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The present paper focuses on the influence of Rayleigh and Love waves on the seismic structural performance of a simplified nonlinear beam structure representing a bridge column. The impact of surface waves in the structure is quantified directly by a coupled 3D SEM-FEM numerical wavepropagation simulation from the earthquake source to the structure using the Domain Reduction Method.In the first step, ground motions, including basin-induced surface waves, are generated from a regional model containing the earthquake source and a simplified basin. Surface waves are extracted and characterized with the Normalized Inner Product (NIP) in terms of amplitude andfrequency content from ground motions at different locations inside the basin. In the second step, the seismic wavefield from the SE simulation is imposed in a FE model composed of a nonlinear structure placed over a portion of the basin sediments. The model considers soil-structureinteraction and structural non-linearity through a multifiber beam approach.By placing the structure in different positions, the extracted surface waves and the structural damage can be linked to a specific location inside the basin. Therefore, the spatial variability of the structural damage and the surface wave characteristics can be quantified. Consequently, this workevaluates if structural damage can be estimated only from typical ground motion intensity parameters or if other parameters associated with surface wave characteristics are necessary. The results show a correlation between obtained seismic damage with rotational components fromsurface waves (torsion for Love waves and rocking for Rayleigh waves).

International audience

The prediction of the seismic response of critical structures is highly sensitive to many aspects, among which the earthquake source and the geological setting are prominent. The related uncertainty issues must be taken into account in seismic risk mitigation studies, for example through the evaluation of several realizations of a future earthquake scenario. This aspect is crucial when addressing vulnerability studies at a regional scale. When opting for physical-based numerical simulations (PBS), however, the computational burden increases along with the expected degree of fidelity, making it difficult to evaluate more than a few dozens of alternatives. To cope with this disadvantage, in this work an alternative method is proposed, which exploits a rather low number of synthetic earthquake simulations and combines them with the empirical Green function (EGF) method, to finally generate thousands of alternative yet realistic seismic response of the site of interest. This hybrid strong motion predictions benefit of both (i) PBS high fidelity and (ii) data assimilation of strong ground motion records in the seismic area of interest, via EGF method, producing broadband synthetics at a relative cheap computational price. The power of the hybrid method is tested on a real case scenario, embodied by the ground-shaking prediction at the nuclear site of Cadarache, in the surroundings of the fault of Middle Durance, in South-Eastern France. Thousands of broadband (0–15 Hz) hybrid synthetic seismic response are generated, associated with different fault parameters (EGF method) and based upon a few key physics-based simulations, accurate up to 5 Hz.

The study focuses on both the effects of soil foundation liquefaction on the induced damage of an embankment and on the generation of a probabilistic seismic demand model that relates few specific characteristics of seismic hazard at a site with the liquefaction-induced settlement. To this aim, several non-linear dynamic Finite Element (FE) analyses were performed. However, given the costly evaluation of the numerical model simulations for a large number of earthquake records, a surrogate model based on multi-fidelity approach is used to represent the output of the expensive FE model. In this approach, the training database is composed by computational low-fidelity data together with limited high-fidelity one. Thus, the proposed methodology is used to generate the curves describing the annual rate of exceeding different values of damage levels. A comparison with the FE reference results suggests that the accuracy of the prediction of the proposed surrogate model is comparable to those from direct numerical FE analysis. Findings also illustrate clearly the importance and the advantages of an adequate definition of the input parameters to build the surrogate model.

International audience; This contribution provides an overview of the SINAPS@ French research project and its main achievements. SINAPS@ stands for ''Earthquake and Nuclear Facility: Improving and Sustaining Safety'', and it has gathered the broad research community together to propose an innovative seismic safety analysis for nuclear facilities. This five-year project was funded by the French government after the 2011 Japanese Tohoku large earthquake and associated tsunami that caused a major accident at the Fukushima Daı¨chiDaı¨chi nuclear power plant. Soon after this disaster, the international community involved in nuclear safety questioned the current methodologies used to define and to account for seismic loadings for nuclear facilities during the design and periodic assessment review phases. Within this framework, worldwide nuclear authorities asked nuclear licensees to perform 'stress tests' to estimate the capacity of their existing facilities for sustaining extreme seismic motions. As an introduction, the French nuclear regulatory framework is presented here, to emphasize the key issues and the scientific challenges. An analysis of the current French practices and the need to better assess the seismic margin of nuclear facilities contributed to the shaping of the scientific road-map of SINAPS@. SINAPS@ was aimed at conducting a continuous analysis of completeness and gaps in databases (for all data types, including geology, seismology, site characterization, materials), of reliability or deficiency of models available to describe physical phenomena (i.e., prediction of seismic motion, site effects, soil and structure interactions, linear and nonlinear wave propagation, material constitutive laws in the nonlinear domain for structural analysis), and of the relevance or weakness of methodologies used for seismic safety assessment. This critical analysis that confronts the methods (either deterministic or prob-abilistic) and the available data in terms of the international state of the art systematically addresses the uncertainty issues. We present the key results achieved in SINAPS@ at each step of the full seismic analysis, with a focus on uncertainty identification, quantification, and propagation. The main lessons learned from SINAPS@ are highlighted. SINAPS@ promotes an innovative integrated approach that is consistent with Guidelines #22, as recently published by the French Nuclear Safety Authority (Guidelines ASN #22 2017), and opens the perspectives to improve current French practice.

International audience; When assessing seismic risk at a city scale, local site conditions can significantly modify the destructive potential of an earthquake. This was the case in Mexico City in 1985 and 2017, which is located on a sedimentary valley. For that reason, characterization and consideration of these site effects, in addition to assessing the probability of occurrence of a destructive earthquake in a given region, are crucial. For this purpose, a tri-dimensional model was developed using a numerical code that permit to carry out such kind of studies. The code is based on the spectral element method allowing solving the waves propagation problem in tri-dimensional solid media. The seismic phenomenon is simulated in its entirety: from the seismic source to the site using a representative model of the complexity of the wave path. However, this introduces uncertainties that must be quantified, controlled and reduced by validating the results of the numerical tool with measurements on a real study site. This work aims to study numerically the effect of the geometric structure of soil and subsoil on the prediction of ground motion at the regional scale. The first obtained results show the importance of the in-situ measures on the regional scale simulations.

The excavation and construction of metro structures in a high-density urban area require cautions in the design process. The knowledge of ground should warn the engineers and enable them to take measures to avoid or at least to minimize the potential risks. To achieve that task, numerical simulations are used to determine the deformations due to the construction process. The role played by soil behavior is as fundamental as the values of its parameters. Due to the heterogeneity character of the soil, its random parameters influence on the response of the numerical simulation. A good understanding of that response could be addressed through sensitivity analysis, that is, the assessment of the impact of individual input parameters or sets of input parameters on the response of the model. In this paper, a sensitivity analysis is performed to illustrate the effect of the uncertainty of the input parameters on the response of a numerical simulation of tunnel construction through the finite element code Zsoil. For this purpose, the first-order sensitivity and the total order sensitivity based on Fourier Amplitude Sensitivity (FAST) technics will be performed.

International audience; In practice, the performance of the structure is studied based on a seismic scenario composed of independent single earthquakes. But in real life, the structure is subjected to multiple earthquakes during its typical design working life, which will produce an evolution of damage with time. The main purpose of this paper is to quantify the liquefaction-induced damage of an embankment due to sequential earthquakes during a defined working life. Moreover, a non-parametric survival analysis is used to estimate the time (in years) until a defined damage level is reached during a specific time interval. For this purpose, a site was chosen where its seismicity and its Probabilistic Seismic Hazard Analysis (PSHA) were identified. First, a site-specific seismic analysis was assessed, that consists in finding the relation between the Intensity Measures (IM) and the Engineering Demand Parameter (EDP). Second, in order to estimate the lifetime distribution as well as the Mean Time To Failure (MTTF) of the embankment, survival functions were drawn. The used time histories were stochastically generated from synthetic ground motion models. In this study, an elastoplastic multi-mechanism soil behavior model was used. According to the obtained results, after the sequential loading, the cumulative damage is either progressive with or without extensive damages or sudden with drastic damages. Moreover, based on the chosen ground motion model, the embankment reaches a moderate damage level before its defined working life. In addition, a numerical parametric analysis is performed in order to quantify the impact of considering (or not) the loading history and the recovery time between each ground motion on the obtained MTTF of the embankment. This study pointed out on the importance of the history of loading since it affects the overall performance of the embankment. Finally, two synthetic ground motion models were assessed in order to generalize, to a certain extent, this work.

The seismic response of Aratozawa rockfill dam (Japan) is simulated in the present work by using ECP constitutive model and Aster FE code [1]. Static calculation is first performed for computing initial stress and strain fields. Then, the numerical convergence problem in dynamic step under two-component seismic loadings is discussed. It is found that the numerical damping induced by time-integration algorithms does not help solving the numerical convergence problem. However, the augmentation of subdivision level of calculation step is very efficient. The total duration of calculation is extended but practically acceptable. Finally, the dynamic response of Aratozwa dam is compared with real measurements presented in the literature with three sets of model parameters. All results show great agreement with the measurements and also be reconfirmed by Anderson’s criteria.

The major cause of earthquake damage to an embankment is the liquefaction of the soil foundation that induces ground level deformations. It is well known that the liquefaction appears when the soil loses its shear strength due to the excess of pore water pressure. This phenomenon leads to several disastrous damages of the soil foundation. The aim of this paper is to assess numerically the effect of the liquefaction-induced settlement of the soil foundation on an embankment due to 76 real earthquakes extracted from the PEER database. For this purpose, a 2D finite element model of a dam founded on a layered soil/rock profile was considered. An elastoplastic multi-mechanism model was used to represent the soil behaviour. The crest settlement of the embankment was selected as the quantifiable damage variable of the study. Fragility functions were drawn to give the probability exceedance of some proposed damage levels as function of a seismic severity parameter. In addition, the anisotropy was tested by the change in the soil permeability and a comparison with the isotropy was held. According to the results, the crest settlement increases with the peak ground acceleration and the fragility functions showed that above 0.2g, the probability to have moderate damage in the anisotropic case reaches unity whereas it is lesser in the isotropic case. The embankment will not show serious damage for this same value of acceleration in the two cases., Comment: Geo-Risk 2017 : Reliability-Based Design and Code Developments, 2017, Denver, United States

In this paper, a finite element modeling technique, taking into account the effects of soil-structure interaction (SSI) is proposed for structural analysis and design. The one-dimensional model of a nonlinear multilayered soil profile is assembled with a multi-story multi-span frame model and the dynamic equilibrium problem is solved directly. The one-directional propagation of three-component seismic waves (1D-3C) is modeled taking into account the SSI, in the case of rigid shallow foundation and negligible rocking effects. The 1D-3C wave propagation model provides the three components of motion at the base of the frame structure, allowing the reduction of mesh size and computation time, compared with a fully three-dimensional model, and avoiding modeling difficulties to realize a reliable three-dimensional soil domain, related among others to boundary conditions. The proposed model allows the analysis of those structural dynamic features, seismic wave and local soil stratigraphy, that produce changes in the ground motion at the surface. The model reproduces well expected phenomena, in the case of layered soil with increasing nonlinearity and for different inertia distribution in the frame structure. SSI combined with seismic site effects is analyzed in a Japanese soil profile, using as seismic loading a 3C record of 2011 Tohoku earthquake.

A binary mixture homogenization model is proposed for predicting the effects on liquefaction-induced settlement after soil improvement based on the consideration of the added spatial variability between the natural and the treated soil. A 2D finite element model of an inelastic structure founded on a shallow foundation was coupled with a binary random field. Nonlinear soil behavior is used and the model is tested for different mesh size, model parameters and input motions. Historical evidence as well as physical and numerical modeling indicate that improved sites present less liquefaction and ground deformation. In most cases this improvement is modeled as homogeneous; however, in-situ measurements evidence the high level of heterogeneity in the deposit. Inherent spatial variability in the soil and the application of some soil improvement techniques such as biogrouting and Bentonite permeations will necessary introduce heterogeneity in the soil deposit shown as clusters of the treated material in the natural soil. Hence, in this study, improvement zones are regarded as a two-phase mixture that will present a nonlinear relation due to the level of complexity of seismic liquefaction and the consequent settlement in a structure. This relation is greatly affected by the mechanical behavior of the soils used and the input motion. The effect on the latter can be efficiently related to the equivalent wave period as the proposed homogenization model depends on the stiffness demand of the input motion.

This study investigates the sensitivity of physics-based earthquake prediction to the choice of the regional geological model. The generally poor information on the mechanical properties of the Earth’s crust induces large uncertainty margins on the synthetic seismic response. Therefore, uncertainty quantification must be associated with high-fidelity numerical simulation, especially when verging on broad-band simulations (i.e., numerical theoretical accuracy higher than the conventional 1 Hz limit). In this paper, the synthetic seismic response of the Niigata region (Japan), during the Ch u etsu offshore earthquake (MW6.6) serves as representative case study. Three plausible three-dimensional (3-D) geological structures are compared for two point-wise aftershock numerical simulations, duly validated. The framework of comparison targets the Ground Motion Prediction Equation (GMPE) for pseudo-spectral acceleration at the surface. The impact of the geology on the variability of between-event and the within-event residuals is inferred from synthetic simulations and related to common parameters representing site-specific conditions.

This article presents the main results of the validation phase of the PRENOLIN project. PRENOLIN is an international benchmark on 1D nonlinear (NL) site‐response analysis. This project involved 19 teams with 23 different codes tested. It was divided into two phases; with the first phase verifying the numerical solution of these codes on idealized soil profiles using simple signals and real seismic records. The second phase described in this article referred to code validation for the analysis of real instrumented sites. This validation phase was performed on two sites (KSRH10 and Sendai) of the Japanese strong‐motion networks KiK‐net and Port and Airport Research Institute (PARI), respectively, with a pair of accelerometers at surface and depth. Extensive additional site characterizations were performed at both sites involving in situ and laboratory measurements of the soil properties. At each site, sets of input motions were selected to represent different peak ground acceleration (PGA) and frequency content. It was found that the code‐to‐code variability given by the standard deviation of the computed surface‐response spectra is around 0.1 (in log10 scale) regardless of the site and input motions. This indicates a quite large influence of the numerical methods on site‐effect assessment and more generally on seismic hazard. Besides, it was observed that site‐specific measurements are of primary importance for defining the input data in site‐response analysis. The NL parameters obtained from the laboratory measurements should be compared with curves coming from the literature. Finally, the lessons learned from this exercise are synthesized, resulting also in a few recommendations for future benchmarking studies, and the use of 1D NL, total stress site‐response analysis.

The spatial incoherence of ground motion during an earthquake can have a significant effect on the dynamic response of engineering structures such as bridges, dams, nuclear power plants and lifeline facilities. The main objective of this paper is to study the effect of anisotropic heterogeneities in a soil layer overlying homogeneous bedrock on the lagged coherency of surface ground motion. A set of numerical experiments is performed based on 2D spatial variability of shear-wave velocities modeled as a homogeneous stationary random field and discretized by the EOLE method (Expansion Optimal Linear Estimation). Seismic ground motions were simulated using FLAC2D software in the 1–25 Hz band for a plane wave excitation with SV polarization. The soil is characterized by horizontal and vertical autocorrelation distances ranging between 5 and 20 m and 1 and 2 m, respectively, and a coefficient of variation of the shear-wave velocity varying between 5% and 40%. The synthetic seismograms calculated for 9 parameter sets (100 realizations each) clearly show seismic waves scattering and surface waves diffracted locally by the ground heterogeneities, generating large spatial variations in coherence mainly controlled by the coefficient of variation of shear-wave velocity. Consistently with existing models and experimental data, the numerical coherency curves decrease with frequency and receiver distance, however at a rate which is lower than that observed in the experimental data. This difference is probably due to intrinsic attenuation that is not accounted for in the simulations and/or to our 2D simulations that do not reproduce the complete wavefield. The numerical average coherency curves for each parameter set exhibit maxima within narrow frequency bands caused by the vertically trapped body waves and surface wave propagation properties within the average ground model. This interpretation is supported by experimental data recorded in the Koutavos-Argostoli valley (Greece).

In this study, we analyze the acceleration time histories data at the Belleplaine (Guadeloupe, French West Indies) vertical array, recorded between 2008 and 2014, to evaluate the seismic response of sediments. First, we apply seismic interferometry by deconvolution method to compute the in-situ shear wave velocity between the sensor at the surface and the two shallow sensors located at GL-15m and GL-39m depth. The efficiency of this method is discussed by studying the variability of the velocity profile obtained and comparing with the in-situ geophysical survey of the site. Computed strains between sensors remain very weak, lower than 10 −5 , meaning that nonlinearities are not expected for these events. Moreover, the small dispersion of shear wave velocities values deduced from seismic interferometry may be related to the elastic behavior of the soil column. Furthermore, the transfer functions between each sensor combination are inverted to obtain a new velocity profile compatible with the geological knowledge of the site. The lag times calculated by seismic interferometry are then used to constrain random perturbations of the inverted velocity profile, allowing to study the variability of the 1D soil response. Since recorded motion has a PGA less than 10 cm/s2 in the dataset, we numerically predict the nonlinear response of the site using strong motion from a worldwide dataset. Furthermore, we study the ratio between the PGV and the medium shear velocity as a proxy showing the development of shear deformation during strong motion. Finally, using strong motion events from a worldwide dataset, we numerically predict the nonlinear response of the site based on shear wave velocity variation and the strain proxy computed by the particle velocity versus shear wave velocity ratio. We conclude that seismic interferometry by deconvolution is a robust and accurate solution to help extracting the shear wave velocity profile and to monitor the soil nonlinear response. This technique can be used when strong earthquakes will be recorded at this experimental site in order to track and assess nonlinear effects in the soil column.

Spatial variability of earthquake ground motion (SVEGM) refers to the differences in amplitude and phase between recordings of the same earthquake at different locations. In the near-surface, geological processes (sedimentation, erosion) and anthropogenic activities can lead to small scale spatial heterogeneities of soil mechanical properties, which may affect SVEGM. In this paper, the effect of shallow 2D spatial variability of the shear wave velocity (Vs) on the surface ground motion is assessed through a set of numerical experiments, using a simple 2D velocity structure (a sedimentary layer over a half-space). Non-linearity or damping are not considered in the wave propagation calculation in order to solely focus on the effects of soil elastic property variability. Vs is modeled as a random field using the EOLE method (Expansion Optimal Linear Estimation) and considering three statistical parameters: the coefficient of variation, and the horizontal and vertical autocorrelation distances. Seismic ground motions are numerically simulated for a plane wave excitation with SV polarization. Modeling results clearly highlight the scattering of surface waves by ground heterogeneities, leading to large spatial variations in surface ground motion. We computed surface ground motion indicators (resonance frequency, spectral amplification, Arias intensity and duration) and we showed that their spatial variability is mainly controlled by the Vs coefficient of variation. A comparison between 2D and 1D ground motion probabilistic modeling shows that the 1D probabilistic approach may correctly reproduce average fundamental resonance frequencies and corresponding amplification. However, the 1D approach significantly under-predicts both ground motion amplification at higher frequencies and related variabilities, as well as Arias intensities and inferred durations, which are all controlled by the generation of locally diffracted surface waves.

This paper presents the mechanical behaviors of the lacustrine deposit, a representative soil in Bogotá, Colombia. Initially, the physical characterization of the deposit is performed via laboratory tests (grain size distribution, scanning electron microscopy, Atterberg limits and water content). This characterization intends to explain the special characteristics of the mechanical behaviors of this soil. Then, various triaxial tests are carried out with controlled loading path, strain rate change, relaxation, extensile stress, and cyclic loading. The test results reveal the shape of the yield curve for Bogotá soil (in a natural state), and also show that an increasing effect of the strain rate depends on the liquid limit. This effect is also preserved with extensile stresses (which are poorly studied in soil mechanics). Finally, other effects, such as the loss of structure in the reconstituted samples and the effect of shear modulus at low strains, are studied for Bogotá soil. Keywords: Cyclic triaxial tests, Triaxial compression test, Time-dependent response, Lacustrine soils, Soil compressibility, Yield curve

International audience; Understanding and modeling the evolution of structural systems throughout time, especially by considering its cumulative damage, is a key point for risk decision making. This concept is of extreme importance for design criteria definition, operational policies, robust life-cycle cost estimations and real time-dependent vulnerability assessment. In particular, an important objective of these type of analyses, is the estimation of the structure lifetime distribution and its corresponding mean time to failure (MTTF). However, analytic solutions of these two main concepts are not an easy task. Therefore , it is necessary to develop new approaches that can be used to better approximate the lifetime of structures in an accurate and useful way for engineering purposes. Within this context, the objective of this research work is to present a methodology to estimate the lifetime distribution of structures, and the derived properties of a structural system located in a seismic region. Mainshocks are modelled as a homogeneous Poisson process with constant mean rate of occurrence. The model, assumes that the deterioration of a given structure is mainly controlled by the cumulative damage generated by a set of consecutive earthquake events in a certain period of time. This approach can be easily implemented and provides a good estimation of the lifetime distribution of a structure, without venturing into the mathematical complexities of an analytic solution but retaining the main features of the system performance. Finally, an illustrative practical case at a real site is provided.

In this study, a series of nonlinear 2D finite difference analyses were carried out to study the seismic behavior of non-yielding gravity-type earth retaining walls founded in rock site subjected to “Real Near-Fault ground motions”. Numerical analyses were performed by two dimensional explicit FLAC2Dfinite difference code. Various sets of real data (forty accelerograms) records were applied at the bedrock level to assess model’s dynamic response for different earthquake scenarios. All ground motions have a baseline correction and all output accelerograms obtained from the dynamic analyses are filtered using a non-causal bandpass filter of order 4, between 0.1 and 25 Hz. In these calculations, the foundation non-deformability, the seismic amplification or attenuation and the non-linearity of the soil placed behind the retaining wall are considered. We highlighted an important correlation between the PGA (Pic Ground Acceleration) calculated in free field (accounting for the wave propagation) and the obtained pressure. Numerical results are compared to theoretical calculation methods available in the literature. Among them, Wood's method seems to be the most precise one, presenting small deviations with the numerical methods. Moreover, it is the safest method, in the sense that it predicts the highest pressure values, not only in the elastic cases but even in some situations when non-linearity appears. In addition, we found that the time corresponding to the maximum calculated values of lateral earth pressure acting on the wall matches with the time of the calculated (PGAff). So, the main takeaway of this observation is the zero effect of seismic duration on pressure evolution.

International audience

The aim of this paper is to assess numerically the recorded response of the Aratozawa dam to the Iwate-Miyagu Nairiku earthquake in June 14 of 2008. For this purpose, a 2D Finite Element model of the dam was considered. An elastoplastic multi-mechanism model was used to represent the soil behaviour. A mechanical-equivalent fully drained decoupled analysis is performed to simulate the behaviour of the core and the upstream rock-fill. In addition, a “half-space bedrock’s boundary condition” is used to simulate the borehole condition found at the gallery level. Finally, the obtained results show that the two conditions assumed to define the initial state of all materials could be used as a first approach to simulate the dam behaviour.

International audience; The increasing importance of performance-based earthquake engineering analysis points out the necessity to assess quantitatively the risk of liquefaction of embankment-type structures. In this extreme scenario of soil liquefaction, devastating consequences are observed, e.g., excessive settlements, lateral spreading and slope instability. The present work discusses the global dynamic response and interaction of an earth structure-foundation system, so as to determine quantitatively the collapse mechanism due to foundation’s soil liquefaction. A levee-foundation system is simulated, and the influence of characteristics of input ground motion, as well as of the position of liquefied layer on the liquefaction-induced failure, is evaluated. For the current levee model, its induced damage level (i.e., induced crest settlements) is strongly related to both liquefaction apparition and dissipation of excess pore water pressure on the foundation. The respective role of input ground motion characteristics is a key component for soil liquefaction apparition, as long duration of mainshock can lead to important nonlinearity and extended soil liquefaction. A circular collapse surface is generated inside the liquefied region and extends toward the crest in both sides of the levee. Even so, when the liquefied layer is situated in depth, no significant effect on the levee response is found. This research work provides a reference case study for seismic assessment of embankment-type structures subjected to earthquake and proposes a high-performance computational framework accessible to engineers.

International audience; The scope of this paper is to give an insight into the advantages of a new, all-embracing, modeling approach of a strong ground motion scenario, by carrying out a source-to-structure analysis at regional scale, accounting explicitly for the uncertainties related to the databases and the models. To this end, a suitable case-study is represented by the 2007 Mw6.6 Niigata-Ken Ch¯ uetsu-Oki seismic sequence (west Japan), that damaged the Kashiwazaki Kariwa Nuclear Power Plant. This study describes the effect of the wave propagation path within the Earth's crust on the seismic response of nuclear reactor buildings located nearby a seismogenic source. The multiscale problem is de-coupled into three steps: (1) a parallel simulation of seismic-wave propagation throughout the Earth's crust at regional scale (≈ 60 km wide, major 3-D geological interfaces found below the nuclear site), reliable up to 5.0 Hz; (2) a mid hybridization step consisting in enriching the synthetic wave-field at high frequency (up to 30 Hz), employing an Artificial Neural Network to predict the short-period (SP) spectral ordinates; (3) a high-resolution structural dynamic analysis, introducing the hybrid broad-band synthetics as input wave-motion. A simplified stress-test is performed, ✩ Fully documented templates are available in the elsarticle package on CTAN. by simulating two small point-wise aftershocks at different source-site position. The impact of the underground 3-D geology on the structural components is finally quantified, by injecting the obtained broad-band time-histories in a Soil-Structure Interaction (SSI) model of the nuclear reactor building. The good fit obtained in terms of amplification factor at different recording stations assures the high-fidelity of the holistic philosophy endorsed.

International audience; The aim of this paper is to clarify the extent of near-source effects and non-linear soil response that took place at the Japanese nuclear site of Kashiwazaki-Kariwa,during the MW 6.6 Niigata-Ken Chūetsu-Oki earthquake (July, 16th 2007). The interest ofthis case study stems from the relative small source-to-site distance and shallowhypocenter depth, coupled with the consistent seismic record database available from twodown-hole arrays of strong motion accelerometers, installed within the nuclear site.Records were processed first to highlight those features related to near-source conditions,such as directivity and polarization, and, subsequently, to identify dependence of siteresponse on the direction of motion and on the non-linear soil behaviour. Moreover,borehole interferometry was used to check the two available velocity profiles (estimated byin situ PS logging) used for 1D linear equivalent numerical simulations. In one case, animproved agreement with the empirical amplification functions was obtained using asmoothed profile. The main non-linear features highlighted by signal processing wereglobally reproduced by means of linear-equivalent analyses, that pointed out the stronginfluence of the input motion direction. Among the principal results of this research, it wasfound that the hanging-wall and directivity effects along with the non-linear site-effectsdominate the ground response during the main shock, and that the site amplificationfeatures are strongly dependent on the rotation angle of the horizontal components.

The current seismic design philosophy is based on nonlinear behavior of structures where the foundation soil is often simplified by a modification of the input acceleration depending on the expected site effects. The latter are generally limited to depend on the shear-wave velocity profile or a classification of the site. Findings presented in this work illustrate the importance of accounting for both soil nonlinearity due to seismic liquefaction and for soil-structure interaction when dealing with liquefiable soil deposits. This paper concerns the assessment of the effect of excess pore pressure ( $$\Delta p_{w}$$ ) and deformation for the nonlinear response of liquefiable soils on the structure’s performance. For this purpose a coupled $$\Delta p_{w}$$ and soil deformation (CPD) analysis is used to represent the soil behavior. A mechanical-equivalent fully drained decoupled (DPD) analysis is also performed. The differences between the analyses on different engineering demand parameters are evaluated. The results allow to identify and to quantify the differences between the analyses. Thus, it is possible to establish the situations for which the fully drained analysis might tend to overestimate or underestimate the structure’s demand.

International audience; The major cause of earthquake damage to an embankment is the liquefaction of the soil foundation that induces ground level deformations. The aim of this paper is to assess numerically the effect of the liquefaction-induced settlement of the soil foundation on an levee due to real earthquakes. The seismic vulnerability is evaluated in terms of analytical fragility curves constructed on the basis of non-linear dynamic Finite Elements (FE) analysis. However, FE analysis can be expensive due to very large number of simulations needed for an accurate assessment of the system failure behaviour. This problem is addressed by building a Gaussian Process (GP) emulator to represent the output of the expensive FE model. A comparison with the FE reference results suggests that the proposed GP model works well and can be successfully used as a predictive tool to compute the induced damage on the levee. Findings also illustrate clearly the importance and the advantages of an adequate definition of the input parameters to built the GP model.

International audience

International audience; A finite element soil-structure interaction model is coupled with a discrete auto-regressive code, in order to analyze the effect of added spatial variability due to soil improvement in seismic risk analysis. The success of soil improvement techniques is related to the effectiveness of the method-i.e. how much of the soil is being changed-but also to its efficiency in improving the soil behavior-i.e. how much are the liquefaction and liquefaction-induced settlement reduced. As these techniques can add spatial variability to a deposit, it can affect the triggering of liquefaction on the soil and the behavior of the structures above it. In this study, this heterogeneity is modeled as a binary mixture, composed by the original liquefiable sand and the added treated sand. The soil behavior is represented by a fully nonlinear elastoplastic multi-mechanism model. The co-seismic settlements of the structure and the liquefaction of the soil deposit are estimated for different effectiveness levels-measured by mixture fractions-and for different spatial distributions. In general, both very small or very high mixture fractions presented low efficiency as the improvement in the relative settlement was small. Additionally, results show that the interaction between loose and dense deposits is highly dependent on the spatial distribution. Therefore , homogeneous equivalent models will rarely correspond to the average of the heterogeneous response.

The assessment of seismic site effects such as ground motion and permanent displacement requires the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading from small to medium and at large strains. The main objective of this paper is to enhance and validate the performance of an elastoplastic constitutive law in modelling non-linear soil behaviour, with particular attention to the stiffness and damping evolution with deformation. First, a simple and rational strategy is presented to derive model parameters related to shear hardening based on experimental data. Secondly, as the elastoplastic law tends to overestimate damping in the large strain range in comparison with experimental data (Ishihara, 1996; Puzrin, 2012), a new parameter is introduced in the model to overcome this issue. The modified model response exhibits lower stiffness than the standard one. For sands, an effective reduction of the damping factor is achieved and good agreement is obtained for hysteretic loop and straindependent stiffness and damping curves. For clays, the reduction in damping is also achieved for large strains, but it also has a significant effect on the soil stiffness. Finally, numerical simulations of one-dimensional ground seismic response show that for sands the new parameter has no visible effect on the seismic soil response due to maximum shear strain level achieved, while for clays the reduction in both damping and stiffness occurs.

International audience; The Tohoku earthquake and associated tsunami in March 2011 caused a severe nuclear accident at the Fukushima Daiichi Nuclear Power Plant, where level 7 (International Atomic Energy Agency (IAEA) – INES scale) meltdown at three reactors occurred. The underestimation of the seismic and tsunami hazards has been recognized and the seismic margins assessment of the nuclear plants remains a priority for the whole nuclear community. In this framework a five-year research project called SINAPS@ (Earthquake and Nuclear Installations: Ensuring and Sustaining Safety) is currently on-going in France. A reliable estimate of seismic margins is possible only if all uncertainties, epistemic and aleatory, are effectively identified, quantified and integrated in the seismic risk analysis. SINAPS@ brings together a multidisciplinary community of researchers and engineers from the academic and the nuclear world. SINAPS@ aims at exploring the uncertainties associated to databases, physical processes and methods used at each stage of seismic hazard, site effects, soil and structure interaction, structural and nuclear components vulnerability assessments, in a safety approach: the main objective is ultimately to identify the sources of potential seismic margins resulting from assumptions or when selecting the seismic design level or the design strategy. The whole project is built around an “integrating” work package enabling to test state-of-the-art practices and to challenge new methodologies for seismic risk assessment: the real case of Kashiwazaki-Kariwa Japanese nuclear plant, shocked by the severe earthquake in 2007 provided a rich dataset which will be used to compare with the predictions. The present paper proposes for each step of the seismic risk analysis a review of the state of practice in France in the nuclear field and then precise the objectives and research strategy of SINAPS@ to overcome identified limitations or weaknesses. Scientific issues are illustrated through preliminary results of the project.

International audience; The physics-based numerical simulation is a reliable tool to build-up source-to-site strong ground motion earthquake scenarios. In this paper, we enhance those forward simulations by including (1) the hysteretic non-linear behaviour of geomaterials and (2) the heterogeneous nature of soils. Scattering-induced damping, ground motion spatial incoherence and de-amplification may therefore be reproduced. A classical case study is considered herein: a seismic wave generated by a localized double-couple earthquake propagating towards the surface through layered elastic homogeneous bedrock, underlying a heterogeneous non-linear soil stratum. 3D numerical simulations were performed by means of a Spectral Element Method (SEM) code. The latter was coupled with a highly scalable random field generator to reproduce the media heterogeneity. Moreover, an extension to J 2 elasto-plasticity numerical integration was introduced. Time-histories and lagged-coherency curves at the surface show the ground motion de-amplification (mainly related to soil non-linearity) and loss of coherency (due to the wave-scattering caused by soil heterogeneity).

International audience

International audience; Soil structures such as river dikes, highway embankments, and earth dams have been frequently damaged during past major earthquakes. In most cases, large deformations occurred due to liquefaction of the supporting loose cohesionless foundation soil, resulting in cracks, settlement, lateral spreading, and slumping. Some researchers showed that river levees resting on non-liquefiable foundation soil have been damaged. In this regard, the base of such levees subsided in a bowl shape due to foundation consolidation that was shown to have the principal contribution to liquefaction as an underlying mechanism. This paper aims at describing the global dynamic response of a thin Loose Sand layer located buried in deep (10m) stratum of Clay (less permeable), situated at the foundation of a levee, due to liquefaction phenomenon. This study purpose is to reproduce such behavior by applying numerical simulations, adopting the open-source computational platform OpenSees. In particular, this study considers a 2D soil model of a levee subjected to earthquakes in order to investigate the failure of embankments induced by non-liquefiable soil foundation with a thin sand layer with partially drained condition. A parametric analysis using ground motions at multiple levels of intensity was performed to highlight the influence of parameters such as, the thickness of saturated zone, the permeability ratio between saturated zone and non-liquefiable soil (i.e. drain condition) on the obtained crest settlement and on the induced damage level of the embankment.

Minisymposium: The SINAPS@ French research project on integrated seismic risk assessment for nuclear safety; International audience; This study presents a preliminary calibration of a large-scale seismological model of the M W 6.6 Niigata-Ken Chuetsu-Oki (Japan) earthquake of July, 16 th 2007. The strong ground motion affected a wide area in the surrounding of the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP). Due to the relative small source-to-site distance and shallow hypocenter depth, this seismic scenario resulted very interesting and well documented (a consistent database of seismic recordings is available). In this context, the test-case represents a suitable benchmark for the work-packages of the SINAPS@ project. SINAPS@ is the first French research project with the objective to quantify the uncertainty of the procedures to estimate the seismic risk. In this context, an omni-comprehensive approach is followed, modelling the wave-propagation from the fault to the structural components. This study is intended to describe the steps to build up and calibrate a reliable seismic scenario, capable to provide a synthetic wave-field at the regional scale. This objective is pursued by (1) assessing a stratified geological model for the Niigata region, (2) testing the effect of the source parameters in a kinematic approach (e.g. the rise time and the shape of the Source Time Function) and (3) checking the topography effect. A series of 3D source-to-site numerical simulations of the M W 4.4 NCOEQ2007 aftershock was therefore carried out with this regard (performed by means of the Spectral Element Method, SEM). The seismic scenario was calibrated with the aid of the semi-analytical solution provided by the Wave-Number Integration Method (WNI) and by comparing the synthetics with the recordings at several locations (i.e. the KNET-Kik-Net stations nearby and the KKNPP site). Finally, the forward physics-based analysis ended up by providing broad-band synthetic time-histories to be exploited in further studies as a reliable regional incident wave-field for the engineering bedrock

International audience; We look at the behavior of structural systems under the occurrence of seismic events with the aim of identifying the fragility curves. Artificial Neural Network (ANN) empirical regression models are employed as fast-running surrogates of the (long-running) Finite Element Models (FEMs) that are typically adopted for the simulation of the system structural response. However, the use of regression models in safety critical applications raises concerns with regards to accuracy and precision. For this reason, we use the bootstrap method to quantify the uncertainty introduced by the ANN metamodel. An application is provided with respect to the evaluation of the structural damage (in this case, the maximal top displacement) of a masonry building subject to seismic risk. A family of structure fragility curves is identified, that accounts for both the (epistemic) uncertainty due to the use of ANN metamodels and the (epistemic) uncertainty due to the paucity of data available to infer the fragility parameters.

The aim of this work is to assess numerically the influence of track geomaterials variability on the railway track stiffness. A non-intrusive probabilistic methodology based on in situ cone resistance tests is implemented in a 2D bidimensional finite element model with a modified plane strain condition. This model is used to estimate the track response to a moving load, which is characterized by the track stiffness measurement rolling stock. Spatial variability is taken into account by considering the cone resistance of each track layer as independent random fields, each one characterized by a marginal probability density function obtained from a statistical description of measured in situ data and a theoretical autocorrelation function. Despite input data variability, results presented much less variability than the input, which could be explained by both: load repartition over steppers, i.e. homogenization of the track stiffness measure, and deterministic characteristic of rail pads. Moreover, reduction of variance is observed, which means that less variance is observed for smaller correlation distances. In addition, a sensitivity analysis is also performed based on the Fourier Amplitude Sensitivity Test (FAST) and it showed, for the present case study, that the platform presents the highest first-order sensitivity index for all analyzed cases.

The present paper deals with the influence of soil non-linearity, introduced by soil liquefaction, on the soil-foundation–structure interaction phenomena. Numerical simulations are carried out so as to study an improvement method to reduce the liquefaction potential in a sandy soil profile subjected to a shaking. The efficiency of the preloading in both the mitigation of a liquefiable soil and the reduction of induced structure relative settlements is showed. However, the intervention at the foundation soil modifies the dynamic characteristics of soil–structure system and it seems to increase the induced seismic forces during earthquake. In addition, a numerical parametric analysis is performed so as to quantify the impact of the uncertainties associated with the input signal on both the ground motion and the apparition of liquefaction phenomena.

International audience; The aim of the work, described in this paper, is to propose a method enabling the in-situ mechanical characterisation of railway materials from the use of acceleration records of a downhole seismic instrumentation network installed in a research facility of the national French Railway Company. This is done using some geophysical methods (i.e. interferometry and time-frequency analysis) to analyse the vibrations induced by the dynamic loading of a passing trains. According to the recorded data from the instrumented site, it is shown that the response of rail-embankment-ground system is mainly non-linear elastic.

Numerical simulations demonstrate mesh dependency problems which can change the response of the model, especially when localization phenomena emerge. The use of a regularization method, called first gradient of dilation, is evaluated for the analysis of shear bands under dynamic conditions. It aims to eliminate the mesh dependency of the results by taking into account an enriched kinematic approach. While under static loading this method provides satisfactory results, under dynamic conditions it introduces a noise. An analytical solution of coupled S–P wave propagation in nonlinear micromorphic media and numerical simulations describe the irregular dynamic response of regularized media.

The excess pore pressure ( $$\Delta p_w$$ ) generation and consequent reduction in effective stress lead to the softening of a liquefiable soil deposit that can alter ground motions in terms of amplitude, frequency content and duration. However, total stress models, which are the most currently used, do not take into account coupling of excess pore pressures and soil deformations. To assess this effect, two analyses were made: (1) a Biot hydraulic and mechanical computation of a saturated soil deposit with coupling pore pressures and soil deformations and (2) a mechanical computation of a decoupled model with same initial behaviour. Both analyses were performed with a fully nonlinear elastoplastic multi-mechanism model. As $$\Delta p_w$$ depends on the soil properties, two soils were analysed: loose-to-medium and medium-to-dense sand. The results regarding the profile of maximum accelerations and shear strains, the surface accelerations and their corresponding response spectra are analysed. The mean values of the normalized response spectra ratio of surface accelerations between the coupled and decoupled model show a deamplification of low and high frequencies (i.e. at frequencies lower than 1.0 Hz and higher than 10 Hz) that tend to increase with the liquefaction zone size. Coupling of $$\Delta p_w$$ and soil deformation is therefore of great importance to accurately model the ground motion response. On the contrary, while peak acceleration predictions could be conservative, the amplification on the low frequencies could be largely underestimated which could be highly prejudicial for flexible buildings.

© 2016 Seismological Society of America. All rights reserved. PREdiction of NOn-LINear soil behavior (PRENOLIN) is an international benchmark aiming to test multiple numerical simulation codes that are capable of predicting nonlinear seismic site response with various constitutive models. One of the objectives of this project is the assessment of the uncertainties associated with nonlinear simulation of 1D site effects. A first verification phase (i.e., comparison between numerical codes on simple idealistic cases) will be followed by a validation phase, comparing the predictions of such numerical estimations with actual strongmotion recordings obtained at well-known sites. The benchmark presently involves 21 teams and 23 different computational codes. We present here the main results of the verification phase dealing with simple cases. Three different idealized soil profiles were tested over a wide range of shear strains with different input motions and different boundary conditions at the sediment/bedrock interface. A first iteration focusing on the elastic and viscoelastic cases was proved to be useful to ensure a common understanding and to identify numerical issues before pursuing the nonlinear modeling. Besides minor mistakes in the implementation of input parameters and output units, the initial discrepancies between the numerical results can be attributed to (1) different understanding of the expression “input motion” in different communities, and (2) different implementations of material damping and possible numerical energy dissipation. The second round of computations thus allowed a convergence of all teams to the Haskell–Thomson analytical solution in elastic and viscoelastic cases. For nonlinear computations, we investigate the epistemic uncertainties related only to wave propagation modeling using different nonlinear constitutive models. Such epistemic uncertainties are shown to increase with the strain level and to reach values around 0.2 (log10scale) for a peak ground acceleration of 5 m=s2at the base of the soil column, which may be reduced by almost 50% when the various constitutive models used the same shear strength and damping implementation.

This article presents an assessment of the effects of pore water pressure generation of the soil foundation on the seismic road embankment response. Numerical simulations were carried out to study the preloading technique as an improvement method for reducing the liquefaction potential and the induced settlements in a sandy soil profile. The analyses showed that the use of preloading reduces the induced settlements mostly because of the increase in lateral confinement in the superficial soil layers that results from an increase of the coefficient of lateral earth pressure at rest (ko). The research also showed that the efficiency of the countermeasure method was limited to cases in which earthquakes produced a liquefaction zone lower than the depth of the overconsolidated soil.

L’objectif de ce travail est d’etudier les effets du comportement non lineaire du sol, introduit par la liquefaction, sur l’interaction sol-structure non lineaire lors d’un seisme en utilisant des simulations numeriques. On evalue aussi l’efficacite d’une methode de renforcement de sols dans la reduction du potentiel de liquefaction d’un profil de sol. Les effets favorables ou defavorables de l’utilisation d’inclusions rigides dans la reponse sismique d’une structure reposant sur un profil de sol liquefiable sont presentes. Cette analyse montre l’efficacite de la methode a reduire la liquefaction et par consequent les tassements induits mais elle montre aussi que cette intervention modifie les caracteristiques dynamiques du signal a la surface et en consequence augmente le niveau des deplacements subits par la structure.

International audience; ABSTRACT. The seismic margins assessment of the nuclear plants is a priority for the whole nuclear community, further enhanced since the Tohoku Japan earthquake in 2011. In this framework a 5 years research project called SINAPS@ (Earthquake and 9ème Colloque National AFPS 2015 – IFSTTAR 2 Nuclear Plants: Ensuring and Sustaining Safety) is currently ongoing in France. A reliable estimate of seismic margins is possible only if all uncertainties, epistemic and aleatory, are effectively identified, quantified and integrated in the seismic risk analysis. SINAPS@ brings together a multidisciplinary community of researchers and engineers from the academic and nuclear worlds. SINAPS@ aims at exploring the uncertainties associated to databases, physical processes and methods used at each stage of seismic hazard, site effects, soil and structure interaction, structural and nuclear components vulnerability assessments, in a safety approach: The main objective is ultimately to identify the sources of potential seismic margins resulting from assumptions or when selecting the seismic design level or the design strategy. The whole project is built around an " integrating " work package enabling to test state-of-the-art practices and to challenge new methodologies for seismic risk assessment. The present paper illustrates the crucial links and interactions between all actors of the project to reach the objectives.; L'évaluation des marges sismiques des installations nucléaires est une priorité pour la communauté nucléaire internationale, renforcée par le séisme de Tohoku au Japon (2011). Dans ce cadre, un projet de recherche de 5 ans intitulé SINAPS@ (Séisme et les Installations Nucléaires : Améliorer et Pérenniser la Sûreté) est actuellement en cours en France, soutenu par le Programme d'Investissements d'Avenir. Une estimation fiable des marges sismiques n'est possible que si toutes les incertitudes, épistémiques et aléatoires, sont effectivement identifiées, quantifiées et intégrées dans l'analyse complète du risque sismique. SINAPS@ rassemble une communauté multidisciplinaire de chercheurs et ingénieurs du monde académique et nucléaire. SINAPS@ vise à explorer les incertitudes liées aux bases de données, aux processus physiques et aux méthodes utilisées à chaque étape de l'évaluation de l'aléa sismique, des effets de site, et de l'interaction entre le champ d'ondes, avec le sol, l'ouvrage et les composants importants pour la sûreté. Un des principaux objectifs de SINAPS@ est finalement d'identifier les sources potentielles de marges sismiques résultant d'hypothèses ou de la sélection du niveau sismique retenu pour le dimensionnement ou enfin, de la stratégie de conception. L'ensemble du projet est construit autour d'un volet "intégrateur" permettant de tester les pratiques à l'état de l'art dans l'estimation tant de l'aléa que de la vulnérabilité sismiques, et de tester de nouvelles méthodologies pour l'évaluation du risque sismique. La présente publication illustre les liens et les interactions cruciales entre tous les acteurs du projet pour atteindre les objectifs.

International audience; The Koutavos-Argostoli (Kefalonia, Greece) site was selected within the ANR-PIA SINAPS@ project (www.institut-seism.fr/projets/sinaps/) to host a vertical accelerometricarray. The long term goal is to validate 3D nonlinear numerical simulation codes. This article shortly presents the site and its geodynamic, geological and seismic backgrounds, the borehole instrumentation and the associated geotechnical information, and the first results of the post-seismic campaign organized following the seismic sequence of January-February 2014 including two M6 + shocks and numerous aftershocks.; Le site d'Argostoli-Koutavos (Céphalonie, Grèce) a été sélectionné dans le cadre du projet ANR-PIA SINAPS@ (www.institut-seism.fr/projets/sinaps/) pour faire l'objet d'une instrumentation longue durée en réseau accélérométrique vertical. Le but à long terme est de valider les codes de simulation numérique 3D non-linéaires. Cet article présente brièvement le site et son contexte géodynamique, géologique et sismique, l'instrumentation en forage et les informations géotechniques associées, ainsi que les premiers résultats de la campagne post-sismiqueorganisée à la suite de la séquence sismique de janvier-février 2014, comprenant deux chocs de magnitude M6+ et de très nombreuses répliques.

International audience; We look at the (failure) behavior of structural systems under the occurrence of seismic events. Detailed, long-running Finite Element Models (FEMs) are typically adopted for the simulation of the system structural response. However, since a very large number of simulations (e.g., several thousands) is usually required for an accurate assessment of the system failure behavior under different seismic conditions, the computational burden associated to the approach may be at times impractical. To address this issue, we resort to (fast-running) Artificial Neural Network (ANN) regression models, optimally trained to approximate the response of the original FEM. In particular, we embrace a wrapper approach based on Genetic Algorithm (GA) optimization to search for the optimal set of model inputs (features) that maximize the ANN representation accuracy. The ANN is trained, validated and tested with respect to the optimal feature subset identified; then, the results are compared with those produced by the original FEM. We illustrate the approach on a case study of seismic risk assessment involving the estimation of the fragility curves for a masonry structure.