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This paper examines the specific role and interdependencies between soil density, particle size, particle shape, and gradation on the water entry pressure of hydrophobized sands. The tested granular materials include quartz sands of three size ranges, glass beads, and crushed glass. All granular materials were initially silanized with polydimethylsiloxane (PDMS) coatings to achieve the same intrinsic hydrophobicity. The water-ponding method was adopted to measure the water entry pressure in a comprehensive parametric study that consisted of 96 tests. Despite an acute sensitivity of the water entry pressure to relative density, the results revealed a more dominant effect of particle size. The largest water entry pressure (hydrophobized fine sand) was 14 times that of the lowest (hydrophobized coarse sand). Relatively higher water entry pressures were recorded with sands having larger coefficients of uniformity. A comparison between hydrophobized glass beads and crushed glass also revealed that rounded particles were less effective in retarding water infiltration in a dense state. A relationship, based on Jurin's law, was proposed for dense sands whereby the water entry pressure is obtained from the coefficient of uniformity, mean particle size, and particle shape. Key words: hydrophobized sand, hydrophobicity, water entry pressure, gradation, particle shape, relative density Cet article examine le role specifique et les interdependances entre la densite du sol, la taille des particules, la forme des particules et la gradation sur la pression d'entree d'eau des sables hydrophobises. Les materiaux granulaires testes comprennent des sables de quartz de trois gammes de taille, des billes de verre et du verre concasse. Tous les materiaux granulaires ont ete initialement silanises avec des revetements en polydimethylsiloxane (PDMS) pour obtenir la meme hydrophobie intrinseque. La methode de l'etang d'eau a ete adoptee pour mesurer la pression d'entree de l'eau dans une etude parametrique complete qui comprenait 96 tests. Malgre une sensibilite aigue de la pression d'entree de l'eau a la densite relative, les resultats ont revele un effet plus dominant de la taille des particules. La pression d'entree d'eau la plus importante (sable fin hydrophobise) etait 14 fois superieure a celle de la plus faible (sable grossier hydrophobise). Des pressions d'entree d'eau relativement plus elevees ont ete enregistrees avec les sables ayant des coefficients d'uniformite plus importants. Une comparaison entre les billes de verre hydrophobisees et le verre concasse a egalement revele que les particules arrondies etaient moins efficaces pour retarder l'infiltration d'eau a l'etat dense. Une relation, basee sur la loi de Jurin, a ete proposee pour les sables denses, dans laquelle la pression d'entree de l'eau est obtenue a partir du coefficient d'uniformite, de la taille moyenne des particules et de leur forme. [Traduit par la Redaction] Mots-cles : sable hydrophobise, hydrophobie, pression d'entree de l'eau, gradation, forme des particules, densite relative, 1. Introduction Soil hydrophobicity retards water infiltration, influencing water movement and evaporation (Fink et al. 1980; Ritsema and Dekker 1994; Hall et al. 2010; Wallach 2010; Bardet et al. 2014; [...]

An increase in the operation speed of high-speed trains often leads to an increase in the loading frequency on subgrade soil. Hence, the long-term dynamic behavior of the subgrade and the service performance of high-speed tracks are affected. To determine the stress-strain characteristics of granular soil under high-frequency loading, a triaxial test setup was modified to investigate the effects of loading acceleration and duration, water content, vibration frequency, cell pressure, and initial soil density. The experimental results indicate that there are reductions in axial stress and volumetric strain during high-frequency loading. The reduction in axial stress is as high as 40%, and that of volumetric strain, which is permanent, could approach 0.1%. The stress reduction, strain compression, and excess pore pressure are found to vary linearly with vibration acceleration when a/g > 0.02, where a is vertical vibration acceleration and g is gravitational acceleration. The reduction in strength and strains are found to depend on the loading acceleration and effective cell pressure, but independent of the loading duration, water content, frequency, and initial density. A threshold acceleration a = 0.02g is observed, below which the changes in the shear strength and volumetric strain induced by vibration are negligible. At high vibration acceleration, the strain amplitude could increase, eventually leading to a collapse of the specimen. Key words: granular soil, critical state, fluidization, deviatoric stress, volumetric strain. L'augmentation de la vitesse d'exploitation des trains a grande vitesse entraine souvent une augmentation de la frequence de chargement du sol de la plate-forme. Le comportement dynamique a long terme de la plate-forme et les performances de service des voies a grande vitesse sont donc affectes. Afin de determiner les caracteristiques de contraintedeformation du sol granulaire sous un chargement a haute frequence, un montage d'essai triaxial a ete modifie pour etudier les effets de l'acceleration et de la duree du chargement, de la teneur en eau, de la frequence de vibration, de la pression des cellules et de la densite initiale du sol. Les resultats experimentaux indiquent qu'il y a des reductions de la contrainte axiale et de la deformation volumetrique pendant le chargement a haute frequence. La reduction de la contrainte axiale peut atteindre 40% et celle de la deformation volumetrique, qui est permanente, peut approcher 0,1%. La reduction des contraintes, la compression des deformations et l'exces de pression interstitielle varient lineairement avec l'acceleration des vibrations lorsque a/g > 0,02 ou a est l'acceleration de vibration verticale et g est l'acceleration gravitationnelle. La reduction de la resistance et des deformations depend de l'acceleration de la charge et de la pression effective des cellules, mais est independante de la duree de la charge, de la teneur en eau, de la frequence et de la densite initiale. Un seuil d'acceleration a = 0.02g est observe, en dessous duquel les changements de la resistance au cisaillement et de la deformation volumetrique induits par la vibration sont negligeables. En cas d'acceleration elevee, l'amplitude de la deformation peut augmenter et conduire a l'effondrement du specimen. [Traduit par la Redaction] Mots-cles: sol granulaire, etat critique, fluidization, contrainte deviatorique, deformation volumetrique., 1. Introduction Vibrations induced by high-speed trains frequently lead to long-term settlement of the track owing to the permanent compression of the subgrade. When the speed of a high-speed train [...]