Back analysis of the 2023 rockfall event of Martigny (Switzerland): trajectography prediction to future potential hazard along road

In this study, we back analysed a rockfall that occurred on a road in Martigny, Switzerland, on 15 March 2023 to determine the trajectory involving block fragments of approximately 43 m³ in total with block maximum 15 m³ and to identify factors that could contribute to future rockfalls in the area. A combination of remote sensing techniques such as LiDAR, photomosaic, and SfM (Structure for Motion) from drone have been performed to reconstruct the rockfall event and to predict the future potential for rockfalls. Our results suggest that the rockfall was caused by a combination of factors, including the  sliding failure mechanism occurred along a surface deeping to the valley with an angle of 54.5^o, the presence of jointed and cracks in the rock with high aperture. A series of 10,000 of block propagations using the scarring model algorithm from stnParabel to produce an area of deposition in agreement with observation made in the field, with corresponding energy line from simulation average has an angle of 35.5 ^o. The trajectories of blocks are attributed to the high damping effects of the ground conditions and the vineyard rock fences which reduced the distance travelled by the falling rock, and the vineyard terraces slope angle lower than the average slope. While rock protections fences have been installed for protection on the falling block area, however there is a need to consider additional measures, as the rock structure in this area is larger than the width of the cliff face, which makes it more susceptible to rockfalls. Such study points out that the calibration of rockfall simulation based on only few blocks is very challenging.