57 research outputs found
The Effect of the Significant Duration on the Site Response Analysis of Liquefiable Soils
No full textInfluence of local soil conditions on the damage distribution in Izmir Bay during the October 30, 2020, Samos earthquake
No full textOn October 30, 2020, a damaging earthquake of moment magnitude 6.6 struck about 14 km northeast of the island of Samos,Greece, and about 70 km from the center of the city of Izmir inTurkey. Even though the epicenterwas relatively far away, the effects of the seismic event in the highly populated city center of Izmir were destructive causing over 100 fatalities and significant structural damage. Multiple failures of high buildings constituted the major source of the fatalities. This paper aims to understand the link between the localized damage distribution and the nature of amplification effects that have been observed in Izmir Bay, starting from collection and data analysis interpretation of seismic records and targeted damage assessment of the built environment, as well as geological and morphological characteristics of the area and the geotechnical properties of soils. Critical analysis of the numerous recorded signals shows the key role of the young alluvium and shallow marine deposits of the basin on which Izmir Bay was growing. The coupling mechanism between the frequency content of the shaking and the fundamental frequencies of the damaged buildings contributed to exacerbating the inertial forces acting on the collapsed buildings
Geotechnical Assessment of the Pore Water Pressure Build-up in Izmir During the October 30, 2020, Samos Earthquake
No full textOn October 30, 2020, a damaging earthquake of moment magnitude 6.6 struck about 14 km northeast of the island of Samos, Greece, and about 70 km from the center of the city of Izmir in Turkey. Even though the epicenter was relatively far away, the effects of the seismic event in the highly populated city center of Izmir were destructive causing over 100 fatalities and significant structural damage. Apart from the site effects that characterized this earthquake, a few liquefaction manifestations were observed during the event. This paper documented the pore water pressure build-up observed in the Bayrakli district after the October 30, 2020 earthquake. Approximate properties of the foundation soils were defined based on a fragmentary reconstruction of the field investigation before the construction of the building. The safety factor against liquefaction was then estimated and it was consistent with the absence of liquefaction manifestation in the area. Simplified prediction of the expected excess pore water pressure based on a simple relationship as a function of safety factor allowed preliminary assessment of the mechanism that is behind the observed phenomena. The proposed methodology is particularly convenient for rapid screening of the expected earthquake-induced effects since it can be directly applied to the safety factor without the identification of additional input data
Türkiye Mw 7.7 Pazarcık and Mw 7.6 Elbistan earthquakes of February 6th, 2023: Contribution of valley effects on damage pattern
No full textOn February 6th, 2023, southeastern Türkiye was shaken by two catastrophic earthquakes, close to northwestern Syrian border. The first earthquake (Pazarcık) occurred 45 km west of Gaziantep at 1:17:32 (UTC), with a shallow strike-slip faulting at a depth of approximately 8.6 km and a moment magnitude (MW) of around 7.7. The second event (Elbistan) took place 9 h later, 66 km north-east of Kahramanmaraş city center, also with shallow strike-slip faulting at a depth approximately 7 km and an MW of around 7.6. Turkish authorities reported a death toll of over 59,000 in Türkiye and about 8500 in Syria. The destructive effect of the earthquake resulted from widespread strong ground shaking, a rupture length exceeding 300 km, causing collapse of a large number of buildings. The catastrophic destruction of the built environment was accompanied by a range of other earthquake-related effects, including fault ruptures, landslides, and soil liquefaction. The aim of the study is to analyze the distribution of ground motion and their relationships with the observed damages for the two events. Spectral accelerations of key importance were assessed across a large area in the southeastern part of Türkiye. Notably, these accelerations were generally much higher than existing design spectra. A significant correlation between the observed concentration of damage and the significant amplification of motion induced by local soil conditions (such as soft soils and valley effects). The distinct tectonic structure of the region could be the main reason for the high amplification in the valleys (associated with basin effects), even at large distances from the epicenter, especially in correspondence with the bidimensional graben-type geological structures. The investigation delved into the analysis of four specific regions in detail: Antakya and Hassa (both in the Hatay province), Kahramanmaraş and Göksun. Notably, the observable valley effects were found to play a significant role and could account for the significant damage observed in these regions
Site effects observed in Antakya after the Mw 7.7 Pazarcik and Mw 7.6 Elbistan Earthquakes on the 6th February 2023 (Türkiye)
No full textOn February 6, 2023 Eastern Türkiye was shaken by two consecutive catastrophic earthquakes of moment magnitudes 7.7. and 7.6, induced by a left-lateral strike-slip fault in Eastern Anatolian Fault Zone. The first earthquake with a moment magnitude 7.6 was felt at 4:17 local time in the morning, while, approximately nine hours later, the second earthquake with a moment magnitude 7.7 increased the massive damage that occurred in eleven provinces of Türkiye including Hatay, Kahramanmaraş, Adıyaman, Malatya, Osmaniye, Gaziantep, Kilis, Şanlıurfa, Diyarbakır, Adana and Elazığ. In this paper, a specific focus is devoted to show the site effects observed in Antakya after the strong shakings as revealed by an extensive analysis of the collected ground motion records and geological and geotechnical data. It is shown that basin effects are associated with a higher level of damage compared to areas with the same level of ground shaking but without detrimental conditions of the local soils. The lessons learned from this seismic event highlight the key role played by the seismic response analysis and related tools of microzonation studies for the mitigation of the seismic risk
Évaluation du module de cisaillement des sols granulaires, avec corrélations du module de petites à grandes déformations
No full textUne estimation correcte du module de cisaillement (G) des sols constitue une partie fondamentale de l’analyse de la réponse dynamique des sols, des interactions sismiques sol-
structure, et du potentiel de liquéfaction du sol. Le module de cisaillement à petites déformations (Go) peut être systématiquement obtenu à partir de mesures en laboratoire des vitesses des ondes de cisaillement (Vs), car la rigidité élastique du sol est directement liée à sa vitesse de propagation des ondes de cisaillement. Cependant, les mesures du module de cisaillement sur une large gamme de déformations de cisaillement nécessitent des d’appareils spécialisés. Dans la présente étude, des corrélations entre le Go et le module contraint de l’oedomètre (Moedo)
à de grandes déformations ont été établies. Pour établir ces corrélations, des Vs de 22 sols granulaires de diverses caractéristiques physiques ont été mesurés expérimentalement en utilisant la méthode P-RAT incorpore dans la cellule oedométrique conventionnelle. Pour chaque échantillon testé, l’évolution de Moedo avec la densité relative (Id), ainsi que l’indice des vides (e), ont été enregistrées. Ensuite, les tendances Vs et Moedo /Go obtenues ont été corrélées aux paramètres physiques des sols granulaires testés avec le développement de e et Id. Une application pratique en génie géotechnique a également été évaluée. Sur la base des corrélations proposées, les ingénieurs en géotechniques peuvent facilement estimer le tassement in-situ à partir des valeurs de Moedo et Id prédites à l’aide de mesures in situ simples. De plus, en tant qu’étape importante vers une modélisation plus précise du comportement de déformation du sol, une relation entre Vs et d’autres paramètres géotechniques des sols en enrochement à grandes déformations a été étudiée en vue d’une modélisation plus précise du comportement des structures en terre. Quatre échantillons d’enrochement de différentes gradations, extraits des matériaux d’enrochement utilisés dans la construction du barrage de la Romaine II, ont été expérimentés pour corréler Vs au module initial de Duncan-Chang (Ei). Des simulations numériques utilisant la méthode des différences finies (FDM) bidimensionnelles (2D) ont été effectuées sur la base du modèle hyperbolique de Duncan-Chang pour valider les corrélations obtenues. Sur la base des données expérimentales et numériques, une relation entre Ei et Vs des échantillons d’enrochement testés a été établie. Des études de validation ont également été menées sur des mesures in situ, montrant la capacité des relations proposées à prédire efficacement Ei liée à la contrainte principale mineure (
3) de la mesure Vs in situ. En outre, comme les résultats du RC ont montré une incompatibilité avec d'autres appareils, des simulations de différences finies (FD) tridimensionnelles (3D) du test RC ont été utilisées pour examiner l'influence de certaines sources d'erreur sur les résultats RC tels que la masse motrice, la géométrie de l’échantillon, le mode de vibrations et les conditions aux limites sur les résultats des tests RC. Les résultats ont montré que la fixation de l’instrumentation sur l’échantillon est le facteur principal contribuant à l’erreur dans l’estimation des caractéristiques dynamiques du sol. Enfin, quatre techniques ont été utilisées pour estimer avec précision le module de cisaillement du sable avec différents niveaux de déformation : la colonne résonante (RC), la technique des anneaux piézoélectrique (P-RAT), le cisaillement simple triaxial (TxSS), et test de cisaillement simple direct (DSS). Les résultats montrent que le RC a surestimé les valeurs de Go par rapport au P-RAT en particulier à l'état lâche en raison du comportement non uniforme du sol. Basé sur un modèle SIG-4 à fonction sigmoïde; la réponse cyclique du sol a été modélise sur une large gamme de déformation basée sur les résultats de TxSS.A proper estimation of the strain-dependent shear modulus (G) of soils constitutes a fundamental part of analyzing the dynamic response of grounds, seismic soil–structure interactions, and soil liquefaction potential. The initial shear modulus (Go) can be systematically obtained from laboratory measurements of shear-wave velocities (Vs) as the soil elastic stiffness is straightforwardly related to its shear-wave propagation velocity. However, the shear modulus measurements over a broad range of shear strains can be performed through specialized testing apparatus. In the current study, correlations between Go and oedometer constrained modulus (Moedo) at large deformations were established, as an important step toward more precise modelling of soil deformation behavior. To establish these correlations, Vs of 22 different granular soils of various physical characteristics were measured experimentally using the piezoelectric ringactuator technique (P-RAT) incorporated in the conventional oedometer cell. For each sample tested, the development of Moedo with the development of relative density (Id), as well as the void ratio (e), was recorded. Then, the obtained Vs and Moedo/Go trends were correlated to the physical parameters of the tested granular soils with the development of e and Id. A practical application employing the achievements in geotechnical engineering design was also evaluated. Based on the proposed correlations, geotechnical designers can easily estimate in situ stress-settlement behavior from the predicted Moedo and Id values using simple in situ measurements. In addition, as a practical application of using Vs to estimate different geotechnical parameters, a relationship between Vs and other geotechnical parameters of rockfill soils at large strains was investigated towards more precise modelling of earth-structure deformation behaviour. Four rockfill samples of different gradations, extracted from the rockfill materials used in the construction of the Romaine II dam, were experimented to correlate Vs to Duncan-Chang initial modulus (Ei). Numerical simulations using a two-dimensional (2D) finite difference method (FDM) were performed based on the Duncan-Chang hyperbolic model to validate the obtained correlations. Based on the experimental and numerical data, a relation between Ei and Vs of the ii tested rockfill samples has been established. Verification studies were also carried out on insitu measurements, proofing the ability of the proposed relationships to efficiently predict Ei related to the minor principal stress ( 3) from in-situ Vs measurement. Furthermore, as the RC method, in particular, constitutes one of the most popular apparatus used to generate modulus reduction curves for soils, a three-dimensional (3D) finite-difference (FD) simulations of RC test was used to examine the influence of some sources of error affect the RC results such as driving mass, the geometry of the specimen, mode of vibrations, and boundary conditions on RC test. Results showed that the attachment of the instrumentation on the sample is a driving factor to contribute the error in the estimation of the soil dynamic characteristics. Finally, four laboratory techniques were used to estimate the strain-dependent shear modulus of clean sand with different strain () levels: Resonant column test (RC), piezoelectric ringactuator technique (P-RAT), triaxial simple shear test (TxSS) and direct simple shear test (DSS). The results show that the RC overestimated the values of Go compared with P-RAT especially at loose state due to the non-elastic behavior of soil. TxSS and DSS results showed acceptable compatibility in the estimation of G at strains more than 0.1%. Based on a sigmoid function SIG-4 model; the cyclic soil response over a wide range of strains based on TxSS results was predicted
Modélisation numérique de la distribution de la poussée latérale des terres en excavations profondes étançonnées
No full textThis thesis aims to study the various parameters that may affect the lateral pressure on propped deep excavations. The parametric studies were carried out using numerical modeling based on the finite element method. Extensive parametric studies were performed to explore the effect of soil parameters and the arrangement and the properties of the retaining system on the distribution of lateral pressure. The results of numerical modeling are generally comparable to those obtained with classical design approaches using the apparent pressure diagrams that were developed by Peck (1969) and Tschebotarioff (1973). In the case of small thicknesses as well as small penetration depths, the lower struts reveal higher prop forces. According to the configuration of the excavation, the prestressing force may vary from one prop to another. Finally, some practical recommendations are given for geotechnical design of supported deep excavations
Insights on the role of local site effects on damage distribution in the Izmir metropolitan area induced by the October 30, 2020 Samos earthquake
No full textOn the 30th of October 2020, a 6.6 magnitude earthquake occurred 14 km north of Samos Island, causing 119 casualties (117 in Izmir, Türkiye, and 2 in Samos, Greece) and significant damage in the 3rd biggest city of Türkiye, Izmir. Although the city is roughly 70 km far away from the epicenter, the damage was significant and concentrated in the city center settled on alluviums. This paper aims to analyze the distribution of damage in Izmir province, by crosschecking the recorded motions, the subsoil conditions and the evidence of damage as collected by an ad-hoc on-site reconnaissance. The intrinsic behavior of the Samos earthquake was investigated by employing three different ground-motion prediction equations. The results of the analyses revealed that site effects play a significant role in the amplification of ground motions, and valley effects are responsible for the concentration of damage. The damage in buildings was classified in terms of the intensity and structural typologies for the 30 districts of Izmir metropolitan area. In-depth analysis of the distribution of damages revealed that the earthquake caused damage all over the boundaries of Izmir province, and the concentration of damage in Bornova and Karşıyaka districts has a clear correlation with double resonance effects
Modélisation numérique de la distribution de la poussée latérale des terres en excavations profondes étançonnées
No full textThis thesis aims to study the various parameters that may affect the lateral pressure on propped deep excavations. The parametric studies were carried out using numerical modeling based on the finite element method. Extensive parametric studies were performed to explore the effect of soil parameters and the arrangement and the properties of the retaining system on the distribution of lateral pressure. The results of numerical modeling are generally comparable to those obtained with classical design approaches using the apparent pressure diagrams that were developed by Peck (1969) and Tschebotarioff (1973). In the case of small thicknesses as well as small penetration depths, the lower struts reveal higher prop forces. According to the configuration of the excavation, the prestressing force may vary from one prop to another. Finally, some practical recommendations are given for geotechnical design of supported deep excavations
Analyse numérique de la réponse des pieux sous sollicitations latérales
No full textRésumé : Afin de contribuer dans la réponse latérale des pieux sous sollicitations latérales et notamment prendre en compte des plusieurs paramètres en relation avec les pieux (matériau, diamètre, rigidité, inclinaison) et le sol (nature, rigidité), des analyses numériques en différences finies 2D et 3D ont été réalisées en considérant des pieux chargés latéralement et ancrés dans des sols sableux, argileux et même sableux-argileux. Des modèles numériques simulés avec les codes en différences finies FLAC pour l’analyse 2D et FLAC[indice supérieur 3D] pour l’analyse 3D ont été inspirés des modèles de pieux réduits et en vraie grandeur, faisant l’objet de publications. Des enregistrements du déplacement latéral ou/et de la capacité latérale ou/et du moment fléchissant des pieux considérés ont été pris lors de ces essais. Ces modèles numériques ont été validés à travers diverses comparaisons entre les mesures, les calculs de FLAC et/ou FLAC3D et dans des cas les calculs d’autres méthodes utilisées dans la pratique. Une comparaison entre l’analyse 2D et l’analyse 3D de la réponse latérale d’un pieu rigide chargé latéralement dans un sol cohérent, a été réalisée dans le but de connaître les limites de l’analyse 2D et la possibilité de corréler ses résultats à ceux de l’analyse 3D. L’influence de la charge verticale sur la réponse latérale (capacité latérale et moment fléchissant maximal) d’un pieu en béton, chargé latéralement dans des sols sableux et argileux, a été étudiée avec une analyse numérique 3D. Il a été démontré que pour le cas des sols sableux, la charge verticale n’a pas un effet considérable sur la réponse latérale des pieux soumis à des charges latérales. Par contre, la charge verticale conduit à une diminution significative de la capacité latérale des pieux dans des sols argileux. Il est également constaté que l'influence des charges verticales sur la réponse latérale du pieu installé dans une argile surconsolidée avec une résistance au cisaillement non drainée proportionnelle à la profondeur et un OCR variant de 1,5 à 4,0 est très différent de celle correspondante à une résistance au cisaillement non drainée constante quelle que soit la valeur d’OCR. Des analyses 3D ont été, également, effectuées pour étudier la réponse latérale de pieux inclinés et chargés latéralement. La capacité latérale des pieux inclinés dans les sols sableux est considérablement augmentée avec l’augmentation de la valeur de l’inclinaison du pieu correspondante à la direction opposée à la direction de la charge latérale, et la densité du sable. Mais lorsque la direction de l’inclinaison du pieu et la même que celle correspondante à la charge latérale, cette capacité latérale est légèrement à modérément augmentée tout dépendamment de la valeur et le signe de l'angle ainsi que de la densité du sable. L’influence de l’angle d’inclinaison associé avec la charge verticale sur la capacité latérale de pieux inclinés est aussi très importante pour les sols sableux. Pour les sols argileux, l'influence de l'angle d’inclinaison sur la capacité latérale dépend seulement de l'angle d’inclinaison. En effet, la capacité latérale est modérément augmentée. Par contre, L'effet combiné de l’angle et la charge verticale est assez important. // Abstract : This thesis pertains to numerical analyses conducted primarily to evaluate the lateral response of piles and the contribution of several parameters related to piles (e.g., material, diameter, stiffness, inclination) and the soil (e.g., type, rigidity). Numerical finite differences analysis in 2D and 3D have been performed modelizing laterally loaded piles in sandy, clayey, and even sandy-clayey soils. Numerical models, simulated with finite difference codes FLAC for analysis in 2D and FLAC[superscript 3D] for 3D analysis, were inspired from experimental laboratory and full scale models available in literature. Measurements of lateral deflection and/or lateral capacity and/or bending moment of tested piles were recorded during these tests. These numerical models have been validated through comparison between the various
measurements, predictions with FLAC and/or FLAC3D and for some cases the calculations with other methods used in practice. Comparison between 2D and 3D analyses of the response of laterally loaded rigid piles in cohesive soils, was performed in order to investigate the 2D analysis limitations and the possibility of correlating the 2D results with those of 3D analysis.
A series of 3D finite differences analyses is also conducted to evaluate the influence of
vertical loads on the lateral response of pile foundations. Numerical results have shown that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at loosest stat. However, vertical load leads to a significant decrease in lateral capacity of piles in homogeneous and inhomogeneous clay layers. It is also found that the influence of vertical loads on the lateral response of pile installed in over-consolidated clay with undrained strength proportional to depth and different OCR in the range of 1.5 to 4.0 is quite different from that with constant undrained strength regardless the adopted OCR value.
The 3D finite difference analyses have been, also, carried out to investigate the lateral
response of battered piles. The lateral capacity of the battered piles in sandy soils is
considerably increased when the value of pile inclination corresponding to the opposite
direction of the lateral load increases and when the sand density increases. But in the case of pile inclination corresponding to the same direction of the lateral load, the lateral capacity is slightly increased regardless to the adopted value of batter angle and the sand density. In clayey soil, it was found that the influence of the batter angle on the lateral capacity of piles depends only on the batter angle and not on the clay rigidity. For the case of pile inclination corresponding to the opposite direction of the lateral load, the lateral capacity is moderately increased and for the other case of inclination, the effects are not significant. The influence of both batter angle and vertical load on lateral capacity of battered pile in clayey soils is
moderately pronounced
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