Model Uncertainty of Unsaturated Hydraulic Properties and Effects on Slope Reliability

Abstract

The unsaturated soil hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (PF) are the most important soil properties to influence the pore-water pressure distribution in soil slopes under rainfall condition. Estimation methods based on empirical pedotransfer functions (PTFs) have been developed as rapid and inexpensive ways to determine unsaturated soil hydraulic properties. In this study, more than 700 samples of measured SWCCs and PFs are selected from the database of UNSODA. The statistics and model error of the estimated van Genuchten and Mualem model using PTFs are analyzed. A parametric study of reliability analysis is conducted for a hypothetical slope which is subjected to heavy storm. The effects of both the uncertainties of soil hydraulic parameters and the model error on pore water pressure distribution and slope stability are investigated and discussed. It is shown the effect of the model error of PF estimation on variation of slope stability is smaller than the soil hydraulic parameters n and K0, but is similar to the effect of a and L. The reliability index of the slope is reduced when the prediction uncertainties of the estimation models is considered.