Technical NoteSuction stress in unsaturated sand at different relative densities

- The suction stress in unsaturated sand at different relative densities was estimated.
- The matric suction and VWC were measured by an automated SWCC apparatus.
- The suction stress was estimated by Lu and Likos (2006) method.
- The suction stress increased until the soil was saturated and decreased to zero.
- The maximum suction stress decreased with increasing relative density in wet path.

The purpose of this study is to estimate and compare the suction stresses in unsaturated sand for various relative densities. The matric suction and volumetric water content were measured in the drying and wetting processes for sands with different relative densities of 40%, 60% and 75% using an automated soil-water characteristic curve (SWCC) apparatus, and the SWCCs were estimated by the van Genuchten (1980) model based on the measured results. As the relative density increased, the air entry value (AEV) decreased but the water entry value (WEV) increased. Also, the fitting parameter αin the wetting process is larger than that in the drying process. The suction stress characteristic curves (SSCCs) proposed by Lu and Likos (2006) were also estimated using the SWCC parameters. The suction stress increased with the effective degree of saturation but suddenly decreased just before the soil was fully saturated. When the matric suction was higher than the AEV or WEV, the suction stress decreased. As the relative density increased, the maximum suction stress increased in the drying process but decreased in the wetting process. The SWCCs and SSCCs exhibited hysteretic behaviors between the drying and wetting processes.