Le phénomène de suffusion correspond à la migration des particules fines érodées dans un milieu poreux sous l'action d’un flux hydraulique. Ce mécanisme pourrait être la cause principale des ruptures des remblais et des barrages en terre. De nombreuses études expérimentales ont été menées pour comprendre la suffusion et mettre en évidence les phénomènes couplés associés. Au niveau numérique, on trouve beaucoup de modèles analytiques et numériques mais rares sont ceux qui prennent en compte l’arrachement des particules, leur transport et leur dépôt éventuel (par un processus de colmatage ou pour des vitesses d’écoulement suffisamment faibles).En se basant sur une loi d’écoulement de type Darcy, sur la loi d’érosion de Papamichos et al (2001) modifiée par Bendahmane (2005)et sur une loi d’évolution de la viscosité de fluide (relation d’Einstein), nous développons une nouvelle approche hydromécanique de la suffusion. La résolution numérique du problème est réalisée par la méthode des éléments finis. Deux aspects sont présentés: le cadre général du modèle proposé (réalisé en 2D) avec une étude paramétrique et la validation du modèle avec une modélisation 3D réalisée avec le modèle géométrique de l’essai (Cross Erosion Test) (CET), ce qui permet de décrire à la fois les phénomènes d’érosion, de transport et de dépôt des particules érodées dans un milieu poreux saturé.Pour cela, nous avons choisi un outil de modélisation approprié à la représentation de phénomènes couplés tels que ceux mobilisés par l’érosion interne. Le logiciel Comsol-Multiphysics 3.4b, basé sur la méthode des éléments finis, a été retenu car il permet d’implanter relativement facilement de nouvelles équations constitutives des phénomènes. Dans un deuxième temps, le modèle a été validé sur des expériences de référence reflétant les phénomènes étudiés. Nous avons utilisé les résultats expérimentaux de Nguyen (2013) qui a mis au point un nouveau dispositif expérimental au laboratoire 3SR appelé " l'Essai d’Érosion Transverse " ou Cross Érosion Test. Deux types de sol ont été considérés : un sol gravelo-sableux(noté S3) et un sol limoneux de l’Isère (noté S4 et S4-a).Afin de discuter des aspects transitoire et dynamique du phénomène de suffusion, les vitesses d’écoulement, les gradients hydrauliques, la distribution de la porosité et de la perméabilité, la distribution de la concentration des particules érodées en suspension, et enfin la masse érodée sortantes ont mesurés au cours du temps et comparés aux résultats du modèle physique. / The phenomenon of Suffusion corresponds to the migration of fine eroded particles in a porous medium under the action of an internal water flow. This mechanism could be the main origin of damage in embankments and earth dams. Many experimental studies have been done to analyse the suffusion but actually understanding this phenomenon appears as a major scientific challenge. On the other hand, numerically, only a few studies were found which associate the mechanisms of detachment, transport and deposition of eroded particles.Based on the Darcy’s law model, the erosion model of Papamichos et al (2001) modified by Bendahmane (2005) and the fluid viscosity evolution law (Einstein relation), we developed a new hydro-mechanical approach of suffusion. The numerical solution of the problem is carried out by using a finite element method. Two aspects are presented: first, the general framework of the proposed model (implemented in 2D) with a parametric study and then the validation of the numerical model realized with a 3D study of the geometric model of the experimental study of Cross Erosion Test (CET). This model describes the three phenomena of suffusion: erosion, transport and deposition of eroded particles in a saturated soil.Furthermore, the numerical modeling of coupled phenomena of internal erosion is performed using the commercial software "Comsol Multiphysics-3.4b". However, to validate the model, experimental results on two types of soil: sandy gravel soil (S3) and the silt of Isère (S4 and S4-a) are used. These results are found in the PhD thesis of Nguyen(2013) who has developed a new apparatus called Cross Erosion Test (CET).Moreover, to discuss the transient and dynamic aspects of the phenomenon, the evaluation of the mass conservation with different figures of flow velocity, hydraulic gradient, hydraulic head, porosity and permeability distribution, concentration distribution, and of outgoing eroded particles, are measured over time and compared with experimental results.

No description available.

$aL’objectif de cette thèse est de comprendre le phénomène de suffusion (érosion interne) dans ses processus et ses conséquences sur le comportement mécanique des sols à faible cohésion par l’établissement d’une relation directe ou indirecte entre la stabilité interne de ces matériaux et leur critère de rupture. L’érosion interne vue essentiellement sous l’angle de la suffusion a été analysée par des modélisations numériques et des essais expérimentaux. Les principaux essais utilisés sont : - Ecoulements d’eau à travers un matériau granulaire dans une colonne. - Essais de cisaillement triaxial non drainés. Pour la modélisation numérique, PFC3D a été utilisé pour les simulations d’essais triaxiaux et la prise en charge du couplage fluide solide a été possible grâce à une option de type CFD (Coupling Fluid Dynamique). Ce code DEM a permis le développement d’une nouvelle méthode de génération d’échantillon granulaire à partir de sa courbe granulométrique et de sa porosité cibles. L’évolution des porosités, celle des courbes granulométriques et de l’état de stabilité interne avant et après écoulement ont été identifiées comme indicateur du niveau de suffusion. Les critères de stabilité de Kenney & Lau et de Kezdi ont permis d’apprécier la stabilité interne des échantillons. Les conséquences de la suffusion se sont manifestées par : Une diminution de l’angle de frottement interne dans le cas d’une suffusion interne; une augmentation de l’angle de frottement dans le cas d’une suffusion externe. Les comparaisons des résultats expérimentaux et numériques tant pour les écoulements que pour les essais triaxiaux ont présenté de bonnes concordances. Enfin, une proposition d’un nouveau critère de stabilité interne est établie, elle est déduite de l’analyse des relations entre le comportement mécanique et la stabilité interne, notamment la contractance du matériau. / The objective of this thesis is to understand the phenomenon of suffusion (internal erosion) in its process and its effects on the mechanical behavior of loose soil by establishing a direct or indirect relationship between the internal stability of these materials and failure criterion. Numerical modeling and experimental tests analyzed the internal erosion in terms of the suffusion. The main tests used are : - Water flows through a granular material in a column. - Undrained shear triaxial tests. For numerical modeling, PFC3D was used for simulations of triaxial tests and the treatment of solid fluid coupling was possible through a CFD type of option (Coupling Fluid Dynamics). This DEM code has allowed the development of a new method of generating granular sample from its grading curve and its target porosity. The evolutions of porosity, grading curves and the state of internal stability before and after discharge were identified as indicator of suffusion. Kenney & Lau and Kezdi stability criteria were used to assess the internal stability of samples. The consequences of suffusion were expressed by: A reduction of the internal friction angle in the case of an internal suffusion; an increase of the friction angle in the case of an external suffusion. Comparisons of experimental and numerical results for both flows and triaxial tests have shown good agreements. Finally, a proposal of a new criterion of internal stability is established, it is deducted from the analysis of the relationship between the mechanical behavior and internal stability, including the material contractance.

Numerical analyses are presented in this thesis to address potential stability problems that may occur during gradual raisings and under seismic loading conditions of Aitik tailings dam in northern Sweden. The dam is mainly raised using upstream construction method. It is planned to raise the dam gradually in several stages. Two dam parts were studied. The first dam part is a straight dam portion, and the second dam part is a corner. The main concerns associated with future raisings of the straight dam part were: (i) the stability of the dam could be affected by an increase in excess pore pressures during sequential raisings, (ii) how to gradually strengthen the dam by using rockfill berms as supports in such a way that required slope stability can be achieved with a minimum volume of rockfill berms, and (iii) if the dam is subjected to seismic loading, whether or not an increase in excess pore pressures could lead to extensive liquefaction which may cause a failure. The problems related to the dam corner were that tension zones and/or low compression zones could develop because of the horizontal pressure of the stored tailings on the inside of the curvature of the dam corner.Numerical analyses were conducted on both the dam parts using finite element method. Two dimensional (2D) plane strain finite element model was utilized to analyse the straight dam. The dam corner was analysed with both the three dimensional (3D) finite element model, and the 2D axisymmetric finite element model. Coupled deformation and consolidation analyses, and slope stability analyses were performed on both the dam parts to simulate gradual raisings, and to compute safety factors. In addition to this, dynamic analyses were carried out on the straight dam part to evaluate the potential for liquefaction, and seismic stability of the dam. The seismic behaviour of the dam was analysed for two cases: (i) a normal case (earthquake of 3.6 Swedish local magnitude), and (ii) an extreme case (earthquake of 5.8 moment magnitude).The results of the straight dam part, with only previously existing rockfill berms, indicate that stability of the dam was reduced due to an increase in excess pore pressures during raisings. Rockfill berms were utilized as supports to raise the dam with enough safety. An optimization technique was utilized to minimize the volume of rockfill berms. This technique could result in significant saving of cost of rockfill berms.The results of the dam corner show that tension zones and/or low compression zones were located on the surface of the dam corner, mainly above the phreatic level. It is interpreted that there is no risk of internal erosion through the embankments because no seepage path occurs above the phreatic level, and a filter zone exists along the slope of the dam. It is suggested to gradually strengthen the dam corner with rockfill berms. The results of the 2D axisymmetric analyses of the dam corner were in a fairly good agreement with those of the 3D analyses. This implies that the 2D axisymmetric analyses are valid for this dam corner. This is an important finding as 2D axisymmetric analyses require much less computational time compared to 3D analyses.The results of the dynamic analyses performed on the straight dam (including additional rockfill berms) suggest that, for the extreme case, liquefaction could occur in a limited zone that is located below the surface near the embankments. For both the normal and the extreme case, (i) seismically induced displacements seem to be tolerable, and (ii) the post seismic stability of the dam is considered to be sufficient.The findings of this study have been practically applied to the Aitik tailings dam. In general, the modelling procedure and the optimization technique to minimize volume of rockfill berms, presented in this study, could be applied to other tailings dams. / Godkänd; 2013; 20130513 (muhauc); Tillkännagivande disputation 2013-05-20 Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Muhammad Auchar Zardari Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Avhandling: Numerical Analyses of Stability of a Gradually Raised Tailings Dam Opponent: Professor Daichao Sheng, School of Engineering, The University of Newcastle, New South Wales, Australia Ordförande: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Tid: Torsdag den 13 juni 2013, kl 10.00 Plats: F1031, Luleå tekniska universitet

Les géo-structures telles que les barrages et les digues sont soumises à des écoulements hydrauliques variant dans le temps et dans l'espace. L'eau qui traverse ces milieux poreux peut entraîner le détachement et le transport de certaines particules des sols constituant les structures et leurs fondations. Ce problème est généralement appelé "érosion interne". Le terme suffusion, un type d'érosion interne, se réfère au détachement et au transport de particules les plus fines à traversune matrice de sol poreuse plus grossière en raison d'un écoulement hydraulique. L'évolution temporelle de la suffusion peut modifier les propriétés hydrauliques et mécaniques des sols et peut entraîner des changements importants dans le comportement de telles structures pouvant aller jusqu’à leur effondrement. Ce travail de thèse tente de contribuer à la conception et à la durabilité des ouvrages en ingénierie géotechnique et hydraulique en mettant un accent particulier sur les barrages, les levées et les digues. Il a été consacré à développer un modèle numérique de suffusion en introduisant d’une part le couplage des phénomènes hydrauliques et mécaniques et d’autre part le couplage des phénomènes d'érosion et de filtration. / Geo-structures such as dams and levees or dikes are subjected to seepage varying in time and space. The water flowing through these porous media can lead to the detachment and transport of part of the soil particles within the structures or their foundations. This problem is usually called internal erosion. The term suffusion, one type of internal erosion, refers to the detachment and transport of finer particles through a coarser porous soil matrix due to seepage flow. Suffusion can modify with time the hydraulic and mechanical properties of the soils and may trigger significant damage on such structures and lead eventually to their collapse. This research attempts to contribute to the design and sustainability of geotechnical and hydraulic engineering structures, with a particular focus on embankment dams, levees, and dikes. It aims to develop a numerical model of suffusion by introducing, on the one hand, the coupling of the hydraulic and mechanical phenomena and, on the other hand, the coupling of erosion and filtration.

Les discontinuités granulaires dans les ouvrages hydrauliques ou dans leur fondation constituent une source majeure d’instabilités à l’origine des phénomènes d’érosion. L’érosion interne est ainsi définie comme une migration de particules engendrée par un écoulement interne parasite, dans un sol ou dans un ouvrage en terre. A long terme, les conséquences de cette migration peut affecter la stabilité des ouvrages et peut même conduire à leur rupture. La sécurité des ouvrages en terre dépend principalement de la performance de leurs filtres, c’est-à-dire de la capacité du filtre, mis en interne en phase de conception ou en externe en phase de réparation, à retenir les particules fines. L’espace poral d’un filtre granulaire est divisé en volumes élémentaires, appelés pores, reliés entre eux par des étranglements plus étroits appelés constrictions. Des recherches récentes ont montré que la distribution des tailles de constriction (CSD) joue un rôle fondamental dans la compréhension des propriétés de filtration des sols granulaires. Ce travail vise à étudier la CSD et son impact sur les mécanismes de filtration dans les matériaux granulaires. Pour atteindre cet objectif, deux approches ont été suivies dans ce travail: l’une numérique et l’autre analytique. Dans le cas des matériaux de forme sphérique, la méthode des éléments discrets (DEM) permet de calculer la CSD en s’appuyant sur une partition de Delaunay en tétraèdres. Cependant, une CSD plus réaliste peut être obtenue par association des tétraèdres voisins selon un critère basé sur le chevauchement de leurs sphères de vide inscrites. A partir de cette considération et en se basant sur les modèles analytiques existants, un modèle révisé est proposé pour obtenir rapidement la CSD. Les échantillons DEM générés sont ensuite utilisés pour examiner le potentiel de transport des particules fines à travers un filtre d’épaisseur donnée. Les résultats des essais de filtration numériques menés ont montré une corrélation entre la CSD et la possibilité de migration des particules fines. En conséquence, une formule analytique a été proposée pour calculer le diamètre d’ouverture de contrôle des filtres granulaires. Cette taille caractéristique qui prend en compte la granulométrie et la densité du matériau granulaire, a été introduite dans un critère de filtre construit sur la base de la CSD, en vue de le représenter de manière plus physique. Le critère proposé reproduit correctement des résultats expérimentaux rapportés dans la littérature. / The granular discontinuities in hydraulic structures or in their foundation constitute a major source of instabilities causing erosion phenomena, process by which finer soil particles are transported through the voids between coarser particles, under seepage flow. In the long term, the microstructure of the soil will change and the excessive migration become prejudicial to the stability of the structures and may also induce their failure. The safety of earth structures is mainly dependent on the reliability of their filter performance, i.e. the ability of the filter placed inside the structure during construction or outside during repair, to retain fine particles. Indeed, the void space of a granular filter is divided into larger volumes, called pores, connected together by throats or constrictions. Recent researches showed that the distribution of throats (Constriction Size Distribution or CSD) between pores plays a key role to understand the filtration properties of a granular soil. This research is devoted to investigate the constriction sizes and their impact on the mechanisms of filtration in granular spherical materials. To achieve this objective, two approaches were followed in this work: numerical and analytical approaches. In the case of spherical materials, the Discrete Element Method (DEM) can help to compute the CSD using the Delaunay tessellation method. However, a more realistic CSD can be obtained by merging adjacent Delaunay cells based on the concept of the overlap of their maximal inscribed void spheres. Following this consideration and by extending the previously developed analytical models of CSD, a revised model is proposed to quickly obtain the CSD. The DEM data generated are then used to explore the potential of transport of fine particles through a filter of a given thickness by means of numerical filtration tests. A correlation has been found between the CSD and the possibility of migration of fine grains. Accordingly, an analytical formula has been proposed to calculate the controlling constriction size of a filter material. This characteristic size, which takes into account the particle size distribution (PSD) and the density of the material, has been used to reformulate a constriction-based criterion in a more physical manner. The proposed filter design criterion is verified based on experimental data from past studies and a good agreement has been found.

Ce travail de thèse s’est attaché à investiguer, d’une part, le mécanisme d’érosion interne par suffusion dans les ouvrages hydrauliques en terre, et d’autre part, les conséquences qu’il pourrait avoir sur le comportement mécanique du sol, l’objectif principal étant d’améliorer notre compréhension de ce processus et du comportement des sols érodés. La démarche adoptée est principalement expérimentale, réalisée à différentes échelles : du macroscopique, à l’échelle du matériau, au microscopique, à l’échelle des grains constitutifs. A l’échelle macroscopique, des essais de suffusion ont été réalisés sur des échantillons de sol à l’aide d’un nouveau dispositif d’essai d’érosion, appelé perméamètre de suffusion, développé dans le cadre de cette thèse. Après érosion dans le perméamètre, les échantillons érodés sont transférés par une procédure de congélation / décongélation dans un dispositif d’essai triaxial afin d’étudier leur comportement sous chargement mécanique. Les résultats obtenus à cette échelle ont permis de donner un aperçu général du mécanisme de suffusion et de mettre en évidence son impact sur les propriétés de résistance au cisaillement du sol. A l’échelle microscopique, une analyse fine a pu être menée en réalisant un essai de suffusion des mesures in-operando de tomographie à rayons X et de la visualisation locale par techniques optiques sur un sol artificiel. La caractérisation du sol à cette échelle microstructurale a permis de mieux comprendre le processus de suffusion, notamment en mettant en évidence l’apparition et le développement de fortes hétérogénéités qui semblent avoir une influence importante sur la réponse mécanique des sols érodés / This thesis work has investigated, on the one hand, the mechanism of internal erosion by suffusion in earthen hydraulic structures, and, on the other hand, the consequences suffusion can cause on the mechanical behavior of soils, the main objective being to improve our understanding of both the suffusion process and the behavior of eroded soils. The approach adopted was mainly experimental, by a multi-scale scope: from macroscopic, at the material scale, to microscopic, at the grain scale. At the macroscopic scale, suffusion experiments were performed on gap-graded cohesionless soil samples using a newly developed testing device, called the suffusion permeameter. Then, the eroded samples are transferred by a freeze/thaw procedure to a triaxial device to study their behavior under mechanical loading. The achieved results provide a general overview of the suffusion mechanism at the sample scale and highlight its impact on soil shear resistance properties. At the microscopic scale, the suffusion mechanism has been studied by performing a suffusion test with in-operando x-ray tomography and using local visualization based on optical techniques in an artificial soil. Subsequent grain-scale analysis has provided a deeper understanding of suffusion process through the characterization of the eroded soil microstructure, particularly highlighting the occurrence and development of strong heterogeneities, which appear to play a key role in the macroscopic mechanical behavior of eroded soils

Embankment dams are widely used as water-retaining structures through the world. Two principal structural failure modes of embankment dams are internal erosion and slope instability. The objective of this thesis is to investigate the feasibility of applying probabilistic methods in embankment dam assessment. Compared to deterministic methods, probabilistic methods considers the variability in material properties and the results are more assessable. Meanwhile, the derived sensitivity factors of the variables can be used to find the most influential one.Through a literature review, it is found that the difficulties in defining a limit state function for the full process of internal erosion for embankment dams hold back the application of reliability-based methods. However, reliability-based methods have been recognized as suitable for slope stability assessment.In this thesis, both deterministic and probabilistic calculations have been performed for a homogenous embankment dam. The deterministic calculation is carried out in Slope/W to first find out the most critical slip surface. The failure probability of this slip surface is estimated by both Monte Carlo simulations in Slope/W and FORM analysis in Comrel. Then, the 34 most critical slip surfaces from Slope/W are chosen to calculate the system reliability with simple bounds and applied integration. The results from the deterministic and probabilistic calculations showed that the studied dam has a higher risk of failure than allowed. In the system reliability calculation, simple bounds gives a wide range, especially the upper bounds. It was found that classification of different slip surfaces into different groups with respect to geometry and material was useful to simplify the calculations. Not much improvement in accuracy of the system probability of failure is found when increasing the numbers (from 1 to 5) of the most critical slip surfaces from each group. Even the combination of 1 slip surface from each group only gives an error of 6.5%. Categorizing slip surfaces before performing a system reliability analysis is a good way for simplification of the calculations. Due to this, the criteria used for categorization of the slip surfaces are of interest. In this work, it was found that the slip geometry in combination with the materials included in the slip surface constitute a possible way forward to do this. / Fyllningsdammar används ofta som dämmande konstruktioner runt om i världen. Två potentiella brottmoder för fyllningsdammar är inre erosion och släntinstabilitet.Syftet med detta examensarbete är att undersöka möjligheten att tillämpa probabilistiska metoder vid utvärdering av fyllningsdammars säkerhet för dessa brottmoder. Jämfört med deterministiska metoder betraktar probabilistiska metoder även variationen i materialegenskaper. Erhållna känslighetsfaktorer för ingående variabler kan även användas för att hitta de som har störst inverkan på det studerade problemet.I litteraturstudien framkom att det är svårt att definiera en gränsfunktion som beskriver inre erosion för fyllnadsdammar, vilket begränsar dess användbarhet med probabilistiska metoder. För analys av släntstabilitet är dock probabilistiska metoder användbara. Både deterministiska och probabilistiska beräkningar av släntstabiliteten för en fyllnadsdamm har genomförts inom ramen för detta arbete. De deterministiska beräkningarna har utförts med programmet Slope/W, där den mest kritiska glidytan först har analyserats. Brottsannolikheten för dammen har beräknats med både Monte Carlo-simulering i Slope/W och FORM-analys i Comrel. En begränsning med att enbart beräkna brottsannolikheten för den mest kritiska glidytan är att brottsannolikheten kan underskattas då inverkan från andra potentiella glidytor inte beaktas. De potentiella glidytorna kan betraktas som ett seriesystem, där glidytorna är delvis korrelerade med varandra. För att studera denna fråga valdes de 34 mest kritiska glidytorna från Slope/W ut för att beräkna systemets tillförlitlighet. Resultaten från de deterministiska och probabilistiska beräkningarna visade att den studerade dammen hade en oacceptabel brottsannolikhet. I beräkningarna av gränserna för systemets brottsannolikhet visade resultaten att brottsannolikheten kan variera stort beroende på korrelationen mellan glidytorna. Genom att klassificera glidytorna i olika grupper med hänsyn till geometri och ingående material kan beräkningarna för systemets brottsannolikhet förenklas. Resultaten visade att noggrannheten i beräkningarna för brottsannolikheten av systemet inte förbättrades i någon större utsträckning när antalet valda glidytor (från 1 till 5) från varje grupp av likartade glidytor inkluderades i beräkningen. Kombinationen av 1 glidyta från varje grupp gav endast ett fel på 6,5% jämfört med om alla 34 glidytorna inkluderades. Kategorisering av glidytor av samma karaktär i olika grupper rekommenderas därför att genomföras innan systemets tillförlitlighet analyseras. I detta arbete framkom att glidytan geometri i kombination med ingående material i glidytan utgör ett lämpligt kriterium för att göra denna indelning.

Embankment dams are widely used as water-retaining structures through the world. Two principal structural failure modes of embankment dams are internal erosion and slope instability. The objective of this thesis is to investigate the feasibility of applying probabilistic methods in embankment dam assessment. Compared to deterministic methods, probabilistic methods considers the variability in material properties and the results are more assessable. Meanwhile, the derived sensitivity factors of the variables can be used to find the most influential one.Through a literature review, it is found that the difficulties in defining a limit state function for the full process of internal erosion for embankment dams hold back the application of reliability-based methods. However, reliability-based methods have been recognized as suitable for slope stability assessment.In this thesis, both deterministic and probabilistic calculations have been performed for a homogenous embankment dam. The deterministic calculation is carried out in Slope/W to first find out the most critical slip surface. The failure probability of this slip surface is estimated by both Monte Carlo simulations in Slope/W and FORM analysis in Comrel. Then, the 34 most critical slip surfaces from Slope/W are chosen to calculate the system reliability with simple bounds and applied integration. The results from the deterministic and probabilistic calculations showed that the studied dam has a higher risk of failure than allowed. In the system reliability calculation, simple bounds gives a wide range, especially the upper bounds. It was found that classification of different slip surfaces into different groups with respect to geometry and material was useful to simplify the calculations. Not much improvement in accuracy of the system probability of failure is found when increasing the numbers (from 1 to 5) of the most critical slip surfaces from each group. Even the combination of 1 slip surface from each group only gives an error of 6.5%. Categorizing slip surfaces before performing a system reliability analysis is a good way for simplification of the calculations. Due to this, the criteria used for categorization of the slip surfaces are of interest. In this work, it was found that the slip geometry in combination with the materials included in the slip surface constitute a possible way forward to do this.

In this study, two major internal erosion initiation processes, suffusion and concentrated leak mechanisms, which lead to both defect formation in a dam’s body and its foundation and high throughflow in dams subjected to internal erosion were studied. This understanding has the potential to facilitate numerical modelling and expedite dam safety assessment studies.  The throughflow properties of coarse rockfill material were studied by; analysing filed pump test data, performing extensive laboratory experiments with a large-scale apparatus and numerically simulating the three-dimensional flow through coarse rock materials, replicating the material used in the laboratory experiments. Results from the tests demonstrate that the parameters of the nonlinear momentum equation of the flow depend on the Reynolds number for pore Reynolds numbers lower than 60000.  Numerical studies were also carried out to conduct numerical experiments. By applying a Lagrangian particle tracking method, a model for estimating the lengths of the flow channels in the porous media was developed.  The shear forces exerted on the coarse particles in the porous media were found to be significantly dependent on the inertial forces of the flow. Suffusion and concentrated leak mechanisms were also studied by means of laboratory experiments to develop a theoretical framework for continuum-based numerical modelling. An erosion apparatus was designed and constructed with the capability of applying hydraulic and mechanical loading. Results were then used to develop constitutive laws of the soil erosion as a function of the applied hydromechanical load for both suffusion and concentrated leak mechanisms. Both the initiation and mass removal rate of were found to be dependent on the soil in-situ stresses. A three-dimensional electrical-resistivity-based tomography method was also adopted for the internal erosion apparatus and was found to be successful in visualising the porosity evolution due to suffusion. / <p>QC 20161006</p>