Empirical correlations: Drained shear strength for slope stability analyses

Empirical correlations provide estimates of parameter values for preliminary design, verification of laboratory shear test data,and confirmation of back-analysis of a failed slope. The empirical correlations presented herein use liquid limit, clay-size fraction,and effective normal stress to capture the variability and stress-dependent nature of drained residual and fully softened strength envelopes. This paper describes the testing and analysis used to increase the number of data points in the existing correlations,expand the residual strength correlation to include an effective normal stress of 50 kPa, and develop correlations between values of liquid limit and clay-size fraction measured using sample processed through a No. 40 sieve (ASTM procedure) and values derived usingball-milled/disaggregated sample. In addition, equations are presented to express the empirical correlations used to develop a spreadsheet that estimates the residual and fully softened friction angles based on entered values of liquid limit and clay-size fraction.