Probabilistic slope stability assessment considering uncertainties in hydraulic soil parameters of 1-d infiltration model

Abstract

Research in the area of slope stability has brought about the realization that the infiltration of rainwater into a slope decreases the stability of the slope. When raining, rainwater infiltrates into the subsurface soil through the upper unsaturated zone of the slope. This process results in a wetting zone at shallow depth near the slope surface and may lead to a slope failure during a prolonged or heavy rainfall period. The Mein & Larson (1973) infiltration model is adopted here to study the effect of rainwater infiltration on slopes. This model is easy-to-use and yields scientifically-based estimates using soil-hydraulic and climatic parameters representative of the prevailing site conditions. Proceeding from the well-known infiltration model proposed by Mein & Larson and several extensions, explicit equations for time-dependent infiltration rate and cumulative infiltration are proposed in this paper. However, there are many uncertainties associated with the choice of variables to use in the analysis of slope stability. All soils are heterogeneous, and therefore soil properties vary with depth and location. The depth of wetting front which represents the depth from the ground surface to the slip surface depends on many parameters. It is very difficult to provide reasonable solutions with respect to the uncertainties of soil parameters in general slope stability analyses based on deterministic nature. In order to identify the effects of these uncertainties on searching for a critical slip surface, probabilistic approaches should be employed in a rational engineering manner. By combining rainfall infiltration model and probabilistic analysis, the proposed model can estimate probability distribution of the depth of wetting front $z_w$. It would be advantageous to know how much this wetting depth reduces the stability of a slope, and then limit equilibrium methods require that the critical wetting depth $z_{cr}$ be determined as a part of the analysis. Ultima...