During the excavation of shafts and galleries in the deep subsurface for disposing of high-level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries. Such zones could influence the transfer behavior 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 and so on before, during, and after gallery excavation in galleries of 140 and 250 m in depth in an area of soft sedimentary rock in Japan. The results demonstrate that the extent of fractures induced by the gallery excavation related with EDZ was confined to 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 an unsaturated zone did not appear in the 250 m gallery.
During the excavation of shafts and galleries in the deep subsurface for disposing of high-level radioactive waste (HLW), an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries (Tsang et al. 2005). In such zones, several phenomena, for example the creation of fractures induced by excavation, the evolution of unsaturated zones due to the decrease in pore water pressure or degassing, and stress redistribution, will occur. These phenomena will lead to an increase in hydraulic conductivity and influence the transfer behavior of radioactive nuclides. Therefore, the development of an EdZ or EDZ may have significant impacts on the operation and long-term behavior of HLW disposal.
In this study, we performed in situ experiments such as seismic and electrical resistivity tomography and so on before, during, and after gallery excavation in an area of soft sedimentary rock in Japan in order to investigate the behavior of EdZ and EDZ.
