Effect of Mode of Treatment of Brevibacillus Brevis on Plasticity Characteristics of Bio-Treated Lateritic Soil in Microbial-Induced Calcite Precipitation Application

An economical and sustainable method of soil improvement known as Microbial Induced Calcite Precipitation (MICP) has received significant attention in the past decade. The plasticity of lateritic soil bio-treated at stepped Brevibacillus brevis (B. brevis) suspension density and cementation reagent concentration using three mode of treatment (i.e. mixing, injection and spraying method). The B. brevis suspension densities and cementation reagents used to trigger the MICP process are 0, 0.5, 2.0, 4.0, 6.0 and 8.0 McFarland Standards (i.e., 0, 1.50 × 108, 6.0 × 108, 1.20 × 109, 1.80 × 109 and 2.40 × 109 cells/ml and 0.25, 0.5, 0.75 and 1.0 M, respectively. The liquid limit value used to prepare the samples with three mix proportions of the bacteria and cementation reagent (viz: 25% bacteria-75% cementation reagent, 50% bacteria-50% cementation reagent and 75% bacteria-25% cementation reagent) is the one obtained from natural lateritic soil for all the three modes outlined. Atterberg limits and calcite content using the acid wash method tests were conducted on the treated specimens for all the three treatment modes. Results obtained show a general decrease in the Atterberg limits with higher B. brevis suspension density and cementation reagent concentration for mixing, injection and spraying method respectively. The best enhancement of plasticity index was obtained for lateritic soil sample treated with a mix ratio of 75 % B. brevis (2.40 × 109 cells/ml for mixing an injection as well as 1.8 × 109 cells/ml for spraying method of treatment ): 25 % cementation reagent (0.50M, 0.25 M and 0.75M for mixing, injection and spraying mode) with a corresponding peak calcite content of 12.0 (2.40 × 109 cells/ml and 1.0M), 5.38 (2.40 × 109 cells/ml and 1.0M) and 3.50% (1.8 × 109 cells/ml and 1.0M) for mixing, injection and spraying treatment mode respectively.