Effect of confining pressure on hysteresis of soil-water characteristic curves

• Main Author: Eng, Ngee Kiang
• Other Authors: Leong, Eng Choon
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/61020
• Institution: Nanyang Technological University

The determination of soil-water characteristic curve (SWCC) is of paramount importance in understanding the behaviour of unsaturated soils. It is also noted that soil-water relationship follows different paths during drying and wetting, where the soil under drying has a higher water content than the soil under wetting at a given matric suction. The difference in water content is termed as hysteresis. Hysteresis is one of the important phenomenona that needs to be further investigated for better understanding of the properties and behaviour of an unsaturated soil. For decades, experimental researches have been conducted on drying SWCC due to simplicity of its measurement. However, wetting SWCC is also an important consideration in geotechnical engineering problems, such as seepage through unsaturated soils which causes slope instability. Furthermore, SWCC tests are usually conducted under zero net confining pressure condition. In this project, river sand specimens of different fine contents (5% and 30% fines) were subjected to multi-cycles of drying and wetting at non-zero net confining pressures using the SWCC Apparatus. Tempe cell was used to determine drying SWCCs at zero net confining pressure. The SWCC Apparatus was designed for this project to overcome the limitations of the Tempe cell. It has two components, a SWCC flexible-wall cell and a wooden slider device for drying and wetting SWCCs to be performed with a net confining pressure applied. The SWCC test data were fitted using the Fredlund and Xing equation (1994) and van Genuchten (1980) equation to obtain the best-fit SWCCs. Hysteresis of the SWCCs were quantified using four different proposed hysteresis indices. The efficacies of the hysteresis indices in terms of ease of computation as well as yielding the most consistent and accurate trend in hysteresis quantification, were also evaluated. The SWCC test results showed that higher net confining pressures result in a larger air-entry value, residual matric suction and water-entry value, as well as smaller hysteresis between the drying and wetting SWCCs.