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幌延深地層研究計画における低アルカリ性セメント系材料の適用性; 140m調査坑道における原位置吹付け施工試験

Study on applicability of low alkaline cement in Horonobe Underground Research Laboratory Project; In-situ experiment at 140 m gallery

中山 雅; 佐藤 治夫; 杉田 裕; 野口 聡

Nakayama, Masashi; Sato, Haruo; Sugita, Yutaka; Noguchi, Akira

地層処分施設は、地下300m以深に建設されることから、坑道の空洞安定性確保や掘削に伴う湧水量の抑制のため、セメント系材料を用いた支保工が検討されている。従来の地下構造物に一般的に用いられるセメント系材料であるOPCはセメント硬化体の細孔溶液中に含まれるアルカリ成分により、pHが12-13程度の高アルカリ性を呈する。地層処分施設においては、上記の高アルカリ成分が地下水に溶出した場合、人工バリア及び天然バリアの性能に影響を与える可能性がある。このような影響を低減するために、原子力機構では、HFSCを開発し、化学的特性,施工性などについて検討を実施してきた。現在までの検討結果から、HFSCが幌延URLの設計基準強度を上まわる強度発現が可能であること、OPCと同等の施工性を有することが示されたので、幌延URLの坑道において、吹付け施工試験を実施した。その結果、HFSCはOPCと同等もしくは良好な施工性を示し、地下坑道への適用性が確認された。これまで、低アルカリ性セメントを用いた小規模な吹付け施工試験は海外で例があるものの、今回実施した幌延の地下施設での原位置試験のように、低アルカリ性セメントを実際の坑道の工事に使用した本格的な施工は世界初である。

In Japan, any high level radioactive waste repository is to be constructed at over 300 m depth below surface. Tunnel support is used for safety during the construction and operation, and shotcrete and concrete lining are used as the tunnel support. Concrete is a composite material comprised of aggregate, cement and various additives. Low alkaline cement has been developed for the long term stability of the barrier systems whose performance could be negatively affected by highly alkaline conditions arising due to cement used in a repository. JAEA has developed a low alkaline cement, named as HFSC, containing over 60wt% of SF and FA. JAEA are presently constructing an URL at Horonobe for research and development in the geosciences and repository engineering technology. HFSC was used experimentally as the shotcrete material in construction of part of the 140 m deep gallery in Horonobe URL. The objective of this experiment was to assess the performance of HFSC shotcrete in terms of mechanics, workability, durability, and so on. HFSC used in this experiment is composed of 40wt% OPC, 20wt% SF, and 40wt% FA. This composition was determined based on mechanical testing of various mixes of the above components. Because of the low OPC content, the strength of HFSC tends to be lower than that of OPC in normal concrete. The total length of tunnel using HFSC shotcrete is about 73 m and about 500 m$$^{3}$$ of HFSC was used. This experimental construction confirmed the workability of HFSC shotcrete. Although several in-situ experiments using low alkaline cement as shotcrete have been performed at a small scale, this application of HFSC at the Horonobe URL is the first full scale application of low alkaline cement in the construction of a URL in the world. In this report, we present detailed results of the in-situ construction test.

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