Residual strength after liquefaction: A rheological approach

The motion of a sphere pulled through liquefied sand of low relative density has been observed. Long triaxial specimens were prepared around a 12.7 mm-diameter sphere loaded by a wire/deadweight system. Velocities and drag forces were measured over a large range of shear strains and strain rates. Typical behavior involved a rapid drop to a non-zero minimum drag resistance followed by an increase in resistance with velocity. These results suggest that residual strength of sand after liquefaction is rate-dependent, and that the Bingham Plastic model seems a reasonable fit to the observed behavior over a large range of sliding velocities. Shear stresses calculated from the hydrodynamics of the sphere are of the same order as those inferred from field case histories.