely utilized in road construction, building foundations, embankments, and other civil engineering works. Despite their abundance and economic advantages, the engineering performance of these soils varies considerably due to differences in parent rock composition, weathering intensity, climatic conditions, and mineralogical characteristics. Inadequate characterization and improper utilization of these soils have contributed significantly to numerous cases of structural distress, pavement deterioration, and foundation failures. This study investigates the physical, index, and mechanical properties of tropical residual soils collected from selected locations in Edo State, Nigeria, namely Auchi, Ikpeshi, and Igarra, with the objective of assessing their suitability for multipurpose structural and geotechnical applications. Comprehensive laboratory investigations were carried out, including determination of natural moisture content, particle size distribution, Atterberg limits, specific gravity, compaction characteristics, California Bearing Ratio (CBR), and direct shear strength parameters. The results revealed relatively low natural moisture contents ranging from 4.14% to 9.69%, non-plastic to slightly plastic characteristics, satisfactory specific gravity values, and moderate shear strength properties. The soils exhibited varying load-bearing capacities and compaction responses depending on their geological origin and location. Although the materials generally demonstrated acceptable engineering properties for light- to medium-duty construction applications, a noticeable reduction in strength and bearing capacity was observed under soaked conditions, indicating susceptibility to moisture-induced performance deterioration. Consequently, the study emphasizes the importance of adequate compaction, effective drainage systems, and where necessary, soil stabilization measures to enhance long-term performance. The findings provide valuable site-specific geotechnical data and practical recommendations for the sustainable utilization of tropical residual soils in foundation engineering, pavement construction, and other multipurpose infrastructure projects within tropical environments.