Investigation of an excavation damaged zone in the east access shaft at the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei  ; Ishii, Eiichi   ; Fujita, Tomoo ; Motoshima, Takayuki*

The objective of this research is to investigate the extent and failure mechanism of an Excavation Damaged Zone (EDZ) induced around the East Access Shaft in the Horonobe Underground Research Laboratory. As a result of hydraulic tests, hydraulic conductivity within 2 m from the shaft wall was increased by 1 to 3 orders of magnitude. This result is consistent with the extent of the development of fractures detected by borehole televiewer surveys. Furthermore, the dominant failure mechanism of the fractures around the shaft wall was almost tensile; also these fractures were caused by the short-term excavation-induced unloading.