Deformation features and evolution of deep-seated gravitational slope deformation in underdip slate slopes: insights from distinct element modeling

Abstract Deep-seated gravitational slope deformation (DSGSD) plays a crucial role in shaping landscapes and is a precursor to disastrous rock slope failures, particularly in mountainous regions composed of slate. How can a slate slope’s deep structure and morphology variation correlate to the DSGSD evolution in space and time? Further, what kinematics and deformation displacements can we expect to observe at specific locations in a DSGSD from a monitoring system? This study aims to address these research questions by adopting distinct element modeling, which enables consideration of the anisotropic behavior and structural geometry of slate slopes. We focus on the slate slope with cataclinal features in the Chingjing region, Taiwan, and perform parametric two-dimensional mechanical modeling using synthetic slope models with different slope heights, slope angles, and cleavage dip angles. The results show that an active deformation is initiated by sliding along the cleavages at the crest after the river incision. The deformation then drives the rock masses to topple at the toe of the slope, and a basal shear plane develops gradually in response to the buckling of the cleavages. For the slope model up to 300 m in height, the thickness of the DSGSD block reaches almost 150 m, and a series of potential sliding planes are identified above the basal shear planes as the DSGSD continues. Mechanical modeling reveals that the surficial and subsurface displacement patterns depend on the evolution stage of the DSGSD process and installation locations. Despite the simplifications inherent in the synthetic slope model, the discrete element modeling captures the DSGSD characteristics observed in natural slate slopes. The geometric and kinematic model and generalized statistical results proposed in this study are expected to be applied in monitoring deployment and data interpretation for DSGSD at the regional scale.