On 27 August 2023, after heavy rainfall, a rockfall occurred on the La Praz cliffs in the Maurienne Valley, France. Fortunately, there were no human casualties.

With an estimated volume of almost 15,000 m³, this rockfall closed the RD1006 departmental road, the A43 motorway and the transalpine rail link between Lyon-Modane (France) and Turin (Italy). After extensive safety works, traffic has finally been restored on two of these routes, with the railway line is not expected to reopen until the end of 2024.

Under the a priori assumption of limited interaction between blocks in this “fragmental” rockfall, we implemented its simulation using the RocPro3D stochastic software. Based on available topographic data (RGE ALTI® 1m) and using a methodology that allows an initial assessment of the situation, the 3D trajectory modelling is carried out in a about 1 hour, taking into account 10 million blocks. It immediately provides a first map of the block’s stopping positions and their propagation probability, the first of which turns out to be quite close to the observations. Although these initial simulations could certainly be refined with field data, such quick answer looks interesting, doesn’t it?