3D modelling support to the design of massive rockfall protection structures

Design of structural countermeasures is a major step in rockfall protection. Design inputs in-clude the definition of rockfall trajectories for rockfall events with different magnitude, the values and variability or related dynamic quantities, and the locations and energy of impacts against protection structures. When frequent high-energy rockfalls affect steep rockwalls with complex 3D morphology, massive protection structures are required. Their design is particu-larly challenging, due to the extreme expected loads and the high variability in block volumes, rockfall paths, and dynamics. We discuss the potential of 3D runout modelling as a supporting tool for the design of chal-lenging countermeasures for a case study in the Como Lake area (Italy). Here subvertical cliffs up to 600 m high impend on a narrow strip of flat land, and a massive embankment has been considered to reduce risk. Models were set up using the code Hy-STONE, explicitly in-tegrating countermeasure geometry into a HR-DEM. Parameters were calibrated by back analysis of previous rockfalls, and forward simulations performed for different rockfall sce-narios. Results allowed countermeasure design verification and the quantification of different descriptors of embankment efficiency and residual risk. These descriptors, combined with full information on impacts against the structures, provided critical inputs for design optimization.