3D failure envelope of a single pile in sand

International audiencePile foundations are widely used in geotechnical and offshore engineering. When subjected to a combination of horizontal, vertical forces and bending moments, a 3D failure envelope is necessary in order to evaluate the safety of the pile-soil system. We present a study on the failure envelope of a single elastic pile in sand. In order to find it in the three-dimensional space (i.e. horizontal force H, bending moment M and vertical force V), the radial displacement method and swipe tests are numerically performed. An analytical equation providing good agreement with the 3D numerical results is finally proposed

Using centrifuge tests data to identify the dynamic soil properties: Application to Fontainebleau sand

Knowledge of the dynamic properties of the soil is of great importance as the dynamic shear modulus and damping ratio are necessary input data in finite element modeling programs. This paper presents a post-processing strategy to identify the shear modulus and damping ratio vs. shear strain curves using the experimental results of a dynamic centrifuge program. Application is presented for the Fontainebleau sand. The proposed methodology is fast, robust and able to capture the nonlinear hysteretic behavior of the material. Based on the results, specific parameters for the Fontainebleau sand are identified for the empirical equation of shear modulus and damping ratio proposed by Ishibashi and Zhang. It is found that confining pressure has an important influence on both shear modulus evolution and damping ratio

Numerical study of the 3D failure envelope of a single pile in sand

International audienceThe paper presents a comprehensive study of the failure envelope (or capacity diagram) of a single elastic pile in sand. The behavior of a pile subjected to different load combinations is simulated using a large number of finite element numerical calculations. The sand is modeled using a constitutive law based on hypoplasticity. In order to find the failure envelope in the three-dimensional space (i.e. horizontal force H, bending moment M and vertical force V), the radial displacement method and swipe tests are numerically performed. It is found that with increasing vertical load the horizontal bearing capacity of the pile decreases. Furthermore, the presence of bending moment on the pile head significantly influences the horizontal bearing capacity and the capacity diagram in the H-M plane manifests an inclined elliptical shape. An analytical equation providing good agreement with the 3D numerical results is finally proposed. The formula is useful for design purposes and the development of simplified modeling numerical strategies such as macro-element

Centrifuge modeling of batter pile foundations under sinusoidal dynamic excitation

International audienceBatter pile (or inclined pile) foundations are widely used in civil engineering structures. However, their behavior under dynamic loadings is not yet thoroughly understood. This paper presents an experimental work on the behavior of batter and vertical piles considering dynamic soil-pile-superstructure interactions. A series of dynamic centrifuge tests were performed using sinusoidal excitations. The influence of the base shaking (frequency content and amplitude) and of the height of the center of gravity of the superstructure is investigated. Seismic responses are analyzed considering the pile cap displacements and forces (total base shear, overturning and residual moments, axial forces). It is found that in certain cases batter piles play a beneficial role on the dynamic behavior of the pile foundation system. This novel experimental work provides an important database on the behavior of batter pile foundations under dynamic loadings

Centrifuge modelling of inclined pile foundations under seismic actions

International audienceAlthough inclined pile foundations are sometimes used in civil engineering structures, their behavior under seismic loadings is not yet thoroughly understood. This paper presents an experimental work on inclined pile foundations under earthquake loadings. Dynamic centrifuge tests are performed to investigate the influence of inclined piles on the superstructures and to quantify the soil-structure interaction. Some key parameters are analyzed such as the residual bending moment, the total bending moment and the axial forces. It is found that in certain cases inclination plays a beneficial role to the seismic behavior of the pile foundation system and that the presence of inclined piles increases its natural frequency. Comparing to a vertical pile foundation, the residual bending moment envelope curve is different and larger values are observed. This novel experimental work provides significant data to understand the behavior of inclined pile foundations in seismic regions

Pratos e mais pratos: louças domésticas, divisões culturais e limites sociais no Rio de Janeiro, século XIX

Reply to ten comments on a paper published in the last issue of this journal. The discussion follows along six main lines: History museums, identity, ideology and the category of nation; the need of material collections and their modalities: patrimonial, operational, virtual; theater versus laboratory; visitors and their ambiguities; Public History: the museum and the academy.Resposta aos comentários de dez especialistas que contribuíram no debate de texto publicado no último número desta revista. A discussão orientou-se segundo seis tópicos principais: museus históricos, identidade, ideologia e a categoria de nação; a necessidade de acervos materiais e suas modalidades: acervo patrimonial, operacional, virtual; teatro versus laboratório; o público e suas ambigüidades; História Pública: o museu e a Academia

Caractérisation expérimentale du comportement hydromécanique des argilites de Meuse/Haute-Marne

Dans le cadre d'une étude de faisabilité d'un stockage de déchets radioactifs en profondeur la caractérisation expérimentale du comportement couplé de la couche hôte est de première importance. Ce travail s'articule autour de caractérisation expérimentale en laboratoire du comportement poroélastique des argilites qui constituent la couche hôte du futur laboratoire souterrain de l'ANDRA situé à la limite Meuse/Haute-Marne. L'approche choisie est celle de la thermodynamique des milieux poreux proposée par Coussy [1991] qui a l'avantage de fournir une formulation des lois de comportement à l'aide de paramètres en principe mesurables en laboratoire. Les difficultés ou encore la faisabilité des essais de caractérisation du comportement couplé de ces roches sont liées à leur très faible perméabilité qui nécessite une adaptation des dispositifs expérimentaux initialement utilisés sur des roches plus perméables. Dans un premier temps une synthèse sur l'état de l'art des connaissances des paramètres poroélastiques déterminés sur les argilites de Meuse/Haute-Marne suivie d'une première approche de l'utilisation des études de sensibilité comme outils d'aide à la décision sont proposées. En effet si les difficultés expérimentales rencontrées par les divers expérimentateurs s'illustrent par la diversité des choix expérimentaux, par la durée des essais ou encore par la disparité des résultats, étant donné l'enjeu à la fois économique politique ou encore écologique d'un tel projet de stockage les études de sensibilité pourraient le cas échéant permettre d'orienter les efforts expérimentaux en apportant des indications sur les paramètres prépondérants dans le comportement couplé d'un massif. Dans un second temps, après la présentation des mesures de caractérisation physique des matériaux utilisés, des essais de mesure de perméabilité par pulse test, de détermination du coefficient de Biot en cellule oedométrique et de paramètres poroélastiques sous chargement isotrope en condition drainée et non drainée sont décrits. Ces essais dont la complexité est notamment liée à l'atteinte des limites expérimentales actuelles sont présentés dans le détail, du rappel théorique à la description détaillée des essais, en passant par un effort particulier mené sur le dimensionnement et une description de l'appareillage et des protocoles expérimentaux.NANCY/VANDOEUVRE-INPL (545472102) / SudocSudocFranceF

Study on the stiffness degradation and damping of pile foundations under dynamic loadings

International audienceThis paper presents a comprehensive study on the different behaviour of batter and vertical pile foundations in terms of stiffness degradation and damping properties under dynamic loadings. Firstly, dynamic centrifuge tests were carried out and the variations of translational/rotational stiffness and the associated damping properties were identified from a series of hysteretic loops. Results show that for the rocking behaviour, the presence of batter piles causes a small decrease of the rotational stiffness and a great increase of the rotational damping; for the horizontal translation behaviour, batter pile foundation has much higher horizontal stiffness and transla-tional damping compared to the vertical foundation. Then, a set of stiffness degradation and damping curves for the translational and rotational behaviour of batter and vertical pile foundations are proposed. Finally, the proposed stiffness degradation and damping curves were validated numerically by using equivalent linear approach. The numerical validation shows a good agreement with the experimental results

Centrifuge Modelling of Inclined Pile Foundations under Seismic Actions

The behaviour of inclined pile foundations under seismic actions is not thoroughly investigated. This paper provides new experimental data on the responses of inclined pile foundations tested using the centrifuge modelling technique. The experiments are designed to investigate soil-structure interaction. Different mock-ups are subjected to several earthquakes with low intensities and the evolution of their frequency components is identified. Experimental results are analyzed in terms of response frequencies and section forces in the piles. Numerical simulation of the soil-structure systems is conducted in the linear viscoelastic domain. Comparison of the experimental and the numerical response both in the frequency and in the time domain is satisfactory. From both the experimental and numerical results preliminary conclusions can be drawn concerning the dynamic characteristics of the soil-structure systems and the effects of inclined piles

Centrifuge modeling of batter pile foundations under earthquake excitation

International audienceAlthough batter pile foundations are widely used in civil engineering structures, their behavior under seismic loadings is not yet thoroughly understood. This paper provides insights about the differences in the behavior of batter and vertical piles under seismic soil-pile-superstructure interaction. An experimental dynamic centrifuge program is presented, where the influences of the base shaking signal and the height of the gravity center of the superstructure are investigated. Various seismic responses are analyzed (displacement and rotation of the pile cap, total shear force at the pile cap level, overturning moment, residual bending moment, total bending moment and axial forces in piles). It is found that in certain cases batter piles play a beneficial role on the seismic behavior of the pile foundation system. The performance of batter piles depends not only on the characteristics of the earthquakes (frequency content and amplitude) but also on the type of superstructures they support. This novel experimental work provides a new experimental database to better understand the behavior of batter pile foundations in seismic regions