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Microbial induced calcium carbonate precipitation (MICP) offers a sustainable technique to improve geologic properties of soils in engineering structures. The applications encompass improved soil strength, scour mitigation, fracture sealing, and in situ contaminant immobilization. Previous studies have presented fundamental processes and implementation in lab- and field-scale. Most of these studies were examined in saturated conditions despite many MICP applications including those in coastal and riverside areas which will likely take place under unsaturated conditions. The study herein investigated the effect of soil water retention curve (SWRC) parameters and attachment coefficient (Kat) on CaCO3 precipitation in sand. Using numerical analyses, a continuum model was developed in which unsaturated flow and transport were coupled with biological and chemical reactions in variably saturated conditions. Predictive modeling results compare mass percentage of calcium carbonate resulting from MICP at degrees of soil water saturations of 20%, 40%, 80%, and 100% in sandy soil media. The results indicate the bacteria attachment coefficient increases by a factor of 3 as the degree of saturation is decreased from 100% to 20%, as the higher suctions at lower saturation levels improve bacteria fixation. The drying branch of SWRC versus wetting front yields higher CaCO3 for identical MICP treatment. Numerical results show the trend in hydraulic conductivity with increasing cementation level. [ABSTRACT FROM AUTHOR]

Since the mid-1990s, several empirical unsaturated shear strength equations have been proposed for use in geotechnical engineering practice. Most of the equations have been based on information associated with the measured drying soil-water characteristic curve (SWCC) in combination with the effective shear strength parameters of the saturated soil. There have been few studies, however, undertaken on verifying and comparing the suitability of the proposed unsaturated shear strength equations. This study involves consideration of a wide range of possible drying SWCCs plotted as a relationship between the degree of saturation and suction (saturation soil-water characteristic curve (S-SWCC)). The study forms the basis for comparing five methodologies that have been proposed for the estimation of the shear strength of unsaturated soils. The SWCCs are defined by the fitting parameters for the Fredlund and Xing (1994) sigmoidal equation. This study supports the use of unsaturated soil shear strength empirical estimation methods using the S-SWCC anchor points of air-entry value and residual suction of the soil. [ABSTRACT FROM AUTHOR]

This paper investigates the compression behavior of unsaturated clay under mean stresses up to 160 MPa and different drainage conditions. A new isotropic pressure cell was developed that incorporates matric suction control using the axistranslation technique, and a high-pressure syringe pump operated in displacement-control mode was used to control the total stress and track specimen volume changes. In addition to presenting results from characterization tests on the cell, results from a series of isotropic compression tests performed on compacted clay specimens under drained and undrained conditions are presented. These results permit evaluation of the hardening mechanisms and transition points in the compression curve with increasing effective stress. As expected, specimens tested under undrained conditions were much stiffer than those tested under drained conditions. In the drained tests, the rate of compression was sufficient to permit steady-state dissipation of excess pore-water pressure except under the highest stress ranges. Suction-induced hardening was observed when comparing saturated and unsaturated specimens tested in the drained compression tests. In both the drained and undrained compression tests, the range of applied stresses was sufficient to cause collapse or dissolution of the air voids (pressurized saturation) and convergence of the virgin compression lines for unsaturated specimens with that measured for saturated specimens. A gradual transition to full-void closure was observed at high stresses when the compression curves were plotted on a natural scale, but the shapes of the compression curves at high stresses were not consistent with conventional soil mechanics models when plotted on a semilogarithmic scale. The results from this study provide insight into how constitutive models for unsaturated soils can be extended to high stress conditions for drained and undrained conditions.

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Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hydration occurring in cemented paste backfill (CPB) is shown to generate matric suction through self-desiccation. This complicates determination of the water-retention curve and mechanical properties during curing, which are important in stope design, and renders problematic the use of axis-translation testing procedure to control suctions in strength testing. An alternative is to monitor suction directly during testing. To this end, a miniature tensiometer is inserted into the base of a triaxial cell. A series of unconfined and confined tests are performed on early-age (less than two weeks old) CPB. The observed behaviour is similar to that observed in weakly cemented soils, showing a distinct tendency to dilate during shearing. On a montré que l’hydratation qui se produit dans les remblais de pâte de ciment « CPB génère une succion matricielle par auto-dessiccation. Ceci complique la détermination de la courbe de rétention d’eau et des propriétés mécaniques durant le mûrissage, qui sont importantes dans la conception de gradins, et rend problématique l’utilisation de la procédure d’essais par translation d’axe pour contrôler les succions dans les essais de résistance. Une alternative consiste à mesurer la succion directement durant l’essai. À cette fin, un tensiomètre miniature est inséré dans la base de la cellule triaxiale. Une série d’essais confinés et non confinés sont réalisés tôt dans l’histoire de la pâte « CPB (moins de deux semaines). Le comportement observé est similaire à celui observé dans les sols faiblement cimentés, montrant une tendance distincte à se dilater durant le cisaillement. [ABSTRACT FROM AUTHOR]

The shear strength characteristics of statically compacted unsaturated soil specimens of commercial kaolin (Ip = 15%) were determined using conventional triaxial shear testing apparatus extending total stress analysis. The testing program consists of two different types of confined compression shear strength tests on unsaturated soil specimens. In the first series of tests, the specimens were sheared immediately after the application of the confining pressure under undrained loading conditions. In the second series of tests, the specimens were first allowed to come to equilibrium with respect to volume change and suction value under the applied confining pressure and sheared at two different rates of strain. A psychrometer was used for measuring suction values. In addition, conventional consolidated undrained tests were also conducted on specimens that were saturated using the back pressure technique before shearing. Comparisons with respect to the shear strength behavior are provided for both saturated and unsaturated soil specimens. The shear strength contribution towards suction was determined from test results on unsaturated soil specimens extending state variable approach in terms of total stresses. Discussion is presented to understand the influence of the following factors (i) suction, (ii) confining pressure, and (iii) rate of strain on the shear strength. Les caractéristiques de résistance au cisaillement d’échantillons de kaolin commercial (Ip = 15 %) non-saturés compactés statiquement ont été déterminées à l’aide d’un appareil triaxial conventionnel en utilisant une analyse de la contrainte totale. Le programme d’essais comprenait deux types d’essais triaxiaux confinés en compression. Dans la première série d’essais, les échantillons ont été soumis au cisaillement immédiatement après l’application de la pression de confinement dans des conditions de chargement non-drainé. Dans la deuxième série d’essais, on a d’abord permis aux échantillons d’atteindre l’équilibre de volume et succion sous la pression de confinement appliquée, puis, ils ont été soumis au cisaillement à deux taux de déformation relative différents. La succion a été mesurée à l’aide d’un psychromètre. De plus, des essais conventionnels consolidés non-drainés ont également été menés sur des spécimens ayant été saturés par la technique de contre-pression avant le cisaillement. Des comparaisons du comportement de résistance au cisaillement sont fournies autant pour les échantillons saturés que non-saturés. La contribution de la succion à la résistance au cisaillement a été déterminée d’après les résultats d’essais de cisaillement sur des échantillons non-saturés en utilisant l’approche de la variable d’état en termes de la contrainte totale. Une discussion est présentée afin de mieux comprendre l’influence des facteurs suivants (i) succion, (ii) pression de confinement, et (iii) la vitesse de déformation, sur la résistance au cisaillement. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A suction-controlled true triaxial apparatus for unsaturated soil was developed from the existing true triaxial apparatus for sand by attaching a device to supply matric suction to specimens. Using the developed apparatus, true triaxial tests (σ[sub 1] σ[sub 2] σ[sub 3] ; where σ[sub 1] , σ[sub 2] , and σ[sub 3] are the three different principal stresses) on an unsaturated silty soil were carried out under constant suction using the negative pore-water pressure method (s = –u[sub w] > 0; u[sub a] = 0) for applying the matric suction, s (s = u[sub a] – u[sub w] ; where u[sub a] is the pore-air pressure and u[sub w] is the pore-water pressure). It was found that the true triaxial test results under three different principal stresses are uniquely arranged on the "extended spatially mobilized plane (extended SMP)" for frictional and cohesive materials that is modified from the original SMP for frictional materials by introducing "a bonding stress, σ[sub 0] (= c·cotφ, where c is cohesion and φ is the internal friction angle)." It was also found that the shear strengths of the unsaturated silty clay obtained by the true triaxial apparatus nearly agree with the extended SMP failure criterion (Î[sub 1] Î[sub 2] /Î[sub 3] = constant, where Î[sub 1] , Î[sub 2] , and Î[sub 3] are the first, second, and third invariants of the translated stress tensor). The measured stress-strain-strength behaviour of the unsaturated soil in three-dimensional (3D) stresses can be well simulated by an elastoplastic model with the transformed stress based on the extended SMP criterion and a special hardening parameter.Key words: failure criterion, shear strength, special shear test, suction, stress path, unsaturated soil.Un appareil triaxial vrai à succion contrôlée pour sol non saturé a été développé en partant de l'appareil triaxial vrai pour le sable en y ajoutant un dispositif permettant de fournir la succion matricielle aux spécimens. Au moyen de l'appareil développé, les essais triaxiaux vrais (σ[sub 1] σ[sub 2] σ[sub 3] ) sur un sol limoneux non saturé ont été réalisés sous une succion constante en utilisant la méthode de pression interstitielle négative (s = –u[sub w] > 0; u[sub a] = 0) pour appliquer la succion matricielle s (s = u[sub a] – u[sub w] ; u[sub a] : pression de l'air interstitielle, u[sub w] : pression de l'eau interstitielle). On trouve que les résultats de l'essai triaxial vrai sous trois différentes contraintes principales sont disposés de façon unique sur le plan élargi mobilisé dans l'espace (PME élargi) pour les matériaux cohérents et pulvérulents, modifié en partant du PME original pour les matériaux pulvérulents et en introduisant « une contrainte de cimentation σ[sub 0] (= c·cotφ). » On trouve également que les résistances au cisaillement de l'argile limoneuse non saturée obtenues par l'appareil triaxial vrai concordent presque avec le critère de rupture élargi PME (Î[sub 1] Î[sub 2] /Î[sub 3] = const.). Le comportement mesuré contrainte-déformation-résistance du sol non saturé en contraintes tridimensionnelles (3D) peut être bien simulé par un modèle élastoplastique avec la contrainte transformée sur la base du critère élargi PME et d'un paramètre spécial d'écrouissage.Mots clés : critère de rupture, résistance au cisaillement, essai de cisaillement spécial, succion, cheminement de contrainte, sol non saturé.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

A saturated silty soil sample is centrifuged in a geotechnical centrifuge to create an unsaturated state. The change in water content of the soil sample is recorded at different points along the length of the sample to obtain the water-content profile, which is then used to obtain the unsaturated hydraulic conductivity of the soil sample. These hydraulic conductivity values are compared with those obtained and reported by previous researchers by conducting accelerated falling-head tests on this soil sample in a centrifuge. The study demonstrates the use of centrifugation techniques to obtain hydraulic conductivities of unsaturated soils.Key words: silty soil, saturated soil, unsaturated soil, hydraulic conductivity, centrifuge testing.Un échantillon de sol limoneux saturé a été centrifugé dans un centrifuge géotechnique pour produire un état non saturé. Le changement en teneur en eau de l'échantillon de sol est enregistré à différents points le long de l'échantillon pour obtenir un profil de teneur en eau qui a été ensuite utilisé pour obtenir la conductivité hydraulique non saturée de l'échantillon de sol. Ces valeurs de conductivité hydraulique sont comparées avec les conductivités hydrauliques obtenues et rapportées antérieurement par des chercheurs qui ont conduit des essais accélérés à tête variable sur ces échantillons de sol dans un centrifuge. Cette étude démontre l'utilisation des techniques de centrifugation pour obtenir les conductivités hydrauliques des sols non saturés.Mots clés : sol limoneux, sol saturé, sol non saturé, conductivité hydraulique, essai au centrifuge.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The paper proposes equations describing the transport of gases through the initially unsaturated core of a dam by dissolution and diffusion in water and examines different numerical simulations based on these equations. The simulation results provide pore-water pressure distributions similar to those observed in several earth dams, with higher pore-water pressures than expected in the downstream part of the core. Practical considerations to estimate the implications of the phenomenon are then discussed.Key words: dam, unsaturated soil, pore pressure, dissolution of gas, diffusion of gas, hydraulic conductivity.L'article propose des équations décrivant le transport des gaz par dissolution et diffusion dans l'eau à travers le noyau initialement non saturé d'un barrage et examine différentes simulations numériques basées sur ces équations. Les résultats des simulations fournissent des distributions de pressions interstitielles semblables à celles observées dans plusieurs barrages en terre, avec des pressions interstitielles plus élevées qu'escomptées dans la partie aval du noyau. On discute alors de considérations pratiques pour évaluer les implications du phénomène.Mots clés : barrages, sol non saturé, pression interstitielle, dissolution des gaz, diffusion des gaz, conductivité hydraulique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

A number of empirical equations have been proposed for the soil-water characteristic curve. A nonlinear, least squares method was used to determine best-fit parameters for several empirical equations that were best-fit to 230 water content versus soil suction data sets. In addition, two proposed correction methods to accommodate high soil suctions up to 1 000 000 kPa were applied to the various soil-water characteristic curve equations. The data sets of water content versus soil suction were arranged into one of the USDA soil classifications based on their relative amounts of sand, silt, and clay (only eight soil classifications had sufficient data for later analysis). The quality of fit for each model was compared using the Akaike Information Criterion. A series of conclusions were arrived at regarding (i) the relationship between two- and three-parameter equations, (ii) the relationship between exponential and sigmoidal type equations, and (iii) the value of correction factors for the high soil suction range.Key words: soil-water characteristic curve, unsaturated soil, soil suction, regression analysis, SWCC models, Akaike Information Criterion.Un certain nombre d'équations empiriques ont été proposées pour la courbe caractéristique sol-eau. Une méthode non linéaire des moindres carrés a été utilisée pour déterminer les paramètres de la meilleure concordance pour plusieurs équations empiriques ayant la meilleure concordance pour 230 ensembles de teneur en eau en fonction de la succion du sol. De plus, deux méthodes de correction proposées pour traiter de fortes succions atteignant 1 000 000 kPa ont été appliquées à diverses équations de courbes caractéristiques sol-eau. Les ensembles de données de teneur en eau versus succion du sol ont été arrangés dans une des classifications de sols du USDA basée sur les quantités relatives de sable, silt et argile (seulement huit classifications de sols avaient suffisamment de données pour des analyses subséquentes). La qualité du lissage pour chaque modèle a été comparée en utilisant le critère d'information de Akaike. On en est arrivé à une série de conclusions concernant: (i) la relation entre les équations à 2 et 3 paramètres, (ii) la relation entre les équations de types exponentiel et sigmoïdal, et (iii) la valeur des facteurs de correction pour la plage des fortes succions du sol.Mots clés : courbe caractéristique sol-eau, sol non saturé, succion du sol, analyse de régression, modèles SWCC, critère d'information de Akaike.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The seepage rate through homogeneous or zoned dikes includes saturated and unsaturated flow. The latter is often neglected but should be considered to obtain the positions of the water table and the seepage face that may develop either on the downstream slope of a homogeneous dike or within the filter layer behind the core of a zoned dike. Different dikes with heights of 5, 10, 20, and 50 m have been analyzed numerically with a two-dimensional finite element code. The cases investigated include the most frequent types of small dikes designed to retain municipal or industrial wastewater. Solutions are proposed to solve numerically two difficulties related to the representation of saturated and unsaturated physical flow conditions. One difficulty is treating a downstream seepage face. The other is treating the passage of water from the core into a draining layer. The paper presents simple expressions to predict the total (saturated and unsaturated) seepage flow rate through a dike and discusses precautions to be taken.Key words: dams, dikes, seepage, saturated soil, unsaturated soil, numerical modeling.Le débit de fuite des digues homogènes ou zonées inclut les écoulements saturés et non saturés. Ces derniers sont souvent négligés mais devraient être considérés pour avoir les positions de la nappe et de la surface de suintement qui peut se développer sur la pente aval d'une digue homogène ou dans le filtre à l'arrière du noyau d'une digue zonée. Différentes digues de hauteurs 5, 10, 20 et 50 m ont été analysées numériquement avec un code bidimensionnel d'éléments finis. Les cas étudiés comprennent les types les plus fréquents de petites digues conçues pour retenir des eaux usées municipales ou industrielles. On propose des solutions pour résoudre numériquement deux difficultés reliées à la représentation des conditions physiques d'écoulement saturé et non saturé. Une difficulté est le traitement d'une surface de suintement. L'autre est le traitement du passage de l'eau du noyau dans une couche drainante. L'article propose des expressions simples pour prédire le débit de fuite total (saturé et non saturé) à travers une digue et discute des précautions à prendre.Mots clés : barrages, digues, écoulement, sol saturé, sol non saturé, modèle numérique. [ABSTRACT FROM AUTHOR]

The finite element method provides a popular means of analyzing groundwater flow in an unsaturated soil. In such problems, oscillatory results are often observed in the finite element solution. Such a phenomenon is observed, for example, when a typical finite element program such as Seep/w is used to model water infiltration into unsaturated soils. Numerical oscillations are often found near the wetting front where the hydraulic gradient is the steepest. These oscillations do not always reduce with decreasing or increasing time-step size alone; rather, an appropriate ratio between time-step size and element size is required. As the pore-water pressures predicted from a transient seepage analysis are used as input groundwater conditions for other types of analysis such as slope stability, contaminant transport, and capillary barrier, these oscillations may have important practical ramifications. Since seepage analysis is common in engineering practice, it is important that appropriate criteria are identified to minimize, if not to remove, the oscillations. In this paper, numerical examples are provided to demonstrate that a simple set of criteria, developed in heat diffusion problems with constant properties to control oscillation, is also applicable to one- and two-dimensional unsaturated seepage analyses, for a range of material nonlinearities that are frequently encountered in unsaturated soils.Key words: unsaturated soil, soil-water characteristic curve, seepage analysis, finite element method, numerical oscillation.La méthode des éléments finis constitue un moyen populaire pour analyser l'écoulement de l'eau souterraine dans un sol non-saturé. Dans de tels problèmes, on observe souvent des résultats oscillants dans la solution en éléments finis. Par exemple, de tels phénomènes sont observés lorsqu'un programme typique en éléments finis tel que Seep/w est utilisé pour modéliser l'infiltration d'eau dans les sols non-saturés. Des oscillations numériques sont souvent obtenues près du front mouillé, là où le gradient hydraulique est le plus grand. Ces oscillations ne sont pas toujours réduites à la suite seulement de diminutions ou d'augmentations des dimension des étapes de temps. Lorsque les pressions interstitielles prédites par une analyse d'infiltration transitoire sont utilisées comme conditions d'entrée d'infiltration pour d'autres types d'analyses tels que la stabilité des talus, le transport des contaminants, et l'analyse d'une barrière de capillarité, ces oscillations peuvent avoir d'importantes ramifications pratiques. Comme l'analyse de l'infiltration est courante dans la pratique du génie, il est important que des critères appropriés soient identifiés pour minimiser, sinon éliminer les oscillations. Dans cet article, des exemples numériques sont fournis pour démontrer qu'un simple ensemble de critères, développés dans les problèmes de diffusion de chaleur avec des propriétés constantes pour contrôler l'oscillation, est aussi applicable à des analyses d'infiltration non-saturée unidimensionnelles et bidimensionnelles, pour une plage de matériaux avec des non-linéarités qui sont fréquentes dans les sols non-saturés.Mots clés : sol non-saturé, courbe des caractéristiques sol-eau, analyse de l'infiltration, méthode d'éléments finis, oscillation numérique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

To investigate the soil structure and mechanical behavior of an unsaturated expansive clay soil, triaxial and mercury intrusion tests have been performed and are presented in this paper. Also an optical test system was developed for studying the internal structure evolution of the unsaturated expansive soil during shear-loading tests. The research results show a linear relationship between the cohesion intercept and the degree of saturation of the unsaturated clay for the test data. For the tested soil, the pore-size distribution curves were found to be bimodal. The measurement results from mercury intrusion tests confirm that the micropores of Guangxi expansive soils of this study remain constant, and that the macropores vary with the dry density of soil samples. Comparing the volumetric strain curves with the soil particle area curves, some correlation and dependence on the macropore variation of soil samples during shear-loading tests can be shown to exist. [ABSTRACT FROM AUTHOR]