Abstract: A novel ground treatment technique, microbial-induced calcite precipitation(MICP), has recently emerged in geotechnical engineering, which utilizes the calcite precipitation to bind loose particles together; and therefore, the mechanical properties of sand can be enhanced. The objective of this study is to investigate the effect of chemical treatment on the strength of bio-cemented sand. Sporosarcina pasteurii is used to induce calcite precipitation, and all the specimens are prepared by injecting a single concentration or multiple different concentrations of chemical solutions. In this study, 0.5 and 1.0 mol urea-calcium chloride solutions are used for the former chemical treatment, while for the latter one, 0.5 mol urea-calcium chloride solution is firstly injected; and subsequently, 1.0 mol urea-calcium chloride solution is utilized. Based on the experiment, the strength, failure modes and calcite content are analyzed. From the experimental results, it can be found that chemical treatment has significant influence on the unconfined compressive strength of bio-cemented sand soil, but no pronounced effect can be seen in the failure modes and calcite content. Injecting multiple different concentrations of chemical solutions can be beneficial to obtain relative high compressive strength by using less treatment times. Finally, the mechanism analysis corresponding to the effect of chemical treatment on the strength of bio-cemented soil is further conducted.

Key words: microbial-induced calcite precipitation(MICP), sand, chemical treatment, unconfined compressive strength test, mechanism analysis