New approaches using synthetic rock mass models to evaluate rockfall hazard

In Austria, the ONR 24810 guideline currently regulates technical rockfall protection. It specifies that rockfall protection measures (at slope scale) should be dimensioned on the so-called design block (V95-V98). The design block method is increasingly being used for hazard zoning (at larger scale), which can be problematic for several reasons. Hazard is generally defined by the intensity of an event times its probability of occurrence. For rockfall hazard assessment, not only the intensity and bounce height of events, but also the propagation and the frequency (probability) of these events can be decisive. Neglecting all small and the largest blocks results in distorted courses of energies and bounce heights. To evaluate the hazard, as many events as possible must be simulated with their associated frequencies. We have developed a practicable method for determining a holistic block size distribution that provides many blocks over the entire block size range. Due to its holistic nature, relative event frequencies (magnitude/frequency relations) within a homogeneous area can be derived, and hazard zones can be evaluated more realistically.