Papers by Stephane Bonelli
C2.03-Limites des critères de susceptibilité à la suffusion vis-à-vis de la stabilité mécanique d... more C2.03-Limites des critères de susceptibilité à la suffusion vis-à-vis de la stabilité mécanique des ouvrages en remblai
Nous considérons une digue en terre soumise à un écoulement de surverse. La modélisation physique... more Nous considérons une digue en terre soumise à un écoulement de surverse. La modélisation physique et numérique d'un tel phénomène est en général un compromis entre pertinence physique, précision numérique et temps de calcul. Nous nous sommes attachés à l'analyse de l'écoulement à surface libre caractéristique d'une surverse, éludant momentanément les phénomènes d'érosion et de transport sédimentaire qui seront inclus ultérieurement par couplage. L'hydrodynamique complexe associée à la surverse est traitée grâce à un modèle bi-fluide Eulérien à faible nombre de Mach. Ce modèle bi-fluide, non visqueux et faiblement compressible est physiquement plus pertinent que des modèles de type Saint-Venant généralement utilisés. En effet, on observe dans l'écoulement des jets et des recirculations plus facilement appréhendés par un modèle diphasique. Ce modèle est évidemment moins riche qu'un modèle de Navier-Stokes avec ou sans turbulence, mais sa formulation per...
Le traitement des sols à la chaux est couramment utilisé pour l'amélioration et la stabilisat... more Le traitement des sols à la chaux est couramment utilisé pour l'amélioration et la stabilisation des sols limoneux et argileux, dans le cadre de la construction d'infrastructures. L'intérêt de cette technique dans le cadre des ouvrages hydrauliques en terre est croissant. En effet, il a été montré lors de programmes de recherche que le matériau sol-chaux pouvait efficacement remplir une série de fonctions pertinentes pour les ouvrages hydrauliques : stabilité, faible niveau de perméabilité, résistance à l'érosion interne et de surface. Des expérimentations à l'échelle du laboratoire et sur des réalisations en vraie grandeur, ainsi que des retours d'expérience à travers le monde, ont appuyé ces constats. Récemment, dans le cadre du projet de R&D DigueELITE, la résistance à la surverse d'une digue en sol traité à la chaux le long de la rivière Vidourle (Gard, France) a pu être quantifiée, à l'aide d'un dispositif d'essai de surverse in situ inno...
La rupture d'une digue fluviale suite à une crue dépassant la crête de l'ouvrage constitu... more La rupture d'une digue fluviale suite à une crue dépassant la crête de l'ouvrage constitue un scénario de l'étude de dangers. Il est capital de quantifier la résistance à la surverse. Lorsque le tronçon est équipé d'une protection de surface, la pratique est d'utiliser des abaques (par exemple celles du CIRIA). En revanche, il est actuellement impossible de qualifier, vis à vis de sa résistance à un écoulement de surverse, un sol constitutif d'un tronçon de digue. En conséquence, on considère actuellement en France que « les digues en terre ne supportent pas la surverse ». C'est la raison pour laquelle Irstea a développé un simulateur de surverse in situ, à échelle un. Le dispositif a été déployé dans le cadre du projet de recherche DigueELITE sur une digue expérimentale (hauteur de 3,5 m) construite en 2015, dans 2 canaux de 61 cm de large et 15 m de long, couvrant le talus aval (pente 1,5H/1V) et la plate-forme aval : l'un sur sol-chaux, l'autre...
Le traitement des sols par des liants (chaux et ciment) est une technique très répandue dans le d... more Le traitement des sols par des liants (chaux et ciment) est une technique très répandue dans le domaine des terrassements routiers et ferroviaires. La mise en oeuvre de traitement des sols pour les barrages et les digues est, encore à ce jour, assez marginale. Le groupe de travail du CFBR sur les barrages (et digues) en remblai dur et sols traités (groupe miroir du comité technique P de la CIGB-Comité des barrages en remblai cimenté) travaille depuis plusieurs années sur la mise au point de ces techniques pour les barrages et les digues, en considérant les améliorations mécaniques apportées par le traitement dès le stade de la conception.
The Friant-Kern irrigation canal is located along the foothills of the Sierra Nevada, southeast o... more The Friant-Kern irrigation canal is located along the foothills of the Sierra Nevada, southeast of Fresno, California. It has a length of approximately 240 km, and was designed for a maximum waterflow of 150 m/s. It was built in the late 1940’s using highly expansive clay; the earth-lined sections have 2:1 slopes, a bottom of 17.7 m width, and a top width of 45 m. Since the construction period, the earthen banks have suffered periodic damage from cracks, slips and slides. Concrete –lined sections also show failures due to the swelling of expansive soils. In the 1970’s, the Bureau of Reclamation decided to repair approximately 13.5 km of failed sections using lime treatment of clays taken from the banks of the canal. The methodology and devices used for the quicklime treatment are explained in the paper. The treated clay was replaced and compacted by a sheep-foot roller, to achieve a typical thickness between 60 cm (top and bottom of the canal) to 1.2 m (slopes). The observed perform...
L'analyse du risque d'erosion interne dans les barrages en remblai, les digues et leurs f... more L'analyse du risque d'erosion interne dans les barrages en remblai, les digues et leurs fondations a fait l'objet de recherches croissantes depuis plus de 25 ans, au niveau international au sein du groupe de travail europeen sur l'erosion interne (EWGIE) lance par le club europeen de la CIGB (EURCOLD) et au niveau national, principalement au sein du projet de recherche ERINOH et maintenant au sein du groupe de travail CFBR « barrages en remblai ». Ces collaborations entre maitres d'ouvrage, bureaux d'etude et centres de recherche ont abouti a des methodologies d'analyse du risque d'erosion interne dans les barrages en remblai, pour les etudes de reevaluation de la surete : bulletin CIGB n° 164, guides du projet ERINOH. Dans un premiere partie, la declinaison actuelle par EDF-CIH de la methodologie d'analyse du risque d'erosion interne est resumee. Dans une seconde partie, l'analyse de niveau 1 d'ERINOH est evoquee, elle peut etre menee...
Cette communication dresse tout d'abord un panorama des donnees sur les ruptures par surverse... more Cette communication dresse tout d'abord un panorama des donnees sur les ruptures par surverse des barrages en remblai et des digues, ainsi que les actions menees recemment au niveau national et international pour synthetiser et faire progresser l'etat de l'art : GT CFBR, Workshop International d'Aussois de 2017, European Working Group on Overflowing and Overtopping Erosion. Elle propose ensuite une methodologie d'analyse de ce mode de rupture et l'etat de l'art associe a chaque etape. Enfin, elle presente la pratique et le retour d'experience d'EDF dans l'analyse du risque d'erosion par surverse des barrages en remblai et des digues et pointe les lacunes de l'etat de l'art actuel et les besoins de recherche et developpement associes.
European Journal of Environmental and Civil engineering, 2011
Suffusion is an internal erosion process which occurs when finer soil particles are detached by s... more Suffusion is an internal erosion process which occurs when finer soil particles are detached by seepage flow and start moving within the pore space of larger particles. Suffusion can be viewed as clay/water interface erosion. The aim of this study is to use a numerical model for simulating surface erosion occurring at a fluid/soil interface subject to a flow process at pore scale. Balance equations with jump relations are used. A penalization procedure including a fictitious domain method is used to compute the Stokes flow around obstacles, in order to avoid body-fitted unstructured meshes and instead use fast and efficient finite volume approximations on Cartesian meshes. The evolution of the water/soil interface is described by using a Level Set function. The ability of the model to predict suffusion is confirmed by several numerical simulations. RÉSUMÉ. La suffusion est un processus par lequel les particules les plus fines du sol se détachent de la matrice solide et sont transportées par un écoulement interstitiel à travers les pores du milieu. Le but de cette étude est de présenter un modèle numérique pour simuler l'érosion apparaissant à l'interface eau/sol à l'échelle des pores. Une procédure de pénalisation ou « domaine fictif » est utilisée pour simuler l'écoulement de Stokes autours d'obstacles, afin de s'affranchir des contraintes de maillage, grâce à un efficace solveur volume fini sur grille cartésienne. L'évolution de l'interface eau/sol est décrite par des fonctions Level Set. L'aptitude du modèle à prédire les phénomènes de suffusion est confirmée par quelques exemples.
Modeling of Interfacial Erosion
Bonelli/Erosion of Geomaterials, 2012
ABSTRACT In Chapter 6, Stéphane Bonelli, Frédéric Golay and Fabienne Mercier present an original ... more ABSTRACT In Chapter 6, Stéphane Bonelli, Frédéric Golay and Fabienne Mercier present an original modelling of interfacial surface erosion. The modelling of a two-phase flow with erosion and transport is simplified, and two numerical models are proposed: one of them is based on the fictitious domain method and the level-set method, while the other is based on remeshing. Several examples of validation and illustration are presented, with wide applicability to laboratory tests.
Concentrated Leak Erosion
Bonelli/Erosion of Geomaterials, 2012
ABSTRACT Chapter 5, written by Nadia Benahmed, Christophe Chevalier and Stéphane Bonelli, is conc... more ABSTRACT Chapter 5, written by Nadia Benahmed, Christophe Chevalier and Stéphane Bonelli, is concerned with flow erosion as it takes place in a pipe. In fact, this chapter thoroughly analyzes the “Hole Erosion Test”, which was carried out for hydraulic structures in the United States and Australia, and recently in France. Several laboratory tests show the influence on erosion parameters of the clay nature, of the soil water content and of its density. Finally, this chapter emphasizes the importance of the coefficient of erosion needed to evaluate the safety of hydraulic structures in relation to the risks of failure caused by pipe flow with erosion.
Revue européenne de génie civil, 2008
Effective control of dam safety requires that the measured pore-pressure data be interpreted in t... more Effective control of dam safety requires that the measured pore-pressure data be interpreted in the shortest possible time following the readings. Direct resolution based on partial differential equations are not appropriate. We present a relevant formalism for analysing pore-pressure monitoring data: the Impulse Response Function Analysis (IRFA) method. The model based on approximations for the impulse response of the dam gives the variations in the pore-pressure measurement resulting from changes in the reservoir and rainfall levels. An expression for the explicit estimation of in situ hydraulic diffusivity is derived. The model were applied to the analysis of monitoring data obtained at a zoned earthdam. Obtained results proved that essential aspects of the observed phenomenon in most cells data can be described in this linear framework, and that they are taking into account.
Piping is the most serious menace to the safety of an earth hydraulic work. We present the study ... more Piping is the most serious menace to the safety of an earth hydraulic work. We present the study of the piping erosion identification by means of temperature analysis. Extensive steady and un- steady numerical computations for the coupled heat and water transport in the porous domain, with the downstream side pipe opening, are described. Choice of the numerical RANS (Reynolds-averaged Navier-Stokes) model is explained to take into account mixed laminar and turbulent water flow in the pipe. Computation covered the range of hydraulic diffusivity from 10-7 to 10-4 m2/s and made use of the finite volume method with the FLUENT numerical modelization platform. The basic principles of the pipe thermal influences are presented with the evaluation of the possibilities of identifying piping pa- rameters with temperature measurements. Correct identification of the pipe thermal influence was found to be important in interpretating thermal data measured that are necessary for hydraulic earthwork...
Journal of Hydraulic Engineering, 2014
The Jet Erosion Test (JET) is an experimental device increasingly used to quantify the resistance... more The Jet Erosion Test (JET) is an experimental device increasingly used to quantify the resistance of soils to erosion. This resistance is characterised by two geotechnical parameters: the critical shear stress and the erosion coefficient. The JET interpretation model of provides an estimation of these erosion parameters. But Hanson's model is simplified, semi-empirical and several assumed hypotheses can be discussed. Our aim is to determine the relevance of the JET interpretation model. Therefore, we developed a numerical model able to predict the erosion of a cohesive soil by a turbulent flow. Our numerical model is first validated on a benchmark: erosion of an erodible pipe by a laminar flow. The numerical results are satisfactorily compared with the theoretical solution. Then, three JETs are modelled numerically, with values of erosion parameters obtained experimentally. A parametric study is also conducted to validate the accuracy of the numerical results and a good agreement is observed. The erosion parameters found experimentally permit to predict numerically the evolution of the erosion pattern within good accuracy. This result contributes to the validation of the JET's semi-empirical model. The numerical model also gives a complete description of the flow, including vortices which can be observed in the cavity created by erosion. The whole erosion pattern evolution is given by the numerical results. Our numerical model gives information that is not available otherwise.
International Journal for Numerical and Analytical Methods in Geomechanics, 2009
Tél 33 (0)4 42 66 99 53 Fax 33 (0)4 42 66 88 65 ABSTRACT This modelling study deals with the time... more Tél 33 (0)4 42 66 99 53 Fax 33 (0)4 42 66 88 65 ABSTRACT This modelling study deals with the time-dependent behaviour of rockfill media, which is of particular interest during the life of rockfill dams. Breakage of rock blocks and crack
International Journal for Numerical and Analytical Methods in Geomechanics, 2008
Tél 33 (0)4 42 66 99 53 Fax 33 (0)4 42 66 88 65 E-mail address: stephane.bonelli@cemagref.fr
… des Eléments Finis, 1993
In numerous non stationary and non linear problems, the determination of the time step necessary ... more In numerous non stationary and non linear problems, the determination of the time step necessary to the good sequence of simulation of finite elements is very often tedious. We propose, therefore, a strategy of autoadaptive steps and we apply it to a resolution by ...
European Journal of Mechanics - B/Fluids, 2007
To better understand the phenomena involved in hydraulic erosion of soils, the influence of the e... more To better understand the phenomena involved in hydraulic erosion of soils, the influence of the eroded mass flow rate on the velocity field of the water flow is investigated by an original theoretical model. We consider the situation of a turbulent two-phase fluid flow over an erodable solid medium, with both turbulent stresses and turbulent particles diffusion in the flow. In the reference frame linked to the ground surface, the flow can be considered as a quasi-steady state and modelled by the boundary layer equations with addition of mass injection from the ground to account for erosion. To solve completely the problem, the prescription of a local erosion criterion is necessary to evaluate the local eroded mass flow rate. We consider here a purely mechanical process: the eroded flow rate is proportional to the difference between the tangential stress induced by the flow and a critical value characteristic of the soil. In this theoretical frame, we can study the influence of several parameters, as the slope of the ground or the sediments density. One of the main results obtained is the existence for a given set of the parameters of a critical slope angle separating two different erosion regimes.
European Journal of Mechanics - B/Fluids, 2014
This study focuses on 2D Computational Fluid Dynamics (CFD) numerical modelling of the erosion of... more This study focuses on 2D Computational Fluid Dynamics (CFD) numerical modelling of the erosion of a cohesive soil by a circular impinging turbulent jet. Initially, the model is validated in the case of a non-erodible flat plate. Several turbulence models are compared to experimental results and to simplified formulas available in the literature. The results obtained show that the Reynolds Stress Model (RSM) is in good agreement with the semi-empirical results in the literature. Nonetheless, the RSM cannot be used with successive remeshings, due to its convergence issues. The shear stress at the wall is well-described by the k-ε model while the pressure is better-described by the k-ω model. The numerical model of erosion is based on adaptive remeshing of the water/soil interface to ensure the good precision of the mechanical values at the wall. The two erosion parameters are the critical shear stress and the erosion coefficient. The results obtained are compared with the semi-empirical model interpreting the Jet Erosion Test. The k-ε model underestimates the shear stress and does not allow simulating the entire erosion process, whereas the results obtained with the k-ω model agree well with the semi-empirical model and experimental data. A study of the influence of erosion parameters on erosion kinetics and scouring depth shows that the shape and depth of scouring are influenced solely by the critical shear stress while the duration of scouring depends on both erosion parameters. Further research is nonetheless required to better understand the erosion mechanisms in the stagnation zone.
Continuum Mechanics and Thermodynamics, 2007
In order to build for granular media an unified modelling by means of Eulerian averaged equations... more In order to build for granular media an unified modelling by means of Eulerian averaged equations, it is necessary to study two contributions in the "effective Cauchy stress tensor": the first one concerns the solid and fluid matter, but also the contacts and collisions between grains, and the second one is due to the random movements of the grains and the fluid, similar to the "Reynolds stress" for turbulent flows. It is shown that the point of view of "piecewise continuous media" already used for two phase flows allows to derive a constitutive equation for the first contribution, under the form of a partial differential equation. Similarly as for the Reynolds stress in turbulent flows, this equation cannot be written only in terms of averaged quantities without adequate approximations. The structure of the closed equation is discussed with respect to irreversible thermodynamics, and in connection with some already existing models. It is emphasized that numerical simulations by Discrete Elements Method can be used in order to validate these approximations, through numerical experiments statistically considered. Finally an extension of this approach to the second contribution of the effective Cauchy stress tensor is briefly discussed, showing how the modelling of both contributions have to be coupled.
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Papers by Stephane Bonelli