Investigation of unsaturated permeability function of soil with multi-modal porosity

• Main Author: Lee, Boris Su Sheng
• Other Authors: Harianto Rahardjo
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Civil engineering::Geotechnical
• Online Access: https://hdl.handle.net/10356/166966
• Institution: Nanyang Technological University

The fundamental parameters determining most of the engineering features of soil are hydraulic properties, such as the unsaturated permeability function and soil-water characteristic curve (SWCC), which are studied in unsaturated soil mechanics. Soil stability refers to the ability of soil to maintain its structure and resist erosion, compaction, and other forms of degradation. This can be achieved by accurately measuring the soil's soil-water characteristic curve (SWCC) and unsaturated permeability function. Soils with multimodal porosity and characteristics have shown to have greater water retention capabilities which help slope stability against rainfall, plant wilting during the extended drought, and infrastructure damage caused by heaving and subsidence. By adjusting or enhancing the physical and chemical properties we can affect its SWCC, improving the soil's water retention and hydraulic properties to enable soil to withstand heavy precipitation better, maintains moisture during droughts, and provides a more stable foundation for infrastructure, reducing the risks of slope failure, plant wilting, and infrastructure damage. This can lead to improved crop yields, reduced water usage, increased carbon sequestration, and better overall soil health. Additionally, it can help to mitigate the effects of climate change, as the optimized soil can better absorb and retain water, reducing the risk of flooding and improving groundwater recharge. Overall, optimizing the SWCC is an important strategy for improving soil quality and resilience, which can have a wide range of positive impacts on the environment and human society. The main objective of this project is to investigate the permeability function of unsaturated soils with multimodal porosity using laboratory setups and statistical modeling. The scope of the project involves laboratory measurements of SWCC, direct measurements and indirect estimation of the unsaturated permeability function of soils with multimodal porosity. Three compacted soil mixtures: sand-kaolin (SK), sand-kaolin-mica (SKM) and sand-kaolin-powdered activated carbon (SKP) were studied. These soil mixtures would be compacted either dynamically or statically. Drying SWCC tests were conducted incorporating saturated and direct unsaturated permeability tests and as well as indirect permeability determination through permeability function test. The project determines unsaturated permeability of samples using the statistical method from SWCC data from the drying SWCC. The drying SWCC tests were done by three methods, 1) the conventional method by using Tempe cell and pressure plate, 2) Schindler (1980)’s method by using HYPROP device and 3) the newly proposed Osmotic Tensiometer (OT) permeameter. The direct measurement of unsaturated permeability using Schindler (1980)’s method was then compared with the permeability functions estimated from the statistical modeling for trimodal SWCC.