Excavation analysis using crack tensor theory at the Mizunami Underground Research Laboratory, Japan

Sanada, Hiroyuki; Hikima, Ryoichi; Tanno, Takeo; Sato, Toshinori  ; Goke, Mitsuo*; Tada, Hiroyuki*; Kumasaka, Hiroo*

Japan Atomic Energy Agency (JAEA) has been implementing the Mizunami Underground Research Laboratory (MIU) Project for the R&D of geological disposal of High-level Radioactive Waste (HLW) in granite. The MIU Project has been divided into three overlapping phases: Surface-based Investigation Phase (Phase I), Construction Phase (Phase II), and Operation Phase (Phase III). In this paper, FEM analysis using crack tensor theory at the MIU was carried out in order to estimate deformation around the horizontal tunnel for investigations and construction during Phase III, and to confirm the validity of FEM analysis results including parameter settings using fracture information from the vertical borehole drilled during Phase I. The relationship between statistical observations on tunnel walls and pilot boreholes was used to estimate the crack tensor for the investigated area. FEM analysis in this work described the increase of stress in concrete liners due to decrease of Young's Modulus compared to Phase I. Since investigations during Phase II could effectively detected high angle fractures, which couldn't be satisfactorily detected during Phase I, the crack tensor was improved using the Phase II results. Predictions and applicability of the analysis method are to be confirmed with in situ experiments during Phase III.