In order to perform reliable forecasts of the behavior of slow-moving rock slides in the surrounding of large dam reservoirs deformation processes and failure mechanisms need to be understood profoundly. The impacts of the geometry, kinematics and groundwater flow play a significant role concerning the deformation behavior. Especially, the spatial distribution and geometry of the rock slide toe are considered as key factors, in particular with regard to the ability of "self-stabilization". In this study, the impact of the rock slide geometry on the evolution of the stability during reservoir impoundment is investigated. Therefore, various generic rock slide models are established and systematically analyzed based on limit equilibrium approaches.
The geometry of numerous deep-seated rock slides in metamorphic rocks is mainly controlled by pre-existing discontinuities such as brittle fault zones, shear and tensile fractures, foliation and bedding planes (Agliardi et al. 2000, Bonzanigo et al. 2007 and Zangerl et al. 2012). These geological structures affect the shape of the basal shear zone. During downslope displacements, the strain localization causes intensive fragmentation and shearing and consequently forms fault gouges and breccias along the shear zone (Zangerl et al. 2007). Accompanied by internal deformation and weakening of the rock mass a change in slope topography takes place (Bonzanigo et al. 2007). Several observed rock slides in an advanced deformation stage show a concave topography in the middle to upper part and a convex, bulge-like topography at the bottom of the slope (Zangerl et al. 2012).
Deep-seated rock slides either develop a rotational, a translational or a bi-linear (combination of rotational and translational) rupture surface. Hungr et al. (2014) describes a translational slide as sliding body that is entirely in an "active" state. Compound slides with a bi-linear rupture surface are composed of an upper driving ("active") block, pushing the stabilizing ("passive") block situated at the slope toe. Sliding along a compound rupture surface is kinematically only possible if significant internal fracturing and shearing of the moving mass occurs (Hungr et al. 2014).