Flume tests were conducted in the Hong Kong University of Science and Technology using the 28-m-long flume for investigating the efficacy of single and dual rigid and flexible barriers. These tests were utilised as part of a “Class A prediction” exercise in May 2022, with the international research community involved. In this context a numerical model based on Material Point Method (MPM) was used to forecast the flow dynamics and the flow-barrier interactions [1]. These predictions were made in advance, without knowledge of the outcomes to be predicted, and were based on limited input quantities such as geometry, barrier setup and material properties. The capabilities and limitations of the employed MPM numerical model are discussed [2]. One-phase and two-phase MPM models were adopted comparing the results against experimental data. While the models showed satisfactory agreement for certain variables, such as flow depth and front velocity, mismatches were observed for others, particularly regarding basal pore-water pressure and basal normal force. These discrepancies may stem from experimental factors such as flow turbulence or limitations in modelling highly time-dependent variables in numerical simulations. The MPM analysis of pore-water pressure factor provided valuable insights into the impact mechanisms of debris flows on the barriers. The contrasting mechanisms acting at the impact zone, including the increase of soil normal stress and the reduction of soil shear stress due to extra pore water pressure, were observed and analysed. The behaviour significantly differs from rigid to flexible barriers, reflecting the draining capabilities of the barriers and their influence on flow dynamics. References [1] Cuomo, S., Di Perna, A., & Martinelli, M. (2022). Analytical and numerical models of debris flow impact. Engineering Geology, 308, 106818. (https://doi.org/10.1016/j.enggeo.2022.106818) [2] Cuomo, S., Di Perna, A., Martinelli, M., Ng, C. W., De Silva, W. A. R. K., & Choi, C. E. (2024). Class A prediction of debris flow impact forces on dual rigid and flexible barriers: MPM modelling. Computers and Geotechnics, 173, 106556. (https://doi.org/10.1016/j.compgeo.2024.106556)