Effects of biostimulation treatment methods on mechanical properties and microstructure characteristics of biocemented soil

The objective of the current study is to explore the effect of biostimulation treatment methods on the mechanical properties and microstructure characteristics of biocemented soil. Biostimulated microbially induced carbonate precipitation (MICP) is an eco-friendly and economical soil reinforcement measure. It relies on the stimulation of the urease-producing bacteria (UPB) in situ for the MICP process. Different biostimulation treatment methods involve different oxygen availability, stimulation solution content and distribution, and number of biostimulation treatments. There may be differences in the effect of UPB stimulation and biocementation when different biostimulation treatment methods are used. In this study, four biostimulation treatment methods, i.e., unsaturated single biostimulation treatment (USBT), unsaturated multiple biostimulation treatments (UMBT), saturated single biostimulation treatment (SSBT) and saturated–unsaturated-combined single biostimulation treatment (CSBT), were used to stimulate native UPB in soil columns, and then, the same cementation treatment was applied to the soil columns. Subsequently, the mechanical behavior and microstructural properties of the biocemented soil were investigated. The results indicated that the saturated single biostimulation treatment was more conducive to stimulating native UPB to induce CaCO₃ precipitation. Samples subjected to the saturated single biostimulation treatment exhibited higher CaCO₃ precipitation content (CCP), dry density, unconfined compressive strength (UCS) and lower permeability within the same cementation treatment cycle (N_C). However, UCS was not only determined by CCP, but was also regulated by CaCO₃ spatial distribution and precipitation pattern. This study could help guide the selection of biostimulation treatment methods.