A Practical Model for Advanced Nonlinear Analysis of Earthquake Effects in Clay Slopes

Presented in this paper is an effort in providing an advanced yet practical tool with a reasonable level of complexity for modeling of clays in realistic geotechnical engineering problems. SANICLAY model is a Simple ANIsotropic CLAY plasticity model that has been developed by Dafalias et al. (2006). The SANICLAY model provides successful simulation of both undrained and drained rateindependent behavior of normally consolidated clays, and to a satisfactory degree of accuracy of overconsolidated clays. An associated flow rule extension of the SANICLAY model has been employed in the present study, trading simplicity for some accuracy in simulations. The model requires just three constants more than those of the Modified Cam-Clay model, all of which can easily be calibrated from well-established laboratory tests. In order to make the model applicable to practical problems in geotechnical engineering, this simple version of SANICLAY model has been efficiently integrated in FLAC3D program. An illustrative example describing earthquake behavior of saturated clayey slope using the simple form of the SANICLAY model is presented and discussed

A viscoplastic SANICLAY model for natural soft soils

This paper focuses on constitutive and numerical modeling of strain-rate dependency in natural clays while also accounting for anisotropy and destructuration. For this purpose the SANICLAY model that accounts for the fabric anisotropy with the additional destructuration feature that accounts for sensitivity of natural clays, is considered as the reference model. An associated flow rule is adopted for simplicity. The model formulation is refined to also account for the important feature of strain-rate dependency using the Perzyna’s overstress theory. The model is then implicitly integrated in finite element program PLAXIS. Performance of the developed and implemented model is explored by comparing the simulation results of several element tests and a boundary value problem to the available experimental data. The element tests include the constant strain-rate under one-dimensional and triaxial conditions on different clays. The boundary value problem includes a test embankment, namely embankment D constructed at Saint Alban, Quebec. For comparison, the test embankment is also analyzed using the Modified Cam-Clay (MCC) model, the SANICLAY model, and the viscoplastic model but without destructuration. Results demonstrate the success of the developed and implemented viscoplastic SANICLAY in reproducing the strain-rate dependent behavior of natural soft soils.Support to conduct this study is provided by the University of Nottingham’s Dean of Engineering award, and the Natural Sciences and Engineering Research Council of Canada (NSERC)

Evaluation of four advanced plasticity and hypoplasticity models in simulating cyclic response of sands

Numerous constitutive models have been developed for the simulation of the response of granular soils under cyclic loading. While these models have succeeded in capturing certain aspects of the stress-strain response under a number of idealized loading paths, certain common limitations are encountered in simulating these and other paths, and also certain complex aspects of response. Examples of these include cyclic oedometeric stiffness, shear strain accumulation in cyclic mobility, cyclic liquefaction strength curves, among others. These limitations are rather crucial for the end-users. Discussing these limitations and providing the mechanisms to avoid them if possible, therefore, would be of great value for both applications and further developments. Relying on cyclic loading experimental test data of Karlsruhe fine sand, the present study conducts direct comparison between the experiments and the corresponding simulation results using four advanced constitutive models: two bounding surface elastoplasticity (Dafalias and Manzari 2004, Yang et al. 2021) and two hypoplasticity models (Niemunis and Herle 1997, Fuentes et al. 2020) – with the models in each category following a hierarchical order of complexity. The presented results elaborate on the specific capabilities and limitations of these advanced models in simulating several essential aspects of cyclic loading of sands

PRENOLIN project. Results of the validation phase at sendai site

One of the objectives of the PRENOLIN project is the assessment of uncertainties associated with non-linear simulation of 1D site effects. An international benchmark is underway to test several numerical codes, including various non-linear soil constitutive models, to compute the non-linear seismic site response. The preliminary verification phase (i.e. comparison between numerical codes on simple, idealistic cases) is now followed by the validation phase, which compares predictions of such numerical estimations with actual strong motion data recorded from well-known sites. The benchmark presently involves 21 teams and 21 different non-linear computations. Extensive site characterization was performed at three sites of the Japanese KiK-net and PARI networks. This paper focuses on SENDAI site. The first results indicate that a careful analysis of the data for the lab measurement is required. The linear site response is overestimated while the non-linear effects are underestimated in the first iteration. According to these observations, a first set of recommendations for defining the non-linear soil parameters from lab measurements is proposed. PRENOLIN is part of two larger projects: SINAPS@, funded by the ANR (French National Research Agency) and SIGMA, funded by a consortium of nuclear operators (EDF, CEA, AREVA, ENL)

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

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)

LEAP-2017: Comparison of the Type-B Numerical Simulations with Centrifuge Test Results

This paper presents comparisons of 11 sets of Type-B numerical simulations with the results of a selected set of centrifuge tests conducted in the LEAP-2017 project. Time histories of accelerations, excess pore water pressures, and lateral displacement of the ground surface are compared to the results of nine centrifuge tests. A number of numerical simulations showed trends similar to those observed in the experiments. While achieving a close match to all measured responses (accelerations, pore pressures, and displacements) is quite challenging, the numerical simulations show promising capabilities that can be further improved with the availability of additional high-quality experimental results

A framework to assess Newmark-type simplified methods for evaluation of earthquake-induced deformation of embankments

The simplified procedures for evaluation of the earthquake induced displacement in earth and rockfill dams are widely used in practice. These methods are simple, inexpensive, and substantially less time consuming as compared to the complicated stress-deformation approaches. They are especially recommended to be used as a screening tool, to identify embankments with marginal factor of safety, assuming that these methods always give conservative estimates of settlements. However recent studies show that application of these methods may not be conservative in some cases, especially when the tuning ratio of a dam is within a certain range. In this paper the fundamental theory behind the simplified methods is critically reviewed. A case in which the results of the simplified methods are reportedly non-conservative is investigated in detail and possible reasons are discussed. The reliability of the simplified methods is examined here based on the existing thresholds proposed in the literature and accounting for the embankment geometry and type, and the seismic activity characterization, and a practical framework is proposed accordingly. The effectiveness of this framework is evaluated in the study of seismic behaviour of a rockfill dam where all simplified procedures failed to predict the order of deformation experienced by the dam under a recent earthquake event