Discrete fracture networks

Numerically, these processes can be modeled by different techniques, such as finite-difference methods (FDM), finite-element methods (FEM). and discrete-element methods (DEM), as well as discrete fracture network (DFN) methods. In addition, many of the coupled processes are nonlinear, and the... 

AD-equation a Peclet number of Pe=10 is used. This gives a spread in the RTD (dispersion) that is within the range of observed values in the field. The standard deviation of the transmissivities of the channels in the network model was chosen such that the RTD of a nonsorbing tracer also has a Pe=10. In the time scale presented there seem not be dramatic differences between the model results for the Network and the AD-models. It should be noted, however, that the early arrival times are of special interest for radionuclides that decay. There the differences are considerable. Similar results were obtained in comparisons of different models using very similar data bases (Selroos et a. 2002). In that comparison a discrete fracture network model, a channel network model and a stochastic continuum model were used. 

Hybrid model of Discrete Fracture Network (DFN) and Discrete Element Method (DEM) for coupled stress-flow analysis of rock slope stability (Wang, 2000) ... 

Wang H. 2000. Hybrid model of discrete fracture network and discrete element method for rock slope stability analysis. J. of Hydrogeology Engineering Geology, Vol. 2, pp. 30-34. 

Abstract A methodology for quantifying the contributions of hydro-mechanical processes to fractured rock hydraulic property distributions has been developed and tested. Simulations have been carried out on discrete fracture networks to study the sensitivity of hydraulic properties to mechanical properties, stress changes with depth, mechanical boundary conditions, initial mechanical apertures and fracture network geometry. The results indicate that the most important (and uncertain) parameters for modelling HM processes in fractured rock are fracture density and rock/fracture mechanical properties. Aperture variation with depth below ground surface is found to be of second order importance. 

The two-dimensional distinct element code, UDEC (Itasca, 2000) is applied for the modeling of mechanical and hydraulic behaviours. UDEC simulates the response of a fractured rock mass represented as an assemblage of discrete deformable blocks, subjected to the mechanical stress and hydraulic pressure boundary condition. Numerical experiment consists of 1) generation of a Discrete Fracture Network (DFN) as a geometric model, 2) application of various stress conditions, and 3) application of fluid boundary condition and calculation of equivalent permeability. 

A realistic Discrete Fracture Network is generated based on statistical information on fracture by Monte Carlo simulations (Min and Jing, 2003). Data for this analysis is taken from the result of a site investigation at Sellafield undertaken by Nirex, UK (Table 1, Decovalex 2000). 

Cacas, M. C., Ledoux, E., de Marsily, G., Tillie, B., Barbreau, B., Durand, A., Feuga B. and Peaudecerf, P. 1990. Modeling fracture flow with a stochastic discrete fracture network Calibration and validation, 1, The flow model. Water Resour. Res., 26(3), pp. 479-489. 

Depending on the purpose established in (A), different suites of parameters should be chosen to define the domains. For example fracture characteristics for input to discrete fracture network modeling. 

The efficiency of a rock formation as a transport barrier depends on fluid flow and on radionuclide retention in the rock due to a variety of physical and chemical processes. Open fissures or fractures in the rock provide pathways through which water and radionuclides may travel. Although most radionuclides have a strong tendency to sorb to mineral grains in the rock, tracers first have to diffuse from fractures into the rock matrix in order to access the extensive pool of sorption sites (Neretnieks, 1980). Diffusion in turn depends on mass transfer properties of the rock matrix and on the hydrodynamics of fracture networks, emphasizing the interaction between water flow, advective transport and retention processes. Although models for reactive transport in discrete fracture networks have been around for some time, it is only recently that a theoretical framework is available for systematic studies of the hydrodynamic impact on retention (e.g., Cvetkovic et al., 1999, 2002). 

In the following, we shall use discrete fracture network (DFN) simulations (Gutters and Shuttle, 2000 Gutters, 2002) to exemplify the estimate of P using k = 2Sf jn,. ... 

Dershowitz, B., Eiben, T., Follinf, S., and Andersson, J., 1999. SR-97 - alternative models project. Discrete fracture network modelling for performance assessment of Aberg. R-99-43, Swedish Nuclear Fuel and Waste Management Co. (SKB). 

Gutters, N., 2003. A generic study of discrete fracture network transport properties using fracman/mafic. R-03-XX, Swedish Nuclear Fuel and Waste Management Co. (SKB). Gutters, N. and Shuttle, D., 2000. Sensitivity analysis of a discrete fracture network model... 

Generation of the discrete fracture network (DFN) of rock mass... 

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