Hydrogeological Change in Borehole Damage Zone (BDZ) by Expanding Diameter of Borehole

This presentation describes the results of a study on the change in hydrogeological properties that can occur in natural barriers after excavating a disposal hole. We performed a series of hydraulic tests at a borehole in the KURT area to understand the change in the hydrogeological characteristics around the drilling-induced damage zone after excavating the disposal hole. As a result, it was confirmed that the transmissivity of fractured rock was increased from several times to tens of times. It was caused by the drilling-induced damage generated around the borehole surface by expanding the diameter of the borehole. In particular, the change in transmissivity was increased in the test section with low transmissivity. In the end, the permeability in the borehole damage zone had a high transmissivity overall, and the hydraulic connection within the borehole damage zone was expanded. Additionally, it was confirmed that the range of hydrogeological influence of the borehole damage zone decreases as the distance from the borehole hole. The results, which analyzed the hydrogeological effect of the borehole damage zone by the borehole expansion, differ in size from the actual disposal hole in the repository. However, compared to large-scale research on an excavation damage zone conducted in tunnels, researchers can easily access it. Therefore, it will be used in various studies to analyze qualitative phenomena.