INFLUENCE OF BACILLUS PUMILUS ON THE PLASTICITY OF TREATED LATERITIC SOIL

Abstract

The effect of Bacillus pumilus (B. pumilus) on the improvement potential of some selected geotechnical properties of lateritic soil was studied. Air-dried soils were cured in paced Bacillus pumilus suspensions between 0 and 2.4 × 109 cells/ml. Cured test samples adopted mix ratios of 50% B. pumilus / 50 % cementation reagent(50 % B – 50 % C)  for sample A and 25% B. pumilus / 75 % cementation reagent(25% B – 75% C), for sample B, all conforming to the liquid limit of the soil. The geotechnical properties of the lateritic soil showed different levels of improvement with increasing B. pumilus suspension densities. The specific gravity generally diminished with rise in B. pumilus suspension from 2.55 for the natural soil to 2.33 and 2.26 at 2.4 × 109 cells/ml for samples A and B, respectively. The cation exchange capacity (CEC) decreased from 26.6Cmol/kg for the natural soil to 8.7Cmol/kg at B. pumilus suspension of 1.8 × 109 cells/ml. The Atterberg Limits of lateritic soil specifically, plasticity index (PI) decreased from 19.0% and 29.1% for the natural and control lateritic soil to values of 6.2 and 8.9 % for samples A (50 % B – 50 % C) and B (25% B – 75% C), respectively, at optimal  B. pumilus suspension density of 2.4 × 109 cells/ml, Sample B (25 % B – 75% C) recorded a better improvement in terms of the plasticity of the treated soils