Abstract: Flexural toppling often occurs in anti-dip layered rock slopes, where rock mass shows failure behaviors similar to those of superimposed cantilever beams. Slopes in this failure mode may evolve into large landslides. Taking the left bank slope at the Ecuador’s Delsitanisagua hydropower station as an example, this paper describes its geological and geomorphological characteristics and examines the field data monitored during construction. Generally, typical rock structure (anti-dip and steep-dip) and special lithologic composition (thin-layered gneiss) are prerequisites for flexural toppling, while external factors such as excavation and heavy rainfall trigger and aggravate the deformation of rock layers. Numerical simulation using discrete elements shows that rock mass excavation below elevation 1493 m causes a deep-seated toppling failure of the entire slope; deformation of rock layers is featured with an obvious ductility, and a secondary fracture of reverse buckling develops inside the toppling mass. And in the slope mass, evolution of plastic zones reflects the propagation of rock mass rupture, and a fracture of straight failure with an inclination angle of 21° can be determined from the maximum shear strain and tensile stress distribution. Finally, control over the excavation height and angle at the slope bottom proves an effective way to reduce toppling deformation.

Key words: flexural toppling, rock slope, discrete element, deformation analysis, failure mechanism