Occurrence of high-permeability fracture estimated by grouting in Horonobe URL of Japan

幌延深地層研究所におけるグラウト注入状況からの透水性割れ目の産状

常盤 哲也; 澤田 純之; 落合 彰二; 宮川 和也   

Tokiwa, Tetsuya; Sawada, Sumiyuki; Ochiai, Shoji; Miyakawa, Kazuya

高透水性の割れ目の産状を把握するため、グラウト材の注入状況に着目した地質観察を換気立坑の深度250350mで行った。換気立坑の本深度に認められる割れ目はおもに剪断割れ目であり、断層岩類を伴う連続性の良い割れ目(断層)や引張割れ目を伴う。また、掘削に伴う割れ目も多数観察された。注入されたグラウト材は断層から派生した割れ目に多く認められ、断層自体に多くのグラウト材が入っているのではないことがわかった。この結果は、高透水性の割れ目は断層から派生した割れ目であることを示唆する。

In the Horonobe area of Japan, underground facilities have been excavated in soft sedimentary rocks in order to enhance the reliability of relevant technologies for geological disposal of high-level radioactive waste in Japan. Pre-excavation grouting was carried out at 250 to 380 m depth at the location of the planned Ventilation Shaft. After the grouting, the shaft was excavated from 250 to 350 m depth, and fracture mapping was carried out to understand the characteristics of water conductive fractures by focusing on the occurrence of injected grout. Fractures consist mainly of shear fractures, and extension fractures and faults are observed in the shaft. The faults are associated with fault rocks and high continuity. Grout was mainly observed in fractures located on the branching part from faults rather than the fault itself, and therefore high-permeability fractures are not the fault itself (fault core) but fractures located on the branching part in the damage zone of the fault.