Gas permeability in the excavation damaged zone at KURT

An in-situ experiment to measure the gas permeability using nitrogen gas has been carried out at KURT (KAERI Underground Research Tunnel) to investigate the change of permeability in the EDZ (excavation damaged zone). The results showed that the permeability decreases with an increasing distance to a location about 2 m deep from the tunnel wall, and then maintains a somewhat constant value. The size of the EDZ can be estimated to be about 2 m from the viewpoint of permeability, and in the EDZ, the permeabilities seem to be increased up to 2 orders of magnitude compared with those in the intact rock. The EDZ was estimated to be 1.2 m from the tunnel wall on the basis of the deformation modulus measured through a Goodman jack test. The EDZ size estimated based on the permeability is larger than that from the Goodman jack test. The fractures have a more significant influence on the hydrological properties compared with the mechanical ones because a fluid flow occurs principally through fractures in the crystalline rock.