No abstract

[1] Infiltration is often assumed to occur with little or no impedance from the air within the vadose zone. If this assumption is not valid air counterflow may occur, while the infiltration rate and degree of saturation within the transmission zone may be significantly reduced. Accurate predictions of infiltration rates are important for applications such as moisture balance calculations and predictions of pore water pressures in landslide triggering. Existing results for confined infiltration show contradictory evidence for either air pressure remaining at a threshold or continual increase of air pressure. In this paper, the effect of air entrapment is investigated in the laboratory using recently developed techniques of unsaturated transparent porous media and digital photograph interpretation. These techniques enable the full saturation profile to be quantified every 5 s. The experimental data are used to quantify the decrease in infiltration rate and degree of saturation within the transmission zone in the confined infiltration, to accurately locate the wetting front, and to assess the stability of the wetting front. The results confirm previous observations in which infiltration in an open system was observed to occur significantly faster than in a closed system. However, in this study, the air pressure ahead of the wetting front was observed to reach a threshold value, which was a function of the ponding height and suction at the wetting front. A Green-Ampt infiltration model based on this observation of air confinement was observed to provide a better fit to the experimental data than the one based on the continual increase in air pressure assumption.

The results of an experimental program undertaken to evaluate the impact of pore fluid salinity on the hydromechanical performance of light and dense backfill materials are presented. Light and dense backfills are engineered barrier materials that are being examined in the Canadian concept for storage of spent fuel in a deep geological repository. The current research investigates the impact of pore fluid chemistry on the swelling, compressibility, stiffness, and hydraulic conductivity parameters of light and dense backfills that are required as material parameters for analysis and design. In these tests, pore fluid chemistry was selected to represent groundwater within potential host units including granite and limestone rock. Results show that the performance of light backfill is significantly affected by changes in pore fluid chemistry. The swell potential of light backfill decreases with increasing salinity of the solution. The hydraulic conductivity decreases with increasing effective montmorillonite dry density and specimens saturated with saline solution have higher hydraulic conductivity than those saturated with distilled water. Conversely, the behaviour of dense backfill is governed mainly by the crushed granite component and therefore changes to the pore fluid chemistry have relatively little effect. Results of dense backfill tests confirm the material performance as a sealing material.

Core Ideas Imaging techniques are powerful for investigating multiphase flow in porous media. Transparent porous media can be used to quantify local fluid saturations. Efficient methods to calibrate intensity–saturation relationships are required. Our new procedure uses fewer images and measurements. Predicted saturations based on calibrated images matched independent measurements. Experiments using transparent porous media, where the indices of refraction of the solid grains and the wetting fluid are matched, can be used to quantify fluid saturations from digital images. In this study, significantly more efficient calibration and validation methods for unsaturated transparent porous media were developed, which used just three images and one saturation measurement. Imbibition and drainage column experiments were used to define the pixel intensity and saturation at residual wetting fluid saturation, as well as at residual nonwetting fluid saturation in two gradations of transparent porous media used for validation. The other images were pixel intensity at 100 and 0% wetting fluid saturation. Results from the drainage and imbibition experiments on the two transparent porous media gradations showed a log‐linear saturation–pixel intensity relationship, which agreed with the validation points from this study as well as those using a previous calibration method. We expect that this new calibration procedure will allow efficient development of saturation–pixel intensity relationships for the investigation of multiphase flow using transparent porous media under a variety of conditions.

Infiltration is a vadose zone process of interest to a wide range of research communities including agriculture, soil physics, and geotechnical engineering. In geotechnical engineering, transient infiltration is important to moisture balance problems such as cover systems, capillary breaks, and landslide triggering. Design of cover systems, capillary breaks, and landslide analysis applications depend on accurate models for the transient pore pressure and moisture migration response under a wide range of environmental conditions. Infiltration is typically modeled using Richards’ equation, which assumes no impedance from the pore-air phase. However, if this assumption is invalid, the ground response during infiltration is significantly affected. An optically matched pore fluid – transparent soil, which allows for high temporal and resolution measurements of degree of saturation, was used to examine the effect of air entrapment on infiltration. Homogeneous and layered profiles were subjected to closed and open infiltration conditions. Following the completion of the experimental program, the results were simulated using a finite element program that allows for consideration of the air phase during infiltration. The results show the impact of ignoring the effect of air entrapment is to significantly underpredict the time to saturation and overpredict the pore pressure response.

Swelling soils are found in many regions throughout the world. Damage caused to infrastructure by these types of soils is measured annually in billions of dollars. These excessive damages are, in part, due to the lack of proper design, resulting from a need for better tools for practitioners to assess the impact of swelling soils in typical design applications. This paper presents an experimental testing program with interpretations to provide a framework for predicting the behaviour of swelling soils under general stress and volume state conditions for practical applications. The experimental testing adopted a new automated triaxial apparatus that controls boundary stress and strain while applying liquid infiltration conditions at the perimeter or center of triaxial specimens. Results demonstrate the influence of a range of boundary conditions on the behaviour of swelling soil during liquid infiltration. The range of boundary conditions examined in the experimental testing include constant mean stress (CMS), where the mean stress applied during the swelling stage is constant; constant volume (CV), where the volume is held constant during the liquid infiltration; as well as a flexible spring-type boundary condition (CS) that applies increases in stress as a specified function of the volume increase. These boundary conditions represent the broad spectrum of experiences in the field. The experimental results show the dominance of boundary conditions on the development of swell pressure and volume expansion to give evidence for a new swell equilibrium limit (SEL) relationship. The SEL shows promise in providing a framework for swelling soils to predict the final soil state under wetting conditions for the range of boundary conditions examined. Application of the SEL relationship in practice is presented as a concept for examining swelling induced pressures and volume expansion in applications of liquid infiltration of swelling soils.

Experimental characterization of unsaturated soils is of primary importance to further understanding of fundamental behavior, as well as allow for accurate modeling and predictions, of constitutive and field behavior. In the laboratory, the most common research methodology used to investigate the hydraulic behavior of unsaturated soils involves placing the unsaturated soil in a column apparatus with measurements of pore pressure and moisture content being made at discrete locations distributed along the elevation of column. These types of tests have provided many valuable insights into unsaturated flow phenomena; however, there are some limitations with this methodology including the discrete nature of the measurement points. In this paper, an alternative method is proposed which aims to combine the use of digital image analysis with a transparent soil to avoid the ambiguity of traditional boundary image measurements of moisture content in column experiments. At 100% saturation, the transparent soil particles appear invisible and allows for the ability to see through the soil mass. Any air bubbles will be visible within the soil voids and as a result, at varying degrees of saturation less than 100%, the soil will become progressively non-transparent. The relationship between pixel intensity of the unsaturated soil and degree of saturation is defined and validated. This relationship allows definition of the degree of saturation throughout the column profile thus giving the opportunity to verify and further develop constitutive models for unsaturated hydraulic behavior.

Time-dependent behaviour can have a significant influence on the compressibility characteristics of soils. However, most of the research on this topic has investigated the behaviour of soft soils. In this paper, the time-dependent behaviour of a hard clay shale (Bearpaw Shale) is investigated using both one-dimensional multi-staged loading (MSL) oedometer and constant rate of strain (CRS) oedometer consolidation tests conducted on 25.0 and 16.9 mm diameter specimens. The results show that soft clays and hard clay shales that share the same Cae/C Ã c ratio (where Cae is the secondary compression index and C Ã c is the incremental compression index) will show the same approximately 7% change in pre-consolidation pressure for an increase of one log cycle of strain rate despite the many orders of magnitude difference in pre-consolidation pressure. In the case of the Bearpaw Shale, this 7% change in pre-consolidation pressure corresponds to approximately 700 kPa. The time-dependent behaviour of the Bearpaw Shale during unloading (Cae/C Ã s , where C Ã s is the incremental swelling index) was observed to follow a similar ratio to that observed in compression (C ae /C Ã c ). While the exact nature of the compression and swelling events that have occurred over the life of the Bearpaw Formation is not clear, the influence of secondary compression cannot be ignored for interpretation of the geological history of this deposit.Résumé : Le comportement dépendant du temps peut avoir une influence significative sur les caractéristiques de compressibilité des sols. Cependant, la plupart des travaux de recherche sur ce sujet se sont penchés sur le comportement des sols mous. Dans cet article, le comportement dépendant du temps d'un schiste argileux dur (schiste de Bearpaw) est étudié à l'aide d'essais unidimensionnels de consolidation à l'odomètre avec chargement multi-étapes (CME) et avec un taux de dé-formation constant (TDC) réalisés sur des échantillons de 25,0 et 16,9 mm de diamètre. Les résultats démontrent que les schistes argileux mous et durs qui partagent le même ratio Cae/C Ã c présentent le même 7 % environ de variation dans la pression de préconsolidation pour causer une augmentation d'un log de cycle de déformation, malgré plusieurs ordres de magnitudes de différence dans la pression de préconsolidation. Dans le cas du schiste de Bearpaw, cette variation de 7 % de la pression de préconsolidation correspond à environ 700 kPa. Le comportement dépendant du temps du schiste de Bearpaw durant le déchargement (C ae /C Ã s ) suivait un ratio similaire à celui observé en compression (C ae /C Ã c ). Même si la nature exacte des événements de compression et de gonflements qui se sont produits sur la durée de vie du formation de Bearpaw n'est pas claire, l'influence de la compression secondaire ne peut pas être ignorée lors de l'interprétation de son historique géolo-gique.