Statistical insights regarding fully softened shear strength.

The fully softened shear strength (FSS) concept is a practical approximation of the mobilized drained shear strength of first-time slides in stiff-fissured clays. There has been a recent increase in interest in measurement and estimation of FSS secant friction angle (FSS-ϕ′sec) to develop correlations for preliminary design and cost approximation. However, such correlations do not help in understanding the cause and effect relationship between soil properties and FSS-ϕ′sec. In this study, a laboratory database containing FSS-ϕ′sec values (output) and soil properties (inputs) of several overconsolidated clays is used to develop a predictive model for FSS-ϕ′sec (output or response). The goal is to detect which inputs from the whole parameter space dominate the response while creating an accurate prediction tool to provide statistical insights regarding the FSS-ϕ′sec. The proposed methodology is used to assess and quantify the relationships among variables, estimate testing device effects on FSS-ϕ′sec, and analyze the danger of extrapolation due to model constraints. The applicability of the predicted FSS-ϕ′sec is also evaluated and compared. Recommendations regarding the studied prediction tools for slope stability design in stiff-fissured clays are provided.