Abstract
Based on a critical review of the available data in creep tests previously published by many investigators, a new concept of flow envelope is presented and substantiated for normally consolidated clays. It is shown that the flow envelope is expressed by a simple equation irrespective of the type of clays, water content, drainage condition and stress history. This fact provides a clue from field observations for more proper understanding of the dividing line between the secondary compression-type deformation and the plastic flow-type deformation. A flow envelope for a lightly overconsolidated clay is also obtained, which suggests that even a moderate overconsolidation is effective in suppressing the rate of the subsequent flow.In order to elucidate the loading path dependency of stress-dilatancy relationship, a series of drained incremental creep tests were performed on a normally consolidated clay. The results indicate that while a linear relationship between volumetric strain and deviatoric strain holds for each increment of sustained loads, its slope is larger than that predicted by a theory of quasistatic equilibrium but it is finally reduced to the value associated with an equilibrium state as the increment value of effective stress ratio decreases.
