Effect of Reagent Concentration on Strength of Lateritic Soil Bio-treated with Bacillus Thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer

The strength of lateritic soil bio-treated with Bacillus thuringiensis (Bt)-induced calcite precipitate was investigated using a pocket penetrometer (PPT). The effect of bacterial (Bt) and cementation concentration solutions (C_s) on the strength of the microbial-induced calcite precipitate (MICP) worked soil was also evaluated. Soil samples were treated with Bt and C_s using three mix ratios (i.e., 25 % Bt : 75 % C_s, 50 % Bt : 50 % C_s and 75 % Bt : 25 % C_s) based on natural soil liquid limit (LL = 36.0 %). Bt suspension densities of 0, 1.5 x 10⁸, 6.0 x 10⁸, 12 x 10⁸, 18 x 10⁸ and 24 x 10⁸ cells/ml were applied to the soil with four varying C_s concentrations (i.e., 0.25, 0.5, 0.75 and 1 M). The prepared specimens were allowed to homogenise and equilibrate at laboratory conditions. A pocket penetrometer-PPT was used to test the unconfined compressive strength (UCS) of the prepared specimens at 3, 5, and 7 days after bio-treatment to evaluate the strength of the MICP worked soil at different moisture contents. The results obtained show that UCS values increased with higher Bt and C_s as well as with reduction in moisture content as the bio-treated soil equilibrated with the environment. The recorded UCS values for the mix ratios considered are in the order: 50 % Bt : 50 % C_s > 25 % Bt : 75 % C_s > 75 % Bt : 25 % C_s. Therefore, PPT can be used as a quick check for strength of treated soil.