Heterogeneity of hydraulic conductivity of a fault in sedimentary sequences at the Tono Mine, central Japan

Hydraulic conductivity of a fault zone in sedimentary sequences is discussed, and hydrogeological models of faults are generated. The hydrological data were obtained by long-term piezometric head observation as part of the Shaft Excavation Effect Experiment. Prior to shaft excavation, the heads measured in boreholes on the upthrown side of the fault were lowered by the presence of the existing mine gallery located on the same side of the fault. On the upthrown side, the heads were drawn down simultaneously with the shaft excavation, on the downthrown side the heads were drawn down more slowly. A comparison between changes of piezometric head and results of in-situ hydraulic tests revealed no relation between the size and transient behavior of piezometric drawdown and the hydraulic conductivity of the immediately surrounding rocks. These observations show that the fault behaves as a low conductivity zone. (author)