Creep properties of clastic soil in a reactivated slow-moving landslide in the Three Gorges Reservoir Region, China

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 non-attenuating 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. •We give insight intos the time-dependent behavior of clastic soil in a slow-moving landslide in TGR region, China.•The landslide exhibits stepwise movement pattern according to recent monitoring data.•In-situ direct shear creep test and laboratory ring shear creep test were carried out to interpret the movement mechanism of the landslide.•The stepwise movement of the landslide was explained on the basis of the strain rate effect.