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Hongbin Zhan - One of the best experts on this subject based on the ideXlab platform.
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non Darcian Flow for an artificial recharge well in a confined aquifer with clogging related permeability reduction
Advances in Water Resources, 2021Co-Authors: L I Jiong, Hongbin Zhan, Xiaohe Xia, L I Mingguang, Jinjian ChenAbstract:Abstract To consider the non-Darcian nature of groundwater Flow and the permeability reduction owing to well and aquifer clogging, an Izbash's law-based analytical model with a time-dependent hydraulic conductivity function is proposed for constant-rate recharge and constant-head recharge. By means of linearization approximations, variable substitutions and the Laplace transform, approximate analytical solutions for the model are derived. Comparison of developed approximate analytical solutions with numerical solutions indicates that the approximate solutions are highly accurate except during the short period of initial recharge stage. The proposed model provides a theoretical basis for managed aquifer recharge involving clogging-related permeability reduction and non-Darcian Flow.
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nonlinear drainage model of viscoelastic aquitards considering non Darcian Flow
Journal of Hydrology, 2020Co-Authors: Xiaohe Xia, Jinjian Chen, Hongbin ZhanAbstract:Abstract Numerous aquitard drainage models for dewatering-induced land subsidence have been proposed in the past. Most of them are based on one or more of the following assumptions, including the validity of Darcy's law, neglect of rheological nature and constant soil properties. However, these assumptions may fail to reflect actual characteristics of viscoelastic aquitards. For this reason, the present study improves Terzaghi’s one-dimensional (1-D) consolidation model by incorporating the exponential non-Darcian law, the Merchant viscoelastic model and the nonlinear correlations between soil compressibility, hydraulic conductivity, and void ratio. The numerical solutions for the pore pressure change are obtained using a finite volume method. The expression for compaction and consolidation of aquitard is derived. A parametric study and comparison between the proposed model and the Terzaghi model indicate that the nonlinear permeability and the rheological nature reduce the pore pressure change and the degree of consolidation in the aquitard. The effects are more apparent for an aquitard with a higher compressibility and more obvious non-Darcian Flow nature. Meanwhile, the reduction in pore pressure change decreases the effective stress acting on the soil skeleton, resulting in smaller compaction for an aquitard with more obvious nonlinear permeability, rheological property and non-Darcian Flow nature. Besides, although the higher nonlinear compressibility also reduces the pore pressure change, yet it can induce more significant compaction in the aquitard.
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Editorial of Special Issue “Advances in Groundwater Flow and Solute Transport: Pushing the Hidden Boundary”
MDPI AG, 2019Co-Authors: Hongbin Zhan, Quanrong Wang, Zhang WenAbstract:The theme of this special issue is to explore the new territories beyond conventional subsurface Flow and transport theories. We have selected 12 articles in this special issue and these articles cover a wide range of problems including (1) Non-Fickian chemical transport in various environments; (2) Non-Darcian Flow; (3) Flow and transport in low-permeability media; (4) Vadose zone process; (5) Regional scale groundwater Flow and groundwater-surface interaction; (6) Innovative numerical methods. The major contributions of these papers are summarized in this editorial
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Non-Darcian Flow toward a larger-diameter partially penetrating well in a confined aquifer
Environmental Earth Sciences, 2014Co-Authors: Zhang Wen, Kai Liu, Hongbin ZhanAbstract:In this study, non-Darcian Flow to a larger-diameter partially penetrating well in a confined aquifer was investigated. The Flow in the horizontal direction was assumed to be non-Darcian and described by the Izbash equation, and the Flow in the vertical direction was assumed to be Darcian. A linearization procedure was used to approximate the nonlinear governing equation. The Laplace transform associated with the finite cosine Fourier transform was used to solve such non-Darcian Flow model. Both the drawdowns inside the well and in the aquifer were analyzed under different conditions. The results indicated that the drawdowns inside the well were generally the same at early times under different conditions, and the features of the drawdowns inside the well at late times were similar to those of the drawdowns in the aquifer. The drawdown in the aquifer for the non-Darcian Flow case was larger at early times and smaller at late times than their counterparts of Darcian Flow case. The drawdowns for a partially penetrating well were the same as those of a fully penetrating well at early times, and were larger than those for a fully penetrating well at late times. A longer well screen resulted in a smaller drawdown in the aquifer at late times. A larger power index n in the Izbash equation resulted in a larger drawdown in the aquifer at early times and led to a smaller drawdown in the aquifer at late times. A larger well radius led to a smaller drawdown at early times, but it had little impact on the drawdown at late times. The wellbore storage effect disappears earlier when n is larger.
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experimental study of solute transport under non Darcian Flow in a single fracture
Journal of Hydrology, 2011Co-Authors: Jiazhong Qian, Hongbin Zhan, Zhou Chen, Hao YeAbstract:Summary We have experimentally studied solute transport in a single fracture (SF) under non-Darcian Flow condition which was found to closely follow the Forchheimer equation at Reynolds numbers around 12.2–86.0 when fracture apertures were between 4 mm and 9 mm. The measured breakthrough curves (BTCs) under the non-Darcian Flow condition had some features that are difficult to explain using the Fickian type advection–dispersion equation (ADE). All the measured BTCs showed long tails, which might be caused by mass transfer between the boundary layer near the fracture wall and the mobile domain near the plane of symmetry, as supported by the boundary layer dispersion theories of Koch and Brady, 1985 , Koch and Brady, 1987 . A mobile–immobile (MIM) model was used to simulate the measured BTCs. To show that the MIM model was doing a better job than the ADE model in describing the observed BTCs, we conducted statistical analysis on the goodness of fitting with these two models. The results showed that the correlation coefficients for the MIM model were greater than those for the ADE model and were close to unity, indicating a nearly perfect fit with the MIM. The mass transfer rate between the mobile domain and the boundary layer increased when the mobile water fraction became larger. The best fit dispersivity values using the MIM model varied between 1.05 mm and 9.29 mm whereas their counterparts using the ADE model varied between 245 mm and 462 mm for the experimental condition of this study. Several issues such as the possible bimodal concentration distribution and the scale-dependent transport in a SF were discussed and would be investigated in the future.
Zhang Wen - One of the best experts on this subject based on the ideXlab platform.
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combined role of leaky and non Darcian effects on the Flow to a pumping well with a non uniform flux well face boundary
Journal of Hydrology, 2020Co-Authors: Qi Zhu, Zhang WenAbstract:Abstract In this study, a non-Darcian Flow model was developed for a constant-rate test of a partially penetrating well with a non-uniform flux boundary in a leaky confined aquifer. The Izbash equation was applied to describe non-Darcian Flow in the radial direction. Both analytical and numerical methods were employed to solve this model. It was found that the analytical solution with linearization was adequate only when non-Darcian effects were relatively small. With the finite difference method, the radial and vertical fluxes along the well screen were analyzed under four different cases involving leaky and non-Darcian effects. The leaky and non-Darcian effects on the drawdowns with non-uniform flux (NUF) boundary were compared with those with uniform flux (UF) boundary. The results indicate that both leaky and non-Darcian effects can reduce the fluxes along the well screen, while non-Darcian effects can diminish the leakage-induced differences of flux and drawdown between the two well screen ends. Non-Darcian effects can reduce the differences between UF and NUF drawdowns at any elevation with the greatest reduction difference at the elevation of the top end of the screen. The UF solution can replace the NUF solution when the distance is far from the well, as this distance is smallest at the elevation of the screen midpoint and can be distinctly reduced by non-Darcian effects. In general, the results are most sensitive to the power index n , moderately sensitive to the other aquifer parameters and least sensitive to the parameters of the aquitard.
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Editorial of Special Issue “Advances in Groundwater Flow and Solute Transport: Pushing the Hidden Boundary”
MDPI AG, 2019Co-Authors: Hongbin Zhan, Quanrong Wang, Zhang WenAbstract:The theme of this special issue is to explore the new territories beyond conventional subsurface Flow and transport theories. We have selected 12 articles in this special issue and these articles cover a wide range of problems including (1) Non-Fickian chemical transport in various environments; (2) Non-Darcian Flow; (3) Flow and transport in low-permeability media; (4) Vadose zone process; (5) Regional scale groundwater Flow and groundwater-surface interaction; (6) Innovative numerical methods. The major contributions of these papers are summarized in this editorial
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non Darcian Flow to a partially penetrating pumping well in a leaky aquifer considering the aquitard aquifer interface Flow
Journal of Hydrologic Engineering, 2016Co-Authors: Zhang Wen, Qinggao FengAbstract:AbstractIn this study, non-Darcian Flow to a partially penetrating pumping well in a leaky aquifer was investigated. The aquifer system is composed of a main aquifer with an aquitard bounded on the top of the aquifer. The storage of the aquitard was considered in this study, which is the main contribution of this study. The horizontal Flow in the main aquifer is assumed to be non-Darcian, while both the vertical Flows in the main aquifer and the aquitard were assumed to be Darcian due to the relative low velocities. The non-Darcian Flow was described by the Izbash equation. A linearization procedure associated with Laplace transform and separate variable method were used to solve the non-Darcian Flow model. Semianalytical solutions (Laplace-domain solutions) were obtained then inverted to time domain by using the Stehfest method. The results indicated that the power index n in the Izbash equation results in a smaller drawdown at late times, the Flow approaches quasi steady state earlier, and the leakage h...
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non Darcian Flow to a partially penetrating well in a confined aquifer with a finite thickness skin
Hydrogeology Journal, 2016Co-Authors: Qinggao Feng, Zhang WenAbstract:Non-Darcian Flow to a partially penetrating well in a confined aquifer with a finite-thickness skin was investigated. The Izbash equation is used to describe the non-Darcian Flow in the horizontal direction, and the vertical Flow is described as Darcian. The solution for the newly developed non-Darcian Flow model can be obtained by applying the linearization procedure in conjunction with the Laplace transform and the finite Fourier cosine transform. The Flow model combines the effects of the non-Darcian Flow, partial penetration of the well, and the finite thickness of the well skin. The results show that the depression cone spread is larger for the Darcian Flow than for the non-Darcian Flow. The drawdowns within the skin zone for a fully penetrating well are smaller than those for the partially penetrating well. The skin type and skin thickness have great impact on the drawdown in the skin zone, while they have little influence on drawdown in the formation zone. The sensitivity analysis indicates that the drawdown in the formation zone is sensitive to the power index (n), the length of well screen (w), the apparent radial hydraulic conductivity of the formation zone (Kr2), and the specific storage of the formation zone (Ss2) at early times, and it is very sensitive to the parameters n, w and Kr2 at late times, especially to n, while it is not sensitive to the skin thickness (rs).
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Non-Darcian Flow toward a larger-diameter partially penetrating well in a confined aquifer
Environmental Earth Sciences, 2014Co-Authors: Zhang Wen, Kai Liu, Hongbin ZhanAbstract:In this study, non-Darcian Flow to a larger-diameter partially penetrating well in a confined aquifer was investigated. The Flow in the horizontal direction was assumed to be non-Darcian and described by the Izbash equation, and the Flow in the vertical direction was assumed to be Darcian. A linearization procedure was used to approximate the nonlinear governing equation. The Laplace transform associated with the finite cosine Fourier transform was used to solve such non-Darcian Flow model. Both the drawdowns inside the well and in the aquifer were analyzed under different conditions. The results indicated that the drawdowns inside the well were generally the same at early times under different conditions, and the features of the drawdowns inside the well at late times were similar to those of the drawdowns in the aquifer. The drawdown in the aquifer for the non-Darcian Flow case was larger at early times and smaller at late times than their counterparts of Darcian Flow case. The drawdowns for a partially penetrating well were the same as those of a fully penetrating well at early times, and were larger than those for a fully penetrating well at late times. A longer well screen resulted in a smaller drawdown in the aquifer at late times. A larger power index n in the Izbash equation resulted in a larger drawdown in the aquifer at early times and led to a smaller drawdown in the aquifer at late times. A larger well radius led to a smaller drawdown at early times, but it had little impact on the drawdown at late times. The wellbore storage effect disappears earlier when n is larger.
Giovanni Radilla - One of the best experts on this subject based on the ideXlab platform.
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non Darcian Flow of shear thinning fluids through packed beads experiments and predictions using forchheimer s law and ergun s equation
Advances in Water Resources, 2017Co-Authors: Antonio Rodriguez De Castro, Giovanni RadillaAbstract:Abstract The Flow of shear-thinning fluids through unconsolidated porous media is present in a number of important industrial applications such as soil depollution, Enhanced Oil Recovery or filtration of polymeric liquids. Therefore, predicting the pressure drop–Flow rate relationship in model porous media has been the scope of major research efforts during the last decades. Although the Flow of Newtonian fluids through packs of spherical particles is well understood in most cases, much less is known regarding the Flow of shear-thinning fluids as high molecular weight polymer aqueous solutions. In particular, the experimental data for the non-Darcian Flow of shear-thinning fluids are scarce and so are the current approaches for their prediction. Given the relevance of non-Darcian shear-thinning Flow, the scope of this work is to perform an experimental study to systematically evaluate the effects of fluid shear rheology on the Flow rate–pressure drop relationships for the non-Darcian Flow through different packs of glass spheres. To do so, xanthan gum aqueous solutions with different polymer concentrations are injected through four packs of glass spheres with uniform size under Darcian and inertial Flow regimes. A total of 1560 experimental data are then compared with predictions coming from different methods based on the extension of widely used Ergun's equation and Forchheimer's law to the case of shear thinning fluids, determining the accuracy of these predictions. The use of a proper definition for Reynolds number and a realistic model to represent the rheology of the injected fluids results in the porous media are shown to be key aspects to successfully predict pressure drop–Flow rate relationships for the inertial shear-thinning Flow in packed beads.
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Non-Darcian Flow of shear-thinning fluids through packed beads: Experiments and predictions using Forchheimer’s law and Ergun’s equation
Advances in Water Resources, 2017Co-Authors: Antonio Rodriguez De Castro, Giovanni RadillaAbstract:The Flow of shear-thinning fluids through unconsolidated porous media is present in a number of impor- tant industrial applications such as soil depollution, Enhanced Oil Recovery or filtration of polymeric liq- uids. Therefore, predicting the pressure drop–Flow rate relationship in model porous media has been the scope of major research efforts during the last decades. Although the Flow of Newtonian fluids through packs of spherical particles is well understood in most cases, much less is known regarding the Flow of shear-thinning fluids as high molecular weight polymer aqueous solutions. In particular, the experimen- tal data for the non-Darcian Flow of shear-thinning fluids are scarce and so are the current approaches for their prediction. Given the relevance of non-Darcian shear-thinning Flow, the scope of this work is to perform an experimental study to systematically evaluate the effects of fluid shear rheology on the Flow rate–pressure drop relationships for the non-Darcian Flow through different packs of glass spheres. To do so, xanthan gum aqueous solutions with different polymer concentrations are injected through four packs of glass spheres with uniform size under Darcian and inertial Flow regimes. A total of 1560 experimen- tal data are then compared with predictions coming from different methods based on the extension of widely used Ergun’s equation and Forchheimer’s law to the case of shear thinning fluids, determining the accuracy of these predictions. The use of a proper definition for Reynolds number and a realistic model to represent the rheology of the injected fluids results in the porous media are shown to be key aspects to successfully predict pressure drop–Flow rate relationships for the inertial shear-thinning Flow in packed beads.
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non Darcian Flow experiments of shear thinning fluids through rough walled rock fractures
Water Resources Research, 2016Co-Authors: Antonio Rodriguez De Castro, Giovanni RadillaAbstract:Understanding non-Darcian Flow of shear-thinning fluids through rough-walled rock fractures is of vital importance in a number of industrial applications such as hydrogeology or petroleum engineering. Different laws are available to express the deviations from linear Darcy law due to inertial pressure losses. In particular, Darcy's law is often extended through addition of quadratic and cubic terms weighted by two inertial coefficients depending on the strength of the inertia regime. The relations between the effective shear viscosity of the fluid and the apparent viscosity in porous media when inertial deviations are negligible were extensively studied in the past. However, only recent numerical works have investigated the superposition of both inertial and shear-thinning effects, finding that the same inertial coefficients obtained for non-Darcian Newtonian Flow apply in the case of shear-thinning fluids. The objective of this work is to experimentally validate these results, extending their applicability to the case of rough-walled rock fractures. To do so, Flow experiments with aqueous polymer solutions have been conducted using replicas of natural fractures, and the effects of polymer concentration, which determine the shear rheology of the injected fluid, have been evaluated. Our findings show that the experimental pressure loss-Flow rate data for inertial Flow of shear-thinning fluids can be successfully predicted from the empirical parameters obtained during non-Darcian Newtonian Flow and Darcian shear-thinning Flow in a given porous medium. This article is protected by copyright. All rights reserved.
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Non-Darcian Flow experiments of shear-thinning fluids through rough-walled rock fractures
Water Resources Research, 2016Co-Authors: Antonio Rodriguez De Castro, Giovanni RadillaAbstract:Understanding non-Darcian Flow of shear-thinning fluids through rough-walled rock fractures is of vital importance in a number of industrial applications such as hydrogeology or petroleum engineering. Different laws are available to express the deviations from linear Darcy law due to inertial pressure losses. In particular, Darcy’s law is often extended through addition of quadratic and cubic terms weighted by two inertial coefficients depending on the strength of the inertia regime. The relations between the effective shear viscosity of the fluid and the apparent viscosity in porous media when inertial deviations are negligible were extensively studied in the past. However, only recent numerical works have investigated the superposition of both inertial and shear-thinning effects, finding that the same inertial coefficients obtained for non-Darcian Newtonian Flow applied in the case of shear-thinning fluids. The objective of this work is to experimentally validate these results, extending their applicability to the case of rough-walled rock fractures. To do so, Flow experiments with aqueous polymer solutions have been conducted using replicas of natural fractures, and the effects of polymer concentration, which determine the shear rheology of the injected fluid, have been evaluated. Our findings show that the experimental pressure loss-Flow rate data for inertial Flow of shear-thinning fluids can be successfully predicted from the empirical parameters obtained during non-Darcian Newtonian Flow and Darcian shear-thinning Flow in a given porous medium.
Jens Birkholzer - One of the best experts on this subject based on the ideXlab platform.
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on the relationship between water flux and hydraulic gradient for unsaturated and saturated clay
Journal of Hydrology, 2012Co-Authors: Jens BirkholzerAbstract:Summary Experimental results indicate that the traditional form of Darcy’s law is not adequate for describing water Flow processes in clay media because the observed relationship between water flux and hydraulic gradient can be highly non-linear. To capture this non-Darcian Flow behavior, we propose a new relationship between water flux and hydraulic gradient by generalizing the currently existing relationships. The new relationship is shown to be consistent with experimental observations for both saturated and unsaturated conditions. In this paper, we also develop an empirical relationship between permeability and threshold hydraulic gradient, an important measure of non-Darcian behavior. The latter relationship is practically useful because it can reduce the number of parameters whose values need to be determined from experiment data in order to model non-Darcian behavior. How to incorporate the impacts of temperature and electrolyte concentrations into the proposed relationships needs further research.
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unsaturated properties for non Darcian water Flow in clay
Journal of Hydrology, 2012Co-Authors: Huihai Liu, Jens BirkholzerAbstract:Summary Clay rock formations, and compacted clay (e.g., bentonite) used as backfill within disposal drifts, have been considered as natural and engineered barriers, respectively, for isolating high-level nuclear wastes in mined geologic repositories. Accurately modeling unsaturated Flow in those clay materials is important for assessing the performance of a geological repository. While the non-Darcian behavior of water Flow in clay materials has been demonstrated in the literature, a systematic study of modeling unsaturated non-Darcian Flow is still lacking. Based on a hypothesis that pore water in clay becomes non-Newtonian as a result of water–clay interaction, we propose new constitutive relationships for unsaturated Flow, including a relationship between water flux and hydraulic gradient and those among capillary pressure, water saturation, and hydraulic conductivity. An evaluation based on a set of laboratory experimental observations supports the usefulness of the proposed relationships. More experimental studies are desirable for further confirming the non-Newtonian water Flow behavior in clay materials and evaluating the proposed relationships.
Huihai Liu - One of the best experts on this subject based on the ideXlab platform.
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Non-Darcian Flow in low-permeability media: key issues related to geological disposal of high-level nuclear waste in shale formations
Hydrogeology Journal, 2014Co-Authors: Huihai LiuAbstract:在粘土或其他低渗透性介质中,水流呈非达西状态,特征就是水通量和水力梯度之间为非线性关系。本研究致力于探讨高放核废料在粘土/页岩地层中地质处理方面的一些关键问题。研究结果显示,由于非达西水流特性,以至于溶质运移受控于扩散而不是对流,因此,巷道附近损坏带(通常被认为是资源丰富区潜在的优先对流通道)中的水流速度特别低。这个发现也与常常观测到的页岩地层中存在持续异常压力相一致。在相对渗透性为模拟非饱和水流过程的关键参数时,不考虑非达西水流特性,传统测量方法确定相对渗透性值就会出现很大的误差。核废料产生热量、页岩地层通常呈各向异性,因此,地质资源丰富区受附近场的温度演化支配,在考虑这些因素的基础上,展示了处理温度对非达西水流影响的一个方法及计算各向异性介质中非达西水通量的一个构想. In clay or other low-permeability media, water Flow becomes non-Darcian and characterized by the non-linear relationship between water flux and hydraulic gradient. This work is devoted to addressing a number of key issues related to geological disposal of high-level nuclear waste in clay/shale formations. It is demonstrated that water Flow velocity in the damaged zone (often considered as a potential preferential advection paths in a repository) surrounding the tunnel is extremely small, as a result of non-Darcian Flow behavior, such that solute transport is dominated by diffusion, rather than advection. The finding is also consistent with the often-observed existence of persistent abnormal pressures in shale formations. While relative permeability is the key parameter for modeling the unsaturated Flow process, without incorporating non-Darcian Flow behavior, significant errors can occur in the determination of relative permeability values from traditional measurement methods. An approach for dealing with temperature impact on non-Darcian Flow and a formulation to calculate non-Darcian water flux in an anisotropic medium are presented, taking into consideration that a geological repository is subject to temperature evolution in the near field as a result of heat generated by nuclear waste, and that shale formations are generally anisotropic. En las arcillas u otros medios de baja permeabilidad, el flujo de agua se convierte en no Darciano y está caracterizado por una relación no linear entre el flujo de agua y el gradiente hidráulico. Este trabajo se dedica a abordar una serie de cuestiones claves relacionadas a la disposición geológica de residuos nucleares de alta actividad en formaciones de arcillas/esquistos. Se demuestra que la velocidad del flujo de agua en la zona dañada (a menudo considerada como de posible advección por trayectorias preferenciales) que rodea un túnel es extremadamente pequeña, como resultado del comportamiento de un flujo no Darciano, tal que el transporte de soluto es dominado por la difusión, en lugar de la advección. Este hallazgo es también consistente con la frecuente observación de la existencia de presiones anormales persistente en las formaciones de esquisto. Aunque la permeabilidad relativa es el parámetro clave para la modelación del proceso del flujo no saturado, sin incorporar el comportamiento de flujo no Darciano, errores significativos pueden ocurrir en la determinación de los valores de permeabilidad relativa a partir de los métodos de medición tradicional. Se presenta un enfoque para tratar el impacto de la temperatura sobre el flujo no Darciano y una formulación para calcular el flujo no Darciano en una medio anisotrópico, tomando en consideración que un repositorio geológico está sujeto a la evolución de la temperatura en un campo cercano como un resultado del calor generado por el residuo nuclear y que las formaciones de esquistos son generalmente anisotrópicas. Em argilas e noutros meios de baixa permeabilidade, o escoamento subterrâneo torna-se não-Darciano, sendo caracterizado por uma relação não-linear entre o fluxo de água e o gradiente hidráulico. Este trabalho é dedicado à abordagem de questões chave relacionadas com a deposição de resíduos radioativos de elevada atividade em formações geológicas argilosas e xistentas. Demonstra-se que a velocidade da água subterrânea na zona afetada (frequentemente considerada como o caminho preferencial de reposição por advecção) envolvendo o túnel é extremamente baixa, em resultado do comportamento não-Darciano do escoamento, a tal ponto que o transporte de solutos passa a ser dominado pela difusão em vez da advecção. A descoberta é também consistente com a frequente observação da existência de pressões anormais em formações xistentas. Enquanto a permeabilidade relativa é o parâmetro chave para a modelação de escoamentos em meios porosos não-saturados, sem a incorporação de efeitos não-Darcianos no escoamento podem ocorrer erros significativos na determinação dos valores da permeabilidade relativa pelos métodos tradicionais de medição. Apresenta-se uma abordagem para o cálculo do impacte da temperatura em escoamentos com efeitos não-Darcianos e uma formulação para o cálculo do fluxo não-Darciano em meios anisotrópicos, tendo em conta que o repositório geológico é sujeito a evoluções da temperatura no campo próximo em resultado do calor gerado pelos resíduos nucleares, e que as formações xistentas são geralmente anisotrópicas. Dans les argiles ou autres milieux de faible conductivité hydraulique, les écoulements de l’eau deviennent non darciens et sont caractérisés par la relation non linéaire entre l’écoulement et le gradient hydraulique. Ce travail est consacré à régler un certain nombre de questions clefs liées au stockage géologique de déchets nucléaires de haute activité dans des formations argileuses et de schistes. Il est démontré que la vitesse d’écoulement de l’eau dans la zone endommagée (souvent considérée comme une zone potentielle des cheminements préférentiels de type convectif dans un dépôt) entourant un tunnel est extrêmement petite, en raison du comportement non darcien des écoulements, de telle sorte que le transport de soluté est dominé par la diffusion plutôt que par la convection. Ce résultat est également compatible avec l’existence souvent observée de pressions anormales persistantes dans les formations de schistes. Alors que la conductivité hydraulique relative est le paramètre clé pour la modélisation des écoulements en zone non saturée, la non intégration du comportement d’écoulement de type non darcien, peut conduire à des erreurs significatives dans la détermination des valeurs de conductivité hydraulique relative à partir des méthodes traditionnelles de mesures. Une approche pour faire face à l’impact de la température sur les écoulements non darciens et une formulation pour calculer les écoulements non darciens dans un milieu anisotrope sont présentées, en considérant que la zone géologique de dépôt est soumise à une évolution de la température dans son environnement proche, due à la chaleur résultante générée par les déchets nucléaires, et que les formations de schistes sont généralement anisotropes.
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non Darcian Flow in low permeability media key issues related to geological disposal of high level nuclear waste in shale formations
Hydrogeology Journal, 2014Co-Authors: Huihai LiuAbstract:In clay or other low-permeability media, water Flow becomes non-Darcian and characterized by the non-linear relationship between water flux and hydraulic gradient. This work is devoted to addressing a number of key issues related to geological disposal of high-level nuclear waste in clay/shale formations. It is demonstrated that water Flow velocity in the damaged zone (often considered as a potential preferential advection paths in a repository) surrounding the tunnel is extremely small, as a result of non-Darcian Flow behavior, such that solute transport is dominated by diffusion, rather than advection. The finding is also consistent with the often-observed existence of persistent abnormal pressures in shale formations. While relative permeability is the key parameter for modeling the unsaturated Flow process, without incorporating non-Darcian Flow behavior, significant errors can occur in the determination of relative permeability values from traditional measurement methods. An approach for dealing with temperature impact on non-Darcian Flow and a formulation to calculate non-Darcian water flux in an anisotropic medium are presented, taking into consideration that a geological repository is subject to temperature evolution in the near field as a result of heat generated by nuclear waste, and that shale formations are generally anisotropic.
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unsaturated properties for non Darcian water Flow in clay
Journal of Hydrology, 2012Co-Authors: Huihai Liu, Jens BirkholzerAbstract:Summary Clay rock formations, and compacted clay (e.g., bentonite) used as backfill within disposal drifts, have been considered as natural and engineered barriers, respectively, for isolating high-level nuclear wastes in mined geologic repositories. Accurately modeling unsaturated Flow in those clay materials is important for assessing the performance of a geological repository. While the non-Darcian behavior of water Flow in clay materials has been demonstrated in the literature, a systematic study of modeling unsaturated non-Darcian Flow is still lacking. Based on a hypothesis that pore water in clay becomes non-Newtonian as a result of water–clay interaction, we propose new constitutive relationships for unsaturated Flow, including a relationship between water flux and hydraulic gradient and those among capillary pressure, water saturation, and hydraulic conductivity. An evaluation based on a set of laboratory experimental observations supports the usefulness of the proposed relationships. More experimental studies are desirable for further confirming the non-Newtonian water Flow behavior in clay materials and evaluating the proposed relationships.
