China’s government invests in hydropower and explicitly in larger dams. An increasing share of such large dams is globally represented by the type Concrete Face Rockfill Dam (CFRD) due to its safe behaviour at a relatively low construction cost. China is however building them higher than has earlier been done and the lack of worldwide experience requires thorough studies on their behaviour. This report presents a study of the Cihaxia dam that is to be built in the river basin of Huang He, regarding the optimisation of an increased rockfill compaction and its final effects on the settlements of the concrete face. The settlements of a typical cross section of the Cihaxia dam are modelled with a Finite Element Method (FEM) program with varying values for a number of structural properties. The effect of each variation indicates what properties that will have the largest effect on the behaviour of the finished structure and points out where focus shall be laid when optimising the design of a high CFRD. The outcome of the FEM analysis shows the static comportment of the rockfill body and its concrete face at two stages, at the end of construction and after reservoir impoundment. The difference between the two provides data on what effects the water load would cause, which constitute the main displacements of the concrete slabs. It is evident from the obtained results that the most important of the studied parameters alongside with the level of compaction is the geometrical extension downwards and inwards of the zone subject to increased compaction. A higher degree of compaction will always produce a beneficial decrease of settlements but might not always be economically legitimate as costs rapidly increase with higher levels of compaction. An adequate level of a CFRD’s compaction increase can with advantage be determined by comparing different designs regarding the volumetric percentage to compact against the calculated decrease in slab deflection.

Une modélisation numérique des grands barrages en enrochement à masque amont (CFRD) a été entreprise pour mieux comprendre les pathologies observées sur ces ouvrages récemment construits, principalement des fissures horizontales et verticales sur le masque amont en béton en phase de construction et de mise en eau. Le but de cette modélisation est ensuite de confirmer, préciser ou compléter les solutions proposées par les experts pour éviter ces désordres.D‟abord, une loi de comportement développée au sein d‟EDF-CIH appelée L&K-Enroch a été présentée. Il s'agit d'un modèle élastoplastique qui prend en compte les déformations irréversibles de l‟enrochement sous sollicitation déviatorique et isotrope dans les grands CFRD. Cette thèse propose aussi une méthode de calage des paramètres de ce modèle.Deux modélisations des barrages sont également présentées dans cette thèse afin de vérifier la fiabilité de la loi de comportement L&K-Enroch et de mieux comprendre les pathologies sur le masque amont en béton du CFRD. La modélisation en déformation plane (2D) est d‟abord entreprise et a comme support le barrage d‟Aguamilpa (180,5 m), au Mexique. Une modélisation plus poussée en 3D prenant en compte de l'effet de la vallée est ensuite entreprise. Elle a comme support le barrage de Mohale (145 m) au Lesotho.L'effet d‟échelle de l'enrochement est également étudié en comparant les résultats de simulation pour les matériaux de différentes tailles. L'impact de l‟effet d‟échelle sur le comportement du barrage est aussi analysé.Les simulations présentées en 2D et 3D sont une contribution à l'analyse du comportement mécanique des grands CFRD. Les résultats de la modélisation 2D montrent généralement une bonne correspondance avec les mesures in-situ. La modélisation 3D explique, d'une manière plus convaincante, l‟apparition des fissures sur le masque amont en béton des CFRD. Certaines mesures constructives sont finalement proposées afin de limiter ou d'éviter ces désordres dans le masque. / A numerical modeling of high concrete face rockfill dam (CFRD) has been considered in order to better understand the pathology of cracks observed in the recently constructed high CFRD, especially the horizontal and vertical cracks detected on the concrete face slab during the construction and the impoundment. The purpose of this modeling is then to confirm, clarify or complete the solutions proposed by the experts to avoid these disorders.This PhD thesis presents a constitutive model developed by EDF-CIH known as L&K-Enroch. It is an elastoplastic model that takes into account the irreversible deformations of rockfill under deviatoric and isotropic loading in high CFRD. A first attempt of proposing a parameter calibration approach has been made as well.Two dam modellings are also presented in this thesis in order to verify the reliability of the constitutive model and to better understand the pathology of cracks observed on the concrete face slab of CFRD. A 2D modeling is compared to the behaviour of the 180.5 m Aguamilpa Dam, Mexico; a 3D modeling taking into account the valley effect is compared to the behaviour of the 145 m Mohale Dam, Lesotho.This thesis also studies the scale effect of rockfill through a comparison of the simulation results of materials of different sizes. The impact of the scale effect on the dam behavior is analyzed as well.The presented 2D and 3D simulations are a contribution to the analysis of the mechanical behaviour of high CFRD. The results of the 2D modeling show a relatively good agreement with the monitored data. The 3D modeling explains, in a rather convincing way, the pathology of cracks on the slab face of CFRD. Some measures are proposed to limit or avoid these different kinds of cracks.