Influence of the pressure on a fracture aperture controlling a fracture transmissivity

Groundwater flow through fractures is one of major pathways for radioactive contaminants from a subsurface repository to the biosphere. The cubic law introduces that a small change of the aperture can make a big change in the flow rate thus the transmissivity of a fracture. It is known that a sufficiently large water pressure during hydrofracturing makes a change in a fracture aperture thus a fracture transmissivity, and a small change in water pressure during the hydrogeologic characterization works maybe also affect a fracture aperture. In this study, we evaluate the influence of the water pressure on the fracture aperture with a series of field experiments. For the experiments, a borehole is installed in the KAERI underground research tunnel (KURT), and the test interval is determined through the analyses of borehole logging and hydraulic tests. Then, a double packer system, which is able to directly observe the change of an aperture, is developed and installed in the test borehole. Using the double packer system, the aperture of a fracture in the test interval and the flow rate are observed under various water pressures, and the relation between the water pressure and the aperture is quantified.