Within low-permeable rock mass, fractures can provide the essential porosity and permeability. Being a weak feature in a rock, fractures are sensitive to stress changes and the stress dependency on the fracture permeability in rocks is important to know. A natural fracture in a rock sample (siltstone) was analyzed in several flow-experiments at various effective stresses. A numerical model of the experiment was fitted to the obtained experimental results by a numerical inversion of the initial mechanical aperture and contact ratio of the fracture. Once the fracture stiffness, initial and stress-free effective fracture aperture and contact ratio are estimated, the stress dependency for the fracture permeability can be obtained. A good approximation of the first two parameters (stiffness and aperture) could be derived from experimental strain measurements, at various effective stresses, leaving the contact ratio, which generally ranges between zero and 0.5, as the remaining parameter to estimate.

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