Abstract
The effects of time duration of the confining pressure and stress-history patterns were studied through resonant column tests of soil samples. For each soil the dynamic shear modulus obtained at small shearing strain amplitudes was the quantity evaluated as the testing conditions were changed.Under uniform confining pressures an increase in shear modulus occurred which was approximately linear with log time after about 1000 minutes of pressure application. This rate of shear modulus increase per log cycle was expressed as a per cent of the numerical value of the shear modulus at 1000 minutes, to minimize the influence of the pressure magnitude for each test. For soils with median grain size larger than about 0.04 mm the per cent increase in shear modulus per log cycle was about 3% or less. For dry and saturated samples of kaolinite, this increase averaged about 6% to 13%. The effect of overconsolidation was to reduce slightly this rate of shear modulus increase per log cycle.Soils with median grain size of 0.04 mm or greater showed little change in the small amplitude shear modulus as the time of applied confining pressure increased, or little influence of previous preconsolidation. For finer soils (D50«0.04 mm) the effects of time of loading and of preconsolidation were significant. Consequently, extrapolation of laboratory shear moduli of fine-grained soil to field applications requires careful study.
