We study the creep properties of clastic soil in residual state. The intact samples are taken from a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China. Firstly, the patterns of the landslide movement are analysed based on recent monitoring data, which indicate that the soil within the shear zone is undergoing two deformation processes: a creep phase, characterised by different creep rates, and a dormant phase. We then study the creep behaviour of the soil samples through a series of ring shear creep tests under various shear stress conditions. The creep response depends strongly on the ratio of the shear stress to the residual strength, and the normal effective stress, whereas the creep rate decreases due to strength regain. The long-term strength of the clastic soil is close to the residual strength. Therefore, the residual strength obtained from conventional shear test, which is less time consuming than creep test, can be used in longterm stability analyses of creeping landslides.

Hypoplastic constitutive equation based on nonlinear tensor functions possesses a failure surface but no yield surface. In this paper, we consider the numerical integration and FE implementation of a simple hypoplastic constitutive equation. The accuracy of several integration methods, including implicit and explicit methods, is examined by performing a set of triaxial compression tests. Adaptive explicit schemes show the best performance. In addition, the stress drift away from the failure surface is corrected with a predictor-corrector scheme, which is verified by two boundary value problems, i.e. rigid footing tests and slope stability.

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Most slow-moving landslides in the Three Gorges Reservoir (TGR) region of China are characterized by pre-existing shear surfaces. The large deformation within the shear zones usually gives rise to clastic soil formation. The creep properties have large influence on the kinematic feature of landslides. In this paper, we report an in-situ direct shear creep test carried out in the shear zone of a reactivated slow-moving landslide in the TGR region. Correspondingly, some laboratory ring shear creep tests are carried out to interpret the movement pattern of this landslide. The shear zone soil exhibits similar nonattenuating creep responses in both the in-situ direct shear and laboratory ring shear creep tests. At the same stress level, however, the in-situ direct shear creep test yields a larger rate of creep displacement due to shearing along the landslide direction. In the ring shear creep tests, at the prepeak stage, the critical creep stress that triggers creep failure is slightly lower than the peak shear strength but much larger than the residual strength; at the postfailure stage, the critical creep stress of the shear-zone soil is equal to the residual shear strength. The rate-dependent residual shear strength may account for the stepwise movement pattern of the landslide.