Abstract: The abnormal slope unloading is one of the typical engineering problems encountered in large-scale hydropower project construction process in southwest deep valley area. Though field geological investigation, the characteristics of slope unloading was discovered, and three two-dimensional discrete element models were established to simulate the deformation of the slope after five times of valley incision to analyze the influence caused by ductile shear zone and the alteration zone on slope unloading characteristics under condition of considering ductile shear zone and the alteration zone or not. The results show that the anomalies of slope unloading is mainly related to the distribution of ductile shear zone and the alteration rock mass. The soft base effects and weak ability to resist weathering of the ductile shear zone and the alteration zone, which are weaker than normal rock mass in mechanical properties, exacerbate the slope deformation degree. At the same time, the hard and soft slope structure make the phenomenon different shear dislocation along the flat slope surface structure more apparent.

Key words: high rock slope, ductile shear zone, altered rock mass, slope unloading, universal discrete element code (UDEC)