幌延深地層研究計画における地下水流動解析

Groundwater Flow Analysis of Horonobe Underground Research Laboratory Project

操上 広志  ; 竹内 竜史  ; 瀬尾 昭治

Kurikami, Hiroshi; Takeuchi, Ryuji; Seno, Shoji

本報告書は,幌延深地層研究計画における平成16年度までの水理モデル構築・更新のプロセスを示したものである。本計画における第1段階(地上からの調査研究段階)を,「既存情報に基づく調査フェーズ」と「ボーリング孔を利用した調査フェーズ」に分け,各フェーズでの水理モデルの位置づけ,解析プロセス,解析結果について記した。既存情報に基づくフェーズでは,既存情報の分析により抽出された重要な水理特性に基づいて水理モデルを構築し,感度解析によって効率的な調査の提案を行うプロセスを説明した。一方,ボーリング孔を利用した調査フェーズでは,ボーリング調査を含む一連の調査結果の総合的な説明を通じて地下水流動特性の解釈を試みた。既存情報では考慮していなかった,稚内層中の割れ目帯が水理特性に大きく影響を及ぼしているという概念のモデル化のほか,地下水中の塩分の挙動,異常高圧に対する解析的な検討結果についても述べた。

This report shows the process and the result of the research on the hydrogeological modeling and groundwater flow (GW) analyses of Horonobe Underground Research Laboratory(URL) Project until fiscal year 2004. In the report, Surface-based Investigation (Phase I) of the project was divided into two phases; the investigation phase based on literature review and the borehole investigation phase. In the investigation phase based on literature review, the sensitivity analyses were carried out with the hydrogeological model built based on the considerable information from the literature review. The results showed that the sensitivities of recharge rate and hydraulic conductivity of the surface layer on hydraulic head and those of hydraulic conductivities of both Wakkanai formation and Koetoi formation on GW migration time were high. The results also showed that the GW flow system in and around the URL area was governed by the Shimzu river and Penke-ebekorobetsu river in the shallower zone (local GW flow system) and the Teshio river in the deeper zone (regional GW flow system). "Regional scale" analytical domain was defined based on the results. In the borehole investigation phase, the results of both the in-situ hydraulic tests and the laboratory hydraulic tests were summarized as follows: *The deeper it was, the lower the hydraulic conductivity was in the same layer, especially in Wakkanai formation. *The hydraulic conductivity of the upper layer was lower than that of the lower layer in the same depth. *The distribution of hydraulic conductivity was strongly related to that of fracture zone. The GW flow analyses based on newly developed geological model and the results of the hydraulic tests described above were performed. The GW flow analyses were verified by comparing with the measured hydraulic pressures in the boreholes. Besides, the behavior of saline GW was examined. Furthermore, the excavation of the URL shafts and tunnels was simulated. From the results, ...