The role of selected unsaturated permeability models on slope stability analyses

• Main Author: Wee, Jayne Xin Yi
• Other Authors: Harianto Rahardjo
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Civil engineering::Geotechnical
• Online Access: http://hdl.handle.net/10356/64422
• Institution: Nanyang Technological University

The water movement in unsaturated soils is a common concern as it gives rise to many complications in the geotechnical engineering and geo-environmental field. A key parameter in governing water flow in unsaturated soils is the unsaturated permeability. It is necessary to analyse the unsaturated permeability characteristics of soils in the unsaturated zone. Various laboratory apparatuses are readily available for the measurement of the unsaturated permeability. However, the process of obtaining the direct measurements is very lengthy and tedious. Therefore, unsaturated permeability estimation models are commonly used to estimate the unsaturated permeability values. The estimation models use soil-water characteristic curve (SWCC) data and measured saturated permeability. The unsaturated permeability curves estimated by the different models vary from each other. Hence, the objective of this study is to investigate the effect of using different unsaturated permeability estimation models on the stability analyses of Singapore residual soil slopes. The selected models were then evaluated based on seepage and slope stability analyses. Two measured SWCC ranges were assumed. SWCC tests were conducted to obtain the results and the results were best-fitted using the SWCC equations. In addition, the unsaturated permeability test was conducted to obtain the directly measured data. This was done to compare the measured unsaturated permeability data with the unsaturated permeability values estimated by the different models. The three selected estimation models were FCM, VCM with m=1-1/n and FMM. Three factors that caused variation between the estimated unsaturated permeability functions were identified and these factors were measured SWCC data range, best-fit SWCC equation and relative permeability function. The seepage analysis of a soil column was then used to identify the critical affecting parameter, which was measured SWCC data range. With this affecting parameter, it was discovered that the VCM with m=1-1/n model was most sensitive towards the availability of measured SWCC data range. With the selected affecting parameter and the estimation model, the slope stability analyses were performed to evaluate the factor of safety over a period of time. Since the permeability values were low for the soil specimen used in this study, minor differences between the two models with different measured SWCC data range were observed. With higher permeability, the effect of measured SWCC data range was more significant during the analyses.