Time-Dependent Strength Behavior of Frozen Soils

Soil strength, defined in terms of the stress to cause a stated strain-rate, was studied using differential (step-stress) creep tests and constant axial strain-rate tests on two frozen soils, Sault Ste. Marie clay and saturated Ottawa sand. Incremental increases in mean stress, with deviatoric stress constant produce measurable changes in secondary creep rates. Plots of a stress term versus the logarithm of creep rates give straight lines. The linear relationship indicates that creep rate increases exponentially with increases in stress difference and decreases exponentially with increase in the mean stress. The temperature effect on creep behavior is described by an exponential function of the reciprocal of temperature. For a specific creep rate and temperature, several stress circles give a Mohr-Coulomb envelope. The angle of internal friction evaluated for the sand-ice samples falls in the range of values expected for dry sand and appears to be independent of creep rate and temperature. The cohesion is dependent on creep rate.