This study developed an original constant-head permeability apparatus for rocks. This apparatus can freely adjust the confining pressure and hydraulic pressure (hydraulic gradient), and can directly measure the runoff volume using an electronic balance. This apparatus can measure the hydraulic conductivity more accurately than the conventional constant-head method that measures the runoff volume using a measuring cylinder. Second, this study measured the hydraulic conductivity of Inada granite specimens (50 mm in diameter and 40 mm in length) under confining pressure conditions using the constant-head permeability apparatus. The test was performed at 22±1°C in a temperature-controlled room. As result, we found that the hydraulic conductivity of Inada granite, which was measured using this apparatus, is quite similar to that reported by a previous study using transient pulse method. Furthermore, the observed decline in hydraulic conductivity due to the confining pressure is consistent with the observations of the previous study. Therefore, the permeability measurement system used in this study is established and reliable. In addition, this study measured the hydraulic conductivity of various seven intact rocks (granite, basalt, dacite, sandstone, and tuff) under confining pressure conditions using a constant-head permeability apparatus, and we presented how the hydraulic conductivity changes as the confining pressure increases.
