[H-CG28] Nuclear Energy and Geoscience

[HCG28-08] Investigation of the Excavation disturbed Zone due to the excavation of galleries -Study in the Horonobe Underground Research Laboratory-

*Kenji Kubota¹, Yohei Morifuji¹, Kazuhei Aoyagi², Yutaka Sugita² (1.Central Research Institute of Electric Power Industry, 2.Japan Atomic Energy Agency)

Keywords:High level radioactive waste disposal (HLW), Excavation disturbed Zone (EdZ), Soft sedimentary rock, Geophysical exploration

Due to excavation of shafts and galleries in the deep underground for high level radioactive waste disposal, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries. Such zones could influence the transportation of radioactive nuclides, and it is therefore important to understand the mechanical and hydraulic behavior of the EdZ or EDZ. We performed in-situ experiments such as seismic and electrical resistivity tomography, geological survey and so on before, during, and 11 years after excavation of galleries at 140 and 250 m depth in an area of soft sedimentary rock in the Horonobe Underground Research Laboratory, Hokkaido, Japan.
The results demonstrate that the extent of fractures and unsaturated zone induced by the gallery excavation were clarified. The extent of fractures related with EDZ was limited in about 0.45 m from the gallery wall in the 140 m gallery and to about 1 m from the gallery wall in the 250 m gallery. The extent of the unsaturated zone related with EdZ was about 1 m in the 140 m gallery, but it was not appeared in the 250 m gallery. Such changes induced by the gallery excavation occurred within one year after gallery excavation. On the other hand, the extension of the developed fractures and unsaturated zone was hardly clarified in about 11 years after gallery excavation.