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This study presents a full-scale model investigation on variations of soil stress in a geosynthetic-reinforced pile- supported track bed at various water levels and loading cycles, with four testing procedures: water level rising, cyclic loading at high water level, water level lowering, and cyclic loading at low water level. The soil arching effect was revealed, characterized by higher stress above the pile cap. With the water level rising and loading cycles increasing at high water level, this effect becomes more pronounced, until a peak value of dynamic stress concentration ratio is reached. The stable state of soil arching is obtained earlier near the crown of soil arching, but this arching effect develops more significantly at the foot of soil arching. With the water level lowering and loading at low water level, the soil arching effect remains steady, with slightly changed dynamic stresses in the track bed. The geogrid shows a significant impact on the load transfer mechanism for the quasi- static stress: the quasi-static pile-cap stress presents higher values below the geogrid, whereas the opposite trend is observed for the water-bag (subsoil) area. Nevertheless, this mechanism is not obvious with respect to the dynamic stress, with the values showing no distinct difference above and below the geogrid.Key words: geosynthetic-reinforced pile-supported track bed, water level, cyclic loading, soil arching, geogrid reinforcement.Cette etude presente une etude de modele grandeur nature sur les variations des contraintes du sol dans des plates-formes sur pieux renforcees par geosynthetique a differents niveaux d'eau et cycles de chargement, avec quatre procedures d'essai : elevation du niveau d'eau, chargement cyclique a niveau d'eau eleve, abaissement du niveau d'eau et chargement cyclique a niveau d'eau bas. L'effet de voute du sol a ete revele, caracterise par une contrainte plus elevee au-dessus du chapeau de pieu. Lorsque le niveau d'eau augmente et que les cycles de chargement augmentent a niveau d'eau elevee, cet effet devient plus prononce, 'usqu'a ce qu'une valeur maximale du rapport de concentration des contraintes dynamiques soit atteinte. L'etat stable des voutes du sol est obtenu plus tot pres du sommet de voute du sol, mais cet effet de voute se developpe de maniere plus significative au pied de voute du sol. Avec l'abaissement et le chargement du niveau d'eau a un niveau d'eau bas, l'effet de voute du sol reste stable, avec des contraintes dynamiques legerement modifiees dans la plate-forme de la voie. La geogrille montre un impact significatif sur le mecanisme de transfert de charge pour la contrainte quasi-statique : la contrainte quasi statique de chapeau de pieu presente des valeurs plus elevees sous la geogrille, tandis que la tendance inverse est observee pour la zone du sous-sol. Neanmoins, ce mecanisme n'est pas evident pour la contrainte dynamique, les valeurs ne montrant aucune difference nette au-dessus et en dessous de la geogrille. [Traduit par la Redaction]Mots-cles : plate-forme sur pieux renforcee par geosynthetique, niveau d'eau, chargement cyclique, effet de voute du sol, geogrille de renfort., IntroductionCompared to the track bed with subsoil improved by conventional methods, the geosynthetic-reinforced pile-supported (GRPS) track bed presents smaller accumulative settlement and is thus increasingly used in the new high-speed [...]

For the French conventional railway lines, a layer, namely interlayer, was created in the substructure mainly by the interpenetration of ballast grains and subgrade soils. The in situ investigation indicated that the content of coarse grains decreases over depth. In this study, the resilient modulus and damping ratio of the unsaturated lower part of the interlayer soil were investigated at six different volumetric inclusion contents [f.sub.v] (volumetric ratio of dry coarse grains to the whole sample) by carrying out cyclic triaxial tests following a multi-step loading procedure. The results show that the two dynamic parameters (resilient modulus and damping ratio) change significantly at the beginning of loading and the variation rate decreases as the number of cycles increases. Besides, a mean characteristic volumetric inclusion content [f.sub.v-cha] ranging from 27.8% to 28.9% was identified, separating two zones with different inclusion effects. To verify this observation, X-ray microcomputed tomography ([micro]CT) scans were conducted on as-compacted samples. The results obtained strongly support the existence of [f.sub.v-cha]: when [f.sub.v] [less than or equal to] [f.sub.v-cha], the matrix of fines constitutes the skeleton of the sample with inclusions floating in it, leading to slight changes of the two dynamic parameters with [f.sub.v]. By contrast, when [f.sub.v] > [f.sub.v-cha], the inclusions dominate the skeleton of the sample, giving rise to significant changes of the two dynamic parameters with [f.sub.v]. Key words: interlayer soil, cyclic triaxial tests, resilient modulus, damping ratio, X-ray microcomputed tomography ([micro]CT) scans, characteristic volumetric inclusion content. Pour les lignes ferroviaires classiques francaises, une couche dite couche intercalaire a ete creee dans la sous-structure principalement par l'interpenetration des grains de ballast et des sols de fondation. L'enquete in situ a indique que la fraction de grains grossiers diminue avec la profondeur. Dans cette etude, le module de resilience et le coefficient d'amortissement de la partie inferieure non saturee de la couche intermediaire ont ete etudies pour six differentes fractions d'inclusion volumetrique [f.sub.v] (rapport volumetrique de grains grossiers secs sur l'ensemble de l'echantillon) en effectuant des essais triaxiaux cycliques suivant une procedure de chargement en multi-etape. Les resultats montrent que les deux parametres dynamiques (module resilient et le coefficient d'amortissement) changent de maniere significative au debut du chargement et le taux de variation diminue a mesure que le nombre de cycles augmente. En outre, une caracteristique moyenne de la fraction d'inclusion volumetrique [f.sub.v-cha] allant de 27,8 % a 28,9 % a ete identifiee, separant deux zones avec differents effets d'inclusion. Afin de verifier cette observation, des numerisations tomographies microcomputees ([micro]CT) ont ete realisees sur des echantillons compactes. Les resultats obtenus appuient fortement l'existence de [f.sub.v-cha] : quand [f.sub.v] [les than or equal to] [f.sub.v-cha], la matrice des fines constitue le squelette de l'echantillon avec inclusions en suspension, conduisant a de legers changements des deux parametres dynamiques avec [f.sub.v]. En revanche, lorsque[f.sub.v] >[f.sub.v-cha], les inclusions dominent le squelette de l'echantillon, donnant lieu a des changements significatifs des deux parametres dynamiques avec [f.sub.v]. Mots-cles: sol intercalaire, essais triaxiaux cycliques, module de resilience, rapport d'amortissement, numerisations tomographies microcomputees ([micro]CT), contenu d'inclusion volumetrique caracteristique., Introduction In France, 94% of the railway lines were constructed in conventional ways by putting ballast directly on the subgrade without any separation layers. Under the traffic effect, a new [...]

Hydroxy-Fe–Al and cetyltrimethylammonium bromide (CTMAB) were chosen to modified Na-bentonite (Na-bent). The characteristics of Na-bent and modified bentonites were determined with scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR) and zeta potential. It was found that CTMAB mainly entered the interlayer and hydroxy-Fe–Al groups were mostly loaded on the external surface of the Na-bent, respectively. The efficiency to remove Cr (VI) of Na-bent, organic modified bentonite (O-bent), inorganic modified bentonite (I-bent) and composite modified bentonite (Co-bent) followed the order: Co-bent > I-bent > O-bent > Na-bent. Adsorption experiments were carried out by the batch contact method. The highest removal rate of Cr (VI) by Co-bent was found to be 96.2% at optimal pH = 4. The Cr (VI) uptake on Co-bent from 50 mg/L solution rapidly attained equilibrium within 10 min, and the pesudo-second-order kinetic model could provide satisfactory fitting of the kinetic data (R2 = 0.999) compared to the intraparticle diffusion model (R2 = 0.585). The adsorption data were applied to the Langmuir, Freundlich, Temkin isotherm model. The Langmuir was found to be the most suitable equation to fit the experimental data (R2 = 0.956) with a high Cr (VI) adsorption capacity of 27.472 mg/g, and RL values (0.012–0.035) also indicated the adsorption could be accepted. The present study confirmed that Co-bent would be one of candidates for Cr (VI) adsorbent. [ABSTRACT FROM AUTHOR]

A number of potential offshore wind turbines in China will be constructed in sandy silt seabeds, and the monocaisson foundation is an important choice for these offshore wind turbines. A program of large-scale model tests on suction installation and lateral loading of caisson foundations in saturated silt were carried out in a large soil tank at Zhejiang University. Test results of installation resistance during suction installation show that the seepage effect is limited in silt, and the suction required to penetrate the caisson can be well predicted based on the sleeve friction and cone resistance of cone penetration tests. The deformation mechanism and soil-structure interaction of a caisson subjected to lateral loads were investigated. The instantaneous rotation center of the model caisson at failure was at the depth of about four-fifths of the skirt length, almost directly below the lid center. Based on the assumption of a common position of the instantaneous rotation center and dominating resistance forces on the caisson, an analytical expression for the ultimate moment capacity was presented. Key words: suction caisson, silt, offshore wind turbine, installation, lateral loading, soil-structure interaction. Plusieurs eoliennes seront construites en mer dans un fond de silt sablonneux, alors le choix de fondations de type mono-caisson s'avere important pour ces eoliennes en mer. Un programme d'essai, visant a modeliser a grande echelle la succion d'installation et le chargement lateral des fondations des caissons dans du silt sature, a ete realise dans un grand reservoir de sol, a l'universite de Zhejiang. Les resultats des essais en termes de resistance a l'installation durant l'installation par succion montrent que l'effet d'infiltration est limite dans le silt, et que la succion necessaire pour penetrer le caisson peut etre bien predite a l'aide de la friction du manchon et de la resistance du cone obtenue par des essais de penetration du cone. Le mecanisme de deformation et l'interaction sol-structure d'un caisson soumis a des charges laterales ont ete etudies. Le centre de rotation instantane a la rupture du modele de caisson etait situe a une profondeur d'environ 4/5 de la longueur de la collerette, presque directement sous le centre du couvercle. Selon l'hypothese d'une position commune du centre de rotation instantane et des forces de resistance dominantes sur le caisson, une expression analytique pour determiner la capacite du moment ultime est presentee. Mots-cles : caisson de succion, silt, eolienne en mer, installation, chargement lateral, interaction sol-structure. [Traduit par la Redaction], Introduction Development of wind farms in China and used foundations As a strategic choice to reduce carbon dioxide emissions as well as to solve global energy shortages, developing wind energy [...]