Small-Strain Stiffness Model of Shear-Zone Soil in a Reactivated Slow-Moving Landslide

Many slow-moving landslides with pre-existing shear zones exist in the Three Gorges Reservoir (TGR) region. In response to dynamics such as water-level fluctuations, shear-zone soil undergoes repeated small deformations, which sometimes result in slow-moving landslides that accelerate rapidly and fail catastrophically. Therefore, investigating the nonlinear variation of the shear modulus of soil over different strain ranges, especially for small strains, which is not well studied, is important. This paper conducts a series of investigations on shear-zone soil to obtain parameters of the small-strain stiffness [hardening soil (HS)-Small] model, including consolidated drain triaxial unloading–reloading compression, bending elements, and resonant column tests. The parameters were used to analyze the strain and deformation of a reactivated slow-moving landslide in the TGR region through numerical analysis. Correspondingly, in situ deformation monitors carried out in the shear zone are reported. The results illustrate that most regions of the slow-moving landslide are in small-strain states, and the numerical results demonstrate that the HS-Small model shows better consistency for monitoring data than traditional models. Estimation methods for each parameter of the HS-Small model are recommended based on statistical analysis and additional small-strain stiffness tests. A small-strain stiffness prediction empirical formula of shear-zone soil is proposed. The findings demonstrate the potential of the HS-Small model for slow-moving landslides, and the recommended estimation method can be considered for parameter determination.