Influence of fines content on the undrained flow instability of loess

Abstract

The influence of fines content (FC) on flow instability of intact and reconstituted Chinese loess is studied under undrained monotonic loading using conventional triaxial tests. The undrained behaviour of a mixed loess system indicates that the increasing plastic fines reduce the peak strength with little effect on the critical state friction angle. The changing FC can result in parallel translation and rotation of the critical state lines (CSLs) of reconstituted loess in the volumetric plane. A coarse-grain- to fine-grain-dominant transition is found as FC attains 55·5%, with a convergence of CSL for FC ranging from 55·5 to 87·9% using the equivalent interfine void ratio. A similar trend is found for intact specimens, suggesting that fines may act as void fillers at low-stress levels, which indicates a competing effect of structure and interfine contacts. The modified state parameter is robust in characterising the flow behaviour of the Chinese loess with revised range and corresponding descriptors.