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Different empirical formulas have been proposed to describe the water retention curve (WRC) and relative permeability ([k.sub.r]) of soils. This paper presents a Bayesian framework that evaluates not only the [...]

A laboratory testing program was conducted to investigate the effects of microstructure on the water retention curve (WRC) and wetting-drying induced volume change in loess. The axis translation and vapor equilibrium techniques were adopted to control suction in the range of 0-400 kPa and 4-140 MPa, respectively. Hysteresis in the WRC of loess was observed for the entire range of suction studied. Compared to re-compacted loess, intact loess exhibits a more pronounced hysteresis in the suction range below 20 kPa, which can be explained by the ink-bottle pore neck effect or constricted pores. The hypothesis is supported by microstructural evidence of mercury intrusion porosimetry and scanning electron microscopy tests. However, re-compacted loess exhibits larger hysteresis than intact loess for suctions above 30 kPa. A conceptual model was introduced, which links WRC to the corresponding pore-size density (PSD) function. Regarding volume change, more noticeable drying-induced shrinkage, but yielding at a lower suction, was observed for re-compacted loess. This is consistent with the compression test results. Stress has a significant effect on change of PSD and constricted macropores leading to a shift in the main wetting curve and a less pronounced hysteresis. Intact loess exhibits a stress-dependent wetting-induced collapse and drying-induced shrinkage. Key words: loess, microstructure, water retention curve, collapse, shrinkage. Un programme d'essais en laboratoire a ete realise pour etudier les effets de la microstructure sur la courbe de retention d'eau (CRE) et le mouillage-sechage induite par le changement de volume en loess. La translation de l'axe et des techniques d'equilibre de vapeur ont ete adoptees pour controler l'aspiration dans la plage allant de zero a 400 kPa et 4 a 140 MPa, respectivement. L'hysteresis en CRE de loess a ete observee pour l'ensemble de l'aspiration etudiee. Par rapport au loess recompacte, le loess intact presente une hysteresis plus marquee dans la plage d'aspiration inferieure a 20 kPa, ce qui peut etre explique par l'effet de goulot de pores de bouteille d'encre ou de pores retrecis. L'hypothese est corroboree par des preuves microstructurelles des essais par porosimetrie au mercure et par microscopie electronique a balayage. Cependant, le loess recompacte presente une hysteresis plus grande que le loess intact pour l'aspiration au-dessus de 30 kPa. Un modele conceptuel a ete presente, qui relie le CRE a la fonction de densite de la taille de pores correspondants (PSD). En ce qui concerne le changement de volume, un plus sensible retrait induit par sechage a ete observe, mais cedant une aspiration plus faible a ete observee pour le loess recompacte. Ceci est coherent avec les resultats des essais de compression. La contrainte a un effet significatif sur le changement du PSD et des macro-pores resserres conduisant a un decalage de la courbe de mouillage principale et une hysteresis moins prononcee. Le loess intact presente un ecrasement induit de mouillage en fonction de la contrainte et le retrecissement induit par le sechage. [Traduit par la Redaction] Mots-cles: loess, microstructure, courbe de retention d'eau, ecrasement, retrecissement., Introduction The Loess Plateau of China was formed as a result of the deposition of aeolian sediments in Northern China. Because of its aeolian origin, loess has a metastable and [...]

This study proposes two empirical relationships to estimate the parameters of van Genuchten's formula for modeling the water retention curve from the particle-size distribution. The relationships are determined by the Bayesian probabilistic method for selecting the most plausible class of models based on a database of 90 soil samples. The highest plausibility model among the selected relationships shows that the parameter a can be expressed as a first-order function of the particle size at 50% passing (d50) and parameter n is expressed as a third-order polynomial of the reciprocal of the standard deviation of geometric mean particle size (crg). The predictability of proposed relationships for other soils outside the calibrated database is also presented. It is found that the model prediction is highly consistent with the measurements for sands. However it only matches well with the measurements in the low suction regime for soils with at least 20% of fines content. Key words: Bayesian analysis, particle-size distribution, saturation, soil suction, unsaturated soils. Cette etude propose deux relations empiriques pour estimer les parametres de la formule de van Genuchten servant a modeliser la courbe de retention d'eau a partir de la distribution granulometrique. Les relations sont determinees a l'aide de la methode probabiliste bayesienne pour selectionner la classe de modeles la plus plausible a partir d'une base de donnees de 90 echantillons de sol. Le modele etant le plus plausible parmi les relations selectionnees suggere que le parametre a peut etre exprime comme une fonction de premier ordre de la taille des particules a 50 % passant (d50) et que le parametre n peut etre exprime comme une fonction polynomiale de troisieme ordre de la reciproque de l'ecart-type de la moyenne geometrique de la taille des particules (crg). La predictibilite des relations proposees pour d'autres sols en dehors de la base de donnees calibree est aussi presentee. On observe que la prediction du modele est tres consistante avec les mesures pour les sables. Cependant, les predictions correspondent bien aux mesures seulement pour des sols en faible succion ayant un contenu en particules fines d' au moins 20 %. Mots-cles : analyse bayesienne, distribution granulometrique, saturation, succion du sol, sols non satures. [Traduit par la Redaction], Introduction 'Water retention curve' (WRC) refers to the relationship between water content and soil suction. It is an essential input function for modeling the retention and transport of water and [...]

Although it is generally recognized that unsaturated soil behavior is governed by two constitutive variables (matric suction and net normal stress) and that the hydromechanical behavior of unsaturated soil is coupled, a water retention curve obtained from tests under zero stress and assuming no volume change is still fairly common. A relatively limited number of studies on the stress path-dependent water retention curve (SDWRC), particularly under a broader range of stress paths, exist in the literature. In this paper, the SDWRC, shrinkage curve, and swelling curve of a compacted silt subjected to isotropic and deviatoric stress paths are presented. The test results show that the air-entry value (AEV) increases, but the hydraulic hysteresis loop decreases with an increase in net mean stress. Furthermore, for a given stress level, the K0-compressed specimen exhibits higher AEV, but a smaller hysteresis loop than that of the isotropically compressed specimen. A nonlinear shrinkage curve is observed and the gradient of the post-yield shrinkage curve depends on the degree of saturation and net mean stress, but is independent of the stress path. For the range of suction studied, the gradient reduces with a decreasing degree of saturation, but with an increasing net mean stress. Finally, the test results are compared with the prediction of a model based on two independent constitutive stress variables. Key words: unsaturated soil, compacted silt, water retention, shrinkage, stress path. Meme s'il est generalement reconnu que le comportement non sature d'un sol est defini par deux variables constitutives (succion matricielle et contrainte normale nette) et que le comportement hydromecanique d'un sol non sature est couple, il est commun d'obtenir la courbe de retention d'eau a partir d'essais sous zero contrainte et en supposant aucune variation de volume. Un nombre relativement limite d'essais sur les courbes de retention d'eau dependantes du cheminement des contraintes (CREDC), et particulierement sur un eventail large de cheminements des contraintes, existent dans la litterature. Dans cet article, la CREDC, les courbes de retrait et de gonflement d'un silt compacte soumis a des cheminements de contraintes isotropes et deviatoriques sont presentees. Les resultats des essais indiquent que la pression a l'entree d'air (PEA) augmente, mais que la boucle d'hysteresis hydraulique diminue, avec une augmentation de la contrainte nette moyenne. De plus, pour un niveau de contrainte donne, l'echantillon comprime a Ko presente une PEA plus elevee, mais une boucle d'hysteresis plus petite que celle de l'echantillon comprime de facon isotrope. Une courbe de retrait non lineaire est observee et le gradient de la courbe de retrait post-limite elastique depend du degre de saturation et de la contrainte nette moyenne, mais est independant du cheminement des contraintes. Pour les variations de succions etudiees, le gradient diminue avec l' augmentation du degre de saturation mais avec une augmentation de la contrainte nette moyenne. Enfin, les resultats des essais sont compares avec les predictions d'un modele base sur deux variables constitutives independantes liees aux contraintes. Mots-cles : sol non sature, silt compacte, retention d'eau, retrait, cheminement des contraintes. [Traduit par la Redaction], Introduction Unsaturated soils are commonly encountered in many engineering applications. The matric suction, defined as the difference between pore-air pressure ([u.sub.a]) and pore-water pressure ([u.sub.w]), is one of the critical [...]

Unconfined compression and bound-water content tests were conducted to study the effect of humic acid on the mechanical behaviour of solidified dredged material. It is found that the unconfined compressive strength ([q.sub.u]) and the change in bound-water content (Δ[m.sub.bw]) exhibit similar relationships with the humic-acid content and curing time. Both parameters decrease with an increase in humic-acid content until reaching a threshold humic-acid content, above which the magnitudes of both parameters reduce to relatively low and steady values. In addition, both [q.sub.u] and Δ[m.sub.bw] increase nonlinearly with the curing time. A relationship between [q.sub.u] and Δ[m.sub.bw] is presented; Δ[m.sub.bw] may reflect the extent of the hydrates developed in the solidified soil which increases nonlinearly with [q.sub.u]. Key words: dredged material, solidification, cement, humic-acid content, bound water. Des essais de pression non confinee et de teneur en eau liee ont ete effectues pour etudier l'effet de l'acide humique sur le comportement mecanique de residus de dragage solidifies. Il a ete determine que la pression en compression non confinee ([q.sub.u]) et que la variation de la teneur en eau liee (Δ[m.sub.bw]) presentent des relations similaires avec la teneur en acide humique et le temps de curage. Les deux parametres diminuent lorsque la teneur en acide humique augmente jusqu'a une limite au-dessus de laquelle la magnitude des deux parametres est reduite a des valeurs relativement faibles et stables. De plus, quet Δ[m.sub.bw] augmentent de f[a.sub.co]n lineaire selon le temps de curage. Une relation entre [q.sub.u] et Δ[m.sub.bw] est presentee. Le parametre Δ[m.sub.bw] peut representer l'ampleur de l'hydratation des hydrates developpes dans le sol solidifie qui augmente de f[a.sub.co]n non lineaire avec qu. Mots-cles : residus de dragage, solidification, ciment, teneur en acide humique, eau liee. [Traduit par la Redaction], Introduction In general, dredged material (DM) is a soft soil that has a very low shear strength ([c.sub.u] < 50 kPa) and a natural water content higher than its liquid [...]