Soil Stabilisation by Microbial-Induced Calcite Precipitation (MICP): Investigation into Some Physical and Environmental Aspects

Abstract

This work investigates an emerging and promising soil stabilisation method known as bio-cementationusing microbial-induced calcite precipitation (MICP). MICP utilises bacteria to hydrolyse urea to givecarbonate ions which react with a calcium-rich solution (i.e. calcium chloride) to produce calciumcarbonate (calcite) that binds the soil particles together leading to increased soil strength and stiffness.In this paper, the effectiveness of bio-cementation of silica sand under different environmental andphysical conditions was investigated including the initial soil density, temperature and pH of soil. A setof laboratory tests were conducted including soil permeability, unconfined compression strength anddetermination of calcium carbonate content. The results indicate that bio-cementation is more effectivefor sand of high initial density. The results also demonstrate that although the calcium carbonateproduction was facilitated at an elevated temperature of 50oC, the build-up of strength was lessefficient than at room temperature. Also alkaline (pH 9.5) or acidic (pH 3.5) conditions were adverse tostrength development. Sufficient permeability was retained by all bio-cemented samples, whichindicates good drainage ability that allows rapid dissipation of the excess pore water pressure uponloading.A new promising and innovative modification of MICP treatment was also evaluated using theseawater as a replacement for one of the reactants in production of calcium carbonate. This newprocess provides a high potential for using bio-cementation in maritime environment for applicationssuch as coastal erosion prevention. Treatment using the seawater to replace the calcium chloride hasresulted in stabilised soils that exhibit reasonable strength and efficient crystal formation, whichconfirms the viability of the proposed seawater process for bio-cementation.