Some measurements of permeability and effective stress on a heterogeneous soil mixture: implications for recovery of inelastic strains

The results of permeability variations in response to both changes in isotr opic mean effective stress and internal fluid pressure gradients for an art ificial silty clay are presented. While changing confining stress induces a typical elasto-plastic response, with a small increase in permeability dur ing unloading, raising the fluid pressure results in a more pronounced incr ease in permeability, the magnitude of which is similar to that seen during virgin compression. The behaviour is interpreted as reflecting compressibi lity contrasts between rigid quartz grains and more compressible clays. Flu ctuating the confining pressure has a more direct influence on the less com pressible quartz particles, with a subsequent smaller change in permeabilit y upon unloading. Conversely, raised pore fluid pressure affects the clay m atrix more directly and can therefore prompt a different permeability respo nse. The results have implications for predicting the permeability characte ristics of overconsolidated soils that are heterogeneous in nature. (C) 200 0 Elsevier Science B.V. All rights reserved.