EFFECT OF VARYING CEMENTATION REAGENT CONCENTRATION ON THE INDEX AND PHYSICO-CHEMICAL PROPERTIES OF LATERITIC SOIL TREATED WITH BACILLUS SPHAERICUS

This study evaluated the index and physico-chemical characteristics of lateritic soil classified as A-2-6 (1) in the American Association of State Highway and Transportation Officials (AASHTO) system and SC in the Unified Soil Classification System (USCS) treated with stepped Bacillus sphaericus (Bs) suspension density (i.e., 0, 1.5 x 10⁸, 6.0 x 10⁸, 1.2 x 10⁹, 1.8 x 10⁹, 2.4 x 10⁹ cells/ml) for varying cementation reagent (C_r) concentration (i.e., 0.25, 0.5, 0.75 and 1.0 M)using 25 Bs:75 C_r, 50 Bs:50 C_r, 75 Bs:25 C_r mix ratios, respectively. Results obtained show that the optimum calcium carbonate content was 9.0 %, 8.7 %, and 6.5 % for bacteria-cementation mix ratios stated above, respectively, for Bs (1.2 x 10⁹ cells/ml) and C_r (0.5 M) with urease activity of 80.8 ms/cm and optimum pH of 8.99. Bio-treatment of soil with 25% bacteria (1.2 x 10⁹ cells/ml) and 75% C_r (0.5 M) mix ratio reduced the liquid limit (LL) of the natural soil from 36.5 to 34.2 %, and the plasticity index (PI) from 16.4 to 11.6 %. Microanalysis of specimens showed that the treated soil appears more uniform and aggregated. The findings of the study show that lateritic soil bio-treated with 25 Bs (1.2 x 10⁹ cells/ml) : 75 C_r (0.5 M) mix ratio can improve the index and physico-chemical properties of lateritic soil.