Measurement of Suction-Stress Characteristic Curve Under Drying and Wetting Conditions

Abstract

Suction-stress characteristic curve (SSCC) is an important constitutive relation defining variation of effective stress because of changes in soil water content. It can be intrinsically related to soil–water-retention curve. SSCC reflects the amount of mechanical work done to a unit volume of soil by its pore water at a particular state of matric potential or water content. A new testing system, based on a drying cake method was established to measure SSCC under both drying and wetting conditions. A previously developed theory of incremental linear elasticity allows the determination of suction stress by monitoring elastic modulus and deformation of a soil cake under varying water contents. Changes in suction stress and elastic modulus result in radial displacement field of a soil cake. A twin-cake testing procedure was established to independently measure: the elastic modulus change with water content on one cake by using a miniature-loading system, and the displacement field on the other cake by using a digital still camera throughout the drying and wetting processes. A particle image velocimetry technique was used to analyze a series of sequential images to calculate the evolution of radial displacement field and its center. The test results on four different soils, covering from sand to silt and clay, were compared and validated with the results obtained independently by a transient water release and imbibition method. It is demonstrated that this new testing system provides a simple, fast, and non-destructive way to measure SSCC under varying drying and wetting conditions.