ISSN:0022-1686    

DOI:10.1080/00221689809498589

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In solid rock aquifers low matrix permeability is often accompanied with fractures and faults of different scales. Therefore, numerical modeling of such coupled systems is very complex. Flow of groundwater and mass transport processes in fractured systems have to be modeled along discrete surfaces joined to the common matrix representation. This leads to high demands on the quality of finite element mesh generation. Another difficulty is the evaluation of field parameters needed in the design of realistic models to simulate natural systems. This paper presents a strategy to generate three dimensional finite element meshes, which allows the modeling of groundwater flow and contaminant transport in a coupled matrix fracture aquifer system. Software development and data evaluation for the discussed application example comes from the research project “Development and Application of Analytical Methods on Investigations of the Reliability of Disposals in Open Mines” sponsored by the German Ministry of Education and Research. The scope of this project is to determine the influence of a rising groundwater level in closed coal mines on the transport of contaminants from waste material deposits in cut coal seams.

ISSN:0022-1686    

DOI:10.1080/00221689809498590

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Statistical information on sedimentary structures determined from natural gravel deposits in north-eastern Switzerland is used to characterize transport phenomena of aquifers. These aquifers essentially consist of a background gravel matrix with embedded lenses of different hydraulic properties and internal structure. One of the embedded materials is highly conductive open framework gravel which leads to a bimodal probability density function of the hydraulic conductivity of the overall gravel material. Based on an analysis of this information three approaches to modeling macrodispersion are suggested. In the first one distinct unconditioned realizations of synthetic block shaped facies type aquifers are generated numerically such that they exhibit the same statistical properties with respect to facies geometry and hydraulic properties as the deposits themselves. Numerical experiments simulating saturated flow and transport were subsequently performed with the help of a three-dimensional finite element flow model and a corresponding random walk transport model. A total of 100 experiments allowed estimates of apparent, time dependent macrodispersivity values. In the second approach the statistical parameters characterizing the overall gravel deposit were directly applied to an analytical unimodal stochastic model of apparent macrodispersivity according to Dagan (1988). For the modeling of the bimodal nature of the hydraulic conductivity an analytical anisotropic stochastic model was developed based on the isotropic model of Rubin (1995). This third approach was again applied using the appropriate statistical parameters. Differences in the results of the three models are discussed. They can be attributed mainly to uncertainty in the input parameters, and to the complex sedimentary structure predominant in the natural gravel deposits which were investigated.

ISSN:0022-1686    

DOI:10.1080/00221689809498591

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

High Performance Computing (HPC) is a key enabling tool to interconnect the many, varied simulation capabilities required to advance the science of groundwater remediation. The US Army Engineer Waterways Experiment Station is engaged in research and development that will provide a seamless link to tools that combine diverse field data into accurate site characterizations, and perform computer simulations of remediation processes. However, the simulation models on which this capability is founded are still not adequate to simulate real, heterogeneous media that make up the natural groundwater environment. The inadequacy stems from the multi-scale structure of natural media that is masked by the continuum formulations upon which numerical models are based. The range of scales is simply too great to be spanned by any present, or foreseeable, HPC resource. To advance the science of multi-scale simulation, HPC may be viewed as an extension of the laboratory. By stretching present resources to perform scale-spanning simulations, stochastic models are created from data that could not be obtained previously from physical experiments. A detailed description of this process is presented for non-reactive, dispersive transport.

ISSN:0022-1686    

DOI:10.1080/00221689809498592

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The reliability of quantification (measurement and calculation) of the exchange rate between groundwater and small streams is discussed. Concerning measurements, two measuring techniques (discharge difference measurements and seepage meter measurements) are investigated. Discharge difference measurements can give reliable results if the length of the reach, at the ends of which the discharge is measured, is appropriate. Infiltrometer measurements are of questionable value when influenced by difficult to detect installation errors. Concerning calculations the following issues are addressed:

ISSN:0022-1686    

DOI:10.1080/00221689809498593

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689809498594

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Various types of underground space have been developed to support human activities and civilization. The knowledge of groundwater hydraulics is indispensable in keeping excavation processes within safety limits and mitigating impacts on the groundwater environment. This review paper summarises history, categories, hydraulic problems and management in underground space technology. Some topics of mathematical modeling and characteristics in and around underground space structures are demonstrated to illuminate recent advancement in groundwater hydraulics. Attractive themes involving both hydraulics and underground space technology are suggested to boost a future progress.

ISSN:0022-1686    

DOI:10.1080/00221689809498595

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a Lagrangian stochastic approach for modeling field scale contaminant transport in the heterogeneous unsaturated geological environments. We derive the probability distribution function of the travel times of tracers and reactive solutes, without limiting it to be either normal or log-normal, and show how it can be used for computing the moments of solute fluxes and breakthrough curves. We also provide closed-form expressions for the travel time moments of tracers and reactive solutes characterized by linear equilibrium and non-equilibrium sorption kinetics. These expressions are useful for prediction and for interpretation of field experiments. In our derivation we account for soil heterogeneity by modeling the soil parameters, such as the saturated hydraulic conductivity and the pore size distribution parameter, as weakly stationary random space functions. Unlike previous studies, we account for the effect of the spatial variability of the water content and refrain from assuming that the saturation is practically constant in the unit gradient flow zone. The derivation is done using a first-order perturbative expansion of the flow equation, and is thus limited to small variability of the input parameters. The effects of spatial variability on the displacement and travel time statistics are discussed and demonstrated.

ISSN:0022-1686    

DOI:10.1080/00221689809498596

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689809498597

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0022-1686    

DOI:10.1080/00221689809498588

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor