Direct and indirect methods in determination of water retention curve of residual soils

Abstract

Many steep slopes are associated with deep groundwater table so they are located within unsaturated zone. Therefore, it is important to incorporate the unsaturated soil properties in the analysis of slope and design of slope preventive measures. The main property of the unsaturated soil is Water Retention Curve (WRC) describing the relationship between suction and water content. Many researchers developed technologies and methods in the determination of WRC which are associated with certain theory and assumption. The establishment of WRC can be performed using direct and indirect method. This paper focuses on the comparison of three different laboratory testing methods as direct methods to generate WRC. In addition, the paper summarizes the advantages and disadvantages of different methods in the determination of the air-entry value which is the important variable of WRC. The estimation of WRC using indirect method is presented as the practical approach for rapid determination of WRC.