Influence of Degree of Shear Stress Reversal on the Liquefaction Potential of Saturated Sand

Abstract

A series of dynamic cyclic shear tests under undrained conditions were conducted to determine the conditions to induce liquefaction of saturated sands, using a ring torsion apparatus to apply cyclic shear stresses under nearly plane strain conditions. In addition to completely reversed cyclic tests, partially reversed and unreversed cyclic tests were performed by superposing static initial shear stress on dynamic shear stress pulses. Most specimens were of a relative density of approximately 40 per cent, and the frequency of the cyclic shear stress ranged from 1Hz to 12 Hz. Sudden failure of the specimens which was clearly recognized in the completely reversed and partially reversed tests was not observed in the unreversed tests. Irrespective of the degree of stress reversal, liquefaction failure became imminent when the ratio of the peak shear stress to the vertical effective stress reached a certain critical value. The degree of stress reversal had considerable effect on the conditions to cause initial liquefaction, but had no significant effect on the conditions to cause complete liquefaction. For completely reversed tests, the conditions to induce liquefaction was nearly independent of the frequency of the cyclic shear stress from 1Hz to 12Hz.