Stepwise hydrogeological characterisation utilising a geosynthesis methodology; A Case study from the Mizunami Underground Research Laboratory project

統合化手法を用いた段階的な地下水流動特性評価; 瑞浪における超深地層研究所計画を事例として

三枝 博光; 大澤 英昭  ; 尾上 博則 ; 大山 卓也 ; 竹内 竜史  ; 竹内 真司

Saegusa, Hiromitsu; Osawa, Hideaki; Onoe, Hironori; Oyama, Takuya; Takeuchi, Ryuji; Takeuchi, Shinji

超深地層研究所は「結晶質岩花崗岩を主な対象とした深地層の研究施設の一つであり」この計画では「地層処分研究開発の基盤となる深地層の科学的研究の一環として」深部地質環境の調査・解析・評価技術の基盤の整備を全体目標の一つとした調査研究が進められている。この目標を達成するために、統合化手法を構築してきているとともに、それの適用性を確認するための調査研究を進める。超深地層研究所計画の地表からの調査予測研究段階における地下水流動特性評価においては「水理調査と水理地質構造モデルの構築」地下水流動解析を繰り返し実施してきた。その結果「調査の進展に伴い水理地質構造モデルの不確実性が低減したことが確認でき」効率的に地下水流動特性を把握するためには「調査とモデル化・解析を繰り返し実施する」といったアプローチが有効であることが示された。

The Mizunami Underground Research Laboratory (MIU) is now under construction in the Cretaceous Toki granite in the Tono area of central Japan. One of the main goals of the MIU project, which is a broad scientific study of the deep geological environment as a basis of research and development for geological disposal of nuclear wastes, is to establish comprehensive techniques for the investigation, analysis and assessment of the deep geological environment in fractured crystalline rock. For this purpose, a geosynthesis methodology has been developed and will be tested in a dry run to determine if it produces the data required for repository design and associated integrated safety assessment modeling. Surface-based hydrogeological characterization, intended to develop conceptual models of the deep geological environment based on an understanding of the undisturbed conditions before excavation of this URL, was carried out in a stepwise manner. This allows field investigations, construction of geological and hydrogeological models and interpretation of resultant groundwater flow simulations to develop in an iterative manner. Investigations have the goal of obtaining information on factors relevant to repository design, associated construction, operational and post-closure safety assessment, evaluation of the practicality of implementation and environmental impact assessment. Data obtained from field investigations is utilized for the construction of hydrogeological models and groundwater flow simulations, which can be used to identify and prioritize key issues for further investigations. Results show that such an approach, focusing hydrogeological characterizations by a structured geosynthesis methodology, leads to an improved understanding of the deep hydrogeological environment and allows repository-relevant datasets to be produced in an efficient and traceable manner.