Influence of strain-rate on localization and strain-softening in normally consolidated clays with varying strength profiles

The performance of geotechnical structures founded on normally consolidated (NC) clays under static or dynamic loading is dependent on the soil's strain-softening tendency and the potential for localizations to develop. Prior studies of the localization phenomenon have demonstrated that the addition of viscous (or strain-rate dependent) shearing resistance suppresses the onset of localization and provides a measure of regularization for the numerical simulation of the localization process. The onset of localization is delayed when the reduction in strength due to strain softening is counteracted by the increase in strength due to the increased strain rate that develops within a potential localization zone. Understanding localization tendencies is further complicated by spatial variability in clay properties. This paper presents a numerical study that investigates the combined effects of strain-rate, sensitivity, rate of strain softening, and varying strength profiles on the localization tendencies and the global stress-strain behavior of NC clays. The analyses were performed using the finite difference program FLAC 8.0 with the user-defined constitutive model PM4Silt modified to incorporate strain-rate effects. Parametric analyses examine the influence of strain rate, strength profile variations, local soil brittleness, and mesh size on the global post-peak stress-strain behavior of clays