COMPARISON OF DIRECT AND INDIRECT MEASURED SOIL-WATER CHARACTERISTIC CURVES FOR A SILTY SAND

Abstract

It is time consuming and needs sophisticated testing apparatus to determine unsaturated soil properties such as hydraulic conductivity and shear strength. Therefore, engineers hesitate to use unsaturated soil properties in economical geotechnical problem solving. To promote the use of unsaturated soil properties in geotechnical engineering designs, numbers of methods have been developed to estimate/predict unsaturated soil properties. The Soil-water characteristic curve (SWCC) defines the relationship between the soil suction and water content. During past few decades, different measuring and estimation/prediction methods have been developed by researchers to ascertain SWCC of soils.  Among them, direct and indirect methods are widely used to measure the SWCC of soil. Indirect methods such as axis-translation technique are commonly used in the laboratory to determine SWCC. It is important to understand how well the indirectly measured SWCC is related to actual soil-water retention properties of soil during drying and wetting process. Bridging that research gap, in this study, Soil water characteristic curve (SWCC) of sandy soil was measured using both indirect (Axis translation method using Tempe Pressure Cell) and direct methods. The direct measured SWCCs were obtained by subjecting the instrumented soil column and model embankment to wetting and drying cycles. When comparing SWCCs measured by direct and indirect methods, it was found that the indirect method provides a very close agreement with the outcomes of direct methods. This ensures that the SWCCs measured in the laboratory by using indirect methods can be used in Geotechnical Engineering practice.