Suitability of Nigerian Standard Specifications for Evaluation of Composite Lateritic Gravel-Fine Soils for Road Base

Abstract

Five fine lateritic soils collected from five different areas within the suburb of Minna, Niger State, Nigeria were sieved through BS sieve 0.425mm each. Fractions the fine soils passing through the sieve were mixed with lateritic gravel, at 0, 10, 20, 30, 40 and 50 % by mass of the gravel. Index properties, compaction characteristics and California Bearing Ratio of all the mixtures were evaluated. The results showed that the fine soils used, classified under A-2-6 to A-7-6 according to AASHTO soil classification system. The mixtures that gave the minimum 80 % CBR required by Nigeria General Specification for Roads and Bridge Works, for soil to be used for road base were isolated, and their index properties reevaluated. From the five fine soils studied, it was observed that 36 % maximum percentage passing BS sieve 0.075mm, 39 % maximum liquid limit and 14 % maximum plasticity index were adequate to give the 80 % minimum CBR, and can therefore be recommended for materials to be used for road base course as against the 35 % maximum percentage passing sieve 0.075mm, 35 % liquid limit and 12 % plasticity index, specified by the Nigerian General Specification for Roads and Bridge Works.