In-situ backfilling experiment of the small scall drift by spray method in Mizunami Underground Research Laboratory, Japan

Matsui, Hiroya ; Yahagi, Ryoji*; Ishizuka, Hikaru*; Toguri, Satohito*

In situ backfilling experiment using spray method in the small scale drift (approximately 4 by 3 m scale) was conducted at 500 m depth in Mizunami Underground Research Laboratory (MIU) established by JAEA (Japan Atomic Energy Agency). The backfill material consists of sand and bentonite. Specification for the backfill material was designed to satisfy the target permeability of generic host rock (10 m/sec) assumed by NUMO. In this case, effective clay density should be 0.4 Mg/m or more. Quality control of the material before backfilling was performed by setting the initial water contents (average 14%) based on the results of the laboratory testing and preliminary spray testing on ground surface. Densities of the backfilled material measured at any points satisfied the specification and the results suggested the establishment of the practical quality control methodology of the backfilling by spray method under actual deep geological environment. The in situ experiment was sponsored by METI (Ministry of Environment, Trade and Industry).