Index and Strength Characteristics of Residual Lateritic Soils from South-Western Nigeria

Aim: To test consistency and strength of residual lateritic soil of Migmatite Gneiss of the Gneiss Complex from Abeokuta and Ibadan of South-western Nigeria for utilisation as sustainable road construction materials.
Study Design: A reconnaissance survey was carried out for location and identification of major outcrops around the area. The test pit investigative method was adopted by profiling the subsoil 3 m below the ground surface. Disturbed soil samples were used for the determination of the index properties, while shear strength parameters were determined on undisturbed soil specimens.
Place and Duration: The study was undertaken in Ibadan and Abeokuta, Southwest, Nigeria between Dec 2011 and March 2012.
Methodology: All the procedures adopted for the tests were in accordance with the British Standard 1377.The specific gravity of the samples was determined using the pycnometer method. The sieve analysis and hydrometer methods were employed to study the particle size distribution of coarse and fine soils respectively, while the Atterberg tests were performed to investigate the consistency limits of fine grained soils.
Results: The lateritic soils are predominantly well-graded silty, clayey sands with average specific gravity and clay content of 2.72 and 31.8% respectively. The colloidal activity of the clay ranged up to 2.25, signifying considerable volume change when wetted and large shrinkage when dried. Kaolinite and Ca montmorillonite are the principal clay minerals present in the soils. The fines are silty clays of low to medium plasticity.
Conclusion: Fairly strong inverse relationship was established between undrained cohesion and flow index, implying that the rate of loss of shearing stress of the soils is comparatively a function of increase in their moisture content.