Microbial induced calcite precipitation as a viable ground improvement technique

Traditional ground improvement techniques, such as grouting or compaction, can be invasive, energy demanding and expensive. Microbially induced calcite precipitation (MICP) offers a sustainable alternative by utilizing a natural process, and has therefore been the focus of extensive interest and laboratory research over the past decade. Most of that research has been at laboratory-scale on the factors that affect process efficiency. The use of MICP in the field have been discussed in numerous research papers but remains largely theoretical and examples of field-scale trials are rare. MICP uses ureolytic bacteria, such as the common soil bacteria Sporosarcina pasteurii, which are given access to an ample supply of urea and calcium chloride. The bacteria hydrolyse the urea into ammonium and carbonate, raising the pH and in the presence of calcium in solution, facilitating the precipitation of calcite crystals (CaCO3). It is particularly effective when used with fine grained sands as those calcite crystals form a bridge between the individual sand grains, cementing them together and creating a weak bio-sandstone. This project, through bench-scale column experiments on MICP treated sands, has investigated optimization of the influencing factors of the bacteria concentration, the treatment strategy employed and the number of treatment cycles administered. The influence these parameters have on the ultimate core strength, from unconfined compressive strength (UCS) tests, and the homogeneity of the calcite distribution, have been determined. These results have then been used to design an efficient treatment process to underpin large-scale trials of MICP for ground improvement and erosion protection.