Assessment of water retention test by continuous pressurization method

The water retention test involving the stepwise pressurization method (SPM) and a pressure plate extractor has been mainly used to obtain the soil–water characteristic curve (SWCC) of soils. The disadvantage of this test is that the measurement of the drying and wetting paths of the SWCC is time consuming. Thus, a water retention test involving a continuous pressurization method (CPM) in this paper was proposed, and the experiments for three kinds of soil samples were performed. Unlike the SPM, the pore air pressure in the CPM is continuously given to the specimen at a constant pressurization rate. In particular, for the measurement of the transient pore water pressure inside specimen according to the applied pore air pressure, a microtensiometer (height: 25 mm, diameter: 3 mm) was placed vertically at the center of the specimen. The suction for the specimen was defined as the difference between the applied pore air pressure and the measured pore water pressure. It was confirmed that the testing time for the drying and wetting paths of the SWCC in the test involving the CPM was remarkably shortened. The results of the CPM for its verification were compared with those of the SPM under the same initial condition of the specimen. The two test results showed good agreement regardless of the soil samples. Furthermore, the effect of the pressurization rate of the pore air pressure for the CPM was examined. Finally, the proposed water retention test involving the CPM was found to be highly efficient and accurately measure the drying and wetting paths of the SWCC in a short time.