Numerical study on deep-seated gravitational slope deformation in a shale-dominated dip slope due to river incision

• We analyzed evolution of DSGSD triggered by river incision with numerical modeling.
• Plastic shear zones are due to strength reduction of rock mass and river incision.
• The development of DSGSD is structurally restrained by the bedding planes.
• Topographic features are related to internal deformational structures of the slope.

Based on numerical simulation, this study investigates the triggering factors and evolution of deep-seated gravitational deformation in a dip-slope consisting of a shale-dominated sequence of sediments. Results from continuum-based (finite difference) numerical modeling demonstrate that long-term strength degradation of a rock mass is a prerequisite for the development of gravitational slope deformation, and that river incision, resulting in change of slope geometry and corresponding stress concentration and redistribution, is a major driving mechanism for the progressive evolution of deep-seated gravitational slope deformation (DSGSD). Numerical simulation considering the influence of weak planes indicates that the bedding planes control the strength of rock mass and form a structural constraint on the development of gravitational slope deformation. A satisfactory correlation between the distribution of numerically simulated plastic shear bands and weak zones in drill cores demonstrates that the weak zones within the slope are formed due to gravitational slope deformation. Furthermore, numerical simulation shows a link between geomorphological development and internal deformation of the slope, which aids in the understanding of relationships between interior deformation of the slope, the exterior geomorphology and related effect factors including river incision and strength degradation.