Analysis of thermally induced changes in fractured rock permeability during eight years of heating and cooling at the Yucca Mountain Drift Scale Test

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Rutqvist, J.; Freifeld, B.; Min, Ki-Bok; Elsworth, D.; Tsang, Y.
Issue Date
Int J Rock Mech Min Sci 2008;45:1373-89
Fractured rockPermeabilityYucca MountainThermal stressMoisture
We analyzed a data set of thermally induced changes in fractured rock permeability during a 4-year heating (up to 200 1C) and
subsequent 4-year cooling of a large volume, partially saturated and highly fractured volcanic tuff at the Yucca Mountain Drift Scale
Test, Nevada, USA. Permeability estimates were derived from about 700 pneumatic (air-injection) tests, taken periodically at 44 packedoff
borehole intervals during the heating and cooling cycle from November 1997 through November 2005. We analyzed air-permeability
data by numerical modeling of thermally induced stress and moisture movements and their impact on air permeability within the highly
fractured rock. Our analysis shows that changes in air permeability during the initial 4-year heating period, which were limited to about
one order of magnitude, were caused by the combined effects of thermal-mechanically induced stress on fracture aperture and thermalhydrologically
induced changes in fracture moisture content. At the end of the subsequent 4-year cooling period, air-permeability
decreases (to as low as 0.2 of initial) and increases (to as high as 1.8 of initial) were observed. By comparison to the calculated thermohydro-
elastic model results, we identified these remaining increases or decreases in air permeability as irreversible changes in intrinsic
fracture permeability, consistent with either inelastic fracture shear dilation (where permeability increased) or inelastic fracture surfaceasperity
shortening (where permeability decreased). In this paper, we discuss the possibility that such fracture asperity shortening and
associated decrease in fracture permeability might be enhanced by dissolution of highly stressed surface asperities over years of elevated
stress and temperature.
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Energy Systems Engineering (에너지시스템공학부)Journal Papers (저널논문_에너지시스템공학부)
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