Influence of Confinement and Cementation Level on the Behavior of Microbial-Induced Calcite Precipitated Sands under Monotonic Drained Loading

Microbial-induced calcite precipitation (MICP) is a novel ground improvement method to increase strength and stiffness of sand using natural biogeochemical processes. Cementation level and confining pressure are two important factors that control the behavior of MICP sand. The monotonic mechanical response of MICP cemented sand is systematically investigated using four cementation levels (untreated, lightly treated, moderately treated, and heavily treated) and three levels of effective confining pressure (100, 200, and 400 kPa). The results indicate that the stiffness, peak shear strength, and dilation increases with an increase in calcite content at a given effective confining pressure and the dilation is suppressed with an increase in effective confining pressure. This behavior is consistent with soil-like behavior; therefore, all the MICP soils presented herein are evaluated using critical-state soil mechanics and not an analogous fracture-mechanics framework. The experimental results also indicate that the improvement in peak and residual friction angles and initial elastic modulus, Ei, are dependent on the levels of cementation and effective confining pressure. The uniformity of MICP cementation in the laboratory specimens is also discussed.