The advantage of using centrifugal acceleration as a fluid driving force is that it acts as a body force in a way that is similar to that of gravity. To compare the saturated hydraulic conductivity of impermeable rocks, constant head tests under centrifugal acceleration and gravity, and Transient Pulse tests were conducted. Shirahama sandstone and Kabasan granite were used as specimens for determining the hydraulic conductivity. The centrifugal constant head method proved to be low hydraulic conductivity value by an order of 1 or 2 than that by the gravity Transient Pulse method. The reason was assumed to be that an unsaturated region occurred in the bottom of the specimen because the centrifugal force is greater near the bottom (downstream side) than the top of the specimen. To avoid unsaturation inaccuracies as much as possible, appropriate specimen length and sufficient water pond will be necessary for the loading bucket assembly.
Transport ability of rocks are evaluated either by hydraulic conductivity, which is an index of liquid flow smoothness, or by storage coefficient, which indicates rock's capacity to store or to extract of liquid. Because the reservable amount of liquid under hydrostatic condition is usually negligibly small compared to the total volume of a specimen, water permeation tests may focus only on hydraulic conductivity. In permeation tests on low-permeability rocks, measuring techniques and apparatus that take account of very small porosity of samples are used. Several methods have been proposed for this kind of water permeation tests. These are Transient Pulse method (Brace et al. (1968)), Flow Pump method (Olsen et al. (1985)) and Sinusoidai method (Bennion and Goss (1971), Kranz et al. (1990)). Esaki et al. (1996) and Zhang et al. (2000a, 200b) have proposed a technique that determines both hydraulic conductivity and specific storage coefficient at the same time by using exact solution which takes compressibility of apparatus into account.