Abstract:

It is common to quantify fracture mechanical properties by the specific stiffness, which depends upon both the host rock properties and the stress-dependent distribution of aperture within the fracture itself. For example, fractures exhibit increasing specific stiffness with increasing normal stress and narrow-aperture fractures are typically stiffer. Furthermore, differences in the sample size or stress state of a measurement can complicate interpretation of specific stiffness. The "intrinsic stiffness" provides an alternative measure of fracture mechanical properties that removes the first order effects of size and stress-dependence. We demonstrate this concept with a numerical investigation into the scaling of fracture stiffness with the size of the fracture and the normal stress state to which the fracture is exposed. We find that while the specific stiffness exhibits high variability depending on size and stress state, the intrinsic stiffness is far less variable. This suggests that the intrinsic stiffness can provide a useful objective measure of the stiffness of fractures regardless of their size or normal stress states at which they are analyzed.

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