Effect of Treatment Compositions on the Plasticity of Tropical Red Soil Treated with Bacillus Coagulans

The study evaluated the effect of four treatment compositions on the plasticity of tropical red soil (Lateritic soil) admixed with Bacillus coagulans (B. coagulans). Samples for Atterberg limits test were prepared using four treatment compositional variables. They include 25% B. coagulans suspension and 75% cementation reagent, (25%B /75%C); 50% B. coagulans suspension and 50% cementation reagent (50% B /50%C); 75% B. coagulans suspension and 25% cementation reagent, (75%B /25% C) with the above three being in equivalent volumes of the corresponding liquid limit(LL) and 50% of the optimum moisture content (OMC) of compaction, to be both  B. coagulans suspension and cementation reagent (i.e. 50% OMC B /50%OMC  C) of the natural soil. Results showed that the LL for; 25%B /75% C, 50% B /50% C and 75% B /25%C generally increased from 0 up to peak values at 1.8 x 109 cells/ml and then declined at 2.4 x 109 cells/ml. In the case of samples treated with 50% OMC B/50% OMC C, the LL initially decreased from 0 up to 6.0 x 108 cells/ml and thereafter increased significantly. Plastic limit (PL), Plasticity index (PI) and Linear shrinkage (LS), recorded improvement. Regression analysis for the best treatment composition (i.e 75%B /25%C) has regression coefficient of 91.8%. Based on the four treatment compositions considered, 75%B/25%C enhanced the soil workability significantly and is suggested for geotechnical engineering applications such as road pavements that are lightly trafficked

Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with <i>Bacillus thuringiensis</i>-Induced Calcite Precipitate Tested with Pocket Penetrometer

The strength of lateritic soil bio-treated with a Bacillus thuringiensis (Bt)-induced calcite precipitate was investigated using a pocket penetrometer (PPT). The effect of bacterial (Bt) and cementation solution concentration (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 the natural soil liquid limit (LL = 36.0%). Bt suspension densities of 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, and 2.4 × 109 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 the UCS values increased with higher Bt and Cs as well as with a reduction in moisture content as the bio-treated soil equilibrated with the environment. The recorded UCS values for the mix ratios considered were in the order: 50% Bt: 50% Cs > 25% Bt: 75% Cs > 75% Bt: 25% Cs. Therefore, a PPT can be used to determine the approximate unconfined compressive strength of treated soil

A Laboratory study on water transfer properties of unsaturated compacted lateritic Soil – Bacillus coagulans mixtures

A study on soil water characteristic curves (SWCC) and unsaturated hydraulic conductivity (UHC) of lateritic soil–Bacillus coagulans mixes was done. Three well known models (i.e van Genuchten (VG), Brooks-Corey(BC) and Fredlund-Xing (FX)) were used to predict SWCC and UHC from laboratory test results. &nbsp;Soil samples for&nbsp; the test were admixed with B. coagulans at one-third (1/3) pore in step suspension densities of 0 to 2.4x109cells/ml. Soil samples were then compacted differently with Reduced British Standard light (RBSL), British Standard light(BSL),West African Standard (WAS) and British Standard heavy(BSH) compactive efforts. Cementitious reagent was injected into the compacted soil using gravity up until saturation was attained. Specimens after being compacted were then cored out from the mould using stainless steel cylindrical moulds. The specimens (i.e., inside the stainless steel cylindrical moulds) were then immersed in water chamber till the samples were completely saturated via capillary action and thereafter allowed&nbsp; to undergo a pressure plate drying(PPD) test. Matric suctions of 0, 10, 30, 100, 500, 1000 and 1500kPa, respectively, were used. Result of SWCCs show that with a rise in matric suction, the volumetric water content(θ) declined progressively for all the models (i.e van Genuchten (VG), Brooks-Corey(BC) and Fredlund-Xing(FX)) and the experimental measured values. The UHC slightly reduced with rise in&nbsp; B.coagulans suspension density for VG, BC and FX models. At 500 and 1500kPa matric suctions (MS), BC model documented the least UHC values and satisfied the regulatory lowest hydraulic conductivity value of 1.0×10-9m/s for use in containment system. Thus, is suggested for modelling the UHC of lateritic soil ̶ B.coagulans mixtures

A comparative study of soil-water characteristic curves for compacted lateritic soil – bacillus

A comparative study of soil-water characteristic curves (SWCCs) for compacted lateritic soil ̶ Bacillus coagulans (B. coagulans) mixtures for municipal solid waste (MSW) application was studied. Soil treatment was performed at approximately about one-third pore volume of the microbes (i.e., B. coagulans) for suspension densities of 0, 1.5×108, 6.0×108, 1.2×109, 1.8×109 and 2.4×109cells/ml, correspondingly. Soil specimens were prepared at optimum moisture content (OMC) of British Standard light (BSL) compaction energy. Cementation reagent was applied on the compacted soil and permitted to penetrate until partial saturation was achieved. A set-up of pressure plate extractor was employed to measure the volumetric water content, θ (VWC) in the laboratory for varying matric suctions with a minimum of 10 kPa up to a maximum of 1,500 kPa. The unsaturated hydraulic conductivity (UHC) and VWC were assessed using Brooks - Corey (BC) and Fredlund - Xing (FX) models. Largely, BC and FX models overrated the VWC. Also, the VWC decreased with higher matric suction for the two models considered and the laboratory measured values. The UHC predicted for matric suctions of 500 and 1,500 kPa initially decreased for B. coagulans suspension density up to 1.2×109 cells/ml for BC and FX models, with the exception of a few cases, but thereafter increased with increase in microbial density. For FX model at 1,500 kPa, UHC values of 2.42×10–9, 2.02×10–9, 9.31×10–10, 8.09×10–10 , 1.29×10–9 and 2.27×10–9m/s were recorded at 0, 1.5×108, 6.0×108, 1.2×109, 1.8×109 and 2.4×109cells/ml, respectively. In the case of BC model, values of 2.26×10–17, 1.41×10–14, 2.2×10–14, 4.6×10–19 , 3.25×10–17 and 2.45×10–14m/s were recorded at 0, 1.5×108, 6.0×108, 1.2×109, 1.8×109 and 2.4×109cells/ml, respectively. Thus, the FX model met the design maximum hydraulic conductivity value of 1 x 10–9 m/s requirement for MSW system when lateritic soil was treated with B. coagulans suspension density of 1.2×109 cells/ml, while the BC model satisfied the requirement for all the microbial densities considered and it is recommended for modelling of UHC of lateritic soil admixed with B. coagulans for MSW containment application

Unsaturated hydraulic conductivity of compacted bio-cemented lateritic soil in municipal solid waste containment application

Most engineering infrastructures, including municipal solid waste containment facilities, are situated in unsaturated zone. The use of chemical additives for soil improvement has been linked to the adverse environmental issues being experienced globally. Research into more sustainable methods of soil improvement has led to the discovery of a novel and innovative method known as microbial induced calcite precipitation (MICP). Lateritic soil was treated with stepped Sporosarcina pasteurii (S. pasteurii) suspension density up to 2.40 x 109 cells/ml at moulding water content (MWC) -2, 0 and +2 % relative to optimum moisture content (OMC) before compaction using Reduced British Standard light (RBSL), British Standard light (BSL), West African Standard (WAS) or Intermediate and British Standard heavy (BSH) energies. Compacted specimens were saturated with cementation reagent in three cycles with 1/3rd pore volume at 6 hours’ interval to induce calcite precipitation at an ambient laboratory temperature of 24±2°C. The soil-water characteristics curves (SWCC) of the specimens were determined using pressure plate extractor over a pressure range of 10-1500 kPa. Unsaturated hydraulic conductivity values were predicted for the S. pasteurii suspension densities considered using Brooks-Corey, van Genuchten as well as Fredlund and Xing curve fitting prediction models. Results show that the unsaturated hydraulic conductivity values of specimens prepared at lower, MWC relative to OMC were generally higher than at higher MWC regardless of compactive efforts and S. pasteurii suspension densities considered. The Brooks-Corey model gave the best predicted unsaturated hydraulic conductivity values which fit the requirements for waste containment facilities over the matric suction range and S. pasteurii suspension densities considered, than the van Genuchten and Fredlund – Xing, when compared with measured values

Effects of Varying Cementation Reagent Concentrations on the Index and Physico-chemical Properties of Lateritic Soil Treated with <i>Bacillus sphaericus</i>

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 densities (i.e., 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, 2.4 × 109 cells/mL) for varying cementation reagent (Cr) concentrations (i.e., 0.25, 0.5, 0.75 and 1.0 M), using 25 Bs:75 Cr, 50 Bs:50 Cr, and 75 Bs:25 Cr mix ratios, respectively. The results obtained show that the optimum calcium carbonate contents were 9.0%, 8.7%, and 6.5% for the mix ratios stated above, respectively, for Bs (1.2 × 109 cells/mL) and Cr (0.5 M) with urease activity of 80.8 ms/cm and an optimum pH of 8.99. The bio-treatment of soil with 25% bacteria (1.2 × 109 cells/mL) and 75% Cr (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%. A microanalysis of specimens showed that the treated soil appeared more uniform and aggregated. The findings of the study show that bio-treatment with 25 Bs (1.2 × 109 cells/mL):75 Cr (0.5 M) mix ratio improved the index and physico-chemical properties of the lateritic soil considered in the study