Abstract: Although the filter paper method has been widely used in the study of soil-water characteristics of unsaturated soil, the test data of the filter paper method and the pressure plate test data are always not continuous and smooth. For this reason, a series of indoor pressure plate tests, filter paper tests and soil shrinkage tests were carried out based on the water change path and volume change of the samples, and quantitative analysis of statistical indicators was conducted based on the test results of the soil water characteristic curve (SWCC). The research results show that the SWCC test data measured by the filter paper method and the pressure plate method along the drying path from saturation can be effectively connected, while the SWCC test data measured by these methods along the path without water change may be staggered or crossed during the connection, especially for the soil with significant deformation. In this paper, an improved method is proposed so as to accurately estimate the SWCC based on degree of saturation, which the soil shrinkage test is only required to supplement. A reasonable explanation is given for the differences in the performance of different filter paper method test results. The research results can not only provide important theoretical guidance for the test personnel when they deal with the test data of filter paper method and pressure plate method simultaneously, but also expand the application scope of filter paper method.

Key words: unsaturated soil, drying path, water change path, volume change, soil-water characteristic curve