Liquefaction Experiments and Analysis Projects (LEAP) is an international collaborative project that aims to validate and quantify uncertainties in centrifuge tests and numerical simulations on liquefaction. The LEAP-2020 and LEAP-2022 exercises focused on studying the response of a uniform liquefiable sand layer supported by a sheet pile wall with varying embedment depths. This paper presents the results of five centrifuge tests conducted at Ehime University, which were performed to verify the reproducibility of the experiments and assess the effects of relative density of the soil and embedment depth of the sheet pile. The paper provides detailed information on the model preparation process, including the arrangement of sensors, sand placement, and saturation procedures. It presents profiles of penetration resistance obtained from cone penetration tests and compares them with results from previous LEAP exercise. The paper describes typical experimental results, including acceleration response, excess pore pressure response, and sheet pile wall response. The paper also discusses soil deformation, visualized using the PIV technique from a side view of the model.

The primary objective of this research study is to conduct a comprehensive sensitivity analysis that evaluates two critical aspects: the impact of joint element parameter settings in the self-weight analysis stage to the dynamic analysis and the influence of variations in the Rayleigh damping ratio during the dynamic analysis stage. This investigation extends previous research to identify the causes of instability observed in the LEAP 2022 prediction B data. While prior studies have addressed calibration issues, this paper focuses on the role of initial boundary condition settings and the Rayleigh damping ratio. Two critical sensitivity analyses were carried out in this study. The first analysis focused on joint element parameters from those utilized in the 2022 LEAP project and modified. By systematically altering these parameters, the study aimed to understand their impact on three key performance indicators: the displacement of sheet piles, excess pore water pressure, and acceleration response. The second sensitivity analysis was centered on the Rayleigh damping ratio during the dynamic analysis stage. This analysis was unique in that it adjusted the Rayleigh damping ratio to scrutinize its influence on the displacement of sheet piles with various calibration sets. The various calibration sets were employed to ensure the robustness of the findings. The finite element numerical analysis program FLIP was used to perform these sensitivity analyses. The results generated from FLIP, using multiple calibration sets, provided valuable insights into the response of the system under different initial conditions and parameter settings. The study underscored that even minor alterations in initial boundary conditions can significantly impact the accuracy and stability of dynamic analysis outcomes. This study provides valuable insights while discussing limitations that can be improved through further research and suggests areas for future study. The study aims to enhance the accuracy and reliability of dynamic analysis in numerical simulations, contributing to earthquake engineering and geotechnical investigations in a similar vein with the objectives of the LEAP project by providing a comprehensive understanding of factors affecting stability and accuracy.

The Liquefaction Experiments and Analysis Projects (LEAP) have provided an excellent international collaborative platform for liquefaction research and have stimulated advances in both experimental and numerical modelling. This paper summarizes the findings gained by the Tsinghua University team within the LEAP events from 2017 to 2022 from a numerical simulation perspective. Numerical prediction and simulation of two categories of centrifuge models, mildly sloping ground and sheet pile wall in saturated sand, were performed in four LEAP events during this period at Tsinghua University, using the CycLiq plasticity constitutive model, which was developed with special attention on reflecting soil liquefaction behaviour. Development and calibration of the constitutive model advanced with the accumulation of element test data, from triaxial tests, hollow cylinder torsional shear tests, and direct simple shear tests. These developments have shown to be crucial to improving the prediction capabilities for soil liquefaction for boundary value problems. Two numerical simulation frameworks, OpenSees and FLAC3D, were used for the simulation of the two categories of centrifuge models, respectively. Insights were also gained on key numerical aspects for the successful simulation of the centrifuge tests.

Analysis of the seismic design of retaining structures is complex due to the intricate interplay between the response of backfill soil and supporting wall. When dealing with liquefiable soils, numerical modeling is often employed to gain insight into the mechanisms behind the resulting deformation of retaining walls during earthquakes. This paper focuses on detailed numerical modeling of two well-documented centrifuge tests of such systems from the last two rounds of LEAP, with different embedment ratios and shaking intensities, and their impacts on the system response of the sheet-pile wall supporting a liquefiable submerged deposit. First, a soil constitutive model is calibrated using data from cyclic direct simple shear tests. The two centrifuge models with different wall embedment ratios and shaking intensities are then simulated and used for validation and assessment purposes. The numerical model shows a successful performance in capturing the system response for both models. Assessing details of the stress-strain response in the numerical model reveals two dominant cyclic deformation mechanisms in the backfill soil: cyclic mobility and the accumulation of residual deformation. The success of the adopted numerical approach in capturing the experimental results is attributed to the constitutive model's ability to simulate both of these cyclic deformation mechanisms.

The 2020 Liquefaction Experiments and Analysis Projects (LEAP) included 23 centrifuge tests of a saturated Ottawa sand deposit supported by a cantilever (rigid) sheet-pile quay wall. In this paper, a Gaussian process regression is used to assess the complex non-linear relationship between the backfill lateral displacements and the input motion initial experimental conditions. The conducted analyses showed that the LEAP-2020 experimental results are consistent and shed light on a number of salient characteristics and trends of the soil lateral displacements and interaction with the retaining wall during liquefaction.

Seismic response of geostructures in liquefiable soils is often quite complex and may involve several factors that contribute to the key mechanisms affecting the overall performance. However, in some cases, if critical mechanisms are well understood, it might be possible to estimate the system response by using relatively simple analytical tools. This study investigates the potential use of direct simple shear (DSS) test in estimating the seismic response of sheet-pile retaining structures supporting liquefiable soils. Through a comprehensive analysis of the centrifuge experiments carried out as part of the 2022 Liquefaction Experiments and Analysis Projects (LEAP-2022), coupled with Type-C numerical simulations of the centrifuge experiments, it is observed that the sheet-pile wall response is critically related to the stress-strain response of the soil near the tip of the sheet-pile wall which is embedded in a dense layer of Ottawa F65 sand. An in-depth understanding of such stress-strain response using laboratory-based element tests might provide a means to estimate the wall rotation and its lateral displacements. To this end, simplified numerical analyses were performed to estimate the initial vertical effective stress and time-history of shear stresses caused by the earthquake near the tip of the sheet-pile wall. Then, several specimens of Ottawa F65 sand were prepared at relative densities comparable to the values achieved in the LEAP-2022 centrifuge experiments and were subjected to the estimated shear stress time-histories. By assuming a rigid body motion of the sheet-pile wall during earthquake, the rotation of the wall at the end of earthquake motion was then estimated using the permanent shear strains measured in the DSS tests. It is observed that the estimated rotations of the sheet-pile wall compare well with the rotations observed in the centrifuge tests and those obtained in Type-C numerical simulations. In these cases, DSS tests are shown to provide a relatively simple means for estimating the rotations of the sheet-pile wall.

Seismic performance of bridge abutments founded in potentially liquefiable soils is of significant interest to researcher and practitioners in geotechnical earthquake engineering. Piles are typically a key element of these geo-structures and may undergo large deformations and rotations when their lateral support is significantly reduced or momentarily lost due to the occurrence of earthquake-induced soil liquefaction. Observations from the past earthquakes show that in addition to material nonlinearity, geometric nonlinearity of the pile may also play an important role in the overall response of the foundation. In this work, a series of finite element analyses are carried out to assess the effects of material and geometric nonlinearities on the response of a pile embedded in liquefiable soil. The results of these numerical simulations are compared with the responses observed in the centrifuge experiments, performed at Kyoto University, modeling the same boundary value problem in Toyoura sand. The constitutive model used in the simulations is calibrated against a series of cyclic direct simple shear (CDSS) tests conducted at the George Washington University on Toyoura sand. The simulation results demonstrate that in addition to material nonlinearity of the pile material, geometric nonlinearity plays a critical role in modeling of the pile response, and without proper consideration of these effect, the overall response of the pile will not be accurately represented by the numerical simulations.