Rapid concurrent measurement of the soil water characteristics curve and the hydraulic conductivity function utilizing the continuous pressurization method

Natural disasters including earthquakes, typhoons and heavy rainfalls induce various risks such as slope failures. The conventional unsaturated soils hydrological properties mainly the Soil Water Characteristics Curve (SWCC) and the Hydraulic Conductivity Function (HCF) determination techniques are limited due to the complexity and prolonged time required. Thus a simple method that considers short time and high accuracy under the drying and the wetting phases considering remolded and undisturbed samples is lacking. Through this paper, a novel systematic testing setup utilizing the Continuous Pressurization Method (CPM) that allows rapid, concurrent, continuous, direct determination of the SWCC and the HCF considering both remolded and undisturbed samples was developed. It was found that the air pressurizing rate influence on the obtained SWCC using the developed system can be neglected. It was confirmed that remolded samples do not properly represent the in-situ conditions with significant error that should be carefully considered. It must be noted that applying low air pressurizing rate induces almost linear suction profile, however, it changes into higher order non-linear profile when applying high air pressurizing rates or achieving low degrees of saturation. A correction function based on Van Genuchten (VG) model was proposed which has finally led to obtaining accurate reliable HCFs. Finally, it was concluded that the developed system is rapid, direct, reliable, continuous with accurate repeatability that allows concurrent determination of both the SWCC and the HCF under the drying and wetting phases. Where the system allows concurrent determination of the SWCC and HCF in less than 7% of the testing time required using the conventional methods and considers testing both remolded and undisturbed soil samples.