It is known that the rock strength increases with an increase in loading rate. Many studies on the loadingrate dependence of rock strength have been performed under two environments, namely water-saturated and airdried conditions, and the loading-rate dependence has not been investigated well under the conditions of various water saturations observed in situ rock masses. In addition, the quantitative relation between the loading-rate dependence and water saturation has not been examined. In this study, the uniaxial compression test of Sanjome andesite under various water saturations was carried out and the dependence of the strength on the loading rate and water saturation was investigated. The test was performed with alternating two loading rates and the strength corresponding to each loading rate was determined from a single specimen. The test results show that the strength increase with a ten-fold increase in loading rate is almost the same under various water saturations and that the strength increases with a decrease in water saturation. Based on the test results, the theory to explain the dependence of the strength on the loading rate and water saturation was suggested. The variation in the strength was discussed to validate the theory.
Environmental impact assessment was conducted at the Ohitachi Mine (Cu-Zn-Pb) located in Odate, Akita Prefecture, Japan. Zn concentration in river water exceeded the environmental standard (30 µg/L) even in the downstream of the Mine. Here, treatment facility for acid mine drainage had already constructed, however, the capacity of the facility was not enough to protect the environmental standard of Zn in the downstream. We calculated Zn load (mg/s) and concentration of Zn (µg/L) in individual watershed along the mainstream and branches. Several watersheds which emitted high concentration of Zn were recognized in the mining area. Particularly, discharge of Zn along the mainstream and watershed which includes open adit shows strong effects to concentration and load of Zn in river water. Based on concentration of Zn in river water and flow rate, we calculated mass balance of Zn load between sampling points. In order to protect environmental standard of Zn (30 µg/L) around village in downstream, we have to reduce 4.22 mg/s of Zn load. In that case, we have to reduce discharge of Zn along the mainstream and from open adit in the mining area. Based on the load and concentration of Zn in individual watershed around the mining area, quantitative evaluation is possible to estimate environmental risks of heavy metals in the river water caused by abundant mine.