Centrifuge Model Testing of Liquefaction Mitigation via Microbially Induced Calcite Precipitation

Abstract

A set of saturated Ottawa sand models were treated with Microbially Induced Calcite Precipitation (MICP) and subjected to repeated shaking events using the 1-m radius centrifuge at the UC Davis Center for Geotechnical Modeling. Centrifuge models were constructed to initial relative densities (DR0) of approximately 38% and treated to light, moderate, and heavy levels of cementation (calcium carbonate contents by mass of approximately 0.8%, 1.4%, and 2.2%, respectively) as indicated by shear wave velocities (light ≈200 m/s, moderate ≈325 m/s, and heavy ≈600 m/s). The cemented centrifuge models are compared to a pair of uncemented saturated Ottawa sand models with initial DR0s of ≈38 and ≈53% and subjected to similar levels of shaking. Cone penetration resistances and shear wave velocities are monitored throughout shaking to investigate (1) the effect of cementation on cone penetration resistance, shear wave velocity, and cyclic resistance to liquefaction triggering and (2) the effect of shaking on cementation degradation. Accelerometers, pore pressure transducers, and a linear potentiometer are used to monitor the effect of cementation on liquefaction triggering and consequences. Cone penetration resistances and shear wave velocities are sensitive to light, moderate, and heavy levels of cementation (increases in penetration resistance from 2 to 5 MPa, 2 to 10 MPa, and 2 to 18 MPa and shear wave velocity from 140 to 200 m/s, 140 to 325 m/s, and 140 to 660 m/s, respectively), and are able to capture the effects of cementation degradation.

Centrifuge Model Testing of Liquefaction Mitigation via Microbially Induced Calcite Precipitation

“…After reaching the target Vs level, ≈ 40 L of a deaired solution of methycellulose and DI water prepared to a viscosity of ≈ 5 x10 -5 m 2 /s was pumped through each cemented model from the base ports at a rate of 0.35 L/min. Previous studies (e.g., Darby et al 2018) had not increased the pore fluid viscosity post treatment, and they observed significant drainage effects during shaking. Based on those observations, this study used an increased pore fluid viscosity to better match dynamic scaling laws at elevated g-level and minimize partial drainage during cyclic loading while ensuring the model was constructible (Stewart et al 1998).…”

“…MICP achieves bio-cementation through the addition of calcium ions in treatment solutions and microbial urea hydrolysis wherein urease enzymes hydrolyze supplied urea to produce ammonia and dissolved inorganic carbon (Fujita et al 2008). Bio-cementation has been shown to improve the engineering properties of sands including: increased initial shear stiffness, peak shear strength, and resistance to liquefaction triggering (DeJong et al 2006;Whiffin et al 2007;Montoya et al 2013;Montoya and DeJong 2015;Zamani and Montoya 2017;Darby et al 2018;Feng and Montoya 2017;Xiao et al 2018).…”

Cyclic behavior of bio-cemented soils using relatively large grains

“…Larger peak base accelerations were needed to trigger liquefaction in MICP-treated samples compared to untreated samples. These improvements increased with increasing cementation level (Darby et al, 2019). In cyclic triaxial studies, https://doi.org/10.3208/jgssp.v09.cpeg147 reduced build-up of excess pore pressure was also observed.…”

Characteristic limitations of advanced plasticity and hypoplasticity models for cyclic loading of sands

“…In the literature, different criteria were proposed to define initial liquefaction. A common approach is based on the excess pore pressure ratio r u ¼ u acc w =p 0 0 ¼ 0:95 [1,9,54] or r u ¼ 1 [29,70,73], where u acc w is the excess pore water pressure. In addition, some other works defined initial liquefaction based on a single strain amplitude (maximum strain in a given cycle only in compression or extension) of e SA 1 ¼ 2:5% [e.g., 57,59,23,47] or double strain amplitudes (the strain amplitude of a given cycle in compression and extension) of e DA 1 ¼ 5% [e.g., 27,32,66].…”