Investigation on the Deformation and Failure Patterns of Loess Cut Slope Based on the Unsaturated Triaxial Test in Yan’an, China

The large-scale implementation of the Gully Stabilization and Land Reclamation (GSLR) project induces various failures of loess slopes due to excavation in Yan’ an, China. However, the deformation and failure behavior of these excavated loess slopes have not been fully understood. In this study, field investigation was undertaken for analyzing the distributions and failure features of excavation-induced loess slope failures. It is found that plastic failure mainly occurs in Q 3 loess layers and brittle failure in Q 2 . To understand the underlying failure mechanism, a series of triaxial shear tests were conducted on intact Q 3 and Q 2 loess samples that with different water contents, namely natural water content (natural), dry side of the natural value (drying 5%), and wet side (wetting 5%). The characteristics of stress-strain curves and failure modes of the samples were analyzed. Results show that the stress-strain curves of Q 2 samples are dominated by strain-softening characteristics, while Q 3 samples mainly exhibit strain-harden features except in the drying state. Correspondingly, shear failures of Q 3 specimens are mainly caused by shear crack planes (single, X or V-shaped). For Q 2 loess, the dominance of tensile cracks is observed on the surface of damaged specimens. These disclose the different failure modes of excavated slopes located in different strata, that is, the arc sliding failure of Q 3 loess slopes and the stepped tensile failure of Q 2 loess slopes, and are helpful in the design and management of the ongoing GSLR projects in the Loess Plateau.