Centrifuge Tests to Investigate the Effect of MICP Treatment Zone on Foundation System Performance

Ground improvement is often used in engineering practice to mitigate the effects of liquefaction in the built environment. Prior centrifuge studies using bio-cementation (microbially induced calcite precipitation, MICP) have demonstrated increased liquefaction triggering resistance and reduced associated settlements by treating the entire soil model. One additional centrifuge test that treated discrete MICP zones within the soil model also showed improvement, but the complex interactions between the treated zones made it difficult to elucidate how treatment depth impacted system performance. This paper presents 1-m centrifuge experiments performed at the Center for Geotechnical Modeling at the University of California, Davis, to investigate how performance improvement relates to the dimensions and cementation level of a discrete MICP treated zone. Models were constructed with Ottawa F-65 sand at an initially loose state (D_R ≤ 50%) with different treatment zone dimensions. In one model, the entire soil body was cemented (18.9 × 39.6 × 8.22 m in prototype scale), while in the second and third models an 8 × 8 m plan area was treated to a depth of 8.22 m (100% depth), and 3.05 m (37% depth). The stiffness levels for the treated zone were selected and tracked using shear wave velocity with a target of ΔV_s = 300 m/s relative to an untreated model. In addition, a baseline uncemented model constructed at the same relative density was tested for comparison. All models were subjected to eight shaking events. Shear wave velocity measurements tracked changes in biocementation integrity through the progression of the shaking events. System performance during shaking was monitored using accelerometers, a linear potentiometer, and pore pressure transducers. Cone penetration soundings were used to measure the initial model state and track the model evolution. All models treated with MICP showed improved liquefaction resistance when compared to untreated models, which varied with MICP treatment zone dimensions.