Reactivation mechanism of a deep-seated landslide along fault zones in Baihetan reservoir area

Many reservoir landslides have started undergoing rapid deformation in the Baihetan Reservoir region (BRR) by the complex structural background and initial impoundment, posing a significant risk to human life and infrastructure. In order to understand the intrinsic relationships between the geological structure, reservoir water, and landslide deformation, a detailed analysis of the Gengdi landslide along fault zones during the first water level circulation fluctuation in the BBR was conducted. The investigation was conducted systematically by means of comprehensive in situ monitoring, drilled cores, adit, high-density resistivity method, field investigations and engineering mapping, and aerial photographs. The Gengdi landslide showed a characteristic type of bending flowing and fracturing. The shear outlets of the landslide are the top and bottom of the fault gouge respectively. Hydrodynamic pressure and fault gouge softening are the trigger factors of the landslide. The main deformation of the landslide was along a deep fault zone. The maximum rate of landslide deformation occurred during the period when the reservoir water level fluctuation between the top and bottom of fault gouge. The findings revealed that the reservoir water level fluctuation caused the compression of the fault gouge and dragged the upper rock mass of fault zone. This study provided a detailed geological model for the formation of the landslide in fault zone. The likelihood of large-scale landslides is significantly high with the current deformation rate of the Gengdi landslide. Therefore, the analysis of reactivation mechanism and control of this type of landslide should be strengthened.