Numerical Analysis of Dams

ICOLD Committee on Computational Aspects of Analysis and Design of Dams organized the 15th International Benchmark Workshop in Milan, Italy, in September 2019. Theme A of the workshop is related to a seismic analysis of Pine Flat Dam. The study proposed in the Milan workshop is a continuation of investigations initiated by the United States Society on Dams Concrete Dams Committee and Earthquakes Committee during the workshop Evaluation of Numerical Models and Input Parameters in the Analysis of Concrete Dams held in Miami, Florida, on May 3, 2018. The purpose of Theme A investigations is to define uncertainties in numerical analyses of concrete dams in a focused, systematic, and controlled way with collaborative participation from the international dam industry and academia. The objectives of these investigations are to identify key uncertainties that may lead to differences among analysis results, to advance best practices for analyses of concrete dams, and to determine further research needs. Overall, 27 teams, representing 16 countries, submitted solutions to the formulated six study cases for Theme A, together with technical papers that documented the methods and approaches used in the analyses. The summary of the benchmark studies can serve as a reference in verification of computational models used in seismic analysis of concrete dams.

In this paper, seismic analyses of Pine Flat Concrete dam performed as part of theme A in the 15th benchmark workshop are presented. The results presented focuses on differences between mass and massless foundation and the influence from non-linear material behavior. The analyses performed with mass foundation using analytical free field input records and infinite boundary elements corresponded with the expected free surface results, for lower frequencies. For higher frequencies some discrepancies caused by the influence from the dam and the reservoir as expected. The corresponding analyses with massless foundation showed significantly higher accelerations but good agreement with the expected free surface displacement at the dam toe. To consider the influence from nonlinear material behavior, a dynamic push-over analysis (endurance time acceleration function, ETAF) was performed. It was possible to perform the analysis for the full duration of the record, despite significant non-linear material behavior. The initial damage occurred at the upstream toe and then showed significant induced damage as the level of excitation successively increased. In the end of the analysis, the top of the dam is cracked through which would cause an instability failure of the top of the dam.

The seismic FEM modelling of the tallest non-overflow monolith of Pine Flat Dam, a large concrete gravity dam located on King’s River, in California, has been proposed as Theme A of the 15th ICOLD Benchmark Workshop on the Numerical Analysis of Dams. Different case studies have been proposed to study the response of the dam-reservoir-foundation system considering different dynamic loadings and approaches to simulate dam-foundation interaction, different behaviours for the dam concrete and different water levels: all the mandatory cases have been performed together with the non-linear case with the Endurance Time Analysis (ETA) method and the cases with massless foundation, still widely used in Italy for the seismic safety assessment of dams. The analyses have been carried out using the FEM code Abaqus, able to suitably model both the advanced dam-reservoir-foundation interaction and the non-linear behaviour of concrete. The performed set of simulations highlights the benefits of each of the studied approaches in the assessment of the seismic response of a dam-reservoir-foundation system.

Accurate seismic analysis of concrete dams has a great impact not only on design of the new dams but also on the stability assessment of the existing ones. In this regard, one of the challenging issues is to consider the dynamic effects of radiation damping due to the mass of the foundation rock on the seismic responses. In this paper, an absorbing boundary condition, which is comprised of the viscous boundary traction and a free-field column, has been adopted in time domain. Based on the adopted methodology, a finite element model has been prepared for Pine Flat concrete dam using ABAQUS. In order to evaluate the damage level, the concrete damage plasticity model has been assumed for the concrete constitutive relation. The damage level in concrete has been evaluated under Taft earthquake. In addition, the response spectrum that Pine Flat dam can endure has been determined using an endurance time analysis.

The seismic analysis of Pine Flat Dam, a 122 m high concrete gravity dam in California is the subject of the Theme A of the 15th ICOLD Benchmark Workshop on Numerical Analysis of Dams. For that purpose different steps of analyses have been carried out from eigenmodes determination and wave propagation calculations to linear and non-linear time history simulations. The use of free-field boundary conditions in order to model a semi-infinite medium confirms the results from previous works, such as those of the theme B of 14th ICOLD Benchmark Workshop [1]. The use of Endurance Time Acceleration Function (ETAF) record in order to assess the dynamic stability of the dam has been investigated. Finally, the hypotheses and the results of the non-linear analyses are analyzed and discussed.

This paper presents a numerical study of the Pine Flat Dam, a 120 m high concrete gravity dam. The paper deals with the dynamic finite element analysis of the dam for different loads and water levels. The fluid structure interaction is considered through the explicit modeling of the reservoir as acoustic domain within ANSYS. The paper aims at showing the influence of the water level on the dynamic behavior of the dam. Furthermore, the differences in the dynamic behavior comparing the results of a 2D to the results of a 3D model are highlighted. The presented work is a contribution to the “15th ICOLD International Benchmark Workshop on Numerical Analysis of Dams” held in 2019.

Pine Flat Dam, located on King’s River, east of Fresno, California, was constructed by the US Army Corps of Engineers in 1954 with height of 122 m. The dam’s behavior was extensively studied in the 1970’s and 1980’s at the University of California at Berkeley that provide measured and calculated responses for correlation and comparison. For such purpose the dam was analyzed at action of various seismic excitations by taking in consideration linear and non-linear material properties as well and the effect of wave velocities of the rock foundation. The numerical analysis was carried out by preparation of 3D model of the dam thus applying code SOFiSTiK.

The concrete gravity dam proposed for the 15th International Benchmark Workshop on Numerical Analysis of dams (Theme A) was numerically studied using computational finite element modules developed by the authors for dam analysis. The computational models allow non-reflecting boundary conditions, free-field boundary conditions, fluid structure interaction following a Lagrangian displacement based formulation for the fluid and nonlinear material behaviour, both continuum damage and discrete crack approaches. The seismic analysis is carried out using a central difference method, a Newmark implicit integration scheme can be adopted for other types of loading. The computational modules have been used in the assessment of the behaviour of several operating dams. The natural frequencies and force vibration analysis (Case A), the seismic analysis for various reservoir levels following a linear elastic model (Case D) and non-linear seismic type analysis including nonlinear behaviour (Case E) are assessed and discussed using both 2D and 3D modules.

Seismic safety of Pine Flat gravity dam is reevaluated by conducting a dam-reservoir-foundation interaction analysis. Contrary to conventional procedures, a foundation with mass is assumed and to avoid unrealistic detrimental effects of wave reflection at truncated boundaries of model, resort is made to non-reflecting boundary conditions. Plane strain 2D model with different element types are prepared. Solid elements are used to model dam and foundation. Compressible fluid elements is utilized in reservoir. Solid and fluid elements are tied (coupled) together on wet interfaces. To simulate elastic wave propagation in a uniform half-space and non-reflecting conditions at boundaries of truncated FE model, infinite elements along with appropriate free-field boundary conditions are incorporated. Efficiency of adopted numerical model is verified by imposing the foundation block to high and low frequency shear traction impulses applied at the base and calculating resulting velocity responses. Loading consists of self-weight, hydrostatic pressure, harmonic nodal force and base excitations due to earthquake records. Since, the FE model is a foundation with mass, thus the deconvolved acceleration records or the equivalent shear traction records are imposed at the base of foundation. Linear and nonlinear material properties are assumed for concrete. Nonlinearity is consistent with concrete damage plasticity model. In compression, uniaxial stress-strain relation as proposed by Saenz and in tension, stress-crack opening displacement relation as suggested by Hordijk are adopted. Analysis works consist of eigenvalue solution, displacement, acceleration and hydrodynamic pressure time histories for a few selected points. In addition, extent of damage suffered in dam when exposed to earthquake records of Taft and Endurance Time Acceleration Function is estimated.

The theme of this numerical benchmark workshop is related to the seismic analysis of Pine Flat Dam. The dam consists of 47 concrete monoliths and can thus be numerically modelled as a 2D structure. The analysis in this paper is conducted using the commercial finite element solver ANSYS. A comparison between results achieved with the typically used massless foundation and the viscous spring model is given as well as a comparison between results achieved with linear and non-linear concrete material models. In the latter case, the damaged plasticity model for concrete according to Menetrey and Willam is used. It is shown that as long as the loading is weak to moderate, the linear material model can provide a first guess of the response. However, once the loading is moderate to strong, the effects of concrete damage and cracking are significant and the models neglecting material nonlinearity are too conservative regarding expected stresses and cannot predict the real system behavior. Regarding the influence of the analysis approach, a clear tendency for the massless foundation model to reach higher peak responses that the viscous spring model is documented. The latter seems more accurate but is also more complex to set up.

This paper presents studies (models used, calculations and results) performed at Sixense Necs in the context of the 15th ICOLD International Benchmark Workshop on Numerical Analysis of Dams. This work has been proposed by United States Society on Dams (USSD) and concerns the Pine Flat Gravity Dam. The formulated case studies define several different dynamic analyses of the dam, rock foundation and reservoir system. The model consists of the 15.24 m-wide 16th dam monolith (the tallest the monolithic block) and a corresponding strip of the foundation. The tri-dimensional mesh is exclusively composed of linear hexahedron elements. Mechanical behavior of the dam and the foundation is described using 3D continuous medium elements. Displacement restrictions are implemented as dam and foundation boundary conditions, adapted for each involved face. We use the first suggested case to discuss two assumptions: first the reservoir water level modelling influence (added mass or acoustic elements) and secondly massless foundation hypothesis consequences on modal analyses. This work leads us to better describe and understand harmonic crest excitation results and highlight modal analyses dependency of single harmonic excitations. Seismic transient linear and nonlinear analyses are then computed, with seismic loading introduced as an inertial loading. Several results such as dam crest acceleration and dam heel hydrodynamic pressure are presented and compared in order to assess the importance of reservoir water levels and dam material properties. Nonlinear computations show higher crest amplifications, which indicate a loss of dam body stiffness. All numerical analyses are carried out with Code_Aster® software [1].

This paper presents the analyses performed by EDF regarding the seismic analyses of Pine Flat dam proposed by the 2019 ICOLD Benchmark. The results will not be fully presented as they will be summarized and compared with other participants by the formulator. The paper will focus on the numerical analyses methods instead.

The paper presents both a discussion of and results from a structural analysis conducted for Pine Flat Dam as formulated for Theme A of the 15th International Committee on Large Dams (ICOLD) International Benchmark Workshop on Numerical Analysis of Dams. The primary focus of this paper is to examine some basic problems that can arise when using reduced-domain models of a semi-infinite medium. We explore the use of two finite element (FE) codes to model seismic wave propagations in an elastic medium, and we evaluate their accuracy for some simple simulations where the answer is known a priori. We show that significant errors can arise due to the absence of the free-field boundary condition in FE simulations of elastic wave propagation.

Within the “15th International Benchmark Workshop on numerical analyses of Dams”, held in Milan (Italy) in September 2019 and organized by the International Commission on Large Dams (ICOLD), the static and dynamic behavior of a Concrete Gravity Dam was analyzed by means of 2D Finite Element Analyses (FEA). Aim of this paper is to investigate the advantages given by the adoption of a sophisticated FEA method with respect to a simplified analytical model.

A 2D plane strain model is adopted. After some sensitivity studies an average mesh size of 15 m is selected, resulting in about only 700 nodes. Two methods are considered for fluid-structure interaction modelling: full finite element and Westergaard’s added mass approach, leading to non-significant differences in the results, at least for relatively low input motion. The dam nonlinear response is analyzed through an equivalent linearization technique, based on conventional damage model. Damage is tensile strain controlled and results in a lowered effective concrete Young Modulus. Implementation of the method requires an iterative procedure, which converges in a few iterations. Damage development in dam can be measured by the calculated effective frequency. An output is that the Taft input motion does not generate damage either in the dam body or at the dam-foundation interface. Under ETAF, with the adopted definitions of damage, the dam fails at about 9 s.

Since 1991 the Committee on Computational Aspects of Analysis and Design of Dams within the International Commission on Large Dams (ICOLD) organizes the bi-annual held Benchmark Workshops. The 15th Benchmark Workshop, held in Milan (Italy) is dedicated to three formulated themes as well as an open theme. Numerical studies on the seismic response of the highest monolith of Pine Flat Dam are defined in Theme A, which the present paper is focused on. Several numerical studies are part of Theme A, like modal analyses and transient seismic analyses in which the mass of the foundation is respected. Generally, 2D finite element models with plain strain formulation are used. To simulate a far field solution of the given problem, infinite elements are used for static and dynamic load cases. Furthermore, linear elastic material behavior is assumed together with the so-called concrete damaged plasticity model, a non-linear material model, which is applied to the dam body. To account for hydrodynamic effects due to seismic loading acoustic elements are coupled to the solid structural parts to enable the fluid-structure-interaction.

This paper focuses on the Theme A of the 15th International Benchmark Workshop on Numerical Analysis of Dams. The seismic analysis of Pine Flat Concrete Dam proposed by formulators is performed by the Finite Element Method. And several two-dimensional FE models are established for the case studies. All the obligatory and optional cases have been completed, including Case A for EMVG test simulation, Case B for foundation analysis using impulsive loads, Case C for dynamic analysis using impulsive loads, Case D for dynamic analysis using Taft records, Case E for non-linear dynamic analysis, and Case F for dynamic analysis using massless foundation. Results show that the effect of reservoir level is notable in EMVG Test Simulation, and the exist of dam can influence the dynamic response on the top of foundation. Besides, the weak parts of the gravity dam body against seismic are dam heel, dam toe, dam neck, and the upper part of downstream dam body, and dynamic responses computed in model with massless foundation are overestimated.

Investigating the dynamic response of a concrete gravity dam (Pine Flat) is the objective of this study. The acoustic-structure coupling interaction is applied to simulate the reservoir-dam system. The effect of foundation size and the efficiency of the infinite element available in the ABAQUS code to model boundaries are studied. From the comparison of displacement, dynamic pressure and acceleration time history, the evaluation of the dam response to the rising water level is performed. The concrete damaged plasticity model is adopted to evaluate the damage and cracking of the dam caused by Taft earthquake.

The response of concrete gravity dams under seismic loads is a major concern of dam safety assessment in earthquake-prone areas. This study focuses on the seismic analysis of the tallest non-overflow monolith of Pine Flat Dam. The paper presents results of numerical modelling considering the effects of fluid-structure interaction for both linear and nonlinear analysis using accelerations records of the historical Taft earthquake and of an artificially designed Endurance Time Acceleration Function (ETAF). Linear analyses establish the dynamic properties of the reservoir-dam-foundation system and its behavior considering non-zero mass foundation as compared with massless foundation, for two typical reservoir water levels. Whilst the former is physically more complete, it leads to an effective horizontal displacement after the dynamic loading whereas the massless foundation model shows no residual horizontal displacement of the dam base. A damage-plasticity model based on microplane formulation is used to model the extent of damage of the dam body during nonlinear dynamic analysis. Results show the ability of the model to represent cyclic loading conditions, with recovery of the stiffness lost during cracking in the transition from tension to compression state, and subsequent failure of the dam body.

This paper presents numerical modeling and simulation issues seen in static and dynamic analysis of dam-foundation systems. Domain reduction method (DRM) is chosen as the preferred approach for seismic motion input. Proper modeling of inelastic material behavior and seismic energy dissipation is discussed. Verification and validation are essential to ensure reliability of numerical results. Numerical modeling and simulation of a soil/rock—concrete dam system subjected to static and dynamic earthquake loading are presented. It is shown that, in order to make safe and economical design decisions, engineers should have complete understanding and control of the numerical analysis process.

This paper presents a contribution to the analysis of the Pine flat concrete dam, for the 15th ICOLD benchmark. Models developed and main results are presented, as well as additional developments, regarding the influence of some factors on the response of the model to the high frequency impulse and the low frequency impulse defined by the formulators. In order to investigate this frequential behaviour, frequency response analysis is performed. The effect of mesh size, of compressibility of water, and of reflection factor of water in the reservoir is investigated.

Menta Embankment Dam has been selected as Theme B of the International Benchmark Workshop of the International Committee on Large Dams held in Milan in September 2019. The static and seismic behaviour of the dam under seismic input has been evaluated by 13 groups of Contributors coming all around the world. The Menta Dam is a rockfill dam with upstream bituminous facing located in the South of Italy. The major challenge faced by the Contributors was the simulation of the complex dynamic behaviour of rockfill material in order to predict the stress-strain behaviour of the embankment under seismic conditions. Despite the different modeling assumptions proposed by the Contributors, the numerical analyses showed a satisfactorily dynamic performance of the embankment under the proposed seismic input.

The paper describes the results of numerical analyses carried out for the assessment of the seismic behavior of the Menta Bituminous Faced Rockfill Dam, located in Italy. The computer code FLAC based on the finite difference method was used to build a numerical model using the standard input data provided in the framework of the 15th ICOLD International Benchmark Workshop on Numerical Analysis of Dams. The behavior of the rockfill material was modelled using an elasto-plastic constitutive model, taking into account the shear modulus reduction and the hysteretic damping caused by the development of cyclic shear strains in the dam body. Constitutive parameters for rockfill were calibrated using the available laboratory data. Dam seismic behavior with respect to the assigned input accelerograms was inspected; in particular, the seismic performance of the dam was assessed evaluating its response in terms of dam crest acceleration and displacements: the latter turned out to be relatively small at the selected shaking scenario. Finally, the dam seismic behavior was analyzed focusing also on the role of the temperature-dependent bituminous facing stiffness and the return period of the seismic input.

The paper presents a study carried out to evaluate the mechanical behaviour, in static and dynamic conditions, of a 90 m-high bituminous-faced rockfill dam, the Menta dam. This calculation exercise was proposed in the frame of the 15th International Benchmark Workshop on Numerical Analysis of Dams.

Results of static and dynamic analysis of Menta Dam, Italy, for two pre-selected seismic excitations are presented. Static analysis results include effects of: (a) mechanical and fluid flow through the weathered metamorphic rock foundation, (b) staged construction of the dam, and (c) one-step filling of the reservoir. Dynamic analysis results include effects of: (i) natural vibration characteristics of the dam and foundation, (ii) deconvolutions of the seismic accelerations, and (iii) two seismic excitations. Computer programs used include: FLAC (Fast Lagrangian Analysis of Continua) for the static and dynamic analyses; and SHAKE for the deconvolution analyses. Comments on the results presented are included.

Rockfill embankment dams are widely used in areas with high risk of seismic activity because of their good performance for both normal and exceptional loading cases. The paper presents results of 2D numerical analysis with focus on the seismic behaviour of the Menta rockfill dam. The cyclic and highly non-linear mechanical behaviour of rockfill material is one of the main objectives in the simulation. Therefore, the hyperbolic material model has been chosen to model the mechanical behaviour of rockfill material in order to analyse the stress/strain behaviour and potential damages of Menta dam.

Plane strain (2D) finite element method (FEM) simulations are performed in studying the seismic responses of the Menta embankment dam in Italy. An elastoplastic constitutive model is used to account for the static stress-strain behavior of the rockfill materials used, and a Hardin-type dynamic constitute model is employed to consider the dependence of the stiffness and damping on the mean effective stress and the cyclic shear strain amplitude. An empirical permanent strain model is incorporated into the traditional equivalent linear method to capture the earthquake-induced permanent deformation. The involved parameters are calibrated by fitting the available testing results or referring to those of similar materials. The stress and deformation within the dam after reservoir impounding, the acceleration responses during seismic excitation as well as the earthquake-induced permanent deformation are analyzed based on numerical simulations.

The article presents some results of calculations of the stress-strain state of the Menta embankment dam after filling the reservoir, as well as under possible seismic impacts, given by accelerograms of two earthquakes observed in Italy. The calculations were carried out by the finite element method using the software package Plaxis 2D. The dam is divided into three zones according to the stages of construction. Static deformation modules of these zones were considered to be subject to stepwise change during the transition to the next stage of erection. The angle of internal friction was also assumed to be constant for each zone and subject to stepwise change between zones. The dynamic characteristics of the rockfill material for the HS small Plaxis model also are taken different in these three zones. As a result of the calculations, in particular, the residual displacements of the dam after the earthquake and the acceleration on the crest of the dam during seismic impact were determined. The results of the calculations show that the Menta embankment dam is capable of withstanding the considered earthquakes without significant damage.

As a part of seismic analyses of Menta embankment dam (Theme B) in 15th International Benchmark Workshop on Numerical Analysis of Dams, a dynamic elasto-plastic analysis was conducted to study the seismic behavior of Menta dam. An advanced elasto-plastic model to better capture complex loading history, implemented in the finite element procedure Geotechnical Nonlinear Dynamic Analysis (GEODYNA), was adopted to reproduce the dynamic behavior of the rockfill materials. The model parameters of rockfill materials were obtained based on the test results of dynamic modulus and damping ratio. An elasto-plastic soil-structure interface model that can trace the separation and re-contact was used to simulate the interface behaviors between the face slabs and cushion layer, and the model parameters were determined by empirical data published in the literature. The Friuli earthquake occurred in 1976 (1#) and Central Italy earthquake sequence of 2016 (2#) were applied at the bottom boundary of the mesh, respectively. The horizontal records were scaled to a peak acceleration of 0.26 g. The numerical results-initial stress state, acceleration, displacement and slab stress were plotted and analyzed.

Dynamic behaviour of a rockfill dam with bituminous facing is assessed through non-linear time domain FEM (Finite Element Method) analyses. Plaxis HS-small model is used for the rockfill materials. Sensitivities analysis of two different time acceleration histories, bituminous facing stiffness with different temperature and with or without upstream reservoir is undertaken. The dynamic response is generally in line with the expectation. The post-earthquake settlement is estimated 0.21 m, so the dam is unlikely to be overtopped. There could be cracks in the middle part of the bituminous facing. The cracks are more likely to occur when the temperature is 1 °C than 28 °C. Even though a non-linear analysis of this type is more time costly, today’s computer hardware makes it possible for the engineer to perform a full nonlinear dynamic analysis within reasonable time.

The main objective of the reported manuscript is to analyze the seismic behavior of a bituminous-faced rockfill dam (BFRD), specifically the Menta dam. The Menta dam is a rockfill embankment, located in Southern Italy, lying in the heart of Aspromonte Massif. For the purposes of our work we used the GEOSTUDIO 2019 software, were we conducted a series of numerical nonlinear seismic analyses. As a seismic input, recordings from two seismic events (Friuli 1976 and Central Italy 2016) have been considered. Calculated results of the seismic stress/strain behavior, and their brief discussion, are included in the presented paper.

This article presents a simulation of the static and dynamic behaviour of a bituminous faced rockfill dam with the Hujeux constitutive model and the methodology originally developed on code_aster for dams made of saturated granular materials. The calibration procedure of the parameters is carried out on the basis of available tests and static and dynamic results are presented for two seismic signals with different frequency contents. Results are compared with correlations available in the literature. The discrepancies are analysed in terms of the functioning of the behaviour model.

In the analysis of the dynamic response of the bituminous-faced rock-fill dam (BFRD) Menta, is applied non-linear model, where the rock material is approximated by variable sliding modulus, and the asphaltic facing with thickness of 32 cm is applied by joint elements with linear elastic constitutive law. Permanent displacements during the seismic excitation are determined by Dynamic deformation analysis, where the incremental forces are calculated by the difference of the effective stresses in two successive time steps, resulting in adequate deformations. For the state of reservoir rapid filling, as pre-earthquake state by normal water elevation in the reservoir, is used elastoplastic model by variable modulus of elasticity for the rock material. By the dynamic analysis is verified the seismic resistance of the fill dam at action of design earthquakes by PGA of 0.26 g, without disruption of the water impermeability of the asphaltic facing and without danger for rapid and uncontrolled emptying of the reservoir, because the settlements in the dam crest caused by dynamic inertial forces for the earthquake duration amounts 40 cm, i.e. they are much lower than the height above normal elevation in the reservoir till the dam crest, with value of 7.25 m.

In this paper, a seismic analysis of the Menta dam is briefly described. The Menta dam is a bituminous-faced rockfill dam located in Southern Italy, lying in the heart of Aspromonte Massif at an elevation of about 1400 m a.s.l. The embankment is about 90 m high at its deepest point, and the reservoir impounds 1.8 × 107 m3 of water. This dam was designed in the late seventies and built between 1987 and 2000. In the seismic analysis, the dam material has been modelled with an elasto-plastic constitutive law which is characterized by a Young’s modulus dependent on the stress level and on the distortional strain and by a curvilinear yielding surface. Both the calibration of the model and the dynamic analysis has been carried out by means of the FDM code FLAC (Fast Lagrangian Analysis of Continua [1]) version 8.1 which adopts an explicit time-integration scheme.

Large embankment dams are characterized by highly nonlinear material behavior. A main challenge to the numerical investigations of such type of dams is the proper selection of constitutive material models and of the required laboratory and field investigations and tests. It is equally important to model realistically the compaction of the fill layers to account for the pre-consolidation effects that fill material undergoes. This paper presents a FEM nonlinear static and seismic analysis of Menta Dam which is located in Southern Italy and is under operation since 2000. The analysis is aimed at considering in a realistic and precise manner the above-described effects. The FEM model is based on the input data provided in the formulation of Theme B of the 15th ICOLD Benchmark Workshop. The Hardening Soil model combined with the Small Strain Stiffness model is used to simulate the behavior of the rockfill for the considered load combinations. The hydrodynamic pressures caused by the reservoir during earthquake is approximated by means of fluid-structure interaction with incompressible fluid. The foundation is assumed massless. The maximum vertical displacement at the end of the construction is approximately eighty centimeters and is in the central zone of the dam. The first impounding causes re-orientation of the principal stresses in the dam body zone underlying the bituminous face, but it does not entail significant additional displacements. The permanent displacements in case of earthquake are moderate, as the permanent settlements are well within the freeboard of the dam. Based on the results of the analyses performed, recommendations are formulated regarding the constitutive models and the type of analysis to be considered for this dam type.

In an attempt to evaluate current models for the safety assessment of dykes on soft soils, STOWA, the foundation for research on regional dykes in the Netherlands, launched and supported a full scale test on a regional historical dyke, which included observation of the pre-failure response and the design of its failure. The stress test on the dyke included progressive excavation at the toe and rapid drawdown in the ditch next to the toe of the embankment, until failure eventually occurred. The data and the observations collected on site during the test are a unique body of information on the coupled hydro-mechanical pre-failure behaviour and on the resistance of the earth construction. A selection of these data was included in the formulation of the Theme C of the 15th International Benchmark Workshop on Numerical Analysis of Dams, held in September 2019 in Milano, Italy. This contribution presents the main outcomes of the numerical benchmark, coming from the results of the different groups, which analysed the case with current geotechnical constitutive and numerical models.

Smoothed Particle Hydrodynamics (SPH) is a mesh-less Computational Fluid Dynamics method suitable for several application fields such as floods, fast landslides and sediment removal from water bodies. As a preliminary demonstration, this method is herein applied to simulate the on-site experiment of the 3D full-scale Kagerplassen dyke failure. The geometries of the granular media and the water reservoir are elaborated from the available measures by means of analytical procedure. Results are provided in terms of: 3D fluid dynamics fields (medium interfaces and velocity); hydrographs (time series) for the medium/fluid level (maximum height), flow rate, cumulated volumes and velocity. The 3D SPH model simulates the triggering and propagation of the sliding surfaces within the dyke and simulates the following run-out of both the granular material and the water flood.

The main aim of Theme C of the 15th International Benchmark Workshop on Numerical Analysis of Dams is the evaluation of currently available computational techniques and numerical models for the assessment of dykes on soft subsoil. For this purpose, the results of a full-scale test on a regional dyke on soft subsoil located in the Kagerplassen, in South Holland has been applied. In this study, a coupled hydro-mechanical analysis was performed in order to predict and describe the pre-failure and failure behavior of this structure. The 2D finite element code GEOSTUDIO 2016 was utilized for the analysis, where within the modelled period the state of failure of the structure was reached. Subsequently the modelled pre-failure behavior was compared to the measured data gained from the performed full-scale test and a back-analysis was conducted with emphasis on the applied material models and properties.

This paper summarizes the results and the main features of the fully coupled hydro-mechanical analysis of the stress test carried out in the Leendert de Boerpolder levee in the Netherlands. The analyses have been performed with software Midas GTS NX and Abaqus, using two-dimensional coupled pore-displacement elements for transient consolidation analysis. The Midas model featured the Modified Mohr-Coulomb model while the Abaqus model used Modified Cam Clay plasticity with porous elasticity. Material parameters were calibrated based on laboratory data and in situ CPTu tests. Results were compared with field measurements in order to assess the ability of current models to assess the safety characteristics of earth retaining structures subject to groundwater flow and stress. The models predicted failure during the 3rd excavation, in agreement with the planned stress test schedule.

In order to evaluate available models for the safety assessment of levees on soft soils, a full-scale experiment was performed by Dutch authorities bringing a historical dyke to failure. In the paper, the pre-failure and the failure state of the levee are investigated by means of finite element analyses using the software code DIANA. The calculated pre-failure response is successfully validated against the displacements and pore pressures measured during the full-scale experiment. The limit state of the levee is estimated by means of strength reduction analyses using simple plasticity models as well as by more comprehensive stress-strain analyses using the Modified Cam-clay model. Based on the results of the different analyses performed, conclusions are drawn about the type of analysis recommended for the safety assessment of such levees on soft soils. Recommendations are formulated regarding the constitutive model, the hydraulic conditions and the influence of the spatial variation of strength parameters.

The The Nam Ngum 3 dam, actually under construction in Lao PDR, with a maximum height above foundation of 210 m, will be one of the highest CFRDs. ARTELIA is the Owner’s Engineer of Electricité du Laos (EDL) for this 480 MW HPP built on a major tributary of the Mékong. One of the main challenges in the design of the dam comes up from the tight valley. Actually, based on international feedback, extensive concrete face cracking is expected if specific construction provisions were not adopted. Moreover, the concrete face is constructed immediately upstream of the narrowest part of the valley. This results in high stiffness contrast between the banks where the concrete face lies on the bedrock and the central part where it is supported by the rockfill. These peculiar boundary conditions induce a diagonal bending which needs to be addressed with care. Consequently, ARTELIA’s numerical model aims at checking that the design of the dam and its construction provisions are efficient to avoid a detrimental cracking of the concrete face. The Hardening Soil Model constitutive law is used for the rockfill. The material parameters are calibrated by means of large-scale apparatus laboratory tests. A size effect assessed by means of a rational approach is taken into account. Finally, a creep constitutive law is considered in order to anticipate the effects of delayed deformation of the rockfill on the concrete face behavior. The modeled concrete face includes the compression joints with initial opening for which the efficiency in reducing the compression stress is clearly highlighted. Based on the results of the numerical analysis, this paper describes the supplementary construction provisions proposed in order to secure a safe behavior of the dam and guarantee an acceptable watertightness of the concrete face.

FEM simulations are widely recognized as essential tools in the analysis of the behaviour of dam systems. A detailed representation of the dam structure allows for a better understanding of the local response of important structural elements. The present paper intends to provide a FE modelling procedure of concrete arch-gravity dams. Case of study is the arch-gravity dam of Ridracoli. The vertical construction joints are included in the model as solid elements; their influence on the dynamic properties of the structure is investigate and, adopting the CDP—Concrete Damage Plasticity—model for the filling mortar, elasto-plastic damage time-history analyses are performed. Under MCE—Maximum Credible Earthquake—and varying the water level, the damage parameters evolution is analysed. All simulations integrate the structure-foundation and the fluid-structure interaction by means of rock mass solid and acoustic elements, respectively; moreover, the adopted damping coefficients of rock mass and structure are calibrated on linear elastic dynamic analyses. The inclusion of vertical construction joints into finite element models of dams allows us to verify the local behaviour of such real discontinuities under severe seismic events and therefore to verify the seismic vulnerability assessment of the whole structure.

Heightening very high gravity dams is one of the solutions considered as part of the energy transition and to mitigate the effects of climate change. The paper presents a stepwise approach to assess the potential for dam heightening and its impact on the hydroelectric scheme. A first diagnosis focusses on identifying and characterising the main site and operation constraints to dam heightening. Then alternative heightening concepts are screened for feasibility, in particular heightening concepts such as gravity dam, arch dam or multi-arch dam. The selected concept(s) are then developed to create several variants with diverse geometries. Subsequently several steps are undertaken to verify internal and external stability for given selected design criteria. This approach is applied to the case study of the Grande Dixence, the highest gravity dam in the world located in Switzerland, considering heightening solutions up to a maximum of 30 m. Within this heightening window the additional loads of reservoir water and dam weight should be in principle acceptable for the already known foundation conditions. The main site constraints are in fact due to the partial submergence of the main headwater conveyance tunnel and the need to adapt the downstream surge tank of the Fionnay’s power plant. Structurally, heightening the dam with a similar structural concept was preferred from inception when considering joint behaviour of the original and heightened structures. Four alternative heightening geometries were compared in terms of their overall stability for various heights of elevation. The results, obtained by analytical and computational models, showed acceptable values for all four variants. Regarding the economic analysis, a preliminary analysis of the Levelized Cost of Electricity (LCOE) computed considering the additional electricity and the construction costs is remarkably low in comparison with other projects within the Energy Transition and point out that a height increase within 10–15 m would likely be optimal. This study confirms the interest to pursue investigations and studies beyond the feasibility stage, in view of determining the optimal heightening design and further develop the business plan for high-value hydropower production.

Being able to describe the state of a dam regarding the safety requirements is an obligation that dam owners have to fulfil. A constant surveillance is thus established, based on the measurement of structural behavioural parameters. The measurements are used to feed descriptive statistical models which are classically linear, such as the historical HST (Hydrostatic-Season-Time) model. This assumed linearity is a significant shortcoming, which only permit a poor description of the reality when it comes to analysing the piezometry in the foundations of arch dams, and more particularly at the rock-concrete interface. Indeed, the contact between rock and concrete evolves during seasons between an open and closed state, under the influence of the thermal loads, and of the hydrostatic load, but also during the years due to ageing effects. Thus, the effects of those three influencing loads on the piezometry are not merely additive. Consequently, analysing such a complex phenomenon with accuracy is only possible when considering complex interactions between the influencing quantities. This paper presents a model that describes the piezometry at the rock-concrete interface as being a fraction of the total upstream hydrostatic load. Since it has been empirically observed that the permeability variations and the piezometry are non-linearly correlated, this non-linearity is explicitly included into the model formulation. In this work, the resulting model is applied to analyse monitored piezometric levels recorded at the interface of a French arch dam. This approach greatly improves the analysis that could be made by HST, and it permits a thorough physical interpretation of the studied piezometry. Eventually, the temporal evolution of the state of aperture of the contact is assessed, which is a great improvement for dam surveillance.

The seismic response of dams is significantly influenced by dynamic Soil-Structure Interaction (SSI) phenomena. Most of the dedicated methods to perform SSI analyses may be classified within two main approaches, namely, the so-called Direct Method and the Substructure Method. The present discussion focuses on a specific formulation of the Direct Method, valid for uniform free-field motion, and less-often adopted in the main stream practical applications, by which the seismic action is converted into inertial loads directly applied to the structure. A Substructure Method implementation is also considered, in canonical form. First, the equivalence of the Direct Method and Substructure Method approaches is theoretically discussed; then, the seismic responses of the Pine Flat dam gathered from both methods are compared, to confirm the analytical outcomes. This study demonstrates that the adopted Direct Method approach provides a wholly equivalent dynamic response, to that from the Substructure Method, with the advantages of being robust enough and rather efficient for self-implementations, possibly employing commercial FEM computer programs.

To analyze the influence of microscopic parameters on deformation properties of rockfill materials in triaxial test simulation with discrete element method (DEM), a control variable method was adopted to determine the influence on stress-strain and volumetric strain curves. In addition, the influence mechanism was explained. Firstly, the characteristics and development trend of triaxial test simulations of rockfill materials were summarized in detail, and it is determined that the contact bond model is the best choice for simulating triaxial tests of rockfill materials. Subsequently, a detailed DEM model of the triaxial test of rockfill materials was established to study the influences and mechanism of friction coefficient, normal and shear stiffness, normal and shear bond strength. Finally, the relationship between deformation properties and broken bond of rockfill materials was investigated. It is considered that the broken bonds of rockfill materials were obviously influenced by microscopic parameters, and the deformation properties were significantly affected by broken bonds. Therefore, in this paper, the influence of microscopic parameters on the deformation properties of rockfill materials was explored, providing a reference for the calibration of microscopic parameters and laying a foundation for the characteristics research of rockfill materials.

ELC Electroconsult S.p.A. (Italy), in association with NEWJEC Inc. (Japan), is carrying out the updating of a feasibility study and the detailed design of a storage hydropower project in the Himalayas, under a grant from the Asian Development Bank. The project layout includes two powerhouses. The main powerhouse, with a capacity of 600 MW, is located at some 14 km distance from the reservoir. The headrace tunnel to the main powerhouse has a length of 13.3 km. It is located in a region of high seismicity, with lack of access along the tunnel alignment, which it makes it difficult to get comprehensive geotechnical information along the tunnel route. Despite the uncertainties present, it is necessary to provide and assessment of the headrace tunnel cost and schedule to determine the project feasibility. This paper shows the procedure followed by the Consultant to assess a risk-based contingency cost for the tunnel accounting for the uncertainties present. The uncertainties have been grouped in three types: (1) extent of the geological formations, (2) geo-mechanical properties, and (3) the occurrence of adverse events such as collapses, rockfalls, squeezing and tunnel flooding due to groundwater. The objective is to assess a level of cost contingency associated with a certain probability of not being exceeded, to inform the decision on the amount of the contingency cost that should be considered at this stage of the project.

The improvements in monitoring devices result in databases of increasing size showing dam behaviour. Advanced tools are required to extract useful information from such large amounts of data. Machine learning is increasingly used for that purpose worldwide: data-based models are built to estimate the dam response in front of a given combination of loads. The results of the comparison between model predictions and actual measurements can be used for decision support in dam safety evaluations. However, most of the works to date consider each device separately. A different approach is used in this contribution: a set of displacement records are jointly considered to identify patterns using a classification model. First, potential anomaly scenarios are defined and the response of the dam for each of them is obtained with numerical models under a realistic load combination. Then, the resulting displacements are used to generate a machine learning classifier. This model is later used to predict the most probable class of dam behavior corresponding to a new set of records. The methodology is applied to a double-curvature arch dam, showing great potential for anomaly detection.

The installation of automatic data acquisition systems, together with the use of machine learning, allow obtaining useful information on the behaviour of dams. In this contribution, an example of application for a machine learning based predictive model is presented. Specifically, the level in a piezometer and its association with the reservoir level is studied for an embankment dam. The results show the model’s ability to identify changes in dam response by taking full advantage of the available monitoring data. The flexibility of the algorithm allows different types of variables to be analysed without the need to determine a priori which are the most influential loads or how they affect the target value. The model has been implemented in a software tool that includes additional functionalities, specific for the treatment and exploration of dam monitoring data. It can be applied to different dam types and response variables.

The failure of a large gravity dam might have catastrophic effects putting at risk human lives, not counting the considerable economic consequences. Most of dams are located in natural hazard prone areas so the structural control and the evaluation of the dam fragility (in particular against to flood and earthquake) assume great importance both to apply early warning procedures and to define resilience-enhancing strategies. Numerical models assume great importance to predict the seismic behaviour of the complex dam-soil-reservoir interacting system, nevertheless they are affected by different uncertainties. The effects of uncertainties can be reduced by calibrating finite element models with all available data about the structure. Measurements recorded by monitoring systems and in situ test results take on a major role as important sources of information. This paper investigates the effect of the uncertainties in the static and dynamic analysis of existing concrete gravity dams by means of two case studies. The general Polynomial Chaos Expansion technique is used to propagate the uncertainties through the numerical models of the case studies even without High Performance Computing. The effects of the uncertainties are thus quantified in terms of model output variation. General Polynomial Chaos Expansion-based predictive models are then used for the solution of the inverse problem thus reducing the computational burden.

When performing predictions of future behaviour and assessments of the safety for embankment dams, numerical modelling if often needed as support. For embankment dams a usual issue is to obtain values of the material parameters for the material in the dam. Sampling is not easily performed, and it could also negatively affect the performance and safety of the dam. One way to determine values of the material parameters is to create a digital copy of the dam by utilizing so called inverse analysis. The created numerical model is calibrated towards field measurements. To make the reality and the numerical model correspond to each other, the values of material parameters for constitutive models are calibrated. The calibration is done by an automatized process. Further, the calibrated model could be used in predictions of future dam behaviour. The methodology has been shown to work for field data containing errors of a usual magnitude.