Development of empirical approaches to estimate the seismic settlement of embankment dams under earthquake loading

La contribution significative de cette thèse se situe dans le domaine de la déformation sismique de différents types de barrages en enrochement. La déformation excessive permanente à la crête d'un barrage causée par les secousses du sol menacera la sécurité du barrage. Les caractéristiques de ces barrages et la gravité des tremblements de terre (quantifiée par des mesures d'intensité, c'est-à-dire des IM) sont identifiées comme les composants les plus critiques impliquées dans la performance sismique du barrage. Dans la première partie, une étude est réalisée sur la déformation sismique (tassement de la crête) des barrages en enrochement avec masque en béton (CFRD) et sa corrélation avec les IM de mouvements de sol. De cette manière, l'importance des principales caractéristiques des charges cycliques dans une étude de cas CFRD typique modélisée numériquement est soulignée. On en conclut qu'en plus de l'amplitude et de la durée du mouvement de sol, la réponse du barrage est fortement affectée par les caractéristiques de fréquence du séisme. En rassemblant les histoires de cas de CFRD disponibles et en analysant leur tassement sismique, un nouveau IM est proposé pour décrire efficacement le potentiel d'un séisme à induire un règlement dans les CFRD. Une nouvelle relation prédictive est alors établie qui relie la IM suggérée et l'amplitude du tremblement de terre avec le tassement de crête étudié des cas CFRDs. Dans la deuxième partie, les données disponibles pour les barrages en enrochement à noyau de terre (ECRD) comprenant les valeurs de tassement rapportées et les mouvements de sol enregistrés lors des tremblements de terre sont analysées. Deux nouvelles approches sont développées en introduisant deux nouveaux IM et en les corrélant au règlement observé des cas ECRD. Les IM proposés pour les ECRD prennent en compte l'influence des aspects essentiels concernant le comportement non linéaire des barrages lors de séismes violents: dégradation de la rigidité des matériaux, augmentation de l'énergie dissipée et augmentation des périodes de vibration des barrages. Ces problèmes sont affectés par la déformation induite par le tremblement de terre, à travers laquelle la corrélation avec la déformation d'un barrage est découverte. Les analyses ont montré que l'occurrence du tassement est directement affectée par les amplitudes de déformation de cisaillement. Compte tenu de l'importance de la déformation de cisaillement, la dernière partie de cette thèse est consacrée aux caractéristiques dépendantes de la déformation des ECRD. À cette fin, des études empiriques ont été menées sur plusieurs séries chronologiques d'accélération pour les ECRD qui avaient été frappés par des tremblements de terre au Japon. Une série de graphiques et de relations a été établie pour estimer: (i) l'amplitude de la déformation de cisaillement induite; (ii) la diminution du module de cisaillement des noyaux des barrages; et (iii) augmentation des périodes fondamentales des barrages. Cette thèse fournit un assemblage approprié d'outils qui peuvent être utilisés dans la pratique de l'ingénierie, que ce soit à des fins d'analyse dynamique ou de conception. Les graphiques et les relations présentés ici sont basés sur l'examen et l'analyse de la performance réelle de nombreux barrages sous les tremblements de terre. Ils répondent non seulement aux lacunes des méthodes empiriques précédentes, mais sont également précis et efficaces.The significant contribution of this thesis is in the area of earthquake-induced deformation of different types of rockfill dams. The permanent excess deformation at a dam's crest caused by ground-shaking will threaten the dam's safety. The characteristics of these dams and the severity of the earthquakes (quantified by intensity measures, i.e., IMs) are identified as the most critical components involved in the dam's seismic performance. In the first part, a study is performed on the seismic deformation (crest settlement) of concrete-face rockfill dams (CFRDs) and its correlation with ground motion IMs. In this way, the importance of cyclic loads' main characteristics on a numerically modelled typical CFRD case study is underlined. It is concluded that in addition to the amplitude and duration of ground motion, the dam's response is strongly affected by the frequency characteristics of the earthquake. By gathering available CFRD case histories and analyzing their seismic settlement, a new IM is proposed to efficiently describe an earthquake's potential to induce settlement in CFRDs. A new predictive relationship is then established which relates the suggested IM and earthquake magnitude with the surveyed crest settlement of the CFRD cases. In the second part, the data available for earth-core rockfill dams (ECRDs) comprising the reported settlement values and the ground motions recorded during the earthquakes are analyzed. Two novel approaches are developed by introducing two new IMs and correlating them to the observed settlement of the ECRD cases. The IMs proposed for ECRDs take into account the influence of the essential aspects regarding the nonlinear behaviour of the dams during severe earthquakes: stiffness degradation of the materials, increase in dissipated energy, and increase in the dams' periods of vibration. These issues are affected by the earthquake-induced strain, through which the correlation with a dam's deformation is discovered. The analyses showed that the occurrence of settlement is directly affected by the shear strain amplitudes. Given the importance of the shear strain, the last part of this thesis is devoted to the strain-dependent characteristics of ECRDs. To this end, empirical studies were performed on several acceleration time series for ECRDs that had been struck by earthquakes in Japan. A series of graphs and relationships were established to estimate: (i) the amplitude of the induced shear strain; (ii) the decreased shear modulus of the dams' cores; and (iii) increased fundamental periods of the dams. This thesis provides an appropriate assembly of tools that can be utilized in engineering practice, either for dynamic analysis or design purposes. The graphs and relationships presented herein are based on reviewing and analyzing the actual performance of numerous dams under earthquakes. They not only address the shortcomings of previous empirical methods, but are also accurate and efficient

Aspects of Seismic Analysis and Design of Rockfill Dams

Theoretical methods for estimating the dynamic response and predicting the performance of modern rockfill dams subjected to strong earthquake shaking are reviewed. The focus is on methods accounting for nonlinear material behavior, for 3-Dimensional canyon geometry, and asynchronous base excitation. It is shown that both strong nonlinearities and lack of coherence in the seismic excitation tend to reduce the magnitude of the deleterious whip-lash effect computed for tall dams built in rigid-wall narrow canyons. Particular emphasis is accorded to Concrete-Faced Rockfill dams and a case study involving an actually designed dam in a narrow canyon points to some potential problems and suggests some desirable modifications. In the light of theoretical results the paper concludes with a discussion on design rules and defensive measures that would lead to robust design schemes of Earth-Core and Concrete Faced Rockfill dams

Analysis of overburden layer thickness influence on dynamic response of concrete face rock-fill dam

In the past, when performing dynamic response analysis of dams on deep overburden, the dam body and the overburden have often been discussed separately. In this paper, the overburden and the dam body are considered as a whole, and the dynamic response analysis is carried out by using a completely nonlinear dynamic analysis method. From the acceleration of the earth’s surface, the displacement of the dam, and the stress distribution of the panel, the dynamic response of the structure is shown to increase first and then decrease with increasing cover thickness, and the overburden layer thickness corresponding to the extreme point is called the critical thickness. The results obtained in this study can provide a design basis for a face rock-fill dam built on a deep overburden layer

Hydro-mechanical coupling in numerical analysis of geotechnical structures under multi-directional seismic loading

This thesis numerically investigates the seismic behaviour of geotechnical structures under multi-directional loading by employing the coupled hydro-mechanical (HM) formulation of the Imperial College Finite Element Program (ICFEP). The scope of the research work can be summarised as follows: Firstly, the stability of the generalised-α method (CH method) for the coupled consolidation formulation, is analytically investigated for the first time and the corresponding theoretical stability conditions are derived. The analytically derived stability conditions are validated by finite element (FE) analyses considering a range of loading conditions and soil permeability values. Secondly, the site response due to the vertical component of the ground motion is systematically investigated by employing analytical and numerical methods. The compressional wave propagation mechanism in saturated porous soils is investigated by the coupled HM formulation. Furthermore, the undertaken coupled FE analyses explore the effects of the parameters characterising the hydraulic phase, i.e. the soil permeability and soil state conditions, on the vertical site response. Thirdly, three-directional (3-D) site response analyses are conducted for the HINO site of the Japanese KiK-net down-hole array earthquake monitoring system. Different aspects of the numerical modelling for the site response analysis, such as the constitutive model, the use of 3-D input motion and the coupled consolidation formulation, are investigated and validated by the recordings from the KiK-net system. Further parametric studies investigate the impact of the variation of the water table, the soil permeability and the 3-D input motion on the multi-directional site response. Finally, the seismic response of a well-documented Chinese rockfill dam, the Yele dam, is investigated with the dynamic plane-strain FE analysis, accounting for the HM coupling and nonlinear soil response. The numerical predictions are compared against the available static and dynamic monitoring data, which allows for a rigorous validation of the developed numerical model. Furthermore, parametric studies of the Yele dam are conducted to explore the effects of several critical factors on the seismic response of rockfill dams, i.e. the reservoir simulation method, the permeability of materials comprising the dam body, the vertical ground motion and the reservoir water level.Open Acces

Numerical simulation of dynamic centrifuge tests on concrete faced rockfill dam

The design details of concrete faced rockfill dams (CFRDs) have depended extensively on empirical relations and experience. Empirical relations may become insufficient, however, as the height of the dam increases, or when geometric complexities are involved and coupled with complex loading conditions such as seismic loads. To make up for these limitations, numerical tools can give valuable insight into how CFRDs respond to both static and seismic loading conditions. This thesis utilizes numerical simulations using finite element method to study nonlinear dynamic responses of CFRDs. The first part of the study reviews the current state of design details of CFRDs. The design details include properties of commonly used embankment zones, concrete faces, and plinths, including compaction methods of zones, particle sizes, thickness of layers during placement, slab and plinth dimensions, etc. In addition, the performance of some well-documented CFRDs are summarized. The second part of the study evaluates the computed seismic response via numerical simulations representing prototype centrifuge experiments performed on a CFRD model. The effects of two factors on the computed response are investigated: (1) impact of un/reloading rules (hysteretic behavior), and (2) interface type between concrete face and rockfill (welded and friction contact) on the computed seismic response of the CFRDs. The numerical results are evaluated by comparing with measurements in terms of accelerations, bending moment increments of the concrete face, spectral accelerations and lateral deformations. The comparisons show that the proper representation of the hysteretic damping of the rockfill and the interface type have a key role in capturing the measured response of the dam. The analyses demonstrate the effectiveness of employed numerical tools in representing the seismic response of CFRD

Analysis of earth dam-flexible canyon interaction by 3D hybrid FEM-SBFEM

La géométrie et la flexibilité d'un canyon sont les paramètres qui affectent grandement la valeur des périodes naturelles dans les barrages en terre. Le canyon entourant des barrages peut être considéré comme un domaine illimité. Pour prendre en compte ces deux effets, le canyon a été modélisé par SBFEM et le barrage en terre, à géométrie limitée, par FEM. La technique hybride SBFEM-FEM pour l'analyse tridimensionnelle dynamique de l'interaction sol-barrage a été validée avec les résultats disponibles dans la littérature. Comme la matrice de rigidité dynamique du domaine non borné est complexe et dépendante de la fréquence, la méthode classique de superposition de modes n'est pas simple pour le système d'interaction sol-structure. Ainsi, pour obtenir la fréquence propre fondamentale, le barrage a été excité en direction amont-aval. Les périodes naturelles du barrage de terre pour des canyons de formes géométriques et de coefficient de impédance différents ont été obtenues. Ils se sont avérés avoir des effets significatifs sur la période naturelle. Les résultats ont été comparés aux données enregistrées réelles. Il a été constaté que les graphiques proposés dans cette étude peuvent être utilisés par des concepteurs de barrages pour l'estimation des périodes naturelles des barrages en terre dans des canyons de formes et de propriétés matérielles différentes. Plusieurs fonctions d'amplification correspondant à différentes conditions de canyon ont été obtenues en appliquant un déplacement uniforme à la limite du canyon. Une étude approfondie a été réalisée pour examiner les effets de la géométrie et de la flexibilité du canyon sur la réponse en régime permanent du barrage. Ces deux effets ont influencé de manière importante les fonctions d'amplification. Alors que la flexibilité du canyon affecte de manière significative la valeur de la fonction d'amplification maximale, cette valeur ne change pas pour les barrages en terre dans lesquels les canyons ont des formes différentes et la même longueur. De plus, la réponse latérale du barrage de terre dans le domaine temporel a été calculée pour analyser les effets susmentionnés lors d'un tremblement de terre réel. Les fonctions d'amplification proposées ont été utilisées pour comparer les spectres de réponse enregistrés du barrage d'El Infiernillo lors des tremblements de terre de 1966 avec la fonction d'amplification calculée. Un accord raisonnable a été observé entre eux. La méthode linéaire équivalente (EQL) a été implémentée dans le FEM. La technique FEMSBFEM a été étendue pour prendre en compte l'effet du comportement non linéaire des barrages en terre. Il a été observé que le comportement non linéaire affecte grandement la fréquence naturelle, la fonction d'amplification et l'accélération de crête maximale du barrage de terre situé dans les canyons. Les effets de la géométrie et de la flexibilité du canyon sur le comportement non linéaire ont été examinés, et on a vu qu'en augmentant la flexibilité du canyon, l'effet de la non-linéarité était diminué. Le barrage d'El Infiernillo a été modélisé par FEM-SBFEM non linéaire 3D, et une comparaison de la fonction d'amplification de crête obtenue par la méthode proposée avec les données enregistrées montre la précision du FEM-SBFEM non linéaire.The canyon surrounding a dam can be assumed as an unbounded domain, and the geometry and flexibility of a canyon are parameters that greatly affect the values of natural periods in earth dams. In this thesis, in order to take into account these two effects, canyons are modeled by SBFEM, and earth dams, which have limited geometries, are modeled by FEM. The hybrid FEM-SBFEM technique used for the dynamic three-dimensional analysis of soil-earth dam interactions is validated with results available in the literature. Because the dynamic-stiffness matrix of the unbounded domain is complex and frequency-dependent, the classical mode-superposition method is not straightforward for a soil-structure interaction system, and thus, to obtain their fundamental natural frequencies, the modeled dams were excited in the upstream-downstream direction. The natural periods of earth dams in canyons with different geometries shapes and impedance ratios are obtained, and are found to have significant effects on the dams' natural periods. The results are compared with actual recorded data, and it is found that the graphs put forward in this study may be used by practical engineers for the estimation of natural periods of earth dams in canyons with different shapes and material properties. Several amplification functions corresponding to different canyon conditions are obtained by applying a uniform displacement at the canyons' boundaries. A comprehensive study is performed to examine the effects of canyon geometry and flexibility on the steady-state responses of the dams, and it is found that these two effects significantly influence the amplification functions. While the flexibility of the canyon does affect the maximum amplification function value, this value does not change for earth dams in canyons that have different shapes but the same length. In addition, the lateral responses of earth dams in the time domain are computed in order to analyze the aforementioned effects under an actual earthquake. The proposed amplification functions are used to compare the recorded response spectra of the El Infiernillo dam under the two 1966 earthquakes with the calculated amplification function, and a reasonable agreement is observed between them. The equivalent linear method (EQL) is implemented into the FEM, and the FEM-SBFEM technique is extended in order to take into consideration the effect of earth dams' nonlinear behavior. It is observed that such nonlinear behavior greatly affects the natural frequency, the amplification function, and peak crest acceleration of earth dams located in canyons. The effects of canyon geometry and flexibility on the nonlinear behavior are examined, and it is found that by increasing canyon flexibility, the effect of nonlinearity is decreased. The El Infiernillo dam is modeled by the 3D nonlinear FEM-SBFEM, and comparison of the crest amplification function obtained by the proposed method with the recorded data shows the accuracy of the nonlinear FEM-SBFEM

Dam Engineering — Earthquake Analysis

The performance of dams subjected to earthquakes is addressed with particular emphasis of recent earthquakes. Analysis of dams stability during earthquakes by experimental and mathematical models is referred. Foundation studies for soil and rock materials are described and assessment of liquefaction potential is discussed. Selection of design earthquakes by deterministic and probabilistic criteria is presented. Also neotectonics and attenuation relations are described. Monitoring and dam safety during construction and operation are addressed. Reservoir induced seismicity and prototype dynamic tests are treated. Ageing effects and rehabilitation of dams are discussed. Benefits and concerns of dams are referred. Risk analysis is addressed. Some final considerations and topics for discussions are presented

HAZARD CONSISTENT SEISMIC PERFORMANCE ASSESSMENT OF ROCKFILL DAMS

Slope systems such as earth/rockfill dams, waste storage landfill, or natural slopes can undergo significant damage during a seismic event. In the seismic design of slope systems, engineers often consider the amount of seismically-induced displacements as the key engineering demand parameter. The current state of practice procedures to estimate seismically-induced slope displacements are dominated by deterministic or pseudo-probabilistic approaches that do not directly quantify the hazard associated with the estimated displacements. Instead, these approaches assume that the hazard of the ground motion intensity measure of interest (e.g., peak ground acceleration) also represents the hazard of the estimated displacements. In contrast, performance-based approaches, which are the focus of this study, can provide hazard curves for the engineering demand parameter of interest (i.e., the amount of seismically-induced displacements in the context of this study), from which the estimated displacements can be directly related to the hazard design level. In this study, we propose to combine the conditional scenario spectra approach with advanced numerical modeling as a benchmark to evaluate performance-based approaches that rely on simplified and analytical procedures for the estimation of seismically-induced displacements in rockfill dams. The evaluations show that the displacement hazard curves obtained through computationally intensive numerical analyses (performed with three different constitutive models) are more conservative than the hazard curves from simplified or analytical methods. Insights from the comparisons are shared, and potential explanations for the differences are provided. Finally, there are also differences in the displacement hazard curves estimated through numerical analyses, which depend on the trade-off of volumetric/deviatoric mechanisms and damping in each constitutive model.M.S