A New Method to Simultaneously Measure the Soil–Water Characteristic Curve and Hydraulic Conductivity Function Using Filter Paper

The soil–water characteristic curve (SWCC) and hydraulic conductivity function (HCF) are widely used to study the hydraulic conductivity behavior of unsaturated soil. This article proposes a filter paper–based instantaneous profile method to simultaneously measure the SWCC and HCF of unsaturated soil. The method uses a small soil column that comprises several vertically stacked soil specimens sandwiched with filter papers. The water content and matric suction of the soil column are measured by weighing the soil specimens and filter papers, respectively, at regular time intervals. Therefore, the matric suction profiles and water content profiles can be obtained, and the SWCC and HCF can be calculated with the profile data. The method was applied to intact loess soil. The measured suction range is 0 to 2×105 kPa, and the measured hydraulic conductivity range is 10−5 to 10−13 m/s. Both SWCC and HCF curves display a bimodal characteristic and are consistent with previous mathematical models. This method is an inexpensive method to measure the SWCC and HCF in a large suction range.