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

Abstract

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.