Influence of stress conditions on shear behavior of slip zone soil in ring shear test: an experimental study and numerical simulation

Slip zone soil is one of the most inherent factors affecting the stability of landslides. In engineering practice, the in situ slip zone soil layer may experience different stress histories and thus have different stress states. In order to clarify the influence of stress conditions on the shear characteristics of slip zone soil, ring shear tests were performed on specimens with different over-consolidation ratios (OCRs). The consolidation, unloading and shearing processes of the samples were numerically simulated using a particle flow code model, and the underlying mechanisms of soil shear characteristics across varying stress states were analyzed in terms of particle displacement. Moreover, the concept of stable residual strength over-consolidation ratio (SRSOCR) was proposed. During the shearing process, for a constant normal stress, the residual strength of the sample was observed to depend on the relationship between the OCR and the SRSOCR. When OCR values were less than or equal to the SRSOCR, the residual strength of the samples were essentially equal. The pre-consolidation stress increased the peak strength, while post-peak drop led to a reduction in the strength. During the consolidation, unloading and shearing processes, the particle displacement varied with consolidation state, causing different shear behavior of samples. It is necessary to determine the strength parameters of the slip zone soil according to its position in the landslide body and its stress history in order to accurately evaluate the stability of the landslide.