The Effect of Bacillus Coagulans and Moulding Water Content on the Unconfined Compressive Strength of Lateritic Soil

Abstract

The effect of bacterial concentrations of Bacillus coagulans and moulding water content (MWC) on the unconfined compressive strength (UCS) of lateritic soil for use as waste containment material was studied. Tests conducted include index test, pH, calcium carbonate content (CCC), and UCS. Soil samples for all tests were mixed with an increasing number of microbes at step suspension densities of 0 up to 2.4 × 10⁹ cells/ml individually. The soil was prepared at MWC of -2, 0, +2, and +4% in relation to optimum moisture content (OMC) and compacted using the Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS) Compaction and British Standard Heavy (BSH) Compaction Energy (CE) respectively. The cementation reagent was added to the compacted samples and allowed to flow by gravity to a point that saturation was reached. Results revealed an increase in pH, while calcium carbonate content values marginally increased from 3.6% at the natural state to 3.9% maximum value at 2.4 × 10⁹ cells/ml. The UCS values increased with a higher number of microbes. Values increased from 204.6, 278.3, 351.3, and 416.8 kN/m² for the natural soil to peak values of 1,036.3, 1,835.5, 2,076.8, and 2,237.3 kN/m² for specimens prepared at -2% OMC and compacted with RBSL, BSL, WAS and BSH compaction energy, respectively. A similar trend was observed for 0, +2, and +4% in relation to OMC. A minimum regulatory UCS value of 200 kN/m² was achieved at MWC of -2, 0, and +2% OMC for all energies. Therefore, it is recommended that CE, moisture content, and the number of microbes should be carefully studied during field construction of a lateritic soil-compacted clay liner in other to achieve the desired result.