A Model-Scale Investigation for Microbially Induced Calcite Precipitation in Sand

Abstract

New, exciting opportunities for utilizing biological processes to modify the engineering properties of the soil (e.g. strength, stiffness, permeability) have recently emerged. Enabled by interdisciplinary research at the confluence of microbiology, geochemistry, and civil engineering, this new field has the potential to meet society’s ever-expanding needs for innovative treatment processes that improve soil supporting new and existing infrastructure. Ureolytic bacteria are one of the most efficient organisms in producing amounts of carbonate that easily react with the free calcium ions available in the environment. Sporosarcina pasteurii, a robust microbial alkaline environment was used in this work for its high potential in the biocementation process that involves the biomediated calcite precipitation. This study presents the results of a model-scale laboratory investigation conducted on bio-cemented siliceous sand. Chemicals used in this study are commercially available in order investigate the viability of implementing this technique in the field at larger scales. To make it more practical, the microbial cells are directly used with neither sterilization nor utilization of a centrifuge process for the growth medium. Blocks of the bio-treated soil were excavated from the model and were tested to examine the strength and durability parameters of the improved soil. The results show that the unconfined compressive strength (UCS) and slake durability index significant increased upon biological treatment. However, due to the downwards permeation of the fluid due to gravity, samples obtained from the bottom and the center of the treated column gave larger UCS and slake durability indices than those obtained from the top and the sides of the column.