Variability in the Highway Geotechnical Properties of Two Residual Lateritic Soils from Central Nigeria
Abstract
Sixty-four bulk samples of two residual lateritic soils forming the subgrade of the failed sections flexible highway
pavement linking Ilorin to Mokwa in central Nigeria were investigated. This was with a view to determining the level
of variation in the geotechnical properties of soil samples taken systematically within restricted area in two locations
underlain by different bed rocks. One set was developed over sandstone formation of the Southern Bida Basin while the
other set was developed over migmatite-gneiss. Consistency limits, grain size distribution, specific gravity, compaction,
California Bearing Ratio (CBR), permeability and compressibility characteristics of these soils were determined using
the British standard procedures 1377. Coefficient of variation was used to measure the degree of variation in the
determined properties. The coefficients of variations for the sandstone derived soil (1.68% and 56.86%) are higher
than that of the migmatite-gneiss derived soil (1.28%-54.40%). Permeability, linear shrinkage, and coefficient of volume
compressibility possess the highest variability. Atterberg limits and derived indices, amount of fines, soaked and
unsoaked CBR possess moderate variability, while moisture density parameters (MDD and OMC), natural moisture
content and specific gravity exhibits the least variability. In order to prevent design errors, field sampling should be very
thorough involving collection of several samples. This approach will eliminate wrong inferences often associated with
results of testing of few samples