Evaluation and comparison of in-situ soil water characteristics curve with laboratory SWCC curve

Soil Water Characteristic Curve (SWCC) is an essential tool to determine the properties of unsaturated geomaterials, including shear strength, permeability and volume change. Although many SWCCs have been measured using laboratory testing, field studies of the subject are very limited. In the current study, six (6) sets of sensors were installed at different depths and locations of a highway embankment. The sensors measured the volumetric moisture content and matric suction of the soil every hour for a period of three three years. The collected data was processed using a Visual Basic (VB) code and the field SWCC was determinedusing Van Genutchen equation. In addition, undisturbed samples were collected and the SWCC was measured in laboratory under different overburden stress. The field and laboratory SWCC were then compared to determine the possibility, accuracy and precision of the field SWCC. Comparison of the SWCCs indicated the optimum depth of sensor installation to be 2.5 m below the existing ground surface. The field SWCC showed considerable compatibility for the range of suction below the Air Entry Value (AEV) but exhibited lower moisture content when compared to the laboratory for suction values greater than AEV. The AEV for laboratory and field SWCC were 110 kPa and 120 kPa, respectively. It was also concluded the normalized water content (i.e. degree of saturation) shows better comparability than the volumetric water content.