On characteristics of K value and shear behaviour of loess using triaxial test.

Compared with conventional soils, such as sand and clay, little knowledge on the coefficient of lateral earth pressure at-rest (K) has been established for loess in the current literature. This paper presents an experimental investigation on K of compacted loess and the associated impacts on undrained shear behaviour. By adopting a K consolidation module in the triaxial system, the K stress state for loess samples was achieved through a unique feedback control. During the K consolidation, the deviatoric stress (q) increases progressively with the premise that the volumetric strain (ε) of the sample equals to the axial strain (ε). The results show that the K value of compacted loess is in a range of 0.28 to 0.53, which is dependent on the packing density and the clay content. A distinguishable decrease of K was found in the course of K consolidation for the loosely compacted loess sample, whereas a similar trend was not observed in the dense sample. In the undrained shear stage, all loess specimens revealed contractive response in the stress path (q-p') diagram, which can be quantified by a modified collapsibility index (I). The index is consistently higher for the K consolidated loess samples than for the isotropic ones. The experimental results indicate a strong impact of the initial stress state on the shear behaviour of compacted loess.