The critical role of fracture propagation in the evolution of extensive, structurally preconditioned rockslides

The inherited rock mass structure often preconditions rockslides in foliated, metamorphic rock slopes. However, the role of progressive fracturing processes associated with rock slope failure is receiving increasing attention. This paper demonstrates how rock mass fracturing can overcome limitations imposed by the inherited rock mass structure in two high-alpine rockslides with volumes of 670,000 and 1,000,000 m 3 , applying a comprehensive methodological approach. The rockslides' evolution and kinematics are unravelled based on remote sensing campaigns. Geological-geotechnical field and laboratory investigations provide the basis for a complementary numerical approach, utilising discrete-element (DEM) and hybrid-finite-discrete-element (FDEM) models. Leveraging the potential of each numerical approach, the rockslides are back-analysed, investigating the role of inherited structures and fracture propagation in the rockslides' evolution. The inherited structures, particularly foliation layers and tectonic shear zones, strongly precondition both rockslides while imposing specific limitations on their initiation. Nonetheless, progressive fracture propagation overcomes these structural limitations by (i) developing a toe-breakout that provides kinematic freedom for a retrogressive rockslide on a dip-slope, and (ii) forming an active wedge in a compound rockslide, which overcomes the frictional resistance of a tectonically preconditioned basal shear zone. Furthermore, the (iii) complementary DEM-FDEM showcases the advantages of each respective method and reproduces these fracturing processes in remarkable agreement with field observations, holding significant implications for engineering geology and hazard assessment. Thus, this study demonstrates that even in structurally preconditioned rockslides, progressive fracture propagation can dominate over inherited structures in controlling the mechanism and evolution of large rockslides. • Fracture propagation overcomes structural limitations in large rockslides. • Unravelling the interplay between inherited structures and induced fracturing. • Complementary asymmetric-Voronoi and finite-discrete element modelling study. • Active wedge surpasses strength of a tectonic shear zone in a 650,000 m 3 rockslide. • Progressive failure results in a toe-breakout of a 1,000,000 m 3 rockslide.