December 2024
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21 Reads
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December 2024
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21 Reads
November 2024
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29 Reads
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1 Citation
Engineering Geology
August 2024
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111 Reads
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2 Citations
Acta Geotechnica
Granular soil generally exhibits an anisotropic stiffness in engineering but challenging to quantify in situ and laboratory condition, due to a lack of the appropriate factor and quantitative research. In this paper, discrete element method is employed to create two typical types of soil fabric and conduct shear wave measurement in double direction, with the microscopic parameters monitored to investigate the connection with macroscopic stiffness anisotropy. The results show that the reference fabric increases as fabric anisotropy increases first and then decreases with further increase in the XZ stress plane, while always decreases approximately linearly in the XY stress plane. The reference fabric is determined by the contact density in the direction of wave propagation and particle perturbation under microscale examination. The results also reveal a linear relationship between the macroscopic stiffness anisotropy and microscopic fabric anisotropy, which could be used as an effective method to reflect the degree of anisotropy in situ by wave measurement. And the applicability of the expression of small-strain shear modulus is also discussed.
August 2024
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34 Reads
Soil Dynamics and Earthquake Engineering
August 2024
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134 Reads
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1 Citation
Computers and Geotechnics
The hollow cylinder apparatus (HCA) is capable of achieving non-proportional stress paths and has been extensively employed to replicate stress paths with rotating principal stress in laboratory element tests. However, only macro-mechanical parameters could be observed in laboratory HCA tests and there is lack of information to understand the evolution of microscale parameters during the loading process. As a promising numerical technique, the discrete element method (DEM) allows investigation of the responses of virtual granular samples under general loading conditions and provides ideal numerical results to overcome the aforementioned limitations. In this study, a novel approach to DEM simulation of the hollow torsional shear apparatus for achieving the general loading paths was introduced. Two algorithms including the stress-controlled and the mixed-controlled loading were developed. Application cases indicated that both undrained monotonic and cyclic loading paths were successfully reproduced by using the proposed algorithms. Compared with results from the literature, DEM results demonstrated that this approach could reasonably reproduce the behaviour of granular material under general loading conditions, including aspects such as dilatancy and pore water pressure generation.
June 2024
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21 Reads
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1 Citation
Soil Dynamics and Earthquake Engineering
Existing study shows that small-strain shear modulus is a promising parameter for characterizing soil liquefaction resistance, while liquefaction resistance is liquefaction type dependent. In this study, firstly a revisit of laboratory tests on saturated sands was conducted to explore the relationship between liquefaction resistance CRR and small-strain shear modulus Gmax with emphasis on cyclic mobility type of liquefaction. The investigation indicates that in the stress-normalized space of cyclic resistance and small-strain shear modulus, the fitting curve of soil testing data does not always approach to the coordinate origin and there will be an intercept on the abscissa axis. Based on this finding, a more general form of the power function between liquefaction resistance and small strain shear modulus is proposed. Then, undrained cyclic triaxial tests were conducted in conjunction with the data available from LEAP to establish the power function between CRR and Gmax for medium dense to dense Ottawa F-65 sand, which leads to an updated characterization model on the basis of Zhou-Chen model. Finally, centrifuge model tests of submerged gently sloping ground of Ottawa F-65 sand conducted at Zhejiang University (i.e., ZJU) for LEAP were used to compile liquefaction and non-liquefaction case histories with shear wave velocity measurement to investigate the validity of the updated model for evaluating the cyclic mobility type of liquefaction. The test results show that the updated model could classify the case history datasets produced by centrifuge model tests well. And the further consideration of initial shear stress acting on the slope could enhance the evaluation performance of this characterization model, which is worth of further research.
June 2024
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43 Reads
Japanese Geotechnical Society Special Publication
To validate the generalized scaling law (GSL) from both macroscopic and microscopic scales, and investigate the validity of Rocha's assumption under both drained and undrained condition, the monotonic drained and undrained triaxial tests of granular assembly were performed by using discrete element method (DEM) simulations. The tests were performed with initial confining pressures of 50 kPa, 100 kPa, 200 kPa and 500 kPa, where the specimens of 500 kPa were considered as the prototype and the others treated as the model. The results of the drained triaxial tests show that, if a normalized strain is introduced, the stress-strain relationship and the evolution of microscopic parameter ac could be normalized before the peak, which implies that the Rocha's assumption holds true at both macroscopic and microscopic scales before the peak. However, the normalized strain is smaller than that recommended by the Type II GSL. The undrained test results indicate that the stress-strain curve could be normalized before phase transformation state, while could not be normalized due to the difference of initial mechanical average coordination number between the model and the prototype after phase transformation state.
June 2024
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41 Reads
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4 Citations
Soil Dynamics and Earthquake Engineering
May 2024
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27 Reads
Computers and Geotechnics
This paper presents a computational sand model based on the well-known pressure dependent multi-surface constitutive model to solve the necessity of employing a separate set of model parameters for each soil relative density change. The proposed model correlates the original model parameters with the soil relative density through critical-state-based soil mechanics formulations to provide a single set of model constants that adapt to different soil states. Model formulation updates are performed for the flow rules, material moduli calculations, and the computation of stress ratios at the phase transformation and failure stages. The model parameters are calibrated for Ottawa F-65 sand against cyclic soil element tests with different stress levels and various soil densities. Thereafter, numerical simulations are conducted for centrifuge experiments of gently sloped grounds to validate the proposed model. Throughout numerical simulations, the proposed model accurately replicates the sand cyclic undrained behavior as similar to laboratory-measured responses for different soil relative densities with a single calibrated set of model parameters and provides reliable numerical predictions in finite element simulations of the engaged centrifuge experiments. Overall, the proposed model robustly simulates the saturated sand seismic response, which can improve the numerical prediction accuracy of liquefaction-induced damage in different engineering applications.
April 2024
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22 Reads
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1 Citation
Engineering Geology
... In addition, the CRR-V s1 correlation of Ottawa F-65 sand was established using a modified Zhou and Chen model [37] as follows: ...
June 2024
Soil Dynamics and Earthquake Engineering
... The CPT results before and after shaking of RPI10-2020 are shown in Fig. 4. The CPT probe malfunctioned during the RPI_REP-2020 test. The linearity of the shown curves indicates that the model was constructed with practically uniform relative density (i.e., constant along the depth [16]). Overall, the measured CPT results are consistent with the ones obtained in LEAP-2017 tests that were conducted with Dr = 65% [10,17]. ...
June 2024
Soil Dynamics and Earthquake Engineering
... In the first phase (i.e., model calibration), the numerical simulation teams were provided with a series of hollow cylinder torsional shear tests and direct simple shear tests to calibrate their constitutive models. Ueda et al. (2023) present an overview of the results of the first phase. In the second phase of the simulation exercise, the numerical simulation teams performed Type-C or Type-B simulations using their constitutive models, which were calibrated in the first phase, with or without iterative adjustment of the model parameters. ...
February 2024
... The constitutive model and the analysis platform used by each numerical simulation team are also listed in the table. Mode-detailed information of each constitutive model and the numerical simulation techniques used by each simulation team are provided in separate papers(Tanaka et al., 2023;Hyodo & Ichii, 2023;Fasano et al., 2023;Qiu & Elgamal, 2023;Elbadawy & Zhou, 2023;Reyes et al., 2023; Wang et al., 2023). ...
February 2024
... Figure 3.3 illustrates the surface marker locations for displacement measurement (top view). As part of the LEAP-ASIA-2019 project, 10 institutes performed 24 centrifuge model tests in total (Tobita et al., 2022Madabhushi et al., 2023;Stone et al., 2023;Escoffier et al., 2023;Manandhar et al., 2023;Vargas et al., 2023;Korre et al., 2023;Ma et al., 2023). Since another aim of the LEAP-ASIA-2019 project is to validate the "generalized scaling law" for centrifuge modeling (Iai et al., 2005) as noted in Introduction, 11 model tests applied the conventional centrifuge scaling law (hereafter called "Model A"), while 13 model tests did the "generalized scaling law" (hereafter called "Model B"). ...
February 2024
... A lateral expansion is brought on by applying a load at the top of the stone column, which in turn increases the stone column's additional confinement by the surrounding clay. As a result of reaching equilibrium, the vertical displacement is reduced [39][40][41]. This technique was first used to improve native soil in France around 1830. ...
February 2024
Soil Dynamics and Earthquake Engineering
... Research indicates that Deep Soil Mixing (DSM) columns are effective in reducing liquefaction potential by preventing shear deformation and reducing excess pore water pressure. Numerous numerical studies have been conducted to understand the performance of DSM columns and their impact on liquefiable soils (Baez 1995;Özener 2019, 2022;Zhang et al. 2022a, b;Hasheminezhad and Bahadori 2023;Khoshemehr and Bahadori 2023;Montesi et al. 2023;Can et al. 2024;Cao et al. 2024). ...
February 2024
Computers and Geotechnics
... Zhou et al. (2020) conducted several centrifuge experiments and noticed a similar response for the newly developed servohydraulic actuator installed on the geotechnical centrifuge facility at Zhejiang University. They suggested that the interaction of the system could be a possible cause of the high-frequency FFT component and should be considered an inherent characteristic of the shaking table (Cao et al., 2024). However, the extent of high-frequency FFT spectral magnitude in the case of servohydraulic actuator depend on the particular custom-made earthquake simulator and may be nullified depending on the shaker (as an example, shaker at the Nippon Koei Co. Ltd. depicted in Figure 16(c)). ...
January 2024
Soil Dynamics and Earthquake Engineering
... where ρ is the saturated density of soils, z is the coordinate in vertical direction, t is time and u is the displacement in x direction. Then, the horizontal shear stresses were converted to CSR 7.5 following the procedures introduced by Ref. [34]. Herein, CSR 7.5 is the cyclic stress ratio corresponding to the earthquake magnitude of M w = 7.5, the equivalent loading cycles of which is N eq = 15 in most cases [35]. ...
October 2023
Soil Dynamics and Earthquake Engineering
... With the increase in computing power, state-of-the-art methods for two-or three-dimensional models have been developed to simulate soil seismic response in more complex conditions. [15][16][17] However, creating an accurate physics-based soil seismic response model requires extensive prior knowledge of soil site characteristics, including physical and mechanical parameters. Unfortunately, obtaining precise parameters proves challenging due to the inherent complexity of geotechnical materials. ...
June 2023
Earthquake Engineering & Structural Dynamics