Modelling the influence of rock mechanical properties and rock structure on the 2023 Brienz “Insel” failure

In June 2023, the "Insel" compartment of the Brienz/Brinzauls landslide system in Switzerland failed, mobilising approximately 1.9 million m³ of rock and almost reaching the village of Brienz/Brinzauls. As the event occurred at night, it could not be directly observed, highlighting the need for numerical modelling to better understand its initiation mechanism and kinematics.

Mechanical numerical modelling provides a powerful tool for investigating slope instabilities, allowing researchers to test hypotheses about failure processes and gain insights into kinematical behaviour when direct observations are not available. To explore the influence of mechanical and geometrical properties on the "Insel" failure, we conducted a parameter study using the distinct element code 3DEC. The study makes use of the extensive monitoring data available for the Brienz/Brinzauls landslide system, examining the effects of varying rock mechanical properties, sliding surface characteristics, joint orientations, sliding surface geometry, model resolution and dimension on the failure behaviour.

Our results highlight the critical role of accurately representing geological structures, such as bedding orientations and block shapes, as well as the sliding surface geometry. These factors significantly influence the model outcomes and the simulated failure dynamics. The model successfully reproduced the observed depositional patterns within the rupture zone and provided insights into the internal movements and temporal evolution of the “Insel” compartment during the failure offering a deeper understanding of the event and its underlying mechanisms.