Yielding of rockfill in relative humidity-controlled triaxial experiments

The final publication is available at Springer via http://dx.doi.org/10.1007/s11440-016-0437-9The paper reports the results of suction controlled triaxial tests performed on compacted samples of two well graded granular materials in the range of coarse sand-medium gravel particle sizes: a quartzitic slate and a hard limestone. The evolution of grain size distributions is discussed. Dilatancy rules were investigated. Dilatancy could be described in terms of stress ratio, plastic work input and average confining stress. The shape of the yield locus in a triaxial plane was established by different experimental techniques. Yielding loci in both types of lithology is well represented by approximate elliptic shapes whose major axis follows approximately the Ko line. Relative humidity was found to affect in a significant way the evolution of grain size distribution, the deviatoric stress-strain response and the dilatancy rules.Peer ReviewedPostprint (author's final draft

Evaluation of hardening soil model on numerical simulation of behaviors of high rockfill dams

With the continual increase in the height of concrete face rockfill dams constructed during this decade, the hyperbolicelastic model conventionally used in the numerical analyses of lower-height rockfill dams in the past practice becomes insufficientto reproduce the key responses of rockfills of high dam constructions and impoundments. This research aims atevaluating the ability of the elasto-plastic with isotropic hardening (HS) model for simulating more realistic responses in theanalysis of high concrete face rockfill dams. The HS model and, for comparison, the hyperbolic elastic model are numericallyimplemented into a finite element program ABAQUS through the user subroutine to analyze the behaviors of rockfills underconstruction of a 182 m high dam. To obtain the reliable parameters in the analyses, the laboratory triaxial testing data ofrockfills from actual construction are adopted and the calibration by model simulation is also conducted. The analysis resultsfrom both models are compared to the high-quality instrumented data of dam construction. It is proven that by using the HSconstitutive model with the appropriately calibrated model parameters, the response of the rockfills under dam constructioncondition can be more accurately simulated

A case study on the seismic performance of earth dams

The seismic non-linear behaviour of earth dams is investigated by using a well-documented case study and employing advanced static and dynamic coupled-consolidation finite-element analysis. The static part of the analysis considers the layered construction, reservoir impoundment and consolidation, whereas the dynamic part considers the response of the dam to two earthquakes of different magnitude, duration and frequency content. The results of the analysis are compared with the recorded response of the dam and exhibit a generally good agreement. The effects of the narrow canyon geometry, the reservoir impoundment and the elasto-plastic soil behaviour on the seismic dam behaviour are investigated. Finally the implications of the adopted constitutive modelling assumptions on the predicted response are discussed

Numerical analysis of rapid drawdown: applications in real cases

In this study, rapid drawdown scenarios were analyzed by means of numerical examples as well as modeling of real cases with in situ measurements. The aim of the study was to evaluate different approaches available for calculating pore water pressure distributions during and after a drawdown. To do that, a single slope subjected to a drawdown was first analyzed under different calculation alternatives, and numerical results were discussed. Simple methods, such as undrained analysis and pure flow analysis, implicitly assuming a rigid soil skeleton, lead to significant errors in pore water pressure distributions when compared with coupled flow-deformation analysis. A similar analysis was performed for the upstream slope of the Glen Shira Dam, Scotland, and numerical results were compared with field measurements during a controlled drawdown. Field records indicate that classical undrained calculations are conservative but unrealistic. Then, a recent case of a major landslide triggered by a rapid drawdown in a reservoir was interpreted. A key aspect of the case was the correct characterization of permeability of a representative soil profile. This was achieved by combining laboratory test results and a back analysis of pore water pressure time records during a period of reservoir water level fluctuations. The results highlight the difficulty of predicting whether the pore water pressure is overestimated or underestimated when using simplified approaches, and it is concluded that predicting the pore water pressure distribution in a slope after a rapid drawdown requires a coupled flow-deformation analysis in saturated and unsaturated porous media.Peer ReviewedPostprint (published version

Calculating the state parameter in crushable sands

The state parameter (y) measures the distance from the current state to the critical state line (CSL) in the compression plane. The existence of a correlation between both the peak angle of shearing resistance (�# ) and peak dilatancy and y is central to many constitutive models used to predict granular soil behaviour. These correlations do not explicitly consider particle crushing. Crushing induced evolution of the particle size distribution influences the CSL position and recent research supports used of a critical state plane (CSP) to account for changes in grading. This contribution evaluates the whether the CSP can be used to calculate y and thus enable prediction of the peak angle of �# and peak dilatancy where crushing takes place. The data considered were generated from a validated DEM model of Fontainebleau sand that considers particle crushing. It is shown that where y is calculated by considering the CSL of the original uncrushed material there can be in a significant error in predicting the material response. Where the CSP is used there is a significant improvement in our ability to predict behaviour whether the CSP is accurately determined using a large number of tests or approximated using crushing yield envelopes. It is shown that the state parameter calculated using the previously available definition can give a false sense of security when assessing liquefaction potential of potentially crushable soils. The contribution also highlights the stress-path dependency of the relationship between �# $ and y whichever approach is used to determine

Numerical modeling of the behavior of Rockfill Dams during construction and impoundment

Cette thèse vise à modéliser numériquement des barrages en enrochements pendant les phases de construction et de mise en eau. Ceci est fait en se basant sur des essais en laboratoire et l’analyse des données de l'instrumentation insitu. Des essais triaxiaux en compression monotone à déformation/contrainte contrôlée sont effectués sur des assemblages compactés de particules de granit. Les échantillons utilisés en laboratoire ont initialement été préparés à différentes densités sèches et à différentes granulométries. Une loi de comportement élastoplastique parfait, en considérant l’élasticité non linéaire est implémentée dans le logiciel FLAC. Ceci est fait pour modéliser le comportement des particules de roche pendant les essais. Le nouveau modèle est basé sur le comportement hyperbolique, en considérant le critère de rupture de Mohr-Coulomb avec une règle d'écoulement non associé pour considérer la dilatance à cause du cisaillement. La technique de relaxation des contraintes de Nobari-Duncan est également implémentée dans FLAC avec les procédures modifiées et les nouveaux algorithmes pour reproduire les déformations causées par le mouillage. À l'aide de neuf paramètres, le modèle réussi à reproduire le comportement observé pendant les essais triaxiaux et à caractériser l'assemblage des particules de roche. Les effets de temps et de saturation sont également discutés en détail. Finalement, le modèle est utilisé pour la modélisation des étapes de la construction et de la mise en eau du barrage en enrochement LG4 construit au Québec, Canada. Les résultats de la modélisation sont comparés avec les données de l'instrumentation. Aussi, les efforts antérieurs de modélisation de ce barrage et les avantages du nouveau modèle sont discutés.This thesis contributes to the field of numerical modeling of rockfill dams during construction and impoundment based on laboratory research and field instrumentation. Data is presented from monotonic triaxial compression tests, in both stress and strain-controlled conditions, on compacted assemblages of granite rock particles prepared in the laboratory using different initial dry densities and grain size distribution. A nonlinear elastic-perfectly plastic constitutive model is implemented into the commercial software, FLAC, to simulate the behavior of the rock particles during the tests. The new implemented model is the traditional hyperbolic model coupled with the Mohr-Coulomb plastic failure criteria, and with a non-associated flow rule to consider shear dilatancy. The Nobari-Duncan stress relaxation technique with modified procedures and algorithms is also implemented in FLAC to reproduce the collapse deformations due to wetting. Using nine parameters, the model is successful to capture the observed behavior in the triaxial tests and to characterize the assemblage of rock particles. The effects of time and saturation are also discussed in detail. Finally, the model is used to simulate the construction and impoundment stages of LG4 rockfill dam in Quebec, Canada. The results of the modeling of both stages are compared with the instrumentation data and previous efforts of the modeling of this dam and the advantages of the new model are discussed

Use of particulate mechanics concept in agricultural and geotechnical engineering applications

Discrete Element Method (DEM) is a numerical process that uses the concept of particulate mechanics, and it is capable of modelling the discontinuous response of particulate materials. It was utilized in this research for agricultural and geotechnical engineering applications. In an agricultural engineering application, the particle contact microparameters of various crop residues - canola, corn, flax, oats, and wheat - and their interfaces with soil were characterized. These microparameters can be used to improve the reliability of soil-tool-residue DEM models, which in turn is important for the design of high-performance soil-engaging tools. Microparameters for the materials were determined by using a calibration methodology. Laboratory tests were initially performed to obtain information on the macroscopic behavior of the material. Then, discrete element models of the tests were generated to back-calculate the microparameters by simulating the laboratory test results. Linear contact model, with particle stiffness and friction as microparameters, was used to describe the behavior of the interactions between crop residue particles and of the soil-residue interfaces. Ring shear test was conducted to identify the internal friction angle of the crop residues, while direct shear test was carried out to measure the friction angle of the soil-residue interfaces. The DEM models of ring shear and direct shear tests were then developed and used in simulating the measured test results. The DEM simulations of both tests were found to efficiently calibrate the microparameters for residue-residue and soil-residue interactions. In a geotechnical engineering application, the microparameters of the main constituents of an earth fill dam were characterized by conducting DEM simulations of triaxial and large-scale direct shear tests. These microparameters were utilized in developing a landslide DEM model that simulated the observed excessive movements (landslide) in the dam. Validation of the DEM model was successful as it was able to simulate the observed depression at the crest and bulging at the toe of the dam. The DEM model can then be used as basis in assessing the risks of future slope movements in other similar earth fill dam.February 202

Seismic behaviour of geotechnical structures

This paper deals with some fundamental considerations regarding the behaviour of geotechnical structures under seismic loading. First a complete definition of the earthquake disaster risk is provided, followed by the importance of performing site-specific hazard analysis. Then some suggestions are provided in regard to adequate assessment of soil parameters, a crucial point to properly analyze the seismic behaviour of geotechnical structures. The core of the paper is centered on a critical review of the analysis methods available for studying geotechnical structures under seismic loadings. All of the available methods can be classified into three main classes, including the pseudo-static, pseudo-dynamic and dynamic approaches, each of which is reviewed for applicability. A more advanced analysis procedure, suitable for a so-called performance-based design approach, is also described in the paper. Finally, the seismic behaviour of the El Infiernillo Dam was investigated. It was shown that coupled elastoplastic dynamic analyses disclose some of the important features of dam behaviour under seismic loading, confirmed by comparing analytical computation and experimental measurements on the dam body during and after a past earthquake