Analysis of Thermally Induced Changes in Fractured Rock Permeability during Eight Years of Heating and Cooling at the Yucca Mountain Drift Scale Test Page: 4 of 48
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previous analyses were focused on permeability evolution in a few selected locations within
the rock mass, here we analyze all available air-permeability data. This includes air-
permeability data from over 700 pneumatic (air-injection) tests taken in 44 packed-off
borehole intervals from November 1997 through November 2005. By analyzing data from the
entire heating and cooling cycle, we are here able to identify irreversible changes in intrinsic
fracture permeability and discuss the potential mechanisms behind such irreversibility.
2 THE YUCCA MOUNTAIN DRIFT SCALE TEST
The DST is located at Yucca Mountain, Nevada, in a side alcove of an underground tunnel,
the Exploratory Studies Facility (ESF), at a depth of about 250 m in partially saturated, highly
fractured volcanic tuff (Fig. la) . The DST is centered around a drift, denoted the Heated
Drift, which is about 50 m long and 5 m in diameter. It is located in a highly fractured welded
tuff described as Topopah Spring Tuff (Formation), Crystal-Poor (Member), Middle Non
Lithophysal (Zone) (Tptpmn), and is one of the units considered for siting the proposed
nuclear waste repository at Yucca Mountain.
From a hydrological perspective, the highly fractured welded tuff at the site may be
characterized as a partially saturated dual-continuum medium, consisting of interacting
fracture and matrix continua. The effective rock-mass permeability at the site of the DST is on
the order of 1x 10-1 m2, dominated by the permeability of the fracture system, whereas the
permeability of the rock matrix is on the order of 1x 10-17 m2 [2, 5]. The main part of the 11%
total rock-mass porosity is comprised of matrix porosity, with fracture porosity estimated to
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Rutqvist, J.; Freifeld, B.; Min, K.-B.; Elsworth, D. & Tsang, Y. Analysis of Thermally Induced Changes in Fractured Rock Permeability during Eight Years of Heating and Cooling at the Yucca Mountain Drift Scale Test, article, June 1, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc899651/m1/4/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.