Coupled Effect of Cementation Solution, Curing Period, Molding Water Content, and Compactive Effort on Strength Performance of Biotreated Lateritic Soil for Municipal Solid Waste Containment Application

Abstract

Microbial-induced calcite precipitation (MICP) is a soil improvement technique that has shown great potential in several geotechnical applications in the previous decade. Some factors that led to the improved strength included cementation concentration. The combined influence of these factors with the cementation reagent was paramount to the calcite precipitation level within soil grain contact of a biotreated compacted fine-grained soil. In this study, the influence of the concentration of the cementation solution [(CCS) 0.25, 0.5, 0.75 and 1.00 M], curing time [(CT) 24 h, 3, 7, 14, and 28 days], and molding water content [MWC (9.8%–19.6%)] of biomediated lateritic soil or lateritic soil that was bioinfused with ureolytic microbes at different suspension densities (cells/mL) and compacted with Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS), and British Standard Heavy (BSH) energy, respectively, were evaluated. In addition, this study focused on unconfined compressive strength (UCS). The results showed an increased UCS with the corresponding average calcite content up to peak values at 0.5 M cementation concentration for the five considered bacterial cells/mL. In addition, the results showed a linear relationship between UCS and average calcite content for the CCS that were considered. The effect of the curing period on UCS was marginal within individual cementation concentrations regardless of bacterial cells/mL. The UCS of the specimen that contained the optimal 0.5 M cementation concentration increased with higher bacterial cells/mL but decreased with the MWC. The qualitative microanalysis that used scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses that evaluated the untreated and biotreated specimens showed the formation of calcite, which increased the soil strength by blocking the soil pores through grain–grain contacts. Microbial-induced calcite precipitation (MICP) techniques have been carried out successfully in numerous studies under laboratory conditions for civil engineering infrastructures. However, data on its application in engineered municipal solid waste (MSW) containment that uses lateritic soil remains limited. Upscaled MICPs have been used in geotechnical applications. In addition, the increased attention, expectations or both of other application areas has established how the previous laboratory scale studies corroborated the field expectations and applications. This study showed the applicability of a ureolytic MICP process (i.e., through ex situ biostimulation). This was used to improve the shear strength performance of lateritic soil under several selective coupled factors when the overburden stress in a barrier waste containment application was contained. The requirements of materials for use in satisfactory waste containment include a number of factors; however, this study was limited to shear strength performance. This is one of the significant criteria that are used when delineating a suitable acceptable zone or limit when materials for engineered barrier systems are selected. This laboratory scale study could provide practical applications for biotreated lateritic soils, which satisfy the strength requirement (i.e., ≥200 kN/m2) for MSW containment applications.