Geomechanical assessment of excavation damaged zone in the Horonobe Underground Research Laboratory, Japan

Aoyagi, Kazuhei  ; Tsusaka, Kimikazu; Tokiwa, Tetsuya; Kondo, Keiji; Inagaki, Daisuke

In a high-level radioactive waste (HLW) disposal project, quantitative evaluation of the extent of excavation damaged zone (EDZ), which is estimated to cause the mechanical, hydrological and geochemical effect to the rock. In Horonobe URL, P-wave tomography survey and rock core observation in the tomography area were conducted at the depth of 250 m to evaluate EDZ. In addition to these in-situ measurement and observation, the authors conducted numerical analysis to identify damaged zone. As a result of P-wave tomography, remarkable low velocity layer was extended about 0.6 m from the drift wall. From the result of rock core observation, the region which has several EDZ fractures developed to 0.3 m from the gallery wall. Furthermore, the numerical analysis showed that the failure zone was extended about 0.2 m from the drift wall. From these results, the authors concluded that the extension of remarkable low velocity layer matched with the extension of the region which has several EDZ fractures.