Analyse retard des mesures d'auscultation de barrages

National audienceL'auscultation des barrages fournit des séries chronologiques de mesures qui doivent être analysées. Pour comprendre le comportement hydraulique de l'ouvrage, il est essentiel de représenter les effets différés dus à la diffusion en milieu poreux. Un modèle permettant une analyse retard des mesures de pression interstitielle est présenté. Il est basé sur une représentation approchée de la réponse impulsionnelle de l'ouvrage permettant de reconstituer les variations mesurées qui sont provoquées par le niveau de la retenue et par la pluie. Après une analyse théorique, le modèle est comparé à des solutions exactes d'un problème de diffusion linéaire, puis appliqué à l'analyse de quelques mesures d'auscultation de trois barrages

Modélisation du renard hydraulique et interprétation de l'essai d'érosion de trou

National audienceL'érosion par renard hydraulique est l'une des causes de rupture des ouvrages hydrauliques. Elle est liée à la formation et au développement d'un tunnel continu entre l'amont et l'aval. L'essai d'érosion au trou est très utilisé pour quantifier la cinétique d'érosion par renard. Toutefois, peu de travaux ont porté sur la modélisation de cette expérimentation. A partir des équations d'écoulement diphasique avec diffusion, et des équations de saut avec érosion, un modèle à deux paramètres décrivant l'agrandissement d'un conduit par érosion hydraulique est proposé. Le premier paramètre est la contrainte seuil. Le second paramètre est le coefficient d'érosion. La comparaison avec des résultats expérimentaux publiés valide le modèle. Nous en déduisons alors, pour un ouvrage hydraulique (barrage , digue), une évaluation du temps restant jusqu'à la brêche

(Article) Fracture of rigid solids: a discrete approach based on damaging interface modelling

International audienceWe describe the progressive and delayed fracture of rigid solids by a discrete modelling. Each rigid solid is considered as an assembly of particles with initial cohesive bonds, the latter decreasing progressively during the loading. A damaging interface model is proposed to describe this progressive phenomenon. The model has been implemented in a discrete element code. The first illustrative example, which is actually a parametric study, deals with the progressive damage and sudden fracture of a single interface submitted to an uniaxial tension. The second example is related to the crushing of an assembly of rigid solids--i.e. a granular medium--submitted to an oedometric compression

Impulse response function analysis of pore pressure in earthdams

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 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

Impulse response function analysis model application to the thermical seepage monitoring in the earth dams

Internal erosion, linked with the leakage presence, is a well known menace for the dams and the dikes safety. In the paper we present a method called Impulse Response Function Thermic Analysis (IRFTA) and its application to earths dams monitoring. IRFTA model allows precisely describe the coupled heat and water transport in dams body and in consequence recognizing even minimal seepage appearance and changing. Application of IRFTA model to analyze the temperature measurements realized with fiber optic for two earth dams are presented in the article

Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed

On the numerical modelling of the Jet Erosion Test

International audienceEvaluating the erodibility of a soil, both in terms of erosion threshold (initiation) and erosion rate (progression), is critical for the evaluation of the safety of water retaining structures. Indeed different soils can erode at different rates. However, the relationship between the erosion parameters and the geotechnical and chemical properties of soils remains largely unknown. The jet erosion test appears to be an efficient and simple means for quantifying the two erosion parameters involved. The first parameter is the critical stress while the second parameter is the erosion coefficient. A simplified model of this test has been drawn up by G. Hanson et al. to interpret the experimental curves. Few attempts have been made so far to model the whole process, however. The aim of this study is to simulate the impinging jet and to take into account the erosion of the soil by means of computational fluid dynamics (CFD) numerical modelling. The key point was the time dependence of the problem, due to erosion processes, however the turbulent flow could be considered as steady because of the assumption of low kinetics erosion assumption. The results of the present modelling study are compared to the simplified model and to experimental data. This comparison is a first confirmation of the validity of the simplified model as a means of assessing the critical stress and the erosion coefficient with jet erosion tests

One-dimensional modeling of piping flow erosion

International audienceA process called "piping", which often occurs in water-retaining structures (earth-dams, dykes, levees), involving the formation and progression of a continuous tunnel between the upstream and downstream sides, is one of the main cause of structure failure. Starting with the diphasic flow volume equations and the jump equations including the erosion processes, a simplified one-dimensional model for two-phase piping flow erosion was developed. The numerical simulation based on constant input and output pressures showed that the particle concentration can be a significant factor at the very beginning of the process, resulting in the enlargement of the hole at the exit. However, it was concluded that this influence is a secondary factor: the dilute flow assumption, which considerably simplifies the description, is relevant here

A discrete model for fracture of rigid solids based on a damaging interface

We describe the progressive and delayed fracture of rigid solids by a discrete modelling. Each rigid solid is considered as an assembly of particles with initial cohesive bonds, the latter decreasing progressively during the loading. A damaging interface model is proposed to describe this progressive pehenomenon. This model has been implemented in a numerical code based on a discrete element method. The illustrative example is related to the crushing of an assembly of rigid solids - i.e. a granular medium - due to an œdometric compression