A reevaluation of S_u(mob) = 0.22σ′_p using laboratory shear tests

The expression S_u(morb) = 0.22σ′_p for the average undrained shear strength mobilized on a slip surface in the field resulted from in situ vane S_u/σ′_vo and oedometer σ′_p/σ′_vo data, combined with a correction factor μ obtained from the computed factor of safety of unstable embankments, footings, and excavations. It is shown here that the same expression for mobilized undrained strength of soft clays is also obtained from laboratory shear tests by taking into account anisotropy and time effects. This result is highly significant, since the laboratory undrained shear strength data, as well as the correction factor for the time effect, are completely unrelated to the in situ data that previously resulted in the expression for field mobilized undrained shear strength. -Author