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

¹ Civil Engineering Department, Ahmadu Bello University, Zaria, Nigeria
^1* Civil Engineering Department and Africa Centre of Excellence on New pedagogies in Engineering Education, Ahmadu Bello University, Zaria, Nigeria
² Civil Engineering Department, University of Jos, Nigeria

^* Corresponding author: aeberemu@yahoo.com

Abstract

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.