The Geotechnical Engineering Proceedings Lecture – Understanding Rainfall-induced Slope Failures through Unsaturated Soil Mechanics

Synopsis

Rainfall-induced slope failures are commonly observed in residual soils during rainy seasons. Numerous residual soil slopes are generally unsaturated because of the commonly deep groundwater table. The unsaturated soil zone is greatly affected by the environmental changes. Therefore, rainfall-induced slope failure mechanism and its preventive measures can be better understood using unsaturated soil mechanics and unsaturated soil properties that will become the emphasis of this lecture.

Incorporating unsaturated soil properties in the development of slope susceptibility map will result in more realistic and sustainable assessments of regional stability of slopes under rainfall. The development of such a susceptibility map is made possible through regional seepage analysis and three-dimensional slope stability assessment. Several selected residual soil slopes with past failure history were analysed to evaluate the slope susceptibility map. The results were found to be comparable with the results from two-dimensional seepage and slope stability analyses. It is equally important to monitor suction values in the field to assess the stability of the slope. The role of soil suction can be significant in maintaining the stability of the slope during rainfall. The conventional water-filled tensiometer and the osmotic tensiometer have been found to be effective in measuring low to high values of suction, respectively.

Several slope improvement methods using principles of unsaturated soil mechanics such as the Capillary Barrier System (CBS), GeoBarrier System (GBS) and vegetation cover will be illustrated with some case studies.