Liquefaction triggering and post-triggering behavior of biocemented loose sand

Abstract

Biocementation is a biomediated ground improvement technique that can improve the engineering behavior of granular soils. The process has received significant attention as an earthquake-induced liquefaction mitigation technique; however, critical gaps have remained in our understanding of how liquefaction behaviors may shift with differences in loading magnitudes and cementation levels. In this study, direct simple shear tests were performed to examine the undrained shearing behaviors of biocemented loose Ottawa F-65 sand prepared to varying cementation levels corresponding to Vs increases up to 523 m/s. Significant increases in liquefaction triggering resistances were observed with added cementation across a broad range of loading magnitudes (CSR = 0.1–1.75) and exceeded improvements obtainable through densification alone. Following triggering, modest improvements in post-triggering strain accumulation and reconsolidation behaviors were observed that could be primarily attributed to the densification of specimens from added mineral solids at low cementation levels (Δ Vs < 150 m/s). At higher cementation magnitudes, however, post-triggering behavioral enhancements exceeded those that would be expected from densification alone. Outcomes from this study improve our understanding of the liquefaction behaviors of biocemented soils, the metrics by which these behaviors can be effectively characterized, and the mechanisms responsible for behavioral enhancements, ultimately furthering our understanding of how the technology may be employed for liquefaction mitigation.