ABSTRACT
Black cotton soil classified as an A-7-6(24) soil on the AASHTO classification collected from New Marte area of Borno State was modified with up to 4% lime and locust bean waste ash (LBWA) up to 8% by weight of dry soil. The effect of LBWA on the lime modified soil was studied with respect to particle size distribution, Atterberg limits, compaction characteristics and shear strength parameters using three (3) compactive efforts of British Standard light (BSL), West African Standard (WAS), and British Standard heavy (BSH). Statistical analysis was carried out on results obtained from the tests conducted to determine significant difference (i.e ,p<0.05) on the various soil-lime-LBWA mixtures using a two way Analysis of Variance(ANOVA) with the Microsoft Excel Analysis Tool Pak Software Package. Analysis of the results of the soil-lime mixtures considered showed increase in percentage of fine fraction, improvement in the plasticity index, decrease in maximum dry density (MDD), with increase in optimum moisture content (OMC), as well as a decrease in cohesion with increasing angle of internal friction all with higher locust bean waste ash contents. The results also showed that the modified soil met the requirements of the Nigerian General Specifications of not more than 35% passing sieve No.200, maximum plasticity (PI) index of 12%, and liquid limits (LL) of a maximum of 50% when used as a subgrade material in road construction. An optimal blend of 4% lime 8%LBWA is recommended for the modification of black cotton soil.