岩盤の傾斜量を用いた水理地質構造要素の推定に関わる解析業務

The analysis about presumption of the element of the hydrogeological structure using surface tilt data of the rock mass

新井 孝志*; 葛木 建大*; 大村 一夫*

Arai, Takashi*; Katsuragi, Takehiro*; Omura, Kazuo*

本研究は、地下水の流動を規制する水理地質構造要素を推定する手法のひとつとして、地表付近の微小な傾斜量を指標とした水理地質構造推定手法の適用性を確認するものである。本業務では、瑞浪超深地層研究所用地を含む領域を対象として構築した簡易な地質環境モデルに基づき揚水試験に伴う傾斜量の変化を算出した。また、この結果を用いて逆解析的に岩盤の体積歪分布を求め、推定される水理地質構造を抽出した。さらに、本手法により水理地質構造の推定にあたって最適な計測位置や計測点数等について検討を行った。

We calculated the deformation of surface tilt followed by pumping tests around the Mizunami underground Research Laboratory site, on the basis of the simple model in geo-environment. The inversion analysis of the surface tilt data showed high validity on the presumption of hydrogeological structures. Through this research, we evaluated the optimal installation points and arrangement of the Tiltmeters for the pumping point. The results are summarized as follows: (1)The surface tilt data by the forward analysis show 11.5 nanoradians at its maximum, assuming that the total pumping rate was 86.4 m (20 l/min for 72 hours). Where the pumping time is about 72 hours and more, therefore, we can certainly detect surface tilts. (2)We carried out the inversion analysis of the distribution of fluid volume change on the unknown domain. The analytical result indicates the good reproducibility and also enables us to interpret hydrogeological structures on the model. The center of volume change as pumping point tends to be distributed among approximately 200 m shallower in depth than the model. It is high possibility that we obtain theoretically the good results reflecting hydrogeological structures by the inversion analysis, whereas the results still include such an above tendency. (3)We concluded that the optimal installation points and arrangement for the Tiltmeters are 4 points and mostly straight array across the faults in the Laboratory site. We recommend the installation array of 4 to 8 points, when the research area is expanded to all range of the Laboratory sites.