PLASTICITY BEHAVIOR OF LATERITIC SOIL TREATED WITH BACILLUS PUMILUS IN MICROBIAL INDUCED CALCITE PRECIPITATE APPLICATION IN EROSION MITIGATION
Keywords:
Bacillus Pumilus, Cementation reagent, Lateritic soil, Microbial-induced calcite, precipitation (MICP), PlasticityAbstract
Lateritic soil which is found in the tropical areas is usually prone to erosion due to low plasticity. To improve the soil’s plasticity behavior in mitigating erosion, stepped Bacillus pumilus (B. Pumilus) suspension densities of 0, 1.5 x 108, 6.0 x 108, 12 x 108, 18 x 108, and 24 x 108 cells/ml, respectively, where mixed with the soil sample and a cementitious reagent to initiate microbial induced calcite precipitation (MICP) process. Urease activity, pH value, calcite content and atterberg limit tests were examined to determine the plasticity behavior of the bio-treated soil. The liquid and plastic limits values initially decreased from 35.4% and 17.1% for the natural soil to minimum values of 31.5% and 11% with higher B. pumilus suspension densities up to 2.40 × 108 cells/ml. On the other hand, plasticity index and linear shrinkage values decreased with higher bacteria suspension densities from 18.27% and 15.67% for the natural soil to 8.73% and 6.98% with higher B. pumilus suspension densities up to 24 × 108 cells/ml. The plasticity Index (8.73%) of the bio-treated soil was achieved for 75% bacteria - 25% cementation reagent at Bacillus pumilus suspension density of 18.0 x 108 cells/ml with corresponding peak 10.86% calcite. The hard crust layer on soil caused by MICP is responsible for the mitigation mechanism because it binds soil particles together and fills pores with precipitated calcium carbonate. The hard crust's strong structure can withstand both the impact of rainfall and erosion resistant.