Dynamic response of liquefiable sand improved by microbial-induced calcite precipitation

TLDR

The study explores microbial‑induced calcite precipitation (MICP) as a bio‑mediated method to mitigate liquefaction in sand. The authors performed centrifuge tests on MICP‑treated sands at light, moderate, and heavy cementation levels, measuring shear‑wave velocity, pore pressures, accelerations, and settlements under sine‑wave ground motions to assess cementation integrity and dynamic response. Cementation changed behavior from soil‑like to rock‑like, increasing resistance to liquefaction, reducing excess pore pressure ratios and post‑shaking settlements, but heavy cementation amplified surface accelerations, indicating a trade‑off between liquefaction resistance and surface acceleration.

Abstract

Microbial-induced calcite precipitation (MICP), a novel bio-mediated ground improvement method, was explored to mitigate liquefaction-prone soils. Geotechnical centrifuge tests were used to evaluate cementation integrity and the response of MICP cemented sands to dynamic loading. The cementation integrity testing reveals a change in behaviour from ‘soil like' to ‘rock like', with an increase in treatment level. Results from dynamic testing demonstrate a clear increase in resistance to liquefaction of MICP-treated sands compared to untreated loose sand. The MICP sands were treated to varying levels of cementation (light, moderate and heavy cementation levels) and assessed using non-destructive shear wave velocity measurements. The centrifuge models were all subjected to ground motions consisting of sine waves with increasing amplitudes. Accelerations, pore pressures and settlements were measured in the soil during shaking, and the changes in soil behaviour and post-shaking shear wave velocity for soils prepared to different cementation levels are discussed. Increased resistance to liquefaction was demonstrated with a decrease in excess pore pressure ratios in the MICP-treated models, as well as in reduced post-shaking settlements; however, surface accelerations were amplified at heavy levels of cementation. A tradeoff between improving liquefaction resistance and minimising undesirable higher surface accelerations needs to be considered when designing the soil improvement level.