PLASTICITY AND COMPRESSIBILITY CHARACTERISTICS OF LATERITIC SOIL FROM SOUTHWESTERN NIGERIA

Plasticity index and coefficient of compressibility amongst other characteristics were determined for some lateritic soil samples of Southwestern Nigeria with a view to establishing the relationship between their plasticity and compressibility as well as predicting their in-situ compressibility and also determine the effect of the parent rocks on the plasticity and compressibility.  Two study areas were chosen in Ibadan, Southwestern Nigeria where ten disturbed and ten undisturbed samples each were collected.  The disturbed samples were subjected to a number of geotechnical tests: grain size, distribution analysis, specific grant and consistency test.  The undisturbed samples were subjected to consolidation test.   The study revealed the rock type in study area A to be quartzschist and area B to be granitic.  The specific gravity of the soil grains ranged between 2.48 and 2.72; while the plasticity index value was between 9.7 and 21.4%.   Coefficient of consolidation ranged between 29.39mm 2 /min and 32.56mm 2 /mm with coefficient of volume compressibility between 1.08 x10 -3 m 2 /KN and 1.94 x10 -3 m 2 /KN.  The soil samples were generally well-graded reddish brown, sandy-silt-clay of medium plasticity and compressibility with dominant kaoline clay mineral in the quartzschist derived soil while the dominant clay mineral in the granite derived soil is illite.  The most influenced parameter of the parent rocks was the coefficient of compressibility, which revealed the samples of the two study areas to be suitable for construction work as well as landfill site with little compaction.