Effect of confining pressure on the soil-water characteristic curves of a sandy soil
Leong, Yoke Mun
Date of Issue2017-05-09
School of Civil and Environmental Engineering
The soil-water characteristic curve (SWCC) which relates water content and matric suction of the soil is an important property to understand unsaturated soil. It is known that the water content of the soil during the drying process is higher than that during the wetting process at a given matric suction. The difference between these two paths forms the hysteresis of the SWCC. Due to the time-consuming processes involved in the determination of the SWCC, experiments are mainly done on the drying process of soil under zero confining pressure. However, these studies are only relevant to soil at shallow depth. Thus, to further study the SWCC of soil at a deeper depth, this project investigates the effect of net confining pressure on the first drying, first wetting and second drying curves of the SWCC. Well-graded sand was subjected to repeated drying and wetting processes under zero, 20 kPa and 200 kPa net confining pressures. The experiment for soil sample under zero confining pressure was conducted using a volumetric pressure plate extractor while the tests for 20 kPa and 200 kPa net confining pressures were conducted using the flexible-wall SWCC apparatus. Over the years, numerous equations have been proposed to describe the SWCC. In this project, the Fredlund and Xing (1994) equation was used to curve-fit the SWCC. Test results showed that as net confining pressure increases, the air-entry value, residual matric suction and water-entry value increase while the hysteresis decreases. Chin et al. (2010) method was also applied to the first drying curve of the SWCC to predict the SWCC with a measured point. Chin et al. (2010) method works well for the SWCC under zero net confining pressure but needs to be modified if applied to soil under net confining pressure.
Final Year Project (FYP)
Nanyang Technological University