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Effect of Reagent Concentration on Strength of Lateritic Soil Bio-treated with Bacillus Thuringiensis-Induced Calcite Precipitate Tested with Pocket Penetrometer
* 1, 2 , 3 , 3, 4 , 3
1  Department of Civil Engineering, Joseph Sarwuan Tarka University, Makurdi, Benue State, Nigeria
2  Graduate student, Ahmadu Bello University, Zaria, Kaduna State, Nigeria
3  Department of Civil Engineering, Ahmadu Bello University, Zaria, Kaduna State Nigeria.
4  African Center of Excellence on New Pedagogies in Engineering Education (ACENPEE), Ahmadu Bello University, Zaria, Kaduna State, Nigeria.
Academic Editor: Simeone Chianese

Abstract:

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 (Cs) on the strength of the microbial-induced calcite precipitate (MICP) worked soil was also evaluated. Soil samples were treated with Bt and Cs using three mix ratios (i.e., 25 % Bt : 75 % Cs, 50 % Bt : 50 % Cs and 75 % Bt : 25 % Cs) 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 Cs 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 Cs 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 % Cs > 25 % Bt : 75 % Cs > 75 % Bt : 25 % Cs. Therefore, PPT can be used as a quick check for strength of treated soil.

Keywords: Bacillus thuringiensis, pocket penetrometer, strength, lateritic soil, MICP.
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