More Like this

1. Modeling the cyclic response of sands for liquefaction analysis

   Manzari, M.T.; El Ghoraiby, M.A.; Kutter, B.L.; Zeghal, M. (July 2019, Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions – Silvestri & Moraci (Eds) © 2019 Associazione Geotecnica Italiana, Rome, Italy, ISBN 978-0-367-14328-2)

   Constitutive relations used to describe the stress-strain-strength behavior of soils in cyclic loading are known to play a critical role on our ability to predict the response of geo-structures to seismic loading. The extent and intricacies of this role, however, are highly problem-dependent and often difficult to discern from the effects of other ingredients of a numerical simulation. Moreover, realistic assessments of constitutive models and numerical analysis techniques require detailed comparisons of their performances with reliable experimental observations. The experimental data that have been produced in the course of recent Liquefaction Experiments and Analysis Projects (LEAP-2015 and LEAP-2017) provide an opportunity for a more thorough assessment of the capabilities and limitations of constitutive models for sands over a wide range of strains. The LEAP experimental data along with a large number of cyclic element tests are used here to explore the performance of several constitutive models in numerical simulation of soil liquefaction and its effects on lateral spreading of mildly sloping grounds. 

   more » « less
2. On Suitability of Element Tests to Represent Constitutive Response of Liquefiable Soils

   https://doi.org/ascelibrary.org/doi/abs/10.1061/9780784480779.227  

   Manzari, M.T.; Yonten, K.Y. (July 2017, Sixth Biot Conference on Poromechanics)

   Calibration and validation of constitutive models and numerical modeling techniques used in analysis of soil liquefaction and its effects are often based on extensive comparisons with the results of element tests and centrifuge experiments. While good quality experimental data are available to understand and quantify the stress-strain-strength response of liquefiable soils in monotonic and cyclic drained/undrained element (triaxial and direct simple shear) tests, the results of these experiments are often less repeatable when the soil approaches liquefaction state and relatively large deviatoric strains suddenly develop within a few cycles of loading. The main source of these less repeatable patterns of soil behavior appears to be instability rather than the attainment of a state of material failure. The goal of this paper is to investigate the role of instability on the stress-strain response of liquefiable soils by using a critical state sand plasticity model that is enriched with an internal length scale representing the potential shear bands that may develop during monotonic or cyclic loading conditions. Through a series of numerical simulations, it is shown that the global stress-strain response measured in the element tests is a good approximation of the soil constitutive response before an unstable condition such as shear banding or liquefaction develops in the soil specimen. 

   more » « less
3. LEAP-2017 GWU Laboratory Tests

   https://doi.org/10.17603/DS2210X  

   ElGhoraiby, Mohamed; Park, Hanna; Manzari, Majid; Washington, George University (October 2018, Designsafe-CI)

   This project documents an extensive series of laboratory tests performed at the George Washington University to characterize the basic properties and stress-strain-strength response of Ottawa F-65 sand in cyclic loading conditions. The results of these experiments as well the monotonic and cyclic triaxial tests conducted in LEAP-2015 project were provided to all the numerical simulation teams who participated in the LEAP-2017 prediction exercise. The simulation teams used these results to calibrate the constitutive models that they planned to use in numerical simulations of LEAP-2017 centrifuge tests. 

   more » « less
4. 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). 

   more » « less
5. Numerical Simulations of Sand Elements Based on Constant-Volume versus True-Undrained Data from Cyclic Direct Simple Shear Tests

   https://doi.org/10.1061/9780784485996.028  

   Nguyen, Catherine T; Kwan, Wing_Shun; Leal, Cesar (February 2025, American Society of Civil Engineers)

   Numerical simulation of liquefiable soil under cyclic undrained loading is essential for predicting earthquake-induced deformation of geotechnical structures in liquefaction hazard evaluation. Successful simulation of soil response requires constitutive models that can reasonably predict soil behavior under dynamic loading. Many advanced constitutive models have been developed for soil liquefaction hazard evaluation in the past four decades. These advanced models are built on plasticity theories with different modifications and assumptions. Nevertheless, the core part of all models was mainly developed based on observations from constant-volume (CV) cyclic direct simple shear (DSS) tests. While CV tests are standardized in the widely recognized ASTM D8296-19, true-undrained (TU) cyclic DSS tests wherein pore water pressure (PWP) is directly measured have also been performed in academic research. CV and TU cyclic DSS data were successfully generated at California State University, Los Angeles (Cal State LA), from the same apparatus. In this paper, the PM4Sand plasticity model is calibrated using CV and TU data. The performance of CV- and TU-calibrated models is cross-compared with TU and CV data, respectively. While results suggest trends in liquefaction capacity predictions, further data is required for comprehensive validation. The outcomes of this paper also provide insight into the calibration of PM4Sand over a range of relative densities and loading conditions. 

   more » « less