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Journal Articles

Excavation cycle times recorded during sinking of a deep shaft in crystalline rock; A Case example at ventilation shaft of Mizunami URL, Japan

Sanada, Hiroyuki; Sato, Toshinori; Horiuchi, Yasuharu*; Mikake, Shinichiro; Okihara, Mitsunobu*; Yahagi, Ryoji*; Kobayashi, Shinji*

Tunnelling and Underground Space Technology, 50, p.68 - 78, 2015/08

 Times Cited Count:3 Percentile:18.27(Construction & Building Technology)

The Japan Atomic Energy Agency (JAEA) is implementing the Mizunami Underground Research Laboratory (MIU) Project to establish the scientific and technological basis for the geological disposal of High-level Radioactive Waste (HLW) in crystalline rocks. Excavation cycle times were recorded during the Ventilation Shaft sinking and compared with the planned excavation cycle times for evaluation of the baseline design plan. This included review of the cycle times in the design process and comparison with the actual construction results. The recorded results indicate that actual cycle times were twice as long as the design plan. This paper describes discussions on differences in cycle times between the design and actual times.

Journal Articles

Influence of fracture orientation on excavatability of soft sedimentary rock using a hydraulic impact hammer; A Case study in the Horonobe Underground Research Laboratory

Tsusaka, Kimikazu; Tokiwa, Tetsuya

Tunnelling and Underground Space Technology, 38, p.542 - 549, 2013/09

 Times Cited Count:5 Percentile:27.17(Construction & Building Technology)

In the Japanese deep geological disposal project for high-level radioactive waste, the ease of excavation of a potential host rock is a key issue for the economics of project implementation. This is because it is estimated that about 300-kilometers of disposal drifts will need to be excavated for the disposal of 40,000 waste packages deep underground. In this study, the influence not only of the mechanical properties of intact host rock, but also fracture characteristics and their effect on the practical excavation rate of drifts using a hydraulic impact hammer were analyzed. The drifts were excavated through soft sedimentary rock in the Horonobe Underground Research Laboratory. Fracture mapping was conducted at the excavation face before every excavation round for the evaluation of fracture characteristics. Equotip hardness testing was also conducted to estimate the strength of intact rock. The results indicate that the excavation rate of the drift excavated in the direction perpendicular to pre-existing fractures was faster than the excavation of the drift excavated in the direction parallel to pre-existing fractures. In addition, the drift excavated in the direction perpendicular to pre-existing fractures had a good correlation with fracture frequency. This result suggests that the preferred direction of disposal drifts should be perpendicular to the major pre-existing fractures in the host rock to optimize excavatability in any deep geological disposal project.

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