Centrifuge Model Tests to Investigate the Effect of Microbially Induced Calcite Precipitation Treatment Extent within a Loose Liquefiable Sand Profile

Ground improvement of liquefiable soils through microbially induced calcite precipitation (MICP) has been shown in previous experiments to be a viable option to increase liquefaction triggering resistance. However, it is unknown how the spatial extent of improvement affects the system performance of an MICP improved soil. In this study, centrifuge experiments were performed on models with treatment depths ranging from 37% to 100% of the liquefiable layer thickness. Additional tests were conducted on untreated (uncemented) and fully cemented baseline models were included for comparison. All models were pluviated with loose Ottawa F-65 sand (DR∼40%) and were subjected to eight sinusoidal shaking events. Dense in situ instrumentation arrays tracked accelerations, pore pressure generation, and liquefaction triggering. Bender elements within the cemented zones measured cementation degradation. Through this study, it is shown that partial MICP improvement with depth can generate a base isolation-type mechanism when underlying soil liquefies and thus reduce the intensity of the ground motion in the overlying improved zone. Reductions in ground seismic demand decreases the extent of cementation degradation and prevents liquefaction triggering within the cemented zone. In contrast, MICP cementation improvement of the entire (100%) depth transmits significant shear stress through the soil column, which results in rapid cementation degradation.