Meta-analysis of 301 slope failure calculations. II: Database analysis

In response to the growing need for statistical information regarding slope stability risk analysis, this work applies inferential analysis to a compiled database of 157 failed slopes and corresponding 301 safety factor (SF) calculations. As presented in the companion paper, this database also includes a number of slope stability factors, including analytical method used, stress approach (effective versus total), assumed slip surface geometry, slope type, applied correction factors, and soil Atterburg limits. Although the SF data were found to be fairly well fit by a lognormal distribution, pronounced curvature of the residuals was observed, likely related to various unaccounted slope factors. In response, inferential statistics are used in this paper to analyze the effects of analytical method, slope type, soil plasticity, and effective versus total stress analysis. ANOVA hypothesis testing indicated significant differences between analytical methods and significant interactions between slope types and pore-water stress approaches. Direct SF calculation methods, such as infinite slope, wedge, and the ordinary method of slices were found to produce SF near 1 as expected, but higher order methods in general, and force methods in particular, predicted safety factors significantly greater than 1. Clay content alone was not a discernible influence on SF calculations. A reduced factor ANOVA model was developed to predict SF, given analytical method (a main effect) and the interactions between analytical method with both slope type and pore-water pressure approach.