Testing Procedure Effects on Dynamic Soil Behavior

Cyclic triaxial tests were performed on dry and saturated undrained sands using stage testing methods to investigate the influence of repeated cyclic straining and specimen reconsolidation on equivalent linear modulus and damping values on both a total stress and on an effective stress basis. It was found that: (1) Modulus and damping values for dry sand are not significantly affected by stage testing; (2) damping values are not significantly higher for saturated specimens than for dry specimens; (3) volume changes in saturated specimens induced by stage testing can be severe and can severely change initial testing densities; and (4) modulus values for saturated sands are significantly higher for stage tested specimens than for fresh specimens at the same shear strain levels after the same number of cycles. It was concluded that stage testing methods may not give reasonable values of dynamic soil properties for saturated undrained sands for shear strain levels greater than about 0.1% or for more than about 25 strain cycles.