Drying and wetting soil-water characteristic curves (SWCC) of compacted soils

• Main Author: Harivansh, Poorooye
• Other Authors: Leong Eng Choon
• Format: Final Year Project
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Civil engineering
• Online Access: http://hdl.handle.net/10356/78604
• Institution: Nanyang Technological University

Residual soil refers to materials that result from the in-situ weathering of rocks, In Singapore, residual soils are mostly from the Jurong Formation and Bukit Timah Granite. Together, they cover around two thirds of the island. Compaction is pivotal in the construction of engineering structures because loose soils need to be compacted to raise their unit weight. Moreover, this process strengthens the soil, which in turn raises the bearing capacity of the foundations constructed in the soil. Compaction improves slope stability and prevents excessive and unwanted settlement too. In this project, soil specimens having a height of 20 mm and a diameter of 63.5 mm were compacted using both static and dynamic compaction methods. Both the standard and modified Proctor methods were utilized. The soil-water characteristic curves (SWCCs) were generated using the pressure plate test and the filter paper test. The objective was to compare the SWCCs of soil compacted at several moisture contents to see if there is any difference due soil fabric and void ratio. The shape of weight loss graph has been found to be similar for all the soil specimens. Moreover, the shrinkage curve was found to be a good indicator of the air entry value when used in conjunction with the gravimetric water content SWCC. The filter paper tests were used to extend the results to matric suctions beyond the pressure plate test range to give a more in-depth analysis. The pressure plate test was able to successfully obtain the drying SWCCs. Unfortunately, owing to time constraints and breakdowns of the laboratory air compressor several times, the wetting process of the soil specimens were delayed and could not be done. The filter paper tests were only able to show the drying SWCC. The time taken for the soil specimens to reach equilibrium at each matric suction was around 15 days. The results showed that the shape of the weight loss curves is similar for all soil specimens. Moreover, it showed that samples at similar degree of saturation also have the same air entry value regardless of the compaction effort. They generally have a higher air entry value if they are dynamically compacted instead of statically compacted.