Received: 02 Mar 2022 – Discussion started: 28 Mar 2022
Abstract. Many rockfall simulation software provide great flexibility to the user at the expense of a hardly achievable parameter unification. With sensitive site-dependent parameters that are hardly generalizable from the literature and case studies, the user must properly calibrate simulations for the desired site by performing back calculation analyses. Thus, rockfall trajectory reconstruction methods are needed. For that purpose, a computer-assisted videogrammetric 3D trajectory reconstruction method (CAVR) built on earlier approaches is proposed. Rockfall impacts are visually identified and timed from video footage, and are manually transposed on detailed high-resolution 3D terrain models that act as the spatial reference. This shift of reference removes the dependency on steady and precisely positioned cameras, ensuring that the CAVR method can be used for reconstructing trajectories from witnessed previous records with nonoptimal video footage. For validation, the method is applied to reconstruct some trajectories from a rockfall experiment performed by the WSL Institute for Snow and Avalanche Research SLF. The results are compared to previous ones from the SLF and share many similarities. Indeed, the translational energies, bounce heights, rotational energies and impact positions against a flexible barrier compare well with those from the SLF. Interestingly, only dissipative impact processes are observed with the CAVR method, contrary to the previous results from the SLF. The comparison shows that the presented cost-effective and flexible CAVR method can reproduce proper 3D rockfall trajectories from experiments or real rockfall events.
The authors present an cost-effective method to reproduce 3D rockfall trajectories from and CAVR. It has the advantage that uses the 3D terrain model as the spatial reference for the falling block instead of the videocameras and considers a proper offset of the center of mass in the reconstruction of the trajectories. Nice sutdy, clear presentation and meaningful results.
Only a few comments:
1) In my opinion, the sentence "only dissipative impacts are observed with CAVR..." should be removed from the summary. The authors to the SLF experiments. The sentence may be misleading because although it refers to the SLF experiment, the reader may interpret it to be generalizable to other experiments.
2) Lines 34-35 For ease of reading, it is convenient to explain here the difference between the rebound model parameters and the apparent coefficient of restitution.
3) Section 3.3. As the authors mention, it is necessary to evaluate the geometry of the rock block to adequately compensate the impact positions to the center of mass to obtain the correct trajectories. However, the reconstruction the 3D model of the blocks is not fully described. It seems that the model is obtained from the frames but there may be hidden parts of the blocks that can affect the reconstruction of the shape and volume, as well as the measured dynamic parameters. It is convenient to explain in more detail the procedure followed to reconstruct the volume of the blocks and also provide an estimation of the errors.
4) There is an issuet that has not been treated by the authors but that appears in other experiments. It is the presence of dust during the impact. Has dust been generated? If so, how have the authors resolved this circumstance? Is it the algorithm that determines the point of impact and the kinematic parameters?
5) Please, check the references, some references are incomplete or the source can not be easily identified (e.g Berger, 2011; Domaas, 1995; Garcia, 2019; Girardeau-Mountaut, 2006; Sanchez 2020; ...)
Rockfall simulations are often performed to make sure infrastructures are safe. For that purpose, rockfall trajectory data is needed to calibrate the simulation models. In this paper, an affordable, flexible, and efficient trajectory reconstruction method is proposed. The method is tested by reconstructing trajectories from a full-scale rockfall experiment involving 2670 kg rocks and a flexible barrier. The results highlight improvements in precision and accuracy of the proposed method.
Rockfall simulations are often performed to make sure infrastructures are safe. For that...
