Saturated Unsaturated Porous Media Research Articles

One-dimensional simulation of solute transfer in saturated–unsaturated porous media using the discontinuous finite elements method

A one-dimensional transport model for simulating water flow and solute transport in homogeneous–heterogeneous, saturated–unsaturated porous media is presented. The model is composed of a combination of accurate numerical algorithms for solving the nonlinear Richard's and advection–dispersion equations (ADE). The mixed form of Richard's equation is solved using a standard finite element method (FEM) with primary variable switching. The transport equation is solved using operator splitting, with the discontinuous finite element method (DFE) for discretization of the advective term. A slope limiting procedure for DFE avoids numerical instabilities but creates very limited numerical dispersion for high Peclet numbers. An implicit finite differences scheme (FD) is used for the dispersive term. The unsaturated flow and transport model (Wamos-T) is applied to a variety of rigorous problems including transient flow, heterogeneous medium and abrupt variations of velocity in magnitude and direction due to time-varying boundary conditions. It produces accurate and mass-conservative solutions for a very large range of grid Peclet numbers. The Wamos-T model is a good and robust alternative for the simulation of mass transport in unsaturated domain.

Modeling of 2D Density-Dependent Flow and Transport in the Subsurface

A 2-dimensional finite-element model for density-dependent flow and transport through saturated-unsaturated porous media has been developed. The combined flow and transport model can handle a wide range of real-world problems, including the simulations of flow alone, contaminant transport alone, and combined flow and transport. The conventional finite-element methods and a hybrid Lagrangian-Eulerian finite-element method were incorporated in the transport module. Saltwater intrusion problems and instability caused by denser water on the top were investigated in this paper. Because the fundamental mechanism causing saltwater intrusion most likely is caused by density-induced convection and dispersion, the developed model was used to assess the interplay between density-driven flow and the subsurface media through which the saltwater intrusion occurs. The mathematical formulation of the model is comprised of fluid flow and solute transport equations, coupled by fluid density. In the specific case of saltwater intrusion and unstable brine transport problems, this set of governing equations is nonlinear and requires iterative methods to solve them simultaneously. Three case studies, which include a wide spectrum of physical conditions, show the verification and effectiveness of the model by comparing previously published solutions from other researchers with the simulation results of the present model. Two demonstrated problems examine the model capabilities to handle saltwater intrusion problems through unsaturated-saturated porous media and density-dependent flow and transport under unstable conditions.

Simulation and analysis of frost heaving in subsoils and granular fills of roads

Laboratory data were utilized to verify the finite-element program MELEF for simultaneous water flow, heat and solute transport simulations in saturated-unsaturated porous media. Firstly, numerical simulations were used to predict observed frost heaves in the soil columns, using measured and estimated physical properties as well as experimental conditions as input. The comparison of the predictions and the laboratory experiments showed differences less than 5% between calculated and observed frost heaves at the end of the freezing tests. Secondly, a sensitivity analysis for laboratory conditions allowed the verification of various parameters used in the model (thermal and hydraulic conductivities, capillary height, pore distribution index, residual saturation and clay distribution factor). The analysis showed that frost heaving could be chiefly influenced by the parameters defining the soil moisture retention curve, that is, capillary height, pore distribution index and residual saturation. Finally, frost heaving sensitivity tests were performed with MELEF in order to assess likely transient frost heaves of a particular road submitted to different conditions during a particular winter. The previously studied materials were used as inputs with different water table heights and climatic conditions normally encountered in the Quebec region. Results show that improving road drainage could constitute an appropriate solution to the problems of frost deformation, when the sampled materials contain less fine grains. Materials with similar frost-susceptibility indexes but with different physical properties, did not necessarily have similar frost heaving behaviours for the same road drainage conditions. These findings should help to find better solutions to the engineering problems due to ground freezing by making possible a better correlation between the frost-susceptibility of soils, as measured by various laboratory tests, and the amount of heave observed in the field.

飽和・不飽和多孔体中の熱移動とヒステリシスを伴う浸透流の連成解析

A two-dimensional mathematical model for simulating coupled problems of water flow and heat transport in saturated-unsaturated porous media is presented. The model is composed of two submodels; that is, a saturated-unsaturated water flow submodel and a heat transport submodel. The saturatedunsaturated water flow submodel can take into consideration thermal convection in saturated zone due to temperature gradient, soil water hysteresis accompanied by unsaturated flow, and temperature effect on the density and viscosity of water together with the typical forced convection. The heat transport submodel can handle heat conduction, heat dispersion, and forced and thermal convection in saturatedunsaturated porous media. The numerical method proposed in this paper is based on the finite elements for water flow and the characteristic finite elements for heat transport.The model was applied to two experimental problems with laboratory and field data. First, water flow in saturated-unsaturated soil column was analyzed under hysteretic and isothermal condition. Then, the model was applied to a problem of coupled transport of water and heat in saturated-unsaturated porous media. The latter problem is accommodated to account for an aquifer thermal energy storage experiment conducted in Sanrihama dune sand area where serial tests of artificial recharge of warm and cold water and recovery for agricultural use have been taken place for several years. Although it was not possible to compare the simulation and experimental results in a strict sense due to the lack of adequate experimental data, it was qualitatively proved that the model can be successfully applied to this type of coupled problems.

A coupled thermoelastic model for saturated–unsaturated porous media

The determination of the heat and mass flow in porous media is a problem of great importance in many engineering and technical processes. Typical problems include the accumulation of moisture under pavements, geothermal energy utilization, thermal enhancement of oil recovery and the disposal of hazardous wastes. The phenomenon also has a bearing on geology, meteorology and agricultural problems. The existing predictive models of heat and mass flow in porous media fail to incorporate the coupling effects between the flowing components (heat, moisture and gas), or the flowing components and solid particles. In addition, some models do not represent the flow phenomena thoroughly (i.e. heat flow due to convection is ignored in many models) or less emphasis is given to the soil parameters and their variations with respect to soil moisture and temperature. This Paper presents a mathematical model for the flow of heat, moisture and gas in porous media. In the model presented the coupling effects between moisture, heat and gas flow and soil skeleton volume changes are considered. Soil parameters (i.e. thermal, hydraulic and gas conductivities, and volume change) have been selected through a comprehensive survey of the literature in related areas. A finite element method has been used for the numerical solution of the mathematical model developed. Finally, some case histories are reproduced and solved numerically using the model developed. The computed results are then compared with those of measured or computed data available in case histories. For cases where no case histories were obtained, the computer results are analysed and discussed. La détermination de l'écoulement de chaleur et de masse dans un environnement poreux crée des problèmes très importants dans beaucoup de procéssus de construction et de technologie. Notamment en ce qui concerne l'accumulation d'humidité sous les chaussées, l'utilisation de Penergie géothermique, l'amélioration thermique de la récupération des huiles et le dépôt des déchets dangereux. Le phènomène influence aussi beaucoup de problèmes de géologie, de météorologie et d'agriculture. Les modèles actuels pour prédire l'écoulement de chaleur et de masse dans un environnement poreux n'incluent pas les effets de couplement entre les constituants mêmes de l'écoulement (chaleur, humidité, gaz) ni entre de tels constituants et les particules solides. D'autres modèles ne représentent pas les phénomènes d'écoulement de façon complète (beaucoup de modèles ignorent l'écoulement de chaleur causée par la convection) ou bien les paramètres du sol et leurs variations selon l'humidité et la température du sol sont négligés. Cet article présente un modéle mathématique pour l'écoulement de chaleur, d'humidité et de gaz dans un environnement poreux. Ce modele tient compte des effets de couplement entre l'écoulement de chaleur, d'humidite et de gaz et les changements dans le volume du squelette du sol. Des paramètres du sol (les conductibilités thermique, hydraulique et gazeuse et le comportement lors des changements dans le volume) ont été sélectionnés d'un examen détaillé de la littérature à la suite technique correspondante. Une méthode à éléments finis est utilisée pour la solution numérique du modèle mathématique développe. Puis des exemples réels sont présentés et résolus numériquement par l'emploi du modèle développé. Ceci est suivi d'une comparaison entre les résultats calculés et les donnees mesurées ou calculées disponibles dans des exemples réels. Là où il n'y avait aucun exemple de cas réel l'article analyse et discute les resultats obtenus à partir de l'ordinateur.

Geohydrochemical Considerations in Land Disposal of Low-Level Wastes

Geohydrochemical factors that affect the transport of low-level wastes in saturated-unsaturated porous media are described. Depending on the availability of those geohydrochemical parameters and the detail of information desired, three levels of analyses can be undertaken. Two examples used to illustrate these three levels of analyses are the seepage pond problem and the shallow trench burial problem. The former example indicates that the lower level of resolution gives the more conservative estimate of the breakthrough time for the contaminant. The latter example exemplifies the cases that simple levels of resolution are not adequate nor possible because the flow variables and parameters cannot be determined with rational assumptions. The level 1 model can best be used for screening purposes while level 2 analysis can be employed to rank the alternative sites. Level 3 models should be used for detailed studies of the impact of the chosen site or for predictive assessment of operational sites and decomission scenarios.

Correction [to “Analysis of water and heat flow in unsaturated‐saturated porous media” by Marios Sophocleous

Water Resources ResearchVolume 16, Issue 1 p. 256-256 CorrectionsFree Access Correction [to “Analysis of water and heat flow in unsaturated-saturated porous media” by Marios Sophocleous] Marios Sophocleous, Marios SophocleousSearch for more papers by this author Marios Sophocleous, Marios SophocleousSearch for more papers by this author First published: February 1980 https://doi.org/10.1029/WR016i001p00256AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. Volume16, Issue1February 1980Pages 256-256 RelatedInformation

Transient Seepage Analysis of Guri Dam

The transient seepage analysis of the 95-m (312-ft) high Guri earthfill dam was undertaken to investigate the saturation of earthfill and foundation during and after staged reservoir filling. Saturated-unsaturated porous media flow theory and Galerkin-type finite element techniques were applied. The phreatic surfaces were treated as zero pore pressure lines. The zero pore pressure line was obtained from the calculated pore pressures, including negative pressures in partially saturated zones. The movements of the saturation (wetting) fronts and the pore pressure distributions in the earthfill and its foundation were used in the investigation of deformation and stability of the Guri earthfill dam under staged construction and reservoir filling.

Saturated-Unsaturated Seepage by Finite Elements

A Galerkin-type finite element method is employed to solve the quasilinear partial differential equations of transient seepage in saturated-unsaturated porous media. The resulting computer program is capable of handling nonuniform flow regions having complex boundaries and arbitrary degrees of local anisotropy. Flow can take place in a vertical plane, in a horizontal plane, or in a three-dimensional system with radial symmetry. An arbitrary number of seepage faces can be considered simultaneously, and the positions of the exit points on these boundaries are adjusted automatically during each time step. Two examples, one of seepage through an earth dam with a sloping core and horizontal drainage blanket, and the other of seepage through a layered medium cut by a complex topography, are included. These examples indicate that the classical concept of a free surface is not always applicable when dealing with transient seepage through soils.