PRELIMINARY STUDY OF THE CREEP MECHANISM OF JINPINGZI ZONE Ⅱ SLOW MOVING LANDSLIDE IN LOWER REACHES OF JINSHA RIVER

Jinpingzi landslide is the nearest deep-seated colluvial debris landslide to the arch dam of Wudongde hydropower station in the downstream direction in lower reaches of Jinsha River. Its active zone Ⅱ was studied. Based on geotechnical investigation and long-term monitoring, the physical and mechanical property of the landslide materials and the long-term kinematics, especially the relationships among the landslide movement, rainfall and the groundwater were analysed. The response of the groundwater regime to the precipitation was further analyzed under different initial water content conditions based on the Green-Ampt infiltration model. Relationships between resisting forces and driving forces were discussed by limit equilibrium method assuming rigid-plastic frictional slip. Results showed that the long-term continuous movement was mostly due to the viscous component of the slip zone. Surface and subsurface displacement both showed a retrogressive type with average surface displacement rate 0.19~0.87mm·d^-1 from 2005 to 2016. Basal sliding accounted for most of the deformation with different degrees of internal deformation in different parts. Rainfall was the predominant factor affecting the landslide activity but it is hard for rainfall water infiltrating to the deeply buried groundwater regime. Unlike some shallow landslides, the mechanism of Jinpingzi zone Ⅱ slow moving landslide was more likely to be the formation of transient saturated zone in shallow depth. The change of unit weight of the sliding mass and the effect of seepage affected the kinematics of the landslide.