Stress-dependent permeability of fractured rock masses: a numerical study

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Min, Ki-Bok; Rutqvist, J.; Tsang, Chin-Fu; Jing, Lanru
Issue Date
Int J Rock Mech Min Sci 2004;41:1191-210
Stress-dependent permeabilityFractured rockDistinct element methodDiscrete fracture networkChanneling
We investigate the stress-dependent permeability issue in fractured rock masses considering the effects of nonlinear normal
deformation and shear dilation of fractures using a two-dimensional distinct element method program, UDEC, based on a realistic
discrete fracture network realization. A series of ‘‘numerical’’ experiments were conducted to calculate changes in the permeability of
simulated fractured rock masses under various loading conditions. Numerical experiments were conducted in two ways: (1)
increasing the overall stresses with a fixed ratio of horizontal to vertical stresses components; and (2) increasing the differential
stresses (i.e., the difference between the horizontal and vertical stresses) while keeping the magnitude of vertical stress constant.
These numerical experiments show that the permeability of fractured rocks decreases with increased stress magnitudes when the
stress ratio is not large enough to cause shear dilation of fractures, whereas permeability increases with increased stress when the
stress ratio is large enough. Permeability changes at low stress levels are more sensitive than at high stress levels due to the nonlinear
fracture normal stress-displacement relation. Significant stress-induced channeling is observed as the shear dilation causes the
concentration of fluid flow along connected shear fractures. Anisotropy of permeability emerges with the increase of differential
stresses, and this anisotropy can become more prominent with the influence of shear dilation and localized flow paths. A set of
empirical equations in closed-form, accounting for both normal closure and shear dilation of the fractures, is proposed to model the
stress-dependent permeability. These equations prove to be in good agreement with the results obtained from our numerical
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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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