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1.
Groundwater flow and solute transport through fractured rock is highly responsive to the hydraulic anisotropy and heterogeneity that are specific to every major fracture. A major fracture is modeled as the combination of some primal master fractures and several splay fractures that branch out from primal master fractures: step structures (or jog parts). Step structures are commonly observed along a major fracture on various scales. Master fractures were formed and developed by shear movement while some splay fractures were formed by extension normal to their wall. This difference in fracturing process may lead to a permeability difference between master fractures and splay fractures which seems to be one of the major factors controlling flow and solute transport through the fracture networks due to its hydraulic anisotropic and heterogeneous features. This study is composed of two major components: (1) identification and characterization of a step structure from borehole data; (2) evaluation of effect of some idealized step structures on breakthrough curve by numerical simulations. The fracture data of four 1000-m boreholes were used to make clear fracture patterns in the Tono area of Japan. Some major fractures were identified using stereographic projection technique. On the basis of these results, several idealized models of a major fracture having a step was constructed for the numerical study. The obtained results from numerical simulations clearly imply that geometry of step structure plays an important role in flow and transport through the fracture networks.  相似文献   

2.
A test tunnel for the study of airfoil performances under air/water two-phase flow condition has been designed and constructed. This facility will serve for a better understanding of the flow phenomena and characteristics of hydraulic machinery under gas/ liquid two-phase flow operating conditions. At the test section of the tunnel, a two-dimensional isolated airfoil or a cascade of airfoils is installed in a two-phase inlet flow with a uniform velocity (up to 10 m/s) and void fraction (up to 12%) distribution. The details of the tunnel structure and the measuring systems are described and the basic characteristics of the constructed tunnel are also given. As an example of the test results, void fraction distribution around a test airfoil is shown.Dedicated to the 60th Birthday of Professor Klaus Gersten  相似文献   

3.
广西北山岩溶管道—裂隙—孔隙地下水流数值模拟初探   总被引：12，自引：1，他引：11  
本文从水动力学角度分析各种岩溶含水介质中的水流特征,将其归纳为储水介质、导水介质和控水介质,并根据折算渗透系数ＫＬ的概念和建立耦合达西流和百达西流于一体的岩溶管道－裂隙－孔隙三重介质地下水模型,对广西环江北山矿区岩溶含水系统进行了初步探讨。北山实例的模拟结果表明,三重介质模型较全面地刻画了岩溶水动态的特征,反映了相对均匀裂隙流与控制性管道流并存、线性流与非线性流相互转变的运动特点,不仅理论上比较合  相似文献   

4.
The effect of homogeneous sand lenses on the groundwater flow in an otherwise homogeneous clayey deposit is examined by performing Monte Carlo simulations using a finite element flow model. In the simulations, the locations of the sand lenses are assumed to be mutually independent. The paper examines the effect on the flow field in a clayey deposit of (a) different percentages of sand lenses, (b) different hydraulic conductivities of the sand lenses, (c) different average sand lens sizes, (d) non-uniformity of the sizes of the sand lenses, and (e) localization of the sand lenses. The effect of these non-uniform flow fields on contaminant migration is then examined using a finite element contaminant transport model. For the range of cases considered it is shown that: the volume of sand lenses present has a greater influence than the shape, size, location and hydraulic conductivity of the sand lenses; simplified calculations performed using the geometric and harmonic means of hydraulic conductivity bracket the behaviour evident from more complex analyses; and the maximum impact on an aquifer separated from a waste disposal facility by a deposit containing sand lenses can be modelled to sufficient accuracy, using quite simple flow and contaminant transport models.  相似文献   

5.
Severe land subsidence due to groundwater extraction may occur in multiaquifer systems where highly compressible aquitards are present. The highly compressible nature of the aquitards leads to nonlinear consolidation where the groundwater flow parameters are stress-dependent. The case is further complicated by the heterogeneity of the hydrogeologic and geotechnical properties of the aquitards. The effect of realistic vertical heterogeneity of hydrogeologic and geotechnical parameters on the consolidation of highly compressible aquitards is investigated by means of one-dimensional Monte Carlo numerical simulations where the lower boundary represents the effect of an instant drop in hydraulic head due to groundwater pumping. Two thousand realizations are generated for each of the following parameters: hydraulic conductivity (K), compression index (C c), void ratio (e) and m (an empirical parameter relating hydraulic conductivity and void ratio). The correlation structure, the mean and the variance for each parameter were obtained from a literature review about field studies in the lacustrine sediments of Mexico City. The results indicate that among the parameters considered, random K has the largest effect on the ensemble average behavior of the system when compared to a nonlinear consolidation model with deterministic initial parameters. The deterministic solution underestimates the ensemble average of total settlement when initial K is random. In addition, random K leads to the largest variance (and therefore largest uncertainty) of total settlement, groundwater flux and time to reach steady-state conditions.  相似文献   

6.
This article represents the second of two articles, which review the main results of the international radioecological projects: Chernobyl Pilot Site Project (1999–2003) and Experimental Platform in Chernobyl (2004–2008). These projects studied radionuclide migration from the near-surface radioactive waste trench at the Red Forest waste dump in the Chernobyl zone, which contained nuclear fuel particles. This article presents results from the comprehensive hydrogeological site characterization program including the following issues: geological structure of the study site, hydraulic properties of the deposits, tracer tests in the aquifer, results of groundwater monitoring and unsaturated zone regime studies, as well as data on the 90Sr distribution in the unsaturated zone and aquifer, and analyses of 90Sr sorption behavior. The derived parameters were used to develop and calibrate 1D (flow tube) and 2D (cross-section) models describing the migration of 90Sr from the studied waste trench to the unsaturated zone and aquifer over a 16-a period (1986–2002). The models involved the following sub-models: (1) the geostatistical (structural) model for radioactivity distribution in the trench (using GSLIB); and (2) the radionuclide source term model (STERM1D) describing dissolution of fuel particles and a 1D of radionuclide redistribution in the trench body and unsaturated zone. The MODFLOW – MT3D codes were used to model the 2D 90Sr transport in the aquifer cross-section. Calibration of the 1D model with respect to Kds and dispersivities allowed quite accurate reproduction of 90Sr migration behavior for the early period (1995–1998). The less perfect fit between the 1D and 2D modeling results and monitoring data for the later period (1999–2002) suggests the need to improve the conceptual radionuclide migration model (i.e. to account for transient hydraulic and geochemical regimes of the waste site).  相似文献   

7.
A modeling study was carried out to evaluate the influence of aquifer heterogeneity, as represented by geologic layering, on heat transport and storage in an aquifer thermal energy storage (ATES) system in Agassiz, British Columbia, Canada. Two 3D heat transport models were developed and calibrated using the flow and heat transport code FEFLOW including: a “non-layered” model domain with homogeneous hydraulic and thermal properties; and, a “layered” model domain with variable hydraulic and thermal properties assigned to discrete geological units to represent aquifer heterogeneity. The base model (non-layered) shows limited sensitivity for the ranges of all thermal and hydraulic properties expected at the site; the model is most sensitive to vertical anisotropy and hydraulic gradient. Simulated and observed temperatures within the wells reflect a combination of screen placement and layering, with inconsistencies largely explained by the lateral continuity of high permeability layers represented in the model. Simulation of heat injection, storage and recovery show preferential transport along high permeability layers, resulting in longitudinal plume distortion, and overall higher short-term storage efficiencies.  相似文献   

8.
Sediment accumulation downstream of hydraulic jumps can occur in many settings but the architectures of such deposits are poorly documented. Here, three flume runs were used to examine the influence of sediment grain size and transport rate on the characteristics of hydraulic‐jump unit bars. In one of these runs six hydraulic‐jump unit bars formed a hydraulic‐jump bar complex. In another, the same sediment was supplied more quickly and only two unit bars formed. In the third run with the same sediment supply rate, but different grain size, only one large unit bar formed. All unit bars developed in a similar way but their size and internal architecture differed; they all resulted from a reduction in sediment transport capacity at the transition from supercritical flow to subcritical flow in the hydraulic jump. After initial onset of sedimentation and unit bar formation, generation of subsequent unit bars may be: (i) related to small changes in sediment flux; and (ii) independent of changes in the hydraulic jump. Continued sedimentation caused changes from oscillating to weak hydraulic jumps and hydraulic‐jump unit bars formed in both circumstances. The flow of water and suspended sediment becomes shallower over the lee of the bar complex. This leads to flow acceleration and a return to supercritical flow conditions. In turn, a chain of such features can form and generate a chute and pool bed morphology. There is an inherent upper size limit to a hydraulic‐jump bar complex due to the changing flow conditions over the growing deposit as the water above it becomes shallower. There is also an amplitude minimum for the development of foresets and subsequent unit bar growth. Hydraulic‐jump unit bars have architectures that should be recognizable in the rock record and because their size is constrained by the flow conditions, their identification should be useful for interpreting palaeoenvironment.  相似文献   

9.
多孔介质渗透系数的空间尺度效应研究进展   总被引：6，自引：1，他引：5  
多孔介质渗透系数的空间尺度问题是一个与地下流体运动和溶质运移的数值模拟密切相关的应用性课题,广泛的应用需求和新的计算方法使其成为近年的热门课题之一。它涉及到相互联系的两个方面：①非均质介质场渗透系数空间尺度行为的分析与模拟;②将局部测量尺度下的试验参数转化为数值模拟网格尺度下的参数输入值的升尺度（ｕｐｓｃａｌｉｎｇ）方法和计算模型。首先介绍了该课题在概念上的拓展及其物理含义,进而以方法为主线,对这一领域具有代表性的研究成果进行了分类和评述,讨论了该课题的研究对地下水流和溶质运移的模拟分析乃至整个多孔介质流体运动研究的意义。  相似文献   

10.
Combining groundwater flow models with solute transport models represents a common challenge in groundwater resources assessments and contaminant transport modeling. Groundwater flow models are usually constructed at somewhat larger scales (involving a coarser discretization) to include natural boundary conditions. They are commonly calibrated using observed groundwater levels and flows (if available). The groundwater solute transport models may be constructed at a smaller scale with finer discretization than the flow models in order to accurately delineate the solute source and the modeled target, to capture any heterogeneity that may affect contaminant migration, and to minimize numerical dispersion while still maintaining a reasonable computing time. The solution that is explored here is based on defining a finer grid subdomain within a larger coarser domain. The local-grid refinement (LGR) implemented in the Modular 3D finite-difference ground-water flow model (MODFLOW) code has such a provision to simulate groundwater flow in two nested grids: a higher-resolution sub-grid within a coarse grid. Under the premise that the interface between both models was well defined, a comprehensive sensitivity and uncertainty analysis was performed whereby the effect of a parameter perturbation in a coarser-grid model on transport predictions using a higher-resolution grid was quantified. This approach was tested for a groundwater flow and solute transport analysis in support of a safety evaluation of the future Belgian near-surface radioactive waste disposal facility. Our reference coarse-grid groundwater flow model was coupled with a smaller fine sub-grid model in two different ways. While the reference flow model was calibrated using observed groundwater levels at a scale commensurate with that of the coarse-grid model, the fine sub-grid model was used to run a solute transport simulation quantifying concentrations in a hypothetical well nearby the disposal facility. When LGR coupling was compared to a one-way coupling, LGR was found to provide a smoother flow solution resulting in a more CPU-efficient transport solution. Parameter sensitivities performed with the groundwater flow model resulted in sensitivities at the head observation locations. These sensitivities identified the recharge as the most sensitive parameter, with the hydraulic conductivity of the upper aquifer as the second most sensitive parameter in regard to calculated groundwater heads. Based on one-percent sensitivity maps, the spatial distribution of the observations with the highest sensitivities is slightly different for the upper aquifer hydraulic conductivity than for recharge. Sensitivity analyses were further performed to assess the prediction scaled sensitivities for hypothetical contaminant concentrations using the combined groundwater flow and solute transport models. Including all pertinent parameters into the sensitivity analysis identified the hydraulic conductivity of the upper aquifer as the most sensitive parameter with regard to the prediction of contaminant concentrations.  相似文献   

11.
Modern geostatistical techniques allow the generation of high-resolution heterogeneous models of hydraulic conductivity containing millions to billions of cells. Selective upscaling is a numerical approach for the change of scale of fine-scale hydraulic conductivity models into coarser scale models that are suitable for numerical simulations of groundwater flow and mass transport. Selective upscaling uses an elastic gridding technique to selectively determine the geometry of the coarse grid by an iterative procedure. The geometry of the coarse grid is built so that the variances of flow velocities within the coarse blocks are minimum. Selective upscaling is able to handle complex geological formations and flow patterns, and provides full hydraulic conductivity tensor for each block. Selective upscaling is applied to a cross-bedded formation in which the fine-scale hydraulic conductivities are full tensors with principal directions not parallel to the statistical anisotropy of their spatial distribution. Mass transport results from three coarse-scale models constructed by different upscaling techniques are compared to the fine-scale results for different flow conditions. Selective upscaling provides coarse grids in which mass transport simulation is in good agreement with the fine-scale simulations, and consistently superior to simulations on traditional regular (equal-sized) grids or elastic grids built without accounting for flow velocities.  相似文献   

12.
Krzaczek  M.  Nitka  M.  Kozicki  J.  Tejchman  J. 《Acta Geotechnica》2020,15(2):297-324

The paper deals with two-dimensional (2D) numerical modelling of hydro-fracking (hydraulic fracturing) in rocks at the meso-scale. A numerical model was developed to characterize the properties of fluid-driven fractures in rocks by combining the discrete element method (DEM) with computational fluid dynamics (CFD). The mechanical behaviour of the rock matrix was simulated with DEM and the behaviour of the fracturing fluid flow in newly developed and pre-existing fractures with CFD. The changes in the void geometry in the rock matrix were taken into account. The initial 2D hydro-fracking simulation tests were carried out for a rock segment under biaxial compression with one injection slot in order to validate the numerical model. The qualitative effect of several parameters on the propagation of a hydraulic fracture was studied: initial porosity of the rock matrix, dynamic viscosity of the fracking fluid, rock strength and pre-existing fracture. The characteristic features of a fractured rock mass due to a high-pressure injection of fluid were realistically modelled by the proposed coupled approach.

  相似文献   

13.
Karst systems show high spatial variability of hydraulic parameters over small distances and this makes their modeling a difficult task with several uncertainties. Interconnections of fractures have a major role on the transport of groundwater, but many of the stochastic methods in use do not have the capability to reproduce these complex structures. A methodology is presented for the quantification of tortuosity using the single normal equation simulation (SNESIM) algorithm and a groundwater flow model. A training image was produced based on the statistical parameters of fractures and then used in the simulation process. The SNESIM algorithm was used to generate 75 realizations of the four classes of fractures in a karst aquifer in Iran. The results from six dye tracing tests were used to assign hydraulic conductivity values to each class of fractures. In the next step, the MODFLOW-CFP and MODPATH codes were consecutively implemented to compute the groundwater flow paths. The 9,000 flow paths obtained from the MODPATH code were further analyzed to calculate the tortuosity factor. Finally, the hydraulic conductivity values calculated from the dye tracing experiments were refined using the actual flow paths of groundwater. The key outcomes of this research are: (1) a methodology for the quantification of tortuosity; (2) hydraulic conductivities, that are incorrectly estimated (biased low) with empirical equations that assume Darcian (laminar) flow with parallel rather than tortuous streamlines; and (3) an understanding of the scale-dependence and non-normal distributions of tortuosity.  相似文献   

14.
The Tongue Creek watershed lies on the south flank of Grand Mesa in western Colorado, USA and is a site with 1.5 km of topographic relief, heat flow of 100 mW/m2, thermal conductivity of 3.3 W m–1 °C–1, hydraulic conductivity of 10-8 m/s, a water table that closely follows surface topography, and groundwater temperatures 3–15°C above mean surface temperatures. These data suggest that convective heat transport by groundwater flow has modified the thermal regime of the site. Steady state three-dimensional numerical simulations of heat flow, groundwater flow, and convective transport were used to model these thermal and hydrological data. The simulations provided estimates for the scale of hydraulic conductivity and bedrock base flow discharge within the watershed. The numerical models show that (1) complex three-dimensional flow systems develop with a range of scales from tens of meters to tens of kilometers; (2) mapped springs are frequently found at locations where contours of hydraulic head indicate strong vertical flow at the water table, and; (3) the distribution of groundwater temperatures in water wells as a function of surface elevation is predicted by the model.  相似文献   

15.
 The coastal aquifer system of southern Oahu, Hawaii, USA, consists of highly permeable volcanic aquifers overlain by weathered volcanic rocks and interbedded marine and terrestrial sediments of both high and low permeability. The weathered volcanic rocks and sediments are collectively known as caprock, because they impede the free discharge of groundwater from the underlying volcanic aquifers. A cross-sectional groundwater flow and transport model was used to evaluate the hydrogeologic controls on the regional flow system in southwestern Oahu. Controls considered were: (a) overall caprock hydraulic conductivity; and (b) stratigraphic variations of hydraulic conductivity in the caprock. Within the caprock, variations in hydraulic conductivity, caused by stratigraphy or discontinuities of the stratigraphic units, are a major control on the direction of groundwater flow and the distribution of water levels and salinity. Results of cross-sectional modeling confirm the general groundwater flow pattern that would be expected in a layered coastal system. Groundwater flow is: (a) predominantly upward in the low-permeability sedimentary units; and (b) predominantly horizontal in the high-permeability sedimentary units. Received, October 1996 Revised, August 1997 Accepted, September 1997  相似文献   

16.
岩溶含水介质由管道、裂隙与孔隙３类空隙介质组成，它们对地下水流动具有不同的贡献。简述了当前岩溶水的几种主要定量评价方法，提出折算渗透系数尺概念，建立了岩溶三重空隙介质地下水流统一的控制方程，引出管道与裂隙在达西流与非达西流状态下的渗透系数与折算渗透系数的表达式，从而将达西流与非达西流耦合在一个模型中。本文提出岩溶三重介质地下水流的模拟方法，并给出理想模型的模拟结果。  相似文献   

17.
新吹填淤泥处于“稀泥汤”状态,工程特性极差,几乎无承载力,现有真空预压技术加固效果不理想,地基有效加固深度小,土体强度增长有限。为此,提出了“真空预压联合化学加固”的新思路。室内采用3种环保型化学加固剂设计了3种真空预压联合化学加固方案（VPCT1、VPCT2、VPCT3）和1种纯化学加固方案（CT）,与现行真空预压加固方案（VPT）进行了对比试验研究。研究结果表明：(1) 添加有效的化学加固剂后,新吹填淤泥在抽真空前较短的静置时间内就基本完成了自重沉积过程;(2) 化学加固剂选取得当能有效提高土体的加固效果;(3) 宏观上,VPCT3方案加固效果较均匀,加固后土体中黏粒含量明显降低、湿密度最大,孔隙比降低幅度明显,无侧限抗压强度也最大,为66.7 kPa（为VPT方案的3.5倍）;(4) 微观上,VPCT3方案加固后,土颗粒之间的孔隙总面积、孔隙平均周长、总孔隙数、孔隙比、孔隙率等最小,单元体之间有良好的定向度、排序性最好,连结方式以面-面为主导,相互之间接触紧密,团聚现象最明显。因此,相对于现行的真空预压技术而言,VPCT3方案土体加固效果非常明显,也较均匀,可以进一步开展现场试验研究,探讨其付诸于工程实践的可行性。  相似文献   

18.
为深入探究含水层中多孔介质的不规则形态和分布对于地下水流场及溶质运移的作用,根据沉积环境中已被发现的倾斜交叉分层地质单元结构,人为构造多孔介质双层交叉鱼骨结构,使其形成宏观各向异性水力传导特征,通过数值模拟研究该结构及其空间位置对于流场和溶质运移的影响。研究发现:宏观各向异性多孔介质引发了螺旋状流动,导致流线的拉伸和折叠,使得溶质羽发生不规则变形,显著提升了非反应性溶质的稀释程度;宏观各向异性结构和溶质羽在三维空间中的垂向相对位置对于溶质运移具有显著影响。  相似文献   

19.
This paper presents results from two flume runs of an ongoing series examining flow structure, sediment transport and deposition in hydraulic jumps. It concludes in the presentation of a model for the development of sedimentary architecture, considered characteristic of a hydraulic jump over a non-eroding bed. In Run 1, a hydraulic jump was formed in sediment-free water over the solid plane sloping flume floor. Ultrasonic Doppler velocity profilers recorded the flow structure within the hydraulic jump in fine detail. Run 2 had identical initial flow conditions and a near-steady addition of sand, which formed beds with two distinct characteristics: a laterally extensive, basal, wedge-shaped massive sand bed overlain by cross-laminated sand beds. Each cross-laminated bed recorded the initiation and growth of a single surface feature, here defined as a hydraulic-jump unit bar . A small massive sand mound formed on the flume floor and grew upstream and downstream without migrating to form a unit bar. In the upstream portion of the unit bar, sand finer than the bulk load formed a set of laminae dipping upstream. This set passed downstream through the small volume of massive sand into a foreset, which was initially relatively coarse-grained and became finer-grained downstream. This downstream-fining coincided with cessation of the growth of the upstream-dipping cross-set. At intervals, a new bed feature developed above and upstream of the preceding hydraulic-jump unit bar and grew in the same way, with the foreset climbing the older unit bar. The composite architecture of the superimposed unit bars formed a fanning, climbing coset above the massive wedge, defined as one unit: a hydraulic-jump bar complex .  相似文献   

20.
The hydraulic conductivity represents an important indicator parameter in the generation and redistribution of excess pore pressure of sand–silt mixture soil deposits during earthquakes. This paper aims to determine the relationship between the undrained shear strength (liquefaction resistance) and the saturated hydraulic conductivity of the sand–silt mixtures and how much they are affected by the percentage of low plastic fines (finer than 0.074 mm) and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests carried out on samples reconstituted from Chlef river sand with 0, 10, 20, 30, 40, and 50 % non-plastic silt at an effective confining pressure of 100 kPa and two initial relative densities (D r = 20, 91 %) are presented and discussed. It was found that the undrained shear strength (liquefaction resistance) can be correlated to the fines content, intergranular void ratio and saturated hydraulic conductivity. The results obtained from this study reveal that the saturated hydraulic conductivity (k sat) of the sand mixed with 50 % low plastic fines can be, in average, four orders of magnitude smaller than that of the clean sand. The results show also that the global void ratio could not be used as a pertinent parameter to explain the undrained shear strength and saturated hydraulic conductivity response of the sand–silt mixtures.  相似文献   

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