Supporting rockfall countermeasure design in difficult conditions

Rockfall protection is a major issue in areas exposed to severe rockfall hazard. The design of structural countermeasures, usually required to ensure such protection, needs careful evaluation of rockfall trajectories, distribution and intensity of impacts, and magnitude and variability of involved dynamic quantities. Protection against rockfalls from high rock walls is especially difficult, due to the widespread occurrence of rockfall sources, the spatial variability of block volumes and rockfall trajectories, and the high involved kinetic energies. In these cases, complex design and construction issues related to massive countermeasures must be addressed. We show the potential of 3D rockfall modelling to support challenging countermeasure design by discussing a case study in the Southern Alps (Italy). Here subvertical limestone cliffs up to 600 m high impend on a narrow strip of flat land, with potentially unstable individual block volumes ranging between 0.5 and 15 m3. Slope benching and a massive embankment were designed to protect a sector of this area. We explicitly integrated countermeasure design geometry into a HRDEM, calibrated modelling parameters by the back analysis of previous rockfalls, and performed predictive simulations considering different block size scenarios. Countermeasure design was verified according to the spatial pattern, heights and overpassing probabilities of expected trajectories. Design optimisation scenarios including additional flexible barriers were also evaluated. Finally we discuss the advantages and requirements of 3D for design support applications.