An improved permeameter utilizing the steady-state method for hydraulic conductivity of unsaturated Toyoura sand using membrane filter technique

In this study, a novel permeameter test system has been developed to perform rapid steady-state permeability tests on unsaturated cohesionless soils under low suction range. In this system, the membrane filter was used as the filter to stop air drainage during water seepage, where the filter was innovatively secured with double-sided tape rather than traditionally fixed by metal plate combing O-ring sealing. This enables an enlarged seepage area to enhance hydraulic continuity and reduce equilibration time. Hydraulic conductivity ( k ) of unsaturated Toyoura sand with a degree of saturation ( S r ) of 20% < S r < 80% was tested using the membrane filters with pore sizes of 0.45 µm and 5.0 µm. Test results indicate that the steady-state flow can be rapidly established with this permeameter, although filter with pore size of 5.0 μm can only be applied in 30% < S r < 80%. It was found that the hydraulic head difference ( h ) can be very small (e.g. one order smaller) compared to the supported total hydraulic head difference ( h t ) and it becomes even smaller during the seepage because of the filter clogging. Comparing with k data in previous studies and model predicted k , it is confident to conclude that the k values measured in this study are of high accuracy, repeatability and consistency.