Improving water stability and mechanical behavior of surface clayey soil by bio-constructed barrier

Soil erosion induced by water is one of the most common natural disasters. Microbially-induced calcite precipitation (MICP) technique was investigated as a possible method for improving soil hydro-mechanical characteristics against erosion. Although many studies have been performed on hydraulic and mechanical properties of MICP-treated soils, they have mostly focused on sandy soils and less on clayey soils that are commonly susceptible to erosion. This study proposes a bio-mediated approach using MICP to construct a barrier on clayey soil surface with sand additive. Five groups of MICP-treated clayey soil samples with different sand contents (0%, 10%, 20%, 30%, and 40%) and five control samples with the same sand contents were prepared. A series of slaking tests and penetration tests was conducted to characterize the soil hydro-mechanical properties. The experimental results show that MICP-treated samples exhibited better water stability than untreated samples. The penetration resistance of samples was increased significantly after MICP treatment. Sand additives significantly improve the MICP treatment effects, which becomes pronounced when sand content reaches 20% or more. This is mainly due to that sand additives provide relatively spacious pore structures facilitating MICP treatment solution infiltration. Furthermore, sand additives form a skeleton and significantly increase MICP-treated soil structure strength. Analyses of soil particle size distribution curves and SEM images indicate that a stable soil structure was formed contributing to sand skeleton, calcite precipitation, and clayey soil aggregations. The bridge and cementation effect of MICP and the skeleton effect of sand combine to provide prospective resistance against soil erosion.