Engineering Geological Study on Exudation of Acid Water from Rock Mucks. Evaluation Methods of Rocks at the Hakkouda Tunnel near Mine Area.

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  • 酸性水発生に関わる掘削残土の応用地質学的検討　　鉱山に近接して施工される八甲田トンネルにおける岩石特性評価法
  • サンセイスイ ハッセイ ニ カカワル クッサクザンド ノ オウヨウ チシツガクテキ ケントウ コウザン ニ キンセツ シテ セコウ サレル ハッコウダサン トンネル ニ オケル ガンセキ トクセイ ヒョウカホウ
  • Evaluation Methods of Rocks at the Hakkouda Tunnel near Mine Area
  • 鉱山に近接して施工される八甲田トンネルにおける岩石特性評価法

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Water pollution in surface and ground water caused by the inflow of acid water that enriched in heavy metals becomes serious environmental problems around the mining areas the excavation sites where the chemical resolution of sulfide minerals such as pyrite occurs. The Hakkouda Tunnel in northern Honshu passes near the mine area, so it is feared that water pollution around this tunnel occur due to acid water generated from sulfide-containing rocks as muck.<BR>To establish the evaluating method regarding exudation of acid water from rocks, we examined the batch leaching test, the magnetic susceptibility and the chemical composition for the rocks distributed in this tunnel. For all rock types distributed in this tunnel, the rocks that can exude the acid water are rich in sulfur and poor in CaO, and the SO42- contents of elution water increase according to the rise of the sulfur contents in rocks. Therefore it is assumed that the sulfuric acid is liquated out by resolution of sulfide such as pyrite. The Ca-containing minerals in mudstones such as calcite and plagioclase will be decomposed continuously, and these minerals will counteract on the sulfuric acidic water. This processes are estimated by the relationship between SO42- contents, Ca2+ contents and pH in elution water. In the case of volcanic rocks, as the magnetic susceptibility become lower the sulfur content of rocks become larger and the pH of elution water become lower.<BR>From these results, it becomes clear that the exudation of acid water from rocks distributed in the mining area can be evaluated by the four indices as follows. (1) the magnetic susceptibility that is applied only volcanic rocks, (2) the pH value after one hour in batch leaching test, (3) the sulfur contents and (4) the S/Ca mol ratio for only mudstones.

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