Meaning, Measurement, and Field Application of Fully Softened Shear Strength of Stiff Clays and Clay Shales

Fully softened shear strength mobilized in first-time slope failures, introduced by Skempton 1970, corresponds to a random edge-face arrangement and interaction of clay particles an entirely destructured fabric stiff clays shales. A series triaxial compression tests was conducted on reconstituted normally consolidated specimens 15 shale compositions. Based the laboratory results empirical correlation for secant fully friction angle, ϕ'fssσ'n, developed compositions with plasticity index range 10 250%, effective normal stress 700 kPa. The measurements confirm equation terms parameters ϕ'fss100 mfs. field application angle examined stability analyses 63 failures 38 geologic materials. These include 45 segment observed slip surface at residual condition back-scarp mobilizing strength, 18 entire condition. back-calculated angles are good agreement ϕ'fssσ'n based tests.