STABILIZATION OF BLACK COTTON SOIL WITH IRON ORE TAILING

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Department of Engineering

ABSTRACT
Results of preliminary investigation of the natural black cotton soil used in the study shows that it belongs to A – 7 – 6 (13) or CH in the AASHTO and Unified Soil Classification System (USCS), respectively. Soils under these groups are highly plastic and of poor engineering benefit. The soil was treated with up to 16% iron ore tailing, IOT (a mining waste) by dry weight of soil and compacted using three energy levels (British Standard light, BSL, West African Standard, WAS and British Standard heavy, BSH). Tests were carried out to determine index properties, compaction characteristics, strength characteristics, durability and microanalysis of specimens. Test results showed an increase in the particle sizes with higher IOT content as particle size distribution curves shifted from the region of fine-grained soils to coarse-grained soil. The liquid limit and plastic limit initially increased from 64.5 and 25.0% for the natural soil to peak values of 71.0 and 34.9 % for 2 and 8% IOT treatments, respectively, and thereafter decreased with higher IOT treatments to 59.9 and 27.5% at 16% IOT content. The linear shrinkage generally reduced with higher IOT treatment from 27.14% for the natural soil to 18.0% at 16% IOT content. Generally, the maximum dry density (MDD) increased while optimum moisture content (OMC) decreased with higher IOT treatment. The 7day unconfined compressive strength (UCS) values for the natural soil are 172.59, 328.38 and 448.83 kN/m2 when compacted with BSL, WAS and BSH energies, respectively, increased to peak values of 337.77, 487.57 and 821.57 kN/m2 at 16, 10 and 12% IOT contents, respectively. However, the recorded values did not meet the 1034.25 or 1710 kN/m2 requirement for adequate lime or cement stabilization, respectively. Similarly, the California bearing ratio (CBR) values (unsoaked) of the compacted natural soil increased from 7.89, 9.82 and 15.03 % to peak values of 16.62, 19.64, and 29.06% at 12, 14 and 12% IOT using BSL, WAS and BSH energies, respectively. For the 24 hour soaked condition the CBR values of 3, 4 and 5 % for the natural vii soil increased to 5.66, 8.69 and 11.33% for BSL, WAS and BSH compactive energies at 12% IOT treatments. The resistance to loss in strength increased from 10. 81, 11.84 and 13.09 % for the natural soil to peak values of 24.71, 24.73 and 17.18% at 8, 12 and 10 % IOT treatments for BSL, WAS and BSH compactions, respectively. Microanalysis of specimens treated with an optimal 10% IOT and statistical analysis of the results using the analysis of variance (ANOVA) showed that the soil characteristics improved. The results recorded show that although iron ore tailing (IOT) improved the properties of black cotton soil (as demonstrated by its statistically significant effect on soil properties), however, it cannot be used as a stand-alone stabilizer but in admixture stabilization of the soil.