• Slope Instrumentation
• Instrumentation Reading
• Evaporation
• Variations in Groundwater Table
• Case Studies

Unsaturated Soil Mechanics for Slope Stability Analyses

Mechanisms of rainfall-induced slope failure, Rahardjo et al 2012
Numerous slope failures occur in steep residual soil slopes with a deep groundwater table during rainfalls. A significant thickness of unsaturated soil zone above the groundwater table is a general characteristic of steep residual soil slopes. The negative pore-water pressure in unsaturated soil is highly influenced by the flux boundary condition changes (i.e., infiltration, evaporation and transpiration) resulting from the variation in climatic conditions. On the other hand, the negative pore-water pressure contributes additional shear strength to the unsaturated soil. As water infiltrates into the slope, pore-water pressure in the slope increases (matric suction decreases), and the additional shear strength due to matric suction will decrease or even disappear, causing the slope to be more susceptible to failure. Evaporation and transpiration will restore the loss of matric suction in the slope and this climatic variation occurs at all times. In other words, the unsaturated zone is a dynamic interface of the slope with the environment and as a result, factor of safety of slope is affected dynamically by climatic changes.

Rainfall-induced slope failure within residual soil, Rahardjo et al 2005

References

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2. Rahardjo, H., Satyanaga, A. and Leong, E. C. (2012). “Unsaturated soil mechanics for slope stabilization.” Geotechnical Engineering Journal of the SEAGS & AGSSEA, March, 43(1), 48-58.
3. Rahardjo, H., Santoso, V. A., Leong, E. C., Ng, Y. S. and Hua, C. J. (2011). “Performance of horizontal drains in residual soil slope.” Soils and Foundations, Japanese Geotechnical Society, June, 51(3), 437-447. doi | handle
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