Effect of sand particle size on interface shear behaviour between bio-cemented sand by MICP treatment and steel structure

This study presents an experimental investigation of the effect of sand particle size on the shear behaviour of bio-cemented sand-steel structure interface, with sand treated by microbially induced calcite precipitation (MICP). Five sand groups were involved with different median particle sizes. The MICP treatment followed the surface percolation method featuring bacterial suspensions with a fixed optical density (linearly related to active cell concentration or urease activity). Scanning electron microscopy was used to identify the microstructure of the samples, while interface shear test was performed to observe the macroscale mechanical behaviour. The testing results indicated that smaller sand particle size was associated with a relatively larger effective calcium carbonate bonding area, providing a more significant bonding effect. Thus, smaller sand particle sizes in the treated samples were associated with higher values for the interface cohesion and a more pronounced increase in the interface friction angle at the peak state (compared to the corresponding untreated samples). By contrast, because the bonding effect broke close to the interface during shearing, the bottom of the treated samples became planar and smooth. Hence, a lower interface friction angle at the ultimate state was identified for a treated sample, compared to the corresponding untreated one.