Quantifying Level of Microbial-Induced Cementation for Cyclically Loaded Sand

Abstract

Microbial-induced calcite precipitation (MICP) is a novel soil-improvement technique that improves the behavior of sands subjected to dynamic loading. The level of cementation of MICP-treated sands is commonly quantified using mass of calcite precipitation; however, mass of calcite is not a unique measure for material behavior as other factors, such as the distribution of calcite precipitation at the particle contacts, would also affect the mechanical behavior of MICP-treated sands. Therefore, mass of calcite alone may not be appropriate to characterize material behavior. This study illustrates the importance of using shear-wave velocity in addition to mass of calcite to quantify the level of MICP cementation to the corresponding material behavior, since shear-wave velocity is not only affected by the mass of calcite, but also influenced by the distribution of calcite precipitation at the particle contacts. Two specimens are cemented with the MICP process to the same mass of calcite value but to different shear-wave velocities and then cyclically loaded. The observed mechanical behavior of the specimens indicates the specimen with higher shear-wave velocity possesses larger liquefaction resistance compared to the specimen with lower shear velocity, which provides evidence that the material behavior of MICP-treated sands is not only affected by the precipitated mass of calcite, but also influenced by the distribution pattern of calcite precipitation.