Fluid flow in a fractured rock mass
The geological formations in the unsaturated zone underlying Yucca Mountain, on and adjacent to the Nevada Test Site, are being evaluated by the Nevada Nuclear Waste Storage Investigations project. They are composed of tuffaceous materials, sometimes highly fractured, whose hydrologic properties must be evaluated to estimate the rate at which radionuclides could migrate to the accessible environment. Hydrologic flow models used for postclosure performance assessment of the prospective repository must take into account the potential for water movement in both the rock matrix and the fractures. Calculations using models that explicitly account for the effects of individual fractures are not feasible, because of the extremely large number of fractures contained in a site-scale problem and the difficulties in characterizing and modeling the fracture geometries. Two approaches were used to develop a continuum model to evaluate water movement in a fractured rock mass. Both approaches assume that the pressure head in the fractures and the matrix are identical along a line perpendicular to flow. The first approach uses this assumption and separate equations for flow in the fractures and in the matrix to derive both a single flow equation for an equivalent, porous medium and mathematical expressions for the unsaturated, hydrologic properties in this flow equation. The second approach assumes a fluid continuity equation for a porous medium. Information on the physical structure of the rock mass, along with theoretical considerations from capillary theory, is used to derive the mathematical expressions for the rock-mass unsaturated hydrologic properties. Both approaches lead to a single flow equation for a fractured rock mass. The two approaches were used to calculate unsaturated hydrologic properties for several types of tuff underlying Yucca Mountain.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 59794
- Report Number(s):
- SAND--85-0855C; CONF-8505236--1; ON: DE86004619
- Country of Publication:
- United States
- Language:
- English
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