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1. Liquefaction of a sloping deposit: LEAP-2017 centrifuge tests at Rensselaer Polytechnic Institute

   Korre, E.; Abdoun, T.; Zeghal, M. (April 2020, Soil dynamics and earthquake engineering)

   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. 

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2. LEAP-UCD-2017 Centrifuge Test at University of California, Davis

   https://doi.org/10.1007/978-3-030-22818-7_13  

   Carey, Trevor J.; Stone, Nicholas; Bonab, Masoud H.; Kutter, Bruce L. (January 2020, Model Tests and Numerical Simulations of Liquefaction and Lateral Spreading)

   Three centrifuge experiments were performed at the University of California, Davis, for LEAP-UCD-2017. LEAP is a collaborative effort to assess repeatability of centrifuge test results and to provide data for the validation of numerical models used to predict the effects of liquefaction. The model configuration used the same geometry as the LEAP-GWU-2015 exercise: a submerged slope of Ottawa F-65 sand inclined at 5 degrees in a rigid container. This paper focuses on presenting results from the two destructive ground motions from each of the three centrifuge models. The effect of each destructive ground motion is evaluated by accelerometer recordings, pore pressure response, and lateral deformation of the soil surface. New techniques were implemented for measuring liquefaction-induced lateral deformations using five GoPro cameras and GEO-PIV software. The methods for measuring the achieved density of the as-built model are also discussed. 

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3. Development of Experimental P-Y Curves from Centrifuge Tests for Piles Subjected to Static Loading and Liquefaction-Induced Lateral Spreading

   https://doi.org/10.37308/DFIJnl.20191120.212  

   Souri, Milad (October 2020, DFI Journal The Journal of the Deep Foundations Institute)

   The results of five centrifuge models were used to evaluate the response of pile-supported wharves subjected to inertial and liquefaction-induced lateral spreading loads. The centrifuge models contained pile groups that were embedded in rockfill dikes over layers of loose to dense sand and were shaken by a series of ground motions. The p-y curves were back-calculated for both dynamic and static loading from centrifuge data and were compared against commonly used American Petroleum Institute p-y relationships. It was found that liquefaction in loose sand resulted in a significant reduction in ultimate soil resistance. It was also found that incorporating p-multipliers that are proportional to the pore water pressure ratio in granular materials is adequate for estimating pile demands in pseudo-static analysis. The unique contribution of this study is that the piles in these tests were subjected to combined effects of inertial loads from the superstructure and kinematic loads from liquefaction-induced lateral spreading. 

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4. Effects of Small Variability of Soil Density on the Consequences of Liquefaction

   https://doi.org/http://ascelibrary.org/doi/abs/10.1061/9780784480700.002  

   ElGhoraiby, M.A.; Manzari, M.T.; Hamdar, S.H. (June 2017, Geo-Risk 2017)

   The effects of small inherent variability of soil density on the consequences of liquefaction such as lateral spreading and excessive settlements may have significant practical implications. Here, the effect of variability on soil density is evaluated for mildly sloping soil specimens that are tested in a series of centrifuge tests at different facilities. While every effort was made to prepare the specimens with uniform densities, the achieved densities at different facilities showed a small variation relative to the target density. This paper presents an attempt to investigate the impact of such variability on the expected response of the soil, particularly when it reaches a liquefaction state. A Monte Carlo simulation was conducted using a non-linear effective stress analysis and an elastoplastic constitutive model for sand. The simulation results show that the small variation of density in the soil specimen leads to a relatively small range of variation for lateral displacements, acceleration, and excess pore pressure ratios. However the range of settlements calculated on the ground surface was rather large, with the coefficient of variation ranging from 8% to 30% depending on the type of variability considered. Potential reasons for such drastic differences among various components of the soil response are discussed. 

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5. LEAP-2017 Simulation Exercise: Calibration of Constitutive Models and Simulation of the Element Tests

   https://doi.org/10.1007/978-3-030-22818-7_9  

   Manzari, M.T. (November 2019, Proceedings of LEAP-UCD-2017 workshop)

   This paper presents a summary of the element test simulations (calibration simulations) submitted by 11 numerical simulation (prediction) teams that participated in the LEAP-2017 prediction exercise. A significant number of monotonic and cyclic triaxial (Vasko, An investigation into the behavior of Ottawa sand through monotonic and cyclic shear tests. Masters Thesis, The George Washington University, 2015; Vasko et al., LEAP-GWU-2015 Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019) and direct simple shear tests (Bastidas, Ottawa F-65 Sand Characterization. PhD Dissertation, University of California, Davis, 2016) are available for Ottawa F-65 sand. The focus of this element test simulation exercise is to assess the performance of the constitutive models used by participating team in simulating the results of undrained stress-controlled cyclic triaxial tests on Ottawa F-65 sand for three different void ratios (El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019). The simulated stress paths, stress-strain responses, and liquefaction strength curves show that majority of the models used in this exercise are able to provide a reasonably good match to liquefaction strength curves for the highest void ratio (0.585) but the differences between the simulations and experiments become larger for the lower void ratios (0.542 and 0.515). 

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