The present study was conducted to examine the behaviour of instrumented ‰exible piles in dry sand under lateral cyclic loading using centrifuged models. Considering load service conditions, the in‰uence of the number of cycles of their amplitude and of the soil density on the pile cap displacement and the maximum bending moment of the pile is examined. An empirical law to evaluate pile head displacements at application point is proposed. From the bending moment proˆle recorded during loading, P-y reaction curves are identiˆed. A reduction coe‹cient r (P-multiplier) is introduced to quantify the eŠects of cyclic loads on P-y curves.

International audienceUnder the effect of internal flows, a liner can undergo a washing out of particles, which modifies the particle size distribution and affects hydraulic, chemical and mechanical characteristics. This paper discusses the effects of internal flows on sand/kaolin mixture, in terms of rate of erosion and modification of the hydraulic conductivity. A parametric study is conducted with a specific device that consists of three modified triaxial cells. These cells allow isotropically consolidating and confining specimens, they prevent a parasitic flow and survey large deformations of specimen. The tests reveal that suffusion of clay is accompanied by a clogging in the specimen that induces a drop in hydraulic conductivity. For high gradients the erosion of clay is accompanied by the backward erosion of sand and finally the specimen collapses. The erosion rate then depends on the values of the different parameters considered (hydraulic gradient, clay content and filter pore opening size)

Three basic elements (cement, water and admixture) usually make up injectable cement grouts used for prestressed cable coating, repair and consolidation of masonry, soil grouting, etc… The present study was divided into two parts. First, in order to characterize rheologically fresh cement paste with W/C ratios (water/cement ratio) varying between 0.35 and 1, an experimental study was carried out and has revealed that the cement past behaves like a shear-thinning material whatever W/C. second, to study the time evolution of their density, a gammadensitometer bench was used. Relying on the water content and the density measured, we demonstrate that the computation of the degree of hydration of cement is possible. The cement/geotechnics interdisciplinary approach proposed here has made it possible to obtain a large range of original results useful to improve our understanding of the sedimentation processes for cement pastes with different W/C ratios.

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International audienceThe appearance of breaches in recent hydraulic earthstructures due to internal erosion confirms that improving our physical understanding of the phenomenon is urgent. Under the effect of internal flows, earthstructures can undergo a migration of their particles, which modifies the particle size distribution and affects both hydraulic and mechanical characteristics. This paper initially presents a parametric study conducted on sand/kaolin samples. The experimental device described here consists of three modified triaxial cells used to control sample confinement, prevent any parasitic flow and survey sample large deformations. The tests reveal that internal erosion (suffusion or piping) is initiated by the transport of clay particles. The erosion rate, then, depends on the values of the different parameters considered (hydraulic gradient, clay content and filter pore opening size).La rupture par érosion interne de récents ouvrages hydrauliques en terre souligne la nécessité d’améliorer la compréhension physique de ce phénomène. Les écoulements internes peuvent engendrer une migration de particules constitutives des ouvrages hydrauliques en terre. Cette migration affecte la distribution granulométrique, modifie la porosité ainsi que les caractéristiques mécaniques et hydrauliques. Nous proposons une étude expérimentale réalisée sur des échantillons constitués de mélanges de sable et de kaolin. Le montage expérimental est constitué de trois cellules triaxiales modifiées qui permettent de contrôler le confinement des échantillons, d’éviter tout écoulement parasite et de suivre les grandes déformations des échantillons. Les essais réalisés indiquent que l’érosion interne (suffusion ou renard) est initiée par la migration des particules d’argile. Le taux d’érosion dépend du gradient hydraulique appliqué, du pourcentage d’argile et de l’ouverture des pores du filtre

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