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Retaining structures in waterfront areas are sensitive to seismically triggered liquefaction, leading to large deformations of the backfill and the retaining structure. The response of such systems depends heavily on the soil parameters, one of the most important being its relative density. This paper summarizes the key aspects of three centrifuge experiments performed at the Center for Earthquake Engineering Simulation (CEES) at Rensselaer Polytechnic Institute in 2020 as part of the experimental campaign for the Liquefaction Experiments and Analysis Project (LEAP-2020). The three models reflected the same prototype problem of a rigid floating sheet-pile quay wall supporting a 3-m-deep liquefiable soil deposit, of loose, medium dense and dense soil relative densities. The three models observed the same building technique and were subjected to the same target dynamic input motion. 

The LEAP (Liquefaction Experiment and Analysis Project) is a continuing international collaboration to create a reliable databank of high-quality experimental results for the validation of numerical tools. This paper investigates the response of a floating rigid sheet-pile quay wall under conditions of seismically induced liquefaction, embedded in dense sand and supporting a saturated liquefiable soil deposit. The experimental challenges related to repeatability in physical modeling in such a soil-structure-interaction regime are also discussed. To this end, three experiments performed at Rensselaer Polytechnic Institute (RPI) as part of the experimental campaign for the LEAP-2020 are discussed herein. Models RPI_REP-2020 and RPI10-2020 investigate the repeatability potential in centrifuge modeling in the presence of soil-structure-interaction. Model RPI_P-2020 is the pilot test of the LEAP-2020 experimental campaign at RPI and investigates the effect of the wall’s initial orientation on the system’s dynamic response and soil liquefaction, as a possible “defect” in the model construction procedure. The three models were built in a consistent way, employed comparable instrumentation layout while simulating the same prototype and comparable soil conditions. The three models were subjected to the same acceleration target input motion, which was repeated across all three models with high consistency. 

Two centrifuge experiments were conducted at Rensselaer Polytechnic Institute (RPI) to evaluate and assess the validity of the generalized scaling laws. The experiments were performed within the framework of the Liquefaction Experiments and Analysis Project (LEAP) and consisted of testing a saturated sloping deposit subjected to a tapered base input acceleration. The two tested models reflected consistent soil conditions but were built based on different scaling principles. The first model observed the conventional scaling laws for centrifuge physical modeling. The second model reflected the generalized scaling laws. The two tested models exhibited consistent response before liquefaction. The generalized scaling model showed a higher susceptibility to liquefaction and had a higher rate of pore pressure buildup. 

A series of centrifuge tests of a sloping ground were conducted at Rensselaer Polytechnic Institute (RPI). These tests were used to monitor and assess the soil response, in terms of generated accelerations, excess pore water pressure (EPWP) and associated lateral spreading, as a function of variations in the dynamic input motion and soil relative density. This series of tests are part of the Liquefaction Experiments and Analysis Projects (LEAP-2017), an international effort to assess the repeatability and reproducibility of centrifuge experimental results, and verify and validate soil liquefaction numerical tools using the experimental data. 

An analysis is conducted to assess the sensitivity of 17 replicas of a saturated sloping deposit tests conducted within the 2017 Liquefaction Experiments and Analysis Projects (LEAP). A difference analysis is first used to quantify the dissimilarities between recorded input acceleration time histories. This analysis provided a unique decomposition of the differences in terms of phase, frequency-shift, amplitude at 1 Hz, and amplitude of frequency components higher than 2 Hz (2+Hz). A kriging analysis was used to evaluate the sensitivity of the deposit response accelerations to differences in input motion amplitude at 1Hz and 2+Hz and cone penetration resistance. The analysis showed a response that is more sensitive to variations in cone penetration resistance values than to amplitude of the input 1Hz and 2+Hz motion (frequency) components. 

The mean squared deviation between acceleration time histories (of soil-system test replicas) is expressed as a unique aggregate of three discrepancy measures associated with shape, phase, and frequency-shift. The shape-measure quantifies the deviations associated with dissimilarities in form and amplitude. The phase-measure estimates the deviations associated with differences in phase angle. The frequency-shift-measure quantifies the deviations associated with differences in frequency components. These measures were used to assess the discrepancies among six replicas of a centrifuge experiment of a liquefiable soil tested at six different facilities. A sensitivity analysis was thereafter used to assess the effects of input motion discrepancies on a liquefiable soil response. The conducted analysis showed that the acceleration response of the analyzed soil is more sensitive to discrepancies in input motion frequency than in phase or amplitude.