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A set of saturated Ottawa sand models was 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 were compared to a pair of uncemented saturated Ottawa sand models with initial DR0≈38 and 53% and subjected to similar levels of shaking. Cone penetration resistances and shear wave velocities were 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 were used to monitor the effect of cementation on liquefaction triggering and consequences. Cone penetration resistances and shear wave velocities were sensitive to light, moderate, and heavy levels of cementation (increases in penetration resistance from 2 to 5 MPa, from 2 to 10 MPa, and from 2 to 18 MPa and increases in shear wave velocity from 140 to 200 m/s, from 140 to 325 m/s, and from 140 to 660 m/s, respectively), and were able to capture the effects of cementation degradation.

The effects of shaking history on cone penetration test (CPT)-based liquefaction triggering correlations for clean saturated sand are examined by using cone penetration resistance and cyclic strength data pairs from dynamic centrifuge model tests. Three model tests on a 9-m-radius centrifuge examined the liquefaction responses of level profiles of saturated Ottawa F-65 sand subjected to multiple (17-29) shaking events that produced successive changes in density and model response characteristics. Inverse analysis of data from dense accelerometer arrays were used to define time series of cyclic stress ratios and shear strains throughout the profile. Cyclic resistance ratios against triggering of ~100% excess pore pressure ratio in 15 equivalent uniform cycles were computed at multiple depths based on weighting of the cyclic stress ratio time series up to the time of triggering. Cone penetration tests performed at select times during each model test were used to define the variation in cone tip resistances with depth and shaking history. The resulting data pairs, with normalized cone tip resistances ranging from 20 to 340 and cyclic resistance ratios ranging from 0.1 to 2.0, show that both quantities progressively increase as a result of recurrent liquefaction events and generally follow the trends predicted by case history-based liquefaction triggering correlations. Three 1-m-radius centrifuge tests of similar configurations produced consistent results. Implications for the interpretation of case histories and engineering practice are discussed.

Inverse analyses were used to evaluate the degree of partial drainage occurring during dynamic shaking of liquefying soil profiles in a set of centrifuge model tests. Three tests were performed using the 9-m radius centrifuge at the UC Davis Center for Geotechnical Modeling on saturated Ottawa sand models with initial relative densities of 25, 43, and 80%. Models were subjected to multiple sinusoidal shaking events with acceleration amplitudes ranging from 0.03 to 0.55g. Densely spaced pore pressure transducer arrays provided profiles of pore pressure generation and dissipation; inverse analyses of the pore pressure data were used to obtain volumetric strain profiles during shaking and dissipation. Surface settlements computed by integrating the volumetric strain profiles are compared to surface settlements measured from linear potentiometers. The magnitude of the volumetric strains due to partial drainage and their potential effects on liquefaction responses are discussed.