Evaluating slope stability using regional water balance analysis

• Main Author: Rangarajan, Saranya
• Other Authors: Harianto Rahardjo
• Format: Thesis-Master by Research
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Civil engineering; Geotechnical
• Online Access: https://hdl.handle.net/10356/175914
• Institution: Nanyang Technological University

The common occurrences of extreme weather conditions such as high intensity rainfall and longer periods of drought have brought about concerns regarding the impact of such weather conditions on rainfall-induced slope failures and plant health. The soil volumetric water content (VWC) is a parameter that can be correlated to slope stability and plant health. An increase in VWC during rainfall which increases the pore-water pressures (PWPs) in the soil could result in slope failures. Therefore, the primary objective of this study is to perform regional three-dimensional (3D) water balance analyses using GEOtop software to evaluate the VWC changes in the soil under extreme rainfall conditions for three zones in Singapore. The water balance results from the extreme rainfall analyses were used to perform regional slope stability analyses using Scoops3D to obtain the factor of safety (FOS) maps. The results from GEOtop – Scoops3D were then compared with two-dimensional (2D) seepage and slope stability analyses for selected slopes. The 3D subsurface flow in unsaturated soil from GEOtop analyses was found to have a significant influence on slope stability due to the higher PWPs. Subsequently, the relationship between FOS and VWC was established using a linear regression line for the selected slopes. Vegetations play an important role in slope stability. Hence, it is important to intervene before the wilting point of the plant is reached during extreme dry conditions. The secondary objective of this study is to utilize the water balance model to evaluate changes in soil VWC under extreme dry conditions and their effects on plant health. A parametric study was conducted for different vegetation properties and its influence on evapotranspiration (ET) and VWC under 30 days of extreme dry conditions was evaluated. The key findings of the study showed that the soil type greatly influenced the ET rate. The vegetation properties that result in a high ET rate were then used to analyse the VWC of the soil in three regions under extreme dry conditions. The changes in VWC under extreme ET conditions were then used to evaluate the availability of water in the soil to the plant and thus the effect on plant health. This was achieved by developing a plant health map showing the variation of grass health during 30 days of extreme dry conditions. The plant health maps showed that grass grown in clayey soil can survive longer than grass grown in sandy soil.